ML12305A017

Surry Units 1 & 2, Millstone Units 2 & 3, Kewaunee Power Station, Response to NRC Bulletin 2012-01 - Design Vulnerability in Electric Power System

ML12305A017
Person / Time
Site:	Millstone, Kewaunee, Surry, North Anna
Issue date:	10/24/2012
From:	Price J A Dominion, Dominion Resources Services
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
BL-12-001
Download: ML12305A017 (74)

Text

Dominion Resources Services, Inc.Innsbrook Technical Center 5000 Dominion Boulevard, 2SE, Glen Allen, VA 23060 October 24, 2012 U.S. Nuclear Regulatory Commission Serial No.12-519 Attention:

Document Control Desk NL&OS/ETS R3 Washington, D.C. 20555 Docket Nos. 50-338/339 50-280/281 50-336/423 50-305 License Nos. NPF-4/7 DPR-32/37 DPR-65 NPF-49 DPR-43 Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPANY DOMINION NUCLEAR CONNECTICUT.

INC DOMINION ENERGY KEWAUNEE, INC NORTH ANNA POWER STATION UNITS I AND 2 SURRY POWER STATION UNITS 1 AND 2 MILLSTONE POWER STATION UNITS 2 AND 3 KEWAUNEE POWER STATION RESPONSE TO NRC BULLETIN 2012-01 -DESIGN VULNERABILITY IN ELECTRIC POWER SYSTEM On July 27, 2012, the NRC issued NRC Bulletin 2012-01, "Design Vulnerability in Electric Power System," to 1) request information regarding the facilities' electric power system design in light of the recent operating experience that involved the loss on one of the three phases of the offsite power circuits at Byron Station Unit 2 and 2) require a comprehensive verification of the facilities' compliance with the regulatory requirements of GDC 17, "Electric Power Systems," in Appendix A, General Design Criteria (GDC) for Nuclear Power Plants to 10 CFR Part 50 or the applicable principal design criteria in the updated final safety analysis report. The Bulletin requires a response to the Required Actions within 90 days of the date of this bulletin.Consistent with the current licensing basis and GDC 17, existing protective circuitry will separate the engineered safety features (ESF) buses from a connected failed source due to a loss of voltage or a sustained, balanced degraded grid voltage concurrent with certain design basis accidents.

Dominion is following the industry efforts to identify a protective relay scheme that can automatically protect against an open phase condition in an offsite or preferred power fKK Serial No.12-519 Docket Nos. 50-338/339/280/281/336/423/305 Page 2 of 3 source without degrading the reliability of the existing design and determine if design changes are applicable and needed at our nuclear stations.The enclosures to this letter provide the requested information for North Anna, Surry Millstone and Kewaunee Power Stations.If you have any questions or require additional information, please contact Mr. Thomas Shaub at (804) 273-2763.Sincerely, J. an Price _______________.

____...._Vice President-Nuclear Engineering VICKI L. HULL dl Notary PubliclCoinmmonwaI of Virginia 140542 F MCwExermMay 31.2014 COMMONWEALTH OF VIRGINIA COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by J. Alan Price, who is the Vice President

-Nuclear Engineering of Virginia Electric and Power Company, Dominion Nuclear Connecticut, Inc. and Dominion Energy Kewaunee, 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 V2ALay Of 2012.My Commission Expires: Notary Public

Enclosures:

1. North Anna Response to NRC Bulletin 2012-01 2. Surry Response to NRC Bulletin 2012-01 3. Millstone Response to NRC Bulletin 2012-01 4. Kewaunee Response to NRC Bulletin 2012-01 Commitments made in this letter: None cc: Regional Administrator, Region I U. S. Nuclear Regulatory Commission 2100 Renaissance Blvd., Suite 100 King of Prussia, PA 19406-2713 Regional Administrator, Region II U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Avenue, NE Suite 1200 Atlanta, Georgia 30303-1257 Regional Administrator, Region III U. S. Nuclear Regulatory Commission 2443 Warrenville Road Suite 210 Lisle, IL 60532-4352 Mr. J. E. Reasor, Jr.Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.Suite 300 Glen Allen, Virginia 23060 NRC Senior Resident Inspector North Anna Power Station NRC Senior Resident Inspector Surry Power Station NRC Senior Resident Inspector Millstone Power Station NRC Senior Resident Inspector Kewaunee Power Station V. Sreenivas NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G-9A 11555 Rockville Pike Rockville, Maryland 20852-2738 Serial No.12-519 Docket Nos. 50-338/339/280/281/336/423/305 Page 3 of 3 K. R. Cotton NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G-9A 11555 Rockville Pike Rockville, Maryland 20852-2738 J. S. Kim NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 C-2A 11555 Rockville Pike Rockville, Maryland 20852-2738 K. D. Feintuch NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 H-4A 11555 Rockville Pike Rockville, Maryland 20852-2738 Serial No.12-519 Docket Nos. 50-338/339 Enclosure I Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System North Anna Power Station Units 1 and 2 Virginia Electric and Power Company (Dominion)

Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units I and 2 Bulletin Response The Bulletin response is arranged in the following way:* System Description

-Items 2, 1.d, 2.a, 2.c* System Protection

-1, 1.a, 2.b, 2.d , Consequences

-11.b, 1.c, 2.e , Attachment 1 -Simplified One-Line Diagram , Attachment 2 -Tables o Table 1 -ESF Buses Continuously Powered From Offsite Power Source(s)o Table 2 -ESF Buses Not Continuously Powered From Offsite Power Source(s)o Table 3A-3D -ESF Buses Major Loads o Table 4 -Offsite Power Transformers o Table 5 -Protective Devices System Description Items 2, 1.d, 2.a, 2.c request system information and are addressed in this section: 2. Briefly describe the operating configuration of the ESF buses (Class 1E for current operating~plants or non-Class 1E for passive plants) at power (normal operating condition).

See Attachment 1, for a simplified one-line diagram of the station electrical distribution system.As depicted in Attachment 1, there are four 4160VAC Engineered Safeguards Features (ESF)buses (two per unit) at North Anna Power Station (NAPS) (1H, 1J, 2H, and 2J). In the normal operating configuration (at power), the ESF buses are powered from their preferred power source, which are the three reserve station service transformers (RSSTs) (A, B, and C). Each RSST receives power at 34.5kV from three 34.5kV buses (Bus 3, 4, and 5), which are separated by normally open circuit breakers with open disconnect switches.The 34.5kV buses receive power from three transformers (XFMR 1, 2 and 3), which have winding configurations as described in Table 4 (XFMR 1, XFMR 2, and XFMR 3) that are provided power from the point of interconnect on the 500kV and 230kV levels.500-34.5kV XFMR 1 in the switchyard normally supplies 34.5kV Bus 3. Bus 3 normally supplies 34.5-4.16kV RSST-C which is the preferred source for ESF buses 1H and 2J.500-34.5kV XFMR 2 in the switchyard normally supplies 34.5kV Bus 4. Bus 4 normally supplies 34.5-4.16kV RSST-B which is the preferred source for ESF bus 2H.Enclosure 1 -Page 1 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 230-34.5kV XFMR 3 in the switchyard normally supplies 34.5kV Bus 5. Bus 5 normally supplies 34.5-4.16kV RSST-A which is the preferred source for ESF Bus 1J.The above alignment is typical. Only 2 of the 3 34.5kV buses are required for operation.

It is permissible to supply RSST-A and RSST-B from a single source. However, RSST-C is maintained separate from RSST-A and RSST-B in order to maintain separation of the associated ESF buses in accordance with Technical Specifications (TS). This response is based on the normal alignment.

The RSSTs are normally aligned to the ESF buses and the intake circulating water systems.The RSSTs also have the capacity to drive the station auxiliaries in the event of a loss of the normal ac power supply. The normally open feeder breakers from the RSSTs to the normal station service buses (1A, 1 B, 10C, 2A, 2B, and 20) are also depicted in Attachment 1.Although the typical ESF bus alignment is as described above, the Unit 1 ESF buses have cross tie ability to the station service buses (1H to 1B & 1J to 2B). This cross tie alignment is considered a fully qualified offsite power source to the respective Unit 1 ESF buses. This cross tie alignment is noted as one situation where an ESF bus arrangement can be directly connected to the main generators.

The cross tie alignment is typically used only for maintenance evolutions where it would be required to switch RSST-A out online or to perform upstream 4160VAC breaker testing. Since the degraded voltage (DV) and under voltage (UV) protection for the ESF buses is instrumented from the respective ESF buses, offsite source alignment to a cross tie configuration results in the protection scheme being identical to the normal operating configuration protection schemes.1.d. Describe the offsite power transformer (e.g., start-up, reserve, station auxiliary) winding and grounding configurations.

See Attachment 2, Table 4 for offsite power transformer winding and grounding configurations.

2.a. Are the ESF buses powered by offsite power sources? If so, explain what major loads are connected to the buses including their ratings.As described above for item (2), during normal power operating configurations, the ESF buses are powered by their preferred offsite power sources. See Attachment 2, Tables 1 and 2 for the ESF bus power sources.Under normal operation configurations, ESF bus loading is different than for accident conditions.

The 4160VAC loads that are branch fed from the respective ESF buses are listed in Attachment 2, Table 3. However, the majority of the noted loads are only connected to the ESF buses during accident conditions.

Enclosure 1 -Page 2 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 2.c. Confirm that the operating configuration of the ESF buses is consistent with the current licensing basis. Describe any changes in offsite power source alignment to the ESF buses from the original plant licensing.

The electrical distribution system lineup during normal plant operating conditions is the ESF buses powered from offsite power through the RSSTs and is consistent with the current licensing basis. Also, the cross tie alignment to the Unit 1 ESF buses as described in the System Description section is consistent with the current licensing basis. No changes to the offsite power source alignment were identified through this evaluation.

Attachment 2, Table 1 identifies the normal arrangements from the RSSTs to the Unit 1 and Unit 2 ESF buses.System Protection Items 1, l.a, 2.b, 2.d request information regarding electrical system protection and will be addressed in this section: 1. Given the requirements above, describe how the protection scheme for ESF buses (Class 1E for current operating plants or non-Class 1E for passive plants) is designed to detect and automatically respond to a single-phase open circuit condition or high impedance ground fault condition on a credited offsite power circuit or another power sources.Consistent with the current licensing basis and 1 OCFR50, Appendix A, GDC 17, the existing safety related protective circuitry will separate the ESF buses from a connected failed source due to a loss of voltage or a sustained, balanced degraded grid voltage.Although the protection scheme at NAPS was not designed to detect and automatically respond to a single-phase open circuit condition on a credited offsite power circuit, preliminary analysis has shown that in some cases evaluated, the protection schemes will separate the ESF buses in an open phase condition and isolate the affected offsite power source, automatically transferring power to an onsite alternate supply (i.e., Emergency Diesel Generator).

An evaluation of the Byron event has been performed to determine the capability of existing NAPS safety related under voltage relays to detect and automatically respond to single-phase open circuit conditions of off-site power supplies to 4.16kV Class 1 E vital buses. Regarding the ability of the NAPS ESF power distribution system UV relays to detect and respond to an open phase condition, the evaluation is based on analysis performed using EMPT based computer modeling software (PSCAD). Engineering has evaluated the results of the PSCAD analysis using published materials and the ETAP computer code, where possible, to ensure that the results are reasonable.

The NAPS under voltage relay scheme is similar to that described in IEEE Standard 741. The first level of under voltage protection is provided by the loss of voltage relays whose function is to detect and disconnect the Class 1 E buses from the preferred power source upon a total loss of voltage. The UV relay setting equals 50.8V-SEC x 35/1 equals 1778-VPRI (phase-to-neutral Enclosure 1 -Page 3 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 voltage).

Two-of-three UV relays are required to sense the loss voltage condition to initiate tripping of the preferred offsite power supply after 2 seconds.The second level of under voltage protection is provided by the degraded voltage (DV) relays, which are set to detect a low-voltage condition.

The DV relay setting equals 61.8V-SEC x 35/1 equals 2163-VPRI (phase-to-neutral voltage).

Two-of-three DV relays are required to sense the low voltage condition to initiate tripping of the preferred offsite power source after 56 seconds, or after 7.5 seconds coincident with a safety injection signal. The under voltage/degraded relays are connected phase-to-neutral on the secondary of wye-grounded/wye-grounded connected 4200-120V potential transformers.

To determine the ability to detect an open phase from the preferred offsite power source, the phase-to-neutral voltage for each phase was required to be modeled for that condition.

Three scenarios were analyzed to determine the vulnerability at NAPS of an open primary transformer phase condition.

A summary of the results is as follows: 1. An open phase on the primary of one of the 34.5-4.16kV RSSTs will actuate the applicable ESF bus 74% UV relay circuit and separate from offsite power in 2 seconds. The Station Service Transformers (SSTs) utilized for the cross ties (1H to 1B & 1J to 2B) are connected similarly to the normal supply RSSTs (delta-wye low resistance grounded).

In a cross tie configuration, the loss of a phase will be similar for either alignment.

The SST primaries are supplied via the 22kV main generator isolated phase buses and are not subject to a loss of phase. Due to the connection similarities, the effect of a loss of a primary phase of either an SST or RSST would be similar. The results are unchanged assuming that the open transformer terminal is solidly grounded.2. An open phase on the primary of 230-34.5kV XFMR 3 will result in a voltage imbalance on the applicable ESF bus that will not be automatically isolated by the UV or DV relays. The loss of phase would immediately render the offsite power source and applicable ESF inoperable.

Like Byron, the voltage imbalance would impact operation of loads on the affected bus and would ultimately be self revealing.

Unlike the Byron event, only one of two ESF buses per unit would potentially be affected.

230-34.5kV XFMR 3 in the switchyard normally supplies 34.5kV Bus 5. Bus 5 normally supplies the local 34.5kV distribution circuit and 34.5-4.16kV RSST-A, which is the preferred source for ESF Bus 1J. XFMR 3 is connected delta/wye-grounded and RSST-A is connected delta/wye-low resistance-grounded.

The loss of one phase supplying the 230-34.5kV XFMR 3 will result in imbalanced voltages at the 34.5kV bus which, will in-turn, impact the 1J 4160-Volt ESF Bus.XFMR 3 was originally installed as a backup to XFMR 1 or XFMR 2. As stated, it normally supplies RSST-A. However, it is permissible to supply RSST-A and RSST-B or RSST-C from XFMR 3 at any time. It is not permissible to supply both ESF buses for an operating unit from a common offsite source. The open phase condition applies to the leads from the 230kV bus to the transformer.

The bus design ensures that an open phase on the bus or beyond the switchyard does not impact the transformer voltage.Considering the A-phase opens (other single phase open is similar), the summary provided below describes the UV/DV relay sensing abilities.

It should be noted that due to phase winding configurations, an open 230kV A-Phase results in 4.16kV B-Phase dropout.Enclosure 1 -Page 4 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units I and 2 UV Relays [50.8 x 35/1 equals 1778V-PRIMARY LN]The B-Phase UV relay will drop-out due to the loss of voltage on that phase. However, the A-Phase and C-Phase UV relays will not drop-out and the trip circuit will not actuate since only 1 of 3 relays will drop-out (2 of 3 required).

DV Relays [61.8 x 35/1 equals 2163V-PRIMARY LN]The B-Phase DV relay will drop-out due to the loss of voltage on that phase. The A-Phase and C-Phase DV relays will also drop-out starting the 60 second (non-SI) timer before tripping the preferred source circuit breaker. Prior to completion of the 60 second timer the RSST automatic load tap changer (LTC) is expected to correct the overall low voltage and likely prevent the automatic circuit breaker trip; the A-Phase and C-Phase DV relays will pick-up and the circuit will not actuate since only 1 of 3 relays will remain dropped out (2 of 3 required).

