Text

License Amendment Request for Removal of Severe Line Outage Detection from the Offsite Power System
	ML15183A022
Person / Time
Site:	Millstone
Issue date:	06/30/2015
From:	Mark D. Sartain; Dominion Nuclear Connecticut
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	15-297
	Download: ML15183A022 (178)
	v • d • e

Dominion Nuclear Connecticut, Inc. 'I ,

5000 Dominion Boulevard, Glen Allen, VA 23060 - ominion Web Address: www.dom.com June 30, 2015 U.S Nuclear Regulatory Commission Serial No 15-297 Attention: Document Control Desk NSSL/MLC RO Washington, DC 20555 Docket Nos. 50-336/50-423 License Nos. DPR-65/NPF-49 DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNITS 2 AND 3 LICENSE AMENDMENT REQUEST FOR REMOVAL OF SEVERE LINE OUTAGE DETECTION FROM THE OFFSITE POWER SYSTEM Pursuant to 10 CFR 50.90, Dominion Nuclear Connecticut, Inc. (DNC) hereby requests amendments to Facility Operating License No. DPR-65 for Millstone Power Station Unit 2 (MPS2) and to Facility Operating License No. NPF-49 for Millstone Power Station Unit 3 (MPS3). The proposed amendments would revise the MPS2 and MPS3 Final Safety Analysis Reports (FSARs) to: 1) delete the information pertaining to the severe line outage detection (SLOD) special protection system, 2) update the description of the tower structures associated with the four offsite transmission lines feeding Millstone Power Station (MPS), and 3) describe how the current offsite power source configuration and design satisfies the requirements of General Design Criteria (GDC) -17, "Electric Power Systems" and GDC-5, "Sharing of Structures, Systems, and Components." The amendments also request Nuclear Regulatory Commission (NRC) approval of a new Technical Requirements Manual (TRM) requirement, "Offsite Line Power Sources," for MPS2 and MPS3. With one offsite transmission line nonfunctional, the TRM requirement would allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore the nonfunctional line with a provision to allow up to 14 days if specific TRM action requirements are met.

Attachment I provides a description and assessment of the proposed amendments for MPS2 and MPS3. Attachments 2 and 3 provide the marked-up FSAR pages for MPS2 and MPS3, respectively. The new proposed TRM requirements for offsite line power sources for MPS2 and MPS3 are provided in Attachments 4 and 5, respectively. is a letter from ISO-New England which describes the ISO-New England Millstone Facility Out Guide. Due to ISO-New England Information Policy restrictions, if NRC desires to obtain this document for review, a request for this document must be made by the NRC and cannot be made by DNC for NRC. As stated in the ISO-New England letter, this proprietary document can be made available to the NRC upon a direct [written] request to ISO-New England.

To facilitate NRC's review of this LAR, the historical regulatory correspondence related to establishing the original design and licensing basis for the MPS3 offsite power sources is provided in Attachment 7.

Serial No: 15-297 Docket Nos. 50-336/50-423 Page 2 of 3 DNC has reviewed the three criteria set forth in 10 CFR 50.92(c) and determined that the proposed amendments do not involve a significant hazards consideration. The Facility Safety Review Committee has reviewed and concurred with the determinations herein.

Issuance of these amendments is requested by June 30, 2016 with the amendments to be implemented within 60 days after NRC approval.

In accordance with 10 CFR 50.91(b), a copy of this request is being provided to the State of Connecticut.

Should you have any questions in regard to this submittal, please contact Wanda Craft at (804) 273-4687.

Sincerely, Mark D. Sartain Vice President - Nuclear Engineering COMMONWEALTH OF VIRGINIA COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Mark D. Sartain, who is Vice President - Nuclear Engineering of Dominion Nuclear Connecticut, Inc. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true to the best of his knowledge and belief.

Acknowledged before me this _____ day of $YU-e-_ ,2015.

My Commission Expires: 1,11I, I4 CRAIG DSLY Notary Public I Commonwealth of Virginia ot yic Reg. # 7518653 I My Commission Expires December 31, 21 j VV9 0

W Commitments: None.

Serial No: 15-297 Docket Nos. 50-336/50-423 Page 3 of 3 Attachments:

1. Evaluation of Proposed License Amendments (MPS2 and MPS3)

2. Mark-up of Proposed FSAR Changes (MPS2)

3. Mark-up of Proposed FSAR Changes (MPS3)

4. New Technical Requirement for Offsite Line Power Sources, For Information Only (MPS2)

5. New Technical Requirement for Offsite Line Power Sources, For Information Only (MPS3)

6. ISO-New England Millstone Facility Out Guide Letter

7. Historical Regulatory Correspondence Pertaining to MPS3 Offsite Power Sources cc: U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd Suite 100 King of Prussia, PA 19406-2713 R. V. Guzman NRC Senior Project Manager U.S. Nuclear Regulatory Commission, Mail Stop 08 C2 One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Director, Bureau of Air Management Monitoring and Radiation Division Department of Energy and Environmental Protection 79 Elm Street Hartford, CT 06106-5127

Serial No: 15-297 Docket Nos. 50-336/50-423 ATTACHMENT 1 EVALUATION OF PROPOSED LICENSE AMENDMENTS DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNITS 2 AND 3

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 1 of 42 Evaluation of Proposed License Amendments 1.0 Summary Description Pursuant to 10 CFR 50.90, Dominion Nuclear Connecticut, Inc. (DNC) hereby requests amendments to Facility Operating License No. DPR-65 for Millstone Power Station Unit 2 (MPS2) and to Facility Operating License No. NPF-49 for Millstone Power Station Unit 3 (MPS3). The proposed amendments would revise the MPS2 and MPS3 Final Safety Analysis Reports (FSARs) to: 1) delete the information pertaining to the severe line outage detection (SLOD) special protection system, 2) update the description of the tower structures associated with the four offsite transmission lines feeding Millstone Power Station (MPS), and 3) describe how the current offsite power source configuration and design satisfies the requirements of General Design Criteria (GDC) -17, "Electric Power Systems" (Reference 7.1) and GDC-5, "Sharing of Structures, Systems, and Components" (Reference 7.16). The amendments also request Nuclear Regulatory Commission (NRC) approval of a new Technical Requirements Manual (TRM) requirement, "Offsite Line Power Sources," for MPS2 and MPS3. With one offsite transmission line nonfunctional, the TRM requirement would allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore the nonfunctional line with a provision to allow up to 14 days if specific TRM action requirements are met.

2.0 Proposed License Amendment 2.1 FSAR Changes to Reflect Modification of Tower Structures and Removal of SLOD DNC proposes to revise the MPS2 and MPS3 FSARs to: 1) delete the information pertaining to the SLOD special protection system which was removed from service in December 2012, 2) update the description of the tower structures associated with the four offsite transmission lines feeding Millstone Power Station, and 3) describe how the current offsite power source configuration and design satisfies the requirements of GDC-17 and GDC-5. The proposed changes to the MPS2 and MPS3 FSARs are provided in Attachments 2 and 3, respectively.

2.2 New TRM Requirement for Offsite Line Power Sources DNC proposes to add a new technical requirement, "Offsite Line Power Sources," to the MPS2 and MPS3 TRM. The TRMs would require that the four offsite transmission lines be functional when MPS output exceeds 1650 megawatts electric (MWe) net. With one offsite line nonfunctional, the TRM requirements would allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore the nonfunctional line with a provision to allow up to 14 days if specific TRM actions are met.

Attachments 4 and 5 provide the new technical requirements for offsite line power sources for MPS2 and MPS3, respectively. Implementation of these technical requirements is contingent upon NRC approval of this license amendment request.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 2 of 42 3.0 System Description and Background MPS is a three unit site with two operating reactors. Millstone Power Station Unit 1 (MPS1), which received its provisional operating license on October 7, 1970, was permanently shut down on July 21, 1998. MPS2, which received its initial operating license on September 26, 1975, has a licensed reactor power output of 2700 megawatts thermal (MWt) with a gross electrical output of approximately 935 MWe. MPS3, which received its initial operating license on January 31, 1986, has a licensed reactor power output of 3650 MWt with a gross electrical output of approximately 1296 MWe.

3.1 Offsite Power System The net electrical output of the main generators for MPS2 and MPS3 is delivered to a common 345 kV high voltage switchyard, which is located within the owner controlled area of the site. The MPS switchyard is designated as "Millstone 15G" by the transmission operator. The MPS switchyard consists of two 345 kV buses (A and B) and ten 345 kV circuit breakers arranged in a combination breaker and a half and double breaker-double bus switching arrangement. The switchyard interconnects four 345 kV transmission lines, two 345 kV tie lines to the MPS2 and MPS3 generator step-up (GSU) transformers, and two 345 kV tie lines to the reserve station service transformers (RSSTs). The MPS1 GSU transformer and RSST are no longer in service.

The four 345 kV transmission lines which comprise the MPS offsite power supply connect to the Eversource (formerly Northeast Utilities) 345 kV transmission network at four separate substations. Two of the four MPS transmission lines (designated as Lines 371 and 383) feed substations that serve the eastern part of Connecticut. The other two transmission lines (designated as Lines 348 and 310) feed substations that serve the central part of Connecticut. The four 345 kV transmission lines which terminate at the MPS switchyard are:

Line Number 348: Millstone to Haddam and Beseck Substation

" Line Number 310: Millstone to Manchester Substation

" Line Number 371: Millstone to Montville Substation (Line Number 364: Montville Substation to Haddam Neck)

" Line Number 383: Millstone to Card Substation The four 345 kV transmission lines (Lines 348, 310, 371, and 383) proceed north, in parallel, on a common Right-of-Way (ROW). After approximately nine miles, two of the four lines change direction (Line 371 turns east and Line 348 turns west) at the Hunts Brook Junction. Line 364, which proceeds east-west through Hunts Brook Junction, is considered part of Line 371 since it is the only other 345 kV line connected to the Montville Substation. Therefore, because of this condition, Line 371 is crossed over by Lines 383 and 310 at Hunts Brook Junction (See Figure 1).

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 3 of 42 Figure 1 Millstone Transmission System Figure 1 Millstone Transmission System (North)

Manchester 368 368 Card Street 310 383 Haddam Neck 364 (West) (East)

Simplified Diagram of Millstone 345kV Transmission Lines

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 4 of 42 For MPS2, the preferred offsite power supply is the MPS2 RSST which is fed directly from the MPS switchyard. During normal operation, MPS2 station service loads are powered by the MPS2 Normal Station Service Transformer (NSST). The MPS2 RSST feeds power directly to the 4 kV safety-related buses (Buses 24C and 24D) and is available within eight cycles after a plant trip via the fast transfer scheme. The alternate offsite source is the 4 kV cross-tie to MPS3 via the non-safety-related 4 kV buses (34A or 34B) via manual controls. This power source directly feeds Bus 24E which can then be directed to either Bus 24C or 24D.

For MPS3, there are two physically independent transmission lines installed from the MPS switchyard to the onsite distribution system (safety buses). The preferred offsite power supply is the MPS3 NSST. The MPS3 NSST provides power directly to the non-safety-related 4kV buses (Buses 34A and 34B) which then directly feed the safety-related 4 kV buses through bus ties. This offsite connection through the NSST is immediately available after a plant trip. The alternate offsite source is the MPS3 RSST.

The MPS3 RSST feeds power directly to the 4 kV safety-related buses (Buses 34C and 34D). This power source is available via transfer schemes after a plant trip, if the preferred offsite power source is not available.

The Independent System Operator (ISO) New England Millstone Facility Out Guide (Reference 7.20) represents the results of dynamic studies completed in accordance with North American Electric Reliability Corporation (NERC) reliability standards, Northeast Power Coordinating Council (NPCC) directories and ISO-New England procedures. The guide provides real-time guidance to posture MPS generation to maintain generator stability during a facility-out condition. The guide describes the limitations to MPS generation (MPS2 and MPS3) if there are two major elements (line +

line, line + breaker, or breaker + breaker) out-of-service in the MPS switchyard.

Additional potential contingencies are addressed continuously by ISO-New England and Connecticut Valley Electric Exchange which will drive MPS actions as appropriate.

A schematic of the MPS 345 kV transmission system is shown in Figure 2.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 5 of 42 Figure 2 Millstone 345 KV Transmission System MILLSTONE 345KV TRANSMISSION SYSTEM BESECK 9F MANCHESTER 3A UNIT 3 RSST UNIT 3 UU UwJu NSST n-I-n7 3SA 3SB 2S UNIT 2 NSST

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 6 of 42 3.2 Onsite Power System The onsite power system for MPS2 is comprised of the MPS2 electric power systems out to, and including, the GSU transformers (which includes the MPS2 NSST). Similarly, the onsite power system for MPS3 is comprised of the MPS3 electric power systems out to, and including, the GSU transformers (which includes the MPS3 NSST).

The normal power systems for MPS2 and MPS3 include the equipment required to support the main turbine generator, plant systems, and equipment associated with the reactor. Normal operation for both units is when the main generator is transmitting electrical power through the GSU transformer bank and when plant auxiliaries are being supplied from the NSST.

The emergency systems at MPS2 and MPS3 include the electrical distribution equipment required to support the safe shutdown of the units and post-accident operations.

Included in each unit's emergency system are two Emergency Diesel Generators (EDGs), 4 kV switchgear and extensions except those supplying the normal switchgear and RSST. Redundant safety-related loads are divided between trains so that the loss of either train does not impair fulfillment of the minimum shutdown safety requirements.

There are no automatic connections between Class 1 E buses and the loads of redundant trains.

The MPS2 EDGs supplying their respective 4 kV AC emergency bus receive an automatic start signal under either of the following conditions: 1) Engineered Safeguards Actuation System (ESAS) Level 1 Undervoltage actuation signal from the associated 4 kV AC emergency bus, 2) ESAS Safety Injection Actuation Signal (SIAS), or manually.

For MPS3, EDGs are started on loss of power to the respective 4 kV bus to which each generator is connected, by a Safety Injection Signal, by a Containment Depressurization Actuation signal, or manually.

During certain design basis accidents for MPS2 and MPS3, the EDGs are designed to start, whether offsite power is available or not. For a loss of offsite power (LOOP) event, the EDGs will start and when rated voltage and frequency are met, power will be provided to the required safety loads. Additionally, failure of a single active component or train associated with one EDG does not result in the inability of the redundant EDG to provide emergency standby power. Each EDG is capable of producing enough power to supply its respective train.

Both MPS2 and MPS3 have the ability to cope with a loss of offsite power and emergency onsite alternating current (AC) power (defined as a Station Blackout (SBO) event) for up to eight hours. It is assumed that there will be no AC power available during the first hour of the SBO event except for battery-backed power supplies (i.e., vital 120V AC). In accordance with the SBO rule (Reference 7.2) and NUMARC 87-00 (Reference 7.3), only one Millstone unit will experience an SBO event at any one time.

Therefore, following an SBO at one unit, at least one of the two EDGs would be available on the other unit.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 7 of 42 The alternate AC power source is comprised of the MPS3 SBO diesel generator and its support equipment, which is required to provide electric power to equipment necessary to maintain either unit in a safe condition. In the event of a MPS2 SBO, the MPS3 SBO diesel will be made available within one hour by MPS3 operator action and connected to MPS2 Bus 24E by MPS2 operator action.

3.3 Elimination of Double Circuit Towers and SLOD At the time of initial MPS3 licensing, the four 345 kV transmission lines leaving the MPS switchyard followed a common ROW to Hunts Brook Junction. From MPS to Daniels Avenue, the four lines were routed on two double-circuit towers (DCTs) (i.e., two transmission lines sharing a common tower). From Daniels Avenue to Interstate 95, the lines were routed on one DCT and two single circuit towers (SCTs). A simplistic representation of the original DCT design is provided below in Figure 3.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 8 of 42 Figure 3 Double Circuit Tower (DCT) Design TYPICAL RIGHT-OF-WAY CROSS SECTIONS A. WATERFORD: MIULSTONE' SUBSTATION TO.DANIELS, AVE., 1.5 MILES IN SEGMENT 'I 345 KV 345Kv 345KV 345 KV LOOKING NORTH EXISTIN1 5OO. RIGHT OF WAY AND CLEARNG.

B. WATERFORD: DANIELS AVZTO 195: 2. MILES IN SEGMENTS ! AND: 2 345KV 345 KV LOOKING NORTH

345, 0V 345: KV F-251W5 85 .82.5 EISTING 415' RIGHT OF.WAY AND CLEARING C., WATERFORD-MONTVILLE: 195 TO HUNTS BY, JCT., 4.9 MILES IN SEGMENTS 2-4 LOOKING NORTH 345 XV 3iv V3,45 KV 345 KkV

.,5 m--- 82.5, ' 685' -L-21,5e-- z82.5' EXISTING" 4151 RIGHT OF WAY AND CLEARING

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 9 of 42 Northeast Power Coordinating Council (NPCC) Regional Reliability Reference Directory

1, "Design and Operation of the Bulk Power System" (Reference 7.4), requires a phase to ground fault on different phases of each of two adjacent transmission lines on multiple circuit towers be considered as a normal contingency in stability studies when using DCTs. The grid stability studies performed at the time of original licensing of MPS3 showed that with one 345 kV line out of service associated with one DCT, offsite stability would not be maintained with the loss of two 345 kV lines on the other DCT with MPS output greater than 1200 MWe.

To address the grid stability concerns with the DCT design during initial licensing of MPS3, Northeast Utilities installed SLOD to assist in minimizing the probability of coincident loss of both offsite supplies and loss of a nuclear power unit. The SLOD function was credited in both the MPS2 and MPS3 FSARs for GDC-17 compliance by ensuring offsite power was maintained to the MPS switchyard under certain scenarios (e.g., DCT faults).

SLOD was also credited as an additional defense-in-depth feature for multiple circuit breaker failure scenarios associated with the 345 kV breakers in the MPS switchyard.

The 345 kV switchyard is designed so that the loss of more than one transmission line due to failure of a breaker to trip requires at least two circuit breakers to simultaneously fail to operate. The failure of a single 345 kV breaker to trip when required is considered a highly unusual occurrence. SLOD was relied upon for protection in the unlikely event of three 345 kV breakers failing to operate simultaneously (see Northeast Utilities letter dated August 1, 1983 in Attachment 7).

In 2010, Northeast Utilities began the approval process for removal of SLOD and modification of the DCT design which was viewed by the transmission line owner and operator as an overall improvement to grid reliability. Although SLOD was designed as a NPCC Type I special protection system, over time the transmission system had evolved with new contingencies that SLOD would not detect. In addition, it was determined that SLOD could unintentionally arm as occurred in early 2011. As a result, Northeast Utilities obtained transmission regulatory approval to modify the transmission tower design from DCTs to SCTs and disable SLOD.

In December 2012, Northeast Utilities completed the portion of the project that modified the DCT design for the 345 kV transmission lines leaving MPS. Specifically, the modification entailed relocating one of the two 345 kV transmission lines from each of the two existing DCTs onto a new SCT so that each 345 kV transmission line was on its own separate transmission tower. In conjunction with modification of the DCT design, SLOD was also disabled. The transmission line configurations at each of the four substations and Hunts Brook Junction remained unchanged.

A simplistic representation of the new SCT design is shown in Figure 4.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 10 of 42 Figure 4 Single Circuit Tower (SCT) Design MNPS-2 FSAR TYPICAL RIGHT-OF-WAY CROSS SECTIONS A. WATERFORD: MILLSTONE SUBSTATION TO DANIELS AVE.. 1.5 MILES IN SEGMENT 1 345 KV 345 KV 348 LINE 383 LINE LOOKING NORTH 345 KV ,345KV 310 LINE 371 LINE Av 85' - 75' . 180'75' 85' -

EXISTING 500' RIGHT OF WAY AND CLEARING' B. WATERFORD: DANIELS AVE. TO 195 2.6 MILES IN SEGMENTS 1 AND 2 345 KV 348 LINE LOOKING NORTH 345 KV 345 KV 345 KV 310 LINE 371 UNE 383 LINE 82.5' 75' 90 "'85' 82.5' EXISTING 415' RIGHT OF WAY AND CLEARING C. WATERFORD-MONTVILLE: 195 TO HUNTS BK. JCT., 4.9 MILES IN SEGMENTS 2-4 LOOKING NORTH

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 11 of 42 With modification of the DCTs to SCTs, ISO-New England no longer considered double line-to-line ground faults a normal contingency.

With the four transmission lines separated onto SCTs, Northeast Utilities considered leaving SLOD in service as an additional defense-in-depth measure. However, since SLOD created an unnecessary risk of misoperation and transmission operator burdens, Northeast Utilities decided to remove SLOD from service. Dominion agreed with this decision since it would eliminate a potential misoperation of SLOD which could inadvertently trip MPS3. Therefore, SLOD was removed to eliminate a special protection scheme, thereby improving station service grid reliability and operational safety.

3.4 Millstone Power Station LOOP Event On May 25, 2014, a single fault on the transmission system, combined with a relay misoperation, resulted in a LOOP to MPS. The event was initiated when a motor-operated disconnect switch on Line 383 failed, causing the transmission line to trip. At the time of the event, Line 371 was out of service for a scheduled relay scheme upgrade.

A line protection relay misoperation due to an incorrect relay setting on a third 345 kV line (Line 310) caused that line to trip, placing the entire MPS generating output on the last remaining transmission line (Line 348). Line 348 subsequently tripped because its relays experienced large swings in power and voltage as a result of the instability, ultimately causing the disconnection of station output from the grid and a complete LOOP to MPS.

In response to the May 25, 2014 dual unit trip and LOOP event, an NRC special inspection team (SIT) was dispatched to the station. After a comprehensive review of the sequence of events, equipment response, operator performance, and compliance with the NRC's rules and regulations, the NRC concluded that DNC should have performed a full 50.59 evaluation when eliminating SLOD and that removal of SLOD may have resulted in more than a minimal increase in the likelihood of occurrence of a malfunction of an SSC important to safety previously evaluated in the FSAR.

Specifically, the SIT determined that DNC allowed a design change to the offsite power system (removal of SLOD), and failed to conduct a full 50.59 evaluation or provide a basis for the determination that the change did not require a license amendment in accordance with 10 CFR 50.59 (c)(2). The SIT concluded that the change may have resulted in more than a minimal increase in the likelihood of occurrence of an offsite power malfunction because the removal of SLOD decreased the reliability of the offsite power system, reduced the defense-in-depth, and disabled an automatic generator rejection function, which protected the offsite power sources during transients caused by grid-related conditions. The NRC team concluded that removal of SLOD contributed to the likelihood of a dual unit trip and LOOP to both units.

In a letter dated March 31, 2015 (Reference 7.5), in response to NRC's Notice of Violation (NOV), EA-14-126, dated August 28, 2014 (Reference 7.6), DNC committed to submit a LAR that: 1) describes the basis for continued compliance with GDC-17 after modifying the DCTs to SCTs and disabling SLOD, and 2) proposes changes to the

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 12 of 42 FSAR to reflect the currently installed configuration of the offsite power sources, including the modifications that replaced the DCT design with SCTs and removed SLOD.

Additionally, DNC stated that the LAR would likely propose an AOT that would be applicable during the periods when a single offsite line is not in service (due to either an unplanned event or for planned maintenance activities on the transmission system) in conjunction with appropriate operational limitations designed to minimize the risk to the plant and maintain offsite grid stability. The submittal of this LAR is intended to meet the commitment made in the NOV response.

4.0 Technical Evaluation 4.1 FSAR Changes for Modification of Tower Structures and Removal of SLOD Both MPS2 and MPS3 FSARs require revision to reflect modification of the 345 kV transmission line DCTs with SCTs and the removal of SLOD. Attachments 2 and 3 provide the marked-up FSAR pages for MPS2 and MPS3, respectively, to reflect the required changes.

FSAR Figures 8.1-1A (MPS2) and 8.2-1(MPS3) are being deleted since the DCT design has been modified to SCTs and they no longer provide useful information. The four lines are now on SCTs of various designs. Showing a simplified sketch of the various types of SCTs is unnecessary.

FSAR Figures 8.1-1B (MPS2) and 8.2-2 (MPS3), "Hunts Brook Junction," which were used to graphically display transmission line 364 crossing under transmission lines 383, 371 and 310, are being replaced with a more simplified block diagram which more clearly depicts the transmission line cross-overs at Hunts Brook Junction. Additionally, the current figures contain extraneous and outdated information (e.g., Connecticut Yankee is now decommissioned) that is either no longer relevant or not discussed in the FSARs.

The following discussion provides the basis for meeting GDC-17 and GDC-5 after the modification of DCTs to SCTs and removal of SLOD.

Compliance with GDC-1 7, Electric Power Systems The intent of GDC-17 is to ensure electrical power is available to permit functioning of SSCs important to safety. GDC-17 invokes a number of requirements on both the onsite and offsite power systems (two connections from onsite to offsite power system, redundancy, single failure, reliability, etc.) to ensure this intent is met.

At the time of MPS3 licensing, Standard Review Plan (SRP) 8.1, "Electrical Power -

Introduction," Revision 2, and SRP 8.2, "Offsite Power System," Revision 3, provided guidance for meeting the requirements GDC-17. Although the SRP was not in effect at the time of MPS2 licensing, DNC has used the guidance of the above mentioned SRP revisions to the extent possible (recognizing previous design commitments) for addressing compliance with the requirements of GDC-1 7 issued on February 20, 1971.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 13 of 42 In later revisions of SRP 8.1 (i.e., Revision 4 - Reference 7.7) and SRP 8.2 (i.e., Revision 5 - Reference 7.8), the NRC provided staff interpretation of the SRP requirements for meeting GDC-17. The acceptance criteria provided in SRPs 8.1 and 8.2, for meeting the requirements of GDC-17, are the same. This approach to the SRP guidance was used as an aid to document how MPS meets the staff interpretation of GDC-17 with the modification of the DCTs to SCTs and the removal of SLOD.

Table 1 below summarizes each GDC-17 requirement, the NRC staff interpretation of each requirement in SRP 8.1 and SRP 8.2, and how MPS meets the NRC staff interpretation with the modification of the DCTs to SCTs and the removal of SLOD.

Table 1 Evaluation of Compliance with GDC-17 for Millstone Power Station GDC-17 Staff Interpretation. Basi~s for Meeting GDC-1 7 Criterion 17-Electric Power a. Both an offsite and onsite The offsite and onsite power Systems. power system shall be systems continue to be provided, each independent of each other and An onsite electric power independent of the other capable of providing power for system and an offsite and capable of providing required safety functions.

electric power system shall power for all safety Modification of the DCTs to be provided to permit functions. (The offsite SCTs and removal of SLOD functioning of structures, and onsite power have no impact on the onsite systems, and components systems considered power system. The current important to safety. The together must meet the onsite systems, designed to safety function for each single failure criterion on detect a LOOP, start the EDGs system (assuming the a system basis without and provide power to complete other system is not losing the capability to the required safety functions, functioning) shall be to provide power for all remain unchanged and provide sufficient capacity safety functions. In unaffected.

and capability to assure addition, in view of the There is no change to the that (1) specified requirement (b) below, independence between the acceptable fuel design the two systems onsite and offsite power limits and design considered together must systems. Both systems, conditions of the reactor be capable of sustaining coolant pressure boundary considered together, continue to a complete loss of offsite be able to provide power for the are not exceeded as a power and a single required safety functions result of anticipated failure in onsite system, assuming a complete loss of the operational occurrences without losing the offsite system and a single and (2) the core is cooled capability to provide failure on the onsite system.

and containment integrity power for the minimum and other vital functions Therefore, MPS continues to required safety are maintained in the event meet the Staff interpretation of of postulated accidents. functions.)

this portion of GDC-17.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 14 of 42 Table 1 Evaluation of Compliance with GDC-17 for Millstone Power Station GDC-17 Staff Interpretation Basis for Meeting GDC-1 7 The onsite electric power b. The complete onsite Modification of the DOTs to SCTs supplies, including the electric power system and the removal of SLOD have no batteries, and the onsite (Class 1E) must be impact on the onsite power electric distribution system, capable of sustaining a system (e.g., no onsite control shall have sufficient single failure without loss system changes, no onsite independence, of capability to provide loading changes). The onsite redundancy, and testability power for the minimum electrical power system, including to perform their safety required safety function. the batteries, will continue to have functions assuming a sufficient independence, single failure. redundancy, and testability to perform their safety functions assuming a single failure without loss of capability to provide power for the minimum required safety function.

Therefore, MPS continues to meet the Staff interpretation of this portion of GDC-17.

Electric power from the c. The offsite system shall be MPS2 transmission network to comprised of two The MPS2 design provides two the onsite electric physically independent offsite circuits between the distribution system shall be circuits connecting the switchyard and the 4 kV Class 1 E supplied by two physically transmission network buses. The immediately available independent circuits (not (grid) to the onsite offsite supply is the MPS2 RSST necessarily on separate distribution system (safety and the alternate supply is the rights of way) designed buses). (Separate MPS3 bus 34A or 34B.

and located so as to transmission line towers minimize to the extent are required but common The normal supply to MPS2 with practical the likelihood of switchyard structures are the plant online is the NSST. If their simultaneous failure acceptable. No this source is lost due to a plant under operating and requirement for meeting trip, a fast bus transfer scheme postulated accident and the single failure criterion connects the plant electrical environmental conditions. and, in the absolute system (6.9 kV and 4 kV) to the A switchyard common to sense, this criterion RSST. A second or alternate both circuits is acceptable. cannot be met because source of offsite power is there is only one power available by manual control of source, the grid.) MPS3 bus 34A or 34B for 4 kV power to feed MPS2 bus 24E.

Physical separation of the offsite power sources remain unchanged by the modification of the DCTs to SOTs and elimination of SLOD.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 15 of 42 Table 1 Evaluation of Compliance with GDC-17 for Millstone Power Station GDC-17 I Staff Interpretation Basis for Meeting GDC-17 MPS3 The MPS3 design provides two immediate access offsite circuits between the switchyard and the 4 kV Class 1 E buses. Within the switchyard, the tie-line terminations are separated electrically by two circuit breakers so that a fault on one offsite supply circuit along with a breaker failure does not cause the second offsite supply to be lost. The tie-lines are supported on separate structures with one circuit terminating at the GSU transformer dead-end tower and the second tie-line circuit terminating on the RSST dead end tower. The NSST and RSST are located on opposite sides of the unit. The connections from the NSST and RSST to the 4 kV Class 1 E buses are via physically separate and electrically independent underground duct lines.

The offsite source normally available immediately after a unit trip is from the GSU transformer and NSST. This source is not lost on a unit trip because the generator breaker effects the disconnection of the main generator from the grid, leaving the GSU transformer and NSST backfed from the switchyard. The second source of offsite power is available through an automatic transfer to the RSST.

Therefore, MPS continues to meet the Staff interpretation of this portion of GDC-17.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 16 of 42 Table 1 Evaluation of Compliance with GDC-17 for Millstone Power Station GDC-117 Staff Interpretation Bas-is for Meeting GDC-17 Each of these circuits shall d. Each of the two required Modification of the DCTs to SCTs be designed to be offsite power circuits and the removal of SLOD did not available in sufficient time shall be designed to be change the access design of following a loss of all available in sufficient either of the two offsite power onsite alternating current time to effect safe circuit connections to the onsite power supplies and the shutdown in the event of power system for either unit.

other offsite electric power a loss of all onsite power MPS2 circuit, to assure that and the loss of the other specified acceptable fuel offsite circuit. (The staff The design continues to provide design limits and design has designated the two offsite circuits between the conditions of the reactor second circuit as the switchyard and the 4 kV Class 1 E coolant pressure boundary "delayed access circuit." buses. The immediately available are not exceeded. The offsite power offsite supply is the MPS2 RSST system (i.e., the two and the alternate supply is the circuits considered MPS3 bus 34A or 34B. There is together) must meet the no single failure that could impact single failure criterion, access to both offsite circuits but only with respect to simultaneously.

the delayed access MPS3 circuit function.)

The design continues to provide two, physically separate, immediately accessible offsite circuits to the switchyard via the NSST and RSST. There is no single failure that could impact access to both offsite circuits simultaneously.

Therefore, MPS continues to meet the Staff interpretation of this portion of GDC-17.

+

One of these circuits shall e. One of these circuits Modification of the DCTs to SCTs be designed to be shall be designed to be and the removal of SLOD did not available within a few available within a few impact the immediate access of seconds following a loss-of seconds following a loss- one offsite circuit.

coolant accident to assure of-coolant accident. (The MPS2 that core cooling, staff has designated this containment integrity, and circuit as the "immediate With the plant on line, the normal other vital safety functions access circuit." Because supply is the NSST. If this source are maintained. only one such circuit is is lost due to a plant trip, a fast required, the offsite bus transfer scheme connects the power system need not plant electrical system (6.9 kV and meet the single failure 4 kV) to the RSST. The second or criterion with respect to alternate source of offsite power is its immediate access available by manual control of

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 17 of 42 Table 1 Evaluation of Compliance with GDC-1 7 for Millstone Power Station GDC-17 Staff Interpretation Basis for Meeting GDC-17 function.) MPS3 bus 34A or 34B for 4 kV power.

MPS3 Upon loss of power from the generator, the generator breaker is opened to ensure continuous power service to the safety-related buses (immediate access offsite power source). Upon loss of power from the NSST, an automatic transfer to the respective RSST is provided to ensure continuous power service to the 6.9 kV equipment and the 4 kV electrical systems (second access offsite power source).

Therefore, MPS continues to meet the Staff interpretation of this portion of GDC-17.

Provisions shall be f. Analyses (performed by The connections to the system included to minimize the the utility) must verify that were originally designed to probability of losing electric the grid remains stable in comply with the NPCC "Basic power from any of the the event of a loss of the Criteria for the Design and remaining supplies as a nuclear unit generator, Operation of Interconnected result of, or coincident the largest other unit on Power Systems" and the with, the loss of power the grid, or the most "Reliability Standards for the New generated by the nuclear critical transmission line. England Interconnected Power power unit, the loss of (There is no specific Pool" adopted by that Pool.

power from the requirement for meeting These standards have been transmission network, or the single failure criterion, superseded by NPCC Regional the loss of power from the However, overlapping Reliability Reference Directory #1 onsite electric power requirement (a) above (Reference 7.4) and ISO-New supplies, requires the offsite/onsite England Planning Procedure No.

power systems to meet 3 (Reference 7.9), respectively.

this criterion on a system Compliance with these standards basis.) ensures that the supply of offsite power is not lost following severe faults in the interconnected transmission system. Transient stability studies have been performed to verify that widespread or cascading interruptions of service do not

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 18 of 42 Table 1 Evaluation of Compliance with GDC-17 for Millstone Power Station GDQ-17 j Staff. Interpretation Basis for Meeting GDC-17 result from these contingencies.

In addition, the loss of MPS2, MPS3, or any other generating plant in the system does not result in cascading system outages and thus does not cause a LOOP to the units.

Use of DCTs for the 345kV transmission lines leaving MPS, required ISO-New England planning to consider double circuit faults. While two circuits were installed on the DCTs, SLOD was installed to resolve concerns with grid stability. After elimination of the DCT tower configuration, ISO-New England no longer considered double circuit faults a normal contingency and therefore concluded that the automatic action performed by SLOD was no longer necessary to ensure grid stability.

Within the approximate 9-mile ROW for the 345 kV transmission lines leaving the MPS switchyard, there are several points where a single transmission tower is in close enough proximity to affect adjacent towers in the event a tower was to fall. In addition, at Hunts Brook Junction, the Line 371/364 path is crossed over by Lines 383 and 310. The failure of one 345 kV line causing the failure of another 345 kV line is not considered a normal contingency by ISO-New England, but the lines are in close enough proximity such that the failure of one line could impact another line.

The above scenarios are not normal contingencies for ISO-New England and single failure is not required to be applied to the transmission system.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 19 of 42 Table 1 Evaluation of Compliance with GDC-17 for Millstone Power Station GDC-17 Staff Interpretation Basis for Meeting GDC-1i7 Therefore, MPS continues to meet the Staff interpretation of this portion of GDC-17.

Based on the evaluation provided above, DNC meets GDC-17 requirements with the modification of DCTs to SCTs and removal of SLOD. The basis is summarized below.

The modification of the DCTs to SCTs and removal of SLOD does not affect the onsite power system or the two physically separate connections from the onsite power system to the offsite power system.

