Text

Supplement to Proposed License Amendment Request to Revise TS 3.8.1.1, A.C. Sources - Operating, to Support Maintenance and Replacement of the Millstone Unit 3 'A' Reserve Station Service Transformer and 345 Kv South Bus Switchyard Componen
	ML19304A294
Person / Time
Site:	Millstone
Issue date:	10/22/2019
From:	Mark D. Sartain; Dominion Energy Nuclear Connecticut, Dominion Energy
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	19-282B
	Download: ML19304A294 (99)
	v • d • e

Dominion Energy Nuclear Connecticut, Inc.

5000 Dominion Boulevard, Glen Allen, VA 23060 Dominion Energy.com

!ii; Dominion

~ Energy October 22, 2019 U.S. Nuclear Regulatory Commission Serial No 19-282B Attention: Document Control Desk NRA/SS R1 Wa$hington, DC 20555 Docket No. 50-336 License No. DPR-65 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2 SUPPLEMENT TO PROPOSED LICENSE AMENDMENT REQUEST TO REVISE TS 3.8.1.1, "A. C. SOURCES - OPERATING," TO SUPPORT MAINTENANCE AND REPLACEMENT OF THE MILLSTONE UNIT 3 'A' RESERVE STATION SERVICE TRANSFORMER AND 345 KV SOUTH BUS SWITCHYARD COMPONENTS By letter dated August 14, 2019, Dominion Energy Nuclear Connecticut (DENC) submitted a proposed license amendment request (LAR) to the Nuclear Regulatory Commission (NRC) in accordance with 10 CFR 50.90, to revise Millstone Power Station Unit 2 (MPS2) Technical Specification (TS) 3.8.1.1, "A. C. Sources - Operating," to add a permanent Required Action (a.3) that provides an option to extend the allowed outage time (AOT) from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 10 days for one inoperable offsite circuit. A one-time exception to the new proposed Required Action a.3 was also requested that would allow replacement of the Millstone Power Station Unit 3 (MPS3) 'A' RSST, its associated equipment, and other 345 kilovolt south bus switchyard components that are nearing the end of their dependable service life. The NRC staff determined that the information provided in the LAR was not of sufficient detail to enable the NRC staff to proceed with its detailed technical review regarding the acceptability of the proposed LAR.

On October 3, 2019, a telecom was held between the NRC and DENC to discuss the non-acceptance review items. Based on these discussions, DENC decided to supplement the LAR to change the credited supplemental power source from the Millstone Power Station FLEX generators to the MPS3 Station* Blackout diesel generator.

Additional changes to address the NRC's non-acceptance items and other items for consideration are discussed in Attachment 8. A submittal date of October 23, 2019 was agreed upon for the LAR Supplement.

By letter dated October 7, 2019, the NRC formally provided DENC an opportunity to supplement the proposed LAR identified above.

It should be noted that the Attachments in this LAR Supplement supersede the LAR Attachments (submitted in DENC letter dated August 14, 2019) in their entirety. provides a description and evaluation of the proposed license amendment request which includes a risk assessment for the deviations to the criteria outlined in Branch Technical Position (BTP) 8-8. Attachments 2 and 3 provide the marked-up TS and TS Bases pages, respectively. The marked-up TS Bases pages are provided for information only. The changes to the affected TS Bases pages will be incorporated in accordance with the TS Bases Control Program when this amendment request JI- L> ll )

. {'l((t

Serial No: 19-2828 Docket No. 50-336 Page 2 of 3 approved. A summary of the risk management actions for the new proposed permanent TS Required Action and one-time exception is provided in Attachment 4. An evaluation of Probabilistic Risk Assessment Model Quality is provided in Attachment 5. An External Hazards Screening is provided in Attachment 6 and a Progressive Screening Approach for Addressing External Hazards is provided in Attachment 7. Responses to the NRC Non-Acceptance Items and Other Items for Consideration are provided in Attachment 8.

It should also_be n_ot~d _t_hat concll!sion~ of the no significant hazards evaluation and the environmental considerations evaluation have not-cnanged in this LAR Snpplerrrent.

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

Sincerely, tdJowQ~

Mark D. Sartain Vice President - Nuclear Engineering and Fleet Support COMMONWEALTH OF VIRGINIA COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Mark D. Sartain, who is Vice President - Nuclear Engineering and Fleet Support of Dominion Energy Nuclear Connecticut, Inc. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that Company, and that the stateme ~!5 in the document are true to the best of his knowledge and belief.

'22..'""~ay of CJc+t>her-, 2019.

1 Acknowledged before me this My Commission Expires: ~ CCAth o/ > 2.0l.2...

l DIANE E. AITKEN NOTARY PUBLIC

~'t~ Notary Public REG. #7763114 COMMONWEALTH OF VIRGINIA MY COMMISSION EXPIRES MARCH 31, 2022 Commitment:

DENC will add steps to emergency operating procedure(s) (EOP(s)) for Station Blackout response to specifically direct operators to the appropriate EOP for reaching cold shutdown with AC power supplied by the Station Blackout diesel generator, before this LAR is fully implemented.

Attachments:

1. Description and Evaluation of Proposed License Amendment Request

2. Mark-Up of Proposed Technical Specification Changes

3. Mark-Up of Proposed Technical Specification Bases Changes - For Information Only

4. Risk Management Action Summary

5.

Probabilistic Risk Assessment Model Quality

6. External Hazards Screening

7. Progressive Screening Approach for Addressing External Hazards

8. Responses to the NRC Non-Acceptance Items and Other Items for Consideration

Serial No: 19-282B Docket No. 50-336 Page 3 of 3 cc: U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 R. V. Guzman NRC Senior Project Manager

- --u~s~-NuclerarRe-gulatory--commissiorf --------~ -- - ---- --- ---- --- ------- - - ---- ------ ------- -- ----

One White Flint North, Mail Stop 08 C2 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Director, Radiation Division Department of Energy and Environmental Protection 79 Elm Street Hartford, CT 06106-5127

Serial No: 19-282B Docket Nos. 50-336 ATTACHMENT 1 DESCRIPTION AND EVALUATION OF PROPOSED LICENSE AMENDMENT REQUEST DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 1 of 55 ATTACHMENT 1 TABLE OF CONTENTS 1.0

SUMMARY

DESCRIPTION 2.0 DETAILED DESCRIPTION 2.1 Proposed License Amendment Request 2.2 Reason for Proposed Change 3.0 ELECTRICAL POWER DISTRIBUTION SYSTEM DESCRIPTION 3.1 345 kV Switchyard 3.2 MPS2 to Offsite Power Sources 3.3 MPS2 Onsite AC Power System 3.4 MPS3 Onsite AC Power System 3.5 MPS2 Emergency AC Power System 3.6 MPS2 Emergency Diesel Generators 3.7 MPS2 Station Blackout (SBO) 3.8 MPS2 Appendix R 3.9 MPS2 FLEX Strategy 3.10 Switchyard Breaker 13T Background

4.0 TECHNICAL EVALUATION

4.1 Selection-of Extended AOT Durations 4.1.1 Permanent TS Required Action with Extended AOT (10 Day) 4.1.2 One-Time TS Required Action Exception with Extended AOT (35 Day) 4.2 Supplemental Power Source (SPS) for Extended AOTs 4.2.1 General Description 4.2.2 Initial Conditions - Electrical Power Configuration (for 1O-Day/35-Day AOTs) 4.2.3 Initial Event Selection and Description (for 1O-Day/35-Day AOTs) 4.2.4 Operator Actions (for 1O-Day/35-Day AOTs) 4.2.5 SPS Sizing 4.2.6 SPS Physical Connection to MPS2 4.2.7 SPS Testing Capability 4.2.8 SPS Staffing 4.2.9 MPS2 GDC-17 Coping Capability (for 1O-Day/35-Day AOTs) 4.2.10 MPS2 LOOP Coping Capability (for 1O-Day/35-Day AOTs) 4.2.11 MPS2 SBO Coping Capability (for 1O-Day/35-Day AOTs) 4.2.12 MPS2 Appendix R Coping Capability (for 1O-Day/35-Day AOTs) 4.2.13 Training 4.2.14 Work Management 4.2.15 Conformance with MPS3 TS and MPS2/3 Technical Requirements

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 2 of 55 4.3 Assessment Against Branch Technical Position 8-8 4.4 Plant Specific Probabilistic Risk Analysis 4.4.1 Methodology 4.4.2 Summary of Plant Specific Risk Assessment Results 4.5 _Conclusions __ _

4.5.1 Defense-in-Depth and Safety Margins 4.5.2 Reassessment of Cross-Tie LAR USQ #2 Conclusion (13T Position) 4.5.3 Final Conclusions

5.0 REGULATORY EVALUATION

5.1 Applicable Regulatory Requirements/Criteria 5.2 No Significant Hazards Consideration 5.3 Precedents

6.0 ENVIRONMENTAL CONSIDERATION

7.0 REFERENCES

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 3 of 55 Description and Evaluation of Proposed License Amendment Request 1.0

SUMMARY

DESCRIPTION Pursuant to 10 CFR 50.90, Dominion Energy .Nuclear Connecticut, Inc. (DENG) hereby requests an amendment to Facility Operating License No. DPR-65 for Millstone Power

- --- -Station -l:.lnit-z--(MPS2)-. -"Fhe proposed-licenseamendment reqaesr-(tAR) woula revise ____ --- --

Technical Specification (TS) 3.8.1.1, "A. C. Sources - Operating," to add a new permanent Required Action a.3, which provides an option to extend the allowed outage time (AOT) from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 10 days for one inoperable offsite circuit. This new Required Action is needed to complete periodic maintenance and testing of the Millstone Power Station Unit 3 (MPS3) 'A' Reserve Station Service Transformer (RSST) and other 345 kilovolt (kV) south bus switchyard components. Since periodic maintenance and testing of these components cannot typically be completed within the current 72-hour AOT, adoption of an extended AOT reduces: 1) the number of switching evolutions required to complete the work, 2) unavailability time for the equipment, and 3) potential for equipment failures or human performance events. Use of this 10-day AOT will be limited to no more than once per 18 month refueling interval for MPS3.

DENG also proposes a one-time exception to the new proposed Required Action a.3 that would extend the AOT to 35 days for one inoperable offsite circuit. Use of the 35-day AOT would permit replacement of the MPS3 'A' RSST, its associated equipment, and other 345 kV south bus switchyard components that are nearing the end of their dependable service life. This work is planned to take place no later than the fall 2023 outage (3R22) for MPS3.

Replacement of these components is necessary to ensure continued safe and dependable

generation of electric power.

The permanent 10-day AOT and one time 35-day AOT will only be entered if the conditions specified in TS Required Action a.3 are met. Additionally, certain compensatory and risk management actions will be met during both the permanent 10-day AOT and the one-time 35-day AOT which are provided in the TS Bases (and also summarized in Attachment 4) in support of this amendment request.

2.0 DETAILED DESCRIPTION 2.1 Proposed License Amendment Request Currently Required Action a.2 of TS 3.8.1.1 "A. C. Sources - Operating," allows 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to restore an inoperable offsite circuit to operable status. When crediting the MPS3 Normal Station Service Transformer (NSST) as a second offsite circuit, breaker 13T and its associated disconnect switches are required to be open. DENG proposes to revise TS 3.8.1.1, "A. C. Sources - Operating," to add a new permanent Required Action a.3, which provides an option to extend the AOT from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 10 days to allow periodic maintenance and testing of the MPS3 'A' RSST and 345 kV south bus switchyard components. Specifically, DENG intends to perform these maintenance activities with

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 4 of 55 switchyard breaker 13T closed. The proposed TS changes are shown below (added text is italicized and balded).

a.2 Restore the inoperable offsite circuit to OPERABLE status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months (within 10 days if Required ACTION a.3 is met) or be in HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

--- ------ _- - --- ----- -AND-- --- --- ----- --- - ------- - -- -------- -- -- ------- - ---- ----- --- ----- ----- - -- ---- - ------- --- --- - ~

a.3 With MPS3 in MODE 5, 6 or defueled, the MPS3 'A' RSST inoperable, and the MPS3 'A' NSST energized with breaker 15G-13T-2 (13T) and associated disconnect switches closed, restore -either offsite circuit to OPERABLE status within 10 days* if the following requirements are met:

- Within 30 days prior to entering the 10-day AOT, the availability of the supplemental power source (MPS3 SBO diesel generator) shall be.

verified.

- During the 10-day AOT, the availability of the supplemental power_

source shall be checked once per shift. If the supplemental power source becomes unavailable at any time during the 10-day AOT, restore to available status within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months or be in HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

- The risk management actions contained in DENC letter 19-282B, Attachment 4 (also provided in TS Bases 3/4.8), shall remain in effect during the 10-day AOT.

A footnote, denoted by an asterisk, will also be added as a one-time exception to the new proposed Required Action a.3 that would extend the AOT to 35 days to allow replacement of the MPS3 'A' RSST and 345 kV south bus switchyard components. *

To facilitate replacement of the MPS3 'A' RSST and associated equipment, use of a one-time 35-day allowed outage time is permitted provided the requirements of Required ACTION a.3 are met. The work shall be completed no later than the end of MPS3 Refueling Outage 22 (fall 2023).

Openfng breaker 13T and its associated disconnect switches results in exiting either Required Action a.2 or a.3, since this action restores the MPS3 'A' NSST to operable status as an offsite circuit.

A mark-up of TS 3.8.1.1 for the proposed changes is provided in Attachment 2.

A revision to the associated TS Bases section is provided in Attachment 3. The marked-up TS Bases pages are provided for information only. The changes to the affected TS Bases

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 5 of 55 pages will be incorporated in accordance with the TS Bases Control Program after this amendment request is approved.

2.2 Reason for Proposed Change To meet the requirements of General Design Criteria (GDC) 17, "Electric Power Systems,"

M e.s2 __uses_the_M eS3_'A'_B.SST_or_tbe_M eS3__'A'._NSST_as_its_altemate __offsite__ poweL __~-~

source. Therefore, when the MPS3 'A' RSST is taken out of service for required maintenance and testing, MPS2 must credit the MPS3 'A' NSST for GDC-17 compliance.

As such, switchyard breaker 13T must be open to provide adequate separation between MPS2's two offsite power sources. Figure 1 shows the current configuration of the Millstone Power Station (MPS) offsite power sources, along with the switchyard breaker arrangement. When 13T is closed, a failure of the 13T breaker or a fault in the offsite power supply (e.g., fault on north bus) coincident with failure of the 13T breaker to trip open would cause a simultaneous loss of both MPS2 offsite circuits. For this reason, the Bases for TS 3.8.1.1 require breaker 13T to be open for the MPS3 'A' NSST to be considered an operable offsite power source for MPS2. This requirement for breaker 13T was established in the amendment for the cross-tie between MPS2 and MPS3 (Reference 1-24).

However, opening breaker 13T when MPS3 is shut down represents a degradation in the reliability of the offsite supply for MPS3. A failure such as a fault on the 345 kV line that connects to the transmission network at a point between breakers 14T and 15T (348 line circuit) would cause a loss of offsite power for MPS3 if breaker 13T is open. If breaker 13T is closed and a fault occurs on this -345 kV line, the MPS3 'A' NSST would remain energized by the north bus. Therefore, opening the 13T breaker to allow MPS2 to meet GDC-17 requirements increases the probability of a loss of offsite power at MPS3 when

-shut down.

Since the amendment for the MPS2/3 cross:--tie, the station's sensitivity to operating at elevated shutdown risk levels has increased. The MPS3 Shutdown Risk Management program classifies risk colors of Green, Yellow, Orange and Red for key safety functions (KSF). At a high level, the risk colors are summarized as:

Green: KSF is satisfied Yellow: Some reduction exists for KSF Orange: KSF is considered degraded below normally acceptable levels Red: Margin of safety provided by KSF is lost.

In the years following the MPS2/3 cross-tie amendment, the MPS3 Shutdown Risk Management program has reassessed the configuration where the MPS3 'A' RSST is removed from service with switchyard breaker 13T open, and now characterizes it as risk color Orange.

Also, in accordance with the MPS3 shutdown risk procedure (Reference 1-27), one of the following conditions must be satisfied to open 13T with the MPS3 'A' RSST out of service:

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 6 of 55

Refueling cavity full

RCS capable of being pressurized with at least two steam generators able to maintain decay heat removal capability

MPS3 is defueled It should be noted that it would not be necessary to satisfy any of these conditions with the MPS3 'A' RSST out of service, if 13T is closed. Consequently, since opening 13T during MPS3 'A' RSST outages is prohibited during Mode 5 or 6 decreased inventory windows, the time to . conduct necessary transformer maintenance is limited. The evaluation performed in Section 4.4 concludes that the proposed configuration with 13T closed results in a very small increase in the risk metrics for MPS2. Therefore, the proposed permanent TS Required Action and one-time exception increase the time available to conduct MPS3

'A' RSST maintenance while minimizing operational risk at MPS2 and shutdown risk at MPS3. This results in a better overall risk management for the station and provides improved defense-in-depth for MPS3 while shutdown.

Also, since the amendment for the MPS2/3 cross-tie, DENC's experience at MPS indicates that a fault on a transmission line would be a more likely event than a spurious breaker internal fault. DENC has had multiple transmission line outages over the five year span preceding the submittal of this amendment request. Corrective actions have been initiated to prevent future reoccurrences of the outages, however many of the outages are related to external factors beyond the station's control (including storm conditions, bird interactions, etc.). On the other hand, a corrective action review revealed that there have been zero spurious breaker internal faults at MPS. The industry data compiled by the Nuclear Regulatory Commission (NRC) in NUREG/CR-6928 (Reference 1-34) and updated through 2015 also indicates that the spurious operation failure rate of a high voltage circuit breaker is low (4.83E-07/hr).

Performing maintenance activities with breaker 13T closed (in accordance with the proposed permanent TS Required Action and one-time exception) precludes entering a configuration with an elevated shutdown risk for MPS3, while only resulting in a.very small increase in the risk metrics for MPS2 (as concluded in Section 4.4). Furthermore, the requirement to maintain a supplemental power source while in the alignment for the proposed TS Required Action and one-time exception provides additional mitigation capability in the very low likelihood event that a passive failure disables both MPS2 offsite power sources (and assuming that both EDGs fail).