Expected Control Room Annunciator alarms include both the 4kV Bus Blown Fuse Alarm and ESF Bus UV/DV Alarm (after 15 second time delay). The RSST automatic LTC is expected to attempt to correct the low voltage and will likely clear the ESF Bus UV Alarm.However due to the very low voltage on one phase, the 4kV Bus Blown Fuse Alarm is expected to remain in alarm.The results are unchanged assuming that the open transformer terminal is solidly grounded.3. An open phase on the primary of 500-34.5kV XFMR 1 (or 2) will result in a relatively small imbalanced voltage condition at the 34.5kV and 4.16kV levels that will not be detected by the UV or DV relays. In this case, the ESF bus(es) and offsite power source remain operable and capable of performing their design functions.

Considering the A-Phase opens (other single phase open is similar), a voltage mismatch of 2.1% at the ESF bus(es) would occur. A voltage mismatch of this magnitude will not affect ESF bus operation nor prevent the respective ESF buses from performing as designed during normal or accident loading situations.

The open phase condition applies to the leads from the 500kV bus to the transformer.

The bus design ensures that an open phase on the bus or beyond the switchyard does not impact the transformer voltage.If the open phase on the primary of 500-34.5kV XFMR 1 (or 2) is solidly grounded, this will result in a voltage imbalance on the applicable ESF bus(es) that will initially be detected by the UV or DV relays. The RSST automatic LTC is expected to attempt to correct the low voltage and the DV circuit will reset prior to separation of the ESF bus. The loss of phase would immediately render the offsite source and applicable ESF bus inoperable.

Like Byron, the voltage imbalance would impact operation of loads on the affected bus and would at some point be self-revealing.

Unlike the Byron event described in the IER, only one of two ESF buses per unit would potentially be affected.

Expected Control Room Annunciator alarms include 4kV Bus Blown Fuse Alarm and Emergency Bus UV Alarm (after 15 second Enclosure 1 -Page 5 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 time delay, but will reset). Due to the very low voltage on one phase, the 4kV Bus Blown Fuse Alarm could remain.As described above, the analysis included solidly grounding the transformer high side terminal in conjunction with an open phase. A high impedance ground was not evaluated for the open-phase condition.

For a high impedance ground with the three phases intact, protective circuit actuation is expected.

At NAPS, the 500kV, 230kV, and 34.5kV buses are effectively grounded.

The 4.16kV buses are low resistance grounded.

With the low impedance grounding configuration at NAPS, line to neutral short circuit current is sufficiently high when a high impedance ground fault is introduced.

This ensures that protective relays isolate grounded energized phases. Ground over current relay settings typically have a minimum bolted-fault to trip-setting ratio of 2:1 to account for impedance of the fault. This is consistent with Industry practice.

No further evaluation of this condition is warranted.

1.a. The sensitivity of protective devices to detect abnormal operating conditions and the basis for the protective device setpoint(s).

Consistent with the current licensing basis and GDC 17, existing electrical protective devices are sufficiently sensitive to detect design basis conditions, such as a loss of voltage or a degraded voltage, but were not designed to detect a single open phase condition in all offsite source configurations analyzed.See Attachment 2, Table 5 for protective devices and the basis for the device setpoint(s).

2.b. If the ESF buses are not powered by offsite power sources, explain how the surveillance tests are performed to verify that a single-phase open circuit condition or high impedance ground fault condition on an off-site power circuit is detected.The ESF buses at NAPS are powered by offsite power sources.2.d. Do the plant operating procedures, including off-normal operating procedures, specifically call for verification of the voltages on all three phases of the ESF buses?Daily Station Operations rounds procedures verify the presence of each of the three phases of voltage on the ESF buses. Station Operations annunciator response procedures are being modified to include instruction for phase verification when control room annunciator alarms "4kV Bus Blown Fuse Alarm" and "Emergency Bus UV" actuate. The control room annunciators are expected to alarm when there is an open phase in the switchyard.

The additional instruction is intended to assist Operations personnel with diagnosing the open phase condition and further instructs Operations personnel to manually separate from the affected offsite source.Furthermore, as a result of the Byron event, the weekly walk down procedure for switchyard inspections is being revised with specific instruction for inspecting the high-side connections to the offsite sources in the switchyard.

Enclosure 1 -Page 6 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 Consequences Items 1 .b, 1.c, 2.e request information regarding the consequences of an event and are addressed in this section: 1.b. The differences (if any) of the consequences of a loaded (i.e., ESF bus normally aligned to offsite power transformer) or unloaded (e.g., ESF buses normally aligned to unit auxiliary transformer) power source.As described in the System Description portion of this response, the normal at power operating configuration is such that the ESF buses are powered from their preferred power sources which are the three RSSTs. In this configuration, the RSSTs are considered loaded. There is no configuration at NAPS where an unloaded source is awaiting command to transfer to an ESF bus.The System Protection portion of this response identified three scenarios that were analyzed to determine the vulnerability of NAPS to an open primary transformer phase condition.

The following discussion describes the loading characteristics of the subject transformers during the three scenarios:

1. An open phase (ungrounded or solidly grounded) on the primary of one of the 34.5-4.16kV RSSTs (or primary of 1 B or 2B SSTs during cross tie configurations) will result in actuation of the applicable ESF bus 74% UV relay circuit and will result in separation from offsite power in 2 seconds. This scenario remains valid for both normal and accident loading conditions.

2. An open phase (ungrounded or solidly grounded) on the primary of 230-34.5kV XFMR 3 will resultin a voltage imbalance on the applicable ESF bus that will not be automatically isolated by the UV or DV relays. In this case the ESF bus(es) and offsite power source are rendered inoperable.

This scenario remains valid for both normal and accident loading situations.

Furthermore, the noted Control Room Annunciator alarms (4kV Bus Blown Fuse Alarm and Emergency Bus UV Alarm) are expected for both normal and accident loading conditions.

3. An open phase (ungrounded) on the primary of 500-34.5kV XFMR 1 (or 2) will result in a relatively small imbalanced condition at the 34.5kV and 4.16kV levels that will not be detected by the UV or DV relays. In this case, the ESF bus(es) and offsite power source remain operable and capable of performing their design functions for both normal and accident loading conditions.

An open phase (solidly grounded) on the primary of 500-34.5kV XF'MR 1 (or 2) results in a voltage imbalance on the applicable ESF bus that will not be automatically isolated by the UV or DV relays. In this case the ESF bus(es) and offsite power source are rendered inoperable.

This scenario remains valid for both normal and accident loading situations.

Furthermore, the noted Control Room Annunciator alarms (4kV Bus Blown Fuse Alarm and Emergency Bus UV Alarm) are expected for both normal and accident loading conditions.

Enclosure 1 -Page 7 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units I and 2 1.c. If the design does not detect and automatically respond to a single-phase open circuit condition or high impedance ground fault condition on a credited offsite power circuit or another power source, describe the consequences of such an event and the plant response.NAPS is vulnerable to such an event. There are, however, key differences from the Byron event regarding physical construction, electric plant line-ups, and design that minimize the impact if a similar event were to occur at NAPS.1. An open phase (ungrounded or solidly grounded) on the primary of one of the 34.5-4.16kV RSSTs (or primary of 1B or 2B SSTs during cross tie configurations) will result in actuation of the applicable ESF bus 74% UV relay circuit and will result in separation from offsite power in 2 seconds. The impacted ESF bus will align to the EDG and the other redundant train will remain on offsite power.2. An open phase on the primary of XFMR 3 (ungrounded or solidly grounded) will result in an inoperable ESF bus that would not auto separate from the preferred source; the 1J ESF Bus being source fed from RSST-A, Bus 5, and XFMR 3. In this case, however, as identified previously, main control room annunciators 4kV Bus Blown Fuse Alarm and Emergency Bus UV Alarm are expected to actuate if an open phase were to occur on the high-side of XFMR 3. Corrective action is being taken to ensure that the Operations annunciator response procedures are revised to provide clarified guidance for the noted condition.

If the condition were to occur to XFMR 3, only one ESF bus for Unit 1 would be affected (1 J) since the redundant ESF bus (1 H) is source fed from an isolated offsite source (RSST-C, Bus 3, and XFMR 1). If this type of fault were to occur, the main effect on the plant would be increased thermal heating of the 1 J ESF Bus loads due to the voltage imbalance.

A timely response to the expected annunicators by Operations personnel trained to diagnose the failure would minimize the effect on running equipment.

Therefore, the Byron event necessitated the need for additional guidance in the form of annunciator response procedures and training for NAPS Operations personnel.

Preparations for training are being facilitated from corrective actions that were initiated in response to the Byron event.3. An open phase (ungrounded) to XFMR 1 or XFMR 2 is undetectable, however, will not limit the ability of the offsite source to supply power to the affected ESF buses in both normal and accident loading conditions.

Only a small voltage imbalance resulted, which would not render the affected ESF bus inoperable.

Ultimately, if the event occurred to XFMR 1, only ESF Buses 1 H and 2J would be affected, which leaves the other two unit specific redundant buses (1J and 2H) unaffected.

If the subject fault occurred to XFMR 2, only the 2H ESF Bus would be affected leaving the other Unit 2 ESF bus (2J) unaffected.

The robust maintenance program and walk downs, which are performed by subject matter experts, will ensure the condition would not be undetected for a prolonged period. Prior to the Byron event, the Dominion Transmission and Distribution weekly walk down procedure did not specifically mandate high-side phase connection inspections.

However, corrective action has been instituted to ensure phase connections to the offsite circuits are inspected on a weekly frequency.

Enclosure 1 -Page 8 of 18

'Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 An open phase (solidly grounded) on the primary of XFMR 1 (or 2) will result in an inoperable emergency bus with the inability to auto separate from the preferred source; the 1 H and 2J (or 2H) ESF buses being source fed from RSST-C (or RSST-B), Bus 3 (or 4), and XFMR 1 (or 2). In this case, however, as identified previously, main control room annunciators 4kV Bus Blown Fuse Alarm and Emergency Bus UV Alarm are expected to actuate. Corrective action is being taken to ensure that the Operations annunciator response procedures are revised to provide clarified guidance for the noted condition.

If the condition were to occur to XFMR 1 (or 2), only one ESF bus for a unit would be affected.

If this type of fault were to occur, the main effect on the plant would be increased thermal heating of the ESF bus loads due to the voltage imbalance.

A timely response to the expected annunicators by Operations personnel trained to diagnose the failure would minimize the effect on running equipment.

Therefore, the Byron event necessitated the need for additional guidance in the form of annunciator response procedures and training for NAPS Operations personnel.

Preparations for training are being facilitated from corrective actions that were initiated in response to the Byron event.2.e. ff a common or single offsite circuit is used to supply redundant ESF buses, explain why a failure, such as a single-phase open circuit or high impedance ground fault condition, would not adversely affect redundant ESF buses.Item 2.e is not applicable since NAPS does not use a common or single offsite source to supply redundant ESF buses.Enclosure 1 -Page 9 of 18

Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 Attachment 2 -Tables Table 1 -ESF Buses Continuously Powered From Offsite Power Source(s)o :J conne~cted ol.t, : _;Descriptio~nof O~ffsite Power ESFbssonee o Original icensing ba sis-Suoffsite~powelr (normal (I)Suce Configriration configuraiontion)

RSST "C" 1 H ESF Bus Y RSST "A" 1J ESF Bus Y RSST "B" 2H ESF Bus Y RSST "C" 2J ESF Bus Y Table 2 -ESF Buses, Not Continuously Powered From Offsite Power Source(s)De~cipio oOfsie~~oe Original licensing basis Descriti~ti I ýfft Power offsite power (nrmnal Source Configurati6n<ortncniin configuration

(/N.)Cross tie to 1 B Station Service Bus 1H Y Cross tie to 2B Station Service Bus IJ Y'7 Enclosure 1 -Page 11 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 Table 3A,- ESF Bus IH Major Loads Bus Load Mark Load Description -Normal Running Load X Rating (HP) unless,, othierwise noted 1 H, 01-FW-P-3A Motor Driven Aux Feed Pump 450 1H 01-SW-P-4 Aux Service Water Pump 500 X [There are 4 Service Water Pumps. 1 on 1J Train, 1 on 1H 1H 01-SW-P-1A Service Water Pump Train, 1 on 2J Train, 1 on 2H 500 Train. Two pumps run (common system).]X (There are 3 Charging Pumps. 1 on 1J Train, 1 on 1H 1H 01-CH-P-1A Charging Pump Train, and 1 swing pump that .900 can be aligned to either 1 H or 1J. Typically only 1 of 3 run)X (There-are 3 Charging Pumps. 1 on 1J Train, 1 on 1H 1H 01-CH-P-IC Swing Charging Pump Train, and 1 swing pump that 900 can be aligned to either 1 H or_ __ .. ..1J. Typically only 1 of 3 run)1H 01-EE-ST-1H

& 01-EE-ST-TO 4160/480VAC X 1.333 (MVA) & 1.333 1H1 DISTRIBUTION (MVA)1H_ 01-SI-P-1A Low Head SI Pump 250 1 H 01 -RS-P-2A Outside Recirc Spray Pump 400 X (There are 2 Component 1H 01-CC-P-lA Component Cooling Pump Cooling Pumps. 1 on 1J Train 600: and 1 on 1H Train. Typically only_ _ iof 2 run)1H 01 -RH-P-1A -Residual Heat Removal -Pump _ _ _ _ _ 300 _Enclosure 1 -Page 12 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 Table 3B -ESF Bus IJ Major Loads~Rating (HP) unless Bus- Load Mark # Load Description Normal Running Load = X otherwise noted 1J 01-FW-P-3B Motor Driven Aux Feed Pump 450 X [There are 4 Service Water Pumps. 1 on 1J Train, 1 on 1H 1J 01-SW-P-1B Service Water Pump Train, 1 on 2J Train, 1 on 2H 500 Train. Two pumps run (common system).]X (There are 3 Charging Pumps. 1 on 1J Train, 1 on 1H 1J 01-CH-P-1B Charging Pump Train, and 1 swing pump that 900 can be aligned to either 1H or 1J. Typically only 1 of 3 run)X (There are 3 Charging Pumps. 1 on 1J Train, 1 on 1H 1J 01-CH-P-1C Swing Charging Pump Train, and 1 swing pump that 900 can be aligned to either 1H or 1J. Typically only 1 of 3 run)01-EE-ST-1J

& 01-EE-ST-TO 4160/480VAC 1.333 (MVA) &1J1 DISTRIBUTION

_ 0.75(MVA)1J 01-SI-P-1B Low Head SI Pump 250 1J 01-RS-P-2B

-Outside Recirc Spray Pump 400 X (There are 2 Component 1J 01-CC-P-1B Component Cooling Pump Cooling, Pumps. 1 on J Train 600 and 1 on H Train. Typically only 1 of 2 run)Residual Heat Removal 3 1J 01-RH-P-lB P300 Enclosure 1 -Page 13 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 Table 3C -ESF Bus 2H Major Loads'. .. : irl~r .-i : (HP) unless Bus Load Mark,#,"