" The capability of the onsite and offsite power systems to provide the required power to perform their required safety functions remain unchanged from that previously evaluated.

" Even with one 345 kV line out of service and a single failure affecting one additional transmission element (line, breaker, generator, etc.), the ISO-New England Millstone Facility Out Guide shows the offsite system will remain stable.

In addition, since initial licensing of MPS3, there have been many upgrades to the offsite transmission system to make the grid more reliable (e.g., switchyard breaker replacements, disconnect switch replacements, substation transformer replacements).

Compliance with GDC-5, Sharing of Structures, Systems and Components GDC-5 requires that SSCs important to safety shall not be shared among nuclear power units unless it can be shown that such sharing will not significantly impair their ability to perform their safety functions, including, in the event of an accident in one unit, an orderly shutdown and cooldown of the remaining units.

The offsite power system switchyard is common to both MPS2 and MPS3. This configuration was evaluated during the initial licensing of MPS3 and determined to be acceptable to the NRC.

In order for MPS2 to meet its GDC-17 requirements for an alternate offsite source, the following MPS3 equipment may be utilized: GSU transformer, NSST, and RSST. The modification of the DCTs to SCTs, and removal of SLOD, does not impact the above MPS3 component's ability to provide an alternate offsite power source to MPS2.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 20 of 42 In addition, the radioactive gaseous waste system discharge stack is shared between MPS1, MPS2, and MPS3. The modification of the DCTs to SCTs and removal of SLOD has no impact on the radioactive gaseous waste system discharge stack ability to perform its function.

Removal of SLOD from 345 kV Breaker Failure Scenarios As stated in the MPS2 and MPS3 FSARs, breaker failure relays are provided for each of the 345 kV circuit breakers. These relays are designed to trip adjacent breakers in the event that the primary breaker fails to trip. The direct current (DC) power for breaker failure operation is supplied from the backup battery system.

A breaker failure timing relay is initiated every time a main breaker is ordered to trip by either the primary or backup relays. If the breaker has not tripped before the time period has expired, tripping of the adjacent breakers takes place.

The MPS 345 kV circuit breakers have mechanically independent poles and two separate methods of tripping. These installations include two sets of relays and trip coils. There are two sets of current and potential transformers, the wiring for the relay packages are installed in separate duct banks, the relay packages are physically separated in the control house and two separate DC supplies are provided.

Sufficient redundancy is provided in the 345 kV breakers to ensure they reliably isolate a transmission line in the event of a fault. At least three 345 kV breakers would be required to fail-to-trip before three transmission lines would be lost. Failure of a single 345 kV breaker to trip, when required, is considered highly unusual, therefore, having three 345 kV breakers failing to trip simultaneously, is unlikely. As a result, DNC considers that eliminating SLOD as a defense-in-depth measure for maintaining grid stability has a minimal impact on overall grid reliability.

4.2 New Technical Requirement for Offsite Line Power Sources DNC proposes to add a new technical requirement, "Offsite Line Power Sources," to the MPS2 and MPS3 TRMs. The proposed new TRM requirements for MPS2 and MPS3 are provided in Attachments 4 and 5, respectively. The TRMs would be revised to improve operational safety margin and minimize risk to the plants. The TRMs would require that the four offsite transmission lines be functional when MPS output exceeds 1650 MWe net. With one offsite line nonfunctional, the TRM requirements would allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore the nonfunctional line with a provision to allow up to 14 days if specific TRM action requirements are met.

The DCT configuration led to installation of the SLOD special protection system during the original plant licensing for MPS3. The SLOD system was designed to automatically trip MPS3 if three transmission lines were lost and thus, maintain stability of the offsite power supply to MPS. Although SLOD was installed during initial licensing of MPS3 to

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 21 of 42 address overall grid stability, this special protection system also created the potential for an inadvertent reactor trip of MPS3, if it spuriously actuated. Therefore, SLOD was disabled by Northeast Utilities in 2012 following modification of the DCT design to SCTs.

With the four 345 kV transmission lines each on a separate tower and SLOD disabled, DNC considered the likelihood of a double line-to-ground fault causing a loss of offsite power or the potential inadvertent tripping of MPS3, was reduced.

The proposed TRM Action a.1 would allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months with one offsite line removed from service (i.e., nonfunctional). This 72-hour AOT is conservatively based on the loss of one offsite line being equal to the risk of losing one onsite connection to the offsite power system (i.e., TS 3.8.1.1).

The proposed TRM Action a.2 would contain a provision to allow up to 14 days if specific action requirements are met. The 14-day AOT, along with the proposed action requirements, will reduce the likelihood of a LOOP event by minimizing the time that a double circuit failure scenario can result in grid instability and therefore, improve operational safety margin. The 14-day AOT will reduce the risk of a plant perturbation as a result of having to downpower the unit for short duration line outages.

The proposed new TRM requirements for MPS2 and MPS3 are based on a deterministic/qualitative analysis and will rely on both defense-in-depth and configuration management measures. Three elements provide the basis for the new TRM requirements and provide a high degree of assurance of the capability to provide power to the safety related electrical buses when one of four 345 kV transmission lines is out of service. The elements are (1) a traditional engineering analysis, (2) avoidance of plant configurations that could degrade defense-in-depth using appropriate action requirements, and (3) continued implementation of the Configuration Risk Management Program (CRMP) to aid in identification of configurations that could degrade defense-in-depth while the line is out of service.

Element 1 - Traditional Engineering Analysis The New England Bulk Power System is comprised of various interconnected member utilities with several connections to neighboring power systems. Power generation and transmission within the six-state power system is overseen by ISO-New England. The system includes MPS and the four 345 kV transmission lines which terminate at the MPS switchyard.

The MPS offsite transmission lines are designed and operated in accordance with the ISO-New England Planning Procedure No. 3, "Reliability Standards for the New England Area Bulk Power Supply System" (Reference 7.9) and NPCC's Regional Reliability Reference Directory #1, "Design and Operation of the Bulk Power System" (Reference 7.4). The purpose of these New England reliability standards is to ensure the reliability and efficiency of the New England bulk power system.

North American Electric Reliability Corporation (NERC) Reliability Standard NUC-001-2.1, "Nuclear Plant Interface Coordination" (Reference 7.10) requires each nuclear plant

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 22 of 42 generator operator and its associated transmission entities to establish nuclear interface agreements that document the applicable Nuclear Plant Interface Requirements (NPIRs) for the purpose of ensuring nuclear plant safe operation and shutdown. These NPIRs include the following requirements:

" Maintain real-time voltage at the MPS switchyard at or above 345 kV and below 362 kV in order to ensure safe shutdown capability for MPS.

" Coordinate and plan in real-time the outage of any transmission line serving as an offsite power source for MPS.

ISO-New England has performed grid stability studies based on a number of different contingencies. These stability studies show that with three 345 kV lines available and the loss of either MPS2, MPS3, the largest other unit on the grid, or the most critical transmission line, the grid will remain stable and offsite power will be available to MPS.

During the initial licensing of MPS3, the cross-over of lines at Hunts Brook Junction and the DCTs installed within the common ROW north of the MPS switchyard were identified as concerns. The DCTs have been replaced with SCTs, however, the concern regarding the cross-over of lines at Hunts Brook Junction remain. The approximate 9-mile ROW between MPS and Hunts Brook Junction was recently walked down to identify any circuit towers/lines in close enough proximity to allow potential interaction (Reference 7.11).

This walkdown identified the following areas of concern:

e Proximity of Two Lines - At four ROW locations, the spacing separation of two of the independent lines are close enough to enable certain types of limiting line-drop type single failures to impact an adjacent line.

Within the approximately 9-mile ROW going north of the MPS switchyard, there are four AC circuit conductor locations where two lines are supported from different towers in close proximity (horizontal clearance less than about 40 feet) with one line supported at' a higher vertical location (vertical clearance more than 40 feet). This combination of horizontal proximity and support at different vertical heights could potentially allow a dropped or broken conductor from one line to contact a conductor on an adjacent line assuming conditions with sufficient wind velocity and direction (Reference 7.12).

9 Line Cross-Overs - At three specific ROW locations, transmission lines cross-overs exist which enable a limiting line-drop type single failure to also impact an adjacent line.

There are three locations of AC circuit conductor crossovers at Hunts Brook Junction. There are two failure modes for conductors and shield wires that could allow them to fall onto a lower line. If an insulator or cross arm on the support tower on either side of the crossing span were to fail, the conductor or shield wire could drop onto the second line. If a conductor or shield wire were to break within

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 23 of 42 the crossing span, the broken conductor or shield wire could drop onto the second line.

Tower Failures - There are a number of locations where circuit towers are in close proximity such that the failure of one tower could impact another tower.

There are various locations within the ROW where one tower is in close enough proximity to affect another tower in the event of total failure. The transmission towers which support the four 345 kV transmission lines are designed to the National Electric Safety Code, Part C2 and consist of a combination of steel and wooden mono-pole structures, and steel and wooden H-frame structures.

NERC reliability standards do not consider a SCT or line failure affecting another tower or line (regardless of proximity) as a normal contingency. Therefore, ISO-New England stability/transient studies do not assume simultaneous phase-to-ground faults impacting two 345 kV transmission lines when each line is on its own separate tower.

Since DCTs no longer support any of the four 345 kV transmission lines leaving MPS, ISO-New England only considers normal contingencies in the stability/transient studies.

The stability/transient studies conclude that with one 345 kV transmission line out of service, the loss of either MPS2, MPS3, the largest other unit on the grid, or the most critical transmission line, the grid will remain stable and offsite power will be available to MPS. Therefore, ISO-New England does not require MPS to reduce power output in order to maintain offsite power stability when only one of the four 345 kV transmission lines is out of service.

DNC takes a more conservative approach in addressing these limiting areas of concern that could potentially cause the loss of two 345 kV lines due to a single failure. DNC conservatively considers that when less than four 345 kV transmission lines are in service, a degradation of safety margin and defense-in-depth has occurred. Therefore, DNC is proposing to establish appropriate requirements in the TRMs that are applicable whenever MPS output exceeds 1650 MWe net and any one of the four 345 kV transmission lines is out-of-service (i.e., nonfunctional).

Basis for Applicability when Station Output Exceeds 1650 MWe Net ISO-New England has performed stability studies which conclude that when two 345 kV lines are in service, the transmission system will remain stable assuming the additional loss of a third 345 kV line (leaving only one 345 kV line connected to the Millstone switchyard) as long as Millstone Station electrical output is less than the value provided in Millstone Facility Out Guide-Text Document.

Table 1 in the Millstone Facility Out Guide indicates MPS electrical output, with any two transmission lines out-of-service, must be maintained below the specified limit. There would be no required power reduction request from ISO-New England if MPS output is less than 1650 MWe net for any combination of two transmission lines out-of-service.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 24 of 42 Basis for 14-Day Allowed Outage Time The 14-day AOT was selected based on the following:

" The AOT is consistent with the 14-day AOT in Technical Specification 3.8.1.1 for one inoperable EDG for MPS2 and MPS3.

" A 14-day AOT is prescribed for offsite power sources in Branch Technical Position 8-8 (Reference 7.15).

" Given expected frequency and consequences of system challenges, limiting the offsite line AOT to 14 days, along with the proposed TRM action requirements, reduces the likelihood of a LOOP event by minimizing the time that a double circuit failure scenario can result in grid instability and therefore, improves operational safety margin.

" Transmission line outage data shows that establishing a 14-day AOT minimizes the likelihood of having to maneuver the units due to planned and unplanned line outages.

Therefore, establishing TRM requirements that allow up to 14 days of full power operation when any one of the four 345 kV transmission lines is out of service is considered reasonable. The defense-in-depth analysis and historical transmission line data review is provided below.

Defense-in-Depth Analysis

1. System redundancy, independence, and diversity are maintained commensurate with expected frequency and consequences of system challenges.

The ISO-New England Millstone Facility Out Guide concludes that with one 345 kV transmission line out of service and one additional transmission system element failure (line, breaker, generator, etc.), the offsite power system will remain stable. Based on failure history, limiting the offsite line AOT to 14 days, along with the proposed TRM action requirements, reduces the likelihood of a LOOP event by minimizing the time that a double circuit failure scenario can result in grid instability and therefore, improves operational safety margin.

2. Defenses against potential Common Cause Failures (CCF) are maintained and potential for introduction of new CCFs mechanisms are assessed.

Removal of one 345 kV transmission line minimally increases the potential for a LOOP event; however, this is not a new CCF. The proposed TRM requires an initial weather assessment when using the 14 day AOT and then once per shift

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 25 of 42 thereafter. This requirement reduces the likelihood of a single failure causing the concurrent loss of two additional 345 kV transmission lines.

3. Independence of physical barriers is not degraded.

There are four connections (two per unit) between the onsite and offsite power systems. The physical barriers separating these four connections remain unchanged when one 345 kV transmission line is removed from service.

4. Defenses against human errors are maintained.

By establishing an AOT of 14 days, historical data indicates that the number of plant maneuvers due to planned and unplanned transmission line outages will be minimized, thereby minimizing the potential for human error.

5. The intent of plant design criteria is maintained.

The ISO-New England Millstone Facility Out Guide concludes that with one 345 kV transmission line out of service, the loss of either MPS2, MPS3, the largest other unit on the grid, or the most critical transmission line, the grid will remain stable and offsite power will be available to MPS.

Historical Transmission Line Data Review DNC reviewed Eversource data for the four 345 kV transmission lines leaving MPS.

This data includes: transmission line disturbances from 2005 through May 1, 2015, forced transmission line outages from 2005 through August 2014, and planned transmission line outages from 2009 through May 3, 2015 (Reference 7.13).

A review of the disturbance data for the four 345 kV transmission lines leaving MPS showed that most line failures were due to bird fouling, and caused only a momentary loss of the transmission line. There was one conductor failure; however, it did not occur in an area of concern and did not affect two lines. There were three insulator failures, two of which caused significant line outage durations. However, none occurred in an area of concern where two lines could be affected.

There were only two events which caused multiple 345 kV transmission line failures.

One event was Hurricane Sandy during which three momentary losses occurred (two momentary losses of Line 383 at slightly different times and one momentary loss of Line 310). None of these interruptions occurred concurrently. An action requirement, intended to minimize the potential for this failure mechanism, has been included in the proposed TRM requirements which are described below. Specifically, TRM Action a.2.b would require MPS2 and MPS3 to perform an initial weather assessment for the scheduled transmission line outage duration and then once per shift thereafter. If an assessment predicts adverse or inclement weather will exist while the offsite line is nonfunctional (i.e., out of service for planned maintenance), total

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 26 of 42 station output would be reduced to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits, prior to arrival of the adverse or inclement weather.

The second event was the May 25, 2014 dual unit trip and LOOP event. The cause of this event was not due to transmission line failures. Rather, the cause was related to a human performance error associated with a protective relay setting at an offsite location. The cause was corrected as part of the corrective actions to prevent recurrence for the May 25, 2014 dual unit trip and LOOP event (Reference 7.14).

These corrective actions are summarized below:

" Conducted a comprehensive study of the Northeast Utilities 345KV transmission protection systems to determine if other relay setting vulnerabilities exist due to incomplete consideration of the mutual coupling effect.

" Implemented a Northeast Utilities Transmission Lessons Learned document to emphasize the importance of considering the effects of mutual coupling when setting ground instantaneous over current (IOC) elements.

Performed a comprehensive review of relay settings associated with the 345 kV transmission lines connected to Millstone 15G and issued, implemented and tested revised settings which specifically include: 1) Permanently disabling the ground IOC elements for the line terminals at Millstone 15G and remote terminals of Lines 310, 371, and 383. 2) Permanently disabling the ground IOC elements for both line terminals of the 364 line. 3) Re-enabling the ground IOC elements at the 348 line remote terminals only upon a line relay loss of potential condition.

The data showed there were no tower failures during this time period (from 2005 through May 1,2015).

Between 2005 and May 1, 2015, there were a total of 36 transmission line disturbances, 13 of which occurred when MPS output was less than 1650 MWe net (i.e., one Millstone unit was in an outage). Of the remaining 23 disturbances, only one was greater than 3 days in duration (i.e., during the May 25, 2014 LOOP event).

Between 2005 and August 2014, there were seven forced transmission line outages, two of which occurred when MPS output was less than 1650 MWe net (i.e., one Millstone unit was in an outage). None of the forced outages were greater than three days in duration.

Between 2009 and May 3, 2015, there were a total of 67 planned transmission line outages, 22 of which occurred when MPS output was less than 1650 MWe net (i.e.

one Millstone unit was in an outage). Of the remaining 45 planned outages, 12 were greater than three days in duration (this does not include the transmission line outage from the May 25, 2014 LOOP event).

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 27 of 42 Based on these durations and a 72-hour AOT, plant operators would have been required to maneuver the reactor (or plant equipment) a total of 12 additional times between 2009 and May 2015 (Note: During this time period there was only one line outage greater than 14 days.). Implementation of the proposed TRM requirements, which would allow a single line to be out of service for up to 14 days, minimizes the likelihood of having to maneuver the units due to planned and unplanned line outages.

Element 2 - Avoidance of Plant Configurations that Could Degrade Defense-in-Depth Using Appropriate Mitigating Measures The following TRM action requirements are proposed to ensure defense-in-depth is maintained during the 14-day AOT when one 345 kV offsite transmission line is out of service. These action requirements are intended to minimize the likelihood of a LOOP event by ensuring that 1) the remaining 345 kV lines will remain functional during the period of planned maintenance, 2) appropriate actions will be taken to minimize the potential for a adverse or inclement weather conditions event to impact grid reliability, and 3) AC power will be available to support safety-related equipment in the unlikely event of a LOOP when a 345 kV line is out of service. Specifically, the proposed action requirements are:

Once per shift, verify the remaining offsite lines to the Millstone Switchyard are FUNCTIONAL.

" Perform an initial weather assessment for the expected line outage duration and then once per shift thereafter.

" Within one hour prior to or after entering this condition, verify that the EDGs are OPERABLE and the Millstone Unit 3 SBO diesel generator is available and at least once per 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months thereafter.

The basis for each TRM action requirement is discussed below.

TRM Action Reguirement a.2.a "Once per shift, verify the remaining offsite lines to the Millstone Switchyard are FUNCTIONAL.

Basis:

This action requires that Millstone contact Eversource once per shift to verify there are no known issues that could threaten the reliability of the remaining 345 kV transmission lines. This requirement increases confidence that the remaining 345 kV lines will remain functional during the planned outage of the affected 345 kV line.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 28 of 42 TRM Action Requirement a.2.b "Perform an initial weather assessment for the scheduled line outage duration and then once per shift thereafter. If the assessment predicts adverse or inclement weather conditions will exist while the offsite line is nonfunctional (i.e., out-of-service), reduce total station output to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits, prior to arrival of the adverse or inclement weather."

Basis:

The transmission towers which support the four 345 kV lines are designed to the National Electric Safety Code, Part C2 and consist of a combination of steel and wooden mono-pole structures, and steel and wooden H-frame structures.

Accordingly, a review of the transmission tower design requirements and anticipated weather patterns at MPS provide reasonable assurance that the towers will withstand typical weather conditions, except severe conditions such as hurricanes and tornadoes.

A review of Eversource data for unplanned MPS 345 kV transmission line outages from 2005 to May 1, 2015 (Reference 7.13) confirms there have been few weather-related offsite line outages. There were five weather-related events; two due to lightning and three due to Hurricane Sandy. The impact of the five events was minimal in that the line outage durations were negligible (breaker opening and closing). Therefore, thunderstorms with lightning forecasted are not considered adverse or inclement weather conditions. Hurricanes and tornadoes are considered adverse or inclement weather conditions.

The action requirement to perform weather assessments ensures appropriate actions are taken to minimize the potential for a severe event to impact grid reliability with one line nonfunctional (i.e., out-of-service). If an adverse or inclement weather condition is predicted, the nonfunctional 345 kV line must be restored to functional status or station output must be reduced to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits, prior to arrival of the adverse or inclement weather. This action requirement to perform weather assessments is consistent with the requirements contained in the MPS2 and MPS3 TS 3.8.1.1 Bases when using the 14-day TS 3.8.1.1 AOT for extended EDG maintenance.

TRM Action Requirement a.2.c "Within one hour prior to or after entering this condition and at least once per 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months thereafter, verify that both the Millstone Unit 2 EDGs and the Millstone Unit 3 EDGs are OPERABLE and the Millstone Unit 3 SBO diesel generator is available. Restore any inoperable Millstone Unit 2 EDG or Millstone Unit 3 EDG to OPERABLE status and/or the Millstone Unit 3 SBO to available status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months or reduce total station output to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months ."

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 29 of 42 Basis:

Maintaining the EDGs operable and the MPS3 SBO diesel generator available provides a high degree of assurance that AC power will be available to support required safety equipment in the unlikely event of a LOOP when a 345 kV line is nonfunctional.

For the condition where the 14-day AOT is in use for one offsite line nonfunctional (i.e.,

out-of-service) and an EDG is inoperable or the MPS3 SBO diesel generator is unavailable, 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months is allowed to restore the inoperable EDG or unavailable SBO diesel generator or total station output must be reduced to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months .

Two Offsite Lines Nonfunctional For an unplanned failure of one additional 345 kV transmission line during the 14-day AOT, TRM Action b would require DNC to downpower in accordance with the ISO-New England Millstone Facility Out Guide stability operating limits within the next 30 minutes, as required by the NPCC Regional Reliability Reference Directory #1 (Reference 7.4), to prevent any additional 345 kV line failures from causing offsite power stability issues.

Element 3 - Continued Implementation of Configuration Risk Management Program (CRMP) to Aid in Identification of Configurations that Could Degrade Defense-In-Depth During the 14 Day AOT The following describes the elements of the configuration risk management program which ensure reliability of AC power to support required safety equipment:

" Planned transmission line outages are coordinated between ISO-New England and MPS.

" DNC will request transmission operating guides to contain the 14-day AOT TRM limit.

" The MPS2 and MPS3 EDGs will be operable and the MPS3 SBO diesel generator will be available with a TRM provision to allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore an inoperable EDG or unavailable SBO diesel generator.

" Core damage risk associated with performing switchyard work (including transmission line outages and physical work) will continue to be managed under Section (a)(4) of 10 CFR 50.65, "Requirements for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants."

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 30 of 42 Conclusion DNC is proposing to add new requirements to the MPS2 and MPS3 TRMs that would require all four offsite 345 kV transmission lines to be functional when MPS electrical output exceeds 1650 MWe net. The proposed TRM also contains required actions that must be performed when one offsite 345 kV transmission line is non-functional. The TRM actions would allow a 345 kV transmission line to be nonfunctional for up to 14 days provided the applicable TRM Actions are performed. The proposed new TRM requirements provide flexibility to preclude plant downpowers due to planned and unplanned offsite transmission line outages. The TRM requirements provide this flexibility while also maintaining adequate defense in depth to ensure grid reliability and stability are preserved and the ability of the plants to respond to design basis accidents is not adversely affected. The 14-day AOT provides flexibility for conducting maintenance and improves operational safety margin by the following:

Minimizes the number of plant downpowers for short duration 345 kV transmission line outages.

" Reduces the likelihood of a LOOP event by establishing an AOT with additional defense-in-depth measures to minimize the potential for a double circuit failure scenario which can result in grid instability.

5.0 Regulatory Evaluation 5.1 Applicable Regulatory Regluirements/Criteria On February 20, 1971, the Atomic Energy Commission published in the Federal Register the General Design Criteria [GDC] for Nuclear Power Plants. The GDC, which are contained in Appendix A of 10 CFR 50, establish minimum requirements for the principal design criteria for water-cooled nuclear power plants. Although MPS2 was designed and licensed to the GDC, as issued on July, 11, 1967, DNC has attempted to comply with the intent of the newer GDC to the extent possible, recognizing previous design commitments.

The following GDC, regulatory documents, and industry standards establish specific design requirements applicable to the MPS offsite power systems:

" GDC-17, Electric Power Systems

GDC-5, Sharing of Structures, Systems, and Components These design requirements were used for evaluating the adequacy of the MPS offsite power system design.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 31 of 42 GDC-1 7, Electric Power Systems GDC-17 defines requirements for the onsite electric power system and the offsite electric power system. The offsite power system is referred to as the "preferred power supply" -

see Section 8.2 of the NRC's Standard Review Plan (Reference 7.8). However, the preferred power supply is not a Class 1E system.

GDC-17 is part of the design and licensing bases for MPS2 and MPS3. GDC-17 requires the onsite and offsite power system to have sufficient capacity to assure:

a. Specified fuel design limits and design conditions of reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences, and;

b. The core is cooled and containment integrity and other vital functions are maintained in event of postulated accidents.

GDC-5, Sharing of structures, systems, and components GDC-5 requires that structures, systems, and components important to safety shall not be shared among nuclear power units unless it can be shown that such sharing will not significantly impair their ability to perform their safety functions, including, in the event of an accident in one unit, an orderly shutdown and cooldown of the remaining units.

Technical Specifications The MPS2 and MPS3 TS require, "Two physically independent circuits between the offsite transmission network and the onsite Class 1E distribution system" to be operable in Modes 1, 2, 3, and 4 (TS 3.8.1.1). With one offsite circuit inoperable, Surveillance Requirement 4.8.1.1.1 must be performed for the remaining offsite circuit within 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months prior to or after entering the inoperable condition, and at least once per 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months thereafter, until operability is restored. Surveillance Requirement 4.8.1.1.1 involves verifying correct breaker alignments and power available from the offsite circuit. The action statement associated with TS 3.8.1.1 for one offsite circuit inoperable also requires restoration of the inoperable offsite circuit to operable status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months or the plant must be in hot standby within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and cold shutdown within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

For Modes 5 and 6, only "One circuit between the offsite transmission network and the onsite Class 1E distribution system" is required to be operable (TS 3.8.1.2).

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 32 of 42 5.2 Evaluation of 10 CFR 50.36 Criteria DNC is proposing to add new requirements to the MPS2 and MPS3 TRM for offsite line power sources. The TRMs would require that the four 345 kV offsite transmission lines be functional when MPS output exceeds 1650 MWe net. With one offsite line nonfunctional, the TRM requirements would allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore the nonfunctional line with a provision to allow up to 14 days if specific TRM actions are met.

The TRM is a licensee-controlled document that contains requirements for plant operation that do not meet the threshold for inclusion into TSs. Changes to the TRM are controlled under the requirements of 10 CFR 50.59, "Changes, Tests and Experiments."

The Commission's regulatory requirements related to the content of TSs are set forth in 10 CFR 50.36. This regulation requires that the TSs include items in five specific categories. These categories include; 1) safety limits, limiting safety system settings and limiting control settings; 2) limiting conditions for operation (LCOs); 3) surveillance requirements; 4) design features; and 5) administrative controls. However, the regulation does not specify the particular TSs to be included in a plant's license.

Additionally, 10 CFR 50.36(c)(2)(ii) sets forth four criteria to be used in determining whether an LCO is required to be included in the TSs. Specifically, 10 CFR 50.36 (c)(2)(ii) requires a TS LCO must be established for each item meeting the one or more of the following criteria:

1. Installed instrumentation that is used to detect, and indicate in the control room, a significant abnormal degradation of the reactor coolant pressure boundary.

2. A process variable, design feature, or operating restriction that is an initial condition of a design basis accident or transient analysis that assumes either the failure of, or presents a challenge to, the integrity of a fission product barrier.

3. A structure, system, or component that is part of the primary success path and which functions or actuates to mitigate a design-basis accident or transient that either assumes the failure of or presents a challenge to the integrity of a fission product barrier.

4. A structure, system or component which operating experience or probabilistic risk assessment has shown to be significant to public health and safety.

Existing LCOs and related surveillances which satisfy any of the criteria stated above must be retained in TSs. Those requirements which do not satisfy these criteria may be located in other licensee-controlled documents. Since requirements related to the offsite power system beyond the scope of TS 3.8.1.1 have never been included in the MPS2 or MPS3 TSs, DNC is proposing to include the proposed new requirements in the MPS2 and MPS3 TRM.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 33 of 42 The NRC published its Final Policy Statement on TS improvements on July 22, 1993 (58FR39132). The Final Policy Statement provided the four specific criteria above for determining which design features and information should be located in TSs as LCOs.

The four criteria provided in the Final Policy Statement were subsequently codified in 10 CFR 50.36. The Final Policy Statement contains a discussion of each of the four criteria.

Each of the four criteria is listed below, along with the Final Policy Statement discussion related to each criterion, and the DNC evaluation of the proposed requirements for the offsite power system.

1. Installed instrumentation that is used to detect, and indicate in the control room, a significant abnormal degradation of the reactor coolant pressure boundary.

Discussion of Criterion 1 A basic concept in the adequate protection of the public health and safety is the prevention of accidents. Instrumentation is installed to detect significant abnormal degradation of the reactor coolant pressure boundary so as to allow operator actions to either correct the condition or to shut down the plant safely, thus reducing the likelihood of a loss-of-coolant accident.

This criterion is intended to ensure that TSs control those instruments specifically installed to detect excessive reactor coolant system leakage. This criterion should not, however, be interpreted to include instrumentation to detect precursors to reactor coolant pressure boundary leakage or instrumentation to identify the source of actual leakage (e.g., loose parts monitor, seismic instrumentation, valve position indicators).

Evaluation of Criterion 1 The offsite power system does not include instrumentation that detects, or indicates in the control room, degradation of the reactor coolant pressure boundary.

Therefore, the proposed TRM requirements for offsite line power sources do not meet Criterion 1 for inclusion into technical specifications.

2. A process variable, design feature, or operating restriction that is an initial condition of a design basis accident or transient analysis that assumes either the failure of, or presents a challenge to, the integrity of a fission product barrier.

Discussion of Criterion 2 Another basic concept in the adequate protection of the public health and safety is that the plant shall be operated within the bounds of the initial conditions assumed in the existing design basis accident and transient analyses and that the plant will be operated to preclude unanalyzed transients and accidents. These analyses consist of postulated events analyzed in the FSAR for which a structure, system, or component must meet specified functional goals. These analyses are contained in

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 34 of 42 Chapter 14 (or equivalent chapters) and are identified as Condition II, Ill, or IV events (ANSI N18.2) (or equivalent) that either assume the failure of, or present a challenge to, the integrity of a fission product barrier.

As used in Criterion 2, process variables are only those parameters for which specific values or ranges of values have been chosen as reference bounds in the design basis accident or transient analyses and which are monitored and controlled during power operation such that process values remain within the analysis bounds.

Process variables captured by Criterion 2 are not, however, limited to only those directly monitored and controlled from the control room.

These could also include other features or characteristics that are specifically assumed in design basis accident and transient analyses even if they cannot be directly observed in the control room (e.g., moderator temperature coefficient and hot channel factors).

The purpose of this criterion is to capture those process variables that have initial values assumed in the design basis accident and transient analyses, and which are monitored and controlled during power operation. As long as these variables are maintained within the established values, risk to the public safety is presumed to be acceptably low. This criterion also includes active design features (e.g., high pressure/low pressure system valves and interlocks) and operating restrictions (pressure/temperature limits) needed to preclude unanalyzed accidents and transients.

Evaluation of Criterion 2 The offsite power systems are assumed to be available during several FSAR Chapter 14 (MPS2) and Chapter 15 (MPS3) events. Existing TS 3.8.1.1 currently requires connections to the offsite transmission network. The proposed new TRM change to allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore a nonfunctional line with a provision to allow up to 14 days if specific TRM action requirements are met, does not impact offsite power availability. With one 345 kV line nonfunctional, offsite power remains available and the existing analyses remain bounding.

Therefore, the proposed TRM requirements for offsite line power sources do not meet Criterion 2 for inclusion into technical specifications.

3. A structure, system, or component that is part of the primary success path and which functions or actuates to mitigate a design basis accident or transient that either assumes the failure of or presents a challenge to the integrity of a fission product barrier.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 35 of 42 Discussion of Criterion 3 A third concept in the adequate protection of the public health and safety is that in the event that a postulated design basis accident or transient should occur, structures, systems, and components are available to function or to actuate in order to mitigate the consequences of the design basis accident or transient. Safety sequence analyses or their equivalent have been performed in recent years and provide a method of presenting the plant response to an accident. These can be used to define the primary success paths.

A safety sequence analysis is a systematic examination of the actions required to mitigate the consequences of events considered in the plant's design basis accident and transient analyses, as presented in Chapters 14 (or equivalent chapters) of the plant's FSAR. Such a safety sequence analysis considers all applicable events, whether explicitly or implicitly presented.

The primary success path of a safety sequence analysis consists of the combination and sequences of equipment needed to operate (including consideration of the single failure criteria), so that the plant response to design basis accidents and transients limits the consequences of these events to within the appropriate acceptance criteria.

It is the intent of this criterion to capture into TSs only those structures, systems, and components that are part of the primary success path of a safety sequence analysis. Also captured by this criterion are those support and actuation systems that are necessary for items in the primary success path to successfully function.

The primary success path for a particular mode of operation does not include backup and diverse equipment (e.g., rod withdrawal block which is a backup to the average power range monitor high flux trip in the startup mode, safety valves which are backup to low temperature overpressure relief valves during cold shutdown).

Evaluation of Criterion 3 The offsite power systems are assumed to be available during several FSAR Chapter 14 (MPS2) and Chapter 15 (MPS3) events. For these events, connection to the offsite power system is part of the primary success path for which TS LCOs already exist (i.e., TS 3.8.1.1).

The proposed TRM change to allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore a nonfunctional line, with a provision to allow up to 14 days if specific TRM action requirements are met, does not impact offsite power availability and does not adversely impact the primary success path associated with offsite power availability. With one offsite line nonfunctional, offsite power remains available and the existing analyses remain bounding.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 36 of 42 Therefore, the proposed TRM requirements for offsite line power sources do not meet Criterion 3 for inclusion into technical specifications.

4. A structure, system or component which operating experience or probabilistic risk assessment has shown to be significant to public health and safety.

Discussion of Criterion 4 It is the Commission policy that licensees retain in their TSs LCOs, action statements and surveillance requirements for the following systems (as applicable),

which operating experience and PRA have generally shown to be significant to public health and safety and any other structures, systems, or components that meet this criterion:

" Residual Heat Removal, and

Recirculation Pump Trip.

The Commission recognizes that other structures, systems, or components may meet this criterion. Plant and design-specific PRA have yielded valuable insight to unique plant vulnerabilities not fully recognized in design basis accident or transient analyses. It is the intent of this criterion that those requirements for which PRA or operating experience exposes as significant to public health and safety (consistent with the Commission's Safety Goal and Severe Accident Policies), be retained or included in TSs.

The Commission expects that licensees, in preparing TS-related submittals, will utilize any plant-specific PRA or risk survey, as well as any available literature on risk insights from PRA. This material should be employed to strengthen the technical bases for those requirements that remain in TSs, when applicable, and to verify that none of the requirements to be relocated contain constraints of prime importance in limiting the likelihood or severity of the accident sequences that are commonly found to dominate risk.

Similarly, the NRC staff will also employ risk insights and PRA in evaluating TS-related submittals. Further, as a part of the Commission's ongoing program of improving TSs, it will continue to consider methods to make better use of risk and reliability information for defining future generic TS requirements.

Evaluation of Criterion 4 Offsite power systems are not included in NUREG-1431, "Standard Technical Specifications - Westinghouse Plants" (Reference 7.17) or NUREG-1432, "Standard Technical Specifications - Combustion Engineering Plants" (Reference 7.18). Therefore, not including requirements associated with the offsite power system in the TSs is consistent with both past and current industry practice and precedent.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 37 of 42 The MPS2 and MPS3 PRAs do not specifically model the four offsite power transmission lines. Instead, LOOP frequency and consequential LOOP probability values are applied in the PRA models. The values are calculated based on industry LOOP events occurring within a certain time period. For MPS, the May 25, 2014 event represents the only site LOOP event (i.e., a LOOP to all operating units on site) or event initiated following loss of three transmission lines occurring in the station's history. The only other transmission line-related event occurred in 2007 when MPS3 experienced a LOOP (while MPS2 remained in operation) during Refueling Outage 11 due to a switchyard breaker being inadvertently opened by the transmission system operator.