Currently, with one inoperable offsite circuit (which would include aligning MPS3 'A' NSST with switchyard breaker 13T closed), MPS2 TS 3.a.1.1, Required Action a.2 requires the offsite circuit to be restored to operable status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months or the unit must be placed in hot standby within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and cold shutdown within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months . The total amount of time required for the complete evolution to perform preventative maintenance (PM) on the MPS3 'A' RSST and its associated components significantly exceeds 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months (as discussed in Section 4.1 ). Therefore, this LAR proposes a new permanent TS Required Action and a one-time exception with extended AOTs, which will

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 7 of 55 adequately support replacement and continuous maintenance activities (and associated testing) with breaker 13T closed. The proposed changes provide alternatives to TS Required Actions that place* unnecessary administrative burdens on plant personnel that are not justified by the safety significance of the TS Required Action.

3.0 ELECTRICAL POWER DISTRIBUTION SYSTEM DESCRIPTION MPS 1s a three unit site with two operating reactors. Millstone Power Station Unit 1 (MPS1 ), which received its provisional operating license on October 7, 1970, was permanently shut down on July 21, 1998. MPS2, which received its initial operating license on September 26, 1975, has a licensed reactor power output of 2700 megawatts thermal (MWt) *with a gross electrical output of approximately 935 megawatts electric (MWe).

MPS3, which received its initial operating license on January 31, 1986, has a licensed reactor power output of 3650 MWt with a gross electrical output of approximately 1296 MWe.

3.1 345 kV Switchyard MPS is connected to the transmission system by four 345 kV circuits (see Figure 1). The four 345 kV transmission lines which terminate at the Millstone switchyard are:

Line Number 348: Haddam

Line Number 310: Manchester

Line Number 371: Montville

Line Number 383: Card The 345 kV switchyard, which is configured in a combination breaker-and-a-half and double breaker-double bus arrangement, buses together four 345 kV transmission line circuits, two generator circuits and two station service circuits. The MPS1 generator and station service circuits are no longer in service. The breaker arrangement allows the isolation of any of the four transmission lines without affecting the integrity of the switchyard.

Serial No: 19-2826 Docket Nos. 50-336 Attachment 1, Page 8 of 55 Figure 1 Millstone Station AC Power System 348 Line 310 Line 371 Line 383 Line North Bus G

Millstone 345kV Switchyard 8 South Bus 8 MP3SBODG To SBODG load Bank MP2RSST 3EDGA 3EDGB 2EDGA 2EDGB MP3 Main Generator MP2Main MPS3 MPS2 Generator

~MP3toMP2 Cross-Tie ( )

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 9 of 55 3.2 MPS2 to Offsite Power Sources Refer to Figure 1 for current configuration of offsite power sources to MPS2.

The MPS2 design provides two offsite circuits between the switchyard and the 4160 volt (V)

Class 1E buses. The immediately available offsite supply is the MPS2 RSST while the alternate supply is the MPS3 'A' NSST or 'A' RSST from bus 34A or 348 via the MPS3 to MPS2 cross-tie.

The normal supply to MPS2 with the unit online is the MPS2 NSST. If this source is lost due to a plant trip, a.fast bus transfer scheme connects the plant electrical system (6900 V and 4160 V) to the MPS2 RSST. The second or alternate source of offsite power is available by manual controls to MPS3 bus 34A or 348 for 4160 V power. This power source directly feeds bus 24E which can then be directed to either bus 24C or 240.

The MPS2 load requirement for the alternate offsite source (GDC-17) is approximately 3 MVA (Reference 1-10).

Physical separation of the offsite power sources, switchyard protection, redundancy, and the transmission system design based on load flow and stability analyses minimize the possibility of simultaneous failure of all power sources (reserve station service supply, MPS2/3 standby alternating current (AC) emergency diesel generators (EDGs), and MPS3 bus 34A or 348).

3.3 MP$2 Onsite AC Power System The 6900 V system (not shown in Figure 1) is a reliable source of power for the reactor coolant and condensate pumps. The system consists of two buses, 25A and 258 each capable of being fed from the 6900 V winding of either MPS2's NSST or RSST. The 6900 V winding of each transformer is sized to supply the full-load requirements of both buses.

The 4160 V system, shown in Figure 1, consists of five buses, 24A, 248, 24C, 240, and 24E, each consisting of a metal-clad switchgear assembly with vertical lift air circuit breakers. The 4160 V system provides a reliable source of power to large AC motors and to 480 V load centers. During plant operation, power is supplied to buses 24A and 248 from the MPS2 NSST. Bus ties connect buses 24A and 248 to buses 24C and 240, respectively. During other periods, such as startup and shutdown when the MPS2 NSST is not used, power is supplied from the MPS2 RSST directly to buses 24C and 240 and via bus ties to buses 24A and 248. The 24E bus may be fed from either bus 24C or 240, or from MPS3's 'A' RSST or 'A' NSST via the MPS3 to MPS2 cross-tie. All auxiliary loads (other than the 6900 V motors detailed above) are supplied from the 4160 V buses. Motors of 250 horsepower and larger are connected directly to the 4160 V system, while other loads are supplied at 480 V from 4160-480 V unit substations, and 120/208 V sources are available by stepping down from 480 V. '

Buses 24C, 240, and 24E are emergency buses that supply power to equipment required for a loss-of-coolant accident (LOCA) or other transients and conform to the requirements for Class 1E equipment.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 10 of 55 An automatic transfer scheme is provided to ensure continuity of auxiliary power from the preferred source. The transfer scheme will sense conditions resulting in, or leading to, a loss of voltage from the MPS2 NSST and will initiate a transfer for conditions such as a turbine or generator trip.

The transfer is high speed and considered simultaneous. It is not a supervised scheme.

That is, the secondary breakers for both the MPS2's NSST and RSST receive essentially simultaneous signals to open and close, respectively.

3.4 MPS3 Onsite AC Power System .

The MPS3 Class 1E 4160 V system, shown on Figure 1, consists of two redundant emergency buses 34C and 340. Each bus can be supplied from the MPS3 'A' NSST, MPS3 'A' RSST, or an MPS3 EOG.

The MPS3 'A' NSST supplies power to emergency 4160* V buses 34C and 340 via normal buses 34A and 34B, respectively. During normal operation, power is supplied through the MPS3 'A' NSST from the unit generator with the generator breaker closed. The MPS3 'A' NSST has the capacity to supply 4160 V normal auxiliaries and those emergency auxiliaries (both load groups) required during normal operation up to the full output of the main generator plus the capacity to supply MPS2 GDC 17 requirements as an alternate offsite source for minimum post-accident loads.

I 3.5 MPS2 Emergency AC Power System The emergency power system includes that electrical distribution equipment required to support the safe shutdown and post-accident operations for MPS2. Included in the emergency power system are the EDGs, emergency 4160 V switchgear and all extensions except those going to the normal switchgear and the MPS2 RSST. The emergency power system and equipment are Class 1E and safety related.

Redundant safety-related loads are divided between trains so that the loss of either train does not impair fulfillment of the minimum shutdown safety requirements. There are no automatic connections between Class IE buses and loads of redundant trains.

3.6 MPS2 Emergency Diesel Generators Two physically and electrically separate, quick starting, skid-mounted EDGs are provided.

Each EOG set has the capability to initiate the engineered safety features (ESF) in rapid succession, and to supply continuously the sum of the loads needed to be powered at any one time for a LOCA. Each EOG is rated as follows:

2750 kW Continuous

3000 kW 2000 hours0.0231 days 0.556 hours 0.00331 weeks 7.61e-4 months

3250 kW 300 hours0.00347 days 0.0833 hours 4.960317e-4 weeks 1.1415e-4 months The predicted loads are within the continuous rating of the EOG.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 11 of 55 Each EOG is tied to a 4160 V emergency bus through a circuit breaker. MPS2 EOG A feeds bus 24C, while MPS2 EOG B feeds bus 240.

The EOG associated with a 4160 V emergency bus receives an automatic start signal under either of the following conditions:

a. Engineered Safety Features Actuation System (ESAS) Safety Injection Actuation Signal (SIAS)

b. ESAS Level 1 Undervoltage Actuation from the associated 4160 V emergency bus Additionally, failure of a single active component or train associated with one EOG does not result in the inability of the redundant EOG to provide the emergency standby power.

Diesel fuel oil for the EDGs is stored in an above ground diesel oil storage tank (T-148),

with an approximate capacity of 25,000 gallons. The fuel oil is transferred from the storage tank by two 25 gpm diesel fuel oil transfer pumps to the two Class I, diesel oil supply tanks (T-48A and T-488) which are located in the structure that houses the associated EOG. The diesel oil supply tanks each have an approximate capacity of 13,500 gallons. A minimum of 12,000 gallons of fuel oil is stored in each above ground diesel oil supply tank.

3. 7 MPS2 Station Blackout (SBO)

MPS2 has the ability to cope with a loss of preferred and emergency on-site AC power -*

sources for up to eight hours. MPS2 must maintain decay heat removal capability during the event. It is assumed that there will be no AC power available during the first hour of the SBO except for battery backed power supplies (i.e., vital 120 V). Within the first hour, MPS2 will have an alternate AC power source available from the MPS3 Alternate AC (SBO) diesel generator via the MPS3 to MPS2 cross-tie.

MPS2 and MPS3 each have two EDGs in addition to the SBO diesel generator. ,In accordance with the SBO Rule and Nuclear Management and Resources Council (NUMARC) Document 87-00 (Reference 1-40), one of the four EDGs would be available and a station blackout is postulated to occur at one unit only at any one time. In the event of a MPS2 station blackout, the MPS3 SBO diesel will be made available within one hour by MPS3 operator action and connected to MPS2 Bus 24E by operator action.

The MPS3 SBO diesel generator and its support equipment (battery, inverter, computer, ventilation, etc.) is adequately sized to power equipment required to maintain MPS2 in a safe condition in the event both the offsite power system and standby power system are unavailable for up to eight hours.

The MPS2 load requirements for the alignment to the MPS3 SBO diesel generator is less than 1.3 MVA with a maximum duration of 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months (Reference 1-11 ).

During the proposed permanent TS Required Action and one-time exception, DENG will utilize the MPS3 SBO diesel generator as a supplemental power source to the inoperable

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 12 of 55 offsite power source. The technical evaluation to support this approach is provided in Section 4.0.

3.8 MPS2 Appendix R For an Appendix R fire in certain areas, MPS2 relies on MPS3 to provide power for 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to the safe shutdown loads via the MPS3 to MPS2 cross-tie. MPS2 Appendix R requires that AC power for the safe shutdown loads be available within 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months .

During an Appendix R fire at MPS2, no SBO event is assumed to occur simultaneously at MPS3. Therefore, the MPS3 SBO diesel generator will be made available within 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months by MPS3 operator action and connected to MPS2 Bus 24E by MPS2 operator action.

The MPS2 load requirements for the alignment to the MPS3 SBO diesel generator for a MPS2 Appendix R scenario is less than 2.3 MVA with a maximum duration of 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months (Reference 1-12).

3.9 MPS2 FLEX Strategy As pa.rt of the response for EA-12-049, "Order Modifying Licenses with Regard to Requirements for Mitigating Strategies for Beyond Design-Basis External Events" (Reference 1-14), MPS2 has implemented a FLEX strategy that has made available the following onsite portable diesel generators for powering ESF equipment for extended loss of AC power (ELAP), loss of ultimate heat sink (LUHS) and beyond design basis (BOB) external events (BDBEE):

Three (3) FLEX diesel generators 23.5 kW 120 V

Three (3) FLEX diesel generators 500 kW 480 V (one per unit and one spare)

Any onsite 500 kW 480 V FLEX diesel generator can be used for quick connection to power emergency motor control centers for transitional phase (Phase 2) with sufficient power for a charging pump, battery charger, vital instrumentation and required ventilation in the event of a total loss of offsite and onsite AC power.

The FLEX diesel generators are independent from the MPS2 EDGs. The onsite FLEX equipment is located in the BOB storage building inside the owner controlled area but outside the existing power block. The FLEX diesel generators are of a different model and design from the MPS2 EDGs, so a common mode failure is not applicable.

For additional defense-in-depth features, there are three redundant 480 V FLEX diesel generators (only one is required per unit). Furthermore, there are three FLEX 120 V diesel generators (stored in the BOB storage building) available to power vital instrumentation panels in the event of failure to re-power 480 V bus 22F.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 13 of 55 Additionally, two portable 1 MW 4160 V generators are available from an offsite storage facility to power the 4160 V safety buses for a longer term (Phase 3 loads). The FLEX diesel generators include connecting devices and plant implementing procedures.

For the 4160 V generators, the National SAFER Response Center (NSRC) stores nine .

units at their Memphis facility, of which MPS2 needs two (2) generators. Therefore, if any external event disabled the connected and operating 480 V FLEX diesel generator, suitable onsite 480 V diesel generators (one for each unit in the BOB storage building) and offsite 4160 V generators backups are available. The 4160 V generators are deployed from NSRC. Two 4160 V generators are required for an ELAP to power bus 240 at MPS2.

3.10 Switchyard Breaker 13T Background As shown in Figure 1, breaker 13T can be positioned to align or isolate the north bus from the line to the MPS3 Main Generator. Breaker 13T is equipped with two disconnect switches. Switch 15G-13T-4 is located between 13T and the north bus, and. switch 15G-13T-8 is located between breakers 13T and 14T. The arrangement detail is illustrated in MPS2 Updated Final Safety Analysis Report (UFSAR) Figure 8.1-1 D. As stated in MPS2 UFSAR Subsection 8.1.2.2, bullet d., faults can be manually isolated with appropriate disconnect switches in less than eight hours.

MPS2 utilizes either the MPS3 'A' RSST or the MPS3 'A' NSST to meet the requirements of GDC-17 (i.e., alternate offsite source in addition to the MPS2 RSST). If the MPS3 'A' RSST is not available, MPS2 must credit the MPS3 'A' NSST, as the second offsite power supply for GDC-17 compliance. The connection for the MPS3 'A' NSST is between 345 kV breakers 13T and 14T. This connection point provides* one breaker separation (i.e., 13T) between the MPS2 RSST and the MPS3 'A' NSST as the MPS2 RSST is directly tied to the north bus. If breaker 13T is closed, this alignment does not provide adequate separation between the two offsite sources to meet the GDC-17 requirement for physically independent circuits. An internal fault of the 13T breaker or a fault in .the offsite power supply (e.g., fault on north bus) coincident with failure of the 13T breaker to trip open would cause a simultaneous loss of both MPS2 offsite circuits. A 13T breaker fault would result in a loss of the MPS3 'A' NSST and the north bus being stripped (i.e., breakers 7T, 4T, and 1T opening), which results in de-energizing the MPS2 RSST and renders MPS2 with no offsite sources.

To prevent this from occurring, the current MPS2 TSs require that breaker 13T be opened when the MPS3 'A' RSST is. out of service to restore the required separation between the two MPS2 offsite sources. If breaker 13T is closed, MPS2 is not able to credit the MPS3

'A' NSST as the second offsite source, as defined in the MPS2 TS Bases. Per TS 3.8.1.1, maintaining 13T closed with the MPS3 'A' RSST out of service results in MPS2 declaring one offsite circuit inoperable, which currently has an AOT of 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . MPS3 TS 3.8.,1.1 has a 72-hour AOT when one offsite circuit is inoperable (i.e., MPS3 'A' RSST or 'A' NSST) in Mode 1-4. As a result, performing MPS3 'A' RSST maintenance evolutions with breaker 13T closed, while MPS3 is in operation, would cause both MPS2 and MPS3 to enter a 72-hour TS Required Action statement. Therefore, 13T is opened only during extended

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 14 of 55 maintenance evolutions where the MPS3 'A' RSST is not required to be operable per MPS3 TS _(i.e., Mode 5, 6, or defueled).

As documented in License Amendments 252 (MPS2) and 190 (MPS3) which approved the design for the cross-tie between MPS2 and MPS3 (Reference 1-24), the NRC staff reviewed the proposed change and found it acceptable to increase the probability of a loss of offsite power (LOOP) at MPS3, due to a fault on the offsite distribution network being considered a low probability event. The safety evaluation concluded: "The average failure rate for a single unit LOP [loss of offsite power] event occurring in the United States of America is 3.2 x 10-2 per reactor-year. When combined with the expected frequency of removing the MPS3 ['A'] RSST from service of once per MPS3 refueling outage, the probability of a LOP at MPS3 when shut down as a result of breaker 13T being open is acceptably low."

Although maintaining 13T closed does not allow the MPS3 'A' NSST to be considered an operable offsite power source for MPS2 per the description in the TS Bases, it is noted that aligning breaker 13T in this position has no adverse impact on the ability of the MPS3 'A' NSST to supply power to the 4160 V buses for MPS2/3. The requirement to consider the MPS3 'A' NSST inoperable when 13T is closed is only to comply with the GDC-17 requirement for physically independent circuitry (due to the loss of independence at the single point of breaker 13T).

4.0 TECHNICAL EVALUATION

4.1 Selection of Extended AOT Durations 4.1.1 Permanent TS Required Action with Extended AOT (10 Day)

During typical MPS3 outage work involving the MPS3 'A' RSST or south bus, breaker 13T is closed to minimize LOOP risk to MPS3. However, this requires entering MPS2 TS 3.8.1.1 Required Action a.2, which limits the amount of time that breaker 13T can be closed to 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . For example, during 3R18 (fall 2017) with switchyard breaker 13T closed, MPS3 'A' RSST PM activities were broken down into two windows (each less than 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months ) and not all planned PM activities could be completed. Utilizing an extended AOT period reduces the number of switching evolutions, which in turn decreases the total unavailability time and limits the potential for equipment failures and human performance events. The requested 10-day AOT will allow DENC to perform the preventative maintenance and testing on the MPS3 'A' RSST and/or the south bus components within the proposed AOT window, with breaker 13T closed.