Load Description Normal Running Load = X Rting nles otherwise noted 2H 02-FW-P-3A Motor Driven Aux Feed Pump 450 2H 02-SW-P-4 Aux Service Water Pump -- 500 X [There are 4 Service Water Pumps. 1 on 1J Train, 1 on 1H 2H 02-SW-P-1A Service Water Pump Train, 1 on 2J Train, 1 on 2H 500 Train. Two pumps run (common system).]X (There are 3 Charging Pumps. 1 on 2J Train, 1 on 2H 2H 02-CH-P-1A Charging Pump Train, and 1 swing pump that 900 can be aligned to either 2H or 2J. Typically only 1 of 3 run)X (There are 3 Charging Pumps. 1 on 2J Train, 1 on 2H 2H 02-CH-P-1C Swing Charging Pump Train, and 1 swing pump that 900 can be aligned to either 2H or 2J. Typically only 1 of 3 run)2H 02-EE-ST-2H

& 02-EE-ST-TO 4160/480VAC X 1.333 (MVA) & 1.333 2H1 DISTRIBUTION (MVA)2H SI-P-1A Low Head SI Pump -- 250 2H 02-RS-P-2A Outside Recirc Spray Pump -- 400 X (There are 2 Component 2H 02-CC-P-lA Component Cooling Pump Cooling Pumps. 1 on 2J Train 600 and 1 on 2H Train. Typically only 1 of 2 run)202-RH-P1A Residual Heat Removal 300 2H___ _ 02-RH-P-1A

_ _ _ u p _ __ _ __ _ __ _ __ _ _ _3__ __ _ __ _Enclosure 1 -Page 14 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 Table 3D -ESF Bus 2J Major Loads... ... ." " ....Rating (HP) unless Bus Load Mark # Load Description Normal Running Load=X R ( u_________________________ .otherwise noted 2J 02-FW-P-3B Motor Driven Aux Feed Pump 450 X [There are 4 Service Water Pumps. 1 on 1J Train, 1 on 1H 2J 02-SW-P-1 B Service Water Pump Train, 1 on 2J Train, 1 on 2H 500 Train. Two pumps run (common system).]X (There are 3 Charging Pumps. 1 on 2J Train, 1 on 2H 2J 02-CH-P-1 B Charging Pump Train, and 1 swing pump that 900 can be aligned to either 2H or 2J. Typically only 1 of 3.run)X (There are 3 Charging Pumps. 1 on 2J Train, 1 on 2H 2J 02-CH-P-1C Swing Charging Pump Train, and 1 swing pump that 900 can be aligned to either 2H or 2J. Typically only 1 of 3 run)TO 41 60/480VAC 1.333 (MVA) &2J 02-EE-ST-2J

& 02-EE-ST-2J1 TRIBUTIONX 0.75 (MVA)DISTRIBUTION 0.75 (MVA)2J 02-SI-P-1B Low Head SI Pump 250 2J 02-RS-P-2B Outside Recirc Spray Pump 400 X (There are 2 Component 2J 02-CC-P-1 B Component Cooling Pump Cooling Pumps. 1 on 2J Train 600 and 1 on 2H Train. Typically only 1 of 2 run)2J 02-RH-P-1B Residual Heat Removal 300 2J I ~Pump [-Enclosure 1 -Page 15 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 Table 4 -Offsite Power TransformersTransformer Winding Configuiration"'

MVA ize .A' Voltage Rating Grounding Configuaion (High.Side:LowSide)

A..A) (Primary/Secondary):

34.5kV Bus is Effectively Grounded.RSST "A" Delta:Wye Low Resistance 20.16/26.88/33.6 34.5kV/4.16kV RSST 'A" is Wye Low Resistance Grounded (OA/FA/FOA)

Grounded (on secondary).

Delta:Wye Low Resistance 20.16/26.88/33.6 34.5kV Bus is Effectively Grounded.RSST "B" Grounded (Oa/F/FOA) 34.5kV/4.16kV RSST "B" is Wye Low Resistance Grounded (on secondary).

34.5kV Bus is Effectively Grounded.RSST "C" Delta:Wye Low Resistance 20.16/26.88/33.6 34.5kV/4.16kV RSST "C" is Wye Low Resistance Grounded (OAIFA/FOA)

Grounded (on secondary).

SST "1 B" Delta:Wye Low Resistance 16.8/22.4 22kV/4.4kV SST "I B" is Wye Low Resistance Grounded (ONAN/ONAF)

Grounded (on secondary).

SST "2B" Delta:Wye Low Resistance 16.8/22.4 22kV/4.4kV SST "2B" is Wye Low Resistance Grounded (ONAN/ONAF)

Grounded (on secondary).

500kV bus is Effectively Grounded.6 6 XFMR 1 is Wye Solid'Grounded (on XFMR 1 Wye Grounded:Delta 512.5kV/36.5kV primary).

XFMR 1 is grounded via Nzig-zag ground bank (on secondary).

500kV bus is Effectively Grounded.9 XFMR 2 is Wye Solid Grounded (on XFMR 2 Wye Grounded:Delta 67.2/89.6/112 512.5kV/36.5kV primary).

XFMR 2 is grounded via S(ONAN/ONAF/ONAF) zig-zag ground bank (on secondary).

67.2i89.6/i112 230kV Bus is Effectively Grounded.XFMR 3 Delta:Wye Grounded (ONAN/ONAF/ONAF 230kV/36.5kV XFMR 3 is Wye Grounded (on secondary).

Enclosure 1 -Page 16 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 Table 5 -Protective Devices::Protection-Zone Protective DeVice. SLetpi-t Sensvity of Basis For Setpoint Loic Nom'ifnal (VAC Device (VAC)Drop out to actuate upon a sustained ESF bus Degraded 1 H ESF Bus Degraded Degraded Voltage Relays 2 of 3 61.8 V LN-Seconary

(+/-) 0.6077 voltage of 90% nominal.graded Vo Setpoint provides a minimum voltage the ESF buses can be operated at indefinitely.

The upper bound is set to ensure that the preferred power source 1 H ESF Bus Under Voltage Loss of Voltage Relays 2 of 3 50.8 VLN-Secondary

(+/-) 2.5423 shall not be disconnected for any transient experienced during the worst case voltage profile.Drop out to actuate upon a sustained ESF bus Degraded 1J ESF Bus Degraded Degraded Voltage Relays 2 of 3 61.8 VLNSecondary

(+/-) 0.6077 voltage of 90% nominal.Voltage Setpoint provides a minimum voltage the ESF buses can be operated at indefinitely.

The upper bound is set to ensure that the preferred power source 1 J ESF Bus Under Voltage Loss of Voltage Relays 2 of 3 50.8 VLN-Secondary

(+/-) 2.5423 shall not be disconnected for any transient experienced during the worst case voltage profile.Enclosure 1 -Page 17 of 18 Serial No.12-519 Docket Nos. 50-338/339 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System North Anna Power Station Units 1 and 2 Table 5 -Protective Devices (Continued)

...""Setpoint Sensitivity of Protection Zone .Protective Device Logic. SiBasis For Setpoint Nominal (VAC), Device (VAC), Drop out to actuate upon a sustained ESF bus Degraded 2H ESF Bus Degraded Degraded Voltage Relays 2 of 3 61.8 V LN-Secondary

(+/-) 0.6077 voltage of 90% nominal.Voltage, Setpoint provides a minimum voltage the ESF buses can be operated at indefinitely The upper bound is set to ensure that the preferred power source 2H ESF Bus Under Voltage Loss of Voltage Relays 2 of 3 50.8 VLN-Secondary

(+/-) 2.5423 shall not be disconnected for any transient experienced during the worst case voltage profile.Drop out to actuate upon a sustained ESF bus Degraded 2J ESF Bus Degraded Degraded Voltage Relays 2 of 3 61.8 V LN-Secondary-0.6077 voltage of 90% nominal.Voltage Setpoint provides a minimum voltage the ESF buses can be operated at indefinitely The upper bound is set to ensure that the preferred power source 2J ESF Bus Under Voltage Loss of Voltage Relays 2 of 3 50.8 VLN.Secondary

(+1-) 2.5423 shall not be disconnected for any transient experienced during the worst case voltage profile.Enclosure 1 -Page 18 of 18 Serial No.12-519 Docket Nos. 50-280/281 ENCLOSURE 2 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units 1 and 2 Virginia Electric and Power Company (Dominion)

Serial No.12-519 Docket Nos. 50--280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units 1 and 2 Bulletin Response The Bulletin response is arranged in the following way:* System Description

-Items 2, 1.d, 2.a, 2.c* System Protection

-1, 1.a, 2.b, 2.d* Consequences

-1.b, 1.c, 2.e* Attachment 1 -Simplified One-Line Diagram* Attachment 2 -Tables o Table 1 -ESF Buses Continuously Powered From Offsite Power Source(s)o Table 2 -ESF Buses Not Continuously Powered From Offsite Power Source(s)o Table 3 -ESF Buses Major Loads o Table 4 -Offsite Power Transformers o Table 5 -Protective Devices System Description Items 2, 1.d, 2.a, 2.c request system information and are addressed in this section: 2. Briefly describe the operating configuration of the ESF buses (Class 1E for current operating plants or non-Class 1E for passive plants) at power (normal operating condition).

See Attachment 1, for a simplified one-line diagram of the station electrical distribution system.It should be noted that "Electric Power Distribution" (figure 8.3-2 from Surry Power Station (SPS) UFSAR Rev. 43.07) is being revised with respect to the completed 34.5kV Switchyard Modifications and will be updated during the next routine UFSAR revision to reflect the changes (Station Drawing 11448-FE-1A2 has already been appropriately updated within the drawing control database).

As depicted in Attachment 1, there are four 4160VAC Engineered Safeguards Features (ESF)buses (two per unit) at SPS (1 H, 1J, 2H, and 2J). The circuits that supply power to the ESF buses through Switchyard Transformers (SRT) Nos. 1, 2, and 4 are known as "primary sources." Each primary source is capable of providing power to an ESF bus on each Unit.Surry Technical Specifications (TS) require a primary source for each ESF bus, during power operations and startup. As described in the Basis for Surry TS, the primary sources are defined as the System Reserve Transformers (SRT); 500-36.5kV Transformer No. 1 and 230-36.5kV Transformer No. 2. Transformer No. 4 (230-36.5kV) serves as a backup for loads supplied by either System Reserve Transformer No. 1 or No. 2.The System Reserve Transformers supply the Reserve Station Service Transformers (RSST);SRT 1 supplies RSST A and RSST B, SRT 2 supplies RSST C. The RSSTs then feed the 4160V Transfer Buses, D, E, and F, and finally, the Transfer Buses supply the ESF Buses and, alternately, the Station Service Buses.The 34.5kV buses receive power from three transformers which have winding configurations described in Table 4 (SRT 1, SRT 2, and SRT 4) which are provided power from the point of interconnect on the 500kV and 230kV levels.Enclosure 2 -Page 1 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units 1 and 2 500-34.5kV SRT 1 in the switchyard normally supplies 34.5kV Bus 5. Bus 5 normally supplies 34.5-4.16kV RSST-A and 34.5-4.16kV RSST-B which are the preferred sources for ESF buses 1J and 2H respectively..

230-34.5kV SRT 2 in the switchyard normally supplies 34.5kV Bus 6. Bus 6 normally supplies 34.5-4.16kV RSST-C which is the preferred source for ESF buses 1H and 2J.230-34.5kV SRT 4 in the switchyard normally supplies 34.5kV Bus 7. Bus 7 is normally energized and has the capability to supply the loads serviced by SRT 1 or SRT 2.The RSSTs are normally aligned to the ESF buses and also have the necessary control logic and capacity to power certain station auxiliaries in the event of a loss of the normal ac power supply. The normally open feeder breakers from the RSSTs to the normal station service buses (1A, 1B, lC, 2A, 2B, and 2C) are also depicted in Attachment 1.1.d. Describe the off-site power transformer (e.g., start-up, reserve, station auxiliary) winding and grounding configurations.

See Attachment 2, Table 4 for offsite power transformer winding and grounding configurations.

2.a. Are the ESF buses powered by off-site power sources? If so, explain what major loads are connected to the buses including their ratings.As described above for item (2), during normal power operating configurations, the ESF buses are powered by their preferred-site power sources. See Attachment 2, Tables 1 and 2 for the ESF bus power sources.Under normal operation configurations, ESF bus loading is different than for accident conditions.

The 4160VAC loads that are branch fed from the respective ESF buses are listed in Attachment 2, Table 3. However, the majority of the noted loads are only connected to the ESF buses during accident conditions.

2.c. Confirm that the operating configuration of the ESF buses is consistent with the current licensing basis. Describe any changes in off-site power source alignment to the ESF buses from the original plant licensing.

The electrical distribution system lineup during normal plant operating conditions is the ESF buses powered from offsite power through the RSSTs and is consistent with the current licensing basis. No changes to the offsite power source alignment were identified through this evaluation.

Attachment 2, Table 1 identifies the normal arrangements from the RSSTs to the Unit 1 and Unit 2 ESF buses.System Protection Items 1, 1.a, 2.b, 2.d request information regarding electrical system protection and will be addressed in this section: Enclosure 2 -Page 2 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units 1 and 2 1. Given the requirements above, describe how the protection scheme for ESF buses (Class 1E for current operating plants or non-Class IE for passive plants) is designed to detect and automatically respond to a single-phase open circuit condition or high impedance ground fault condition on a credited offsite power circuit or another power sources.Consistent with the current licensing basis and 10CFR50, Appendix A, GDC 17, the existing safety related protective circuitry will separate the ESF buses from a connected failed source due to a loss of voltage ora sustained, balanced degraded grid voltage.Although the protection scheme at SPS was not designed to detect and automatically respond to a single-phase open circuit condition on a credited offsite power circuit, preliminary analysis has shown that, in some cases evaluated, the protection schemes will separate the ESF buses in an open phase condition and isolate the affected offsite power source/automatically transferring power to an onsite alternate supply (i.e., Emergency Diesel Generator).

An evaluation of the Byron event has been performed to determine the capability of existing SPS safety related under voltage relays to detect and automatically respond to single-phase open circuit conditions of offsite power supplies to 4.16kV Class 1E vital buses. Regarding the ability of the SPS ESF power distribution system under voltage (UV) relays to detect and respond to an open phase condition, the evaluation is based on analysis performed using EMPT based computer modeling software (PSCAD). Engineering has evaluated the results of the PSCAD analysis using published materials and the ETAP computer code, where possible, to ensure that the results are reasonable.

The SPS ESF under voltage relay scheme is similar to that described in IEEE Std 741.The first level of under voltage protection is provided by the loss of voltage relays whose function is to detect and disconnect the Class 1 E buses from the preferred power supply upon a total loss of voltage (75% of 4160V). The UV relay setting equals 51.47V-SEC x 35/1 equals 1801VPRI (phase-to-neutral voltage).

Two-of-three UV relays are required to sense the loss of voltage condition to initiate tripping of the preferred offsite power supply after 2 seconds.The second level of under voltage protection is provided by the degraded voltage (DV) relays, which are set to detect a low-voltage condition (92.7% of 4160V). The DV relay setting equals 63.6V-SEC x 35/1 equals 2226V-PRI (phase-to-neutral voltage).

Two-of-three DV relays are required to sense the low voltage condition to initiate tripping of the preferred offsite power source after 60 seconds or after 7 second coincident with a safety injection signal. The LJV and DV relays are connected phase-to-neutral on the secondary of wye-grounded/wye-grounded connected 4200-120V potential transformers.

To determine the ability to detect an open phase from the preferred offsite power supply, the phase-to-neutral voltage for each phase was determined for that condition.