Based on transmission line maintenance data, one transmission line is removed from service approximately 10 times per year (Reference 7.13), with the May 25, 2014 event being the only instance during which a loss of three transmission lines occurred. In this event, one line was out for maintenance and a fault occurred on a second transmission line with the third line failing as the result of a latent human error associated with transmission line protective relaying at an offsite location.

One of the corrective actions taken by Eversource after this event was to eliminate the protective relaying element that caused the trip. As a result, corrective actions to prevent recurrence have been taken. With only one event occurring over a relatively extended period (i.e., decades) and the cause of that event eliminated, the 2014 event is not considered representative of the risk impact associated with the removal of one transmission line from service. Consequently, the individual offsite transmission lines, including the specific configuration involving one transmission line out-of-service for maintenance, are not considered significant to public health and safety.

Therefore, the proposed TRM requirements for offsite line power sources do not meet Criterion 4 for inclusion into technical specifications.

Based on the above, DNC has concluded that the proposed new TRM requirements for offsite line power sources do not meet the criteria in 10 CFR 50.36(c)(2)(ii) for establishing a TS LCO. DNC is proposing to locate these requirements in the TRM for MPS2 and MPS3. The TRM is a licensee-controlled, document that contains requirements for plant operation that do not meet the 10 CFR 50.36(c)(2)(ii) criteria for inclusion in the plant TSs. Changes to the TRM are controlled under the requirements of 10 CFR 50.59. The above conclusions are consistent with the NRC Final Policy Statement on TS improvements dated July 22, 1993 (58FR39132).

5.3 No Significant Hazards Consideration Pursuant to 10 CFR 50.90, Dominion Nuclear Connecticut, Inc. (DNC) is requesting an amendment to Operating License DPR-65 for Millstone Power Station Unit 2 (MPS2) and Operating License NPF-49 for Millstone Power Station Unit 3 (MPS3).

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 38 of 42 The proposed amendments will revise the MPS2 and MPS3 Final Safety Analysis Reports (FSAR) to reflect changes made to the offsite transmission system to improve the reliability of offsite power. Specifically, the previous configuration of the four 345 kV offsite transmission lines had four lines sharing two sets of double circuit towers (steel monopole and wooden) in the approximate 9-mile length of right-of-way (ROW) between MPS and Hunts Brook Junction. This tower design was later modified to a single circuit tower design such that each of the four 345 kV offsite transmission lines are now supported on their own separate tower. The new configuration reduces the probability for simultaneous failure of two lines on a common tower. In conjunction with the changes to the support towers, the severe line outage detection (SLOD) protection equipment was disabled.

Additionally, the proposed license amendments would add a new Technical Requirements Manual (TRM) requirement for MPS2 and MPS3 to maintain four offsite lines functional when MPS output exceeds 1650 MWe net. In addition, the proposed new TRM requirement provides required actions when one offsite line is nonfunctional.

Specifically, the proposed TRM requirement would allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months with one offsite line nonfunctional and up to 14 days with one line nonfunctional provided specific actions are performed.

According to 10 CFR 50.92(c), a proposed amendment to an operating license involves no significant hazards consideration if operation of the facility in accordance with the proposed amendment would not:

1. Involve a significant increase in the probability or consequences of an accident previously evaluated; or

2. Create the possibility of a new or different kind of accident from any accident previously evaluated; or

3. Involve a significant reduction in a margin of safety.

In support of this determination, an evaluation of each of the three criteria set forth in 10 CFR 50.92(c) is provided below regarding the proposed license amendment.

Criterion 1 Does the proposed amendment involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No The post-modification configuration of the offsite 345 kV transmission system (four lines separately supported and SLOD disabled) improves overall grid reliability and continues to meet the requirements for two independent sources of offsite power (GDC-17).

Therefore, the post-modification configuration does not significantly increase the probability or consequences of a loss of offsite power event. Likewise, the associated

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 39 of 42 proposed changes to the MPS2 and MPS3 FSARs to document the revised 345 kV transmission line tower design and disabling of SLOD, do not increase the probability or consequences of an accident previously evaluated in the FSARs.

The grid (offsite power) is by design, the preferred power source for the affected units.

The grid provides a reliable source of power to MPS2 and MPS3 while the units are at power, in the event of unit trips, and when the units are shut down for maintenance.

New TRM requirements are proposed that will maintain adequate defense in depth to ensure grid reliability and stability are preserved.

A loss of offsite power event is an anticipated operational occurrence. The proposed changes do not significantly increase the probability of this event. Additionally, as described in Chapter 14 (MPS2) and Chapter 15 (MPS3), several events are assumed to occur coincident with a loss of offsite power. Sufficient onsite power sources are available to mitigate these events and ensure the consequences of the existing analyses for these events remain bounding.

The proposed new TRM requirements for offsite line power sources will not change the plant design or design requirements. The design criteria for the offsite power system remain unchanged. Therefore, the safety analyses as documented in the MPS2 and MPS3 FSARs remain unchanged. Temporary reductions in the number of offsite lines from four to three, in accordance with the proposed TRM action requirements, will not adversely affect offsite power system availability in the event of a loss of either MPS2, MPS3, the largest other unit on the grid, or the most critical transmission line. Use of the proposed TRM requirements will not cause an accident to occur and will not change how accident mitigation equipment is operated. Allowing one offsite line to be nonfunctional for up to 14 days does not increase the probability of any previously evaluated accidents.

Therefore, the proposed changes to the offsite 345 kV transmission system (four lines separately supported and SLOD disabled) and proposed new TRM requirements does not significantly increase the probability or consequences of an accident previously evaluated.

Criterion 2 Does the proposed amendment create the possibility of a new or different kind of accident from any accident previously evaluated?

Response: No The proposed amendments do not change the design function or operation of the offsite power system and do not affect the offsite power systems ability to perform its design function. The proposed amendments do not conflict with the design criteria, codes, or standards committed to in the licensing basis. The existing codes and standards, as they apply to the onsite emergency power systems, remain unchanged. The design

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 40 of 42 criteria for the offsite power system remain unchanged, Therefore, the safety analyses as documented in the MPS2 and MPS3 FSARs remain unchanged.

No credible new failure mechanisms, malfunctions, or accident initiators not considered in the design and licensing basis are created by the proposed amendment. The offsite power system is assumed to be available during several FSAR Chapter 14 (MPS2) and Chapter 15 (MPS3) events. The new TRM requirements would allow 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore a nonfunctional line, and up to 14 days to restore a nonfunctional line if specific TRM action requirements are met. Use of these TRM requirements does not impact offsite power availability and does not create the possibility for a new or different kind of accident from any previously evaluated. Temporary reductions in the number of offsite lines from four to three, in accordance with the proposed TRM requirements, will continue to ensure offsite power system availability in the event of a loss of either MPS2, MPS3, the largest other unit on the grid, or the most critical transmission line.

The proposed amendments have no adverse effect on plant operation or accident mitigation equipment. The response of the plants and the operators following a design basis accident will not be different. In addition, the proposed amendments do not create the possibility of a new failure mode associated with any equipment or personnel failures.

Therefore, the proposed amendments will not create the possibility of a new or different kind of accident from any accident previously evaluated.

Criterion 3 Does the proposed amendment involve a significant reduction in a margin of safety?

Response: No The post-modification configuration of the offsite 345 kV transmission system (four lines separately supported and SLOD disabled) improves overall grid reliability and continues to meet the requirements for two independent sources of offsite power (GDC-17).

Likewise, the addition of TRM requirements that limit the unavailability of offsite lines provides acceptable assurance that line outages will not result in a significant reduction to grid stability and hence also to the margin of safety.

The offsite power systems are assumed to be available during several FSAR Chapter 14 (MPS2) and Chapter 15 (MPS3) events. The loss of the offsite power system is an anticipated operational occurrence. Additionally, as described in Chapter 14 (MPS2) and Chapter 15 (MPS3), several events are assumed to occur coincident with a loss of offsite power. Sufficient onsite power sources are available to mitigate these events and ensure the consequences of the existing analyses for these events remain bounding.

The proposed amendments do not affect the assumptions in the safety analyses or the ability to safely shutdown the reactors and mitigate accident conditions. Station structures, systems, and components will continue to be able to mitigate the design basis

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 41 of 42 accidents as assumed in the safety analyses and ensure proper operation of accident mitigation equipment. In addition, the proposed amendment will not affect equipment design or operation of station structures, systems, and components and there are no changes being made to the safety limits or safety system settings required by technical specifications.

Therefore, the proposed amendments will not result in a significant reduction in a margin of safety.

Conclusion Based upon evaluation of these criteria, DNC concludes that the proposed amendment presents no significant hazards under the standards set forth in 10 CFR 50.92(c) and, accordingly, a finding of "no significant hazards consideration" is justified.

6.0 Environmental Consideration A review has determined that the proposed amendment would change a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or would change an inspection or surveillance requirement. However, the proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluent that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment.

7.0 References 7.1 10 CFR 50, Appendix A, "General Design Criteria for Nuclear Power Plants,"

Criterion 17, "Electric Power Systems."

7.2 10 CFR 50.63, "Loss of All Alternating Current Power."

7.3 Nuclear Management and Resources Council (NUMARC) 87-00, "Guidelines and Technical Bases for NUMARC Initiatives Addressing Station Blackout at Light Water Reactors."

7.4 Northeast Power Coordinating Council (NPCC) Regional Reliability Reference Directory #1, "Design and Operation of the Bulk Power System," Version 1, dated December 1, 2009.

7.5 DNC Letter 15-073, Millstone Power Station Units 2 and 3, "Response to a Notice of Violation," EA-14-126, dated March 31, 2015.

Serial No: 15-297 Docket Nos. 50-336/50-423 Attachment 1, Page 42 of 42 7.6 NRC Letter EA-14-126 (J. A. Trapp) to Dominion Resources (D. Heacock) dated August 28, 2014, "Millstone Power Station Units 2 and 3 - NRC Special Inspection Report 05000336/2014011 and 05000423/2014011" (ADAMS Accession No. ML14288A481).

7.7 NUREG-0800, Standard Review Plan 8.1, "Electrical Power- Introduction,"

Revision 4, dated February 2012.

7.8 NUREG-0800, Standard Review Plan 8.2, "Offsite Power System," Revision 5, May 2010.

7.9 ISO-New England Planning Procedure No. 3, "Reliability Standards for the New England Area Bulk Power Supply System," dated March 1, 2013.

7.10 North American Electric Reliability Corporation (NERC) Reliability Standard NUC-001-2.1, "Nuclear Plant Interface Coordination," April 2010.

7.11 MPR-4189, "Millstone Station GDC-17 License Amendment Support," Revision 0, dated April 10, 2015.

7.12 MPR Calculation No. 0282-1410-001, "Wind Speed Criterion to Prevent Contact Between a Dropped or Broken Transmission Line Conductor and an Adjacent Line," Rev. 2, dated April 9, 2015 7.13 Eversource Historical Data of Millstone 345 KV Lines 348, 310, 383, and 371-364

- Outage Duration and Reason, dated September 29, 2014 and May 7, 2015.

7.14 Northeast Utilities Event Analysis Report, "Loss of Off-Site Power to Millstone Nuclear Power Station May 25, 2014," dated August 5, 2014.

7.15 NUREG-0800, Standard Review Plan Branch Technical Position (BTP) 8-8, "Onsite (Emergency Diesel Generators) and Offsite Power Sources Allowed Outage Time Extensions," Revision 0, dated February 2012.

7.16 10 CFR 50, Appendix A, "General Design Criteria for Nuclear Power Plants,"

Criterion 5, "Sharing of structures, systems, and components."

7.17 NUREG-1431, Revision 4.0, "Standard Technical Specifications, Westinghouse Plants," Volume 1, Specifications.

7.18 NUREG-1432, Revision 4.0, "Standard Technical Specifications, Combustion Engineering Plants," Volume 1, Specifications.

7.19 Dominion Engineering Technical Evaluation, ETE-MP-2015-1039, Millstone Station GDC-1 7 License Amendment Request (LAR) Support Documentation.

7.20 ISO-New England "Millstone Facility Out Guide-Text Document", Revision 1, effective date February 26, 2015.

Serial No: 15-297 Docket No. 50-336 ATTACHMENT 2 MARK-UP OF PROPOSED FSAR CHANGES DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 1 of 23 MPS-2 FSAR L.A AEC GENERAL DESIGN CRITERIA FOR NUCLEAR POWER PLANTS 10 CFR PART 50 APPENDIX A On February 20, 1971, the Atomic Energy Commission published in the Federal Register the General Design Criteria for Nuclear Power Plants. Prior to this date, proposed General Design Criteria for Nuclear Power Plants as issued on July 11, 1967, in the Federal Register were in effect. Before issuance of the construction permit for Millstone Unit 2, discussions reflecting the design intent in consideration of the 1967 proposed criteria were submitted in the PSAR. Design and construction was thus initiated and has been completed based upon the 1967 proposed criteria.

Since February 20, 1971, the applicants have attempted to comply with the intent of the newer General Design Criteria to the extent possible, recognizing previous design commitments. The extent to which this has been possible is reflected in the discussions of the 1971 General Design Criteria which follow.

CRITERION 1 - QUALITY STANDARDS AND RECORDS Structures, systems, and components important to safety are designed, fabricated, erected and tested to quality standards commensurate with the importance of the safety functions performed. Where generally recognized codes and standards are used, they are identified and evaluated to determine their applicability, adequacy, and sufficiency and are supplemented or modified as necessary to assure a quality product in keeping with the required safety function. A quality assurance program has been established and implemented in order to provide adequate assurance that these structures, systems, and components will satisfactorily perform their safety functions. Appropriate records of the design, fabrication, erection and testing of structures, systems, and components important to safety are maintained by or under the control of the nuclear power unit licensee throughout the life of the unit.

Discussion of the quality standards for those structures and components which are essential to the prevention of incidents which would affect the public health and safety or to mitigation of their consequences are presented in appropriate sections of the FSAR. The quality assurance program in effect to assure that these structures, systems, and components will satisfactorily perform their safety functions is discussed in Section 12.8.

For example, components of the safety injection and containment cooling systems are designed and fabricated in accordance with established codes and/or standards as required to assure that their quality is in keeping with the safety function of the component. It is not intended, however, to limit quality standards requirements to this list.

High Pressure Iniection, Low Pressure Iniection, and Containment Spray Pumps

a. Surfaces of pressure retaining materials for the high and low pressure safety injection pumps were examined by liquid penetrant techniques in accordance with l.A-1 Rev. 33 IFor information Only - No Changes I

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 2 of 23 MPS-2 FSAR CRITERION 15 - REACTOR COOLANT SYSTEM DESIGN The reactor coolant system and associated auxiliary, control, and protection system is designed with sufficient margin to assure that the design conditions of the reactor coolant pressure boundary are not exceeded during any condition of normal operation, including anticipated operational occurrences.

The design criteria and bases for the reactor coolant pressure boundary are described in the response to Criterion 14.

The operating conditions established for the normal operation of the plant are discussed in the FSAR and the control systems are designed to maintain the controlled plant variables within these operating limits, thereby ensuring that a satisfactory margin is maintained between the plant operating conditions and the design limits.

The reactor protective system functions to minimize the deviation from normal operating limits in the event of certain anticipated operational occurrences. The results of analyses show that the design limits of the reactor coolant pressure boundary are not exceeded in the event of such occurrences.

CRITERION 16 - CONTAINMENT DESIGN Reactor containment and associated systems are provided to establish an essentially leak-tight barrier against the uncontrolled release of radioactivity to the environment and to assure that the containment design conditions important to safety are not exceeded for as long as postulated accident conditions require.

The reactor containment structure, described in Section 5.2, consists of a prestressed concrete cylinder and dome with a reinforced concrete base. A one-quarter inch thick welded steel liner plate is attached to the inside face of the concrete to provide a high degree of leak tightness.

Designed as a pressure vessel, the containment structure is capable of withstanding all design postulated accident conditions including a loss-of-coolant accident (LOCA). All containment penetrations are sealed as described in Subsection 5.2.7. Isolation valves are provided for all piping systems which penetrate the containment, as described in Subsection 5.2.8.

As an extra measure of safety, an enclosure building completely surrounds the containment. In the event of an accident, the enclosure building filtration region (EBFR), described in Section 6.7.2, is maintained at a slightly negative pressure to preclude leakage to the environment. Potential leakage from the containment is channeled into the enclosure building filtration system as described in Section 6.7. Throughline leakage that can bypass the EBFR is discussed in Section 5.3.4.

CRITERION 17 - ELECTRIC POWER SYSTEMS An on site electric power system and an off site electric power system are provided to permit functioning of structures, systems, and components important to safety. The safety L.A-11 Rev. 33 IFor Information Only - No Changes I

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 3 of 23 MPS-2 FSAR function for each system (assuming the other system is not functioning) is to provide sufficient capacity and capability to assure that (1) specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary (RCPB) are not exceeded as a result of anticipated operational occurrences; and (2) the core is cooled and containment integrity and other vital functions are maintained in the event of postulated accidents.

The on site electric power supplies, including the batteries, and the on site electric distribution system, have sufficient independence, redundancy, and testability to perform their safety functions assuming a single failure.

Electric power from the transmission network to the on site electric distribution system is supplied by two physically independent circuits (not necessarily on separate rights-of-way), designed and located so as to minimize to the extent practical, the likelihood of their simultaneous failure under operating and postulated accident and environmental conditions. A switchyard common to both circuits is acceptable. Each of these circuits is designed to be available in sufficient time following a loss of all on site AC power supplies and the other off site electric power circuit, to assure that specified acceptable fuel design limits and design conditions of the RCPB are not exceeded. One of these circuits is designed so it is available within a few seconds after a loss-of-coolant accident (LOCA) to assure that core cooling, containment integrity, and other vital safety functions are maintained.

Provisions are included to minimize the probability of losing electric power from any of the remaining supplies as a result of,or coincident with, the loss of power generated by the nuclear power unit, the transmission network, or from the on site electric power supplies.

The off site power supplies system is described in Sections 8.1 and 8.2. The preferred source of auxiliary power for unit shutdown is from or through the reserve station service transformers.

System interconnection is provided by four 345 kV circuits. These transmission lines are on a single right-of- ay t . : . .* _ kL.. . . ..- ..... t thI .hiz . f. . &. c .. -. <-.

installed on an independent set of structuresp the structure .s described in Subsection 8.1.2.1.

The combination breaker-and-a-half and double breaker-double bus switching arrangement in the 115-16 345 kV substation includes two full capacity main buses. Primary and backup relaying are provided for each circuit along with circuit breaker failure backup protection. These provisions permit the following:

a. Any circuit can be switched under normal or fault conditions without affecting another circuit.

b. Any single circuit breaker can be isolated for maintenance without interrupting the power or protection to any circuit.

1.A-12 Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 4 of 23 MPS-2 FSAR

c. Short circuits on any section of bus are isolated without interrupting service to any element other than those connected to the faulty bus section.

d. The failure of any circuit breaker to trip within a set time initiates the automatic tripping of the adjacent breakers and thus may result in the loss of a line or generator for this contingency condition; however, power can be restored to the good element in less than eight hours by manually isolating the fault with 115-16 appropriate disconnect switches.

Overhead lines from the switchyard to the reserve station service transformers are separated at the switchyard structure and are carried on separate towers. These transformers are located near each Unit, and are physically isolated from the normal station service transformers and from the main transformers.

In the event of loss of power from the normal station service transformer, there is an immediate automatic transfer of auxiliary loads to the Unit 2 reserve station service transformer. In the unlikely event that power is not available from this source, and from the On site Emergency Diesel mentioned below, the operator can manually connect emergency bus A-5 (24E) to Unit 3 bus 34A or 34B. By means of interlocked circuit breakers, the Unit 2 post accident loads can be fed from this source.

The on site power supply system is described in Sections 8.3 and 8.5. Two full capacity, separate and redundant batteries are provided for all DC loads and for 120 volt AC vital instrument loads.

In the event that off site power is not available when needed, a "start" signal is given to both emergency diesel generators (DG). These generators and their auxiliaries are entirely separate and redundant, and each generator feeds one 4,160 volt emergency bus. A generator is automatically connected to its bus only if there is no bus voltage and only if the dead bus did not result from protective relay action.

The electric power distribution system is described in Section 8.7. The redundancy of the power sources is enhanced by separate and redundant auxiliary power and control distribution systems.

A single failure and any possible related failures in that channel cannot adversely affect equipment and components on the other redundant channel.

Due to the redundancy and separation of power supplies, distribution and control required for vital functions, all components can be readily inspected and tested. Similarly, most subsystems can be tested in their entirety.

CRITERION 18 - INSPECTION AND TESTING OF ELECTRIC POWER SYSTEMS Electric power systems important to safety are designed to permit appropriate periodic inspection and testing of important areas and features, such as wiring, insulation, connections, and switchboards, to assess the continuity of the systems and the condition of their components. The systems shall be designed with a capability to test periodically (1) the operability and functional performance of the components of the systems, such as on L.A-13 Rev. 33 IFor Information Only - No Changes

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 5 of 23 MPS-2 FSAR NOTE: REFER TO THE CONTROLLED PLANT DRAWING FOR THE LATEST REVISION.

CHAPTER 8 - ELECTRICAL SYSTEMS Number Title 8.1-1A ,4t-

..... ssef of:-......

Alty Gro... .. _

8.1-1B Hunts Brook Junction 15-8.1-IC 345 kV Transmission Map of Connecticut and Western Massachusetts 8.1-1D 345 kV Switchyard 8.1-2 Deleted by PKG FSC MP2-UCR-201 1-010 8.2-1 Main Single Line Diagram 8.3-1 Logic Diagram Diesel Generator and Breaker Control 8.3-2 Diesel Generator Control Schematics 8.3-4 Diesel Generator Fuel Oil System/Auxiliary Steam Condensate and Heater Index 8.3-5 Emergency Diesel Generator Cooling Water, Starting Air, and Lube Oil Systems 8.4-1 Charging Pump - Power Supply Crossover 8.4-2 Service Water Strainer - Power Supply Crossover 8.5-1 Single Line Diagram, 125 V DC Emergency and 120 V AC Vital Systems 8.5-2 Reactor Trip Switchgear Schematics 8.7-1 Raceway Plan 8-v Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 6 of 23 MPS-2 FSAR 8.1 ELECTRIC POWER 8.

1.1 INTRODUCTION

This chapter describes the utility grid and its interconnections to other grids and to the Millstone 115-12 Nuclear Power Station 345 kV switchyard. The on site electric system is also described.

Definitions used in this chapter are given below.

Transmission System The transmission system includes all transmission lines coming to the Millstone Nuclear Power Station complex up to, but not including, the point of connection to the 345 kV switchyard.

Off Site System The off-site system includes the transmission system and the 345 kV switchyard and extends up to, but does not include, the main transformer bank. Included in the off site system are the reserve station service transformers, Millstone Units 2 and 3.

On Site System The on-site system includes the Millstone Unit 2 electric power systems out to, and including, the main transformer bank (Figure 8.2-1); this includes the normal station service transformer.

Normal Operation Normal operation is when the main generator is transmitting electrical power through the main transformer bank and when plant auxiliaries are being supplied from the normal station service transformer.

Normal Power System The normal power system includes that equipment required to support the main turbine generator, plant systems, and equipment associated with the reactor.

Emergency Power System The emergency power system includes that electrical distribution equipment required to support the safe shutdown and post-accident operations of Millstone Unit 2. Included in the emergency power system are the emergency 4160 V switchgear and all extensions except those going to the normal switchgear and the reserve station service transformer and Unit 3(Figure 8.2-1). The 115-15 emergency power system and equipment is Class 1E and safety related.

8.1-1 Rev. 33

[For Information Only - No Changes I

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 7 of 23 MPS-2 FSAR Standby Power System The standby power system includes the Class 1E emergency diesel generators, which are referred to as the on-site emergency power supply.

Preferred Power System The preferred off site power supply is from the 345 kV switchyard and the reserve station service transformer.

Alternate Off Site Source The alternate off site source is the 4160-V tie to Millstone Unit 3 via bus 34A or 34B.

8.1.1.1 Design Criteria The 345 kV switchyard and the associated transmission lines provide the off site sources that are the preferred power supplies, as outlined in Section 5.2.3 of IEEE Standard 308-1971 and Criterion 17 of Appendix A of 10 CFR Part 50. The conventional and accepted design of these facilities has been shown to be conservative and reliable.

Transmission facilities connecting the Millstone generating units to the main transmission grid are designed in accordance with the "Design and Operation of the Bulk Power System," developed by 115-15 the Northeast Power Coordinating Council (NPCC).

8.1.1.2 Utility Grid The utility electrical system consists of interconnected diverse energy sources including fossil j 15-12 fueled, hydro-electric and nuclear fueled plants supplying electric energy over a 345/115 kV transmission system (Figure 8. 1-1C).

ISO-New England is the regional transmission organization which has authority over the 15-12 operation of the transmission system in Connecticut. The main transmission system fed by Millstone Power Station is part of the New England power system. The Connecticut Valley Electric Exchange (CONVEX) is one of the local control centers in New England and assists ISO-New England in running the power system in Connecticut.

The electrical output of Millstone Unit 2 is delivered to the 345 kV switchyard (Figure 8. 1-1D).

Four 345 kV transmission lines feed power to the 345 kV system. Two of these lines feed the 15-12 eastern part of Connecticut by connecting respectively to the Card and Montville substations. The remaining two lines feed the central part of Connecticut by connecting to the Beseck, Haddam, and Manchester substations.

8.1-2 Rev. 33 IFor Information Only - No Changes I

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 8 of 23 MPS-2 FSAR 8.1.1.3 Interconnections Millstone Power Station is connected to the Eversource Energy, Inc. transmission system which is 15-15 closely integrated with transmission systems of several other utilities and operating companies.

The New England power system is part of the larger northeast interconnection power grid and is tied through various connections points throughout New England. These interconnections include 345kV, 230kV, 138kV, 115kV, 69kV, and DC lines. The New England power system is also tied to neighboring grids such as New York, Hydro Quebec and New Brunswick, which are under the control of other reliability coordinators within the NPCC region.

8.1.1.4 345-kV Switchyard System at Site The 345 kV switchyard is designed in an arrangement as shown on Figure 8. 1-1D. The switchyard consists often 345 kV breakers, four 345 kV transmission Units 2 and 3 lines, two 345 kV tie lines to the generator step-up transformers, and two 345 kV tie lines to the reserve station service transformers. The Millstone I generator step-up transformer and reserve station service transformer are no longer in service.

The breakers and motor-operated disconnect switches are controlled primarily from CONVEX via the Supervisory Control and Data Acquisition System (SCADA) and from the Millstone Unit 1 Control Room. Millstone 2 Operations is responsible for the switching and tagging of equipment located in the Millstone I Control Roomn Via the Millstone Unit 1 Control Room Millstone 2 Operations has primary control of breakers 8T, and 9T, as well as indication only of the remaining breakers and motor-operated disconnect switches. The Millstone Units 2 and 3 Control Rooms are equipped with remote panels that show the status only of the breakers and motor-operated disconnect switches in the switchyard. Through the operation of control switches, all breakers can be operated at the switchyard, if necessary.

Each element of the Millstone bus and associated line terminations are protected by redundant sets of primary and backup relays. The primary and backup relays are supplied from separate DC sources, separate current transformers, separate coupling capacitor voltage transformers, and communication channels.

The DC power is supplied by two independent batteries, one primary and one backup. Each battery is equipped with its own charger and distribution panel. A manual transfer scheme is provided to allow one battery and charger to carry the DC load upon the failure of the other battery and charger.

A4 sevr; lifte eatag detetzr (SLOP) greeial prfetetizr. 90hem (SPS) It" boom iftswllz in the 315kV s ~ie;z z4aw , .eagziingthat it is 09ile z~ to 09 two 3150 kv 6Zttzt siflt.;ztty a Witkzto N1900 #1. eendifie. es~ .....tofi kwfUtbiy it. fi Omstzsi "s. It i ad " it%antiaipatizn of alzt~

gttizn eirettrfmt, fdolown the eatodgefc@F siwt"Oeiit, 8.1-3 Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 9 of 23 MPS-2 FSAR The SiLOE) Bakhomoa ntr sotnocy ha indi~idual 81041Mo f fcur Spriaial tramfimfiazn clcmfi-nt)1 tzgether with the pzowr. zutpt A-f-A.llztencF"Atz.Girtzna utlc affilomatwa11y if a u;'ztem aondition AriýSzi Whzrz 6ny Of the evitiral aitins emist and gemffAtin is &have prodetenmirz.d l" --..

8.1.2 OFF SITE POWER SYSTEM 8.1.2.1 Description The off site power system is designed to provide reliable sources of power to the on site AC power distribution system adequate for the safe shutdown of the unit. Details of the ef.=t.. e"ff system are shown on the felleing figura: <E-..I 78.11D

&, TFrmsmiosn Rgt of 44y Creso Se~e (Pigw S. 1 LA)

The switchyard, which is configured in a combination breaker-and-a-half and double breaker- I 15-16 double bus arrangement, buses together four 345 kV transmission line circuits, two generator circuits and two station service circuits

(-igwe - 8. ;P). The Millstone 1 generator and station service circuits are no longer in service.

The four transmission line circuits terminated at the switchyard are:

a. Millstone to Beseck (Line Number 348)

b. Millstone to Card (Line Number, 383) tne3*)

c. Millstone to Montville (Line Numbep371)

d. Millstone to Manchester (Line Number...3 10)

These circuits connect the station to the 345 kV system transmission grid and follow a common right-of-way from Millstone to Hunts Brook Junction (9.0 miles). F.; the. ftz 1.7 m*ile oft*2i nkt of wazy (to Daniels Av;zmz, the few. 11i.es t;l "Vo two double eiztt sftel Zle indepanicit singleo ireutztutarka S&H ~ tizn -F- tl-#Afl r~~.gtf . zac drtin(g 91mwetr) and of: a singl; eemnien watzwez at all other leetiens. For the next 2.4 miles, th; sentrua-t-i e tnm ;miats of en; -deuabwAefireui s~el Igo! t.-amnizzinoi lit" (Lin;e Nes. 3 48 and 3 10) md two gingle eiwi w. ed pole H frmn; hotoioe line (Line Number 371 anZd 383). For Fi~gm .1 1A showe; the. ris of-----

wa rs ~~mi h oeon Netng indi;eftl ffiffif"M t@WW floorm OR Mon 149-the 01814001 -H 0 owmaieweneelgetweew4owffs-Inese 8.1-4 Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 10 of 23 "Mtro e now alo te r WhI wl a*ppo" the

%orOn-o Con" ofz a ad" of T&ADQ 'IV ~ D [11 Thetonwm d.*

we doope to eW de IBerniSaet Cod@ Fort C2,and fee -*-z:L=::.!* S_:' _. : * * ... .......t...

.o provide adequate phiysical U1,i ,, vfs* .............

independence of the transniiz-..nes. pow om *vos I*

-Thefou 4 lies 1

MllsoneSwichin etaimp Sttio w*in i vth 6.-17 fMth noh re *it" tha

.- me @4.k.*4 -"_m'==s=e-. lingo* @me@;*Over. OWN@

alinwe iththe8faf raso"e flumtha

--' *dw= .foo r I " -- he z !.

bre ;ak 'i*g will-he ab ; ta sima . .. ly ..affect all circuits in such a way that none of the four circuits can be returned to service in time to prevent fuel design limits or design conditions of the reactor coolant pressure boundary from being exceeded.fo M In l l ,

Atr.Hunt Broo! Juct,ioat H f*our tsrtansm issoline rutan di ergealong thlee. arate rih tsoeep All four of the 345 kV lines leaving Millstone cross over two 115 kV circuit Msich supply the Switching Waterford Substation, and constitutee soffsite source for Millstone Uit cn. However, the or aUabigt mechanical failuro o the 345 kV line, and the consequential failure of the 115 ina kV ldc circuits will not affect the preferred sourcuare suppie power to Millstone p its 2 and 3.t switcy'athrwdt onect*woulmeb.

of-way At Hunts(Figure Brook8.1I-1B).

Junction, L:==o the 3four 48 transmission

=-o=westery line circuits diverge9 along three separate rights-for:appfemi-matey miles

, to a"e B~ek sub isa :;h 10 and lines--I..d

.. .. . sie ...g e .. diretio -'----f or3 m '1e

-. .... 20,t*4 il.e- to eia serrvice reserve station roaatn inspeions and transforser ony is s tessoth , e operaildity d r circuitst aro and fun nebais theS g e p eancoh elctuic pomove 3i10ui 31rvi instledmos s

insulatingoil fo4r teran sfwwormr mi tation tpunra servicetrndesforne 3lne ~ S8effusT) froms tmln. Seevatr sear aesr cue rouins nd in petio esstheop rabliy ad unc'm Thensain .T eecrut of8.1.2.2~~~~~~~~

peare al peora transformeri verifed.

f resede Anlareverilidfroed.fernt ss[ntingenes b p .uscitins ofhe ian, l cti twit, schy sem buard asseroatienstatiocn e thre stom irn ste s onn [*,°0t4o,h* a.

wehe *tos.r~ ~=a*vso e, .31 s p rthepos i bilitur osf po em iz sris y tch r f aircu it sd ue su pp niarfllowing a0rangem ectistn ntl fltle the *e nm m nedonr i f ees n th ben utssn ne cti o n s ircuit i nth e sis,w*M w itnsthese ch yard, sho [ 15 assoiatd inim s itch zedbyardishe fllo ingarrag emntsemt.No1.

aea*n 8.1-5 Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 11 of 23 MPS-2 FSAR

a. The connections to the system have been designed to comply with the NPCC "Design and Operation of the Bulk Power System" and the ISO New England I 15-15 "Reliability Standards for the New England Area Bulk Power Supply System."

Compliance with these criteria ensure that the supply of off-site power will not be lost following contingencies in the interconnected transmission system. Transient 115-15 stability studies have been performed to verify that widespread or cascading interruptions to service will not result from these contingencies. In addition, the loss of Millstone Unit 2 or the loss of any other unit in the system will not result in cascading system outages and thus will not cause loss of off-site power to units 2 and3.

The 345 kV circuit breakers are SF6 puffer type and are pneumatically operated.

Electrical controls are provided for both local and remote Millstone 1 control room or CONVEX operation. Each power circuit breaker has a separate pneumatic supply unit capable of operating the breaker for a minimum of three close-open 115-16 operations after the loss of its pneumatic supply unit. The essential AC station service for the power circuit breaker pneumatic supply units and the other switchyard requirements is supplied by an off site 23 kV line which has transfer capability to a source from Millstone Unit 3. The circuit breakers are equipped with a closing solenoid and two independent trip solenoids. A standard anti-pump and trip-free control scheme is used.

Two 125 VDC batteries are located in the switchyard control and relay enclosure for switchyard relaying and control. Each battery has its own charger and DC distribution panel. The redundant batteries and protective relaying systems are physically and electrically separate.

b. The 345 kV system is protected from lightning and switching surges by overhead electrostatic shield wires, earth grounding at most structures, surge arrestors on the switchyard main buses, surge arrestors at the transformer high voltage bushings, and rod gaps on the line terminals. 115-15

c. Each 345 kV transmission line is protected from phase to phase and phase to ground faults by two sets of diverse protective relays, one primary and one back- 15-16 up, both of which are high speed schemes.

The primary line protection consists of a distance relaying package in a directional 15-16 comparison blocking scheme communicating with the remote terminal over a carrier current channel.

The backup line protection consists of step-distance relays operating 15-16 independently from the remote terminal. This equipment is used with a transfer trip channel to provide a high speed permissive over-reaching scheme. A second transfer trip scheme provides tripping of the breakers at the remote terminal in the event of a stuck breaker at Millstone as well as tripping Millstone breakers following the reception of a trip signal from the remote end.

8.1-6 Rev. 33 IFor Information Only - No Changes I

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 12 of 23 MPS-2 FSAR Pilot wire relaying is used for primary protection of the 345 kV tie lines between the switchyard and the main step-up transformers. Backup protection consists of directional distance, single zone and directional ground overcurrent relays located in the switchyard and for transfer tripping to the plant dual channel audio-tone equipment is used.

Tripping of the switchyard breakers following the operation of the generator or main step-up transformer bank primary and backup relays is accomplished by the means of the transfer trip via pilot wire and audio-tone.