Since the MPS3 'A' RSST ties directly into the south bus, repair work that requires removing the south bus from service also makes the MPS3 'A' RSST inoperable. Because DENC intends to perform this maintenance with breaker 13T closed, the MPS3 'A' RSST and south bus maintenance work is performed concurrently, in an effort to minimize entries into LCO 3.8.1.1. The south bus work scope includes non-discretionary continuous life-cycle maintenance activities that are greater in duration than 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . Configuration risk

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 15 of 55 for removal of the south bus will be assessed and managed in accordance with the requirements of 10 CFR 50.65(a)(4).

A breakdown of the PM activities associated with a typical MPS3 'A' RSST outage is provided in Table 1-1 below. Although a three-day contingency has been added to the schedule for potential weather-related impacts, DENG would return the MPS3 'A' RSST to operable status as soon as practical.

Table 1-1 Normal Preventative Maintenance Schedule for MPS3 'A' RSST

~¢tivity .. Activity Durc1tion *Elapseq Time i1t'YNt> :*.

Act.i~jt~,10~~c.rJ~$i.oli. ,_- __ )M',,u

<: }\/< " ,~Ji11;1to~vs ,:i:1 ;, ,idr*;r .*,:.tri,*

""""' Days :

1 Enter 10-day AOT -- 0 2 Tagout 1 1 Testing of transformer, relays, disconnect 3 switches, cables, voltage transformers, and 5 6 lightning arrestors 4 Clear tags 1 7 5 Contingency for weather impacts on testing 3 10 The cited durations in Table 1-1 for the testing and maintenance activities for MPS3 'A' RSST components are consistent with past MPS2/3 operating experience. For example, during the spring 2013 outage for MPS3 (3R15), the MPS3 'A' RSST outage lasted 188 hours0.00218 days 0.0522 hours 3.108466e-4 weeks 7.1534e-5 months . The length of this outage was primarily driven by the replacement of an RSST bushing, which required draining and processing of oil in addition to the replacement and restoration activities. During the fall 2011 outage for MPS3 (3R14), the MPS3 'A' RSST outage lasted 234.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months . The length of this outage was primarily driven by transformer insulation tests, which are performed in accordance with the PM program. Station revtew of these past durations indicates that the time frame can be reduced in future outages (while in the 10-day AOT). However, this operating experience provides a typical level of effort for these testing and maintenance activities. It should be noted that examples were selected prior to 3R16. After 3R16 restrictions were placed to only permit opening breaker 13T while in configurations with reduced plant risk (as discussed in Section 2.2). As a result, most testing and maintenance activities were divided into shorter windows after 3R16 (as discussed in the first paragraph of this section), which is not consistent with how they would be performed during the proposed 10-day AOT. As previously noted, dividing these activities into windows increases the potential for equipment failures and human performance events. Additionally, tasks like bushing replacements cannot be divided into a series of shorter windows, because once the task is started, the transformer cannot be returned to service until it is completed.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 16 of 55 4.1.2 Orie-Time TS Required Action Exception with Extended AOT (35 Day)

The MPS3 'A' RSST and other switchyard components are reaching the end of their dependable service life. Replacement of the MPS3 'A' RSST and the 345 kV switchyard south bus components will ensure continued dependable and safe generation of electrical power. The proposed one-time 35-day AOT is needed to allow sufficient time to replace the MPS3 'A' RSST and the 345 kV switchyard south bus components while permitting MPS2 to maintain normal power operation and to preclude the unnecessary transient of shutting down MPS2.

A one-time south bus repair project will be conducted for the replacement and upgrading of switches and insulators as part of life cycle management. There are also additional components being replaced. The duration of the south bus work is greater than 10 days, but is expected to be bounded by the duration of the MPS3 'A' RSST replacement project.

The activity schedule supporting the one-time 35-day AOT is provided in Table 1-2 below.

An evaluation of the proposed MPS3 'A' RSST replacement activities determined that 35 days is sufficient time to complete these activities with margin. The requested one-time 35-day AOT will be implemented by no later than MPS3 Refueling Outage 22 (fall 2023).

The 35-day AOT duration for replacement of the MPS3 'A' RSST was derived, where applicable, from previous operating experience associated with the MPS3 NSST replacement project that was completed in April 2019. Some key differences in replacement strategy and configuration include the following:

The new MPS3 'A' RSST will be installed in the same location as the old MPS3 'A' RSST (whereas the new MPS3 NSST was installed in a different location)

A replacement 345 kV motor operated disconnect (MOD) switch will be installed (which was not part of the MPS3 NSST replacement).

The high and low voltage bushings will be connected in a different manner (cabling connections for the MPS3 'A' RSST versus isophase bus for the MPS3 NSST).

Due to differences in replacement strategy and configuration, not all replacement activities could be directly compared. In these cases, durations were derived from vendor operating experience (as identified in Table 1-2). The vendors that will be performing the MPS3 'A RSST replacement are the same vendors that were used for the MPS3 NSST replacement.

The 35-day AOT duration includes an 8-day contingency for weather, plant -conditions and other unforeseen delays. Examples include working around decreased inventory windows and delays due to electrical maintenance testing on downstream electrical cabling and non-segregated bus. The 2019 MPS3 NSST replacement project experienced a delay of approximately two days due to plant conditions. Although an 8-day contingency has been added to the schedule, DENG would return the MPS3 'A' RSST to operable status as soon as practical.

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 17 of 55 Table 1-2 Activity Schedule for Replacement of MPS3 RSST

'~cthfity DescriP,tion ',

1 Enter one-time 35-day AOT 0 N/A Remove 'A' RSST from service, hang MPS3 2 1 1 tags, release work, worker sign-on NSST Remove existing 'A' RSST from 3 4.5 5.5 Vendor OE foundation(Z)

Move new 'A' RSST to existing MPS3 4 1 6.5 foundation NSST 5 Perform A' RSST processing and tie-ins( 3l 11 17.5 Vendor OE MPS3 6 Complete 'A' RSST circuit verification 4.5 22 NSST 5

Perform 'A' RSST pre-energization MPS3 7 (2-day overlap 25 testing, including fire spray test NSST with Activity 6)

Clear tags, align switchyard source/plant MPS3 8 1 26 buses/ loads for energization testing NSST MPS3 9 Perform 'A' RSST energization testing 1 27 NSST Coordination of work activities, weather MPS3 10 8 35 and other contingencies (l) NSST (1) MPS3 6900 V transformer 'B' RSST to be replaced along with the 4160 V transformer RSST 'A' (2) Includes draining oil, disconnecting internal connections, pulling vacuum, removing platforms, disconnecting cables, conduits, fire piping/detectors, 4160 V 2000 MCM cables, lightning arrestors.

(3) Includes pulling vacuum and oil processing (weather dependent), performing vendor site acceptance testing, connecting lightning arrestors, connecting high voltage bushing to new 345 kV motor-operated disconnect switches being installed during the outage, connecting 2000 MCM low voltage cabling, connecting oil-in-gas monitor, connecting power/control/instrumentation conduit and cabling, grounding, connecting plant process computer, installing platform, installing main control room protection scheme upgrades, and installing fire piping/detection.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 18 of 55 Based on the above, DENC is requesting NRC approval for TS changes to:

1. Modify TS 3.8.1.1 Required Action a.2 to add an option to extend the AOT from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 10 days. Use of the 10-day AOT option would allow normal maintenance and testing activities to be performed with MPS2 operating and with breaker 13T closed.

2. Add a new permanent TS 3.8.1.1 Required Action a.3 that specifies the requirements for use of a 10-day AOT option.

3. Add a one-time exception to the proposed Required Action a.3 that would extend the AOT to 35 days. Use of the 35-day AOT would allow the MPS3 'A' RSST, its associated equipment, and 345 kV south bus switchyard components to be replaced with MPS2 operating and with breaker 13T closed.

A supplemental power source must be verified to be available before entering either the proposed permanent TS action or one-time exception, and the availability must also be periodically checked throughout the duration of the extended AOTs. Additionally, certain compensatory and risk management actions will be met during both the permanent 10-day AOT and the one-time 35-day AOT.

4.2 Supplemental Power Source (SPS) for Extended AOTs 4.2.1 General Description NUREG-0800, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition," Branch Technical Position (BTP) 8-8, "Onsite (Emergency Diesel Generators) and Offsite Power Sources Allowed Outage Time Extensions," dated February 2012 (Reference 1-5) provides deterministic guidance related to proposed AOT extensions for offsite power sources.

DENC proposes to use the MPS3 SBO diesel generator as the supplemental power source for the inoperable offsite circuit, to mitigate a postulated LOOP event. The MPS3 SBO diesel generator is selected as the supplemental power source because the MPS2 EDGs (which are the first line of defense) cannot be credited.

Use of the SBO power source to maintain the defense-in-depth design philosophy of the electrical system to meet its intended safety function has been evaluated by DENC. This evaluation is detailed in the remainder of Sections 4.2 and 4.3.

4.2.2 Initial Conditions - Electrical Power Configuration (for 1O-Day/35-Day AOTs)

In evaluating the use of a MPS3 SBO diesel generator as a supplemental power source, the initial conditions for both the permanent 10-day and one-time 35-day AOT, are as follows:

I

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 19 of 55

MPS2 is assumed to be at full power operation.

MPS3 is in cold shutdown, refueling mode or defueled.

MPS3 'A' RSST is unavailable ("Path 2" on Figure 1).

Switchyard breaker 13T is closed

The south bus is de-energized and 345 kV line 310 is assumed to be out of service.

Whenever the switchyard south bus is removed from service, the 310 line will also be removed from service to reduce the plant trip risk to MPS2 due to a fault on this line causing an MPS2 load rejection. Additional rationale for this alignment and selection as the bounding case is provided in Section 4.2.3.

Both MPS2 offsite power sources will be energized through two separate paths (as highlighted on Figure 1) and available for use as follows:

- Preferred offsite power supply-powered from the MPS2 RSST ("Path 1" on Figure 1).

- Alternate offsite power supply-from MPS3 to MPS2 cross-tie powered from MPS3 'A' NSST ("Path 3" on Figure 1).

Although two power sources are available to be energized, the TS 3.8.1.1 Condition

a. for one inoperable offsite circuit *is entered, due to sensitivity to loss of independence at a single point (breaker 13T).

MPS3 SBO diesel generator is available for connection within 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months .

- As required by the new proposed permanent TS Required Action and one-time exception, the availability of the supplemental power source (MPS3 SBO diesel generator) shall be verified within 30 days prior to entering the configuration, and then checked once per shift (detailed further in Section 4.3). *

MPS2 4160 V system (including emergency buses 24C, 240 and 24E) are powered from the MPS2 NSST.

MPS2 EDGs will be operable (except when required to perform surveillance testing) and protected.

MPS2 turbine driven auxiliary feedwater pump (TDAFW) will be operable and protected.

FLEX 120 V portable generators stored in the BOB storage building are available for connection to MPS2 120 V vital panels VA20 and VA40 (to provide backup capability for vital instrumentation).

FLEX 480 V portable generators stored in the BOB storage building are available for connection to MPS2 480 V bus 22F.

FLEX 4160 V portable generators are stored offsite but are available for connection to MPS2 4160 V bus 240.

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 20 of 55 4.2.3 Initial Event Selection and Description (for 1O-Day/35-Day AOTs)

The scenario being evaluated in detail is a postulated fault on switchyard breaker 13T, while in the proposed permanent TS Required Action and one-time exception (with 10-day and 35-day AOTs respectively), with the MPS3 'A' RSST unavailable. The bounding scenario is also based on the south bus and the 310 line being out of service. Three cases are discussed below to provide explanation for how the bounding scenario was selected.

Case 1 In Case 1, the MPS3 'A' RSST is unavailable and the south bus is in service. A postulated breaker 13T fault would result in loss of both TS-required offsite sources to MPS2.

Specifically, the opening of breaker 14T disables MPS3 'A' NSST, and the opening of breakers 1T, 4T, and 7T disables the MPS2 RSST. However, MPS2 would not experience a reactor trip or a LOOP since power is supplied from the MPS2 NSST (which is no.t considered an offsite power source per MPS2 TS 3.8.1.1 ).

Case 2 In Case 2, the MPS3 'A' RSST is unavailable, the south bus is out of service and the 310 line is in service. In this configuration, all of MPS2 output goes through breaker BT, as 9T will already be open to isolate the south bus. A breaker 13T failure in this configuration would not result in an MPS2 reactor trip or LOOP, since power is supplied from the MPS2 NSST (similar to Case 1). However, this alignment exposes MPS2 to a reactor trip from a fault on the 310 line, which results in the opening of breakers BT and 7T to clear the fault.

This fault would result in MPS2 having no path to the transmission network, and which causes a load rejection reactor trip. In this scenario, the north bus and the MPS2 RSST will remain energized, and the 4160 and 6900 V loads would fast transfer to the MPS2 RSST after the MPS2 load rejection trip.

Case 3 In Case 3, the MPS3 'A' RSST is unavailable, the south bus is out of service and the 310 line is out of service. The 310 line is removed from service by opening a manual disconnect switct:i 310-15G-5 (as shown on MPS2 UFSAR Figure 8.1-1 D) and keeping breakers BT and 7T closed. In this configuration, the possibility of a 310 line trip and opening of BT and 7T is eliminated and therefore, trip risk from spurious 310 line fault (from storm conditions, bird interactions, etc.) is reduced. A postulated 13T breaker fault for this configuration would result in both a reactor trip and LOOP for MPS2. This breaker fault would de-energize the north bus, resulting in a load rejection, and would de-energize the MPS2 RSST and the MPS3 'A' NSST.

Removing the 310 line from service with the south bus out of service exposes MPS2 to a LOOP after a 13T fault. However, removing the 310 line eliminates exposure to a reactor trip from a fault on this line. As previously noted, DENC's experience at MPS indicates that a fault on a transmission line would be a more likely event precursor than a spurious

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 21 of 55 breaker internal fault. Therefore, removing the 310 line is considered an appropriate risk management action.

Because DENG intends to remove the 310 line from service whenever the south bus is out of service, Case 3 is considered to be the bounding case for detailed evaluation for a postulated breaker 13T fault. As the remainder of Section 4.2 demonstrates, MPS2 has sufficient capability to mitigate a 13T fault under the Case 3 configuration.

Following the occurrence of the LOOP event in the Case 3 configuration, the reactor will trip, and the plant will initially stabilize at slightly higher than no-load RCS temperature and pressure conditions, with decay heat removal via steam release to the atmosphere through the steam generator safety valves and/or atmospheric dump valves (ADVs). Natural circulation of the reactor coolant system (RCS) will develop to provide core cooling and the TDAFW pump will provide flow from the condensate storage tank to the steam generators to make up for steam release.

4.2.4 Operator Actions (for 1O-Day/35-Day AOTs)

The discussion below provides a bounding timeline of operator actions to restore AC power, under the scenario where a fault on switchyard breaker 13T occurs while in the proposed permanent TS Required Action or one-time exception (with 10-day and 35-day AOTs respectively). The timeline also assumes that the south bus and the 310 line are taken out of service.

It should be noted that the MPS2 EDGs would be the first line of defense for mitigating the event by providing power to the 4160 V buses to bring MPS2 to safe shutdown conditions.

The EDGs are expected to be available (except when required to perform surveillance testing) per MPS2 Limiting Condition for Operation (LCO) 3.8.1.1, which states that two EDGs shall be operable in modes 1, 2, 3, and 4. A risk management action is also included in the TS Bases to monitor MPS2 EOG status once per shift while in the proposed permanent TS Required Action (with a 10-day) and the one-time exception (with a 35-day AOT). Plant operators will perform routine logs and monitoring at least every 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months to ensure that EOG parameters and conditions are normal and will support operation.

Additionally, alarms in the control room will alert operators to abnormal conditions with the EDGs. However, this evaluation assumes that both EOG fail to demonstrate the additional defense-in-depth capability of the SBO equipment to mitigate the event.

Operators will respond to the LOOP event in accordance with emergency operating procedures (EOPs) to confirm RCS, secondary system, and containment conditions. The EOPs direct operators to isolate RCS letdown pathways, confirm natural circulation cooling, verify containment isolation, and establish electrical equipment alignment in preparation for eventual power restoration. The operators control auxiliary feedwater flow to the steam generators, establish local manual control of the steam generator ADVs, and stabilize the RCS at no-load cold leg temperature.

The operators will diagnose a station blackout and EOP 2530, Station Blackout (Reference 1-18) will be entered. The operators would then be directed to request power from MPS3.

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 22 of 55 In this event, the MPS3 SBO diesel generator will be available and the EOPs provide directions to energize MPS2 electrical buses from the MPS3 SBO diesel generator though a 4160 VAC cross-tie.

The MPS operators will start MPS3 SBO diesel generator and align to supply MPS2 in accordance with OP3346D, Station Blackout Diesel (Reference 1-49), and EOP 35 GA-27, Energizing SBO Diesel Auxiliaries with SBO Diesel (Reference 1-48).

Aligning the MPS3 SBO to MPS2 electrical buses and starting a charging pump is a time critical operator action and is completed within one hour of event initiation. This action ensures power is supplied to battery chargers and RCS makeup, within the assumptions of the Station Blackout Analysis (Reference 1-43). This analysis demonstrates that MPS2 can cope with loss of all AC power for one hour. This time critical operator action is periodically verified in accordance with Attachment 7 of C OP 200.18, Time Critical Action Validation and Verification (Reference 1-50).

In parallel, control room operators will be in communication with the transmission system operator to initiate actions to restore offsite power. In this scenario, the transmission system operator will dispatch electricians to the MPS switchyard, isolate the faulted 13T breaker with local disconnect switches 13T-4 and 13T-8, and realign switchyard breakers to restore offsite power to MPS. Opening 13T-4 allows repowering the north bus and the MPS2 RSST. Opening 13T-8 allows repowering the MPS3 terminal (from the 348 line) and the MPS3 'A' NSST which can then provide power to MPS2 via the 4160 V cross-tie and also restore offsite power to MPS3. As described in the Millstone UFSAR, these actions can be completed within 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months .