Three scenarios were analyzed to assess the vulnerability of an open primary transformer phase condition at SPS. A summary of the results is as follows: 1. An open phase on the primary of one of the 34.5-4.16kV RSSTs will actuate the 75% UV relay circuit of the applicable ESF bus and separate from offsite power in 2 seconds. The results are unchanged assuming that the open transformer terminal is solidly grounded.Enclosure 2 -Page 3 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units I and 2 2. An open phase on the primary of the 230-34.5kV Transformer No. 2 (or No. 4) will result in a voltage imbalance on the applicable ESF bus(es) that will not be automatically isolated by the UV or DV relays. After 10 seconds, the Emergency Bus DV Control Room Annunciator will actuate but then will reset as the RSST automatic load tap changer (LTC) is expected to attempt to correct the low voltage: The loss of phase would immediately render the offsite power source and applicable ESF bus inoperable.

Like Byron, the voltage imbalance would impact operation of loads on the affected bus and would ultimately be self revealing.

Contrary to the Byron event, only one of two ESF buses per unit would potentially be affected.The open phase condition applies to the leads from the' 230kV bus to the transformer.

The ring bus design ensures that an open phase on the bus or beyond the switchyard does not impact the transformer voltage.Considering the A phase opens (any other single phase open is similar), the following summary describes the UV/DV relay sensing abilities.

It should be'noted that, due to phase winding configurations, an open 230kV A-Phase results in 4.16kV B-Phase dropout..UV Relays [51.47 x 35/1 equals 1801V-PRIMARY LN]The B-Phase UV relay will drop-out due to the loss of voltage on that phase. However, the A-Phase and C-Phase UV relays will not drop-out and this circuit will not actuate since only 1 of 3 relays will drop-out (2 of 3 required).

DV Relays [63.6 x 35/1 equals 2226V-PRIMARY LN]The B-Phase DV relay will drop-out due to the loss of voltage on that phase. The A-Phase and C-Phase DV relays will also drop-out starting the 60 second (non-SI) timer before tripping the preferred source circuit breaker. Prior to completion of the 60 second timer the RSST automatic LTC is expected to attempt to correct the low voltage and likely will prevent the automatic circuit breaker trip; the A-Phase and C-Phase DV relays will pick-up arid this circuit will not actuate since only 1 of 3 relays will remain dropped out (2 of 3 required).

The Control Room Annunciator for Emergency Bus DV will alarm at 10 seconds. The RSST automatic LTC is expected to attempt to correct the low voltage and will likely clear the ESF Bus DV Alarm.The 60 second DV timer described is based on non-accident conditions, It has not been assumed that the open phase condition occurs coincident with an accident.The results are unchanged assuming that the open transformer terminal is solidly grounded.3. An open phase on the primary of 500-34.5kV Transformer No. 1 will result in a relatively small imbalanced condition at the 34.5kV and 4.16kV levels that will not be detected by the UV or DV relays. In this case, the ESF bus(es) and offsite power supply remain operable and capable of performing their design functions.

Considering the A-Phase opens (other single phase open is similar), a voltage mismatch of 1.8% at the ESF bus(es) would occur. A voltage mismatch of this magnitude will not affect ESF bus operation nor prevent the respective ESF buses from performing as designed Enclosure 2 -Page 4 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units I and 2 during normal or accident loading situations.

The open phase condition applies to the leads from the 500kV bus to the transformer.

The ring bus design ensures that an open phase on the bus or beyond the switchyard does not impact the transformer voltage.If the open phase on the primary of 500-34.5kV Transformer

1. 1 is solidly grounded, this will result in a voltage imbalance on the applicable ESF bus(es) that will initially be detected by the DV relays. After 10 seconds, the Emergency Bus DV Control Room Annunciator will actuate but then the DV circuit will reset prior to separation of the ESF bus(es) as the RSST automatic LTC is expected to attempt to correct the low voltage. The loss of phase would immediately render the offsite source and applicable ESF bus inoperable.

Like Byron, the voltage imbalance would impact operation of loads on the affected bus and would at some point be self-revealing.

Unlike the Byron event, only one of two ESF buses per unit would potentially be affected.As described above, the analysis included solidly grounding the transformer high side terminal in conjunction with an open phase. A high impedance ground was not evaluated for the open-phase condition.

For a high impedance ground with the three phases intact, protective circuit actuation is expected.

At SPS, the 500kV, 230kV, and 34.5kV buses are effectively grounded.

The 4.16kV buses are low resistance grounded.

With the low impedance grounding configuration at SPS, line-to-neutral short circuit currents are sufficiently high when a high impedance ground fault is introduced.

This ensures that protective relays isolate grounded energized phases. Ground over current relay settings typically have a minimum bolted-fault to trip-setting ratio of 2:1 to account for impedance of the fault. This is consistent with industry practice.

No further evaluation of this condition is warranted.

1.a. The sensitivity of protective devices to detect abnormal operating conditions and the basis for the protective device setpoint(s).

Consistent with the current licensing basis and GDC 17, existing electrical protective devices are sufficiently sensitive to detect design basis conditions, such as a loss of voltage or a degraded voltage, but were not designed to detect a single open phase condition in all offsite source configurations analyzed.See Attachment 2, Table 5 for protective devices and the basis for the device setpoint(s).

2.b. If the ESF buses are not powered by offsite power sources, explain how the surveillance tests are performed to verify that a single-phase open circuit condition or high impedance ground fault condition on an off-site power circuit is detected.The ESF buses at SPS are powered by offsite power sources.Enclosure 2 -Page 5 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units I and 2 2.d. Do the plant operating procedures, including off-normal operating procedures, specifically call for verification of the voltages on all three phases of the ESF buses?Plant operating procedures are being changed to include instruction for phase verification when control room annunciator "Bus 1 H (Typical)

Degraded Voltage" actuates.

This control room annunciator is expected in the case where there is an open phase in the switchyard:

The additional instruction is intended to assist Operations personnel with diagnosing the open phase condition and further instructs Operations personnel to manually separate from the affected offsite source. Furthermore, as a result of the Byron event, daily Operations and weekly Electric Transmission walkdown procedures for switchyard inspections have been revised with specific instruction for inspecting the hi-side connections to the offsite sources in the switchyard.

Consequences Items 1.b, 1 .c, 2.e request information regarding the consequences of an event and are addressed in this section: 1.b. The differences (if any) of the consequences of a loaded (i.e., ESF bus normally aligned to offsite power transformer) or unloaded (e.g., ESF buses normally aligned to unit auxiliary transformer) power source.As described in the System Description portion of this response, the normal at power operating configuration is such that the ESF buses are powered from their preferred power source via three RSSTs. In this configuration, the RSSTs are considered loaded. There is no configuration at SPS where an unloaded source is awaiting command to transfer to an ESF bus.The System Protection portion of this response identified three scenarios that were analyzed to determine the vulnerability at SPS to an open primary transformer phase condition.

The following discussion describes the loading characteristics of the subject transformers during the three scenarios:

1. An open phase (ungrounded or solidly grounded) on the primary of one of the 34.5-4.16kV RSSTs will result in actuation of the applicable ESF Bus 75% UV relay circuit and will result in separation from offsite power in 2 seconds. This scenario remains valid for both normal and accident loading conditions.

2. An open phase (ungrounded or solidly grounded) on the primary of 230-34.5kV Transformer No. 2 or No. 4 will result in a voltage imbalance on the applicable ESF bus that will not be automatically isolated by the UV or DV relays. In this case the ESF bus(es) and offsite power source are rendered inoperable.

This scenario remains valid for both normal and accident loading situations.

Furthermore, the noted Control Room Annunciator alarm (Bus 1 H (Typical)

Degraded Voltage) is expected for both normal and accident loading conditions.

3. An open phase (ungrounded) on the primary of 500-34.5kV Transformer No. 1 will result in a relatively small imbalanced condition at the 34.5kV and 4.16kV levels that will not be detected by the UV or DV relays. In this case, the ESF bus(es) and offsite power supply Enclosure 2 -Page 6 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power' System Surry Power Station Units I and 2 remain operable and capable of performing their design functions for both normal and accident loading conditions.

An open phase (solidly grounded) on the primary-of 500-34.5kV Transformer No. 1 will result in a voltage imbalance on the applicable ESF bus that will not be automatically isolated by the UV or DV relays. In this case the ESF bus(es) and offsite power source are rendered inoperable.

This scenario remains valid for both normal and accident loading situations.

Furthermore, the noted Control Room Annunciator alarm (Bus 1 H (Typical)

Degraded Voltage) is expected for both normal and accident loading conditions.

1.c. If the design does not detect and. automatically respond to a single-phase open circuit condition or high impedance ground fault condition on a credited offsite power circuit or another power sources, describe the consequences of such an event and the plant response.SPS is vulnerable to such an event. There are, however, key differences from the Byron event regarding physical construction, electric plant line-ups, and design that minimize the impact if a similar event were to occur at SPS.1 .An open phase (ungrounded or solidly grounded) on the primary of one of the 34.5-4.16kV RSSTs will result in actuation of the applicable ESF bus 75% UV relay circuit and will result in separation from offsite power in 2 seconds. The impacted ESF bus will align to the EDG and the other redundant train will remain on offsite power.2. An open phase (ungrounded or solidly grounded) on the primary of Switchyard' Transformers No. 2 or No. 4 or an open phase (solidly grounded) of Transformer No. 1 will'result in inoperable ESF buses that would not auto separate from the preferred source. In this case, however, as identified previously, main control room annunciator "Bus 1 H (Typical)

Degraded Voltage" Alarm is expected to actuate. Corrective action is being taken to ensure that the Operations annunciator response procedure is revised to provide clarified guidance for the noted condition.

If these conditions were to occur at SPS, only one ESF bus per unit would be affected since the unit redundant ESF buses are source fed from an, independent offsite source. If this type of fault were to occur, the main effect on the plant would be increased thermal heating of the affected ESF bus loads due to the voltage imbalance.

A timely response to the expected annunicators by Operations personnel trained to diagnose the failure would minimize the effect on running equipment.

Therefore, the Byron event necessitated the need for additional guidance in theform of annunciator response procedures and training for SPS Operations personnel.

3. An open phase (ungrounded) on the primary of Transformer No. 1 is undetectable; however, Transformer No. 1 loss does not limit the ability of the offsite source to supply power to the affected ESF buses in both normal and accident loading conditions.

Only a small voltage imbalance will result, which would not render the affected ESF bus inoperable.

Ultimately, if the event occurred on Transformer No. .1, only one ESF bus per unit would be affected, which leaves the other unit specific redundant buses unaffected.

The robust maintenance program and walk downs, which are performed by subject matter experts, will ensure the condition would not be undetected for a prolonged period. Prior to the Byron event, the Enclosure 2 -Page 7 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units 1 and 2 Dominion Transmission and Distribution weekly walk down procedure did not specifically mandate high side phase connection inspections.

However, corrective action has been instituted to ensure phase connections to the offsite circuits are inspected on a daily frequency by Operations Staff and a weekly frequency by Electric Transmission Staff.2.e. If a common or single offsite circuit is used to supply redundant ESF buses, explain why a failure, such as a single-phase open circuit or high impedance ground fault condition, would not adversely affect redundant ESF buses.Item 2e is not applicable since SPS does not use a common or single offsite circuit to supply redundant ESF buses.Enclosure 2 -Page 8 of 15

Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units 1 and 2 Attachment 2 -Tables Table 1 -ESF Buses Continuously Powered From Offsite Power Source(s)D'es~crip'tjion6i , Offfsite Power ESFu'qetQ1t rigilnal' liesing basis Sp.pSru),t anfigur~ation 9f~t~e nrIco'nfigu=rati

,/N op~erating condition)

RSST "C" 1H ESF Bus Y RSST "A" 1J ESF Bus Y RSST "B" 2H ESF Bus Y RSST "C" 2J ESF Bus Y Table 2 -ESF Buses Not Continuously Powered From Offsite Power Source(s)Enclosure 2- Page 10 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units 1 and 2 Table 3 -ESF Buses Major Loads Rating (HP)Bus Load Mark # Load Description Normal Running Load X unless othenrwise noted 1 H 01-FW-P-3A Motor Driven Aux Feed Pump 400 X (There are 3 Charging Pumps. 1 on 1J Train, 1 on 1H Train, and 1 1H 01-CH-P-1A Charging Pump swing pump that can be aligned to 600 either 1H or 1J. Typically only 1 of 3 run)(There are 3 Charging Pumps. 1 on 1H or 01-CH-P.1C Swing Charging Pump 1J Train, 1 on 1H Train, and 1 swing 600 1J pump that can be aligned to either 1H Or 1J. Typically only 1 of 3 run)1H 01-EP-LCC-1H 1.000 (MVA) &1H & 01-EP-LCC-1H1 TO 4160/480VAC Distribution X 1.333 (MVA)X (There are 2 Component Cooling 1H 01-CC-P-1A Component Cooling Pump Pumps. 1 on 1J Train and 1 on 1H 600 Train. Typically only 1 of 2 run)1H 01-RH-P-1A Residual Heat Removal Pump 300 IJ 01-FW-P-3B Motor Driven Aux Feed Pump 400--(There-are 3 Charging Pumps. 1 on 1J 01-CH-P-1B Charging Pump 1J Train, 1 on 1H Train, and 1 swing 600 pump that can be aligned to either 1H or 1J. Typically only 1 of 3 run)01-EP-LCC-1J 1.000 (MVA) &iJ & 01-EP-LCC-1J TO 4160/480VAC Distribution X 1.333(MVA)(There are 2 Component Cooling 1J 01-CC-P-lB1 Component Cooling Pump Pumps. 1 on 1J Train and 1 on 1H 600' Train. Typically only 1 of 2 run)1J J 01-RH-P-1B Residual Heat Removal Pump 300 I Enclosure 2 -Page 11 of 15 Serial No.12-519, Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surrv Power Station Units 1 and 2 Table 3 -ESF.-Buses Major Loads (Continued)

Ratinig (HP)"Bus Load Mark#.o. Load Dsrpt rmal Running Load , X unless.... ... ........ .... .. .... .. .. ... ... othe rw ise noted 2H 02-FW-P-3A Motor Driven Aux Feed Pump 400 X (There are 3 Charging Pumps. 1 on 2H 02-CH-P-1A Charging Pump 2J Train, I on 2H Train, and 1 swing 600 pump that can be aligned to either 2H or 2J. Typically only 1 of 3 run)(There are 3 Charging Pumps. I on 2J 2H or Train, 1 on 2H Train, and 1 swing pump 600 2J 0thatcan be aligned to either 2H or 2J.-____Typically only 1 of 3 run)2H 02-EP-LCC-2H TO 4160/480VAC Distribution X 1.000 (MVA) && 02-EP-LCC-2H1 TD1.333 (MVA)X (There are 2 Component Cooling 2H 01-CC-P-1C Component Cooling Pump Pumps. 1 on 2J Train and 1 on 2H 600 Train. Typically only 1 of 2 run) _.2H .02-RH-P-lA Residual Heat Removal Pump 300-2J 02-FW-P-3B Motor Driven Aux Feed Pump -400 (There are 3 Charging Pumps. Von 2J 2J 02-CH-P-1IB Charging Pump* : Train, 1 on 2HTrain, and 1 swing-pump 600 that can be aligned to either 2H or 2J.._ _Typically only 1 of 3 run) .2J 02-EP-LCC-2J 1.000 (MVA) && 02-EP-LCC-2J1 TO 4160/480VAC Distribution X 1.000 (MVA)(There are 2 Component Cooling 2J 01-CC-P-1D Component Cooling Pump Pumps. 1 on 2J. Train and 1 on 2H 600*__ "Train. Typically only 1 of 2 run)2J " 02-RH-P-lB Residual Heat Removal Pump "_"__ _,_ ,_Enclosure 2 -Page 12 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surrv Power Station Units I and 2 Table 4 -Offsite Power Transformers Winding , MvASize -Voltge RatingG Transformer Configuration Grounding Configuration (Highside:

LrowSde) (OA/FA/FA) (Primary/Secondary)

RSST "A" Delta:Wye Low 18/24/30 34.4kV/4.16kV 34.5kV Bus is Effectively Grounded.