The Millstone 2 RSST 345 kV tie line is protected by two sets of protective relays, one primary and one backup. The directional distance relays detect phase-faults, and the directional ground overcurrent relays detect ground-faults. Operation of these relays will trip the appropriate 345 kV circuit breakers on the A switchyard bus, and send a transfer trip signal via digital teleprotection system with fiber optics communications medium to trip the transformer's low side circuit breaker at the plant. The operation of any of the RSST transformer protective relays at the plant will trip the low side breaker, and send a transfer trip signal via digital teleprotection system with fiber optics communications medium to trip the appropriate switchyard breakers.

Breaker failure relays are provided for each of the 345 kV circuit breakers to trip adjacent breakers in the event that the primary breaker fails to trip. The DC power for breaker failure operation is supplied from the backup battery system.

A breaker failure timing relay is initiated every time a main breaker is signaled to trip by primary or backup relays. If the breaker has not tripped before the time period has expired, tripping of the adjacent breaker will take place.

Phase angle sensitive impedance relays are also included in the backup protection of the main step-up transformer bank tie lines to protect the generator.

Automatic reclosing of 345 kV breakers is allowed following the protective relay tripping of the 345 kV transmission lines. The reclosing is designed for time delay reclosure from the remote ends only. At the switchyard, the breakers will close via synch-check relays.

A synch-check relay is also provided for each circuit breaker to supervise both manual closing and automatic reclosing of the breaker.

d. Primary and backup relaying is provided for each circuit breaker along with breaker failure backup protection. These provisions permit the following:

1. Any circuit can be switched under normal or fault conditions without affecting another circuit.

8.1-7 Rev. 33 IFor Information Only - No Changes I

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 13 of 23 MPS-2 FSAR

2. Any single circuit breaker can be isolated for maintenance without interrupting power or protection of any circuit.

3. Short circuits on any section of a bus are isolated without interrupting service to any element other than those connected to the faulty bus section.

4. The failure of any circuit breaker to trip within a set time initiates the automatic tripping of the adjacent breakers and thus may result in the loss of a line or generator for this contingency condition; however, power can be restored to the good element in less than eight hours by manually 15-16 isolating the fault with appropriate disconnect switches.

Complete battery failure is considered highly unlikely since two independent 125 VDC battery systems are provided. Failure of a single battery system results only in a momentary loss of one set of protective relays until the DC is manually transferred to the other battery. Therefore, no single failure could negate the effectiveness of the relaying to clear a fault.

The Millstone design provides two off site circuits between the switchyard and the 4.16 kV Class 1E buses. The immediately available off site supply is the Millstone Unit 2 RSST while the alternate supply is the Millstone Unit 3 bus 34A or 34B.

The normal supply to the plant with the plant on line is the NSST If this source is lost due to a plant trip, a fast bus transfer scheme connects the plant electrical system (6.9 kV and 4.16 kV) to the RSST. The second or alternate source of off site power is available by manual controls to Millstone Unit 3 bus 34A or 34B for 4.16 kV power.

Physical separation of the off site power sources, switchyard protection, redundancy, and the transmission system design based on load flow and stability analyses minimize the possibility of simultaneous failure of all power sources (reserve station service supply, standby AC emergency generators, and Millstone Unit 3 bus 34A or 34B.

The 345 kV transmission system supplying off site power to Millstone is normally operated at 357 kV at Millstone. This system voltage is controlled by varying the reactive power generation on the Millstone Power Station units. The Millstone Units 2 and 3 operators control the unit excitation as specified by CONVEX Operation Instruction Number 6913. The unit operators are required to balance the reactive power output of the units.

The CONVEX system operator supervises the system reactive power dispatch. The CONVEX operator directs the loading of all the reactive power sources in CONVEX to balance the reactive supply. The CONVEX operator keeps the Millstone Power Station reactive power generation in balance with the Eastern Area requirements so that the effect on the system of voltage variations is minimized when a unit is lost.

One objective of the reactive power dispatch is to prevent the voltage at the Millstone Power Station from going below the minimum required to support actuation of the Engineered Safety Features equipment. A switchyard voltage of 345 kV will assure successful actuation and 8.1-8 Rev. 33 For Information Only - No Changes]

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 14 of 23 MPS-2 FSAR operation of all necessary safeguards loads in the unlikely event Millstone Unit 2 experiences a Loss-of-Coolant Accident and trips off the transmission system. CONVEX operates the system to assure that this minimum voltage requirement will be met, following the loss of the unit. When in Reactor Modes 5 or 6, with the auxiliary electrical system lightly loaded, Millstone Unit 2 can assure successful actuation and operation of all necessary safeguards loads with a switchyard voltage of 335 kV The maximum allowable voltage at Millstone Station is 362 kV based on equipment ratings.

If abnormal system conditions result in voltages approaching minimum levels, system operating 15-12 instructions and procedures direct the CONVEX operator to take specific corrective actions to restore voltage.

Actual experience and system simulations show that the CONVEX operator is able to control the system voltages within the desired limits.

The Millstone plant is connected to the transmission system by four 345 kV circuits (described in Section 8.1.2.1). Fo;r i s*r.t dis--c.., the.s. li.e. .a.mondoub. e-r-t Ma. poi . Transmission operating procedures are in place to ensure that no more than the minimal number of circuits would ever intentionally be taken out of service, except in an emergency, when both Millstone generating units are on-line.

If both Millstone units 2 and 3 are on line at full output, certain contingencies on the transmission system as determined by CONVEX result in procedural restrictions on the station's net output, in order to assure that system synchronous and voltage stability will be maintained. hdditief trlnaz::Jfieff 05"itm 98"fingon~ries xi the not eutpt Afthe AIIlztR"A sigtaeti.

By careful design of the switchyard and protective relays, the possibility of the simultaneous loss of both units 2 and 3 at Millstone has been significantly reduced. The system has been computer modeled for both light load and heavy load conditions. The stability analysis indicates that the rest of the system remains in synchronism after the loss of any one Millstone unit,"@@ Mill..:. 3 is

-'-b-el to.w ov.ie gen.ertion rejeeti The probability of losing both on-line units simultaneously is extremely small because of the preventive measures discussed in the following paragraphs. Accordingly, the Licensee believes it is reasonable to count upon on site power sources to supply the necessary station service power requirements in the very remote event that both Millstone units 2 and 3 should be lost at once accompanied by the total loss of the transmission supply to the station.

A primary objective in designing the connection of the Millstone Nuclear Power Station to the 345 kV transmission network in Connecticut has been to prevent the loss of the entire station output. The reliability criteria of NPCC and ISO New England are a fundamental part of this 15-15 design process. BPS or rt tetz

..... 4h...Millt..;... 9"01

-.. ..... .. d..t0...... 1 ...

insability f s.e4. i.....-..i.v........ , .. Mt....

One ..the"i.. The fellz;i;;$ie most severe outage* which the system has been designed to survive in order to minimize the possibility of a total plant outage, Es Z] 8.1-9 Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 15 of 23 MPS-2 FSAR With any one of the four Millstone 345 kV transmission circuits out of service the plant remains stable for any three-phase fault normally cleared (four cycles) or any one-phase fault with the delayed clearing (eight cycles).

inorder to MO 4eetilifein Moothat no9i816fleehfiftiefliol feýWro, %ooh "a tewer fdling or a 11 m. rpig 10 to gzfit"Otaoouy Offel't all e......f.in 8wh away that 8f .it84 a w~ o xlie-P4. -Alo.,t ginrttoze tin.3hw fxomltho; he@on tooo fer eash of he two eirwoits ;ohiek w ffiwe ntoire"o ooaenm..teor..

11 fhall- Jines in Beorloo the OYtOMamaroins sitrble fop this two eir-9it zdiAturbano.

AIshe I-1ld be rocognioao that the -few:046848t 18"agi the NiAtono4 switahyar arc paired on.tWO widely spasel rON" 8f icublo @i-i-Ouit - Outurc &Fo04lY ft She diotman, aRdi, hones the siopoaur te this dmOuble- -Airewit@%tgop is sanll.

X'Withoto 14611848" UW~t 1 on line, the "Ot 1161118481t srt~o doe@. not IIoth...w oM otability; a*@"o in the 8z06ot of this Jouk!;e ofro..t fxi"t. Rouble eiz...:t feolis 0" the.

Milleaete B606le... OW~ NIlot"O Niefeheo..to linesz do ".of .ee. genertion ree~o in order to 1maiftwin 89,91"" otakiit Or prO;IuA80 (nOn 9ifimutMnOeH) Outa~gO of it-h-O Of A-0hO&O thor iIItono Sirouits (OF any othor aritiMa elemunt) omuf not result in instability, All of the aritieftl ovktageof c thistype effeetim~ly :ozeott in the 1099 Of ho.. of 1k feti. Millotooo a.rettits and leave; the 111lwetoo mm4:oo ;oooy tied to the.t08......,.X,. grid. 4T9 "

iotohaillity f&; thage OOefle~ly @ever@ (and higmy impobable) dimi. teeso, it i

..- esfiryt SPtobhei PLO h"the

-ie les Ofth. two ertiqo The Millstone units are connected to the large interconnected transmission system in the eastern 15-15 half of the United States. The interconnected system frequency is maintained at 60 +/- 0.03 Hz in accordance with NPCC standards for the bulk power system. The system is designed and operated such that the loss of the largest single supply to the grid does not result in the complete loss of preferred power. The system design considers the loss, through a single event, of the largest capacity being supplied to the grid, removal of the largest load from the grid, or loss of the most critical transmission line. This could be the total output of a single Millstone reactor unit, the largest generating unit on the grid, or possibly multiple generators as a result of the loss of a common transmission tower, transformer, or a breaker in a switchyard or substation.

1l * *

I 1q* II

in @orpc to OnnR OF m etu mterooeocro io .0;ilowtag tt:.iwn e;;aoof peowtuooo feulto, an S!PS, or generation rojeetien sehorno, has been inataIlei at the Aiilletoco 9"enor o;;Ktchyaoi. 4he IOD, aootlitOooly fflttoor Ote indii;'im mmOtFt &f fermst.io.,.oo line eiIft f -- ifu a.~bt 1180O 1MG swt..kvyow. together w;ith the.geOrta .O .trto ..t It Millsto..; eampleff. Tho four line eiz..,ilsme 4- Milkitano Mocohoat;; Liii; (Nu~nbor 3 l0'i:

% J4 r.uuomonz iioaoc~ ~L-dun~cO: Jir);

8.1-10 Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 16 of 23 MPS-2 FSAR Hi Qjao ad strzzt WHO RNumber 3a3);

the genertion at hfillsteft is abov a~io prdtenine 1W level, zd twoz gresifieOaftfl...iss...

9tudizz indizzz fhat daring tawtimwe e"tW eer.itizn (2001 MW), Nfilitzon Unit 3 eo h 11115,ldl tripped and 85:-O Oa'mnAtaity rnainLwnd leaving 4illztzao Unit 2 in 85malafiuhznmi mishthedi tranamioaizt notuork gfiudigm indinfla tAnt a Inrg less of geznzrtien in Now England aeuld load to zzetage problemo in New YC+/-k and Penryhaniftwhenhetwy zzztto m po~wert.-zzfrera a 4sing eanz ztheir 85%tem.. A@O New Ensw~d me~itzzez fhe.z loain on ik New. *qrk MW Pe"Myl;...ift 85%ttz to d" fgo"tzerate. w.he..z;-r my m zthe few. (1) wzietl 1....... lz .. it 1nole in the generation zzjeetionz seheme is out efzzzviee, the eotjit of illztzrmz 3 is zdueed to 4ii mafm a flffitewarnus Ofgon1ormzet~z legs, Thz0 erpertizn zf 1he 84 00millk~ete ge"Oretizn ocjzstieft gehzim is based Bit the eutag; eembinatiana 04f azrtinif rtmmifigien zAirzuit :cM antA. Ti symetm czrntinOusuay meznitem the indiv-idulz zttwz @f;the few~ OitiefIt.iX...X...i.........L 4"geote. Wi~hthelz geferzszOzpto o.f the 144fe1Ltzeezr.lem. Genetfiez OwztmzleJ ttzz:..iet..J if a s~yt.... 8811ditX.. dzile When Motion power hm been gretz ohm ;;1750W (Gress) 1660 MIA, Nzt) for Mft* thm 60 98681dz, and there is a 1 af 3 Of th: 4 Oritizol! trmise eieis Ns9zo9ry to Mezt NPGC and NEPOOL efiterift!

M.~Immene 448Ohemeztz Mil~otat. Gard O...hUiliztzn hieftwille Millstone B..ozzle, 4411848" Czzz MWz hIfiztz48M Mont ilW Millstene M&A4H,M llmtzne 11...kzzte. Ozd 146119ton R..zzl 9-99z the speratien of th@ 4,09D gamneron rojeetion 99heme should We@z pliea in Izoo thajz1 eyele t-e ,rini .titiitw, 0-1l t-PRMSz11izsiin line fazuhos m~um be 010zoi at high speed.

With the 91L0P generefien rzjzzien sehermz in serviez, it is pernzisgible to zpzrat with a no!

Milloton; 946681; sutpt 4f2600 MAL, whe my One; of fear erilies line eire"4o in out of sri Reevii te mi mymleb 669r olmit Ev"8"imi ON ev".0 f Millstone UW4 3 to the Metku A~llC.b[ Millhien Gemzz4t Gefnee (HAich( ). *he NIAM(JC limzit is dete.*...4 hemed m.N*PP ... d Penmyvi Jese Moetyled 0 >Loz 0O,.diti.OIN. AS W, ~ rO WO NO LBzgIO.d ..4 tI NPGG, the L.-..o.- mo..~...d to zo...ply with ekhfr f teg fellzoMI-0 evemb~li rzzuireffiznl wit-'o lmn .t f1zoriz 8.1-11 Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 17 of 23 MPS-2 FSAR 4- have 9 LOP filly epramtiznal, lim-it Oh: not tAtiz on tu tz050M n ii the zutput of nHit -3to th NIAOGC limit, it: appliefhle, of reduaz led-tdie itz tetatin zutjut @f6!1;§0 MW (Gross) 1650 MW Riot) within 30 mi4: *Rep the. elmet s am.Vd fe...ve Wit. al lines in t" ........ ; ..the "e ..t.lie.nt .. io. . .d to 2520 MW"` - H...... ...... ......

qubiilt i- manuiftlinz 410§ event @;a double 0auti eenfitiaeztzy T-h-ORo nz-uuii az d Ou[WnOR40 as PAM RAWh CONVEX :pFaratings inztnAein:fr h M41848119 switahkard "d wec reg"We~d by CONVEX. 470:fczilitals roaulatin, CONVEX9 in Ownr orftha "Anditn"At: all lJcAR And tha fistatu Afth: SLD 96heme *~is -AnWwunjaz IZCeted at ath..ird ...

line et of,*it @1 wa g....ion in of 1750 NW' (Gres) 1650 MW t., off-

.... ilale for LSO& d.*.,...4 s-w"L:-- M-fht4.......... .....m ... n.....z th..e p .

i IRAN.2 E cne Conth i"Ppliets.

Evfets iz maniatt Wi the rFOeumea @;Cf oro!

Design Cr@ietcrz (GDG) 17.

ThC 171 aloefui theswithatd protbbility f lomsi M ang ircuitesupply intaidlat with is98sftha ateer post o inyhn e oirnipaed. ofa ee-fh;ae o irwua it for S;fal to cjlea itfit. Beer Within d n poles, trOi4pig 1is611048" 3 by tipping *he withyCm ec icall idepend pfthe ift-z:

*UCCL; r C6hnCC) thz:; 91a4izt..t IC'd

!@'W kiFL .jCd (Whioy is trippsd when CLOD trip: Unt ;) enm h r ansorgimersd by C iNinX

@o!Simth wiehyard brcA "r.Thcrefcrz, he* eff-sit: au"Priesa at-avilable to OrSurr 9Afe' A81440Azwn Of he unkiti ftardan-p vith "GD 17.

andtwosepabreaker (4149d of trippng the circuitm brequiedFr.Teseisalations includiefo 6twoetso 8.1.2.3 Extreme Contingency Events The design ofthe switchyard protective relay schemes and circuit breaker installations is such that at most only one pole or phase of a three-phase circuit breaker will fail to clear a fault. Breakers which are designed to meet this criteria are classified as having independent pole tripping.

Independent pole tripping is ensured by installing breakers with mechanically independent poles and two separate methods of tripping the circuit breaker. These installations include two sets of relays, trip coils, and two sets of current and potential transformers. The wiring for the relay packages are installed in separate duct banks, the relay packages are physically separated in the control house and two separate DC supplies are provided.

I15-11 The 345 kV switchyard at Millstone is designed so that the loss of more than one transmission circuit due to a failure of a breaker to trip requires at least two circuit breakers to simultaneously fail to operate. The failure of even one circuit breaker is very unusual. At least three circuit 8.1-12 Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 18 of 23 MPS-2 FSAR breakers would have to fail before three transmission lines would be lost due to malfunctions in the switchyard. At tt point;, the 9bOD .. n...n r"j..

" tio. eh. m would zporato keep uit in:Aaz-i- . In Az'rz to IRag%tha ploiw= *--n, s atat IGloa Thur ai".t ii muat fail.

8.1.3 STATION BLACKOUT (SBO)

On July 21, 1988, the Code of Federal Regulations 10 CFR Part 50, was amended to include Section 50.63 entitled "Loss of All Alternating Current Power," (Station Blackout [SBO]). The SBO rule requires that each light-water-cooled nuclear power plant be able to withstand and recover from a SBO event of specified duration, requires licensees to submit information as defined in 10 CFR Part 50.63, and requires licensees to provide a plan and schedule for conformance to the SBO rule. The SBO rule further requires that the baseline assumptions, analyses and related information be available for NRC review. Guidance for conformance to the rule is provided by (1) Regulatory Guide (RG) 1.155, Station Blackout; (2) NUMARC 87-00, Guidelines and Technical Bases for NUMARC Initiatives Addressing Station Blackout at Light Water Reactors; and (3) NUMARC 87-00 Supplemental Questions/Answers and Major Assumptions dated December 27, 1989 (issued to the industry by Nuclear Management and Resources Council, Inc. [NUMARC], dated January 4, 1990).

8.1.3.1 Station Blackout Duration Millstone Unit 2 has the ability to cope with a loss of preferred and emergency on-site AC power sources for up to eight hours. Unit 2 must provide decay heat removal during the event. It is assumed that there will be no AC power available during the first hour of the SBO except for battery backed power supplies (i.e., vital 120V AC). Within the first hour, Millstone Unit 2 will have an alternate AC power source available from Millstone Unit 3 Alternate AC (SBO) diesel generator.

Millstone Units 2 and 3 each have two emergency diesel generators in addition to the Unit 3 Alternate AC (SBO) diesel generator. In accordance with the SBO Rule and NUMARC 87-00, one of the four emergency diesel generators would be available and a Station Blackout is postulated to occur at one unit only at any one time. In the event of a Unit 2 station blackout, the Unit 3 AAC diesel will be made available within one hour by Unit 3 operator action and connected to Unit 2 Bus 24E by Unit 2 operator action.

8.1.3.2 Ability to Cope with a Station Blackout Eight-hour coping assessments were performed for the 1) condensate inventory available for decay heat removal, 2) Class 1E battery capacity, 3) compressed air capability, 4) effects of loss of ventilation, 5) containment isolation, 6) emergency lighting, 7) communications, and 8) heat tracing. The results of these assessments are summarized below.

Condensate Inventory Available for Decay Heat Removal A calculation was performed to determine the available volume in the Condensate Storage Tank (CST) for decay heat removal during SBO. The necessary condensate inventory required for 8.1-13 Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 19 of 23 FF -IG-UWRE-871 --I A---D-E L-ETTE51 FSARJ MNPS-2 FSARk-r MNPS-2 TYPICAL'RIGHT-OF-WAY CROSS SECTIONS A. WATERFORD:

3146x MILLSTONE SUBSTATION TO DANIELS AVE., L5 MILES IN SEGMENT I sV*45x 3V 45KcV 345K9 LOOKI NORGTH Ai A.r."1 gxISTING 508 NIGHT OF WAY AND CLI N

&.WATERFORD: DANIELS E, TO 195 2.5 MILES IN OENTS I AND 2 LOOKING "NOT 3 K 3KV345 KV 345 KY EXIasTIN 415! RNIGHTOf WAY AND CL.EARING FIGURE 8.1-1A

/TRANSMISSION RIGHT-OF-WAY CROSS SECTIONS JUNE 1994\

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 20 of 23 MPS-2 FSAR FIGURE 8. 1-IB HUNTS BROOK JUNCTION REV. M,*

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 21 of 23 Insert A (North)

MCAs)

Hunts Brook Junction Note: This figure plac n MP2 FSAR Figure 8.1B-1]

andM23 F'SAsRinFi 8.2-2 gr

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 22 of 23 1l5-15 I,I Rev. 33

Serial No: 15-297 Docket Nos. 50-336 Attachment 2, Page 23 of 23 15-15 MPS-2 FSAR IGURE 8.11D 34bKV SWIICHYARD

-4 v

-I.

I 1

U © I: '4, I-Cxý F -ir fq I I

74 4F F4 I

Rev.33

Serial No: 15-297 Docket Nos. 50-423 ATTACHMENT 3 MARK-UP OF PROPOSED FSAR CHANGES DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 1 of 22 MPS-3 FSAR NOTE: REFER TO THE CONTROLLED PLANT DRAWING FOR THE LATEST REVISION.

CHAPTER 8 - ELECTRIC POWER List of Figur Number Title 8.1-1 Electrical One Line Diagram 8.1-2 345 kV Transmission Map of Connecticut and Western Massachusetts 8.1-3 345 kV Switchyard 8.2-1 Mil.* et,.z M-ehe.,tr 315 kY*4-iffLk 8.2-2 Hunts Brook Junction 8.3-1 Routing of Redundant Circuits 8.3-2 One Line Diagram - 125V DC & 120V AC DISTR SYS - CMPST 8.3-3 120V AC Vital Bus and Safety Related 125V DC Systems 8.3-4 Power Supply - Third Charging Pump 8.3-5 Power Supply - Third Reactor Plant Component Cooling Pump 8.3-6 Emergency Generator Fuel Oil Transfer Pumps 8.3-7 Routing of Preferred Offsite and Standby Onsite Circuits 8.3-9 6.9 kV and 4160 Volt Systems 8.3-10 Emergency Generator Loading 8-iv Rev. 964

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 2 of 22 MPS-3 FSAR CHAPTER 8- ELECTRIC POWER

8.1 INTRODUCTION

The descriptions of the utility grid, its interconnections to other grids and to the Millstone Nuclear Power Station 345 kV switchyard, and the on site electric system include the terms defined below.

Transmission System The transmission system includes all transmission lines coming to the Millstone Nuclear Power Station complex from around the countryside up to, but not including, the point of connection to the 345 kV switchyard.

Off site System The off site system includes the transmission system, the 345 kV switchyard and extends up to, but not including, the main transformers as shown on Figure 8.1-1. Included in the off site system are the Millstone 3 reserve station service transformers and Millstone 2 in its entirety.

On site System The on site system includes the Millstone 3 electric power systems out to, and including, the main transformers (Figure 8.1-1); this includes the normal station service transformers.

Normal QOeration Normal operation is considered to be when the main generator is transmitting electrical power through the main transformers and plant auxiliaries are being supplied from the normal station service transformers.

Normal System The normal system includes that equipment required to support the main turbine generator and nonsafety equipment associated with the reactor. The normal systems and equipment are also referred to as non-Class IE, nonsafety related, nonvital, nonessential, and are color coded blackL Emergency System The emergency system includes that equipment required to support the safe shutdown of the unit and post accident operations. Included in the emergency system are the emergency 4,160 V switchgear and all extensions except those going to the normal switchgear and the reserve station service transformer (Figure 8.1-1). The emergency systems and equipment are also referred to as Class IE, safety related, vital, essential, engineered safety features, and are color coded purple or orange for trains and red, white, blue, or yellow for channels.

8.1-1 Rev. 28 IFor Information Only - No Changesi

Serial No: 15-297 Docket No. 50423 Attachment 3, Page 3 of 22 MPS-3 FSAR Alternate AC Power Source The alternate AC power source (AAC) includes the station blackout (SBO) diesel generator and its support equipment required to provide electrical power to equipment necessary to maintain the plant in a safe condition in the event of a loss of both off site power and the standby power system (defined as a Station Blackout Event).

Standby Power System The standby power system includes the emergency generators, which are also referred to as the on site emergency power supply.

Load froup The load group is an arrangement of busses, switching equipment, and loads with a common power source. The emergency systems are divided into two redundant and independent load groups.

Preferred Power System The preferred power system includes the normal off site source and the alternate off site source.

Normal Off site Source The normal off site source is from the 345 kV switchyard through the main and normal station service transformers with the generator breaker open.

Alternate Off site Source The alternate off site source is from the 345 kV switchyard through the reserve station service transformers.

8.1.1 UTILITY GRID The utility electrical system consists of interconnected diverse energy sources including fossil- 115-12 fueled, hydro-electric and nuclear-fueled plants supplying electric energy over a 345/115 kV transmission system (Figure 8.1-2).

ISO-New England is the regional transmission organization which has authority over the 15-12 operation of the transmission system in Connecticut. The main transmission system fed by Millstone Power Station is part of the New England power system. The Connecticut Valley Electric Exchange (CONVEX) is one of the local control centers in New England and assists ISO-New England in running the power system in Connecticut.

Millstone 3 is rated 1,354.7 MVA, 0.925 pF, 0.50 SCR, 24.0 kV, 1,800 rpm, 3-phase, 60 Hz.

8.1-2 Rev. 28

[For Information Only - No Changes i

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 4 of 22 MPS-3 FSAR The output of Millstone 3 is delivered to a 345 kV switchyard (Figure 8.1-3). Four transmission lines at 345 kV feed power to the 345 kV system. Two of these lines feed the Eastern part of 15-12 Connecticut by connecting respectively to the Card and Montville Substations. The remaining two lines feed the central part of Connecticut by connecting to the Beseck, Haddam, and Manchester Substations.

8.1.2 INTERCONNECTIONS Millstone Power Station is connected to the Eversource Energy, Inc. transmission system which is 15-16 closely integrated with transmission systems of several other utilities and operating companies.

The New England power system is part of the larger northeast interconnection power grid and is tied through various connections points throughout New England. These interconnections include 345kV 230kV, 138kV, 115kV, 69kV, and DC lines. The New England power system is also tied to neighboring grids such as New York, Hydro Quebec and New Brunswick, which are under the control of other reliability coordinators within the NPCC region.

8.1.3 345 KV SWITCHYARD SYSTEM AT SITE The 345 kV switchyard is designed in an arrangement as shown on Figure 8.1-3.

The switchyard consists often 345 kV breakers, four 345 kV transmission lines, two 345 kV tie lines to the generator step-up transformers, and two 345 kV tie lines to the reserve station service transformers. The Millstone I generator step up transformer and reserve station service transformer are no longer in service.

The control and relay equipment is housed in a masonry building with complete separation of primary and backup relaying, cables, etc.

The breakers and motor-operated (M.O.) disconnect switches are controlled locally from the switchyard control panels, from the Connecticut Valley Electric Exchange (CONVEX) via Supervisory Control And Data Acquisition (SCADA) or from the Millstone I Control Room.

Millstone 2 Operations is responsible for the switching and tagging of equipment located in the Millstone 1 Control Room.

With the installation of SCADA in the Millstone I Control Room, Millstone 2 Operations has control of generator breakers 8T and 9T, as well as indication only of the remaining breakers and M.O. disconnect switches via the existing RFL industries supervisory equipment. Millstone 2 and 3 control rooms are equipped with remote panels showing the status only of the breakers and M.O. disconnect switches in the switchyard.

The control side of the switchyard panels also contains the annunciator, control switches, indicating metering, breaker synchronizing check relays, reclosing relays and potential indicating lights.

The relay side contains transmission and generator tie line backup relays, out-of-step tripping relays, breaker failure relays, synchronizing relays, and pilot wire relays.

8.1-3 Rev. 28 For Information Only - No Changesl

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 5 of 22 MPS-3 FSAR An immediate read-out transient recovery system (oscillograph) is provided for recording the magnitude and duration of abnormal conditions.

The primary and backup relays, transfer trip, and carrier equipment are all located on their own individual cabinets.

The DC power is supplied by two independent batteries, one primary and one backup. Each battery is equipped with its own charger and distribution panel. A manual transfer scheme is provided to allow one battery and charger to carry the dc load upon the failure of the other battery and charger.

The 345 kV circuit breakers are pneumatically operated, consisting of three individual pole units.

Each phase consists of a pneumatic operating mechanism with associated linkage to operate the interrupters.

One air compressor is supplied for each breaker, in the case of the loss of one of the compressors another compressor can be used. The breakers are air operated, spring closed. The air opens the breaker and at the same time charges the closing spring for the next operation. The breakers have the capability of interrupting at maximum rating within two cycles after a trip signal has been received. Air capacity allows a minimum of three close-open operations to be available after the 15-17 loss of the compressor.

The low voltage breakers for the closing coil DC supplies to the 345 kV breakers are equipped with shunt trip coils to remove the DC supplies and initiate an alarm in case of breaker failure relay operation.

In accordance with the concept of separating primary and backup relaying, all 345 kV circuit breakers are equipped with two trip coils. The primary and backup relays are supplied from separate DC sources, separate current transformers, separate coupling capacitor potential devices, and communication channels.

Each 345 kV transmission line is protected from phase-faults and ground-faults by two sets of diverse protective relays, one primary and one back-up. The primary relays consists of distance 15-17 relays operating in a directional comparison blocking scheme and communicating with the remote channel over a carrier current channel.

The backup protection consists of step distance relays operating in conjunction with transfer trip 15-17 system over a communication channel. This system provides tripping at the remote channel following the operation of the line backup relays or circuit breaker failure relays, as well as tripping of the switchyard breakers following the reception of the transfer trip signal from the remote end.

A permissive over reaching scheme, utilizing audio-tone channel (via a combination of leased and j 15-16 dedicated fiber communication lines) is used as additional backup protection.

8.1-4 Rev. 28 For Information Only - No Changes

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 6 of 22 MPS-3 FSAR Pilot wire relaying is used for primary protection of the tie lines up to the main step- up transformer. 115-16 Backup protection consists of directional distance, single zone and directional ground over current relays. For transfer tripping to the plant end, dual channel audio-tone equipment is used.

Tripping of the switchyard breakers following the operation of the generator or main step-up transformer primary and backup relays is accomplished by the means of the transfer trip via pilot wire and audio tone channels.

The Millstone 3 reserve station service transformers' (RSST) 345 kV tie line is protected by two sets of protective relays, one primary and one backup. The directional distance relays detect phase-faults, and the directional ground overcurrent relays detect ground-faults. Operation of these relays will trip the appropriate 345 kV circuit breakers on the B switchyard bus, and send a transfer trip signal via audio tone to trip the transformers' low side circuit breakers at the plant.

The operation of any of the RSST transformer protective relays at the plant will trip the low side breakers, and send a transfer trip signal via audio tone to trip the appropriate switchyard breakers.

Breaker failure relays are provided for each of the circuit breakers to trip adjacent breakers in the event that the primary breaker fails to trip. The DC power for breaker failure operation is supplied from the backup battery system.

A breaker failure timing relay is initiated every time a main breaker is ordered to trip by either the primary or backup relays. If the breaker has not tripped before the time period has expired, tripping of the adjacent breakers takes place.

Phase angle sensitive impedance relays are also added to the backup protection of the main step-up transformer tie lines to protect the generator against out-of-step conditions. These relays trip the generator breakers only.

Reclosing of 345 kV breakers is provided following the protective relaying tripping of the 345 kV transmission lines. The reclosing is designed for time delay reclosure from the remote ends only.

At the switchyard, the breakers close via synchronism check relays.

A synch-check relay is provided for each breaker to supervise both time delay and manual reclosures.

A govere line ex+/-~ga aiestzzr (SLOP) pretetzion sehern hz been ir~Awlel4 reees~izig thM it-*'

P00ible t@ 1090 tw#VOiretuit9 9ifultanx0U9lY OR 0-0th-A AzfthcA 4t'wzA lirfct-A

-8Wzr ly zne eirci ith znA.4 449 .z.Zitie" siz emLghi tsblity ofMillytzznz Srzrtiz. kt igraee*J~ llatii 8.1-5 Rev. 28

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 7 of 22 MPS-3 FSAR The O sehzme

,Q- G3ntinuslay mzriitora the 1

--'iia 94HANu Off- W 94iti84 4f#M~i9ii@i sysitem elements together with the power ulput of Ihz N441840110 gznzratizn. Geneisziz is

-tailed awemfiatially 4f system eozritiea w~ises wherz any oft1he Ofritalfl smituastiz~ ziztsB Ond genomfteft at hfi~llte is above a j;;dzLmifteJ rmzgWftt love!. For a mozre detailed ONVlz"Mieft ofeslOD go; 94fiezzti &4.2

he *Ott; evra,*, g time of the &Lo..... gO. . t. -F li 1 i moa

-'e- r... eylg.

_1 8.1.4 ONSITE ELECTRIC SYSTEM The on site electric system consists of the normal and emergency systems (Section 8.3 and Figure 8.1-1).

During normal operation, AC power (Section 8.3.1) is provided to the normal and emergency systems through the normal station service transformers, which are connected to the main generator by isolated phase bus ducts. The normal station service transformers have adequate capacity to supply all normal auxiliaries and those emergency auxiliaries (both load groups) required during normal operation, up to the full output of the main generator plus the capacity to supply Millstone Unit 2 GDC 17 requirements as an alternate off site source for minimum post-accident loads. Upon loss of power from the generator, the generator breaker is opened to ensure continuous power service to the auxiliary buses. Upon loss of power from a normal station service transformer, an automatic high speed transfer to the respective reserve station service transformer is provided to ensure continuous power service to the 6.9 kV equipment and the 4.16 kV electrical system.

During startup or shutdown, each of the preferred power sources (normal and alternate off site) has adequate capacity to supply all normal auxiliaries required for an orderly shutdown together with emergency auxiliaries (both load groups) required for a safe shutdown.

When the Unit 3 RSST is out of service, the Unit 3 NSST connection must be credited as the Unit 2 alternate off site source. A single failure of breaker 13T in the 345 kV switchyard would cause simultaneous loss of both Unit 2 off site sources, and therefore breaker 13T and associated disconnect switches must be maintained "open" when this Unit 3 situation exists. With breaker 13T "open," and the Unit 3 RSST out of service, a fault on the Millstone-Beseck 345 kV line would cause a Unit 3 loss of off site power.

The reserve station service transformers also have adequate capacity to supply normal auxiliaries and those emergency auxiliaries (both load groups) if required during normal operation up to the full output from the main generator plus the capacity to supply Millstone Unit 2 GDC 17 requirements as an alternate off site source for minimum post-accident loads.

The standby power sources provide AC power to the emergency systems for safe shutdown when the off site power sources are unavailable. The standby power sources consist of two independent and redundant ac power emergency generators driven by separate diesel engines. Each standby emergency generator has adequate capacity to supply emergency auxiliaries required (one load group only) for a safe shutdown.

8.1-6 Rev. 28

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 8 of 22 MPS-3 FSAR 8.2 OFF SITE POWER SYSTEM 8.

2.1 DESCRIPTION

The off site power system is designed to provide reliable sources of power to the on site AC power distribution system adequate for the safe shutdown of the unit in compliance with General Design Criterion 17 (GDC- 17). Details of the off site power system are shown on the following figures:

1. Site Layout (Figure 2.1-3)

2. Site Plan (Figure 2.1-4)

3. Plot Plan (Figure 1.2-2)

4. Transmission Map (Figure 8.1-2)

5. 345 kV Switchyard (Figure 8.1-3)

The switchyard, which is configured in an arrangement as shown on FSAR Figure 8.1-3, buses together four 345 kV transmission line circuits, two generator circuits, and two station service circuits. The Millstone 1 generator and station service circuits are no longer in service.