If realignment of the switchyard is unsuccessful and the transmission operator reports long-term loss of offsite power, the operators will transition to other procedures in the EOP procedure network, which will provide directions to cooldown MPS2 to cold shutdown conditions with AC power provided by the MPS3 SBO diesel generator. Existing EOPs include the steps to energize all MPS2 LOOP loads and take MPS2 to cold shutdown, but a regulatory commitment has been created to add steps to EOP(s) for Station Blackout response that will specifically direct operators to the appropriate EOP for reaching cold shutdown with AC power supplied by the Station Blackout diesel generator.

During this scenario, MPS3 EOP 3501, Loss of All AC Power (Modes 5, 6, and Zero)

(Reference 1-41), and EOP 3505, Loss of Shutdown Cooling and/or RCS Inventory (Reference 1-42), provides directions to maintain MPS3 in a safe shutdown condition powered from a MPS3 EOG.

4.2.5 SPS Sizing The MPS3 SBO diesel generator, or alternate alternating current (AAC) source is a 2260 kW, 3-phase, 0.8 power factor, 60 Hz, 4160 VAC diesel generator, which can provide power to either of the MPS3 4160 V emergency buses via the normal buses. The AAC provides a backup to the EDGs and satisfies the requirements of 10 CFR 50.63, Regulatory Guide (RG) 1.155 (Reference 1-7), and NUMARC 87-00 (Reference 1-40) for coping with

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 23 of 55 an SBO event. The AAC can also provide power to MPS2 in the event of a Station Blackout at that unit by means of a 4160 V cross-tie between the AAC output breaker and MPS2 Bus 24E. The AAC is also credited to supply alternate AC power to MPS2 via the same tie in the event of a fire in specifically identified MPS2 Appendix R areas.

The AAC source is comprised of a stand-alone diesel generator unit. The supporting equipment includes: a 3,000 gallon capacity fuel oil day tank, a 15,000 gallon fuel oil storage tank, a motor control center to power auxiliary fans, motors, pumps, starting air compressor, a switchgear center for protective relays and output breaker control, and a microcomputer for monitoring and alarming all AAC functions.

The engine fuel system includes: a 3,000 gallon fuel oil day tank, a 15,000 gallon fuel oil storage tank, fuel injectors, and an engine driven fuel pump. The fuel oil day tank is in a separate enclosure, partially mounted below ground to protect from vehicle or mechanical damage and to provide a concrete fuel vault at the AAC system low point to collect any potential spills. The fuel oil storage tank is a separate above ground tank with an integral containment dike. The 3,000 gallon fuel oil day tank provides a supply of fuel to exceed the eight hour SBO required run time. The 15,000 gallon fuel oil storage tank will provide a supply of fuel to exceed the 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months run time required by Millstone Appendix R.

The engine starting system uses compressed air for starting the engine. The starting system consists of air start motors, air receiver tanks, air compressor, strainers, starting air solenoid valves, air start valves, air line lubricators, shutoff valves, and pressure reducer regulators. Two starting banks are simultaneously used, one on each side of the engine, for maximum reliability. Each bank consists of one receiver supplying two air start motors.

The AAC voltage is specified by the MPS3 SBO diesel generator manufacturer as 4160 +/-

1% for all steady state loads from no load to full load. The AAC voltage and frequency (60 HZ +/- 0.15 HZ) are within the requirements of the MPS2 and MPS3 4160 V emergency buses.

SP-EE-362, MP2 Station Blackout Safe Shutdown Scenario Document (Reference 1-43),

97-ENG-017'74E2, Battery 201A and Charger Associated Cable Device Electrical Verification Calculation (Reference 1-51 ), and 97-ENG-01775E2, Battery 201 B and Charger Associated Cable Device Electrical Verification Calculation (Reference 1-8),

demonstrate that MPS2 has the capability to cope with no offsite or onsite emergency AC power for one hour except for battery backed power supplies (i.e. 120 V AC vital system) with no load shedding. Within the first hour, MPS2 will have an alternate AC power source available from the MPS3 SBO diesel generator. This analysis also demonstrates that MPS2 maintains safe shutdown conditions for 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months with RCS inventory maintained with a MPS2 charging pump, and decay heat removal provided by the turbine driven auxiliary feedwater pump and operation of the atmospheric dump valves, with power provided by the MPS3 SBO qiesel generator.

ENG-02132E2 MP2 Appendix R Loading Calculation (Reference 1-12), and 25203-SP-M2-SU-1046 U2 Appendix R Compliance Report (Reference 1-32), demonstrate capabilities *of the MPS3 SBO diesel generator to power MPS2 loads to attain cold shutdown conditions

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 24 of 55 during certain Appendix R fires at MPS2. These documents analyze all loads needed to bring MPS2 to cold shutdown condition, including a charging pump (72.66 kW), service water pump (332.9 kW), reactor building closed cooling water pump (251.3 kW),** 1ow pressure safety injection (shutdown cooling) pump (301.5 kW), auxiliary feedwater pump (280.75 kW), battery charger (53 kW), containment air recirculating fans (63.58 kW), and miscellaneous loads (461 kW), at a maximum of 1816.77 kW, well below the MPS3 SBO diesel generator continuous rating of 2260 kW.

The MPS3 SBO diesel generator can be aligned to either MPS2 safety electrical bus 24C or 240 to power the loads noted above through bus 24E. Only one safety bus and one facility/ train of equipment is needed to attain cold shutdown at MPS2.

MP-CALC-ENG-MP2-ENG-ETAP-04014E2, MP2 Electrical Distribution System Analysis (Reference 1-11 ), Study Case 2-SC-Att-DF analyzes the short circuit contributions from the MPS3 SBO diesel generator providing power feed to the 24E bus. Bus short circuit levels (momentary and interrupt) are demonstrated to be below the switchgear ratings.

MP-CALC-ENG-90-050-0097E3, MP3 SBO Diesel Generator Power Cable Sizing (Reference 1-52), CCN. 3 provides a cable ampacity and voltage drop evaluation for the cables routing power from the MPS3 SBO diesel generator, 4160 V Buses 34A, 348 and 24E. The analysis shows the cables are adequately sized to handle a full load of 3 MVA which exceeds the full load capabilities of MPS3 SBO diesel generator at the 4160 V buses. The evaluation also shows a minimal voltage drop of 22V (@4160 V), which is acceptable.

MP-CALC-ENG-96-ENG-01272M3, SBO Diesel Generator Run Times (Reference 1-53),

Add. 1 provides justification that the MPS3 SBO diesel generator has a conservative run time 73.7 hours8.101852e-5 days 0.00194 hours 1.157407e-5 weeks 2.6635e-6 months at a load rating of 2574 kW. This evaluation also postulates the fuel day tank and 15,000 gallon storage tank are at both at their respective low level setpoints. In addition, this .calculation also provides justification that the MPS3 SBO diesel generator can run at its rating of 2574 kW for up to 168 hours0.00194 days 0.0467 hours 2.777778e-4 weeks 6.3924e-5 months without requiring maintenance. Therefore, both the fuel volume and diesel generator design support run times in excess of the required 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to attain cold shutdown conditions discussed in 25203-SP-M2-SU-1046 U2 Appendix R Compliance Report (Reference 1-32).

Calculation MP3-ENG-ETAP-04125E3 (Reference 1-54), Study Case 3SB0-2-MSP5, analyzes for adequate MPS2 steady state 4160 V bus voltages when supplied from the MPS3 SBO diesel generator, with the diesel loaded at near capacity. This calculation also starts the largest MPS2 4160 V Service Water Pump, P5A while supplied from the MPS3 SBO diesel generator with acceptable transient bus voltages.

The above calculations demonstrate the ability of MPS2 to cope with a loss of all AC power for one hour independent of an alternate current power source and demonstrate the capability of the MPS3 SBO diesel generator and Millstone Station electrical distribution system to successfully carry all MPS2 LOOP loads to bring the unit to cold shutdown without any load shedding.

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 25 of 55 4.2.6 SPS Physical Connection to MPS2 Figure 1 shows the. MPS electrical distribution system. The MPS3 SBO diesel generator (noted as "MP3 SBODG" on the Figure 1) output breaker ties to MPS3 Buses 34A, 348 or MPS2 Bus 24E. The normal buses feed their corresponding emergency buses by a Class 1E tie breaker. Control for closing feeder breakers to the 34A and 348 buses is available at MPS3 main control board and/or locally at the switchgear. Control for closing the feeder breaker to Bus 24E is available at the MPS2 main control board.

The MPS3 SBO diesel generator provides power to MPS2 by means of a 4160 V cross-tie between the SBO output breaker and Unit 2 Bus 24E.

4.2.7 SPS Testing Capability The availability of the MPS3 SBO diesel generator is verified once per refueling cycle, and breakers required to align electric power from MPS3 to MPS2 are verified per PM program to satisfy MPS2 Appendix R Technical Requirement surveillance requirement item A.

The MPS3 SBO diesel generator is tested quarterly per SP 3670.4, Routine PMs (Reference 1-47), which is performed through a loaded run of the engine.

4.2.8 SPS Staffing Staffing for operation of the MPS3 SBO diesel generator in support of MPS2 is maintained at all times by the normal MPS2 and MPS3 minimum shift compliment. No additional personnel are required for MPS3 to supply power to MPS2 with the SBO diesel generator for the extended AOT.

4.2.9 MPS2 GDC-17 Coping Capability (for 10-Day/3S:-Day AOTs)

Per GDC-17 requirements, the alternate offsite circuit must be available in sufficient time to ensure an orderly shutdown and cooldown without any requirement to postulate a design basis accident condition.

During either extended AOT, the MPS3 to MPS2 cross-tie will remain capable of being energized from the MPS3 'A' NSST. This line is monitored and alarmed in the MPS2 control room for an undervoltage condition. If an alarm is received, operators will determine the cause of the undervoltage condition and restore 4160 V bus 24E from an available source.

4.2.10 MPS2 LOOP Coping Capability (for 1O-Day/35-Day AOTs)

The onsite emergency AC power system is not impacted by the plant electrical line-up configuration while in either the 10-day or 35-day extended AOT. Both EDGs will be operable (except when required to perform surveillance testing) and the capability to bring

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 26 of 55 MPS2 to a cold shutdown condition, is not impacted. Therefore, MPS2's response to a LOOP will be unaffected when in either the 10-day or 35-day extended AOT.

4.2.11 MPS2 SBO Coping Capability (for 1O-Day/35-Day AOTs)

MPS2 utilizes existing EOPs to guide the control room operators through the appropriate steps to systematically cope with a total loss of AC power (i.e., SBO). If the entry conditions for the LOOP-related EdPs are not met, the plant will transition to the SBO-related EOPs.

Crediting the MPS3 SBO diesel generator as a supplemental power source for an extended offsite line AOT at MPS2 has no impacts to MPS2 station blackout coping capability, as there are no changes in MPS3 SBO diesel generator operation or configuration required during the extended AOT. The ability* of the MPS3 SBO diesel generator to power MPS2 loads through the 4160 VAC.cross-tie remains unchanged.

4.2.12 MPS2 Appendix R Coping Capability (for 1O-Day/35-Day AOTs)

Crediting the MPS3 SBO diesel generator as a supplemental power source for an extended offsite line AOT at MPS2 has no impacts to MPS2 Appendix R coping capability, as there are no changes in MPS3 SBO diesel generator operation or configuration required during the extended AOT. The ability of the MPS3 SBO diesel generator to power MPS2 loads through the 4160 VAC cross-tie is unchanged.

4.2.13 Training Training on emergency operating procedures during LOOPs and SBO is conducted periodically in accordance with Millstone station licensed and non-licensed operator training program to maintain proficiency energizing MPS2 emergency buses from the MPS3 SBO diesel generator.

Prior to entering either proposed permanent TS Required Action or one-time exception, pre-job briefs would be conducted to increase awareness of the risk sensitivity associated with the activity.

4.2.14 Work Management The MPS work management program ensures the configuration of plant equipment is appropriately monitored during the extended AOTs.

The Work Management program is designed to minimize risk though a blended approach of quantitative and qualitative risk assessment. The quantitative risk assessment is performed by a risk monitor that includes quantitative insights from PRA. The qualitative risk assessment evaluates the impact of maintenance activities on KSFs by:

Identifying KSFs affected by the system, structure or component (SSC) planned for removal from service.

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 27 of 55

Considering the degree to which removing the SSC from service will impact the KSFs.*

Considering the degree of redundancy and duration of the out-of-service condition.

Identifying appropriate compensatory measures, contingencies, or protective actions that could be taken for the activity under consideration, if appropriate.

For power operation, key plant safety functions are those that:

Ensure the integrity of the reactor coolant pressure boundary.

Ensure the capability to shut down.

Maintain the reactor in a safe shutdown condition.

Ensure the capability to prevent or mitigate the consequences of accidents that could result in potentially significant offsite exposures.

Examples of these key plant safety features include Containment Integrity, Reactivity Control, Reactor Coolant Heat Removal System, Reactor Coolant System Inventory Control, and Power Availability.

Work management of the transmission operator in the MPS switchyard is integrated into the MPS work control process and controls are in place for DENG to provide work task oversight when the transmission operator is performing risk activities.

4.2.15 Conformance with MPS3 TS and MPS2/3 Technical Requirements The proposed revisions to the MPS2 TSs do not necessitate any changes to the MPS3 TSs. The proposed permanent Required Action and one-time exception can only be entered when .MPS3 is shut down. Thus, MPS3 will be in MODE 5 or 6 and TS LCO 3.8.1.2 would be applicable. MPS3 LCO 3.8.1.2 requires only one circuit between the offsite transmission network and the Onsite Class 1E Distribution System to be operable, which would be fulfilled by the MPS3 'A' NSST. The operability of the MPS3 'A' NSST as an offsite power source for MPS3 does not require switchyard breaker 13T to_ be open.

The TS markup in Attachment 2 for both the proposed 10-day and 35-day AOTs states that MPS3 must be in MODE 5, 6 or defueled to permit entry into the Required Action.

MPS2 Technical Requirement (TR) 3.8.1.2 requires that the offsite lines to the MPS switchyard (310, 348, 371 and 383) be functional, when the electrical output at MPS exceeds 1650 MWe net. MPS3 TR 3.8.1 has identical requirements. As previously noted, whenever the switchyard south bus is taken out of service during a MPS3 'A' RSST outage, the 310 line will also be taken out of service (to reduce the risk to MPS2 for a plant trip due to a fault on this line causing an MPS2 load rejection). Extended inoperability of the MPS3

'A' RSST (which would occur when the south bus is removed from service) is only allowed when MPS3 is in shutdown modes, per MPS3 TS 3.8.1.1. Therefore, MPS2 TR 3.8.1.2 and MPS3 TR 3.8.1, "Offsite Line Power Sources," would not be applicable (with MPS

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 28 of 55 electrical output less than 1650 MWe net), which allows the offsite line 310 to be non-functional.

4.3 Assessment Against Branch Technical Position 8-8 The purpose of BTP 8-8 (Reference 1-5) is to provide guidance from a deterministic perspective in reviewing amendment requests for one-time or permanent AOT extensions for the EDGs and offsite power sources. Typically these amendment requests relate to performing online maintenance of EDGs and offsite power sources. BTP 8-8 states that a supplemental power source should be available as a backup to the inoperable EOG or offsite power source, to maintain the defense-in-depth design philosophy of the electrical system to meet its intended safety function.

DENC intends to perform maintenance of switchyard components with breaker 13T closed.

As previously noted, aligning breaker 13T in this position has no adverse impact on the ability of the. MPS3 'A' NSST to supply power to the 4160 V buses. The requirement to consider the MPS3 'A' NSST inoperable when 13T is closed is only due to loss of independence of both MPS2 offsite sources at a single point (breaker 13T). Both offsite sources are energized and available during the extended AOTs. However, DENC has conservatively considered and assessed the criteria of BTP 8-8 for the proposed 10-day and 35-day extended AOTs.

The following is a list of criteria outlined in the initial revision of BTP 8-8 dated February 2012 (Reference 1-5) for an extended AOT. Deviations from the deterministic criteria provided in the BTP 8-8 that require supplemental risk information are supported by an evaluation consistent with RG 1.174, Rev. 3 and RG 1.177, Rev. 1. The results of the risk assessments are provided in Section 4.4 and are acceptable in accordance with RG 1.174 and RG 1.177 criteria.

a) The supplemental source must have the capacity to bring a unit to safe shutdown (cold shutdown) in case of a loss of offsite power (LOOP) concurrent with a single failure during plant operation (Mode 1).

Permanent AOT Request to 1O Days The description provided in Section 4.2.5 demonstrates the ability of MPS2 to cope with a loss of all AC power for one hour independent of an alternate current power source and. demonstrates the capability of the MPS3 SBO diesel generator and Millstone Station electrical distribution system to successfully carry all. MPS2 LOOP loads to bring the unit to cold shutdown without any load shedding.

One-Time AOT Request to 35 Days Same as above.

b) The permanent or temporary power source can be either a diesel generator, gas or combustion turbine, or power from nearby hydro units. This source can be credited as a supplemental source, that can be substituted for an inoperable EOG during the period of extended AOT in the event of a LOOP, provided the risk-informed and

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 29 of 55 deterministic evaluation supports the proposed AOT and the power source has enough capacity to carry all LOOP loads to bring the unit to cold shutdown.

Permanent AOT Request to 10 Days The proposed supplemental power source is the MPS3 SBO diesel generator.

BTP 8-8 states that:

Multi-unit sites that have installed a single AAC power source for SBO cannot substitute it for the inoperable diesel when requesting AOT extensions unless the AAC source has enough capacity to carry all LOOP loads to bring the unit to a cold shutdown as a substitute for the EOG in an extended AOT and carry all SBO loads for the unit that has an SBO event without any load shedding.

However, the permanent TS Required Action with an AOT of 10-days can only be entered when MPS3 is in MODE 5, 6 or defueled (which is a requirement in the TS markup); therefore, MPS3 is already in a cold shutdown condition. MPS2 UFSAR Section 8.1.3.1 and MPS3 UFSAR Section 8.3.1.1.6 state that Station Blackout is postulated to occur at one unit only at any one time.