RSST "A" is Resistance Grounded (OA/FA/FA)

Wye Low Resistance Grounded (on secondary)

RSST "B" Delta:Wye Low 18/24/30 34:4kV/4.16kV 34.5kV Bus is Effectively Grounded.

RSST "B" is Resistance Grounded (OA/FA/FA)

Wye Low Resistance Grounded (on secondary)

RST"" Delta:Wye Low 18/24/30 34k/.6V34.5kV Bus is Effectively Grounded.

RSST "C" is RSST C Resistance Grounded (OA/FAIFA) 3.V/lkVWye Low Resistance Grounded (on secondary) 67.5/90/112.5 500kV Bus is Effectively Grounded.

SRT 1 Wye SRT 1 Wye Grounded:Delta 512.5kV/36.5kV Solid Grounded (on primary), Grounded via zig-zag (OAIFA/FOA)

Ground Bank (on secondary) 67.2/89.6/112 230kV Bus is Effectively Grounded.

SRT 2 Wye SRT 2 Delta:W ye Groun -ded ( A F / O ) 230kV/36.51 kVGr u d d( ns c day (OA/FA/FOA)

Grounded (on secondary)

SRT 4 Delta:Wye Grounded 67.2/89.6/112 230kV/365kV 230kV Bus is Effectively Grounded.

SRT 4 Wye (OA/FA/FOA)

Grounded (on secondary)

Enclosure 2 -Page 13 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Desion Vulnerability in Electric Power System Surry Power Station Units I and 2 Table 5 -Protective Devices Protection Zone Protective Device Logic Setpoint Nominal Sensitivity of Basis For Setpoint (VAC) Device (VAC) .. _... __ass _o _e on .....__Drop out to actuate upon a sustained ESF bus Degraded 1 H ESF Bus Degraded Degraded Voltage Relays 2 of 3 63.6 V LN-Secondary

(+/-) 0.6077 voltage of 92.7% nominal.Voltage Setpoint provides a minimum voltage the ESF buses can be r____________operated at indefinitely.

The upper bound is set to ensure that the preferred power source 1 H ESF Bus Under Voltage Loss of Voltage Relays 2 of 3. 51.47 VLN-Se5.ondary

(+1-) 2.5423 shall not be disconnected for any transient experienced during the worst case voltage profile.Drop out to actuate upon a sustained ESF bus Degraded 1J ESF -Bus Degraded Degraded Voltage Relays -2 of,3 63.6 V LN-Secondary 0.6077 voltage of 92.7% nominal.Voltage Dof 6 Setpoint provides a minimum voltage the ESF buses can be_ _ _operated at indefinitely.

The upper bound is set to ensure that the preferred power source 1J ESF Bus Under Voltage'.

Loss of Voltage Relays 2 of 3 51.47 VLN-Secondary

(+/-) 2.5423 shall not be disconnected for any transient experienced during the worst case voltage profile.Enclosure 2 -Page 14 of 15 Serial No.12-519 Docket Nos. 50-280/281 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Surry Power Station Units I and 2 Table 5 -Protective Devices (Continued)

..........

~ ~ ~ ~ ~ ~ ~ ~ Sepon Nom... :ina Sensitivity.

of ;- :;:::: ;<SProtection Zone Protective Device Logic Setpoint Nomina itivit. of Basis For Setpoint (VAC) Device (VAC)Drop out to actuate upon a sustained ESF bus Degraded 2H ESF Bus Degraded "voltage of 92.7% nominal.Voltaged Degraded Voltage Relays 2 of 3 63.6 V LN-Secndary

(+-) 0.6077 volt of 9 minal.VoltageSetpoint provides a minimum voltage the ESF buses can be-__operated at indefinitely.

The upper bound is set to ensure that.the preferred power source.2H ESF Bus Under Voltage Loss of Voltage Relays 2 of 3 51.47 VN-Secondary

(+/7) 2.5423 shall not be disconnected for any transient experienced during the worst case voltage profile.Drop out to actuate upon a sustained ESF bus Degraded 2J ESF Bus Degraded -" voltage of 92.7% nominal.JE B Daded Degraded Voltage. Relays .2 of 3 63.6 V LN-Secondary

(+/-) 0.6077 Voltage Setpoint provides a minimum voltage the ESF buses can be operated at indefinitely.

'The upper bound is. set to ensure that the preferred power source 2J ESF Bus UnderVoltage Loss of Voltage Relays

• 2 of 3 51.47 VLN-Secondary

(+/-) 2.5423 shall not be disconnected for any transient experienced during the worst case voltage profile.Enclosure 2- Page 15 of 15 Serial No.12-519 Docket Nos. 50-336/423 ENCLOSURE 3 Response to NRC Bulletin 2012-01 Design Vulnerability in Electric Power System Millstone Power Station Units 2 and 3 Dominion Nuclear Connecticut, Inc.(DNC, Inc.)

Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 Bulletin Response The Bulletin response is arranged in the following way:* System Description

-Items 2, 1.d, 2.a, 2.c* System Protection

-1, 1.a, 2.b, 2.d* Consequences

-1.b, 1.c, 2.e* Attachment 1 -Simplified One-Line Diagram* Attachment 2 -Tables o Table 1 -ESF Buses Continuously Powered From Offsite Power Source(s)o Table 2 -ESF Buses Not Continuously Powered From Offsite Power Source(s)o Table 3- ESF Buses Major Loads o Table 4 -Offsite Power Transformers o Table 5 -Protective Devices System Description Items 2, 1 d, 2.a, and 2.c request system information and will be addressed in this section: 2. Briefly describe the operating configuration of the ESF buses (Class 1E for current operating plants or non-Class 1E for passive plants) at power (normal operating condition).

See Attachment 1, for a simplified one-line diagram.The Millstone Power Station Unit 2 (MPS2) Engineering Safeguards Features (ESF) buses consist of facility 1 4160V bus 24C,.facility 2 4160V bus 24D and a swing 4160V bus 24E that is aligned to either 24C or 24D. During normal operation, these buses are powered from the main generator via the Normal Station Service Transformer (NSST). The NSST is connected to non-safety buses 2f4A and 24B. Bus 24C is fed by bus 24A and bus 24D fed by bus 24B. The MPS2 Reserve Station Service Transformer (RSST) is available to power buses 24C and 24D directly if needed. A 4 KV cross tie is also available to provide power from Millstone Power Station Unit 3 (MPS3) to MPS2 if needed. This cross tie connects either bus 34A or 34B to bus 24E.The MPS3 ESF buses consist of train A 4160V bus 34C and train B 4160V bus 34D. During normal operation, both of these buses are powered by the main generator via the NSST. The NSST is connected to non-safety buses 34A and 34B. Bus 34C fed by bus 34A and bus 34D powered by bus 34B. The MPS3 RSST is available to power buses 34C and 34D directly if needed.Enclosure 3 -Page 1 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 1. d Describe the offsite power transformer (e.g., start-up, reserve, station auxiliary) winding and grounding configurations.

See Attachment 2, Table 4 for offsite power transformer winding and grounding configurations.

The MPS2 RSST transformer is scheduled to be replaced in October 2012. The existing models are based on the old transformer.

It is expected that modeling of the replacement transformer will result in similar results. Both the existing and replacement transformer data have been included in Attachment 2, Table 4.2. a. Are the ESF buses powered by offsite power sources? if so, explain what major loads are connected to the buses including their ratings.For at power (normal operating condition) configurations, the ESF buses are not powered by offsite sources. For both MPS2 and MPS3, the ESF buses are powered by theunit's main generator via the unit's NSST.See Attachment 2, Tables 1 and 2 for ESF-bus power sources 2. c. Confirm that the operating configuration of the ESF buses is consistent with the current licensing basis. Describe any changes in offsite power source alignment to the ESF buses from the original plant licensing.

The following at power (normal operating condition) configurations have been confirmed to be consistent with the current licensing basis: Each Millstone Unit is required to have two paths to the offsite power system. The credited paths are: 1. MPS2 circuit 1 :power to bus 24C and 24D via the MPS2 RSST 2. MPS2 circuit 2:power to bus 24C or 24D from bus 24E via the cross tie from MPS3. Either the MPS3 NSST(via buses 34A or 34B) or MPS3 RSST (via buses 34C/34A or 34D/34B) paths can be credited for this supply.3. MPS3 circuit 1:power to bus 34C and 34D via the MPS3 NSST (via buses 34A and 34B, respectively).

4. MPS3 circuit 2: power to bus 34C and 34D via the MPS3 RSST.The only change from original plant licensing concerns the second path for MPS2. Originally, the second path was a cross tie to Millstone Unit 1. When Millstone Unit 1 was decommissioned, this cross tie was realigned to MPS3.System Protection Items 1, 1.a, 2.b, and 2.d request information regarding electrical system protection and will be addressed.in this section: Enclosure 3 -Page 2 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 1. Given the requirements above, describe how the protection scheme for ESF buses (Class 1E for current operating plants or non-Class 1E for passive plants) is designed to detect and automatically respond to a single-phase open circuit condition or high impedance ground fault condition on a credited off-site power circuit or another power sources. Also, include the following information:

Consistent with the current licensing basis and GDC 17, existing protective circuitry will separate the ESF buses from a connected failed source due to a loss of voltage or a sustained, balanced degraded grid voltage.Millstone has modeled various single phase open circuit scenarios to determine how the plant would respond. The ETAP electrical distribution system modeling program used at Millstone does not have the capability to accurately model an open phase on the high side of a station service transformer.

Due to this limitation, corporate engineering worked with Dominion Electric Transmission to combine the Millstone ETAP model with the Electric Transmission PSCAD modeling software to evaluate the Millstone response to these scenarios.

This is the best available modeling at this time. The ETAP software is currently being upgraded to provide a better modeling program. The results of the current modeling are documented in a Millstone Engineering Technical Evaluation.

A summary of the at-power (or with Loss of Coolant Accident (LOCA) load), open circuit, with no ground scenarios evaluated and the results are provided below.Scenario 1 -MPS2 NSST: Mode 1 or LOCA load MPS2 does not have a main generator output breaker. If a single phase open circuit occurs on the NSST side, the main generator negative sequence relay would detect the condition, trip the generator and force a fast transfer to the RSST. This action automatically isolates the single phase open circuit.Scenario 2 -MPS2 RSST: open circuit, no load This scenario is the normal operating scenario where the RSST is in standby with no load. It is not connected to the 4.16 KV bus so degraded voltage and under voltage relays do not monitor the RSST voltage. If a single phase open circuit occurs on the high side of the RSST, the delta winding on the low side of the transformer will create the missing third phase of voltage. Since there are no motor loads connected, there is no damage to plant eq'uipment.

The concern for this scenario is that the RSST would appear to be available for service but would trip when load is added to it. This condition is not detectable by voltage indications.

Scenario 3 -MPS2 RSST: open circuit, Mode 1 or LOCA load This scenario models the load on the RSST after a reactor trip from full power. The RSST is connected to the 4.16 KV bus. If a single phase open circuit occurs on the high side of the RSST, the 4.16 KV bus voltage drops below the degraded voltage relay setting. This will result in the tripping of the RSST feeder breaker after 8 seconds followed by the Emergency Diesel Generator (EDG) starting and repowering the bus.Scenario 4 -MPS3 RSST: open circuit, no load This scenario is the normal operating scenario where the RSST is in standby with no load. It is not connected to the 4.16 KV bus so degraded voltage and under voltage relays do not monitor the RSST voltage. If a single phase open circuit occurs on the high side of the RSST, the delta Enclosure 3 -Page 3 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 monitor the RSST voltage. If a single phase open circuit occurs on the high side of the RSST, the delta winding on the low side of the transformer will create the missing third phase of voltage. Since there are no motor loads connected, there is no damage to plant equipment.

The concern for this scenario is that the RSST would appear to be available for service but would provide unacceptable voltages when load is added to it. This condition is not detectable by voltage indications.

Scenario 5 -MPS3 RSST: open circuit, Mode 1 or LOCA load This scenario models the load on the RSST after a reactor trip from full power combined with a loss of the NSST supply. The RSST is connected to the 4.16 KV bus. If a single phase open circuit occurs on the high side of the RSST, the 4.16 KV bus voltage drops but not low enough to be detected by the degraded voltage relays. This scenario is similar to the Byron event in that there will be voltage imbalances that will create high motor currents.The voltage relays will not detect the problem so the RSST breaker will remain closed and the EDG will not start. Operations will notice many loads tripping on overcurrent and will not be able to start new loads.Scenario 6 -MPS3 NSST open circuit, Mode 1 or LOCA load This scenario would be the normal configuration after a reactor trip. If an open circuit occurs on the high side of the main transformer during plant operation, the main generator negative sequence relay would operate and trip the generator.

This would result in opening the main generator output breaker. The NSST would still be connected to the 4.16 KV bus and would be powered via the Main Transformer operating in a backfeed mode. The 4.16 KV bus voltage would remain above the degraded voltage relay setting and would have a very little voltage imbalance.

Loads on the 4.16 KV bus will continue to operate normally in this condition.

For a high impedance ground with two phases intact and the third phase at reduced voltage simulating a high impedance fault (with or without that phase being open circuited), the bus voltages will vary depending on the amount of impedance to ground. Millstone modeled the effect on the 4 KV buses due to a decreasing phase to neutral voltage (associated with a high impedance ground) on a single 345KV phase. The graphs show the decreasing 4KV voltages and where they cross the degraded voltage allowable values. The MPS2 graph shows the RSST results after a fast bus transfer (FBT). The MPS3 graph shows the NSST results. As the ground impedance drops, protective relaying on the 345KV system will detect the ground and trip the associated breakers, but this action has not been included in the graph.Enclosure 3 -Page 4 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 MP2 RSST 4.16 kV Bus voltages as a result of reduction on one of the phase voltage on 345 kV Grid 24C/D 345KV Ph-C LN Volts Ph-AB PH-BC PH-CA Allowable 70% 3.42 3.531 3.199 3.663 80% 3.618 3.644 3.417 3.663 90% 3.676 3,687 3.585 3.663 Line Volts No Load at 70% volts Ph-AS 4.078 PH-BC 4.097 PH-CA 3.411 MP2 RSST Voltage with Mode-i load 3.800 -3.700 ---3.600 t mo0o -___a a.I 1 3.400 -.4 3.300--Ph-AB..U-PH-SC-PH-CA Alloviable 3.200 3.100 0% 10% 20% 30% 40%S0% 60% 70% 80% 90%loot;345 kV Grid Volts on Phase-C LN volts Enclosure 3 -Page 5 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 MP3 NSST 4.16 kV Bus voltages as a result of reduction on one of the phase voltage on 345 kV Grid DVR 345KV Ph-C LN Volts Ph-AB PH-BC PH-CA Allowabe 0% 3.341 3.438 1.847 3706 20% 3.451 3.521 2261 3.706 40% 3.587 3.634 2.690 3.706 60% 3.742 3.771 3.131 3.706 80% 3914 3928 3.584 3.706 100% 4100 4.102 4.045 3,706 W 17 MP3 NSST Voltage with Mode-1 load 45000 4.000 1,500-*-6-*.A-P-CA-IVR Afwtsbe 1,000 0% 20% 40% 60% M0% 100% 120%345 kV Grid Volts on Phase-C LN volts l.a. The sensitivity of protective devices to detect abnormal operating conditions and the basis for the protective device setpoint(s).