The four transmission line circuits terminated at the switchyard are:

1. Millstone to Card (Line Number 383) tL..4 sH lm Wmsur,$ 3

2. Millstone to Montville (Line Number 371)

3. Millstone to Beseck (Line Number 348)

4. Millstone to Manchester (Line Number 310)

These circuits connect the station to the system transmission grid and follow a common right-of-way from Millstone to Hunts Brook Junction (9.0 miles). For the, fir 1.7 m*il' ofthi, right of W"y the @@"z~iaor~ca~ c~ foi tl~i tez~zializ h dczibk 6-4-uitktzcl Pei@ ha....a 0eafi- zfw' ... ii-- -*a..ig t . iromit so.etrua.- at o.vt'iz wher the righ Of way aihre-' dieoieftiza0 s~g tmturz) andl of& a40 eirflfflzt-z mztue at all

@tkw. lemi*'i=. For ".. namt 2.4 mile., #wze.nst*r-.i* . -zanists of one do"u'@ e-cuit Al pole

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. ... i l.....

,7 Z.." L i . . f, . .

jtr zf w'-- T.. 371 Al; ~S-tin rlc tl" o.., d II fril-i t follow m ow.sry r6i1t4 f .way At- p.....ma 3 .6hmile'-s- t,t Mensiie ..t-ilo.i.t :;h

.T 3 949 ine 8.2-1 Rev. 28

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 9 of 22 Iii...fw hmurnkafmrsdvideaftroosetod on swordot.ducters %lid"arn utroedecrose o4WS540feetwldrn Uitof Wayto proAde edoiequa Iphwi Idspmd~m I Itanesr f~bOSihdO Ur,,.The trnmision towersw "uduppertm kiso fisor red shte aidwmwd., Hfrmw shw~as. Use tosses see eAlped to ts N ehe dos stro~uucuirnes, lvmermc. OvyuWrb..inssmbsem thro Stamdwde fte A few t'usueusdan Nos. orn pesedodaly can CSiS cr conesvmhotof stool od wooden EkacSrkbS CadePurtC2,anid totIsdhow bothstranth andeowdoad dodgefacers to proiesdIfu aawvsonmird"Vs. TMs Inspected fewpr~oerpimple coodilmio.

Wingitalmost aqijivoý, zfwe~d polell friaez~roin~ih ail ~~oop~n :

-t Zt41044W 1 ON 66148zd; f~llzWS 0 Wvo9ta:1y riSt Of W"y f&r *PVFr fiatdlY 31 Mileto thde 140Aak :ukhwtniea' The 31-0 end 39-A Ia i zOtitiffliftg priltaily 94140 aim it we ad rl A H frwm four lines omefe le Millstone Switching Stationa in .~~ame.40- th~letI physiselly Ba~rmto and ondreds"Atso t"a He singleovq Bo) 0-,:Li a so"Iu: fcifl-I: er line br--ki- is able .. @i-------...y affect all circuits in such a way that none of the four circuits can be returned to service in time to prevent fuel design limits or design conditions of the reactor coolant pressure boundary from being exceeded. Fiiro .2 1. taken fise th: .: _.aoo u o,:iting C:s.l 14996i N:. 25, Applsatfien fortk: Millctz.. 4o Nlwelwt:: 315 ikVLline, Aows. ON ssmpnoc~eof kern a pardesofu quo!l pole Ottet..: bet:;::. Miuste" ".1 95 we app.:::iffloly 120 feet abv gr..tW ;wki!

the wool~: ps@Hfoesmk@btenRnee vm n ht ro ~f r qndk mummer, s- - to.

l-th @*on e; Ct :teti Af: f4*ilur: hatq A'-R:andill(tcIs~e An" Wee H rzk jmeioti;~ the. wa" alngatHt probable lmg, ... r me..nta.y :eag: weidd b: f lessAAft~: "uit;Li.e., t tw:heeir....ti on a rooimocko,

. . . - -I

. .R -ple o f n H A .-. M-- O IR .O--.. fallin.g io ta .an. a.e. line . Ow-worsttci s wsold be the Ion loftwo ckaab.I All four of the 345 kV lines leaving Millstone cross over two 115 kV circuits which supply the Waterford Substation, and constitute the off site source for Millstone Unit One. However, the mechanical failure of a single 345 kV line, and the consequential failure of the 115 kV circuits will not affect the fe source of off site power to Millstone units 2 and 3.

do*1 Uta. vepifoe sdifiS*f-wo At Hunts Brook Junction, the foufines 9lV (refer to Figure 8.2-2). The 348 line turns west to the Beseck Substation, the 383 and 310 lines continue north to the Card Street and Manchester Substations, respectively, and the 371 line turns east to Montville Substation. On.:a a W RN=-.R=

3f:le 1 :all ... Ae. 4li* e (M.f-o- !, 69. le.*z:. Nook). aitXwrt only two of the four circuits from the Millstone Switching Station would be removed flmsrIce should a structure collapse or a conductor drop. []t *

6tmtm Separate and independent structures are provided for each of the four 345 kV transmission lines connecting generators 2 and 3 and reserve station service transformers 2 and 3 to the switchyard.

The Millstone 1 generator and station service circuits are no longer in service.

The Millstone 3 design, which provides two immediate access off site circuits from the 345 kV switchyard to the 4.16 kV Class 1E buses, is via separate transformers (main/normal station service and reserve station service). Figure 8.1-1 shows the tie lines, transformer, and bus arrangement connections.

The tie lines to the main/normal station service transformers and to the reserve station service transformer are physically separate and electrically independent. The main/normal station service 8.2-2 Rev. 28

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 10 of 22 MPS-3 FSAR transformers and the reserve station service transformers are located at opposite ends of the plant.

The connections from the normal station service transformers and from the reserve station service transformers to the 4.16 kV Class IE buses are via physically separate and electrically independent underground duct lines. Figure 2.1-4 shows the tie line routes from the switchyard to the main/normal and to the reserve station service transformers. Figure 1.2-2 shows the physical separation between the normal station service and the reserve station service transformers.

Figure 8.3-7, Sheets 1 and 2, shows the embedded conduit duct lines as they enter the redundant switchgear rooms in the control building.

The breakers in the Class lE buses (34C and D) are independently protected with separate relaying. The control power for these buses is from different DC panels and batteries.

These circuits are completely redundant and separated so that no single failure can disable both off site power supplies to the Class 1E buses; therefore, the design is in compliance with General Design Criterion 17, Electrical Power Systems.

The inspection and testing of the 345 kV circuit breakers and the transmission line protective relaying are done on a routine basis, without removing the generators, transformers or transmission lines from service. The insulating oil for the transformers is sampled and tested on a routine basis. During these routine inspections and tests, the operability and functional performance of the electric systems are in compliance with General Design Criterion 18, Inspection and Testing of Electric Power Systems.

8.2.2 ANALYSIS The possibility of power failure due to contingencies in the connections to the system and the 115-16 associated switchyard is minimized by the following arrangements.

1. The connections to the system have been designed to comply with the Northeast Power Coordinating Council's Design and Operation of the Bulk Power System 15-16 and the Reliability Standards for the New England Area Bulk Power System.

Compliance with these criteria ensure that the supply of off site power is not lost following contingencies in the interconnected transmission system. Transient stability studies have been performed to verify that widespread or cascading interruptions to service do not result from these contingencies. In addition, the loss of Millstone 3 or the loss of any other generating plant in the system does not result in cascading system outages and thus does not cause loss of off site power to the units. Electrical facilities shared between Millstone 3 and Millstone Units 1 &

2 are discussed in Section 3.1.2.5, compliance with General Design Criterion 5, Sharing of Structures, Systems, and Components, is ensured. The Millstone 1 generator and station service circuits are no longer in service.

345 kV switchyard is designed in a combination breaker-and-a-half and double I 15-17 breaker-double bus switching arrangement as shown on Figure 8.1-3.

8.2-3 Rev. 28 IFor Information Only - No Changesi

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 11 of 22 MPS-3 FSAR The 345 kV circuit breakers are SF6 gas puffer types and are pneumatically operated. Electrical controls are provided for both local and remote Millstone 1 control room or CONVEX operation. Each power circuit breaker has a separate pneumatic supply unit capable of operating the breaker for a minimum of three 115-17 close-open operations after the loss of the compressor. Each pneumatic compressor is supplied from a separate feeder at the switchyard essential AC panel. The circuit breakers are equipped with a closing solenoid and two trip solenoids. A standard anti-pump and trip-free control scheme is used.

Primary and backup relaying are both high speed protective schemes. Primary and backup protective relays are used, along with breaker failure relaying, to provide redundant protective relaying for the switchyard.

Two 125 VDC batteries are located in the switchyard control and relay enclosure for switchyard relaying and control. Each battery has its own charger and DC distribution panel. The redundant batteries and protective relaying systems are physically and electrically separate. The essential AC station service for the power circuit breaker pneumatic supply units and the other switchyard requirements is supplied from one of two separate sources.

2. The 345 kV system is protected from lightning and switching surges by overhead electrostatic shield wires, earth grounding at most structures surge arrestors on the Switchyard main buses, surge arrestors at the transformer high voltage bushings, and rod gaps on the line terminals. 15-16

3. Primary and backup relaying is provided for each circuit along with circuit breaker failure backup protection. These provisions permit the following.

a. Any circuit can be switched under normal or fault conditions without affecting another circuit.

b. Any single circuit breaker can be isolated for maintenance without interrupting power or protection of any circuit.

C. Short circuits on any section of a bus are isolated without interrupting service to any element other than those connected to the faulty bus section.

d. The failure of any circuit breaker to trip initiates the automatic tripping of the adjacent breaker or breakers and thus may result in the loss of a line or generator for this contingency condition; however, power can be restored to the good element in less than eight hours by manually isolating the fault 15-17 with appropriate disconnect switches.

Complete battery failure is considered highly unlikely since two independent 125 VDC battery systems are provided. Failure of a single battery system results only in a temporary loss of one set 8.2-4 Rev. 28

[For Information Only - No Changes

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 12 of 22 MPS-3 FSAR of protective relays until the DC is manually transferred to the other battery Therefore, no single failure could negate the effectiveness of the relaying to clear a fault.

The Millstone 3 design provides two immediate access off site circuits between the switchyard and the 4.16 kV Class lE buses. Within the switchyard, the tie line terminations are separated electrically by two circuit breakers so that a fault on one off site supply circuit along with a breaker failure does not cause the second off site supply to be lost. The tie lines are supported on separate structures with one circuit terminating at the main transformer dead end tower, and the second tie line circuit terminating on the reserve station service transformer dead end tower. The normal station service transformers and the reserve station service transformers are located on opposite sides of the unit. The connections from the normal station service transformers and from the reserve station service transformers to the 4.16 kV Class 1E buses are via physically separate and electrically independent under ground duct lines. Figure 2.1-4 shows the tie line routes from the switchyard to the main/normal and to the reserve station service transformers. Figure 1.2-2 shows the physical separation between the normal and the reserve station service transformers.

Figure 8.3-7, Sheets 1 and 2, show the embedded conduit duct lines as they enter the redundant switchgear rooms in the control building.

The breakers in the Class 1E buses (34C and 34D) are independently protected with separate relaying. The control power for these buses is from different DC panels and batteries.

Physical separation of the off site power sources, switchyard protection, redundancy, and transmission system design based on load flow and stability analyses minimize the possibility of simultaneous failure of power sources (normal station service supply, reserve station service supply, and standby AC emergency generators) in compliance with General Design Criterion No.

17, Electric Power Systems.

The off site source that is normally available immediately on a unit trip is from the main and normal station service transformers. This source is not lost on a unit trip because the generator breaker effects the disconnection of the unit from the grid leaving the main and normal station service transformers backfed from the switchyard. The second source of off site power is available through an automatic transfer to the reserve station service transformers. Testing the normal immediate access circuit during plant operation would be inappropriate as this would disconnect the unit from the grid. The automatic transfer feature of the alternate immediate access off site circuit is not tested during plant power operation since it risks unnecessary plant trips.

Immediate access is not required of a second off site source. For the Millstone 3 design, if the automatic transfer is not successful, the reserve station service transformers can be connected to the emergency buses by manual control switch operation in an acceptable time.

The automatic transfer of emergency 4.16 kV buses 34C (Train A) and 34D (Train B) from either the normal to the reserve station service transformer or the normal or reserve station transformer to the emergency generators were tested prior to initial startup and will be tested during refueling shutdowns of the unit to prove the operability of the system. Therefore, appropriate testing and testability of the transfer of power upon loss of normal power satisfies the requirements of General Design Criterion 18, Inspection and Testing of Electric Power Systems.

8.2-5 Rev. 28 jFor Information Only - No Changes I

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 13 of 22 MPS-3 FSAR The 345 kV transmission system supplying off site power to Millstone is normally operated at 357 kV at Millstone. This system voltage is controlled by varying the reactive power generation on the Millstone units. The Millstone 2 and 3 operators control the unit excitation as specified by CONVEX Operation Instruction Number 6913. The unit operators are required to balance the reactive power output of the units.

The CONVEX system operator supervises the system reactive power dispatch. He directs the loading of all of the reactive power sources in CONVEX to balance the reactive supply. He keeps the Millstone reactive power generation in balance with the Eastern Area requirements so that the effect on the system of voltage variations is minimized when a unit is lost.

One objective of the reactive power dispatch is to prevent the voltage at Millstone from going below the minimum required to support the actuation of the Engineered Safety Features equipment. A switchyard voltage of 345 kV will assure successful actuation and operation of all necessary safeguards loads in the unlikely event Millstone Unit 3 experiences a Loss-of-Coolant Accident and trips off the transmission system. CONVEX operates the system to assure that this minimum voltage requirement will be met, following the loss of the unit. When in Reactor Modes 5 or 6, with the auxiliary electrical system lightly loaded, Millstone Unit 3 can assure successful actuation and operation of all necessary safeguards loads with a switchyard voltage of 335 kV.

The maximum allowable voltage at Millstone is 362 kV based on equipment ratings.

If abnormal system conditions result in voltages approaching minimum levels, the system 15-12 operating instructions and procedures direct the CONVEX operator to take specific corrective actions to restore voltage.

Actual experience and system simulations show that the CONVEX operator is able to control the system voltages within the desired limits.

The Millstone plant is connected to the transmission system by four 345 kV circuits (described in Section 8.2. 1). Per a-Shoff *: ..t.a.le,, these lineg -Af zat -dau

. eiret z.l pol:e. Transmission operating procedures are in-place to ensure that no more than the minimum number of circuits would ever intentionally be taken out-of-service, except in an emergency, when both Millstone generating units are on-line.

If both Millstone units 2 and 3 are on-line at full output, certain contingencies on the transmission system as determined by CONVEX result in procedural restrictions on the station's net output, in order to assure that system synchronous and voltage stability will be maintained. In addition, proeedwal rezfiatizom en the stetrzn'a o*Jput anZ nzZZZJsry if the Sew.e Line Otfte 9"Oterz (SiLOP) seezial pzetzztze 8yetZ13 is eut of geffiee. 4thio gpczial pmwefietv syawf "ill Zut-.-ier.ly*,t*wi. Sen... n at Mil.flz.z Ti-A 3, dependL"g open zz,-1q--N.... P-2-8 1..- ... -

By careful design of the switchyard and protective relays, the possibility of the simultaneous loss of both units 2 and 3 at Millstone has been significantly reduced. The system has been computer modeled for both light load and heavy load conditions. The stability analysis indicates that the rest of the system remains in synchronism after the loss of any one Millstone unit .si.... M-lla:

7 8.2-6 Rev. 28

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 14 of 22 MPS-3 FSAR oubj*ta to .....t.o ......... .ojl.an*-. The probability of losing both on-line units simultaneously is extremely small because of the preventive measures discussed in the following paragraphs. Accordingly, the Licensee believes it is reasonable to count upon on site power sources to supply the necessary station service power requirements in the very remote event that both Millstone units 2 and 3 should be lost at once accompanied by the total loss of the transmission supply to the station.

A primary objective in designing the connection of the Millstone Nuclear Power Station to the 345 kV transmission network in Connecticut has been to prevent the loss of the entire station output. The reliability criteria of the Northeast Power Coordinating Council (NPCC) and the ISO New England are a fundamental part of this design process. Sp. l ... t......^ Syzom_ (*Pn*) r gosioatizr roatr 31 Z6A15 3Athz AMillAtRNo 9tt44azui~

za;'id n.ii :Mnztailiy &Fr som:

--...-."...ie s-tm ge3a

1t or n.ear** z*.'.h: fl.lz fism '- e most severe outage/which the system has been designed to survive in order to minimize the lossibility of a total plant outage/,-.

e. With any one of the four Millstone 345 kV transmission circuits out of service, the plant remains stable for any three-phase fault normally cleared (four cycles) or any one-phase fault with delayed clearing (eight cycles).

hi szr.z te mm3 the weaosifig rxjuL-zment thAt rnz single mee+/-anieel foailr, zulel With all lines in sevc hk9 Mrm sL..zztble feczttaZ "V zeitmfdiztwbo.ee.

raited got weZ widely groedaws 09 afible siroujt 04mtweer fop ely a hopt dieae wA, henee the wipZsw to t~ double eiravit zuage is zmatA.

Withzut Milmtzne Unit 1 On lin:, the 1Wt hilwtz~z out-pat does flat th~aten onther Mritl itrtzullt lif~t)m it iMwwhestr Nall do nheitl re zu enrtion 0*

thiO t;;zO cffzcti@zY M014 in% t~h@ lzzz AzftlrzzO BfthO fO*r ?.i11Rfznz Sifeuitsandr lzawy the Millsten tzte "onz eay tied to 46z tranniszizr. gri!. TO jrzvz31

,sonforth QtJzSevere La.m Ot..,o, Ree (S160) SP tZ he n s IA10h@1h0z Of, fth@ ; ;..Wt 6441 OzRzzx OOO AMtW WW 0100.~

The Millstone units are connected to the large interconnected transmission system in the eastern half of the United States. The interconnected system frequency is maintained at 60+/-0.03 Hz inm 15-16 accordance with NPCC standards for the bulk power system. Loss of large amounts of generation 8.2-7 Rev. 28

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 15 of 22 MPS-3 FSAR or the isolation of an area can cause a deficiency or surplus of generation respectively. Either case causes frequency deviations. High frequency deviations causes generation to be tripped, and low frequency causes automatic load shedding. Either action applied appropriately helps the frequency to recover to 60 Hz within a few minutes.

The system is designed and operated such that the loss of the largest single supply to the grid does 15-16 not result in the complete loss of preferred power. The system design considers the loss, through a single event, of the largest capacity being supplied to the grid, removal of the largest load from the grid, or loss of the most critical transmission line. This could be the total output of a single Millstone reactor unit, the largest generating unit on the grid, or possibly multiple generators as a result of the loss of a common transmission tower, transformer, or a breaker in a switchyard or substation.

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~~.. .t y 11143 MW with 9 MW NP fiinn 95LOrezfid.

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. l.izdir.. e" th:en1 tNO and pnnzylvei:ft ,ys Nw1Y-=k zf detemine OW ffienum" allowable anfzunti Of-ge"Offife less Wkieh the itoereeRewted system

....... .:--:-e-- t..o,:, 9 is eel 4 th ..O"O...it of Nilloto 3 is. d...d to the!V elewbl smow - o~nfgeneziiznless.

0i Operationa zf z-t SLOP--In t-e ....

h.... .ir. t:L:r... isaI..1-..onthe I .....

ildiYAWz~ ztalm zfthe fwouriti::l t4r.raizziz 010OR4t i~tzethe with th: It"rmo OW19*t z 8.2-8 Rev. 28

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 16 of 22 MPS-3 FSAR ilia Mila614-0 n se"16. Gx iz is orzled WAOtMA.ally if aaao z~tz uaiwo flatizn PeWff ba WOen 9FRzAz OhM 1740 MW (grzaa) 1650 M4W OWz) fc h-An 6 Azzands, 4zr and ther: jaasza-1esefA-nef 046 4citioal tnrIfamiss "- -- miruita.

Neessomy 48 M80zt NpGG OW NEP05OOL :itia!

ztno

--- -hfazhzztz;4614@40"s Cad vzd 46I1184811 4101*411 Mjllztznoff Hook Mlocz od OW Millzzow m zn- i Milblotea Czd, Millztzw 4Mz"Ohzztr and MAiliteft geseek siffee th@ zpeztie" 8ftz SiLoD geOrmzz.t.,. zticheme

... j@6 sho~uld tnh ri- in 1099~ the" 14 05-0108 40 rnzinkiff @tzbiit all tr-im-zaizn !-i"@ fovwnmothoooo.od t ig W"ith 4,00 @LDmo~atnge raqjs@6izn 99hem in @rswig@, kis rfivi fomuible to OPOMAto wilh a 119 M.--ifflztzmer~mitatc "Utt ef 20MWM4 when any Onz Of four aritiol trmanamiziz . ir-- 44 0zut z N;MA4G liv.14iq detz-ine.d hood 0"~NOW YOrk P"Wez Peel R;Ypp) zzd paz ylvenz J..zy NlayLnd (NIA) 9"m... enditfiem. Ae e. memberh. ef WOC ?;@% Englmi and the NPGG, t L:s~ge is it4d to eemply w.ith Omerz aff he folloing spersb aihy .zuirelzzzt* with 0"0 4- 6we~ SLOD) fi.lly epeztienel, linkt he nt A44ein ztoput te, 2500 MWA wmd!iii the zctpu of Urtit 3te the M(AMNGC limit, Wfapplizcble, or

-2 rzdtwolecd :teW it @Wzien. oatu of!! 1740 MMW (S q 1i660 MWA (rA*) within 30 mkoe ~zthe ater element is mmove..d Fmmseyie 4Wth anline in.;~..zservz, the. 84.zti Z11C....4"t iqLcmiled to 2520 MW. T;p will ez...,.nsillf atability i@MkA~intaid iff *1hQVW zf a d8uhIo 949%4.i @Ozntingzczy These i"AtItionq Ox deozfflrlged 89 VOA Of 1hz Gomeelzztizn Vaiy Eizatris Erzhakeg (CONVEX) opording ~~tcafzr the MiIlwes swithyarfd and we rzeguiatzd by CONVEX.

Tc9 fri~ilijt a~tz ~ Go~ljy CON LWr lE qftfdz Gzadit. of ftl Iifteg ffl ONz Stat" ef the 9LOD mehze. -via " O~ ileloahd of CONVE~X (CONVEX is c.an Opervc.. zfigs OIS in.. epemb.ity ... ........ tz spfied abovec....1ht enwe di; opnls 4 cIz etl za~tif... li.. .. il

- SCOOMo and 8000"Ortz ift ON9oa 8f 1750 NIW (@Fez) 1650 OMW (rot), 04948t erdiazZI pc-.-: -&to &Fadhl _-_acz;htdwn; mctaintsi4 syzo~m clabih*t maisimimes the Impbabilitv 8.2-9 Rev. 28

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 17 of 22 MPS-3 FSAR Teznod ntIgn ofkth swit hy i rd pliei. 4hiyshi RO s anAcirhu reaker intallaton s t Resignariteeign (GtG) 17is ndpC 17 &a@ poluir thipin prodba y finsting anbre 844;akers, with independenftle lessy Witd tw1o sprt , metods ofby trippinircuit g the breaker. itakhyet bz.atin in dtwoi setso Sreayfsr trip heo o and WO sets of currnandm NWO p ntia tfonrfrmelay hetwimn eriAor terzelnhay (Whiag i nstra when led seOatdPuUnit ;) OMs he mwereyoad by CONVEX phyisicll se ited in bThaei~

34hVOs hrdO b ath oillstonepis designe lstht th oss ofmo than@on te uransmision mumpda"610 wi4thGD 17 The design of the switchyard protective relay schemes and circuit breaker installations is such that at most only one pole or phase of a t reei-phase circuit breaker will fail to clear a fault. Breakers which are designed to meet this criteria are classified as having independent pole tripping.

Independent pole tripping is ensured by installing breakers with mechanically independent poles and two separate methods of tripping the circuit breaker. These installations include two sets of relays, trip coils, and two sets of current and potential transformers. The wiring for the relay packages are installed in separate duct banks, the relay packages are physically separated in the control house and two separate dc supplies are provided.

115-l1 The 345 kV switchyard at Millstone is designed so that the loss of more than one transmission circuit due to a failure of a breaker to trip requires at least two circuit breakers to simultaneously fail to operate. The failure of even one circuit breaker is very unusual. At least three circuit breakers would have to fail before three transmission lines would be lost due to malfunctions in the switchyard. At poitthe SbLO g mAirai zj:z:-ie'n sehae wozuld opera.te to k:ep z.-

u-mt 406azrvie. In OF&zr to kiazI sha zntir gdatiz at jeams folm fairzuit hbR16kzr m-As f&il 8.2-10 Rev. 28

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 18 of 22 15-16

/

I, 0f For Information Only - No Changesl Rev. 28

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 19 of 22 I* it*

FIGURE 8.1- 1 34bKV SWITCHYARD

.9 I- -

I It CO I Z1ý~

4¸'

10 34T Ii 3 I I I

4

Serial No: 15-297 Docket No. 50-423 , Page 20 of 22

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 21 of 22 MMS-- FSAR FIG~URE 31-2 HUNTS BROOK JUNCTION/ ~paewt NETA Rev. 40s2

Serial No: 15-297 Docket No. 50-423 Attachment 3, Page 22 of 22 Insert A i (North)

Manchester 368 368 Card Street 310 383 Haddam Neck 364 (west) (East)

Hunts Brook Junction Note: This figure replaces existing MP2 FSAR Figure 8.1-1B and MP3 FSAR Figure 8.2-2

Serial No: 15-297 Docket No. 50-336 ATTACHMENT 4 NEW TECHNICAL REQUIREMENT FOR OFFSITE LINE POWER SOURCES (FOR INFORMATION ONLY)

DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2

Serial No: 15-297 Docket No. 50-336 Attachment 4, Page 1 of 3 3/4.8 ELECTRICAL POWER SYSTEMS 3/4.8.1 A.C. SOURCES OFFSITE LINE POWER SOURCES TECHNICAL REQUIREMENT 3.8.1.2 The offsite lines to the Millstone Switchyard: 310, 348, 371 (includes 364 line),

and 383, shall be FUNCTIONAL.

APPLICABILITY:

When Millstone Power Station (MPS) electrical output exceeds 1650 MWe net.

ACTION:

a. With one offsite line nonfunctional, perform the following or reduce total station output to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits within the next 6 hour6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months s:

1. Restore FUNCTIONALITY of the affected offsite line within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months , or

2. Establish the following ACTION requirements AND restore FUNCTIONALITY within 14 days.

a. Once per shift, verify the remaining offsite lines to the MPS switchyard are FUNCTIONAL.

b. Perform an initial weather assessment for the scheduled line outage duration and then once per shift thereafter.

1. If the assessment predicts adverse or inclement weather will exist while the offsite line is nonfunctional (i.e., out of service), reduce total station output to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits, prior to arrival of the adverse or inclement weather.

c. Within one hour prior to or after entering this condition and at least once per 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months thereafter, verify that both the Millstone Unit 2 EDGs and the Millstone Unit 3 EDGs are OPERABLE and the Millstone Unit 3 SBO diesel generator is available. Restore any inoperable Millstone Unit 2 EDG or Millstone Unit 3 EDG to OPERABLE status and/or the Millstone Unit 3 SBO to available status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months or reduce total station output to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months .

Serial No: 15-297 Docket No. 50-336 Attachment 4, Page 2 of 3

b. With two offsite lines nonfunctional, reduce total station output in accordance with the Millstone Facility Out Guide stability operating limits within the next 30 minutes.

TECHNICAL SURVEILLANCE REQUIREMENTS 4.8.1.2 The four offsite lines to the Millstone Switchyard shall be determined to be FUNCTIONAL at least once per 7 days when station output exceeds 1650 MWe net.

BASES:

TR 3.8.1.2 requires that all four offsite 345 kV transmission lines are FUNCTIONAL when MPS electrical output exceeds 1650 MWe net. TR 3.8.1 contains ACTIONS that must be performed when one offsite 345 kV transmission line is nonfunctional.

TR 3.8.1.2 provides flexibility to preclude plant downpowers due to planned and unplanned offsite transmission line outages. The TRM requirements provide this flexibility while also maintaining adequate defense-in-depth to ensure grid reliability and stability are preserved and the ability of the plants to respond to design basis accidents is not adversely affected.

With one offsite line nonfunctional, ACTION a.1 allows 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore FUNCTIONALITY. This 72-hour allowed outage time (AOT) is conservatively based on the loss of one offsite line being equal to the risk of losing one onsite connection to the offsite power system (i.e., TS 3.8.1.1).

With one offsite line nonfunctional, ACTION a.2 contains the provision to allow up to 14 days to restore FUNCTIONALITY if ACTIONS a.2.a, a.2.b, and a.2.c are met. The 14-day AOT reduces the risk of a plant perturbation as a result of having to downpower the unit for short duration line outages. The 14-day AOT provides flexibility for conducting maintenance and improves operational safety margin by the following:

" Minimizes the number of plant downpowers for short duration 345 kV transmission line outages.

Reduces the likelihood of a loss of offsite power event by establishing an AOT with additional defense-in-depth measures to minimize the potential for a double circuit failure scenario which can result in grid instability.

During the 14-day AOT, ACTION a.2.a ensures there are no known issues that could threaten the reliability of the remaining 345 kV transmission lines. Verifying the remaining 345 kV offsite transmission lines to the MPS switchyard are FUNCTIONAL, increases confidence that the remaining 345 kV lines will remain FUNCTIONAL during the planned outage of the affected 345 kV line.

Serial No: 15-297 Docket No. 50-336 Attachment 4, Page 3 of 3 During the 14-day AOT, the action to perform weather assessments as required by ACTION a.2.b ensures appropriate actions are taken to minimize the potential for adverse or inclement weather event to impact grid reliability with one line nonfunctional. If adverse or inclement weather is predicted, the nonfunctional 345 kV line would be restored to FUNCTIONAL status or station output would be reduced to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits prior to the arrival of the adverse or inclement weather.

During the 14-day AOT, ACTION a.2.c (i.e., both the Millstone Unit 2 and Millstone Unit 3 EDGs are operable and the Millstone Unit 3 SBO is available) provides assurance that AC power will be available to support required safety-related equipment in the unlikely event of a complete loss of offsite power during the time one of the 345 kV lines is nonfunctional.

This ACTION ensures that electrical power will be available in a timely manner to perform the required functions to maintain cooling to the reactor core in the unlikely event a loss of offsite power was to occur during this 14-day AOT.

For the condition where the 14-day AOT is in use for one nonfunctional transmission line and one or more of the following components is out-of-service:

a Millstone Unit 2 EDG

" a Millstone Unit 3 EDG

" the Millstone Unit 3 SBO diesel generator 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months is allowed for restoration of the out-of-service component. If any one of these components is not restored within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months , reduce total station output to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months .

REFERENCE:

License Amendment XXX

Serial No: 15-297 Docket No. 50-423 ATTACHMENT 5 NEW TECHNICAL REQUIREMENT FOR OFFSITE LINE POWER SOURCES (FOR INFORMATION ONLY)

DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

Serial No: 15-297 Docket No. 50-423 Attachment 5, Page 1 of 3 3/4.8 ELECTRICAL POWER SYSTEMS 3/4.8.1 A.C. SOURCES OFFSITE LINE POWER SOURCES TECHNICAL REQUIREMENT 3.8.1 The offsite lines to the Millstone Switchyard: 310, 348, 371 (includes 364 line),

and 383, shall be FUNCTIONAL.

APPLICABILITY:

When Millstone Power Station (MPS) electrical output exceeds 1650 MWe net.

ACTION:

a. With one offsite line nonfunctional, perform the following or reduce total station output to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits within the next 6 hour6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months s:

1. Restore FUNCTIONALITY of the affected offsite line within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months , or

2. Establish the following ACTION requirements AND restore FUNCTIONALITY within 14 days.

a. Once per shift, verify the remaining offsite lines to the MPS switchyard are FUNCTIONAL..

b. Perform an initial weather assessment for the scheduled line outage duration and then once per shift thereafter.

1. If the assessment predicts adverse or inclement weather will exist while the offsite line is nonfunctional (i.e., out of service), reduce total station output to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits, prior to arrival of the adverse or inclement weather.

c. Within one hour prior to or after entering this condition and at least once per 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months thereafter, verify that both the Millstone Unit 2 EDGs and the Millstone Unit 3 EDGs are OPERABLE and the Millstone Unit 3 SBO diesel generator is available. Restore any inoperable Millstone Unit 2 EDG or Millstone Unit 3 EDG to OPERABLE status and/or the Millstone Unit 3 SBO to available status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months or reduce total station output to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months .

Serial No: 15-297 Docket No. 50-423 Attachment 5, Page 2 of 3

b. With two offsite lines nonfunctional, reduce total station output in accordance with the Millstone Facility Out Guide stability operating limits within the next 30 minutes.

TECHNICAL SURVEILLANCE REQUIREMENTS 4.8.1 The four offsite lines to the Millstone Switchyard shall be determined to be FUNCTIONAL at least once per 7 days when station output exceeds 1650 MWe net.

BASES:

TR 3.8.1 requires that all four offsite 345 kV transmission lines are FUNCTIONAL when MPS electrical output exceeds 1650 MWe net. TR 3.8.1 contains ACTIONS that must be performed when one offsite 345 kV transmission line is nonfunctional.

TR 3.8.1 provides flexibility to preclude plant downpowers due to planned and unplanned offsite transmission line outages. The TRM requirements provide this flexibility while also maintaining adequate defense-in-depth to ensure grid reliability and stability are preserved and the ability of the plants to respond to design basis accidents is not adversely affected.

With one offsite line nonfunctional, ACTION a.1 allows 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore FUNCTIONALITY. This 72-hour allowed outage time (AOT) is conservatively based on the loss of one offsite line being equal to the risk of losing one onsite connection to the offsite power system (i.e., TS 3.8.1.1).

With one offsite line nonfunctional, ACTION a.2 contains the provision to allow up to 14 days to restore FUNCTIONALITY if ACTIONS a.2.a, a.2.b, and a.2.c are met. The 14-day AOT reduces the risk of a plant perturbation as a result of having to downpower the unit for short duration line outages. The 14-day AOT provides flexibility for conducting maintenance and improves operational safety margin by the following:

" Minimizes the number of plant downpowers for short duration 345 kV transmission line outages.

" Reduces the likelihood of a loss of offsite power event by establishing an AOT with additional defense-in-depth measures to minimize the potential for a double circuit failure scenario which can result in grid instability.

During the 14-day AOT, ACTION a.2.a ensures there are no known issues that could threaten the reliability of the remaining 345 kV transmission lines. Verifying the remaining 345 kV offsite transmission lines to the MPS switchyard are FUNCTIONAL, increases confidence that the remaining 345 kV lines will remain FUNCTIONAL during the planned outage of the affected 345 kV line.

Serial No: 15-297 Docket No. 50-423 Attachment 5, Page 3 of 3 During the 14-day AOT, the action to perform weather assessments as required by ACTION a.2.b ensures appropriate actions are taken to minimize the potential for adverse or inclement weather event to impact grid reliability with one line nonfunctional.

If adverse or inclement weather is predicted, the nonfunctional 345 kV line would be restored to FUNCTIONAL status or station output would be reduced to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits prior to the arrival of the adverse or inclement weather.

During the 14-day AOT, ACTION a.2.c (i.e., both the Millstone Unit 2 and Millstone Unit 3 EDGs are operable and the Millstone Unit 3 SBO is available) provides assurance that AC power will be available to support required safety-related equipment in the unlikely event of a complete loss of offsite power during the time one of the 345 kV lines is nonfunctional. This ACTION ensures that electrical power will be available in a timely manner to perform the required functions to maintain cooling to the reactor core in the unlikely event a loss of offsite power was to occur during this 14-day AOT.

For the condition where the 14-day AOT is in use for one nonfunctional transmission line and one or more of the following components is out-of-service:

a Millstone Unit 2 EDG

a Millstone Unit 3 EDG

the Millstone Unit 3 SBO diesel generator 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months is allowed for restoration of the out-of-service component. If any one of these components is not restored within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months , reduce total station output to the limiting value associated with the loss of one additional line in accordance with the Millstone Facility Out Guide stability operating limits within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months .