During this scenario, MPS3 emergency operating procedures, EOP 3501, Loss of All AC Power (Modes 5, 6, and Zero) (Reference 1-41), and EOP 3505, Loss of Shutdown Cooling and I or RCS Inventory (Reference 1-42), provides directions to maintain MPS3 in a safe shutdown condition powered from a MPS3 EDG. MPS3 LCO 3.8.1.2 requires one MPS3 EDG and one offsite circuit to be OPERABLE when the unit is in MODES 5 and 6.

See the response to bullet a) for explanation of how the MPS3 SBO has enough capacity to carry all LOOP loads to bring MPS2 to cold shutdown without any load shedding.

One-Time AOT Request to 35 Days Same as above.

c) For plants using Alternate Alternating Current (AAC) or supplemental power sources discussed above, the time to make the AAC or supplemental power source available, including accomplishing the cross-connection, should be approximately one hour to enable restoration of battery chargers and control reactor coolant system inventory.

Permanent AOT Request to 10 Days Aligning the MPS3 SBO to MPS2 electrical buses and starting a charging pump is a time critical operator action and is completed within one hour of event initiation. This time critical operator action is periodically verified in accordance with Attachment 7 of C OP 200.18, Time Critical Action Validation and Verification (Reference 1-50). This action ensures power is supplied to battery chargers and reactor coolant system

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 30 of 55 makeup within the assumptions of the Station Blackout Analysis (Reference 1-43). This analysis demonstrates that MPS2 can cope with loss of all AC power for one hour.

One-Time AOT Request to 35 Days Same as above.

d) The availability of AAC or supplemental power source should be verified within the last 30 days before entering extended AOT by operating or bringing the power source to its rated voltage and frequency for 5 minutes and ensuring all its auxiliary support systems are available or operational.

Permanent AOT Request to 10 Days The MPS3 SBO diesel generator will be tested within 30 days prior to entering the extended AOT by bringing the power source to its rated voltage and frequency for more than 5 minutes and ensuring all its auxiliary support systems are available or operational. The proposed Required Action a.3 includes this verification as a requirement for entry.

One-Time AOT Request to 35 Days Same as above.

e) *The plant should have formal engineering calculations for equipment s1zmg and protection and have approved procedures for connecting the AAC or supplemental power sources to the safety buses.

Permanent AOT Request to 1O Days The calculations discussed in Section 4.2.5 demonstrate the ability of MPS2 to cope with a loss of all AC power for one hour independent of an alternate current power source and demonstrate the capability of the MPS3 SBO diesel generator and Millstone Station electrical distribution system to successfully carry all MPS2 LOOP loads to bring the unit to cold shutdown without any load shedding.

As discussed in Section 4.2.4, emergency operating procedure EOP 2530, Station Blackout (Reference 1-18) provides instructions to th.e operators to connect the f\AC to the safety buses.

One-Time AOT Request to 35 Days Same as above.

f) The EOG or offsite power AOT should be limited to 14 days to perform maintenance activities. The licensee must provide justification for the duration of the requested AOT (actual hours plus margin based on plant-specific past operating experience).

Permanent AOT Request to 10 Days DENG is requesting a permanent TS Required Action with an AOT of 10 days in order to perform required maintenance to retain the MPS3 'A' RSST and other switchyard

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 31 of 55 south bus components in good operating condition. An analysis determined that 10 days (see Table 1-1) is needed (assuming a reasonable amount of time for contingency) to perform these maintenance activities. Section 4.1.1 provides detail on how plant-specific past operating experience was used in deriving the permanent 1O-day AOT duration.

One-Time AOT Request to 35 Days DENG is requesting a one-time AOT of 35 days in order to replace the MPS3 'A' RSST because the replacement cannot be completed within the proposed permanent 10-day AOT. An analysis determined that 35 days (see Table 1-2) is needed to complete the MPS3 'A' RSST replacement. Section 4.1.2 provides detail on how plant-specific past operating experience was used in deriving the one-time 35-day AOT duration.

This 35-day AOT is greater than the 14 day criterion provided in BTP 8-8 .. It is listed as an exception in Table 1~3. Additional risk information in accordance with RG 1.174 and RG 1.177 is provided in Section 4.4 to further justify this request and demonstrate that the risk is acceptably low for this one time AOT extension.

g) The TS must contain Required Actions and Completion Times to verify that . the supplemental AC source is available before entering extended AOT.

Permanent AOT Request to 10 Days The proposed permanent TS Required Action will require DENG to validate the onsite MPS3 SBO diesel generator availability by starting and loading the MPS3 SBO diesel generator within 30 days prior to entering the AOT. The proposed TS .Required Action also requires the availability of the MPS3 SBO diesel generator to be checked once per shift.

One-Time AOT Request to 35 Days Same as above.

h) The availability of the AAC or supplemental power source shall be checked every 8-12 hours (once per shift).

Permanent AOT Request to 10 Days The proposed Required Action a.3 includes a once per shift check of the supplemental power source availability as a requirement for remaining within the 10-day extended AOT. This check includes administratively examining logs or other information to determine if the Millstone Unit No. 3 SBO diesel generator is out of service for maintenance or other reasons. This manner of checking is consistent with the existing MPS2 TS Bases discussion for the 14-day EOG AOT. The check also includes local visual observation of MPS3 SBO diesel generator once per shift, along with confirmation of correct switch configuration and indicated power availability once per day.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 32 of 55 One-Time AOT Request to 35 Days Same as above.

i) The extended AOT will be used no more than once in a 24-month period (or refueling interval) on a per diesel basis to perform EOG maintenance activities, or any major maintenance on offsite power transformer or bus.

Permanent AOT Request to 10 Days A permanent AOT of 10 days is requested to allow required preventative maintenance .

on the MPS3 'A' RSST and other switchyard south bus components to ensure their good operating condition no more frequently than once per 18 month refueling interval for MPS3. A risk management action is included in the TS Bases to ensure that the necessary actions are taken for future extended AOT entries.

One-Time AOT Request to 35 Days The planned one-time extended 35-day AOT will be used once for replacing the MPS3

'A' RSST and 345 kV south bus components and no later than the MPS3 refueling outage 22 (fall 2023).

j) The pre-planned maintenance will not be scheduled. if severe weather conditions are anticipated.

Permanent AOT Request to 10 Days Weather conditions will be evaluated prior to entering the extended 10-day AOT will not be entered if official weather forecasts predict severe weather conditions (i.e., tornado or hurricane warnings). Operators will monitor weather forecasts each shift during the extended AOT.

During the development of the Millstone Station Removal of Severe Line Outage Detection from The Offsite Power System LAR (Reference 1-44), a definition for adverse (or severe) weather conditions was established as hurricane watch/warnings and tornado watch/warnings for the purposes of implementing MPS2 TR 4.8.1.2 based on a historical review of plant impacts to Millstone during extreme weather conditions.

This definition will also be used in assessing severe weather, while performing the related risk management action for the proposed permanent 10-day AOT.

MPS2 UFSAR chapter 2 describes measures to protect the unit from severe weather resulting from hurricane conditions. These measures and other risk management actions are detailed in procedures C OP 200.6, Storms and Other Phenomena (Preparation and Recovery) (Reference 1-45), and AOP 2560, Storms, Winds, and High Tides (Reference 1-46). These procedures provide direction for restoration of risk sensitive equipment, walkdowns and site preparations for high wind conditions, mobilization of site personnel, and considerations for plant shutdown / cooldown when entry conditions are experienced or anticipated. These actions include consideration of planning delivery of required fuels for backup power sources. The response also includes regular periodic communication and coordination with the transmission system

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 33 of 55 operator for evaluation of impending severe weather threats to the health of the transmission network, along with discussion of any remedial actions, and preparations for contingencies and restoration activities.

If forecast local weather conditions reach levels deemed by station management as a threat to safe operations or threat to the transmission network, MPS operators will open breaker 13T, shut down, or initiate a plant trip, as appropriate.

A risk management action is included in the TS Bases to ensure that the necessary actions are taken for future extended AOT entries.

One-Time AOT Request to 35 Days Same as above.

k) The system load dispatcher will be contacted once per day to ensure no significant grid perturbations (high grid loading unable to withstand a single contingency of line or generation outage) are expected during the extended AOT.

Permanent AOT Request to 10 Days The system load dispatcher will be contacted once per day to ensure no significant grid perturbations (high grid loading unable to withstand a single contingency of line or generation outage) are expected during the extended AOT. A risk management action is included in the TS Bases to ensure that the necessary actions are taken for future extended AOT entries.

One-Time AOT Request to 35 Days Same as above.

I) Component testing or maintenance of safety systems and important non-safety equipment in the offsite power systems that can increase the likelihood of a plant transient (unit trip) or LOOP will be avoided. In addition, no discretionary switchyard maintenance will be performed.

Permanent AOT Request to 10 Days As part of the work management program, MPS2 will not conduct non-surveillance discretionary testing or maintenance of safety systems. However during this AOT, work may be performed on the 345 kV switchyard south bus which requires the south bus to be taken out of service.

As described in Section 4.2.3, removing the 310 line from service with the south bus out of service exposes MPS2 to a LOOP if 13T experiences a fault. However, removing the 310 line also eliminates exposure to a reactor trip from a fault on that line ..

Performing the switchyard work during the extended AOT as described above is a deviation from the guidance provided in BTP 8-8. It is listed as an exception in Table

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 34 of 55 1-3. Additional risk information in accordance with Regulatory Guide (RG) 1.174 and RG 1.177 is provided in Section* 4.4 to further justify this request and demonstrate that the risk is acceptably low for this permanent AOT extension.

A risk management action is included in the TS Bases to ensure that the necessary actions are taken (considering the noted deviation) for future extended AOT entries.

One-Time AOT Request to 35 Days Same as above except the longer AOT is required to allow replacing the MPS3 'A' RSST and south bus switchyard components. This activity will require longer than 10 days to complete.

m) TS required systems, subsystems, trains, components, and devices that depend on the remaining power sources will be verified to be operable and positive measures will be provided to preclude subsequent testing or maintenance activities on these systems, subsystems, trains, components, and devices.

Permanent AOT Request to 10 Days Selected plant equipment will be protected during the proposed permanent TS change, based ori the Tier 2 assessment in Section 4.4. DENG will continue to operate MPS2 in accordance with the approved TS. A risk management action is included in the TS Bases to ensure that the necessary actions are taken for future extended AOT entries.

One-Time AOT Request to 35 Days Same as above.

n) Steam-driven emergency feedwater pump(s) (in the case of PWR units) will be controlled as protected equipment".

Permanent AOT Request to 10 Days

MPS2 will control the TDAFW pump as "protected equipment." A risk management action is included in the TS Bases to ensure that the necessary actions are taken for future extended AOT entries.

One-Time AOT Request to 35 Days Same as above.

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 35 of 55 Table 1-3 Deviations from Branch Technical Position 8-8 Requiring Supplemental Risk Information The EDG or offsite power AOT should be A one-time AOT of 35 days is being RG 1.174 and RG 1.177 risk information addressing this deviation is 1

limited to 14 days. requested. provided in Section 4.4.

Component testing or maintenance of safety A risk management action for RG 1.174 and RG 1.177 risk information addressing this deviation is systems and important non-safety equipment performing work on_ the south bus with provided in Section 4.4.

in the offsite power systems that can increase line 310 out of service during the 2 the likelihood of a plant transient (unit trip) or permanent 10-day or one-time 35-day LOOP will be avoided. In addition, no AOT is included.

discretionary switchyard maintenance will be performed.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 36 of 55 4.4 Plant Specific Probabilistic Risk Analysis Branch Technical Position (BTP) 8-8 (Reference 1-5) states that it is expected that applications for extended AOTs will contain a PRA assessment. The risk assessment supporting this amendment request is detailed in NOTEBK-PRA-MPS2-RA.Ll.004, "PRA Input to Proposed Technical Specification 3.8.1.1 Change" (Reference 1-38), and summarized in this Section. The risk analysis was performed in accordance with the Regulatory Guide (RG) 1.177 (Reference 1-21) risk-informed approach for evaluating TS changes. The assessment focused on evaluating deviations from BTP 8-8 criteria that require supplemental risk information, as identified in Section 4.3.

4.4.1 Methodology RG 1.177 identifies a three-tiered approach as described below:

Tier 1: Probabilistic Risk Assessment Capability and Insights Tier 1 assesses the impact of the proposed amendment request on Core Damage Frequency (CDF), Incremental Conditional Core Damage Probability (ICCDP), Large Early Release Frequency (LERF), and Incremental Conditional Large Early Release Probability (ICLERP). To support this assessment, two aspects are considered: (1) the acceptability of the PRA and (2) the PRA insights and findings.

PRA insights and findings are generated by determining the impact of the proposed amendment request on plant risk. The scope of the PRA model used to assess the risk impact should include all hazard groups (i.e., internal events, internal flood, internal fires, seismic events, high winds, transportation events, and other external hazards) unless it can be shown that the contribution from specific hazard groups does not affect the decision.

PRA Insights and Findings Model Scope The proposed amendment request introduces a Required Action for maintaining switchyard breaker 13T closed coincident with the MPS3 'A' RSST out of service. This configuration increases the MPS2 offsite power circuit failure probability and ultimately the LOOP frequency. The determination of hazard groups affected by the proposed amendment request and thus, the PRA model scope used for this application, is provided below:

Internal Events and Internal Flood The offsite power sources are credited with mitigating internal events and internal floods.

The MPS2-R05g model (Reference 1-28) was used to calculate the risk impact on internal events and internal floods. The truncation limits were established in accordance with American Society of Mechanical Engineers (ASME) PRA Standard RA-Sa-2009 (per References 1-29 & 1-30). The truncation value used to calculate CDF is 1E-11; whereas, the value used for LERF is 5E-13.

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 37 of 55 Shutdown/Refueling The proposed permanent Required Action and one-time exception are not applicable to shutdown modes (i.e., 5, 6, and defueled) since, per MPS2 TS (Reference 1-2), only one offsite circuit is required to be operable in these modes and maintaining 13T closed only affects the operability of the second offsite circuit. Consequently, there is no shutdown risk impact associated with the proposed amendment request Seismic MPS2 does not have a seismic PRA model and therefo"re, the risk impact for this hazard group will be assessed qualitatively. Per Reference 1-31, the offsite power sources [i.e.,

MPS2 RSST and MPS3 'A' NSST (or 'A' RSST)] are not listed on the seismic Safe Shutdown Equipment List (SSEL) and therefore, are not considered seismic risk mitigqtion equipment. Since *the insulators on switchyard components have relatively high seismic fragility, a loss of offsite power is considered likely during seismic events. Therefore, the conditional seismic risk of unavailability of offsite power sources associated with the proposed amendment request is considered negligible.

Internal Fires MPS2 does not have an internal fire PRA model and therefore, the risk impact for this hazard group will be assessed qualitatively. Per the Appendix R Compliance Report (Reference 1-32), the offsite power sources. [i.e., MPS2 RSST and MPS3 'A' NSST (or RSST)] are not listed on the fire SSEL and therefore are not considered fire safe shutdown equipment. For risk significant fire areas (including the control room, cable vault and switchgear rooms), the proceduralized fire mitigation strategy (e. g. Reference 1-16) de-energizes the MPS2 RSST to ensure that the reactor coolant pumps (RCPs) are stopped to prevent a catastrophic RCP seal failure, and to ensure that spurious operations do not result in unexpected loss of coolant from the RCS. Therefore, the conditional fire risk of unavailability of offsite power sources associated with the proposed amendment request is considered negligible.

Other External Events All other external hazard groups (i.e., not seismic or internal fire) were screened for applicability to the proposed amendment request in accordance with Generic Letter 88-20 (Reference 1-33) and updated to use the criteria in ASME PRA Standard RA-Sa-2009. provides a summary of the other external hazards screening results. provides a summary of the progressive screening approach for external hazards.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 38 of 55 In summary, the PRA model scope for the proposed amendment request includes internal events and internal floods. The risk impact will be quantitatively assessed using the MPS2-R05g model. An assessment of the quality of the PRA model is provided in Attachment 5.

Acceptance Criteria The acceptance criteria for the permanent and one-time TS changes are as follows:

Permanent Change Criteria

ilCDF less than 1E-06/yr (Reference 1-20)

ilLERF less than 1E-07/yr (Reference 1-20)

ICCDP less than 1E-06 (Reference 1-21)

ICLERP less than 1E-07 (Reference 1-21)

One-time Change Criteria

ICCDP less than 1E-06 and ICLERP less than 1E-07 OR

ICCDP less than 1E-05 and ICLERP less than 1E-06 with effective compensatory measures implemented to reduce the sources of increased risk Quantitative Risk Assessment The proposed permanent TS Required Action and one-time exception request maintaining switchyard breaker 13T closed coincident with the MPS3 'A' RSST removed from service.

With 13T closed and the MPS3 'A' RSST out of service, a 13T fault or a fault that de-energizes the north bus coincident with 13T failing to open results in disabling the two available MPS2 offsite power sources (i.e., the MPS2 RSST and MPS3 'A' NSST). Given successful fault isolation, MPS2 would remain online since its main generator is tied in between breakers ST and 9T, which would both remain closed if breaker 7T open~ as designed. Therefore, in this configuration, a MPS2 LOOP would only occur if an additional equipment failure caused a reactor trip.