Consistent with the current licensing basis and GDC 17, existing electrical protective devices are sufficiently sensitive to detect design basis conditions such as a loss of voltage or a degraded voltage, but were not designed to detect a single open phase condition.

See Attachment 2, Table 5 for protective devices and the basis for the device setpoint(s).

The MPS2 and MPS3 4KV systems are grounded systems. The individual loads have ground overcurrent relays but the buses do not have ground protection/alarms.

Enclosure 3 -Page 6 of 16 Serial No.-12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone'Power Station Units 2 and 3 2.b. If the ESF buses are not powered by offsite power sources, explain how the surveillance tests are performed to verify that a single-phase open circuit condition or high impedance ground fault condition on an off-site power circuit is detected.MPS2 Technical Specification (TS) surveillance requirement 4.8.1.1,.1 requires a check of breaker alignment and indicated power availability.

Power availability is checked by monitoring voltages.

With a single phase open circuit, the voltages appear normal. This TS surveillance will not detect a single phase open circuit. Although this surveillance test would not detect a single phase open circuit, MPS2 would detect this condition due to normal plant operation.

MPS2 does not have a main generator output circuit breaker. When MPS2 ,shuts down, the station service loads are transferred to the RSST. As such, a single phase open circuit would be detected on at least a refueling frequency.

MPS3 TS surveillance requirement 4.8.1. .1 .a is similar to MPS2 and will not detect a single phase open circuit. MPS3 has an additional TS surveillance requirement 4.8.1.1 .1.b that requires transferring the power supply from the NSST to the RSST every 18 months.Depending on the bus loading at the time of the surveillance, a single phase open circuit may be detected if motors begin to trip. Additionally, MPS3 station service loads are transferred to the MPS3 RSST periodically in support of breaker PMs of the NSST feeder and 4KV bus tie breakers.Several of the single phase open circuit scenarios result in unacceptable conditions that require additional action: Scenarios 2 and 4 result in a condition that is not detectable by protective relays. Periodic walkdowns of the transformers and switchyard are performed by Operations, Generation Test Services (GTS), Northeast Utilities, and system engineering to identify these conditions.

Due to the delta winding on the low side of the transformers, the voltage on the open circuited line may appear normal. Neither voltage relays nor operator monitoring of voltmeters would detect the single open phase. Since the RSSTs are normally in standby, individual phase currents are approximately zero. Neither negative sequence relays nor operator monitoring of bus/phase currents would detect a single phase open circuit. Caution needs to be taken to ensure that efforts to. identify and isolate the single open phase condition do not result in a decreased reliability of the electrical system that could occur if an offsite power source was isolated unnecessarily.

Based on current industry activities, there is no known protective relay scheme that can detect this unloaded single open phase condition.

Scenario 5 identifies a condition that would challenge the operators with,,overcurrent trips across many systems. This requires the operators to realize the supply -voltage is compromised and trip the associated feeder breaker. Operator training is being developed to increase awareness of this scenario.Although Millstone has not fully modeled the effect of high impedance grounds, preliminary models indicate that there will be voltage imbalances at the 4 KV level. With the affected source carrying load, depending on the magnitude of the ground, this may or may not be detected.Enclosure 3 -Page 7 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 2.d. Do the plant operating procedures, including off-normal operating procedures, specifically call for verification of the voltages on all three phases of the ESF buses?Based on the plant responses predicted by modeling single phase open circuits, Millstone procedures have been evaluated.

Although an ungrounded single phase open circuit on the line feeding a standby RSST will result in almost normal phase voltages, a grounded phase could reduce that phase's voltage. As such, both MPS2 and MPS3 have added a check of each phase of the 4 KV voltage provided by their RSST to their weekly rounds.Only one phase of ESF bus voltage is checked during operator rounds. This is acceptable since these buses are fed from the main generator.

A single phaseopen circuit on the MVIPS2 generator would result in a negative sequence relay trip of the main generator and a fast transfer of the 4 KV buses. to the RSST automatically isolating the open circuit.A single phase open circuit on the MPS3 generator would result in a negative sequence relay trip of the main generator.

Since MPS3 has a generator output breaker, a transfer to the RSST will not occur. The Millstone model predicts the voltages at the 4 KV buses in this scenario will be acceptable., The MPS2 scenario for a loaded RSST with an open circuit shows bus Voltage dropping below the degraded grid voltage relay setpoint.

In this scenario, the RSST feeder breakers will automatically trip open in 8 seconds which will isolate the open circuit. Operator action is not needed in this case so no change to the operating procedure has been made.The MPS3 scenario for a loaded RSST with an open circuit shows the bus voltage dropping, but not low enough to actuate the degraded grid voltage relays. Since the degraded voltage relays, will not actuate, the associated alarm will not be received and the operators will not be looking at that annunciator response procedure.

As such, changes to the degraded grid voltage annunciator response procedure to check each of the three phaseswould not improve the operators' response and no changes are planned for this procedure, In response to the Byron event, Millstone is developing operator training.

Additional changes to operator procedures may result from these training efforts.Consequences Items 1 .b, 1 .c, and 2.e request information regarding the electrical consequences of an'event and will be addressed in this section: 1.b. The differences (if any) of the consequences of a loaded (i.e., ESF bus normally aligned to offsite power transformer) or unloaded (e.g., ESF buses. normally aligned to.unit auxiliary transformer) power source.The installed relays were not designed to detect single open phase conditions.

Existing loss of voltage and degraded voltage relays may respond depending on load and possible grounds. In general, there will be no automatic plant response or operator action for an unloaded RSST Enclosure 3 -Page 8 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 power source in the event of a single-phase open circuit because there is insufficient current to detect a single-phase open circuit in this configuration.

The plant response for the loaded and unloaded scenarios modeled at Millstone is provided in the answer to question 1 above.1.c. If the design does not detect and automatically respond to a single-phase open circuit condition or high impedance ground fault condition on a credited offsite power circuit or another power source, describe the consequences of such an event and the plant response." The Class 1 E ESF buses at Millstone 2 and 3 do not include a protection scheme that are designed to detect and automatically respond to a single-phase open circuit condition on the credited offsite power source..The Millstone Electrical Design Basis is described in the Millstone TS and UFSAR as follows: MPS2 TS 3.8.1.1 -As a minimum, the following A.C. electrical power sources shall be OPERABLE:

Two physically independent circuits between the offsite transmission network and the onsite Class 1 E distribution system.During normal operation, these two paths are the MPS2 RSST and either the MPS3 NSST or MPS3 RSST via a 4 KV cross tie. The MPS2 NSST can be credited if the disconnecting links to the main generator are removed.MPS2 TS 3.3.2.1 -Describes the logic and settings of the 4 KV bus under voltage and degraded voltage relays.MPS3 TS 3.8.1.1 -As a minimum, the following A.C. electrical power sources shall be OPERABLE:

Two physically independent circuits between the offsite transmission network and the onsite Class 1 E Distribution System.The two paths are the MPS3 NSST and the MPS3 RSST.MPS3 TS 3.3.2 -Describes the logic and settings of the 4 KV bus under voltage and degraded voltage relays.Section 8 of each unit's FSAR describes the electrical distribution systems. An overview of the portion of the systems associated with the issues raised by NRC Bulletin 2012-01 is provided below: The offsite power supply to the safety related 4.16 KV bus design is similar for MPS2 and MPS3. Each plant has two safety related,4.16 KV buses. Each plant has a main transformer and a NSST that taps off the 24KV bus between the generator and the main transformer.

Additionally, each plant has a RSST that steps the 345 KV directly down to 4.16 KV. During normal plant operation, the 4.16 KV buses are supplied from the NSST. The NSST connects to two non-safety related 4.16 KV buses which are then connected to two safety-related 4.16 KV Enclosure 3 -Page 9 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 buses by cross tie breakers.

MPS3 has a main generator output circuit breaker. If a plant trip occurs, the 4.16 KV buses remain powered by the NSST. If the generator output' circuit breaker does not trip or there is a failure on the NSST side, a fast transfer of the 4.16 KV buses to the RSST will occur.' MPS2 does not have a main generator output breaker. Every time the plant trips, the 4.16 KV buses fast transfer to the RSST.The degraded grid voltage and under voltage design is the same for MPS2 and MPS3. Each train of the 4.16 KV safety related buses has 4 degraded grid relays/sensors and 4 under voltage relays/sensors.

MPS3 uses relays for this function.

MPS2 uses bistables within its sequencer for this function., The term" relay" will be used throughout this response for both units. Each unit has two degraded grid relays and two under voltage relays monitoring the, phase A-B voltage and two degraded grid relays and two under voltage relays monitoring the phase B-C voltage. These relays are arranged in a 2 of 4 logic such that a single relay failing to operate when desired or spuriously operating (for example in response to a blown fuse) when not desired will not prevent a protective action nor cause a spurious actuation.

The 4.16 KV. bus phase A-C voltage is not monitored by protective relays.At MPS2, if the degraded grid voltage setpoint is Teached and maintained for 8,seconds, the RSST feeder breaker will trip. If the under voltage setpoint is reached.and maintained for 2 seconds, the RSST and bus tie breakers will trip and the EDGs will start and repower the safety related 4.16 KV buses.At MPS3; if the degraded grid voltage setpoint is reached and maintained for 7 seconds with an accident signal (SIS/CDA) or. for 270 seconds without an accident signal present, the, RSST and 4.16 KV bus tie breakers will open, the EDGs will start and repower the safety related 4.16 KV buses. If the under voltage setpoint is reached and maintained for 2 seconds, the plant will attempt an automatic slow transfer of the ESF buses to the RSST. If the slow transfer fails, the., EDGs will repower the safety related 4.16 KV buses.1. Since Millstone did not credit the detection and automatic response to a loss of a single, phase event in the ESF design, an open phase fault was not included in the design criteria for either the loss of voltage or the degraded voltage relay schemes. Additionally, since open phase detection was not credited in the Millstone design basis, no calculations or design documents exist that previously considered this condition.

2. Using the best available modeling programs, Millstone evaluated several single phase open circuit scenarios.

The resuIts are described in the answer to question 1 above.3. Millstone has open corrective actions to monitor industry efforts to improve modeling and protective relay designs and to take additional actions as appropriate.

4. The consequences of a high impedance ground fault are described in the answer to question 1 above.Enclosure 3 -Page10 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 2.e. If a common or single offsite circuit is used to supply redundant ESF buses, explain why a failure, such as a single-phase open circuit or high impedance ground fault condition, would not adversely affect redundant ESF buses.Consistent with the Current Licensing Basis and GDC 17, protective circuitry will separate the ESF buses from a failed source due to a loss of voltage or a sustained balanced degraded grid voltage.Although an ungrounded open phase condition would not be detected by voltage indications, an open phase that shorts to ground would be detectable.

MPS2 and MPS3 have revised their weekly operator rounds to include the three phases of voltage indication in their voltage checks of the RSST.For MPS2, if a single phase open circuit failure occurs on the RSST supply line while it is feeding the ESF buses, the existing models show the 4 KV bus voltages dropping below the degraded voltage relay setpoint.

This will isolate the ESF buses from the degraded source in eight seconds and transfer the ESF buses to the emergency diesel generators.

For MPS3, the NSST will normally continue to supply the ESF buses after a reactor trip. With a single phase open circuit, the existing models show the 4 KV bus voltages will remain above the degraded voltage settings and will remain balanced.

The ESF buses will continue to operate normally in this condition.

Although the MPS3 RSST models show an unacceptable response, it would take a failure of the NSST and an open circuit failure on the RSST supply to reach this condition.

This scenario requires two separate failures.For MPS2 and MPS3, depending on the magnitude of the high impedance ground fault, redundant ESF buses may or may not be affected.

Millstone has open corrective actions to monitor industry efforts to improve modeling and protective relay designs and to take additional actions as appropriate.

Enclosure 3 -Page 11 of 16

Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Millstone "Power Station Units 2 and 3 Attachment 2 -Tables Table I -ESF Buses Continuously Powered From Offsite Power Source(s)ESF buses connected to offsite, Description of Offsite Power poe (noga rial icensing basis KSource Configuration poecn~loeaigonfiguriat~e~ion basis______ _____ ______ ____-condition)

I)N/A N/A N/A Table 2 -ESF Buses Not Continuously Powered From Offsite Power Source(s)D. escription ofOfsite .S, buses connec t o ofite aOrigial licensig Ibasis Power Source buses cnIo lonnecatind condition)l configufration

(:Y/N)Con~figurationp~e~oma prtn MPS2 NSST 24C, 24D, 24E Y MPS3 NSST 34C, 34D Y.Table 3 -ESF Buses Normally Energized Major Loads (Note: Table 3 is N/A for MPS since the ESF buses are not normally powered by offsite power.Ref. Bulletin question 2.a.)Enclosure 3 -Page 14 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Desiqn Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 Table 4 -Offsite Power Transformers Transformer Winding Configuration MVASize Voltage Rating (KV) Grounding (High.Side

-.Low Side) (OAIFA/FA) (Primary/Secondary)

Configuratio6n MPS2 Main Wye:Delta 630/840/1050 345 KV Wye Transformer ONAN/ODAF/ODAF 345/22.8 solid grounded 27/36/45 6.9 KV Wye MPS2 NSST Delta:Delta:Wye OA/FA/FOA 22.8/4.16/6.9 resistance grounded 345 KV Wye MPS2 RSST 27/36/45 solid grounded, (Old Wye:Delta:Wye OA/FA/FOA 345/4.16/6.9 6.9 KV Wye transformer) resistance grounded 345 KV Wye MPS2 RSST 36/48/60 solid grounded, (New Wye:Delta:Wye ONAN/ONAF/ONAF 345/4.16/6.9 6.9 KV Wye transformer) resistance grounded MPS3 Main 900/1200/1500 345 KV Wye Transformer Wye:Delta ONAN/ODAF1/ODAF2 345/22.8 solid grounded 24/32/4022841/.6Nn MPS3 NSST A Delta:Delta:Delta OA/FA/FA 22.8/4.16/4.16 None Both 6.9 KV 30/40/50 windings are MPS3 NSST B Delta:Wye:Wye OA/FA/FA 22.8/6.9/6.9 resistance grounded 27/36/45 345 KV Wye MPS3 RSST A Wye:Delta:Delta OA/FOA/FOA 345/4.16/4.16 solid grounded 345 KV Wye solid grounded 30/40/50 and both 6.9 MPS3 RSST B Wye:Wye:Wye OA/FOA/FOA 345/6.9/6.9 KV windings are resistance grounded Enclosure 3 -Page 15 of 16 Serial No.12-519 Docket Nos. 50-336/423 Response to NRC Bulletin 2012-01 Desian Vulnerability In Electric Power System Millstone Power Station Units 2 and 3 Table 5 -Protective Devices Protection Protective Device Logic Setpoint Nominal (VAC) "Basis For Setpoint Zone Bus 24C Degraded Voltage Relays 2 of 4 3710V (89% of 4160) To actuate upon a balanced grid degraded voltage condition Bus 24C Loss of Voltage Relays 2 of 4 2975V (72% of 4160) To actuate upon a complete loss of ESF bus voltage Bus 24D Degraded Voltage Relays 2 of 4 3710OV (89% of 4160) To actuate upon a balanced grid degraded voltage condition To actuate upon a complete loss of ESF bus Bus 24D Loss of Voltage Relays 2 of 4 2975V (72% of 4160) voltage Bus 34C Degraded Voltage Relays 2 of 4 3730V (90% of 4160) To actuate upon a balanced grid degraded Bus34C DegadeVotag

_Reay 2___ o0fvoltage condition Bus 34C Loss of Voltage Relays 2 of 4 2835 (68% of 4160) To actuate upon a complete loss of ESF bus Bus_3CLosofVltageRelay 2 o4 25(%fvoltage Bus 34D Degraded Voltage Relays 2 of 4 3730V (90% of 4160) To actuate upon a balanced grid degraded_voltage condition Bus 34D Loss of Voltage Relays -2 of 4 2835 (68% of 4160) To actuate upon a complete loss of ESF bus Bus _ 34D _LossofVoltageRelays

_2_of_4_2835_(68%_of_4160)voltage Enclosure 3 -Page 16 of 16 Serial No.12-519 Docket No. 50-305 ENCLOSURE 4 Response to NRC Bulletin 2012-01, Design Vulnerability in Electric Power System Kewaunee Power Station Dominion Energy Kewaunee, Inc.(DEK, Inc.)

Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station Bulletin Response The Bulletin response is arranged in the following way: 0 System Description

-Items 2, 1.d, 2.a, 2.c 0 System Protection

-1, 1.a, 2.b, 2.d* Consequences

-1.b, 1.c, 2.e* Attachment 1 -Simplified One-Line Diagram* Attachment 2 -Tables o Table 1 -ESF Buses Continuously Powered From Offsite Power Source(s)o Table 2 -ESF Buses Not Continuously Powered From Offsite Power Source(s)o Table 3A-3D -ESF Buses Major Loads o Table 4 -Offsite Power Transformers o Table 5 -Protective Devices System Description Items 2, 1.d, 2.a, 2.c request system information and are addressed in this section: 2. Briefly describe the operating configuration of the ESF buses (Class 1E for current operating plants or non-Class 1E for passive plants) at power (normal operating condition).

See Attachment 1 for simplified one-line diagrams of the Kewaunee Power Station (KPS)electrical distribution system.There are two 4.16-kV Engineered Safety Features (ESF) buses at KPS (1-5 and 1-6). In the normal operating configuration (at power), the 4.16-kV ESF buses are provided power from their preferred offsite power source via two independent transformers (Tertiary Auxiliary Transformer (TAT) to Bus 1-5 and Reserve Auxiliary Transformer (RAT) to Bus 1-6).Both of the offsite power supply circuits (TAT and RAT) will normally be energized and will be connected to one or the other of the 4.16-kV ESF buses. Thus, a trip of the reactor, turbine generator, and main station auxiliary source of power (Main Auxiliary Transformer) does not require a transfer for the 4.16-kV ESF buses.The KPS switchyard consists of 345-kV and 138-kV sections.

Both the 345-kV and 138-kV sections have been configured to a double-breaker, double-bus orientation.

The double-bus orientation within the 345-kV section of the switchyard includes the Li bus and L2 bus. The double-bus orientation within the 138-kV section of the switchyard includes the west bus and east bus.The TAT receives power from the Tertiary Supply Transformer (TST) via an underground insulated power cable and the RAT receives power from the Reserve Supply Transformer (RST)via an overhead transmission line. A load tap changer (LTC) is used on both the TST and RST to adjust the voltage to the RAT and TAT as necessary.

The TST and RST receive power from Enclosure 4 -Page 1 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station the 138-kV section of the switchyard from independent points. The TST receives power via an underground insulated power cable that connects to the 138-kV section of the switchyard through two normally closed breakers.

The RST receives power via an overhead transmission line that connects to the 138-kV section of the switchyard through two normally closed breakers (different from those used for the TST) that are each directly connected to the applicable 138-kV west bus and 138-kV east bus.The 138-kV section of the switchyard is connected to the offsite grid via two overhead lines (F-84 and Y-51). Both lines can feed the 138-kV west bus and 138-kV east bus through its applicable normally closed breakers.Additionally, the 138-kV section of the switchyard is connected to the 345-kV section of the switchyard through two independent transformers (T1 0 and T20). Transformer T1 0, which is connected to the 345-kV Li bus, can feed the 138-kV west bus through the applicable normally closed breaker or the TST through the applicable normally closed breaker. Transformer T20, which is connected to the 345-kV L2 bus, can feed the 138-kV east bus through the applicable normally closed breaker or the TST through the applicable normally closed breaker.The RAT also has the capacity to provide power to the 4.16-kV non-ESF buses in the event of a loss of the normal ac power supply from the generator (via the Main Auxiliary Transformer).

The normally open feeder breakers from the RAT to the 4.16-kV non-ESF buses (Bus 1-i, Bus 1-2, Bus 1-3, and Bus 1-4) are also depicted in one of the single line diagrams within Attachment 1.1. d. Describe the offsite power transformer (e.g., start-up, reserve, station auxiliary) winding and grounding configurations.

See Attachment 2, Table 4, for offsite power transformer winding and grounding configurations.

2. a. Are the ESF buses powered by offsite power sources? If so, explain what major loads are connected to the buses including their ratings.For at-power normal operating configurations, the 4.16-kV ESF buses are powered by the described offsite sources.See Attachment 2, Tables 1 and 2, for 4.16-kV ESF bus power sources.The 4.16-kV ESF bus loading during at-power normal operating configurations will be much different than for accident conditions.

In Attachment 2, Table 3, loads that are branch fed from the respective 4.16-kV ESF buses are listed. However, a majority of the noted loads are normally only connected during accident conditions (except surveillance testing during at-power normal operating configurations).

Enclosure 4 -Page 2 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station 2. c. Confirm that the operating configuration of the ESF buses is consistent with the current licensing basis. Describe any changes in offsite power source alignment to the ESF buses from the original plant licensing.

Attachment 2, Table 1, identifies the normal arrangements to the 4.16-kV ESF buses.The current licensing basis configuration (which is the same as the original licensing basis configuration) is the TAT aligned to 4.16-kV ESF Bus 1-5 and the RAT to 4.16-KV ESF Bus 1-6, which requires no transfer upon a trip of the reactor, turbine generator, and main station auxiliary source of power.The original licensing basis configuration did not include the TST and RST, which have load tap changers (LTCs) installed.

Additionally, the original licensing basis configuration did not include a switchyard with a complete double breaker, double bus orientation.

However, these'changes do no not impact the original licensing basis configuration as previously described.

System Protection Items 1, 1.a, 2.b, 2.d request information regarding electrical system protection and will be addressed in this section: 1. Given the requirements above, describe how the protection scheme for ESF buses (Class 1E for current operating plants or non-Class 1E for passive plants) is designed to detect and automatically respond to a single-phase open circuit condition or high impedance ground fault condition on a credited offsite power circuit or another power sources.Consistent with the current licensing basis and the KPS USAR GDC 17 discussion, the existing protective circuitry will separate the ESF buses from a connected failed source due to a loss of voltage or a sustained, balanced degraded grid voltage concurrent with certain design basis accidents.

Although the protection scheme at KPS was not designed to detect and automatically respond to a single-phase open circuit condition (with or without a high impedance ground fault) on a credited offsite power circuit, preliminary analysis (on the portions of the circuit that were evaluated to date) has shown that the degraded voltage (DV) relay protection schemes will separate the ESF buses in an open phase condition (ungrounded or solidly grounded) and isolate the affected power source (automatically transferring power to an alternate supply).Evaluations of the remaining portion of the circuit are ongoing.The preliminary analysis was performed to determine the capability of existing KPS under voltage relays to detect and automatically respond to single-phase open circuit conditions (ungrounded and solidly grounded) of offsite power supplies to 4.16-kV ESF buses. The modeling for the preliminary analysis was performed using EMPT based computer modeling Enclosure 4 -Page 3 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station software (PSCAD). Engineering has evaluated the results of the PSCAD modeling using published materials and the ETAP computer code, where possible, to ensure that the results are reasonable.

The first level of under voltage protection is provided by the loss of voltage (LOV) relays, which function to detect and disconnect the 4.16-kV ESF bus from the preferred offsite power supply upon a total loss of voltage condition.

The LOV relay setting equals 101.69V-SECONDARY x 20/1 equals 2033.8V-PRIMARY (phase-to-neutral voltage).

Two-of-two LOV relays are required to sense the loss of voltage condition to initiate the tripping of the preferred offsite power supply.The LOV relays have two pairs of relays for each 4.16-kV ESF bus.The second level of under voltage protection is provided by the degraded voltage (DV) relays, which function to detect and disconnect the ESF bus from the preferred offsite power supply upon a low-voltage condition.

The DV relay setting equals 112.93V-SECONDARY x 20/1 equals 2258.6V-PRIMARY (phase-to-neutral voltage).

Two-of-two DV relays are required to sense the degraded voltage condition to initiate the tripping of the preferred offsite power supply. The DV relays have one pair of relays for each 4.16-kV ESF bus.The under voltage relays (LOV and DV) are connected phase-to-neutral on single phase to ground (A & C Phase) 4200-120V potential transformers.

To determine the ability to detect an open phase (ungrounded and solidly grounded) from the preferred offsite power supply, the phase-to-neutral voltage for each phase was required to be modeled for that condition.

Two scenarios have been evaluated during the preliminary analysis (evaluation of two other scenarios during .the preliminary analysis remain ongoing) to determine the vulnerability of an open primary transformer phase condition at KPS. A summary of the results is as follows: 1. An open phase (ungrounded and solidly grounded) on the primary of the 138/13.8-kV TST LOV Relays The following discussion assumes the LOV relays drop-out above their Technical Specification (TS) minimum.For the TST feed cases with A or C phase open (ungrounded or solidly grounded), either A Phase or C Phase LOV relays will drop-out and this circuit will not actuate since 1 of 2 relays will drop-out (2 of 2 required).

It will cause alarm 47092G, "Bus 5 Volt Restoring Blown Fuse" to actuate-in

2.5 seconds

or less.For the TST feed case with B phase open (ungrounded or solidly grounded), A Phase*and C Phase LOV relays will not drop-out and this circuit will not actuate or alarm since 0 of 2 relays will drop-out (2 of 2 required to actuate, 1 of 2 to alarm).DV Relays The following discussion assumes the DV relays drop-out above their TS minimum.Enclosure 4 -Page 4 of 18 Serial No. 12-51,9..Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power-Station For the TST feed cases, A Phase and C Phase DV relays will drop-out and this circuit will actuate since 2 of 2 relays will drop-out (2 of 2 required) in 7.4 seconds or less.2. An open phase (ungrounded and solidly 'grounded) on the primary of the 138/2,1-kV RST LOV Relays The following discussion assumes the LOV relays drop-out above their TS minimum.For the RST feed cases with A or C phase open (ungrounded or solidly grounded), either A Phase or C Phase LOV relays will drop-out and this Circuit Will not actuate since 1 of 2 relays will drop-out (2 of 2 needed). It will cause alarm 47092J, "Bus 6 Volt Restoring Blown Fuse" to actuate in 2.5 seconds or less.For the RST feed case with B phase open (ungrounded orsolidly grounded), A. Phase and C Phase LOV relays will not drop-out and this circuit will not actuate or alarm since 0 of 2 relays will drop-out (2 of 2 required to actuate, 1 of 2 to alarm).DV Relays The following discussion assumes' the DV relays drop-out above their TS minimum.For the RST feed cases, A Phase and C Phase DV relays-will drop-out and this circuit will actuate since 2 of 2 relays will drop-out (2 of 2 required) in 7:4 seconds or less.As previously mentioned, the evaluations of two other scenarios during the preliminary analysis remain ongoing. These two other scenarios include an open phase (ungrounded and solidly grounded) on the primary of the 13.2/4.16-kV TAT (secondary of the 138/13.8-kV TST),and an open phase (ungrounded and solidly grounded) on the primary of the 20/4.16-kV RAT (secondary of the 138/21-kV RST).Scenarios have also been evaluated during this preliminary analysis with open phase (ungrounded) locations at points in the 138-kV substation and beyond that would affect both the RST and TST. The results of this preliminary analysis indicated less than a 2% voltage imbalance at both 4.16-kV ESF buses in each scenario evaluated.

This indicates that for KPS there should be no single open phase event that would adversely affect both 4.16-kV ESF buses.A high impedance ground was not evaluated for any of the open phase conditions during this preliminary analysis.For a highimpedance ground with the three phases intact, protective circuit actuation is expected.

At KPS, the 345-kV section of switchyard, the 138-kV section of switchyard, the 13.8-kV feed to the TAT, and the 21-kV feed to the RAT are effectively grounded.

The 4.16-kV ESF buses are low resistance grounded.

With the low impedance grounding configuration at KPS, line to neutral short'circuit currents are sufficiently high when a high impedance ground fault is introduced.

This ensures that protective relays isolated grounded energized phases.,Enclosure 4 -Page 5 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station Ground overcurrent relay settings typically have a minimum bolted-fault to trip-setting ratio of 2:1 to account for impedance of the fault. This is consistent with Industry practice.

No further evaluation of this condition is warranted.

l.a. The sensitivity of protective devices to detect abnormal operating conditions and the basis for the protective device setpoint(s).

Consistent with the current licensing basis and the KPS USAR GDC 17 discussion, existing electrical protective devices are sufficiently sensitive to detect design basis conditions such as a loss of voltage or a degraded voltage, but were not designed to detect a single open phase condition (with or without a high impedance ground fault) in the offsite source configuration analyzed.See Attachment 2, Table 5, for protective devices and the basis for the device setpoint(s).

2.b. If the ESF buses are not powered by offsite power sources, explain how the surveillance tests are performed to verify that a single-phase open circuit condition or high impedance ground fault condition on an offsite power circuit is detected.This question is not applicable, because the 4.16-kV ESF buses at KPS are powered by offsite power sources.2.d. Do the plant operating procedures, including off-normal operating procedures, specifically call for verification of the voltages on all three phases of the ESF buses?Plant operating procedures are being revised to include instruction for phase verification when control room annunciator alarms 47092G ("Bus 5 Volt Restoring Blown Fuse"), 47092J ("Bus 6 Volt Restoring Blown Fuse"), 470911 ("Bus 5 Voltage Degraded"), 47091 L ("Bus 6 Voltage Degraded"), 47091 H ("Bus 5 Voltage Low"), and 47091 K ("Bus 6 Voltage Low") actuate. The additional instruction is intended to assist operators with diagnosing the open phase condition and further instructs operators to manually separate from the affected offsite source if the automatic actuation has failed to do so.Consequences Items 1 .b, 1 .c, 2.e request information regarding the consequences of an event and are addressed in this section: 1.b. The differences (if any) of the consequences of a loaded (i.e., ESF bus normally aligned to offsite power transformer) or unloaded (e.g., ESF buses normally aligned to unit auxiliary transformer) power source.The installed relays were not designed to detect single open phase conditions (with or without a high impedance ground fault). Existing LOV and DV relays may respond depending on load Enclosure 4 -Page 6 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station and possible grounds. In general, there will be no plant response for an unloaded power source in the event of a loss of a single-phase open circuit on a credited offsite power circuit because there is insufficient current to detect a single-phase open circuit for this configuration.