REFERENCE:

License Amendment XXX

Serial No: 15-297 Docket No. 50-336/50-423 ATTACHMENT 6 ISO-NEW ENGLAND MILLSTONE FACILITY OUT GUIDE LETTER DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNITS 2 AND 3

Serial No: 15-297 Docket No. 50-336/50-423 Attachment 6, Page 1 of 1 ISO iinew england June 17, 2015 Deborah MacDonald Manager Nuclear Design Engineering Millstone Generation Power Station, Route 156, Rope Ferry Road Waterford, CT, 06385

Dear Mrs. MacDonald:

This letter is in response to your request for a statement from ISO New Englandregarding the

'Millstone Facility Out Guide. This is to support Dominion's Millstone Station filing to the NRC (DocketNumbers 50-336 and 50-423).

The ISO New England Millstone Facility Out Guide represents the results of dynamic studies completed in accordance with NERC Reliability Standards, NPCC Directories and ISO New England Procedures. The Guide provides real-tiine guidance to posture Millstone generation to maintain generator stability during a facility out condition. The Guide describes the limitations to Millstone Station generation (Millstone 2+3) if there are two major elements (Line + Line, Line + Breaker or Breaker + Breaker) out of service in the Millstone switchyard.

If the NRC would like to review the Millstone Facility Out Guide they will have to make a request directlyto ISO New England. Due to ISO New England Information Policy restrictions, the request cannot be made through Millstone Station.

Sincerely, Kevin Clark Principal Nuclear & System Reliability Coordinator ISO New England Inc.

Or,4 Su5ti.; Rik l.WdF3lw-,c%U010434041 Vmiso-04.om T 41'2 5354A000

Serial No: 15-297 Docket No. 50-423 ATTACHMENT 7 HISTORICAL REGULATORY CORRESPONDENCE PERTAINING TO MPS3 OFFSITE POWER SOURCES DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

Excerpts from NRC Letter Dated May 3, 1983 Request for Additional Information for Millstone Nuclear Power Station, Unit 3

-9 0

UNITEp STIATES LAg NUCLEAR REGULATORY COMMISSION

'-I WASHING1ON, D. C. 20555

~ AlLiS' MAY 3 1983 Docket No, 50-423 Mr. W. G. Counsil RECEIVED Senior Vice President Nuclear Engineering and Operations MAY 4 1993 Northeast Nuclear Energy Company Post Office Box 270 SfrtkOR vICE PRES4DENT' Hartford, Connecticut 06101 Nucfear EnginCee, & Opeiations

Dear Mr. Counsil:

S-ubject Request for Additional Information for Millstone Nuclear Powepr Station, Unit 3 Enclosed are requests for additional information which the staff requires to complete its evaluation of your application for an operating license for Millstone 3, These requests for additional Information are the result of the staff's review of the Information in your FSAR, You should amend your FSAR to include the information requested in Enclosure 1.

Review of certain portions of your application has been delayed and questions concerning these portions are not included in this package. You will be advised of the schedule for transmittal of any questions resulting from this remaining review. Due to the expected number and nature of these questions, the staff expects that you will be able to provide your responses to these questions when you respond to the questions in Enclosure I; however, if necessary, you will be given ninety days from the date of transmittal to provide your responses.

As you were advised In the letter from Darrell G. Eisenhut to you dated Janu-ary 31, 1983 concerning acceptance of your application for docketing, only a single set of questions concerning your FSAR are being transmitted to you for responses. After the staff has reviewed your responses to these questions, a draft SER will be prepared to provide a basis for a series of meetings designed to close out open Items.

You should provide your response to the enclosed request for additional infor-mation In the form of an amendment to the FSAR no later than August l, 1983, For further information or clarification, please contact the Licensing Project Manager, Elizabeth L. Doolittle (301/492-7134).

e1 RECEIVED B.3,1 ounbl6 d, Chief Lc& ing RrnCh ~No, 1 Dlvi ion of Licensing MxAY 1 O983

\. LAUD'N I

I .... - ~

ASCII Text Mr, W. C. Counsil MAY 3 1983

Enclosure:

As Stated c' w/encls.: See next page

W_ ..

ASCII Text REQUEST tOR ADDITIONAL INFORM1AION MILLSTONE NUCLEAR POWER STATION UNIT 3 DOCKET NO. 50-423 430.0 POWER SYSTEMS BRANCH, ELECTRICAL 430.3 Criterlon 50 of Appendix A to 10 CrR BC, IEEE Standard 4B5, Regulatory (sRP 8,1) 'Guide 1,63 and branch technical positions ICSB 4, PSt-I'ard P5B-2 have not been identified Ir Table B.1-2 of the FSAR; thus, a positive statement at to compliance with these criteria and staff guidelines has not been provided in tha FSAR, Provide a statement of compllance and justify areas of noncompliance, 430.4 There are four transmission lines between Rillstone and Hunts Brook (SRP 8.2) Junction that follow a rommon right-of-way. It ii the staff position that no other transmission lines cross over these four lines and that the four lines be physically separate and independent so that no single event such as a tower falling or line breaking will be able to simultaneously affect all circuits in such a way that. none of the four circuits can be returned to service in time to prevent fuel design limits or design conditions of the reactor coolant pressure boundary from being exceeded, Line crdss overs and physical separation of these four transmission lines has not been described in the FSAR.

Provide the description and justify areas of noncompliance with the above staff position.

430.5 The Millstone design provides two immediate access offsite circuits (SRP 8.2) between the switchyard and the 4.16 kv Class It busses. tt Is the staff position -that these two circuits be physically separate and independent such that no single event can simultaneously affect.

both circuits i: such a way that neither can be returned to service in tite to prevent fuel design limits or design conditions of the reactor coolant pressure boundary from being exceeded, The physical separation and Independence of these two circuits has not been described or analyzed in the FSAR. Provide the description and analysis and justify areas of noncompliance with the above staff position. The analysis should include separation and independence of control and protective relaying circuits as well as the power circuits.

430.6 The Millstone design arrangement provides two immediate access offsite (SRP 8.2) circuits. One Bf these circuits utilizes a generator circuit breaker to isolate theturbine generator from the main and normal station service transformers. Other facilities that utilize generator circuit breakers have been required to perform verificatlontesting.

Provide a verification test program with results to demonstrate the breaker's ability to perform its intended function during steady-state operation, power system transients, and major faults, (See additional g*uidelines for this question in Attachment 1,)

ASCII Text]

REQUEST FOR ADDITIONAL INFORNATION MILLSTONE NUCLEAR POWER STATION UNIT 3 DOCKET NO. 50-423 430.0 POWER SYSTErS BRANCH, ELECTRICAL (CONT'D) 430.7 a. It is the staff position that the Millstone grid stability (sRI' 8.2) analy-is must show that loss of the largest single supply to the grid does not result in the complete loss of preferred power., The analysis should consider the loss, through a single event, of the largest capacity being supplied to the grid, removal of the largest load from the grid, or loss of the most critical transmission line, The combined capacity of Millstone Units 1, 2, and 3 Is to be supplied to thL grid through the comnon Millstone switchyard. The combined capacity of the three-units appeias to be th`earget capacity being supplied to the grid and should be considered In the Millstone grld siability analysis. Provide the results of the grid stability analysis when simultaneous loss of the combined capacity of Units 1, 2,.and 3 is considered and justify areas of noncompliance with the above staff position.

b.. There are four transmission circuits that connect the Millstone switehyardto the grid systeam. The four circuits are routed on two tower lines - two circuits. per tower line. Sektion 8.1.3 of the FSAR indicates that a simultaneous failure of either of the two tower lines with only one circuit in service on the other tower 11/2ýe, may result in instability of Millston6 generation. The applicant, in order to prevent Instability, has installed a protection scheme to automatically reduce generatDr output at Millstone Unit 3. Describe the prot ection scheme, 430.8 Each of the 4..16 kV Class IE busses at Millstone is supplied power (SRI' 8.2 froM preferred offsite and standby onmite circuits, It is the 8.3.1) staff position that these circuits should not have common failure modes., Physical separation and independence of these circuitt has not beer described or analysed in the FSAR. Proiide a description and analysis in accordance with Section 5.2.1(5) of IEEE Standard 308-1974.

430.9 Section 8.3.1.1.4 of the FSAR indicates that a degraded voltaqe (SRP B.3.l, scheme With two-out-of-four logic is provided on each of the Appendix 4,16 kV Class IE buses. Provide reference to electric 'schematic BA) drawings that describe the degraded voltage scheme and provid'e a description, with voltage and time setpoit's, to indicate how the Millstone design complies 0ith the guidelines of position 1 of branch technical position PSB-1 (HUREG-DSDO Appendix 8A) and provide justification for any deviations.

430.1 0 As stated In Section 8.3.1.1.3 of the FSAR, the emergency generator (SRk 8.3.1, load sequences (EGLS) has the capability to automatically reset Appendix- during a sustained low voltage condition on the esential bus, eA) It is the staff concern that this capability may unnecessarily

Excerpts from Northeast Utilities Letter Dated August 1, 1983 Millstone Nuclear Power Station, Unit No. 3 Response to Select Requests for Additional Information

ASCII Text "MR 1E~ uU'fl MJ tAMCT*9tA If 1N FY#

fPMW Iyn Coers!a offices

swidon stresl, Berlin. CoMroticut HMELqO "ER WPAl W06flT , P.O. BOX 270 HARTFORD, CONNECTICUT 06i41-020 440=t K,," ImQ y cO'N '

August 2, 1H83 Docket No. M0-423 BIOS5O Director of Nuclear Reactor Regulation Mr. B. 3. Youngblood, Chief Licensing Branch No. I Division of Licensing U. S. Nuclear Reguatory Commission Washington, D.C. 20.55 References. (1) B. 3. Youngblood to W. G. Counsilt Request for Additional Information for Millstone Nuclear Power Station, Unit No. 3, dated May 3, 1983.

(2) W. G. Courtsil to B. 3. Youngblood, Millstone Nuclear Power Station, Unit No. 3. Response to Select Requests lor Additional Information, dated July 22, 1983.

(3) B. J. Youngblood to W. G. Counsil, Request for Additional Information for Millstone Nuclear Power Station, Unit No. 3, dated May 3 1 p1983.

Dear Mr. Youngblood:

Millstone Nuclear Power Station, Unit No. 3:

Response to Select ReqUests for Additional. Information Attached are the remaining responses to those questions contained In Reference (1) that were not forwarded by Reference (2). Attachment I Jists and contains these responses. Additionally, responses to a portion of the questions forwarded by Reference (3) are now being forwarded In advance of the August 29, 1983 due date. Attachment 2 lists and contains these responses. Attachment 3 contains FSAR changes made as a result of responses to questions.

Similar to the transmittal of Reference (2), because our response to Reference (3) is being forwarded via two (2) transmittais, some of the revised FSAk pages associated with responses contained herein are common to those to be forwarded on or before August 29, 1993. Such revisions should not be construed as final until they are forwarded on or before August 29, 1983, As agreed in discussions between your Mr. 3. Sprawl and our Mr. D. 0. Nordquist during a July 7p 1983 meeting, the attached 260 series question responses concerning the Millstone Unit No. 3 Quality Assurance Program have been prepared to address the operational phase. In other words, responses to 260 series questions were prepared considering that these questions were asked as a k

ASCII Text result of the NRCMs review of the Northeast Utilities Quality Assurance Program against NUREG-0SOD, Standard Review Plan Section 17.2, Quality Assurance During the Operational Phase. The 260 series respomes attached are sell-contained. They do not revise FSAR Section 17.2 or NU-QA-1, the Northeast Utilities Quality Assurance Program Topical Report. Howevero as agreed with Mr. Sprawl a decision will be made in the near future to revise one of these documents to include the applicable responses to the 260 series questions.

The responses to Reference WI) contained in both this transmittal and in Reference (2) have been or are being provided as they will appear in Amendment 3 to the PSAR. On or before September 1, 1983,'the required60 copvies of Amendment 3 will be forwarded to you for insertion into your PSAR sets.

Similarly, the responses provided now to Reference (3) and those remaining to be provided August 29, 1983 have been or will be provided as they will appear in Amendment 3 or Amendment 4 to the FSAR which will be forwarded on or before October 1 1993.

II you have any concerns related to cornmitments containvd herein or any queslioný related to our responses, please contact our Licensing representative directly.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY, ET AL By NORTHEAST NUCLEAR ENERGY COMPANY, Their Age-W. t&. Counsil Senior Vice Pt esident SIATE OF CONNECTICUT )

I ss. Berlin COUNTY OF HARTFORD )

Then personally appeared before me W. G. Counsil, who being duly sworn, did state that he is Senior Vice President of Northeast Nuclear Energy Company, a Licensee herein, that he is authorized to execute and file the foregoing information in the name and on behalf of the Licensees herein and that the statements contained in said information are true and correct to the best of his knowledge and belief.

IAY COmMMIts Expie Rarch at, 193

IAScII Text AnACAUnE I Remaining Responses to Those Questions Contained in Reference I That Were Not Forwarded by Reference 2 ROUND 1 QUESTIONS 220.9 241.17 260.32 410.7 220.11 241.18 260.33 410.8 220,12 241.19 260.34 410.9 220.13 241.20 260.35 410.10 220.14 250.2 260.36 410.11 220.15 250.3 260.37 410.12 220.17 250.4 260.38 410.13 220.2] 250.5 260.39 410.15 220.22 250.6 260.40 410.16 220,23 250G7 260.41 410.17 220.24 260.1 260.42 410.21 220.27 260.2 260.43 410,22 220.28 260,3 260,44 410.24 220.29 260.4 260.45 220.30 410.26 260.5 260.46 410.27 220.34 260.6 260,47 410.28 220.35 260.7 260.48 410.31 220.36 260.8 260,49 430.4 220.37 260,9 260.50 430.7 230.3 260.10 260.51 430.9 230.4 260.11 260.52 430.10 230.5 260.12 260.53 430.11 231.1 260.13 260.54 430.12 231.2 260.14 260.55 430,15 231.3 260.15 260.56 430.16 240.1 260,16 260.57 430.17 240.ti 260,]7 280.8 430,18 240.5. 260.18 280.15 430.19 240.6 260.19 280.39 43D.21 240.7 260.20 280.21 430.22 240.8 260,21 280.23 430.23 241.1 260.22 280.25 430.24 241.3 260.23 280.27 430.26 241.4 260,24 281.3 430.29 241.5 260.25 281.4 430.32 241.7 260.26 281.5 430.35 241.8 260.27 281.7 430.36 241.9 260.28 281.8 430.39 241.10 260.29 281.9 430.40 241.13 260.30 281.10 430.41 241.15 260.31 281.13 1 nf 9

] ASCII Text ATTACIM*T 1 (Iont) 430.42 41.14 430.43 471..5 430.44 471.36 430.45 471.17 430.46 471.1.8 430.47 471.39 430.49 471.20 430.50 471.. 21 430,51. 471.22 430.53 47]3.25 430.54 471.26 430.55 473 .27 451.3. 471.28 451 .2 471.29 460.5 491.1 460.J0 630.4 460.11 630.5 460.15 630.8 460.16 630A9 460.27 630,1.0 471.10 630.13.

47],31 640.]

471.1,2 730.1 475..13

11 t MNPS-3 FSAR NRC Letter: Iay 3, 1983 Question No. Q430.4 (SRP Section 8.2)

There are four transmission lines between Millstone and Hunts Brook Junction that follow a common right-of-way. It is the staff position that no other transmission lines cross over these four lines and that the four lines be physically separate and independent so that no single event such as a tower falling or line breaking will be able to simultaneously affect all circuits in such a way that none of the four circuits can be returned to service in time to prevent fuel design limits or design conditions of the reactor coolant pressure boundary from being exceeded. Line crossovers and physical separation of these four transmission lines has not been described in the FSAR. Pxovide the description and justify areas of noncompliance with the -above staff position.

Response

The four lines emanating from the Millstone Switching Station will be in compliance with the staff position. Attached Figure Q430.4-1, taken from the Connecticut Siting Council Docket No. 25, Application for the Millstone to Manchester 345-kV line, shows the right-of-way cross sections between Millstone and Hunts Brook Junction. The double circuit steel-pole structures between Millstone and 1-95 average 120 feet above ground while the wood pole H-frame structures between Daniels Avenue and Hunts Brook Junction average 85 feet above ground.

In the event of a structure failure between Millstone and Hunts Brook Junction, the worst probable longer-than-momentary outage would be a loss of two circuits; i.e., the two circuits on a common steel pole, or an H-frame structure falling into an adjacent line.

At Hunts Brook Junction, the four lines split (see attached Figure Q430.4-2). The 348 line tUrns west to Southington Substation, the 383 and new 310 lines continue north to Card Street and Manchester Substation respectively, and the 371 line turns east to Montville Substation. One aerial crossover of a line from Millstone exists at this junction (383 crosses 371). But, at worst, only two of the four circuits from the Millstone Switching Station would be removed from service should a structure collapse.

Q430.4-1 9

- .. I I .! .1 . - ... - . . - . ..: . . . 1, I .. . . . . ... . . .. . . . . . %- . . .. . ... NFý i

4 TYPICAL RIGHT-OF-WAY CROSS SECTIONS A. WATERFORD: MILLSTONE SUBSTATION TO DANIELS AVE., 1.5 MILES IN SEGMENT 1 345 KV 345 KV 345 KV 345 KV LOOKING NORTH PROPOSED NEW CIRCUIT (ANDARMS)

TO BE ADDED ON EXISTING STRUCTURE (L OF t OF 85 *" -330'

-- 5 EO85 R __ _ _ _ _ _ _ I IB' EXISTING 50d' RIGHT OF WAY AND CLEARING B. WATERFORD: DANIELS AVE. TO 195 2.6 MILES IN SEGMENTS 1 AND 2 345 KV 345 KV 2S- LOOKING NORTH PROPOSED NEW CIRCUIT TO BE

.mn m% M- v'kVIOIII_ 345 KV 345 KV QRUCT p

U I IIII.

STRUCTURE

\/

_OF L

EXISTING OF

.1 XISTIN NG-.Jý I I -

iI 82.5' - 165' 85 82.5 EXISTING 415' RIGHT OF WAY AND CLEARING C.WATERFORD-MONTVILLE: 195 TO HUNTS BK. JCT., 4.9 MILES IN SEGMENTS 2-4 LOOKING NORTH

- 8 2 .5 ' 8 2 5 .. ,-- - - - 8 5' 8 2. 5 " - -

EXISTING-415' RIGHT OF W.r AND CLEARING FIGURE Q 430.4-1 MILLSTONE-MANCHESTER 345KV LINE MILLSTONE NUCLEAR POWER STATION UNIT 3 FINAL SAFETY ANALYSIS REPORT

I I F

ASCII Text NNPS-3 FSAR NRC Lctter: Play 3, 1983 QLestion No. Q4,10.7 (SRP Section 8.2)

a. it is the staff position that the Mlillst*one grLd stability analysis must show that loss of the largest single supply to the grid does not result in the complete loss Of preferred power, Tbe analysis should consider the loss, through a single evelit, of the largest capacity being supplied to the grid, removal of the largest load from the grid, or loss of the most critical tran;mrission line. The combined tapacity of Millstone Units 1, 2, and 3 is to be supplied to the grid through the common

'liillstone switchyard. The combined capacity of the three units appears to he the largest capacity being supplied to the grid and should be considered in the Iillstone grid stability analysis.

Provide the results of the grid stability analysis sten simultaneous loss of the combined capacity of Units 3, 2, and 3 is considered and justify areas of noncompliance with the above staff position.

b. There are four transmi.ssion circuits that connect the Millstone swItchyard to the grid s;yste. The four circuits are roiuted on two tower lines - two circuits per tower line. Section .1.3 of the FSAR indicates that a simultaneous failure of either of the two tower line.s with only one circuit in se*ervice on the other tower line, may result in instability of Hillstocne generation.

The Applicant, in order to prevent instability, has installed a prote2ttaon scheme to autortatica3l:y reduce generator output at tlillstone unit 3. Describe the protection scheme.

Re sponse; Anslwer to Part A By careful design of the switchya+/--d and protective relays, Ni has practically eliminated the possibility of the simultaneou. loss of three uinits at Millstone. Nevertheless, the loss of the Millstone plant and all four transmission circuits has been simuilated in design studios. The transmission circuits were outage- along with the ssa-ion in order to simulate worst case conditions, and this outage was simulated both Ifith and without a fault.

The stability analysis indicates that the rest of the system will remain in synchronism after the ides of the entire output of the Millstone station. The system was modelled for one Set of operating conditions; hence, it iýs possible that a similar test under heavy transfer conditions within the interconnected system might result in iTstability. However, we are certain that the probability of lo.ing all three units siultmaneously is extrenely small b.cuase of the preventive measures discussed below in this . response. Accordingly, miU believes it is reasonable to count upon onsitt. power sources to supply the necessary station service power requirements in the very reraote event that all three Millstone units should be lost at once Qo4Q.7-1

ASCII Text

-NPS-3 FSAR accompanied by the total Ioass of the transmission supply to the station.

A primary objective in designing the connection of the Millstone NUC.lear Power Station to the 345 kV ti-ansmnission network in Connecticut has been to prevent the loss of the entire stationi output. The reliability criteria of The NIrtheast Power Coordinating Couiil (NPCFC) and the New England Power Pool (NEPOOL) are a fundmntental part of Lids de.sign process. The following are the most severe outages which the. system has been designed to survive in order to minimize the possib]ity of a total plant outage:

a. witb any one of the four INi]stone 345 kV transmission circuits out of service, the plant remains stable for any three-phase fault normally cleared (four cycles) or any one-phase fault normally cleared (four cycles) or any on2-phase fault with delayed clearing (nine cyce.s), These tests are done with maximum generation at Millttone, to simulate worst case conditions.

bh The reliability criteria further require testing, to determine if the loss of two circuits on a comaon strurture can be tolerated, The event which is used to test the loss of the two circuits is a sim.ultaneous line to ground fault on different phases of the two circuits. With all lines in service, the system remains stable for this two circuit di5turbance. It should be recognized that the four circuitsi leaving the millstone s-witchyard are paired on two rows of double circuit structures for on]y a short distance, and, hence the exposure to this outage is sna)J,

c. Also, the simultaneous loss of two Millstone circuits on common structut-es following a previous (nonsimuftaneous) outage of either of the other Millstone circuits (or any other critical element) must not result in instability, All of the critical outages of this type effectively result in the loss of three of the four Millstone circuits and leave the Millstone station weakly tied to the transmission grid. To prevent instability for these extremely severe (and hiqhly improbable) disturbances, it is necessary to reduce output after the jnitial line outage and before the loss of the two circuits on co1mmon structures takes place and/or install an automatic generation rejection schemeb Because of the significant economic penalties inivoived, the reduction of generation after" the initial line outage is considered a highly undesirable solution to the potenti3al stability problems identified ill item (c) above and Should be avoided to the extent pussjble.

Therefore, a post disturbance generation curtailment scheme has been provided. This system continuously monitors the individual state of six critical system components together with the generation output at the Millstone complex. Should the system condition arise where

1) any one of the six critics1 1/2Unes or elements is unavailable,

2) the genoration at millstone is above a predetericined 14 level, and

3) two specific transmission circuits are forced out, then generation will automatically be curtailed at Millstone. Stability studies 9430 °7-2

ASCII Text MNPS-3 PSAR indicate that durhig maximrlm output conditions (2640) Nw), NillstDne.

Units I and 3 can be successfully tripped and system stability maintained lecnv'ng Millstone Unit 2 in synchronism with the transmission network. The tripping of these units results in a generation reduction of up to approximately 1810 HW with $70 HKW rema~ning synchronized. This generation reduction scheme is descri*bd in the answer to Part 1 of this question. The scheme is called a Severn Line Outage Detection (SLODý.

Additional testing was carried out for Possible but Improbable (PBI) events which are specified in the NPCC and NEPOOL reliability criteria, The one PBI event which could have a serious effect at 1.fiflstone is a three-phase fault followed by delayed clearing due to a three-phase stuck circuit breaker. This results in the Millstone units losing synchronissm, This stability problem has been eliminated by designing the protective relay schemes snd circuit breaker insteJlations so that et most, one po3e will fall to Clear. The breakers which are designed to meet this criteria are classified as having independent pole tripping.

Il.U insures independent pnle tripping by installing breakers with mechanically Sndependent poIes and two separate methods of tripping the circuit breaker. These installation- include two sets of relays and trip coils. There are two sets of current and potential transformers, the wiring for the 1-elay packages are installed in separate duct banks, the relay packages are physically separated in the control house and two separate dc supplies are provided, The 345 kV switchyard at Millstone is designed so that the loss of more than one transmission circuit due to a failure of a breaker to trip requires at least two circuit breakers to simultaneously fail to operate. The failure of even one circuit breaker is very unusual.

At least three circuit breakers would have to Lail before three transmission lines would be lost due to malfunctions in the switchyard. At that point, the generation rejection scheme would operate to keep one unit in service, In order to. lose the entire stotion, at least four circuit breakers must fail, To summarize: The Company is taking extensive precautions to prevent the sudden loss of the three generating units at Millstone Station and the simultaneous loss of offsite power, We believe these m.easures make the probability of such an occurrence extremely small.

Answer to Part B The operation of the M1il0lstone generation rejection fctieme is based on the outage of combinations of certain transmission circuit elements. The scheme has been narue Severe Line Outogt Detector (SLOD). See reference to 5LOD in the arswer to Part A of this question.

This system will continuously monitor the individual status of six critical transmission elements in the area of the I1llstone Station together with the generatlon output of the Millstohe complex.

90 0.7-3

ASCII Text HNP5-3 FSAR Generation wil) be curtailed automatically if a system condition arises where any of Lentcombinations of the six elements are outaged, ana generation ai NI-listone is above 1200 NW.

To monitor the statu*s of the 345 kV system. SLfl equipment .has been required at the Millstone and at Montville switchyards. In addition, it will be necessary to install high speed backup relay protection with a permissive overreaching audio tone scheme on both endg of the I.li-.stone to Manchester and the Millstone to southington lines.

At Killstone, three logic packages will be provided, The operation of any two logic units will provide a tripping ouitput, The current detecting devices of eacci logic package will sense the available state of each of the four transmission circuits emanating from the Millstone switchyard. Signals indicating the availability state of two remote components (the! Montville 345 1W tie breaker, and the Montville - Haddanm Neck Line) will be transmitted to Nillstone. The megawatt output from each of the Millstone units will be mea*ured and summed to provide an in'dication of the toal megawRtt output of the Millstone units. Should the comparative logic in the SLOD package indicate that. any onE of the combinations of transmission outages listed below exist, ani the generation level at the Millstone Station is above 30DO 1W, then Millstone Units 1 and 3 will be curtailed imTLediately, The combinations of unavailable components which must be monitored o0er J. Necessary to meet NPCC and NEPOOL criteria.

Millstonie Manchester, Mijlstone -Card and Millstone -

montville Millstone - Southington, Millstone - card and Millstone -

Montville F1i lls tone - Montville, Millstone - Manchester and Millstone - Southington Millstone - Card, Millstone - Nanchester and Millstone -

Sou th ington Montville - Haddam Neck, Millstone - Manchester and Millstone - Southington Montville 345 kV tie breaker, Millstone - Manchester and Millstone - Southington

2. Also included to simplify the SLOt package logic but not required to meet NPCC and NEIODL criteria are:

Millstone - Southington, Millstone. - Card and Moritville -

Haddam Neck 9400.7-4

ASCII Text I*JP5-3 PSAR M1illstone - Manchester, Millstone Card and Montville -

Haddam Neck Millstone - Southington, Millstone - Card and Montville 345 kV tie breaker Millstone - Manchester, Millstone - Card and Montville 345 kV tie breaker As mpntioned above, signals indicating the availability status of the two remDte components at Montville -are required at -illstone, To monitDr the status of the 345 1W circuit breaker at Montville. aind the atvsiabillity of the' Hontville-Haddam Neck line, three logic units will be required at Montville. The three independent logic packages will supply information to the Nillstone logic packages via an ind-p-itdent transfer trip tone transmitter.

Since the operation of the generation rejection scheme should take place in less than 12 cycles to maintain stability, all transmission line faults must he cleared at high speed. This will require the aadition of high. speed backup protection using permissive ovorreaching audio, tone equipment on the H{illstone-Manch ester line and the Hillstone-Southington line at both terminals.

With the Generation Rejection scheme in service, it will be permissible to oporate with high Millstone Station output when any one of six critical transmission elements is out of service.

Q430. 7-5

Excerpts from NRC Letter Dated February 24, 1984 Draft SER for Millstone Nuclear Power Station, Unit 3

ASCII Text -

UNITED STA"IE NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C, MW~t Docket No.t 50-423 Mr. William G. CounmIl $ýNiOf V0E. pRESIDEMN Senior Vice President rig f..

NuoLear Fnpi neering and Operations tl:3IOST LnetriflS Northeast N-clear Energy Company P, 0. Box ?70 Hartford, Connecticut 05142-0270

Dear Mr,

Counsil:

Subject:

Draft SER for Millstone Nuclear Power Station, Unit 3 Rofer-ence: (2) B. 0. Youngblood to W. 6, Counsil, Draft SER for Millstone Nuclear Power Station, Unit 3 dated December 30, 1983 Enclosedl is a copy of sections of the DSER not transmitted to you In Reference 3. A list of these sections is shown in the attachnmnt.

Please review this information and issue a writtmn response to the open iteom prior to May 36, 1964 in order to accomodate the schedule for issuance of the final SER on July 16, 1984. The open items are described in sufficient detail in the text of the DSER sections.

A copy of this inforrmtion has been placed in the Commissions Public Document Room end in the. local public docune.nt room in Waterford, Connecticut.

For further information or clarificaticwi please contact the Licensing Pr*j*ct Managor, Elizabeth L. betolittle (301-4911).

Sincfer y, o4 J. he .nb Lic(. nj Br[a.ch eNo. I Divisi n of Licen)slng Attstch.Bnt:

As stated cc: See next page

Raster Image 8.2.2 Compliance With General Design Criterion (GDC) 17 The applicant has met (except as noted) the requirements of GDC 17, "Electric Power Systems," with respect to the offsite power system's (a) capacity and capability to permit functioning of structures, systems, and components important to safety, (b) provisions to minimize the probability of losing electric power from any of the remaining supplies as a result of, or coincident with the loss of power generated by the nuclear power unit or loss of power from the onsite electric power supplies, (c) physical independence of circuits, and (d) availability of circuits.

The following items address the problem areas revealed during the staff review and resolutions or status concerning them.

8.2.2.1 Physical' Separation of Offsite Circuits Within a Common Right-of-Way As described in Section 8.2.1 of the FSAR, there are four transmission lines between Millstone and Hunts Brook Junction that follow a common right-of-way. It is the staff position that no other transmission lines cross over these four lines and that the four lines be physically separate and independent so that no single event such as a tower falling or line breaking will be able to simultaneously affect all circuits in such a way that none of the four circuits can be returned to service in such time to prevent fuel design. limits or design conditions of the reactor coolant pressure boundary from being exceeded. Line cross overs and physical separation of these four transmission lines were not described in the FSAR.

- - . ? . : -T ...... ....... 3 - X I 7 :* .- * *: . * * * . ..-I - * ... * ?~ q * .1* - I- - -*

Raster Image I The applicant, by amendment 3 to the FSAR, documented that their design is in compliance with the above staff position and provided a description of their design. Based on their description, the staff concludes that the transmission lines are physically separate and independent in accordance with the above stated staff position, meet the requirements of GDC 17, and is, therefore, acceptable.

8.2.2.2 Physical Separation of Offsite Circuits Between Switchyard and Class 1E System As implied by Section 8.1.2 of the FSAR, the Millstone design provides two immediate access offsite circuits between the switchyard and the 4.16 kv Class 1E busses. It is the staff position that these two circuits be physically separate and independent such that no single event can simultaneously affect both circuits in such a way that neither can be returned to service in time to prevent fuel design limits or design conditions of the reactor coolant pressure boundary from being exceeded. The physical separation and independence of these two circuits has not been described or analyzed in the FSAR.

The applicant by amendment 3 to the FSAR presented additional information in regard to these circuits. However, based on the additional information the staff was unable to conclude that the design meets GDC 17. This item will continue to be pursued with the applicant and the results of the staff review will be reported in a supplement to this report.

Raster Image

-.7-as a result of or coincident with loss of power generated by the nuclear power unit, meets the requirements of GDC 17, and is, therefore, acceptable.

8.2.2.5 Generation Rejection Scheme There are four transmission circuits that connect the Millstone switchyard to the grid system. The four circuits are routed on two tower lines - two circuits per tower line. Section 8.1.3 of the FSAR indicates that a simultaneous failure of either of the two tower lines with only one circuit in service on the other tower line, may result in instability of Millstone generation. The applicant, in order to prevent instability, has installed a protection scheme to automatically reduce generator output at Millstone Unit 3.

The applicant by amendment 3 to the FSAR, provided a description of the protection scheme. However, in order to conclude that the design meets GDC 17 and 18 for the proposed mode of operation (one of four offsite transmission lines out of service), the staff requires additional description of surveillance, operability requirements, and analysis demonstrating compliance with the requirements of GDC 17 and 18 be documented in the FSAR. This item will be pursued with the applicant the results of the staff review will be reported in a supplement to this report.

Excerpts from Northeast Utilities Letter Dated June 12, 1984 Millstone Nuclear Power Station, Unit No. 3 SummarV/Submittal of Responses to PSB Electrical Draft SER Items

ASCT ext E u NORTHEAST UTILITISS ITCý-AflC-%Jntfl M4YWI ,,r F..,

f1BtG G

,,oc.q',, UTeltk4.ErAc.ef4 Ono.ral Offices vsuIden *,*ret. lldii.,connoclivut P.O. BOX 270 HARTFORD, CONNECTICUT 08141-027; 1223,) 6B6-6911 3une 12, 19S4 Docket No. 50-423 1311223 Director of Nuclear Reactor Regulation Atun: Mr. B. 3I Youngblood, Chief Licensing Branch No, L Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20W55 Ref erences: (1) B. I. Youngblood to V. G. Counsil, Additional Draft SER Sections for Millstone Nuclear Power Station, Unit No. 3, dated February 24, 1984.

Gentlemen; Millslone Nuclear Power Station, Unit No. 3 SUL*nary/Submitta. of Responses to PSB Electrical Draft SER Itenis Reference (1) included the PSB Electrical Draft SER write-up which identified several open items with regard to information provided within our OL applicatiora. We have subsequently held two meetings, May 14, 1984 and May 31, I984, to discuss and resolve these open items. Attachment 1lprovides a summary status of all items originally open, The responses, Attachment 2, rellects those discussed during the mieetings except where the summary status indicates a response was subsequently revised, If you have any questions, please contact our Licensing representative directly.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY et, al.

BY NORTHEAST NUCLEAR ENERGY COMPANY Their Agent W. C.Counsill SenJor Vice President By: C. F. Sears Vice President Nuclear and Environmental Engineeri rpg thi h akettmrnq

ASCII Textj

1. fY.;'*,. -

STATE OP CONNECTICUT

) ss. Berlin COUNTY OF HARTFORD Then pers o0nally appeared before me C. F. Sears, who being duly sworn, that hT is Vice Preshlent of Northeast Nuclear Energy Company, did state herein, that he is aulhorized to execute and file the foregoing an Applicant name and on behalf of the Applicants herein and that the information in the statements contained iri said information are true and correct to the best of his knowledge and belief.

I AX Commission Expires Mlarch 3.1, IDS4 I ~

I,'

2

ASCII TextI IL Attachment 1 Status ol PSB Electrical SER Items Sectio&Question Stat us Remrarks/R.equired Action 8.2.J.1 Closed Attached.

8.2.2.11/430.4 Confirmatory Response to Q43D.' will be incorporated into a future FSAR Amendment per NRC reviewer's request. Once done this item wil) be considered chmsed. Because this item Was originally considered closed and 1he.

response to Q430.4 previously submitted, no further documentation is attached.

8.2.2.214 30.5 Closed Attached.

Closed Attached.

8.2.2.51430. 7b Confirmatory Attached. Response to Q430T7b will be incorporated into a future FSAR Amendment per NRC reviewer's request. Once done this item will be considered closed.

8.2.2.6 Closed Attached.

8.2.3.1 Closed Attached.

S.3.1,2/430.3 Cluse~d Attached.