However, the potential exists to perform maintenance on the south bus while entered into the proposed permanent TS Required Action and one-time exception configuration. To de-energize the south bus, switchyard breakers 2T, 5T, 9T, and 15T are opened. With 9T open, all the MPS2 power output would be transmitted via breaker ST. Since the 310 transmission line ties in between breakers 7T and ST, an interruption of that line would open the ST breaker causing a MPS2 reactor trip. Consequently, if the south bus is de-energized coincident with the MPS3 'A' RSST out of service and 13T closed, the 310 line would also be de-energized to minimize MPS2 reactor trip risk. With the south bus and 310 line de-energized coincident with the MPS3 'A' RSST out and 13T closed, a 13T fault or a fault that de-energizes the north bus coincident with 13T failing to open results in loss of both switchyard buses and thus, a MPS2 reactor trip coupled with a LOOP.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 39 of 55 Therefore, since the consequences of a 13T fault are more severe if the configuration includes a south bus and 310 line outage, the plant configuration analyzed in the risk assessment is:

MPS3 in Mode 5, 6, or defueled

MPS3 'A' RSST out of service

Switchyard breaker 13T closed

South bus de-energized

310 line de-energized The impact of this configuration on MPS2-R05g PRA model (Reference 1-28) inputs is assessed below:

LOOP frequency The analyzed configuration results in an increase in LOOP frequency. Four types of LOOP events are modeled in the PRA: Plant-centered, grid-related, weather-related, and consequential, which are differentiated by event severity (i.e., offsite power non-recovery probability). The LOOP type impacted oy the analyzed configuration is considered grid-related since a 13T fault would result in loss of both switchyard buses (i.e., power to the entire site) and power could not be restored for several hours. It should be noted that a 13T fault is expected to be isolated and offsite power restored to MPS2 within 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months as described in MPS2 UFSAR section 8.1.2.2.d (Reference 1-.1 ).

MPS3 offsite power source availability The PRA model credits one of the two MPS3 offsite power sources, either the 'A' NSST or 'A' RSST, with mitigating a plant-centered MPS2 LOOP (e.g., Reactor trip coincident with MPS2 RSST failure). Since the MPS3 'A' NSST will be energized during the analyzed configuration, it remains capable of mitigating a plant-centered MPS2 LOOP.

Therefore, the MPS3 'A' NSST is credited within the risk assessment.

As a result, the only PRA model input affected by the proposed amendment request is the grid-related LOOP frequency, LOOPGR. The LlLOOPGR was calculated using the following equation:

A13r fault+ A.Fault & 13T fails to open Where, A.Fault & 13T fails to open = (A.North Bus fault + A7T fault + A4r fault + AlT fault +

AMPSZ RSST fault + AMPS3 NSST fault + ,AMPS3 Main XFORMERs) * (P13r fails to open)

It should be noted that MPS3 will not be operating during the proposed permanent TS Required Action and one-time exception configurations. Consequently, main generator

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 40 of 55 output breaker, 15G-3U-2, will be open and therefore, a fault of the output breaker is not a potential failure mechanism.

Based on industry data originally compiled by the NRG in NUREG/CR-6928 (Reference 1-34) and updated through 2015, the spurious operation failure rate of a high voltage circuit breaker is 4.83E-07/hr, the bus fails to operate failure rate is 9.55E-07/hr; the transformer fails to operate failure rate is 2.89E-06/hr, and the fail to open failure rate of a high voltage breaker is 2.83E-03/demand.

Substituting the industry failure rates into the above equation yields the following:

LiLOOPGR = 4.72E-03/yr The risk impact of the proposed permanent and one-time TS changes was then calculated by executing the MPS2-R05g PRA model as described below.

Permanent TS Change Risk Metrics (10-day AOT)

To calculate LiCDF and LiLERF, a yearly average duration of 10 days will be used based on the assumption that the proposed permanent 10-day AOT will be used no more than once per refueling interval. For this calculation, a yearly fraction, 10/365, is applied to the LiLOOPGR calculated above yielding a value of 1.29E-04/yr. This LiLOOPGR value was then added to the baseline LOOPGR value of 1.59E-02/yr, yielding a LOOPGR frequency of 1.60E-02/yr. Substituting this value into the model yields the following:

CDFPermanentTS = 1.953548E~05/yr LE RF Permanent TS = 1.330808E-06/yr The MPS2-R05g model baseline GDF and LERF values are 1.953361 E-05/yr and 1.330591 E-06/yr; respectively. Therefore, the LiCDF and LiLERF values are:

LiCDF = 1.87E-09/yr LiLERF = 2.17E-10/yr Per RG 1.177 (Reference 1-21), ICCDP and ICLERP are defined as follows:

ICCDP = [(Conditional CDF with subject equipment out of service and nominal expected equipment unavailabilities for other equipment permitted to be out of service by the TS) - (baseline GDF with nominal expected equipment unavailabilities)]* [Total duration of single AOT under consideration]

ICLERP = [(Conditional LERF with subject equipment out of service and nominal expected equipment unavailabilities for other equipment permitted to be out of service by the TS) - (baseline LERF with nominal expected equipment unavailabilities)]* [Total duration of single AOT under consideration]

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 41 of 55 To calculate Conditional CDF and Conditional LERF and ultimately ICCDP and ICLERP, the baseline LOOP GR value of 1.59E-02/yr was added to the LiLOOPGR value of 4. 72E-03/yr yielding a LOOPGR frequency of 2.06E-02/yr. Substituting this value into the model yields the following:

Conditional CDFProposed TS= 1.962232E-05/yr Conditional LERFProposed TS = 1.341264E-06/yr Therefore, the ICCDP and ICLERP are calculated as follows:

ICCDP = (1.962232E-05/yr - 1.953361 E-05/yr) * (10/365) yr ICCDP = 2.43E-09 ICLERP = (1.341264E-06/yr-1.330591E-06/yr) * (10/365) yr ICLERP = 2.92E-10 In summary, the proposed permanent TS change risk metrics are listed below:

LiCDF = 1.87E-09/yr LiLERF = 2.17E-10/yr ICCDP = 2.43E-09 ICLERP = 2.92E-10 Although the same configuration duration was used for the calculations, slight differences are noted between the related metrics. The difference is attributed to additional cutsets surviving the truncation value for the conditional CDF/LERF quantifications which set the component failure probability to 1.0.

These values are well below the acceptance criteria listed previously. The proposed permanent TS change results in a very small risk increase as defined by RG 1.174.

One-time TS Change Risk Metrics (35-day AOT)

The only difference between the proposed permanent TS change and the one-time TS change is the AOT duration. The ICCDP and ICLERP for the one-time *35-day AOT change are calculated as follows:

ICCDP = (1.962232E-05/yr - 1.953361 E-05/yr) * (35/365) yr ICCDP = 8.51 E-09 ICLERP = (1.341264E-06/yr - 1.330591 E-06/yr) * (35/365) yr ICLERP = 1.02E-09 These values are well below the acceptance criteria listed previously.

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 42 of 55 Tier 2: Avoidance of Risk-Significant Plant Configurations Tier 2 provides reasonable assurance that risk-significant plant equipment outage configurations will not occur when specific plant equipment is out of service consistent with the proposed amendment request.

A review of the quantification results was conducted to identify significant equipment outage contributors to CDF and LERF given a grid-related LOOP. Based on the review, the following equipment should be protected during the proposed permanent and one-time TS change:

MPS2 EDGs H7A, H7B

MPS3 SBO Diesel Generator 3BGS-EG1

MPS3 Diesel-driven Fire Water Pump M7-7 (which is common to MPS2 and MPS3)

MPS2 Service Water Pumps P5A, P5B, P5C

MPS2 Auxiliary Feedwater Pumps P9A, P9B, P4

MPS2 High Pressure Safety Injection (HPSI) Pumps P41A, P41B, P41C (and associated equipment)

The identified equipment is protected in accordance with the Protected Equipment procedures for MPS2 and MPS3. These procedures provide instructions for usage of barriers, signs, logs, walkdowns, and other considerations for protecting equipment.

The list of equipment above is a subset of a new risk management actions bullet (item 6) that is being added to* the Bases for MPS2 TS 3.8.1.1, to provide additional defense-in depth during the 10-day and 35-day AOTs.

Tier 3: Risk-Informed Configuration Risk Management Tier 3 confirms compliance with 10 CFR 50.65(a)(4), which ensures that the risk impact of out of service equipment is appropriately assessed and managed.

When entered into the proposed permanent Required Action and one-time exception, configuration risk will be assessed and managed in accordance with the requirements of 10 CFR 50.65(a)(4). DENC has implemented real-time risk assessment technology utilizing EPRl-developed software. The software is run continuously with a unit at-power by the on-shift Shift Technical Advisor to ensure that risk is appropriately managed prior to entering any plant configuration and when emergent equipment failures occur: Configurations that approach or exceed the limits defined in NUMARC 93-01 are identified and risk management actions specified as required. Emergent equipment failures are promptly analyzed in accordance with program requirements by the on-shift staff.

4.4.2 Summary of Plant Specific Risk Assessment Results The risk assessment results for the proposed permanent and one-time TS change are provided below. These values are well below the acceptance criteria.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 43 of 55 Table 1-5 Risk Metric Result Comparison to Acceptance Criteria for 10 day AOT 10-day Permanent AOT Extension Risk Metric Value Acceptance Criteria lKDF 1.87E-09/yr < 1.0E-06/yr

~LERF 2.17E-10/yr < 1.0E-07/yr ICCDP 2.43E-09 < 1.0E-06 ICLERP 2.92E-10 < 1.0E-07 Table 1-6 Risk Metric Result Comparison to Acceptance Criteria for 35 day AOT 35-day One-Time AOT Extension Risk Metric Value Acceptance Criteria ICCDP 8.SlE-09 < 1.0E-06 ICLERP 1.02E-09 < 1.0E-07

The risk assessment concludes the following:

The proposed permanent and one-time TS changes result in a very small risk increase that satisfy the acceptance criteria of RG 1.174 and RG 1.177.

The proposed permanent Required Action and one-time exception configurations maintain two available MPS2 offsite sources which provide adequate defense-in-depth. The failure scenario that would disable the available offsite sources involves a very low likelihood passive failure, which has been demonstrated by the quantitative assessment to be an insignificant contributor to MPS2 risk.

The proposed amendment reque$t primarily impacts risk associated with the internal events hazard group. The offsite power sources are not credited in the seismic safe shutdown and fire safe shutdown strategies. The proposed amendment request is considered to have negligible risk impact associated with external hazards including seismic and fire.

Based on the Tier 2 assessment, the following equipment should be protected during the proposed permanent and one-time TS change:

o MPS2 EDGs H7 A, H7B o MPS3 SBO Diesel Generator 3BGS-EG1 o MPS3 Diesel-driven Fire Water Pump M7-7 o MPS2 Service Water Pumps P5A, P5B, P5C o MPS2 Auxiliary Feedwater Pumps P9A, P9B, P4 o MPS2 HPSI Pumps P41A, P41 B, P41 C

The proposed Tier 2 restrictions are not credited within the quantitative risk assessment and therefore, the risk metrics are considered to be conservative.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 44 of 55 4.5 Conclusions 4.5. 1 Defense-in-Depth and Safety Margins Defense-in-Depth for Mitigating a 13T Failure While in the Extended AOTs As detailed in Section 4.2 of this LAR, the MPS3 SBO diesel generator can be utilized in the event that the MPS2 preferred offsite power source and all MPS2 EDGs are lost. This diesel generator can be connected to the MPS2 electrical system in a timely manner to bring MPS2 to a safe and stable shutdown. However, during this postulated event, additional alternate means to mitigate the event could be reasonably expected to be available to the operator. These capabilities are summarized as follows:

The MPS2 EDGs would be the first line of defense for mitigating the event. Either MPS2 EOG can provide power to a 4160 .V bus (24C or 24D), to bring MPS2 to a safe and stable shutdown condition. The MPS2 EDGs are expected to be available (except when required to perform surveillance testing) per MPS2 LCO 3.8. 1.1, which states that two EDGs shall be operable in modes 1, 2, 3, and 4. A risk management action is also included in the TS Bases to monitor MPS2 EDG status once per shift.

However, the evaluation in Section 4.2 of this LAR assumes that both EOG fail, .in order to demonstrate the additional capability of the MPS3 SBO diesel generator.

In parallel with aligning the EOG or the MPS3 SBO diesel generator, the operator would initiate action to isolate the faulted 13T breaker. This is accomplished by opening the 13T-4 and 13T-8 disconnect switches.

o Opening the 13T-4 allows repowering the north bus and MPS2 RSST.

o Opening 13T-8 allows repowering the MPS3 terminal (from 348 line) and the MPS3 'A' NSST, which can then provide power to MPS2 via the 4160 V cross-tie.

As stated in MPS2 UFSAR Subsection 8. 1.2.2, bullet d., faults can be manually isolated with appropriate disconnect switches in less than eight hours. Successful isolation of breaker 13T within eight hours would preclude the need to use the MPS3 SBO diesel generator to reach cold shutdown.

If the alternative actions are unable to restore power, the onsite 480 V FLEX diesel generator can be deployed from the BDB storage to bring MPS2 to hot shutdown conditions. The 4160 V generators from the NSRC location can provide the capability to allow operators to place MPS2 in cold shutdown.

Safety Margins DENG proposes to revise TS 3.8. 1.1, "A. C. Sources - Operating," to add a new permanent Required Action a.3, which provides an option to extend the AOT from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 1O days (with a one-time 35 day exception) to allow periodic maintenance and testing of MPS3 'A' RSST and switchyard components. Specifically, DENC intends to perform this maintenance with breaker 13T closed. As previously noted, aligning breaker 13T in this

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 45 of 55 position has no adverse impact on the ability of the MPS3 'A' NSST to supply power to the 4160 V buses. The requirement to consider the MPS3 'A' NSST inoperable when 13T is closed is only due to loss of indep'endence of both MPS2 offsite sources at a single point (breaker 13T). Therefore, two offsite sources are energized and available as required during the extended AOTs. If breaker 13T fails (which would result in loss of both offsite sources), the breaker can be manually isolated with appropriate disconnect switches. As stated in MPS2 UFSAR Subsection 8.1.2.2, bullet d., breaker faults can be isolated in less than eight hours. Successful isolation of breaker 13T within eight hours would restore power, and preclude the need to use the MPS3 SBO or the MPS 480 V and 4160 V FLEX generators to reach cold shutdown.

A loss of all AC power event would require a loss of both offsite power circuits and also the loss of both onsite EDGs. Power supply defense-in-depth is provided with the existing SBO response plan, which includes equipment, procedures, and training. Therefore, safety margins are maintained during the extended AOTs.

4.5.2 Reassessment of Cross-Tie LAR USQ #2 Conclusion (13T Position)

A LAR (Reference 1-25) was submitted on August 25, 2000 related to the replacement of the existing MPS1 to MPS2 4160 V cross-tie with a new MPS3 to MPS2 4160 V cross-tie.

This modification was needed to support decommissioning of MPS1. While the modification was considered to be safe, the associated 10 CFR 50.59 review identified four unreviewed safety questions (USQs). For this reason, a LAR was submitted to request that the NRC review and approve the USQs.

USQ #2 of the previous LAR related to positioning of switchyard breaker 13T. The LAR notes that opening breaker 13T when MPS3 is shut down represents a degradation in the reliability of the offsite supply for MPS3. A failure such as a fault on the 345 kV line that connects between breakers 14T and 15T (348 line circuit) would cause a loss of offsite power for MPS3 if breaker 13T is open. If breaker 13T is closed and a fault occurs in the 345 kV line, the MPS3 'A' NSST would remain energized by the north bus. Therefore, opening the 13T breaker to allow MPS2 to meet GDC-17 requirements increases the probability of a loss of offsite power at MPS3 when shut down. This 'increases the probability of a malfunction of equipment important to safety at MPS3.

The previous LAR also states in evaluation of USQ #2, that a loss of offsite power at MPS3 due to a fault in the offsite distribution network is a low probability event. When combined with the expected frequency of removing the MPS3 'A' RSST from service of once per MPS3 refueling outage, the probability of a loss of offsite power at MPS3 when shut down as a result of breaker 13T being open is low. In addition, the MPS3 shutdown risk program will evaluate the impact of removing the MPS3 'A' RSST from service and plan accordingly.

This will ensure the MPS3 'A' RSST will be removed from service when the shutdown risk is determined to be acceptably low. If the MPS3 'A' RSST must be removed from service, and plant conditions do not support opening breaker 13T, it will be necessary for MPS2 to enter the Required Actions of LCO 3.8.1.1 for one inoperable offsite circuit. This will require restoration of the inoperable offsite circuit within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months , or MPS2 will be required

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 46 of 55 to shut down. Therefore, operation of MPS3 with 13T open to allow MPS2 compliance with_

GDC-17 requirements is safe.

The NRC staff reviewed and approved the design for the cross-tie between MPS2 and MPS3 (Reference 1-24) in License Amendments 252 (MPS2) and 190 (MPS3). The NRC staff concurred that opening the 13T breaker to allow MPS2 to meet GDC-17 requirements increases the probability of a LOOP at MPS3 when shut down but found the change acceptable because the increase in the probability of a LOOP at MPS3 due to a fault in the offsite distribution network is considered a low probability event. The safety evaluation concluded: "The average failure rate for a single. unit LOP [loss of offsite power] event occurring in the United States of America is 3.2 x 10-2 per reactor-year. When combined with the expected frequency of removing the MPS3 ['A'] RSST from service of once per MPS3 refueling outage, the probability of a LOP at MPS3 when shut down as a result of breaker 13T being* open is acceptably low." Additionally, the NRC staff noted that the licensee has an MPS3 shutdown risk program that will evaluate the impact of removing the MPS3 'A' RSST from service, and plan accordingly.

Since the submittal of the. LAR for the MPS2/3 cross-tie, the station's sensitivity to operating at elevated shutdown risk levels has increased. DENC's experience at the MPS indicates that a fault on a transmission line would be more likely event precursor than a spurious breaker internal fault.

A quantitative risk assessment of the likelihood of such an event was not included as part of the previously submitted LAR. As part of the justification for this LAR, DENG has evaluated the proposed permanent TS Required Action and one-time exception (which model the fault of an initially closed breaker 13T) and has found that the results satisfy the acceptance criteria of RG 1.174 and RG 1.177.

The conclusion from the NRC staff's safety evaluation on the previously submitted LAR remains valid, in stating that operation of MPS3 with 13T open is safe. However, performing maintenance activities with breaker 13T closed (in accordance with the proposed permanent TS Required Action and one-time exception) precludes entering a configuration with an elevated shutdown risk for MPS3, while only resulting in a very small increase in the risk metrics for MPS2. Furthermore, the requirement to maintain a supplemental power source while in the alignment for the proposed permanent TS Required Action and one-time exception provides additional mitigation capability in the very low likelihood event that a passive failure disables both MPS2 offsite power sources.