The plant response for a loaded power source cannot be calculated without specifying the amount of loading and the specific loads involved.The KPS 4.16-kV ESF buses would not be expected to have an unloaded offsite power source.As stated within USAR Chapter 8 Electrical Systems: "Both of the offsite power supply circuits will normally be energized at all times and will be connected to one or the other of the engineered safeguards buses at all times. Thus, loss of the reactor, turbine generator, and main station auxiliary source of power does not even require a transfer for the safeguards buses." 1.c. If the design does not detect and automatically respond to a single-phase open circuit condition or high impedance ground fault condition on a credited offsite power circuit or another power sources, describe the consequences of such an event and the plant response.KPS was not designed (as documented in the Current Licensing Basis (CLB)) for the Class 1 E protection scheme (for the 4.16-kV ESF buses) to detect and automatically respond to a single-phase open circuit condition (with or without a high impedance ground fault) on the credited offsite power source.The offsite power circuits at KPS consist of two independent circuits.

As stated within USAR Chapter 8 Electrical Systems: "The reserve supply transformer is used to furnish power to the 20.0 kV reserve (startup)auxiliary transformer via a 20 kV overhead transmission line from the substation.

The tertiary supply transformer is used to furnish power to the 13.2 kV tertiary auxiliary transformer via an underground insulated power cable. This cable becomes the second of the two physically independent circuits to provide off-site power to the on-site distribution systems.""The reserve supply transformer and the tertiary supply transformer are bifurcated at the substation to connect to either the east or west 138 kV buses. Each leg of the bifurcation is separated from the respective bus with a 138 kV circuit breaker." Since KPS was not designed and licensed for the detection and automatic response to a loss of a single phase event, an open phase fault was not included in the design criteria for the LOV relay scheme, the DV relay scheme or secondary level under voltage protection system (SLUPS) design criteria.

Since open phase detection was not within the KPS design or licensing basis, no design basis calculations or design documents exist that previously considered this condition.

Without formalized engineering calculations or engineering evaluations, the electrical consequences of such an open phase event (including plant response), can only be evaluated Enclosure 4 -Page 7 of 18 Serial No.12-519 Docket No.'50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station to the extent of what has already been published by EPRI and Basler; a generic overview, at best. The difficulty in applying these documents to the KPS specific response is that these are generic assessments and cannot be formally credited as a basis for an accurate response.

The primary reason is that detailed plant specific models need to be developed (e.g., transformer magnetic circuit models, electric distribution models, motor models; including positive, negative, and zero sequence impedances (voltage and currents) would need to be compiled and analyzed for the KPS specific Class 1 E electric distribution system (EDS)).Preliminary analysis was performed to determine the capability of existing KPS under voltage relays to detect and automatically respond to single-phase open circuit conditions (ungrounded and solidly grounded) of offsite power supplies to 4.16-kV ESF buses.Based on this preliminary analysis, an open phase (ungrounded or solidly grounded) on the primary of the RST (LTC) would result in a voltage imbalance on the applicable 4.16-kV ESF bus that would cause an automatic transfer to the applicable Emergency Diesel Generator (EDG) by the applicable DV relays. The event should not cause a plant trip. The loss of phase (ungrounded or solidly grounded) would immediately render the offsite source and applicable 4.16-kV ESF bus inoperable.

Like the event that occurred at the Byron unit, the voltage imbalance would impact operation of loads on the affected 4.16-kV ESF bus until the automatic transfer occurs. Unlike the event that occurred at the Byron unit, only one of two 4.16-kV ESF buses would potentially be affected.Based on this preliminary analysis, an open phase (ungrounded or solidly grounded) on the primary of the TST (LTC) would result in a voltage imbalance on the applicable 4.16-kV ESF bus that would cause automatic transfer to the applicable EDG by the applicable DV relays.The event should not cause a plant trip. The loss of phase (ungrounded or solidly grounded)would immediately render the offsite source and applicable 4.16-kV ESF bus inoperable.

Like the event that occurred at the Byron unit, the voltage imbalance would impact operation of loads on the affected 4.16-kV ESF bus until the automatic transfer occurs. Unlike the event that occurred at the Byron unit, only one of two 4.16-kV ESF buses would potentially be affected.As previously mentioned, the evaluations of two other scenarios during the preliminary analysis are ongoing. These two other scenarios include an open phase (ungrounded or solidly grounded) on the primary of the 13.2/4.16-kV TAT (secondary of the 138/13.8-kV TST) and an open phase (ungrounded or solidly grounded) on the primary of the 20/4.16-kV RAT (secondary of the 138/21-kV RST). While it is unknown whether the impacted 4.16-kV ESF bus would automatically transfer to its associated EDG for these two other scenarios, only one of the two 4.16-kV ESF buses could be affected by each scenario (unlike the event that occurred at the Byron unit).Scenarios have also been evaluated during this preliminary analysis with open phase (ungrounded) locations at points in the 138-kV substation and beyond that would affect both the RST and TST. The results of this preliminary analysis indicated less than a 2% voltage imbalance at both 4.16-kV ESF buses in each scenario evaluated.

This indicates that for KPS there should be no single open phase event that would adversely affect both 4.16-kV ESF buses (unlike the event that occurred at the Byron unit).Enclosure 4 -Page 8 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System, Kewaunee Power Station A high impedance ground was not evaluated for any of the open phase conditions during this preliminary analysis.2.e. If a common or single offsite circuit is used to supply redundant ESF buses, explain why a failure, such as a single-phase open circuit or high impedance ground fault condition, would not adversely affect redundant ESF buses.This question is not applicable because KPS does not use a common or single offsite circuit to supply redundant 4.16-kV ESF buses.Enclosure 4 -Page 9 of 18

Serial No.12-519 Docket No. 50-305 Reslonse to NRC Bulletin 2012-01 Desiqn Vulnerability In Electric Power System Kewaunee Power Station Attachment 2 -Tables Table 1 -ESF Buses Continuously Powered From Offsite Power Source(s)138-kVSection of Switchyard 4.1-Original Licensing us P' we re~y. Ofs ie PowerBai s~ouree 0"nfiguratidn

((NLOema:'rating Conidition) ofgrt tTS'LCt 138-kV Section of Switchyard 4.16-kV Bus 1-5 Yes *to TST (LTC) to TAT 138-ky Section of Switchyard 4.16-ky Bus 1-6 Yes *to RST (LTC) to RAT* The original licensing basis configuration is the TAT aligned to 4.16-kV ESF Bus 1-5 and the RAT to 4.16-KV ESF Bus 1-6, which requires no transfer upon a trip of the reactor, turbine generator, and main station auxiliary source of power.Table 2 -ESF Buses Not Continuously Powered From Offsite Power Source(s)Offsit~ Original Licensing Descri~ption ofO 'ffsite Power ESF BusesPowered by Bais onfgurtio Source Gonfiguration PowerNNormal'Operatig Condition)

NA NA NA Enclosure 4- Page 12 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station Table 3A- 4.16-kV ESF Bus 1-5 Major Loads gtoad...a"t L, us-,-oad Mark # Load Description ONtrmaheunns LoaNote 1-5 1-020 Safety Injection Pump 'A' (4160V) 800 1-5 1 -022 Service Water Pump 'A2' (4160V) X (Typically 3 or 4 of 4 Train 400 1-5_1-022_ServiceWaterPump_'A2

__(4160V)

X'A' and Train 'B' Running) 400 1-5 1-023 Service Water Pump 'Al' (4160V) X (Typically 3 or 4 of 4 Train 400 1-5______

1-023____

_ -tI'A' and Train 'B' Running)1-5 1-024 Auxiliary Feedwater Pump 'A' (4160V) 300 1-5 1-025 Residual Heat Removal Pump 'A' (4160V) 200 1-51 1-013 Fire Pump 'A' (480V) 200 X (Typically Only Train 'A'or25 1-51 1-021 Component Cooling Pump 'A' (480V) X5(Tyalnl TRain'0 Train 'B' Running)1-51 1-107 Containment Spray Pump 'A' (480V) 250 1-51 1-120 Containment Fan Coil Unit 'A (480V) X 125 1-51 1-156 Containment Fan Coil Unit 'B' (480V) X 125 1-52 1-133 .Charging Pump'C'(480V)

X 125 1-52 MCC52A Motor Control Center 1-52A (480V) X 32 kVA *1-52 MCC52B Motor Control Center 1-52B (480V) X 102 kVA *1-52 MCC52BEXT Motor Control Center 1-52B Extension (480V) 0 kVA*1-52 MCC52C -Motor Control Center 1-52C (480V) X 88 kVA *1-52 MCC52D Motor Control Center 1-52D (480V) X 27 kVA *1-52 MCC52E Motor Control Center 1-52E (480V) X 118 kVA *1-52 MCC52F Motor Control Center 1-52F (480V) X 52 kVA *1-52 MCC52FEXT Motor Control Center 1-52F Extension (480V) 0 kVA*1-52 MCC5262 Motor Control Center 1-5262 (480V) X [ 61 kVA *Enclosure 4 -Page 13 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station Table 3B -4.16-kV ESF Bus 1-6 Major Loads Rating (HP ESF Bus Load Mark # Load Description Normal Running Load = X Unless Otherwise Noted)1-6 1-027 Safety Injection Pump 'B' (4160V) 800 1-6 1-029 Service Water Pump 'B2' (4160V) X (Typically 3 or 4 of 4 Train 'A' 400 and Train_'B' Running) 400 1-6 1-030 Service Water Pump 'BI' (4160V) X (Typically 3 or 4 of 4 Train 'A' 400 and Train 'B' Running)1-6 1-031 Auxiliary Feedwater Pump 'B' (4160V) 300 1-6 1-032 Residual Heat Removal Pump 'B' (4160V) 200 1-61 1-028 Component Cooling Pump 'B' (480V) X (Typically Only Train 'A' or 250 Train 'B' Running)1-61 1-121 Containment Fan Coil Unit 'C' (480V) X 125 1-61 1-148 Containment Spray Pump 'B' (480V) 250 1-61 1-157 Containment Fan Coil Unit 'D' (480V) X 125 1-62 1-234 Fire Pump 'B' (480V) 200 1-62 MCC62A Motor Control Center 1-62A (480V) X 17 kVA *1-62 MCC62B Motor Control Center 1-62B (480V) 0 kVA*1-62 MCC62BEXT Motor Control Center 1-62B Extension (480V) 0 kVA*1-62 MCC62C Motor Control Center 1-62C (480V) X 86 kVA *1-62 MCC62D Motor Control Center 1-62D (480V) X 24 kVA *1-62 MCC62E Motor Control Center 1-62E (480V) X 144 kVA *1-62 MCC62G Motor Control Center 1-62G (480V) X 192 kVA *1-62 MCC62H Motor Control Center 1-62H (480V) X 5 kVA *1-62 MCC62J Motor Control Center 1-62J (480V) X 20 kVA ** MCC kVA rating represents normal operation load Enclosure 4 -Page 14 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Desicqn Vulnerability In Electric Power System Kewaunee Power Station Table 4 -Offsite Power Transformers Transformer Winding Configuration' MVA Size IVoltage Rating Grounding (High Side -Low Side) (OAJFAIFA) (PrimalrylSecondary)~

Conf iguration Delta -Wye 12 /16/'20 Wye (Neutral)

Solid TST (Tertiary Supply Transformer) 18k 38k (Wye Lags) (ONAN/ONAF/ONAF) 138 kV- 1 Grounded TAT (Tertiary Auxiliary Transformer)

Delta -Wye 8 /10 /12.5 (Future) 1 Wye (Neutral)

Resistance T (Wye Leads) (ONAN/ONAF/ONAF) 13.2 kV- 4.16 kV Grounded RST (Reserve Supply Transformer)

Delta- Wye 30/40/50 1Wye (Neutral)

Solid (Wye Lags) (ONAN/ONAF/ONAF)

Grounded RAT (Reserve Auxiliary Transformer)

Delta -Wye / Wye 30 / 40 / 50 (HV & XV), 15 / 20 / 25(YV) 20 kV- 4.16 kV./4.16 kV Wye/Wye (Neutral)(Wye / Wye Leads) (ONAN/ONAF/ONAF)

Resistance Grounded Enclosure 4 -Page 15 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station Table 5 -Protective Devices 4 Sensitivity.6of Protection Zone ProtectiveDevice Logic eton Noinl Device (VAC)- Basis For Setpoint.," (VAC),sciei Degraded Voltage 3902.26 (93.8% of The analytical limit of 3856.32V DerddVlae30.6(38 f(92.7% of 4.160) is used to 4160), 112.93 at Relay 112.73 to (Relays 2 of 2. delayof 6.72 113.13 determine the Nominal Dropout*(27AY/B5

& 27CY/B5).

[ e Setpoint including the 0.05%seod]safety margin.A starting point of 3473.6V (83.5% of 4160) results in the Nominal 3513.76 (84.47% of Dropout Setpoint being 4160), 101.69 at Relay conservatively above the Loss of Voltage Relays [time delay of 1.75 101.49 to minimum analytical limits (27A/B5 & 27CZ/B5) seconds for 27A/B5 and 101.89 (including 3452.8V; 83% of-time delay of 0.1 4160). The higher starting point seconds for 27CZ/B5] adds a safety margin and insures increased protection for plant motors.Enclosure 4 -Page 16 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Desiqn Vulnerability In Electric Power System Kewaunee Power Station Table 5 -Protective Devices (continued)

Setpoin tNoi'inal Sensitivity of Protection Zone. -ProtectiveDevice Logic, VAC) Device (VAC)- Basis For Setpoint SP Criteria A starting point of 3473.6V (83.5% of 4160) will result in the 3513.76 (84.47% of Nominal Dropout Setpoint being 4160), 101.69 at Relay conservatively above the Loss of Voltage Relays [time delay of 1.75 101.49 to minimum analytical limits (27C/B5 & 27AZ/B5) seconds for 27C/B5 and 101.89 (including 3452.8V, 83% of time delay of 0.1 4160). The higher starting point seconds for 27AZ/B5] adds a safety margin and insures increased protection for plant motors.e3902.26 (93.8% of The analytical limit of 3856.32V Degraded Voltage at Relay 1. (92.7% of 4160) is used to ESF Bus 1-6 Relays 2 of 2 4160), 112.93 at Relay 112.73 to determine the Nominal Dropout (27AY/B6 & 27CY/B6) [time delay of 6.72 113.13 Setpoint including the 0.05%B & 1) seconds] safety margin.Enclosure 4 -Page 17 of 18 Serial No.12-519 Docket No. 50-305 Response to NRC Bulletin 2012-01 Design Vulnerability In Electric Power System Kewaunee Power Station Table 5 -Protective Devices (continued)

Sensitilvity~of Poci Zone Protective Device Logic Devic (VAC) -Basis For Setpoint +0 7:,+Protection Zone:{! ..> < ,Setpoint Nominal Devic SPCriteria A starting point of 3473.6V (83.5% of 4160) will result in the 3513.76 (84.47% of Nominal Dropout Setpoint being 4160), 101.69 at Relay conservatively above the ESE Bus 1-6 Loss of Voltage Relays 2 of 2 [time delay of 1.75, 101.49 to minimum analytical limits (27A/B6 & 27CZ/B6) seconds for 27A/B6 and 101.89 (including 3452.8V, 83% of time delay of 0.1 4160). The higher starting point seconds for-27CZ/B6]

adds a safety margin and insures increased protection for plant motors.A starting point of 3473.6V (83.5% of 4160) will result in the 3513.76 (84.47% of Nominal Dropout Setpoint being 4160), 101.69 at Relay conservatively above the ESF Bus 1-6 Loss of Voltage Relays 2 of 2 [time delay of 1.75 101.49 to minimum analytical limits*(27C/B6 & 27AZ/B6) seconds for 27C/B6 and 101.89 -(including 3452.8V, 83% of time delay of 0.1 4160). The higher starting point seconds for 27AZ/B6] adds a safety margin and insures increased protection for plant motors.Enclosure 4 -Page 18 of .18