8.3.1.3/430.9 Confirmatory Attached. Response to Q430.9 will be incorporated into a future FSAR Amendment per NRC reviewer's request. Once done this item will be considered closed.

9.3.1.4/430.10 Closed Attached.

8.3.1.51430.11 Confirmatory Attached. Once results of station electric system voltage testing is complete or the predicting analysisj this ilem will be considered closed.

&3.3.1,6/430.12 Closed Attached.

8.3.1-71430.13 Closed Attached.

8.3.1.8/430.14 Closed Attached.

1.......................

ASCII Text Millstone Nuclear Power Station, Unit No. 3 Open Items Power Systems Branch (Electrical)

PSB06 (196) 430.7 GENERATION REJECTION SCiHEME (8.2.2.3)

There are four lrantrmission circuits that connect the Millstone switchyard grid system. The four circuits are routed on two tower lines - two to the circuits per tower line. Section S.1.3 of the FSAR indicates that a ,imultaneous either of the two tower lines with only one circuit in service on the failure of other tower line, may result in instability of Millstone generation. The applicant, prevent instability, has installed a rejection scheme to automatically in orler to generator output at Millstone Unit 3. reduce The applicent, by amendment 3 to the FSAR, provided a description of the.

rejection scheme. However, in order to conclude that the design meets and 1S for the proposed mode of operation Cone of four offsite transmission GI5C 17 ovt of service), the staff requires additional description of lines surveillance, operability requirements, and analysis demonstrating compliance requirements of GDC 17 and 18 be documented in the FSAR, This with the item will be pursued with the applicant the results of the staff review will be reported supplemeni to this report. in a Reeponte e Refer to the revised response 'to question no. 430.7.

ulZl7V fsr* l504/0$/84 MNPS-3 F$AR 245 NRC Letter- May 3, 1983 1.8 Question No. Q00.7 (SRP Section 6.2) 1.11

a. it is the staff position that the f11ilstone analysis must show that loss of thu largest grid stability 1.13 single supply to the 1.14 grid does not result in the complete loss of preferred power.

The analysis should consider the 2oss, through a single nuent, of 1.15 the largest capacity being supplied to the grid, removal of largest load the L,16 from the grid, or loss of the most critical transmission line. The combined capacity of Millstone Units 1, 2, and 3 15 to be supplied to the grid 1,17 through the common

.illstone switchyard. The combined chpacity of the three appears to be thei-rigest capacity being supplied 1,19 iunits to the grid and should be considered in the Hillstone grid stability analysis. 1.20 Provide the results of the grid stability analysis when 1.22 simultaneous loss of the combineS capacity of Units 1, 2, and 3 1.22 is considered and Justify areas of nonaompliance with the above staff position, b, There are four transmission circuits that connect the Nillstone 3.23 switchyard to the grId system. The four circuits are touted on 1.24 two tower lines - two circuits per tower line.

Section $.1,3 of 3,25 the FSAR indicates that a simultaneous faflure of either of the two tower lines with only one circuit in service on the other 1.26 tower line, may result-in instability of Millstone The Applicant, generation.

in order to prevent Instability. has installed protection schene to automatically reduce a 1.27 gener*tor output at 1.28 Millstone Utnit 3. Describe the protection scheme, 1.29 Response :

1 Answer to Part A 1.33 By careful design of the switchyard and protective relays, NU has 1.34 practically eliminated the possibility of the simultaneous loss of 1.36 three units at Millstone. Nevertheless, the loss of the MHiljtone plant and all four transmission circuits hbs 1.37 been simulated in design studies. The transmission circuits were outaged along with the 1.38 station in order to simulate worst case conditions, Was simulated both with and without a fault. and this outsge 1.3t The stability analysis indicates that? the rest of the system will 1.40 remain in synchronism after the loss of the entire output of the 1.41 Millstone station. The system Was modelled for one set of operating 1.42 conditions; Fence, it is possible that a similar test under heavy transfer conditions within the interconnected system might result in 1.43 instability. However, we are certain that the probability all three units simuItaneously is extremely of losing 1.44 preventive measures discussed below in this response. small becuase of the Accordingly, 1.46 KU believes it is reasonable to countupon onsite power sources supply the nelcassary station service power requirements to in the very 1.47 remote event that all three Millstone units should be lost at once Revision 1 Q430, 7-1 may 1984

.1 ASCII Text Vail MPS-3d FSAR 245 accompanied by the total loss of the transynission supply station. to the 1.48 a primary objective in dcesiuinq Nuclear lower Statioh to the connection of the Nillstone the 345 kV transmission 1.49 Connecticut his been to prevent network in 1.50 output. The reliability criteria of The the loss of the entire rtation Northeast Power Coordinating Council (NFPCC) and the Rev England Power 1,51 fundamental part of this design Pool (NEPOOL) are a 1.52 process. The following are the most sEvere outAges which the system 1,53 has been designe4 to survive to minimize the possiblIty of a total plant outage; in order 1.54

a. With any one of the four Millstone 345 kV transmission circuits 1.56 out of service, the plant remains fault normally cleared (four cycles) stable for any three-phase 1.57 normally cleared (four cycles) or any one-phase fault delayed clearing (nine cycles). or any one-phase fault with 1.58 maximu These tests are done with *1.9 generation at Millstone to conditions. simulate worst case -

b. The reliability criteria further require testing to determine the loss of two cirouits on a if 1.60 common structure can be tolerete4, The event which is used to test 2.1 the loss of the two circuits simultaneous line to ground fault is a 2.2 on different phases of the two circuits. With all lives in service, the 2.3 for this two circuit disturbance. system remains stable 2.4 It should be recognized that the tour tircuits leaving the 2.5 millstone switchyard are paired two rows of double circuit structures for only a on and, hence the exposure to this short distance, 2.6 outage is small.

c. Also, the simultaneous loss of two Milstone structures following a previous circuits on to=n=r 2.7 either (nonsimultaneoua> outage of 2.8 of the other Millstone circuits (or element) must not result in instability. any other critical outages of this type effectively All of the critical 2.9 result in the loss of three of the four Millstone circuits weakly tied to the transmissionand leave the Millstgne station grid, To prevent instability 2.10 these extremely severe (and highly for 2.11 is necussary to reduce output after improbable) disturbances, it the initial line outage and before the loss of the twoo tircuits ZIIZ place and/or install an autbmatic on common structures takes generation rejection scheme. 2.13 Because of the significanrt etonomic of generation after the initial penalties involved, the reduction line outage ts 2.15 undesirable solution aonsidered a highly 2.16 to the potential stability in item (c) above and should be avoidetd to the problems Identified Therefore, a post disturbance generation extaent possible.

provided. This system continuously curtailment stheme has been 2.1? 2.10 monitors the individual state of six Critical System components 2.19 together with the generation the Millstone complex. Should the system condition output at 2,20

1) any one of the sie arise where 2.21 critical lines or elements is

2) the generation at Millstone unavailable, is above a predetermined MW level,

3) two specific transmission and 2.22 circuits are forced out, then will automatically be curtailed generation 2.23 at Nill2stne Stability studies 2-24 Revision 1 C430.7-2 Hay 1984

ASCII Text E

.SAR indicate that during mAximum output conditions Units I and 3 can be successfully tripped (2640) MI), Millstone maintained leaving Millstone and system stability 2.25 transmission network. The tripping of Unit Z In synobronism with the generation reduction of up to approximately these units results in a 2.27 remaining synchronized. 101O XW with 870 MR*

This generation reduction scheme described in the answer to Part D of this question. is 2.29 called a Severe Line Outage Detection The scheme is 240 (SLOD],

Additional testing was carried out for Vossible but Improbable (PBI) events which are specified in 2.31 the NPCC and NFPOOL reliability criteria, The one P81 event which could have 2.32 Hillstane is a three-phase fault a serious effect at 2.33 followed by delayed clearing due a three-phase stuck circuit breaker. to 2.34 This results in the Hilsotone units losing synchronism, This stability 2.35 by designing the protective relay problem has been eliminated Z.36 installations so that at rost, one schemes and circuit "breaher pole will fail to clear. The breakers which are designed to 2.38 meet this criteria are classified having indepe-dent pole tripping. as WI insures independent pole tripping mechanically independent poles and by ihstslling breakers with 2.39 two separate methods of tripping the circuit breaker. These installations include two sets 2.40 and trip coils. of relays 2.41 There are two sets of current transformers, and potential 2.42 the wiring for the relay packages separate duct banks, the relay packages are installed in are physically separated in 2.43 the control house and two separate dc supplies are provided.

The 345 kV switchyard at Millstone more then one transmission circuit due isto designed so that the loss of 2.44 trip requires at least two circuit bieakeraa failure of a breaker to n.45 operate. The failure of even one circuit to simultaneously fmil to At least three circuit breakers breaker 1$ very unusual. 2.46 would have to fail before three transmission lines *would be lost 2.47 svitchyard. due to ualfunctkons in the At that point, the generation rejertion sceme would 2.48 operate to keep one 4nit in service, 2.49 In station, at least four circuit breakers order to lose the entire 2.50 must fail.

To sumnarize: The Company is taking extensive precautions to prevent the sudden loss of the three generating 2.51 units at Millstone Station and the SiJmultaneous loss of 2.S2 offsite power. We believe these meaeures make the probability of such 2.53 an occurrence extremely small..

Answer to Part 1 2.55 The operation of the milistone generation rejection on the outage of aomtinations schema is based 2.56 of certain transmission circuit 2.D8 elements 4 The scheme has been name Severe Lint Outage Detector (SLOD). See reference to SLOD in 2.59 the answer to Part A of this question. 2.60 This system will continuously mcnitor the individual status of critical transmission elements in six 3.1 the area of the Millstone Station together with the generation 3.2 output of the MIllstone complex.

Revision 1I4073 Q430.7-3 ~y15 May 1954

ASCII Text u sr 04/0S/84 lPSt-3 FSAR 245 Generatign will be curtailed automatically if a system condition arises where any of teh combinations 3.3 aiud generetion At Millstone of the six elements are outaged, is above 1200

. 3.4 To monitor the status of the 345 kW system, SLOD required at thlc illstone equipment has been 3.5 and at Montville switchyards.

it will be necessary Tz addition, L,7 to install high speed backup with a permissive overreaching relay protection audio tone scheme an both Millstone to Manchester and the Millstone to Southingtob ends of the 3.8 litnes.

At Millstone, three logic packages will ot any two logic units be prwvided. The operation will provide a tripping 3.10 detectiny devices of output. The current 3.11 each logic package will state of each of the four sense the tranAmission circuit& emanating available Millstone switchyard. from the 3,12 two remote components (theSignals indicating the availability Montville 145 kV tie breaker, state of 3.13 11ontvills - Haddam Neck Line) and the megawatt output from each of will be transmitted to Millstone. The summed to provide an itdication the Millstone units will be measured and 3_1S Millstone units. Should the of the toal megawatt output of comparative logic in the SLOD the 3.16 indicate that any one of the conibnations package 3.17 listed below exist, and the of transmission generation level at the Nillstone outages is above 1200 XW, then Millastone Units I Station 3.18 imiedciate3y. and 3 will b4 curtailed 3.19 The combinations of univailable components which must he monitored 3.20 aret

1. Necessary to meet NCC and NEPOOL criteria. 3.22 Hillstone - Manchester, Millstone -Card and Millstone -

Hontvi Ile 3.24 Millstone - Southington, Kontville Millstone - Card anM Millstone - 3.25 Millstone - .fotville, Millstone Millstone - Manchester and

- southiigton 3.26 Millstone - Card, Millstone -

Southington Hanchester and Millstone - 3.27 Hobtville - Haddam feck, Millstone - ganchester Millstone - Southington and 3.28 Kontvillo 345 kV tie breaker.

Millstone Millstone - Manchester and 3.29

- Southington

2. Also inclnded to sImplify the SLOC package logic but not required to meet IJPCC and NEPO0I, criteria are: 3.31 killatoag - Southington, Millstone -

Haddnm Neck Card anid Iontville - 3.33 Revision 1I40 7 Q430.74' ~y18 Ray 1984

S- .....

ASCI17T~e xt:

Killatone - Nanchester, Jllietone - C7rd and 1ontvlle, -

flaida~m flecl Millstone - Southingtoh, HUlStone - Card and Montville 345 RV tie breaawr Millstone A Hancbchter 1 millstone - Card and Eitwoile 345 XV tie breaker' As mentioned abovej aftnals indicating thoe availability remote components at Hozxtville are required status of the two at Millstone, To monitor the status of the 345 RV circuit breaker at Montville, and tke avsilabilfty of the JIoatville-Iaddam Nlck lie, three logic units viia be re4uired at Montvjlle, The three Independent logic packages the Nillstone logic packages via an independent will supply Information to transfer tone transmitter.

Sinee the operation of the generation rejection schetýa should take place in less than 12 cycles to maintain stability, all must be cleared at high speed. WA will require transmission line faults speed backup protection using permissive overreachigs the addition of high on the Nillstone-Manchester line and the Hfllstone-Soutbhngton au4io tonie eqolpment terinanls, line At bPtb With the Generation Rejection scheme it servie,,

operate sith high Millstone Station ouCput it will be permiessible to trrnsmission elements Le out of servioe Umea any one of six crittcal 1 As a member of REPOOL sod the IWCC, the Applicant will be required to comply with either of the fllowing operability requirements with one line out of service:

1) Have SLOD fully operational, or

2) Igduce load to a total station output of 1200 NW within 4 hiurs, These Instructions will be documented as part of the Connecttict Valley ElectrIt L'xchange (CONVJX) operating i*ntructions fr' the Millstone svJNtchyard and Vill be regulated by COW=. To facilitate regulation. CONVEX 3s aware tion of all litres and the statues f of the condi-the SLOD at COWVEX (CO1VOI Is an operatirg division scheme via an annunciator located of NEPOOL),

The operability requirements specified above doulle ciravit 1l.e with a third line a4stures thAt, upon loss of a out of of 1200 NW, o*fatle power will be available service and generation Sn excess systpe stability mInimizes the probability for safe shucdown* aintai-nin of coincident loss of both offelte supplies. This As consistent with the requirements of MDC 17, GDC 17 also requires that the probabIlity of Uosing an offelta supply coinecdent with loss of the noclear power unit be =untiaed, lecaupe Of the necessity for 5,D0 to Ocmplete its functIom victim 12 cycles, SW)D trips Millstone Utnit 3 by tripping the switchyard breakers musteat of the generator breaker (this elitanates the extra tine required for relay mnd comnication channel opera-tion in a tTansfer trip sthene). Under these ecnditinws, atation auxiliary loads high speed transfer to the reserve statiot service transformers, and the normal station service tTansformfr (Nbich is tlipped when SOD trips Unit

3) can be re-4nergited by closing a saitohyard breaker. Therefore, both offsite supplies tl3l be available to assure safe ahutdoM of the unit in accordante With *D 17, q430.7- S

[ASCII T;ext The $LOD scheme was nznufacture4 to be a reliable unit.

Zob line. is mon$torad by a logic package whieh utilipes r~mndant chenaes (2-out-of-3 logic) in ease of a failure of one channel. Each lovic package in. t*h event of a channel failur- and trigger&a MOD troulle alurms Millstone Unit I control room and at COMEX, Also, a fpile4 channel alarm in the arming of the logic. indicatfrg the monitored system causes component to be out of service. Additlona&2ly every eýiht (8) hours, the SLOD scheje automat-4tiA,.4t.4z .,. r~r~t'......... .. n) In the event of failure, a SLOD trouble alarm Is actuated In the Milstone Unit I control ac CObNVfl. Upol receivins the SLOD trouble alarm, the room and operator will Cispatch A person to the Millstone switt¢hyard control house to evaluate the condition of the system. In the event that one tIne the SLOD) system is not operatins in one hour. VO4V is vi11out of service *ld reduce StatiLon output to 1200 I4W ar below during the newt three (3) hours. The continual ctannel surveflfine and perlodia (8-hours) functional tests that are run automaticallyy, esure conformnce to the Coseval )esign C(riteria 10.

cuh r-Lit I'1 E/fr(tr~rify.

kC 1£~. &+)A £ 4 eaY,*(4dfl a-io..h 4

Q430.7- 6

.7= T ASCII Text Millstone NUclear Power Stationp Unit No. 3 Open Items Power Systems Branch (Electrical)

PSB07 (I97) DESCRIPTION AND ANALYSIS DEMONSTRAT[NG COMPLIANCE WITH GflG 17 ( V.. 0 a- C)

A system description and analysis sufIcient to detnristrate compliance with GDC 17 hks not been presented tq Section 3.2 of the FSAR in accordance with the guidelines of Regulatory Guide 1.70. This item will be pursued with the applicant and the results will be reported in a supplement to this report.

Response

Refer to revised FSAR section +2,4?t

I -;.~i~ - -

ASCII Text I uli1l9l2sraSep 04/10/84 245 Us-S TSAR along with breaker failure relaying to provide redundant protective relaying for the switchyard.

Two 125V dc batteries are locatOd in the switchyard control 2.24 and relay enclosure for switchyard relaying and control.

Each battery has its own charger and dc distribution panel. 2,25 The redundant batteries and protective relaying systems are 2.26 physically And electrically separate. The essential ac 2.27 stetion service for the power circuit breaker pneumatic supply units and the other switchyard requirements is 2.28 supplied from one of two separate sourcet.

2. The 345-IW system is'protected from lightning and switching 2.31 surges by overhbea electrostatic shield wires, surge arrestors on main buses, and rod gaps on the disconnect 2.32 switches.

3. Primary and backup relaying is provided for each circuit 2.33 along with circuit breaker failure backup-protection. These 2.34 provisions permit the followings

a. A,y circuit can be switched under normal or fault 2.36 conditions without affecting another circuit.

b. Any single circuit breaker can be isolated for 2.a7 maintenance without interrupting power or protection of any circuit.

c. Short circuits on any section of a bus are isolated 2.38 without. interrupting service to any element other than those connected to the faulty bus section, 2.39

d. The failure of any circuit breaker to trip initiates 2.40 the automatic tripping of the adjapcnt breaker or breakers and thus may result in the loss of a line or 2.41 generator for this contingency condition r however, power can be restored to the good element ir less than 2.4Z i hour by manually isolating the fault with appropriate disconnect switches, 2.43 Comp.ete battery failure is considered highly unlikely since two 2.45 independent 125V dc battery systems are provided. Failure of a 2.46

-single battery system results only in a momentary loss of one set of protective relays until the DC is manually transferred to the other 2.4?

battery. Therefore, no single failure could negate the effectiveness 2.48 of the relaying to clear a fault.

The H4 j2aoe design provides two immediate access offsite circuits 2.49 between tMe switchyard and the 4.16 XV Class I buss;. Within the 2.51 1.2A6 switchyard, the tie line terminations are separated electrically by two circuit breakers so that a fault on one offtite supply circuit 2.52 along with a breaker. failure will not cause the second offuite supply to be lost. The tie lines are supported on 4ad end tower and the 2.53 second tie line circuit tsrminatinu on the'reserve station service 2.54 mendment a 8,2-3 mIayI'M

ASCIJ Text Wi2ll912sra~vp 04/10/84 245 W*J-3 FSAR transformer dead and tover. The orimal. j*6eucW station service 2.55 I transformers and the reserve station service transformers are located on opposite sides of the unit. The connection from the normal 2.57 station service trarsformers And from the reserve station service transformers to the 4.16 Kv Class 1E buses is via physically separate 2.58 and electritally indepeadent under ground duct lines. .Sl" 2.59 Pig ure 1.2-1 shous the tie line routes from the switehyard to the maitnornal and to the reserve station service transformers. qjr 3.1 Figure 1.2-i shows the physical sepa'rtion between the nonMal and the reserve station service transformers4 Figure 8,3-7 Sheets I and 2 3.2 show tha embedded conduit duct lines as they enter the redudont mroom in the control building. 3.3 The cmtrol power for these bus ia from different do panels and 3.4 batteries. The breakers in the Claps Ir buses (34C and 34D) are 3.5 indepeondetly protected with separaterelaying.

The of Esite source that will normlLy be availble imediately on a 3.6 unit trip is from the main and normal station aervice transformers.

This source is not lost on a unit trip because the generator breaker effects the disconneetion of the unit from the grid leaving the main 3.10 and normal station service transformers backfed from the switchyard.

The second source of offsite power is available through a Rast transfer to the reserve stAtion service transformers, 3.11 Testing the normal immediate access circuit during plant operation would be inappropriate as this would disconnect the unit from the grid. The 3.13 fast trAnsfer feature of the alternate imiidiate access offsite circuits will not be tested during plant power operation since it 3.14 risks unevessary plant trips. wmnediate access is not required of a second offsite source, and for the Millstone 3 design, if the fast I..

transfer is not successful the reserve station service transformers 3.15 can be connected to the emergency buses by manual control switch 3.17 operation in an acceptable time, The automatic transfer of emergency 4.16 M' bumses 34C (Train A) and 3.18 34D (TrAin 8) from either the normal to the reserve station service 3.19 transformer or the normal or reserve station transformer to the emergency generators will be tested prior to initial startup and 3.20 during refueling shutdowns of the unit to prove the operability of 3.R1 the system. Therefore, appropriate testing and testability of the 3.22 transfer of power upon loss of normal power satisfies the requirements of General Design Criterion 18, Inspection and Testing 3.23 of Electric Power Systems. - --

Physical separation of the Offoite power sources, switchyard 3.24 protection, redundancy, and transmission system design based on load 3.25 flow and stability analyses minimize the possibility of simultaneous failure of power sources (normal station service supply, legerve 3.26 station service supply and standby ac emergency generators) in compliance with General Design Criterion No. 17 "Electric Ppwer 3.27 /s The 345 Wc transmiasion system supplying offs1it power to Hillstane 3.28 is normally operated at 357 kV at Millstone. This system voltage is 3.29 Amendment 8 8.2-4 May 1984

k, FASCII Text] I:.

Millstone Nuclear Power Station, Unit No. 3 Open Iters Power Systems Branch (Elecwical)

PSFRogS %i) DESCRIPTION AND ANALYSIS DEMONSTRATING COMPLIANCE W1TIH GDC 1s ( .'3.;)

A system description antd analysIs sufficient to demonstrate compliance G3C 18 has not been presented in S5etion 9.2 of the PSAR in accordance with the guidelines of Regulatory Guide 1.70. This item will ble pursued with with the applicant and the results will be reported in a supplement to this report.

.e.sp*on se; Refer to revised FSAR section 8.2.2.

I.

.. ,. ' I....

ASCI Text u1217S12sraBcp 04*10/84 24 S NNP-3 TA transformer dead end tower. The normal teserve station service 2.55 transformers and the reserve station service transformers are located on opposite sides of the unit. The connection from the normal 2.57 station servicc trmnsformetrs and from the reserve station -service transformers to the 4.16 XV Class 1E buses is via physically separate 2.58 aan electrically independent Vnder ground duct lines. cIP 259 U3A.$

Figure 1.2-1 shows the tie line routes from the szitchyard to the main/normal and to the reserve station serviac transformers. 3.1 PX 7 Figtre 1.2-2 shows the physical separation between the normal and the reserve station service transformers. Pigure 8.3-7 Sheets I and 2 3.2 show the embedded cordult duct lines as they enter the redundatt

-tahpa" rooms in the control building. 3.3 The oontrol power for these bus4is from different dc panels and 3.4 batterles. The breakers in the Class IE buses (34C and 34D) are 3.5 independently protectad with separate relaying.

The offsite source that will normally be available immediately on a 3.6 unit trij is from the main and normal Station service transformers. 3,7 This source is not lost on a Unit trip because the generator breaker 3.8 effects the disconnection of the unit from the grid leaving the main, 3.9 ano normal station service transformers baukfed from the switchyard.

The second source of offsite power in available through a -fast a.10 transfer to the reserve station service transfo1rmers. Testing the 3.11 normal immediate access circuit during plant operation wruld be inappropriate as this would disconnect the unit from the grid. The 3.13 fast transfer feature of the alternate ismediate access of fite circuits will not ba - tested during plant power operation since it 3.14 risks untecessary plant trips. Immediate access is not required of a 3 3.115 .Ol}

second offsite source, and for the Millstone 3 design, if the fast transfer is not successful the reserve station service transformers 3.16 can be connected to the emergency buses by manual control switch 3.17 operation In an acceptable time, The automatic transfer of emergency 4.16 KV buses 34C (Train A) and 3.18 34D (Traim B) from either the aoral to the reserve station service 3419 transformer or the normal or reserve station transformer to the emergency generators will be tested prior to initial startup mand 3.20 during refueling shutdowns of the unit to prove the operability of 3.21 the system. Therefore, appropriate testing and testability of the 3.22 transfer of power upon loss of normal power satisfies the requirements of General Design Criterion [8, Inspection and Testing ý.23 of Electric Power Systems.

'Physical separation of the offaite power sources, switchyard 3.24 protection, redundancy, and transmission system design basd* on load 3,25 1t flog and stability analyses minimize the possibility of simultaneous failure of power soures (normal station service supply, reserve 3.26 station serviie supply nd Standby Mc emergency generators) in

\ compliance ystes.," with General Design Criterion No. 17 "Electric Power 3.27 /

The 346 WV transmission system supplyhxg offsite power to Hillstone 3.28 is normally operated at 347 kV at Millstone. This aystem voltage is 3.29 Amendment 8 8.2-4 May i98

I I -

Northeast Utilities Letter Dated April 1, 1985 Millstone Nuclear Power Station, Unit No. 3 Power Systems Branch Electrical (PSBE)

SER Confirmatory Items 44, 45, 46 and 50

IASCII Text Slderi St'eet Rerlin. Cotneeiir.

HIEAST' UTILFIIr.S (ien1.nI Oflices *

h)¶rrr wait.r,,MA CIj.i* J II*HArITFOnD, CONNEm ICUT 00141-0270 66-891 1 S0 April ), 1985

[Docket No.60-423 B11497 Diirector of Nuclear Reaoter Regulation Mr. B. J, Younlgbood, Chief Li eonsiing Branehl No. 1 Dlivision of Licensing U. S. Nuclear Regulatory Cormnmission Wbshington, D. C. 20555 Reference; (1) V. S. Nuclear Regulatory CommissiOn, "Safety E-valuation Report Related to the Operation of Millstone Nuclear t Power Station, Unit No. 3, Docket No. 50-423 (NURJuG-ly3), ' nuly, 12 R4.

J)enr Mr. Youngbloodt Millstone Nuclear Power Station, Unit No. 3 Power Systems Branch l-1oetrieal (PSBE) 4 a6 50 ShItI Confirrnatcory lItes 4 dE4nd Attached are three (3) copies of revisions to Sections 8.2 and 8.3 of the Millstone tPnit No, 3, PSAR. These revisions close SEl Contirmatory Items 44, 45, 46, and

.M) IefeCrTleeI 3). All information contained in the JISAR revisions has been discusse.d with your Mr. John KIiox, Power Systems Branch Elcctrieal, and was provided in our responses to NRC questions 430.4, 430.5, 430.7, and 430.9, eorresponding to SYR Confirmatory Iter's 44, 45, 46 and 5U, respectively. The attaehed revisions respond to Mr. Knox's request for the information to be incorporated in the FSAR text. Revisions are provided as they will appear in Amendment 13 of the FSAR.

If you have any concerns related to the information contained herein, ple-ase contact bur licensing representatie directly.

Very truly yours, N ORTHEAST NUCI 3EAII ENERGY COMPANY et. al.

BY NORTHIEAST NUCLEUAR KN1RRGY COMPANY

'hailt Agent W. 6. Counrsil Se.nior Vice Firesident CF 9?000 1

ASCII Text STAT ]E OF CONNECTICUT )

SSS. le] lit)

COUNTY Ot IHARTFORJJ )

Then personally appeared before me W. GCQounsil, who being duly swon),, did state that he is Senior Vice President of Northeast Nuclear I4kergy Company1 an Applicant herein, that he is authorized to execute and file the foregoing information In the name and on behalf of the Applicants herein and that the stalements contained in said information are true and correct to the best of his knowledge and belief.

My Corinmnssion Lxpares Ntrcl 31, 198a

ASCII Text XNPS-3 FSAR 8.z OFFSITS POWER SYSTEH 8.2.1 Description 1'he offsite power system i& designed to provide reliable sources of power to the onsite ac power distribution systern adequate for the safe shutdown of the unit in compliance with General Design Criterion 17 (aDC-17). Details of the offsitt power systeim art shown on the following figures:

I. Exclusion Area (Figure 1.2-1)

2. Plot Plan (Figure 1.2-2)

3. Transmission Map (Figure 8.1-2)

4. 34S kV Switchyard (Figure 0.1-3)

The switchyard, which is configured in a breaker and a half irrangerment, bu&ses together four 345 k36transmission line circuits, three gener-tor circuits and three station service circuits The four transmission line circuits to be terminattd at the Suitchyard Bret

1. Millstone to Card (t.ine No. 303)

2. )illstone to Montville (Line No. 371)

3. Mi)jstone to Southington (Line No. 348)

4. Millstone to Nanchester (Lime No. 310) - iriservice in 1985 These 6ircuits connect the station to the system transmission grid and follow a commDn right-of-way from Millstone to Hunts Rrook Junction (9.0 mites), For the first 1.7 miles of this right-of-way, the construction consists of twO double circ"uit steel-pole transmission lines, For the next 2,4 miles, the construction consists of one double circuit steel-pole transmission line (Line Nos. SOB and 310) and two sing3e circuit wood-pole H-frame transmission lines (Line Pos, 371 and 383). For the rembining 4.9 miles, single circuit wood-pole H-frahie construction is used for all four circuits.

At Runts Brook ýuncttion, the four transmission line circuits diverge along three seporate rights-of-way. The 371 line consisting predominantly of wood-pole R-frate construction, follows an easterly right-of-way for approximately 3.6 miles to the Hontville substation, The 348 line consisting almost entirely of wood-pole H-frame construction with only a few exceptions where steel structvres are utilized, follows a westerly right-of-way. for 44 miles to the Southlngton substation. The 310 and 383 lines utilizing priiarily single circuit wood-pole -fr-ame construction proceed along a

t ..... . .... . .: ).1 ASCII Text I KWPS-3 FSATR northerly right-of-way for 3ý miles and 20 miles to the Manches ter and Card substations respectively.

U-04 Separate and independent structures are provided for each of the six

$4B kV transmission lines connecting generators 3, 2 aro 3 and reserve station service transformers 1. 2 and 3 to the switchyard.

The inspection and testing of the 345-kV circuit breakers and the I tratnsmission line protective relaying are done on a routine basis, without removing the generators, 'trans forters, and transmission lines from service. The ihrulating oil for the trsformer$+/-iThpe*'-i'd tested on a routine basis. During these routine inspections and tests, the operability and functional performance of the electriv systems are in con*piarnce with General Design Criterion 1S, I.

"Inspection and Testinq of Electric Power Systems."

8.2.2 Analysis The possibility of power failure due to faults Sn the connections to the system and the associated switchyard is minimized by the following arrSnIgehenIsi I. The connections to the systein have been designed to comply with the Northeast Power Coordinating Council "'Basic Criteria for the Design and Operation of Interconnected Tower Systems" and the "Reliability standards for the New England Interconnected Power Pool" adopted by that pool.

Compliance with these criteria ensure that the supply of offsite power will not be lost following severe faults in the Interconnected transmission system. Transient stability studies have been performed to verify that widespread or cascading interruptions to service will not result from these contingencies. In addition, the loss of Hillstone 3 or the loss of any other generating plant in the system will not result in cascading system outages and thus Will not cause loss of offsite power to the units.

The 34S kV circuit breakers are air blast type and are pnepunotcally operated. Electric, controls are provided -e/,

for both loeal and remote Millstone 1 control room operation. E:hch power circuit breaker has a separate-pneumatic supply unit capable of operating the breaker for five close-open operations after the loss of the compressor.

Each pneumatic compressor js supplied from a separate feeder at the switchyard essentia) ac panel. The circuit breakers are equipped with a clsi*ig solenoid and two trip solenoids.

A standard anti-pump abnd trip-free control scheme is used.

Primary and backup relaying are both high speed protective schemes. Primary end backup protective relays are used, along with breaker failure relaying to provide redundant protective relaying for the &witchyard.

ASCII Text HPS-3 FSAR Two 125V dc batteries are ocated in the switchyard control and relay cndlosure for switchyard relaying and control.

Beach battery has its awn charger and dc distrJbution panel.

The redundant batteries a-d protective relaying systems are physically and ,electricai)y separate. The essential ac station service for the power circuit breaker pneumatic supply units and the other switchyard requirements is supplied from one of two separate sources,

2. The 345-kV system is protected from lightning and switching surges by overhead electrostatic shield wires, surge arrestors on main buses, and rod gaps on the disconneat switches.

3. Primary and backup relaying is provided for each circuit blong with circuit breaker failure backup protection. These provisijons permit the followingt

a. Ainy circuit can be switched under normal or fault conditions sithout affecting another circuit.

b. Any single circuit breaker can be isolated for maintenance without Interrupting power or protection of any circuit.

c. Short circuits on any section of a bus are isolated without Interrupting service to any element other than those connected to the 5aulty bus section.

d. The failure of any circuit breaker to trip initiates

,the automatic tripping of the adjacent breaker or breakers and thus may result in the loss of a lime or generator for this contingency condition) hovever, power can'be, restored to the good elemeint it less than 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months by manually isolating the fault uith appropriate disconnect switches.

Complete battery failure is considered highly unlikely since two independent 125V dc battery systems are provided. Failure of. a sJrgle battery system results only in a mmventary loss of oim set of protective relays until the DC is manually transferred to the other battery. Therefore, no single failure could negate the effectiveness of the relaying to clear a faUlt, Physical separation of the offslte power souretS, switchyard protection, redundancy, hnd transmission system design based on load flow and stab$)ity analyses winimize the possibility of simultaneous failure of power sources (normal station service supply, reserve station service supply and standby ac emergency generators) in compliace with General Design Criterion No. 17 "Electric Power Systems."

The 345 kU transmission system supplying vffsIte power to Hiflstone is normally operated at 357 kV at Millstone. This systern voltage is

I :

ASCII Text XNPS-'3 PSAR controlled by Varying the reactive pDwer generation on the Millstone units, The Millstone I and .2operators control the unit excitation as specified by CONVEX Operation Instruction No. Gg63. When E1illstone 3 is placed In service, it will be included in the voltage regulatio*n scheme. The unit operators are required to balanue the reactive power output of the u.itrt.

The CONVEX system operator supervises the system reactive power dispatch. He diretcts the ItWading of all of the reactive power sources in CONVEX to balance the reactive supply. He keeps the iHillstone reoctive power generation in balance with the Eastern Area requirements so that the effect on the system of voltage variations is minimized when a unit is lost.

One objective cf the reactive pomer dispatch it, to prevent itn voltge. at Millstone from going below the minimum required by Millstone I reserve station service transformer. The nTINimum allowable voltage at Hillstowe is 362 kV based on equipment ratings,.

If abnonmnl system conditieos result in voltages approaching minimum levels, the EGuidelines for Dispatch of Reactive Power on the Northeast titilities Systtm" directs the CONVEX operator to take specific corrective actiobs to restore voltage. Hany of these actions will also he lahkn vhen the NillstDne reactive power output reaches 400 UWAR (with two units in service).

Actual experience and system simulations show that the CONVEX operator is able to control the system voltages within the desired limits.

The Hi)lstone plant is connected to the transmission system by four 345-kV circuits (described in Section 8.2.1). For a short distence, these lines are on double circuit steel poles. stsbillty studies show that the plant remains in synchronism with the rest of the system, even if two 34S-ky circuits are lost simultaneously as a result of a 3-phase fault.

The loss of any single 345 kV circuit will have a negligible effect on the Milstone units, Hence, no single circuit is critical to the operation of the units, the switchyard, the transmission system and Q430.l the supply of offsite power. Furthermore, theý loss of i second 2 345 W circuit has been analyzed (i.e., after one has already been switched out of service) and results show that the loss will not result in instability of the Hillstone units and will not cause facilitles remaning in service to be loaded beyond acceptable limiits.

&jioss ofa ills tone- unit will not affect system stability-.