4.5.3 Final Conclusions.

The proposed permanent TS Required Action and one-time exception require the MPS3 SBO diesel generator to be available as a supplemental power source. The availability of the MPS3 SBO diesel generator to connect to the MPS2 electrical distribution system within the required time frame will ensure a reasonable balance is preserved between prevention of core damage, prevention of containment failure and consequence mitigation while in the proposed permanent TS Required Action *and one-time exception. The proposed permanent TS Required Action and the one-time exception will not significantly reduce the effectiveness of any of the layers of defense that exist in the MPS2 plant design.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 47 of 55 The proposed change will not adversely impact MPS2's

response to LOOP, SBO, or Appendix R events.

Performing maintenance activities with breaker 13T closed (in accordance with the proposed permanent TS Required Action and one-time exception) precludes entering a configuration with an elevated shutdown risk for MPS3, and only results in a very small risk increase for MPS2 that satisfies the acceptance criteria of RG 1.174 and RG 1.177. The proposed amendment request primarily impacts risk associated with the internal events hazard group. The offsite power sources are not credited in the seismic safe shutdown and fire safe shutdown strategies. The proposed amendment request is considered to have negligible risk impact associated with. external hazards including Seismic and Fire. The configuration associated with the proposed permanent TS Required Action and one-time exception maintains two available MPS2 offsite sources which provide adequate defense-in-depth. The failure scenario that would disable the available offsite sources involves a very low likelihood passive failure, which has been demonstrated by the quantitative assessment to be an insignificant contributor to MPS2 risk.

Furthermore, the requirement to establish and maintain a supplemental power source while

. in the alignment for the proposed permanent TS Required Action and one-time exception provides additional mitigation capability, in the very low likelihood of a passive failure.

MPS2 and MPS3 also have several alternate means to mitigate a postulated passive breaker failure. These capabilities would be reasonably expected to be available to the operator, and result in additional defense-in-depth.

5.0 REGULATORY EVALUATION

5.1 Applicable Regulatory Requirements/Criteria On February 20, 1971, the Atomic Energy Commission published in the Federal Register the General Design Criteria [GDC] for Nuclear Power Plants. The GDC, which are contained in Appendix A of 10 CFR 50, establish minimum requirements for the principal design criteria for water-cooled nuclear power plants. Although MPS2 was designed and*

licensed to the GDC, as issued on July 11, 1967, DENC has attempted to comply with the intent of the newer GDC to the extent possible, recognizing previous design commitments.

The current regulatory requirements of 10 CFR 50, Appendix A, applicable to the proposed license amendment are:

GDC-5, Sharing of Structures, Systems, and Components

GDC-17, Electric Power Systems

GDC-18, Inspection and Testing of Electric Power System MPS2 is designed and licensed to IEEE Standard 308-1971.

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 48 of 55 GDC-5, Sharing of Structures, Systems and Components The offsite power system switchyard is common to both Units 2 and 3. This was previously evaluated in the MPS3 SER and determined to be acceptable by the NRC based on_ GDC-17 allowance of a common switchyard between units.

GDC-17, Electric Power Systems GDC-17 requires an onsite electric power system and an offsite electric power system shall be provided to permit the functioning of structures, systems, and components important to safety. The safety function for each system (assuming other system is not functioning) shall be to provide sufficient capacity and capability to assure that (1) specified acceptable fuel design limit and design conditions of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences and (2) the core is cooled and containment integrity and other vital functions are maintained in the event of postulated accidents.

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

Electric power from the transmission network to the onsite electric distribution systems shall be supplied by two physically independent circuits (not necessarily on separate rights of way) designed and located so as to minimize to the extent practical the likelihood of their simultaneous failure under operating and postulated accident and environmental conditions. A switchyard common .to both circuits is acceptable. Each of these circuits shall be designed to be available in sufficient time following a loss of all onsite alternating current power supplies and other offsite electric power circuit, to assure the specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded. One of these circuits shall be designed to be available within a few seconds following a loss-of-coolant accident to assure that core cooling, containment integrity and other vital safety functions are maintained. Provisions shall be included to minimize the probability of losing electric power from any of the remaining supplies as a result of, or coincident with the loss of power generated by the nuclear power unit, the loss from the transmission network, or the loss of power from the onsite power supplies.

GDC-18, Inspection and Testing of Electric Power System GDC-18 requires electric power systems important to safety be designed to permit appropriate periodic inspection and testing to assess the continuity of the systems and condition of their components.

5.2 No Significant Hazards Consideration Pursuant to 10 CFR 50.90, Dominion Energy Nuclear Connecticut, Inc. (DENC) is requesting an amendment to Operating License DPR-65 for Millstone Power Station Unit 2 (MPS2). The proposed amendment would revise Technical Specification (TS) 3.8.1.1, "A.

C. Sources - Operating," to:

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 49 of 55

1. Modify TS 3.8.1.1 Required Action a.2 to add an option to extend the AOT from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 10 days. Use of the 10-day AOT option would allow normal maintenance and testing activities to be performed with MPS2 operating and with breaker 13T closed.

2. Add a new permanent TS Required Action a.3 that specifies the requirements for use of a 10 day AOT option. This option is needed to complete periodic maintenance and testing of the Millstone Power Station Unit 3 (MPS3) 'A' Reserve Station Service Transformer (RSST) and other 345 kV south bus switchyard components. Since periodic maintenance and testing of these components cannot be completed within the current 72-hour AOT, use of an extended AOT reduces: the number of switching evolutions required to complete the work, equipment unavailability time, and potential for equipment failures or human performance events. Use of this 10-day AOT will be limited to no more than once per 18 month refueling interval for MPS3.

3. Add a one-time exception to the proposed Required Action a.3 that would extend the AOT to 35 days AOT for one inoperable offsite circuit. Use of the 35-day AOT would allow replacement of the MPS3 'A' RSST, its associated equipment, and other 345 kV south bus switchyard components that are nearing the end of their dependable service life. This work is planned to take place no later than the fall 2023 outage (3R22).

Replacement of these components is necessary to assure continued safe and dependable generation of electric power.

DENG has determined that the proposed amendment does not involve a significant hazards consideration under the standards set forth in 10 CFR 50.92(c). Specifically, a proposed amendment to an operating license involves no significant hazards consideration if operation of the facility in accordance with the proposed amendment would not:

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

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

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

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

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

Response: No Currently, MPS2 TS 3.8.1.1 provides an AOT of 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months for the configuration where switchyard breaker 13T is closed coincident with the MPS3 'A' RSST out of service. The proposed amendment would add a new permanent TS Required Action that provides an

Serial No: 1e~2s2B

Docket Nos. 50-336 Attachment 1, Page 50 of 55 option to extend the AOT from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 10 days and a one-time exception to extend the AOT to 35 days to support MPS3 'A' RSST and south bus switchyard component replacement activities no later than fall 2023 (3R22). For both AOTs, the design basis accidents will remain the same postulated events described in the MPS2 Updated Final Safety Analysis Report (UFSAR).

The proposed amendment would improve shutdown safety by reducing the likelihood of a loss of offsite power event at MPS3 while limiting the MPS2 core damage frequency increase to a very small value that meets the requirements of Regulatory Guide (RG) 1.174, Revision 3 and RG 1.177, Revision *1 for the bounding postulated failure. In addition, adding a permanent TS Required Action with an extended AOT of 10 days and a one-time AOT of 35 days will not impact the consequences of an accident previously evaluated. The consequences of previously evaluated accidents are the same during the proposed 10-day and 35-day AOTs as during the. current 72-hour AOT. The ability of the remaining onsite AC sources to mitigate the consequences of an accident will not be affected since no additional failures are postulated while MPS2 is in the TS AOT. The remaining AC sources are sufficient to mitigate the consequences of any design basis accident. The proposed change will not adversely impact MPS2's response to LOOP, SBO, or Appendix R events.

Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.

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

Response: No The proposed amendment does not affect the configuration or operation of the plant, or the manner in which the electrical distribution subsystems provide plant protection. The proposed amendment only provides an option to extend the time period that one of the offsite circuits can be inoperable. The proposed permanent TS Required Action and one-time exception with extended time durations for one offsite circuit being inoperable have no direct physical impact on the plant and does not create any new accident initiators. Other sources of onsite AC power remain available. The possible impacts that the inoperable equipment may have on supported systems was previously analyzed in the UFSAR. The impacts of inoperable support systems were also previously assessed, and any accident initiators created by the inoperable systems were evaluated. Adding a proposed new Required Action and a one-time exception for MPS2 TS 3.8.1.1 does not create any additional accident initiators for the plant.

The proposed amendment would improve shutdown safety by reducing the likelihood of a loss of offsite power event at MPS3 while limiting the MPS2 core damage frequency increase to an acc.eptably small value that meets the requirements of RG 1.174, Revision 3 and RG 1.177, Revision 1.

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 51 of 55 The proposed amendment does not change any existing accident scenarios, nor create any new or different kind of accident.

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

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

Response: No The existing AOT of 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months for one inoperable offsite circuit was established to ensure that sufficient safety-related equipment is available for response to all accident conditions and that sufficient decay heat removal capability is available for a Loss of Coolant Accident (LOCA) coincident with a Loss of Offsite Power (LOOP) on one unit and simultaneous safe shutdown of the other unit. Although a very slight reduction in the margin of safety may be incurred during the proposed permanent Required Action and one-time exception with extended AOTs (permanent 10-day and one-time 35-day), this slight reduction is not significant due to the low probability of an event occurring during the extended period.

Other sources of onsite AC power remain available and operable during the extended AOTs. The small reduction in safety margin resulting from using the 10 day and 35 day AOTs is not significant because the remaining operable EDGs, the station blackout diesel, and the FLEX diesel generators are available and provide sufficient defense-in-depth to support the station's electrical configurations during the extended AOTs.

The proposed amendment does not affect the acceptance criteria for any analyzed event nor is there a change to any safety limit. The proposed change does not affect any structures, systems or components or their capability to perform their intended functions.

The proposed change does not alter the manner in which safety limits, limiting safety system settings, or limiting conditions for operation are determined. Neither the safety analyse_s nor the safety analysis acceptance criteria are affected by this change. The proposed amendment will not result in plant operation in a configuration outside the current design basis.

Therefore, the proposed change does not involve a significant reduction in a margin of_

safety.

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

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 52 of 55 5.3 Precedents The use of a one-time offsite power source AOT greater than 14 days is similar in fundamental aspects to those referenced in this NRC Safety Evaluation Report:

Surry Power Station, Unit Nos. 1 and 2 - Issuance of Amendment Regarding Technical Specifications Section 3.16, "Emergency Power System," for a T~mporary 21-Day Allowed Outage Time (EPID L-2017-LLA-0380)," dated October 5, 2018, ADAMS Accession# ML18261A099

6.0 ENVIRONMENTAL CONSIDERATION

A review has determined that the proposed amendment would change a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or would change an inspection or surveillance requirement.

However, the proposed* amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluent that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore,

. pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment.

7.0 REFERENCES

1-1. Millstone Power Station Unit 2 Final Safety Analysis Report, Rev. 36.3 Section 8.1.2.2.d.4.

1-2. Millstone Power Station Unit 2 Technical Specifications, Including Change No. 397.

1-3.

GDC 5, "Sharing of Structures, Systems and Components."

1-4. GDC 17, "Electric Power Systems."

1-5. NRC Standard Review Plan Branch Technical Position 8-8, "Onsite (Emergency Diesel Generators) and Offsite Power Sources Allowed Outage Time Extensions,"

Initial, February 2012, ADAMS Accession# ML113640138 1-6. Regulatory Guide 1.93, "Availability of Electric Power Sources."

1-7. Regulatory Guide 1.155, "Station Blackout."

1-8. Millstone Calculation No. 97-ENG-01775E2, "Battery 2018 and Charger Associated Cable Device Electrical Verification Calculation," Rev. 3 through Addendum H.

1-9. Millstone Calculation No. 2013-ENG-04383E2, "Millstone Station Unit 2 Beyond Design Basis-FLEX Electrical 4160V, 480V and 120V AC System Loading Analysis,"

Rev. 2.

1-10. Calculation No. PA079-126-01027E2, "MPS2 EOG Loading" Rev. 03 through Addendum K.

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 53 of 55 1-11. Calculation No.MPS2-ENG-ETAP-04014E2, "MPS2 Electrical Distribution System Analysis," Rev. 3 through Addendum P.

1-12. Calculation No. 98-ENG-02132E2, "Appendix R Loading," Rev. 01 through Change No . .4.

1-13. INPO AP 913, Revision 3, Equipment Reliability Process Description, Institute of Nuclear Power Operations, March 2011.

1-14. EA-12-049, "Order Modifying Licenses with Regard to Requirements for Mitigating Strategies for Beyond Design-Basis External Events."

. 1-15. EOP-2528, "Loss of Offsite Power/Loss of Forced Circulation," Millstone Power Station Unit 2 Emergency Operating Procedure, Rev. 21.

1-16. MP-PROC-OPS-AOP2579A Rev. 12, "Fire Procedure for Hot Standby Appendix R Fire Area R-1."

1-17. FLEX Procedure EOP 25 FSG-05, "Initial Assessment and FLEX Equipment Staging," Rev. 5.

1-18. EOP 2530, "Station Blackout", Millstone Power Station Unit 2 Emergency Operating Procedure, Rev. 17.

1-19. NEI, "Diverse and Flexible Coping Strategies (FLEX) Implementation Guide", NEI 12-06, Revision 0, August 2012.

1-20. Regulatory Guide 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis", Rev. 3.

1-21. Regulatory Guide 1.177, "An Approach for Plant-Specific, Risk-Informed Decision Making: Technical Specifications," Rev. 1.

1-22. NRC Letter Dated September 20, 2018 to Mr. David Crawley, "UPDATED STAFF ASSESSMENT OF NATIONAL SAFER RESPONSE CENTERS ESTABLISHED IN RESPONSE TO ORDER EA-12-049" 1-23. FLEX Procedure EOP 25 FSG-04, "ELAP DC Bus Load Shed/Management," Rev. 1.

1-24. Millstone Nuclear Power Station, Unit Nos_. 2 and 3 - Issuance of Amendment Re:

4160-Volt Electrical Cross-Tie Line (TAC Nos. MA9853 and MA9855)," dated December 21, 2000, ADAMS Accession# ML003779587.

1-25. Millstone Nuclear Power Station, Unit Nos. 2 and 3, License Amendment Request "Proposed Revision to Final Safety Analysis Reports - 4160 Volt Cross-Tie of MP3 to MP2," dated August 25, 2000, ADAMS Accession# ML003743841-26. ETE-CPR-2014-1008, "Millstone Power Station Unit 2 & 3 Beyond Design Basis FLEX Validation for Time Sensitive Actions (TSA's)"

1-27. OU-M3-201, "Shutdown Safety Assessment Checklist," Revision 26 1-28. NOTEBK-PRA-MPS2-MC.1, "MPS2-R05g Interim Model Development," Revision 3 1-29. NOTEBK-PRA-MPS2-RA.029, "Interim Model MPS2-R05g PRA Quantification Notebook," Revision 0 1-30. NOTEBK-PRA-MPS2-LE.1, "Level 2 Analysis," Revision 7

Serial No: 19-2828 Docket Nos. 50-336 Attachment 1, Page 54 of 55 1-31. Millstone Unit 2 SQUG Project, Safe Shutdown Equipment List (SSEL), Report No.

03-0240-1367, Revision 4 (MP2 Calculation 03-0240-1367, Rev 4, US A-46 Safe Shutdown Paths.pdf) 1-32. 25203-SP-M2-SU-1046, "MP2 Appendix R Compliance Report," Revision 1 1-33. Generic Letter 88-20, "Individual Plant Examination of External Events (IPEEE) for Severe Accident Vulnerabilities - 10 CFR 50.54(f), Supplement 4," USN RC, June 1991 1-34. NUREG/CR-6928, "Industry-Average Performance for Components and Initiating Events at U.S. Commercial Nuclear Power Plants," Component Reliability 2010, February 2012 1-35. Deleted 1-36. Watts Bar Nuclear Plant, Unit Nos. 2 and 3 - Issuance of Amendment Regarding Extension of Completion Time for Inoperable Diesel Generator (CAC Nos. MF7147 and MF7148)," dated January, 13, 2017, ADAMS Accession# ML17006A271 1-37. ETE-CEE-2012-1001, "Millstone Beyond Design Basis DC Load Shedding Strategy and Analysis for extended SBO Event" 1-38. NOTEBK-PRA-MPS2-RA.Ll.004, "PRA Input to Proposed Technical Specification 3.8.1.1 Change" Revision 2 1-39. Surry Power Station, Unit Nos. 1 and 2 - Issuance of Amendment Regarding Technical Specifications Section 3.16, "Emergency Power System," for a Temporary 21-Day Allowed Outage Time (EPID L-2017-LLA-0380)," dated October 5, 2018, ADAMS Accession # ML18261A099 1-40. NUMARC 87-00, Revision 0, "Guidelines and Technical Bases for NUMARC Initiatives Addressing Station Blackout at Light Water Reactors," November 1987.

1-41. EOP 3501, "Loss of All AC Power (Modes 5,6, and Zero)," Millstone Power Station Unit 3 Emergency Operating Procedure, Rev. 23.

1-42. EOP 3505, "Loss of Shutdown Cooling and / or RCS Inventory," Millstone Power Station Unit 3 Emergency Operating Procedure, Rev. 17.

1-43. SP-EE-362, "Millstone Unit 2 Station Blackout Safe Shutdown Scenario Document" 1-44. Millstone Power Station Units No. 2 And 3, License Amendment Request, "Removal Of Severe Line Outage Detection From The Offsite Power System," dated July 15, 2015, ADAMS Accession# ML15183A022 1-45. C OP 200.6, "Storms and Other Phenomena (Preparation and Recovery)," Millstone Power Station Common Operating Procedure, Rev. 8.