The Millstone units are connected to the large interconnected trtsnmissiof system in the eastern half of the United States. The interconnected system frequetcy is a 601 0.03 Iz., Loss of large amnournts of generation result in frequencies of as low as 55.54 Hz which recover to cc Hz within a few reinutes.

. - - - -%-- - - , ON 10 ?5 InTAI lrlp"ý

ASCII Text MNPS-3 FSAR In order to have large frequency deviations at millstone, it is necessary to isolate the plant with & large excess of load. The only possible system separation vhich would accomplish this would be to isolate the State of Ionnecticut. This requires the overlapping loss of three 345 kV, one 138 kV, and one 215 kN circuit at a time when Connecticut As importing power.

If the 136 kv and 115 kv ties are neglected and assume that thee outage of the three 345 kV ties are statistically independent evtnts, one Dccurrence every 1.4 million years could be expected. Since the three 345 kV transmitsion circuits are more than 20 miles apart.

steatistical independence is a reasonable assumption. However, even if we assune that only tVo of the three events are statistcially independent, we woxu.d expett the occurrence to be only atie in 1,148 years could he expected.

The occurrence of a large Conr:ecticut import at the same time has not been included In. the statistical calculations. Including the probability of a large import at the tivme the three 345 kV circuits L'ktet lost would increase the time between events.

Amendment 2 6.2-5 April 1983

ASCII Text Tnisert A The four lines emanating from the Millstone Switching Station wiJI be in compliance with the staff position that no other transmission lines cross over these four lines and that the four lines be physically separate and independent so that no single event such as a tower falling or line breaking will be able to sirnrultatreously affect all circuits in such a way Ihat none of the four circuits caln be returned to service in time to prevent fuel design linits or desigri conditions of the reactor coolant pressure boufdary from being exceeded. Figure 8.2-11 taken frorn the Connecticut Siting Council Docket No. 25, Application for the Millstone to Manchester 345 WN line, shows the. right-of-way cross sections between Millstone arid Hunts Brook Junction. The double circuit steel pole structures between Millstone and 1-95 average 120 feet above ground while the wpod pole H-frame structures between Daniels Avenue and Hunts Brook Jurncton average 895 feel above ground.

In the event of a structure failure between Millstone and Hunts Brook 3unctioni the worst probable longer-than-mnoent'ary outage would be a loss of two circuits; i~e., the two circuits on a common steel pole or an H-frame structure falling inlo an adjacent line.

At Hunts Brook Junctiong the fOLur lines split (see Figure 8.2-2). The 3118 line turns west to Southington Substation, the 383 and new 310 lines continue north to Card Street and Manchester Substation respectively, and the 371 line turns east to Morntville Substation. One. aerial crossover of a line from kMillstone exists at this junction (3B3 crosses 371), But, at worst, only two of the four circuits fromn the Millstone Switching Station would be removed from setrvice should a structure collapse.

I I I I. .

ASCII Text 1isert B The Millstone design provides two immnediale access off-slte circuits between the switchyard and tie 4.16 WV Class It- buses. The design of two off-site circuits from the 34S WV switchyard to tht: 4.16 kV Class IE buses is via separate transformers (main/normal station service and reserve station service). FSAR Figure 8.1-1 shows 1he tie lines, transformer and bus arrangement connections.

1he tie. lines to the mainrlnormal station service transformers and to the reserve station service transformer are physically separate and electrically indeperndent.

The main/normal station service transformers and the reserve station sevioc transformers arc located at opposite ends ot the plant. The connection f rom tie normral station service transformers and forn the reserve slation service trarnsformners to the 4.16 W Class It buses is via physically separate z. ,

electrically inde(pendent underground duct lines. FSAR Figure Z.2-1 shows tile tie line routes from the switchyard to the mrain/normal and to the reserve station service transformers. 17SAR Figurev 1.2-2 shows the physical separation betwec'f.

the normal station service. arid the reserve station service transformers. FSAR Vigure g83-7, Sheets I and 2, shows the embedded conduit duct lines as they enler the redundant switchgear rooms irk the control building.

The conlro] power for these buss is from different de paneis and batteries. The breakers in the Class IF buses (3AC arid D) are independently pirotected with separate relaying.

These circults are completely redundant and separated so that no single failure can disable both off-site power supplies to the Class IF, buses; therefore, the design i! in compliance with General Design Criterion 17, Electrical Power Systems.

ASCII Text Insert C By careful design of the switchyard and protective relays, NU has practically eliminated the possibility of the simultaneous loss of three units at Millstone.

Nevertheless, the loss of the Millstone plant and all four transmission circuits has been simulated in design studies. The transmission circuits were outaged along with the station in order to simulate worst case conditions, and this outage was shriulated both with and without a fault.

The stability analysis indicates that the rest of the system will remain in synvhronism after the loss of the entire output of the Millstone station. The system was rnodellcd for one set of operating conditions; hence , it is possible thal a similar test urider heavy transfer condhiions within the interconnected syslem mnight result in instability. However, we are certain that the probahib."y of losing all three units shliwitanrously is extremely small because of the prevenlive measures discussed in the following paragraphs. Accordingly, NU believes it is reasonable to count upon onsite power sources to supply the necessary stat!ior service power requirements in the very remote event that all three Millstone units should be lost at once accompanied by the total loss of the transmission supply to the station.

A primary objective in designing the connection of the Millstone Nuclear Power Station to the 3A5 cV transmission network in Conrecticut has been to prevent the loss of the entire station output. The rellability criteria of the Northeast Power Coordinating Council (NPCC) and the New England l'ower Pool (NEPOOL) arC a fundamental part of this design process. The following are the most severe outages which the system has beers designed to survive in order to minimize the possibility o1 a total plant Outage:

a. With any one of the four Millstone 345 kV transmission circuits out of service, tine plant remains stable for any three-phase fault normally cleared (four cycles) or any one-phase fault normally cleared (lour cycles) or any one-phase fault with delayed clearing (nine cycles). These tests are done with maximum generation at Millstone to simulate worst case conditions.

b. The reliability criteria further requ-irs testing to determine if the loss of two circuits on a common structure can be tolerated, The event which is used to test the loss of the two circuits is a simultaneous line to ground fault Qn different phases ol the two circuits. With all lines jri service, the systerm remains stable for this two circuit disturbance.

It should be recognized lhat the four circuits leaving the Millstone switchyard are paired on two rows of double circuit structures for only a short distance, and, hence the exposure to this outage is small.

c. Also, the simultaneous loss of two Millstone circuits on common structures following a previous (nonsijniultaneous) outage of either of the other Millstone circuits (or any other critical element) must not result in instability. All of the critical outages of this type effectively result in the loss of three of the four Millstone circuits and leave the Millstone station weakly tied to the transmission grid. To prevent instability ior these extremely severe (and highly improbable) disturbances, it is necessary to reduce output after the initial line outage and before the loss of the two circuits on common structures takes place and/or Install an automatic generation rejection scheme.

' ".. :2i T 1 .2 ".'. "::,:',:.@* ,: ._: .! i; i . .. "' c rAS(CII Text Insert I)

Becauso of the significant eco:noTiC penalties involved, the reduction of generation after the Initial line outage is considered a highly undesirable solution to the potential stability problems identified in Item (c) above and should be avoided to the extent possible. Therefore, a post disturbance generation curtailment scheme has been provided. This system continuously monitors the individual state of six critical system components together with the generation output at the Millstone complex. Should the system condition arise where I) any one of the six critical lines or elements is unavailable, 2) the generation at Millstone is above a predetermined MW level and 3) two specific transmission circuits are forced out, then generation will automatically be curtailed at Millstone, Stability studies indicate that during maxiMUM output conditions (2640 MW), Millstone Units J and 3 can be successfully tripped and syst. tn stability maintained leaving Millstone Unit 2 in synchronism with tlt-itransmissio network. The tripping of these units results in a generation reduction of up to approximately 1,S10 MW with 870 MW reraining synchronized. This generation reduction scheme is called a'Severe Line Outage fleteclion (SLOT)).

The operation of the Millstone generation rejection scheme is based on the outage of combinations of certain transmission circuit elements. The scheme has been named Severe Line Outatge Detection (SLOD).

This systetn will continuously monitor the individual status of six critical transmission elements iri the area of the, Millstone Station together with the generatlon output of the Millstone complex.

Genieration will be curtitiled automatically if a system condition arises where any of ten combinations of the six elements are outaged, and generation at Millstone is above 1,200 MW.

To monitor the status of the 345 kV system; S1.01) equipment has been required at the Millstone and at Montville switchyards. In addition, it will be necessary to install high speed back-up relay protection with a permissive overreaching audio-tone scheme on both ends of the Millstone to Manchester and the Millstone to Southington lines.

At Millstone, three logic. packages will be provided. The operallon of any two logic units will provide a tripping output. The current detecting devices of each 1ogic package will sense the available state of taclT of the four transmiss*ion circuits emanating from the Millstone switchyard, Signals indicating the availability state of two remote coinporients (the Moniville 345 kV tie breaker and the Montville - Haddam Neck line) will be transmitted to Millstone. The megawatt output from each of the Millstone units will be measured and summed to provide an indication of the total megawatt output of the Millstone. units.

Should the comparative logic in the SLOD package indicate that any one of the combinalions of transmission outages listed below exist, and the generation level at the Millstone Station is above 1,200 MW, then Millstone Unils I and 3 will be curtailed immediately,

I

. .I II W

"*- 7* 1 I ASCII Textj I-he combinations. of unavailable cornponents which must he rrionLtiored are,

1. Necessary to meet NT)CC and NEPOOL criteria:

Millsione - Manchester, Millstone - Card and Millslone - Montville Millstone - SouthingiorI, MiJlstone - Card and Millstone - Montville Millstone Montvilie, Millstone - Manchester and Millstone -

Southingtont Millslone - Card, Millstone - Manchester and Millstone - Southington Montvile - Haddarn Neck, Millstone - Manchester and Millstone -

Southington Montville 365 kV tie breaker, Millstone - Manchester and Millstone -

Southington

2. Also includcd to simplify the SLeD package logic but nol required to meet NPCC and NEPOOL criteria are:

Millstone - Southington, Millstone - Card arid Montville - Haddam Neck Millstone - Manchester, Millstone - Card and MorLvill - Haddam Neck Millstone - Southington, Millstone - Card and Montville 345 kV tie breaker Millstone - Manchester, Millstone - Card and Montville 315 kV tie breaker As mentioned above, signals indicating the availability status of the two remote components at Motitville are required al Millstone. To monitor the status of the 3tt5 kV circuit breakei at Montville, and the availability of the Montville-Haddam Neck line, three logic unils will be required at Montville. The three independent logic packages will supply information to the. Millstone logic packages via an independerit transfer Irip tone transmitter.

Since tine operation of the generation rejection scheme should take place in less than 12 cycles to maintain stability, all transmiss*ion line faults must be. cleared at high speed. This will require the addition of high speed back-up protection using permissive overreaching audio-tone equipment on the Mill stone-Manchester linre and the Millsione-Southington line at both terminals.

With the gerneration rejection scheme in service, it will be permissible to operate with high) Millstone Station output when any one of six critical transmission elements Js out of service8 As a member of NEPOOL and the NPCC, the Applicant will be required to comply with either of the following operability requirements with one line out of service:

I. have SLOI) fully operational, or

ASCII Text 2, reduce load to a total station output of I p2OO MW within 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months .

Those instructions will be documented as part of the Connecticut Valley Electric Exchange (CONVEX) operating instructions for the Millstone switchyard and will be regulated by CONVEX. To facilitate regulation, CONVEX is aware of the condition of all Jines and the status of the SLOF scheme via an annunciator loctated at CONVEX (CONVE2X is en operating divlion of NEIOOL).

The operability requirements specified above ensure that, upon loss of a double circuit line with a Third line out of service and generation in excess of 11200 MW, olisite power will be available for sacf shu'tdown; maintaining system stability TniniTnlzes the probability of coincident loss of both ofisite supplies. This is consistent with the requiremnents of General Design Criterion (GEC) 17.

GIcC 17 also requires that the probability of losing an offsite supply coincident wilh loss of the nuclear power unit be, minimized. Because of the necessity for SLOD to complete its furnction within 12 cycles, SLOD trips Millstone 3 by tripping the switchyard breakers instead of the generator breaker (this eliminates the extra time required for relay and communication channel operation in a transfer trip scheme). Under 1hese conditions, station auxiliary JoAds high speed transfer to the reserve station service ttansforlners, and the normal station service transformer (which is tripped when SLOB trips Unit 3) can be reenergizcd by closing a switchyard breaker. Therefore, both ofisite supplies will be available to ensure safe shutdown of the unit in accordance with GDC 17.

The SLOOD scheme was matkulactured to be a reliable unit. Each line is monitored by a logic package. which utilizes redurndant channels (two-out-of-three logic) in case of a failure of one channel. Each logic package alarms in the evyent of a channel failure and triggers a SLOT) trouble alarm in the Millstone Unit. I control roorn and at CONVEX. Also, a failed channel causes arming oS tihe logic, indicating the monitored system component to be out of service.

Additionally, every 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months , the SLOB scheme automatically tests one channel, yielding a completc scheme verification once every 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months , In the event of failure, a SLOD trouble alarm is actuated in the Millstone Unit I control room and at CONVEX. Upon receiving the SLOD trouble alarm, the operator will dispatch a person to the Millstone switchyard control house to evaluate the condition of the system. In the evont that one line is out of service and the' SOI1 system is not operating in one hour, CONVEX wilt reduce station output to 1)200 MW or below during the next 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months . The continual channel surveillance and periodic U(8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months ) functional tests that are run automatically esure conformance to GI)C J8.

Additional testing was carried out for possible but improbable (ID) events which are specified in the NPCC and NEPOO0L reliability criteria. The one PBi event which could have a serious effect at Millstone is a three-phase fault followed by delayed clearing due to a three-phase stuck circuit breaker. This results in the Millstone units losing synchronism. This stability problem has been eliminaled by designing the protective relay schemes aid circuit breaker i.nstallattons so that at most, one pole will fail to clear, The breakers which are designed to meet this criteria are classified as having independent pole tripping.

ASCII Text NU insures inde-pendent pole tripping by ihstalling breakers with mechanically independent poles and two separate methods of tripping the circuit breaker.

Thcse installations include two sets of relays aRd trip coils, There are two sets of current and potential transformers, the wiring for the relay package.s are izistalle.d in separate duct banks, the relay packages are physically separated in the control house and two separate dc supplies arc provided, The 345 kV switchyard at Millstone is designed so that the loss of More than one transmission circuit due to a failure of a breaker to trip requires at ieast two circuit breakers to simulataneously fail to operate, The failure of even one circuit breaker is very unusual. At least three circuit breakers would have to fail before three transmission lines would be lost due to malfunctions in the switchyard. At that point, the generation rejection scheme would operate t.

keep one unit in service. In order to lose the entire station, at least four circuit breakers mu.st fail.

lo skmmtnarize! The Company is taking extensive precauitlons to prevent tic-sudden loss of the three generating unils at Millstone Station and the simultaneous loss of off-site power. We believe these, measures make the probability of such an occurrentce extremely small.

ASCII TextI TYPICAL RIGHT-OF--WAY CROSS SECTIONS A. WNTERFORD: MILLSTONE SUIWSTATION TO DANIELS AVE., 1.5 MILES IN SEGMEFNT t 345 KV S4b KV 3045KV 345 KV LOOKIN1G NORTH PROPOSto NW CIRCUIt (AND ARMS)

TO :BE ADDED ONl EKISTING- rRUCTfRE

t. OF t, Or, EXISTING4 EM~S;TIHG-K

X1__

.50d RIGT-F-AYAN'-

EXISTING 500' RIGHT OP WAY AND CLEARINO

-CLEARIN

-- l-'1 B. WATERFORD: DANIELS AVE. TO 195 2.6 MILES IN SEGMENTS 1 AND 2 345KV 345 KV LOOKING, NORTHP PROPDS*D NEW CIRCUIT TO of 345 tV S45 1V ADDE!3 ON EXISTING flilRUCIUR1 IV, t OF EiCISTINIý P EXISTING 415' RIGHT Or WAY AND CLEAARING--

C. wATERFORD-MONTVILLE: 195 TO HUNTS bK. JCT., 4.9 MILES IN SEGMENTS 2-4 LOOXING NORTH me- ---t 8. ,

RIGHT OF W'f AND CLEARING rý:- .- EXISTING-FIGURE c 7453i 1B t MILLSTONE-MANCHESTER Z45KV L INE MILLSTONE NUCLEAR POWER STATION UNWT 3 FINAl. SAFETY ANALYSIS REPORT

- I. - -

SASCII Text IADAM NtCK HUIO PAW 148 TAt W884 LINE tRloot. kWNtf

363 £NP#ýFilo..

ISL MILL STONE P LANN0I ONLY 1563

[DONOT USE OR DESIGN.

IriGuRE:Qjjjj7- g)6.z-2 HUNTS BROOK JUNCTION MILLSTONE NUCLEAR POWER STATION UNIT ý FINAL SAFETY ANALYSIS REPORT

ASCII Text Tinte-Overcurrent relays are provided for the reserve station service supply (i.e. alternate source) breakers. These relays provide protection against overload, low energy multiphase, and phase-to-ground faults. Additionally, instantaneous directional phase overcurrent and ground overcurrent relays are provided for these supply breakers, These relays provide protection against (i.e. by isolatitig the emergency bus) multiphase and ground faults external to the energency bus by isolating the emergency bus.

b. Differential Bus Protection, Emergency Swltchge-r -

Ea emea rgey fih ckV buiis--is protected agaiast rultiphate-to-phate and phase-to-ground faults by high impedance differential relays. Under accident condition when emergency bus Is being fed by the emergency generator, sequential tripping is introduced for ground faults, The generator neutral breaker is tripped first which will clear ground faults by ungrounding the system.

0. Undervolta.e Bus Protection, Elergeno. switchgear-RICh emergency 4,16 kV bus is furnished with Two undervoltage detection schemes.

Loss of voltage scheme with two-out-of-four logic is provided to detect voltage drop below acceptable level.

After sufficient time delay to coordinate with overcurrent fault protection, this scheme will start the diesel generator, trip motors through the sequencer, and load the emergency generator a; required.

Degraded voltage scheme with two-out-of-four logic is provided to detect prolonged voltage drop to the level which could be detrimental to operation of the emergency equipment if allowed to continue. Under accident conditions when the emergency generator is ready, to accept load, this scheme will trip rotors through the sequencer and load the emergency generator as required. Under normal conditions this scheme will start the emergency generator ard, when it is ready to accept load, will trip motors through the sequencer and load the emergency generator as required.

d. Emergency Generator, Emerqency Svýtchgear - The design of the electrical protective trip circuits of the emergency generator is consistent with minimizing the likelihood of false emergency generator trips during emergency conditions. as described in Section 8.3.1.1.3.

":w a=*..:. ""- * ". , ;. ". *.....*. :

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ASCII Text Insert X The degraded voltage scherne with iwo-out-of-four logic jprovided for ea*6 4.16 kV Class I- bus is described in the following drawings, and logic and elementary diagrams (refer to PSAR Section 1.7)t One Line DrawlnpAs 12179-EE-IK 12179-1313-1M Logic Diagramrs 12179-LSK-24-3C, D, HF,3, K 121 79-LSK-24-4A, B1 E lenentay-. Mii..a_ýs 121 79-E"SK-5WI)*, t31,1W I w;*B 1217%M-SK-73, L The MiUstone 3 desigri complies with the guidelines of Position I of branch Technical Position PSB-i of NUREG-OBOD in the following rmtatner:

The second level of protection is in addition to the undervoltage scheme which also employs a two-out-of-four coincidence logic to prevent spurious trips of the offsite power source. Two separate time delays are incorporated in the degraded voltage scheme. The first thne delay establishes the existence of a sustained degraded voltage on the bus. Following the delayý an alarm in the Control room alerts the operator to the degraded condition. The subsequent occurrence of an accident signal (SIS or CDA) will inmmediately separate the Class 111 distribution system fron the olfsite power system. The second lime delay is of a limited duration such that the permanent connected Class 1E loads will not be damaged.

Following the delay, if the operator has failed to restore adequate voltages, the Class JE distribution system is automatically separated frorn the offsite power system. No bypasses are incorporaled in the scheme.

The (Cass 1F, voltage sensors are physically located and electrically connected to the Class JE switchgear. Test and calibration of the voltagn sen.sors during power operation can be performed on an individual relay basis.

rhe Technical Specification will include limiting condition for operalion, surveillance requirements, trip setpoints, and allowable values for the second-level voltage protection sensors and associated lime delay devices.

Excerpts from NRC Letter Dated September 10, 1985 Reauest for Additional Information for Millstone Nuclear Power Station, Unit No. 3

~~~ ....... 4t1- ~. . .. ....

LASCII Text ,

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D Q. 2l0Aig flCEVED Docket No, 50-423 SEP 1 0 19B5 Mr. 3ohn F. Opeka IVLC16,-r £rpaea,.115g & ir Senior Vice President Nuelar Engineering and Operations Northeast Nuclear Energy CoMPany P. 0. Box 270 Hartford, Connecticut 06141-0270

Dear Mr. Opeka:

Subject:

Request for Additional Information for Millstone Nuclear Power Station, Unit No. 3 Enclosure I contains requests for additional information which the staff re-quires to complete Its evaluation of your application for an operating license for MIllstone 3.

Enclosure 2 contains meeting summaries also detailtng information which the staff requires to complete its evaluation of your application for an oper-ating license for Millstone 3.

Please subnit your responses no later thai 30 days of the date of this letter.

Enclosure 3 contains the staffs response -to your requests for approval of use of 3 Code Cases at Millstone 3.

Enclosure 4 contains informatlon related to the staffs reviewp of the Millstone Nuclear Power Station Emergency Plan, Draft 2 to Revision 0.

ror further information or clarification, please contact the Licensing Project Manager, Eli2abeth L. Doolittle at (301) 492-4912.

S' niee B. J. Yo~ngblood, Chief Licenstng Branch No. 1 D'vysion of Licensing cc: See next page

Raster Image A summary of the discussion for each of the above items is presented below:

01 #2 (SER Section 8.3.1.11)

Additional analysis or test data was not available to demonstrate the diesel generator's design capability (in accordance with the requirements of GDC

17) to accept design load after operation at no load. This item remains open.

01 #13 (SER Section 8.3.3.)

The applicant indicated that the design for the PORV and Block valve power supplies is being changed such that it will be in conformance with the staff position stated in the SER. This item remains open pending staff review of the proposed change.

CI #43 (SER Section 8.2.1.1)

This item has been closed by SSER #1.

CI #44 (SER Section 8.2.2.1)

Design description, documented by letters dated May 3, 1983 and August 29, 1983 (response to NRC question number 430.4), has not been incorporated into Section 8.2 of the FSAR. This item remains confirmatory.

CI #45 (SER Section 8.2.2.2)

The offsite power cables between the normal station service transformer and the Class 1E buses and between the Reserve station service transformer and the Class IE buses were traced as part of the confirmatory site visit. Based on the cable tracing, the staff concludes that the cables are routed in accordance with Millstone separation criteria defined in the FSAR with the following exception. The A division cables from the normal station service transformer are not routed in embedded conduit when they pass through the B division cable tunnel shown on figure 8.3-7 of the FSAR. This item will become open.

CI #46 (SER Section 8.2.2.5)

Description of surveillance, operability requirements, and analysis presented by letter dated June 12, 1984 has not been documented in response to question 430.7 or in Section 8.2 of the FSAR. The applicant indicated that the analysis presented for the protection scheme is being changed. When the proposed change is received, this item will become open.

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Excerpts from Northeast Utilities Letter Dated September 19, 1985 Millstone Nuclear Power Station, Unit No. 3 Technical Specifications - Proof and Review

NORTHEAST UTILITIES General cnfwrseftSdun $treti. kBerli. Oonnoctico!

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P.O. BOX 270 CDNNECTIC.LJT 056-5=0D 06141-027.0 Septemhber 19, 1985 DOCket No. 50-423 BI 1731.

Director of Nuclear Reactor Regulation Mr. 1l. 3. Yvourgblood, Chief Licensing Branch No. I Division of Licensing U. S. Nuclear Regulatory Commission Washington, D, C, 20555 Gentlemiem Millstone Nuclear Power Station, Unit No. 3 Techncal Specificatiors - Proof ýand Review with Representatives from Northeast Nuclear Rnergy Company (NNECO) met for the Staff on September 6, 198W to discuss the Tecbnicaý Specificallons Millstone Unit No. 3. NNCO was reqtw.ted to submit additional information concerning certain draft technical speclfications by September 20, 19854 rEnclosed please find NNlCO's response to the questions raised.

We trust the attached will resolve the St,-,f1s concerns. It there are additional questions, please contact our ficensing rep-esentative directly.

Very ti IYy yours, NORTHEAST NUCLEAR ENERGY COMPANY et. al.

BY NORTHEAST NUCLEAR ENERGY COMPANY Their A',gent

3. F. C'peka Senior Vice President

I SER [te*,

Itcm 6: 3/44.31 A. C. Sources SER Se(tion 9.2.20, page 8-4 v tuld r~equire the Severe Line Outage Detector (SLOW) Scheme surveillance and operability requirements for the protective scheme be in technical specifications, NNECO's Response:

Section 8.1.3 of the Millstone Unit No. 3 (NiP-s) rSAR describes a Severe Line Outage betector (SLOD) Scheme. The 5LOI.0 scheme provides protection against potential system instabilli*y in the event of a loss of the two 345KV circuits on either of the two double circuit towers at a time when one of the renailning two circuts is out of service and Millstone site jieneratlon is heavy.

Question 430.7, part b, requesting additiona! details relative to SLOD resulted in NtNhCO subsequently providing this inform;Ltion. It was our understanding 1hat the NRC reviewer, upon detailed review of i hat supplement, found the schene to be acceptable.

The Millst6ne 3 Safety Evaluation Report (SER) wis 4sued in 3uly of 198'.

Section 8.2.2.5 of the SER, entitled Generation Reiectiorn Scheme docum-ents your determinatitn that the design meets CGUC 17 and 13 criterion and is acceptable. Further stated however, is that "Surveillance and operability recquirements for the protection scheme will be included in the Technical Specifications". NNECO strongly disagreei. with this position, for the following reasons.

The transmission system (grid) within the Sta;te of Curmeectiwt is operated by the Connecticut valley Electric Exchange (CON VEX). The Millstone switchyard is an important element of the Connecticut and New England gridsý, and Is operated by CONVEX In tlose coordination with NNECO. Each o* the Millstone generating units has two dedicated connections -o the Millstone switchyard over which the respective unit has administrative control, and addressed by the unit Technical Spe ciii catgions.

All the protective features contained within the switchyard (Millstone and all o-her switchyards) fall under .the iurisdic.ton of the Northeast Utilities.

Transrnis5ior Organization with CONVEX ierving as the operator. The SLOD scheme at Milisione is not Miilstone Unit Noi. 3 specific, but the scheme required by the transmission system, wherein protecdon against the occurrenoe of systemn instability is deemed prudent. In this remiect, it is only one of many system features which in total give-rise -toa highly .-eliable transmission network.

We have co-aiplete conlidence in the abiliký of CONVEX to satisfactorily control the transmisslon system. They have denrvnstrated that ability as evidenced by the high reliability of the Connecticut Power System and by their. sensitivily to the special needs of the nuclear Fnits. CONVEX has in plam operatting procedures1 and their equivalent of limithtg conditions for operation (.complete.

with compensatory in~terim measures), lo p.-ovide for any transmission 5ystem off normal con dition,

ASCII ext iterm No. 6 continued General Design Criterion (GDC) 17 satales that "Electric power. from the transmisslon network to the'onsite electric distributLion system shbal be supplied by two physically independent circuits designed Bid located so as -to rninimize, to the extent practical the likelihood of their shmultancous fallure.4'.

The slatement "n'inimizO to the extent practical" fvlly recognizes the non Class IJ. and non-3eisrmically quallifed nature of the transmission system. T¶he installation of the SLOD scheme )s one element in the design of the transmission system to minimize the probability ol los. of offsite power. The Technical Specifications the NRC desires to impose upon a small portion of that system (SLOW)) are inconsistent with normal CONVEX controls. Although systemr rr'lIab~lity is largely affected by the quality and reliability of the hardware, it is also true that softwiare elements are imporfant to reliability. Such de*isions as to how VARS will Ie dispatched (a continuously chaftging targetjplan) and how much spinning reserve and of what type in what location, are all part of CONVEX's day to day activity.

Regarding SLOD specifically, the scheme was engineered kor transmission system stability purposes, and It will be operated and maintained to support a high degree of reliability. No cffsite Millstone sltichyard transmission lines will be removed from service when all three Millstone Units are operating except under lorced outage circumstan*.cs 11, however unlikely, SLOD is not in service.* at that time, CONVEX will act to reduce Millstone site generation, within a matter of minutes. Similarly, if a line were forced out of service whenever SLOD is in service, (the expected case)

CONVEX will act to optimize load flows and spinning reserve to prepare for the unlikely probability that SLOD could operale, and disconnect significant amount of nuclear generation.

We believe that this response appraises yoi. ol the complexities associated with controlling the transmisslon system, and clarifies thie pkrpose of the SLO]h scheme in relation to the transmissionfgeneration system. Imposing plant specific techical speclficatlions. to address SLOD unavailabillty is inappropriate to effectively ensure the availability of-of l:ite power.

* , * ,-

i.. :;:-i :*::-i' 1 I I ASCII Text]

Table 1.2 (Continued)
Item Status Sectlon*
(35) Confirmatory test related to IE Closed (SSER 2)
Bulletin 80-06 (36) Control building Isolation reset Closed fSSER 2)
(37) Power lockout feature for Closed (SSER 1) motor-operated valves (38) Failure mode and effects analyses Closed ($SER a) of engineered safety features actuation system (39) Non-Class IE control signals to Closed (SSER 2)
Class lE control circuits (40) Sequencer deficiency report Closed (SSER 2)
(41) Balance-of-plant instrumentation Closed (SSER 2) and control system testing capability (42) Instrument accuracy related to Closed (SSER 2)
Positions [Attachments] 4, 5, and 6, NUREG-0737, Iter nrlF.1 (43) Description and analysis Closed (SSER 1) demonstrating compliance with GOC 5
~4444) Physical circuits separation of ofsite within a common right of Closed (SSER 3) 8.2.2.1 way (45) Physical separation of offsite Closed (SSER 3) 8.2.2.2 circuits between switchyard and Class 1E system
+ (45) Generation rejection scheme Closed (SSER 3) 8.2.2.5 (47) Description and analysis Closed (SSER 1) demonstrating compliance with GDC 17 (48) Description and analysis Closed (SSER 1) demonstrating compliance with GDC I8 ASection of this supplement where item is diMcssed.
Millstone 3 SSER 3 1-6
. 'i" :.... ' .. ' . I.* . - . . . .~
. . . . ..... .. .4-. .
ELECTRIC POWER SYSTEMS 8,2 Offsite Electric Power Systen 8.2.2 Compliance With GDC 17 8.2.2.] Physical Separation of Offsite tftcuits Within a Common Right-of-Way In a letter dated April 1, 1985, the applicant provided FSAR revisions as they will appear in FSAR Amendment 13. In this letter, the applicant stated that these revisions incorporate the response to NRC question Q430.4. This resolve$
confirmatory item (44) dealing with the inclusion of the information in the FSAR.
6.22K.2 Physical Separation of Offsite Circuits Between Switchyarti and Class IF System In a letter dated April 1, 1985, the applicant provided FSAR revisions as they will appear in FSAR Amendment 13. In this letter, the applicant stated that these revisions incorporate the response to NRC question Q430.5. This resolves confirmatory item (45) dealing with the inclusion of this information in the ESAR. During a site visit held on April 10 and 11, 1985, the staff observed that the A division cables from the normal station service transformer are routed in cable trays when they pass through the B division cable tunnel. This contradicts sheet 2 of FSAR Figure 8.3-7 which shows this table in embedded con-duit. The applicant has indicated this figure will be corrected to resolve the discrepancy. This is acceptable.
8.2.2.5 Generator Rejection Scheme In the Millstone 3 SER, the staff stated that the surveillance and operability requirements for the generator rejection scheme (also termed the severe line outage detectors SLOD, scheme by the applicant) would be included in the tech-nical specifications, Subsequently, in a letter dated September 19, 1985, the applicant stated that the SLOD scheme is only one of many system features which in total give rise to a highly reliable transmission network. The applicant stated that although system reliability is largely affected by the quality and reliability of the hardware, it is also true that software elements are important to reliability, such as how VARs (volt amperes reactive) will be dispatched and how much spinning reserve and of what type in what location are available, This is handled by the Connecticut Valley Electric Exchange (CONVEX) which operates the transmission system (grid) within the State of Connecticut.
The applicant stated that CONVEX has operating procedures in place, as Well as its equivalent of limiting conditions for operation (complete with compensatory interim measures), to provide for any transmission System off-normal condition.
The applicant stated that no offsite Millstone switchyard transmission lines will be removed from service when all three Millstone units are op2rating, except under forced outage conditions, If SLOD is not in service at that time, CONVEX will act to reduce Millstone site generation, within a matter of minutes, Millstone 3 SSER 8 8-1
I ASCII Text]
to preclude the possibility of an unstable condition arising, Similarl if line were forced out of service whenever $LOD is infservfca, CONVEX wi a Optimize and operate 1oaddisconnect flow and spinning reserve to prepare for the event that SlOg could significant amounts of nuclear generation.
The. staff finds that these provfsions minimize, to the likelihood of the simultaneous failure of both offsite extent practical, the fore eliminate the need for Technical Speciffcation power sources and there-limitations on the SLOD scheme. This closes confirmatory item (46).
8.3 Onsite Power Systems 8.3.1 Onsite AC Power System4s Compliance With GCD 17 8.3.1.3 Description of Compliance With Position I of BTP PSB-i In a letter dated April 1, 1985, the applicant will appear in FSAR Auendnient 13. One of these provided PSAR revisions as they revisions includes the response to NRC question Q430.9 ihich the staff has previously reviewed and found accept-able. This resolves confirmatory item (50). As part Millstone 3 Technical Specifications, the staff will of its review of the level undervoltage protection setpoints are acceptableensure that the second and the description of the logic matches that in the FSAR revision.
,13,1.5 Adequacy of Station Electric Distribution System Voltage As part of the site visit on April 10 and 11, 1985, results of the Millstone 3 voltage drop analysis and the staff reviewed the acceptable; however, the staff noted that the grid voltage found the results to be maintain adequate plant voltages may not be outside limits necessary to extremes, This could result in the grid being incapable of the normal grid voltage voltages to safety loads during periods when the grid of supplying adequate voltage extremes, The staff will pursue this Item withis operating at its normal the applicant and report its resolution in a future SER supplement.
NRC will verify thetest results that substantiate the analysis. This item remains confirmatory pending coopletion Millstone 3 voltage of verification by the staff.
8,3.1.7 Diesel Generator Protective Relaying This item was identified as confirmatory In SER Section assigned a confirmatory item number in SER Table 1.4. 8.3.1.7, but was not The staff reviewed, with the applicant, Stone & Webster Engineering Corporation 12179-ESK-eKN (Rev. 2), 12179-ESK-OKF (Rev, 6), 12179-ESK-SDS (SWEC) drawings
]2179-ESK-BKG (Rev. 6). The staff confirmed that the (Rev, 11), and design for bypassing diesel generator protective relaying under accident conditions meets the staff position. This item is, therefore, considered complete.
8.3.2.11 Diesel Generator Load Acceptance Test After Operation at No Load In SER Section $.Lii, it was stated that the method by which the diesel gen-erator's no-load capability is considered In the load acceptance tests would be Millstone 3 SSER 3 8-2

v t e Letter Sequence Request
TAC:MF6430, (Open)
Initiation Request, Request Acceptance... Administration Questions 13 January 2016 Answers Results Approval... Other: ML16197A459
MONTHYEAR2016-01-13 [Table View]

ML15183A022

Text

1.1 INTRODUCTION

8.1 INTRODUCTION

2.1 DESCRIPTION

REFERENCE:

REFERENCE:

Dear Mrs. MacDonald:

Dear Mr. Counsil:

Enclosure:

Dear Mr. Youngblood:

Response

Dear Mr,

Subject:

Response

Dear Mr. Opeka:

Subject:

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