1-46. AOP 2560, "Storms, Winds, and High Tides," Millstone Power Station Abnormal Operating Procedure, Rev. 19 1-47. SP 3670.4, "Routine PMs," Millstone Power Station Surveillance Procedure, Rev. 42 1-48. EOP 35 GA-27, "Energizing SBO Diesel Auxiliaries with SBO Diesel," Millstone Power Station Emergency Operating Procedure, Rev. 5

Serial No: 19-282B Docket Nos. 50-336 Attachment 1, Page 55 of 55 1-49. OP 3346D, "Station Blackout Diesel," Millstone Power Station System Operating Procedure, Rev. 23.

1-50. C OP 200.18, "Time Critical Action Validation and Verification,". Millstone Power Station General Operating Procedure, Rev. 10.

1-51. Millstone Calculation No. 97-ENG-01774E2, "Battery 201A and Charger Associated Cable Device Electrical Verification Calculation," Rev. 4

_1-52. Millstone Calculation No. MP-CALC-ENG-90-050-00097E3, "MP3 SBO Diesel Generator Power Cable Sizing," Rev. 0 1-53. Millstone Calculation No. MP-CALC-ENG-96-ENG-01272M3, "SBO Diesel Generator Run Times," Rev. 1 1-54. Millstone Calculation No. MP3-ENG-ETAP-04125E3,"MP3 Electrical Distribution System Analysis," Rev. 1

Serial No: 19-282B Docket No. 50-336 ATTACHMENT 2 MARK-UP OF PROPOSED TECHNICAL SPECIFICATION CHANGES DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2

Serial No: 19-282B Docket Nos. 50-336 Attachment 2, Page 1 of 1 Mareh 16, 2G06 3/4.8 ELECTRICAL POWER SYSTEMS 3/4.8.1 A.G. SOURCES OPERA.TING ill1ITING cmmmoN FOR OPERATION 3.8.1.1 As a minimum, the following A.C. electrical power sources shall be OPERABLE:

a. Two physically independent circuits between the offsite transmission network and the onsite Class 1E distribution system, and

b. Two separate and independent diesel generators each with a separate fuel oil supply tank containing a minimum of 12,000 gallons of:fo.el.

APPLICABILITY: MODES 1, 2, 3 and 4.

ACTION:

Inoperable Equipment Required ACTION

a. Oneoffsite a.I Perfo1m Surveillance Requirement 4.8. L1 .1 for circuit remaining offoite circuit within 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months p1'ior to 01* after enteiing this condition,. and at least o.nce per 8 hom-s thereafter.

--*J(wit::., 1G days if Requb;d AND / / ACTIOM a.2 is met)

/

a.2 Restore :f1e~ inoperable ~t~ circuit to OPE~L~ .

.~tatus within 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months s* or be 111 HOT STANDB"Y *w1thin the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and COLD SHUTDOWN v.ithin the follo,ving 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

AND a.l With MPS.3 in MODE s., 6, or defueled,, the MP53 'A' P.55Tinoperable, and the MPS3 'A' NS5I ene'!gized with breaker :15G BT-l (BT) and assodated 0 disccnnectr,*.*itches clru,d, restore either offsita circuit to OPERABlE status w'ithin 10 days* if the following requirements are met:

Within 30 da*rs prior to entering the iO-da*/ 1'.0T, th.;; a*;ailabilit, of the mppl>.mental power source (MP53 sa-0 diesel generator} shall be verified.

- Ou ring the 10-dav AOT, the availability of ,he supp:emen,al power source sh.31! be checked once per shift. If the supplemental p;;,wer source becom<i!i unavailable at an-1 time during the 10-<l.:1 AOT, restore to available stams within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months or biin HOT 5TANOe'{ within the 11e,:t 5 hows and COLO SHUTDOWN wi:nin the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

- .he risk management anions contai11ed ill DENC letter 1.9*2S2B, Attadlment4 (also pro*,*ided in T5 Brnis ~/4.S), shall remain in effect dmi.ng the 10-da*t t.OT.

I: To taollta\;; r;;plJcement or :n~ MPS3 *;.,* RSGT anl ,o;so::ia~ eqlipmer,:. llse or a mE-llmE J5.(Ja)' altr,*1&1 ou:a~ Um;; is permt:;;d pr:r,lde! tne requtr:r:u;nts er!

!Required AC'ilOtl a.3 a"& met. n-a wc.rtt ~'l:;JI be coir.plElad no l,!Jil! 1h.1n !Ila end~ IIIPS3 F:1\Jellng outage 22 (f.;!l 2Il23). /

MILLSTONE - UNlT 2 .3/4 8-1 Amendment No.#, P.+, .gg, ~ .

Serial No: 19-2828 Docket No. 50-336 ATTACHMENT 3 MARK-UP OF PROPOSED TECHNICAL SPECIFICATION BASES CHANGES FOR INFORMATION ONLY DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2

Serial No: 19-282B Docket No. 50-336 Attachment 3, Page 1 of 4 LBDCR 11 MP2 012 Deeember 21, 2011 3/4.8 ELECTRICAL POWER SYSTEMS BASES The OPERABILITY of the A.C. and D.C. power sources and associated distribution systems during operation ensures that sufficient power will be available to supply the safety related equipment required for 1) the safe shutdown of the facility and 2) the mitigation and controf of accident conditions within the facility. The minimum specified independent and redundant A.C. and D.C. power sources and distribution systems satisfy the requirements of General Design Criteria 17 of Appendix "A"to 10 CFR 50.

The required circuits between t.he offsite transmission network and the onsite Class 1E distribution system (Station Busses 24C, 24D, and 24E) that satisfy Technical Specification 3.8.1.1.a (MODES 1, 2, 3, and 4) consist of the following circi.1its. from the switchyard fo the onsite electrical distribution system: *

a. Station safeguards busses 24C and 24D via the Unit 2 Reserve Station Service Transformer; .and r-0 'A' .-1-'

b. Station bus 24E via the Unit 3\eserve Station Service Transfom1er or Unit 3 ~

Normal Station Service Transformer (energized with breaker 15G-13T-2 (13T) and associated disconnect switches open) and bus 34A or 34B.

~

When taking credit for the Unit 3 Normal Station Service Transfo~er as a second offsite circuit, breaker 13T and its associated disconnect switches are required to be open. This removes the potential for a single failure (that of breaker 13T) to cause a simultaneous loss of both <iffsite circuits. Should the other offsite circuit (i.e., the Unit 2 Reserve Station Service Transformer) already be inoperable, the requirement for maintaining breaker 13T and its associated discoru1ect switches open* is no longer applicable. ~

If the plant configuration will not allo ~ 3 to supply power to Unit 2 from the Unit 3 Reserve Station Service Transfonner or Unit ,~:ml Station Service Transformer within 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months , Unit 2 must consider the second offsite source inoperable and enter the appropriate ACTION statement of Technical Specification 3.8.1.1 for a1i .in:operable offsite circuit.

Thi.s is consistent with the GD,C 17 reqµirement for two offsite sources. Each offsite circuit is required to be availa:l:ile'in sufficienttimefollowing a loss ofall onsite alternating current power supplies and the other offsite electric power circuit to assure that specified acceptable fuel desigh limits and design conditions of the reactor coolant pressure boundary are not exceeded.

The first source is ~equired to be available within a few seconds to supply power to safety rel~ted equipment following a loss of coolant accident. The second source is not required to be available immediately and no accident is assumed to occur concurrently with the need to use the second source. However, the second source is required to be available in sufficient time to assure the reactor remains in a safe condition The 3 hour3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months time period is based on the Millstone Unit No. 2 Appeµdix R anaiysis, This analysis has demonstrated that the reactor will remain in a safe condition (i.e., the pressurizer will not empty) if charging is restored within 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months .

MILLSTONE --UNIT2 B 3/4 8-1 Amendment No.+&&,~'~,

Serial No: 19-2828 Docket No. 50-336 Attachment 3, Page 2 of 4 LBDCR H MP2 Q 12 Deeem:eeF.21, 2QU 3/4.8 ELECTRICAL POWER SYSTEMS BASES In MODES 1 through4 (Teclmical Specification 3.8.1.1), the Unit 2 Nonna! Station Service Transformer can be used as the second offsite source after the main generator disconnect links have been removed and the backfeed lineup established.

The required circuit between the offsite transmission network and the onsite Class 1E distribution system (Station Busses 24C, 24D, and 24E) that satisfies Technical Specification

3. 8.1.2.a (MODES 5 and 6) consists of the following circuit from the switch yard to the onsite electrical distribution system:

a. Station safeguards bus 24C or24D via the Unit 2 Reserve Station Service Transfonner; or f

b. Station safeguards bus 24C or 240 via the Unit 2 Normal Station Service Transfom1er and bus 24A or 24B after the main generator disconnect links have been removed and the backfeed lineup established; or

.~ ~

c. Station bus 24E via the Unit 3"Re~e Station Service Transformer or Unit 3 Normal Station Service Transformer and bus 34A or 34B.

When the plant is operating with the main generator connected to the grid, the output of the main generator willnormally be used to supply the onsite Class 1E distribution system.

During this time the required offsite circuits will be.in standby, ready to supply power to the onsite Class 1E distribution system if the main generator is not available. When shut down, only one of the offsite circuits will normally be used to supply the onsite Class 1E distribution system.

The other offsite circuit, if required, will be in standby. Verification of the required offsite circuits consists of checking .control power to the breakers (breaker indicating lights), proper breaker position for the current plau:t configuration, and voltage indication as appropriate for the current I.Jlant confi&uration.

The ACTION requirements specified for the levels of degradation of the power sources provide restriction upon continued facility operation commensurate with the level of degradation.

The OPERABILITY of the power sources are consistent with the initial condition assumptions of the accident analyses and are based upoh maintaining at least one of each of the onsite A.C. and D.C .. power sources and associated distribution systems OPERABLE during accident conditions coincident with ah asslime:-_, ,~1~~2,,

. **,c~~~biJ!fv

<:~t~~oryjc ,,"-"'
Proposed Resolution:
To close this F&O, the documentation of each interim update should include an evaluation that concludes that the current Model of Record results documentation reasonably represents the results documentation expected for the current interim model. The evaluation should also conclude that there are no new insights or conclusions to be obtained based on the changes that would otherwise require fully documenting the results to meet the necessary SRs.
LE-C12-01 LE-C12 Met 2012 Peer Review Comment: Resolved (2012) There is no evidence that MPS2 performed a review of accident progression accident sequences to The significant accident determine if it was possible for continued operation progression sequences for the of equipment or personnel that would reduce LERF. current model, M PS2-R05g, have been reviewed and Dominion disposition of 2012 Comment: documented _in the LERF Significant accident progression sequences have documentation for continued now been reviewed to determine if continued operation of equipment or equipment operation or operator actions after personnel that would reduce containment failure can help reduce LERF. The LERF. Resolution does not review is documented (see above referenced PRA impact the proposed LAR.
notebooks). However, no credit is taken for additional equipment or operator actions because the significant LERF contributors are bypass scenarios, not a failure of containment isolation.
Serial No: 19-282B Docket No. 50-336 Attachment 5, Page 8 of 13 2018 Peer Review Comment:
Documentation is provided and addresses the F&O by adding the appropriate Section and at that time there was a discussion addressing the top 97% of contributions to LERF. This process is still pending for the most current_ interim release, but the process exists and therefore the F&O as generated is considered partially closed. The associated SR LE-C12 requires an approach to be developed and is considered now met.
Proposed Resolution:
To close this F&O, the documentation of each interim update should include an evaluation that concludes that the current Model of Record results documentation reasonably represents the results documentation expected for the current interim model. The evaluation should also conclude that there are no new insights or conclusions to be obtained based on the changes that would otherwise require fully documenting the results to meet the necessary SRs.
LE-Fl-01 LE-Fl Met 2012 Peer Review Comment: Resolved.
(2012) QU.2 Section 2.3.2 provided LERF by initiating event, Section 2.3.6 presented the dominant LERF The LERF documentation has cutsets, Section 2.3.9 presents the LERF importance been updated for the 'current analysis, and Table 15 presents the system model, MPS2-R05g, to include
Serial No: 19-282B Docket No. 50-336 Attachment 5, Page 9 of 13 Finding , Supporting _. Capability '
Qescripti~~ * * . bispositic>n Number, L***Requirement(slt Category (CC) contribution to LERF. Attachment 4 to QU.2 also the relative contribution to presents the containment failure mode contribution LERF from the plant damage to LERF. However, there is no identification of the states. Resolution does not contributors to LERF by plant damage states. impact the proposed LAR.
2018 Peer Review Comment:
N/A Proposed Resolution:
MPS2 needs to calculate and present the dominant LERF contributors to LERF by plant damage state.
LE-F2-01 LE-F2 Not Met 2012 Peer Review Comment: Resolved to meet Capability (2012) There is no evidence that MPS2 reviewed the LERF Category 1/11/111.
contributors for reasonableness. While MPS2 did group and present the LERF results by initiating The LERF contributors for the event, system contribution and containment failure current model, MPS2-R05g, mode, there is no evidence that MPS2 reviewed the were reviewed for results for reasonableness. reasonableness and documented in the PRA LERF 2018 Peer Review Comment: documentation. Resolution 1 does not impact the proposed IN/A LAR.
Proposed Resolution:
MPS2 needs to perform and document a review of the LERF results to show that they are explainable based on what would be expected for the plant.
Serial No: 19-282B Docket No. 50-336 Attachment 5, Page 10 of 13
'\; ,
Finding . Supp9rting Capability . 1 O~scripti<m Disposition Number I\ Requirirnent(s) Category (CC).** .
j LE-GS-01 LE-GS Not Met 2012 Peer Review Comment: Resolved to meet Capability
{2012) MPS2 has not reviewed their Level 2 analysis to Category 1/11/111.
identify any limitations that may have the potential to impact applications. MPS2 needs to review their This issue is associated with Level 2 analysis to identify any limitations that may identifying the limitations have the potential to impact applications. MPS2 associated with the LERF should document the process used for the review analysis for applications.
and the results of the review. If no limitations are Limitations have been identified, this needs to be clearly stated. identified for the LERF analysis, including applicable Dominion disposition of 2012 Comment: modes, the scope of hazards, MPS2 LE.1 RS, section 7.0 PRA Notebook MPS2 LE.1 and limitations with use of has been updated to include documentation of LERF MAAP for Level 2. The Level 2 limitations in Section 7.0 of the notebook. analysis contains sufficient scope and detail for this 2018 Peer Review Comment: application, including The current section provides only general discussion consideration of various and does not provide any support for limitations containment failure modes when applying the LERF model. Limitations in MAAP and plant damage state should be included as well as any plant-specific modeling, which allows the modeling considerations. The SR LE-GS remains not core damage sequences to be met. binned to the EPRI accident classes. A more thorough Proposed Resolution: documentation of LERF The current section on limitations should be analysis limitations that updated to reflect any new or additional limitations accounts for the items identified for the current model of record and the identified in the proposed
Serial No: 19-2828 Docket No. 50-336 Attachment 5, Page 11 of 13 Finding .Supporting Capability
... Description DiSl)OSition Number Requirement(s) 1 Category(CC) quantification results. The documentation should resolution would not impact capture the insights gained from the uncertainty the conclusions of this and sensitivity section and highlight possible assessment. Resolution does limitations with respect to the use of the PRA for not impact the proposed LAR.
applications.
SC-AS-01 SC-AS Met 2018 Peer Review Comment: Open (July 2018) The success path for SGTR includes throttling HPSI to maintain RWST inventory until SOC can be The proposed amendment achieved for safe and stable conditions and requires request affects the grid-32 hours to achieve. The PRA model is based on a related LOOP accident 24 hour2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months mission time. Also, it is not clear how long sequence. Since the finding the RWST can provide inventory affects the SGTR accident sequence, there is no impact Assessment Basis on the proposed LAR.
MPS2-SC.1 identifies the base mission time as safe Therefore, a sensitivity study and stable within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months . No events were is not required to address this identified requiring longer than 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months , however finding.
MPS2-SC.2 identifies that one SGTR sequence requires 32h to reach safe and stable and includes an evaluation that the impact on CDF is not significant.
Proposed Resolution Provide additional analysis to demonstrate that safe and stable conditions can be achieved by 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months , revise the model to account for the extra time, or add a recovery action such as refilling the RWST.
Serial No: 19-2828 Docket No. 50-336 Attachment 5, Page 12 of 13
,. Finding . ,:Supporting CapabiJityc*
.. . DescriF!tion ,Disposition Number
Req~irement{s) Cc1tegory {CC)
IFQU-A7-1 IFQU-A7 Met 2018 Peer Review Comment: Resolved.
(March IFQU-Bl Met Detailed quantification notebook is not available for 2018) the MC documentation. To meet this requirement, The MPS2 PRA documentation a detailed QU notebook will be required. has been updated to address the supporting requirements Assessment Basis: in IFQU-A7 and IFQU-Bl based The quantification process met the requirements of on the latest model, MPS2-QU SR groups A-E. Because these results were not R05g. Resolution does not contained in the model update documentation, a impact the proposed LAR.
finding was given to create a detailed QU that addresses HLR F SRs.
Proposed Resolution:
Generate a detailed QU notebook either for the integrated -PRA model or for the flooding specific model that meets the requirements of IFQU and QU of the standard.
QU-F2-02 QU-F2 Met 2018 Peer Review Comment: Resolved.
(March QU-F3 Met Dominions' PRA update process periodically creates 2018) a new "model of record" that addresses the The MPS2 PRA documentation requirements of QU-F2 & QU-F3. However interim has been updated to address updates are performed to maintain the PRA the supporting requirements consistent with the as-built/as-operated plant that in QU-F2 and QU-F3 based on do not address all of requirements of QU-F2 & QU- the latest model, MPS2-R05g.
F3 to document sensitivities, uncertainty Resolution does not impact assessments and significant contributors. the proposed LAR.
Serial No: 19-2828 Docket No. 50-336 Attachment 5, Page 13 of 13 Finding* . Sl!pporting , ~apabiljty
. Description .
Disposition Numb.er Requfreme.nt(s) . Category,(CC)
Proposed Resolution:
The full quantification analysis, which addresses the SRs for QU-F2 and QU-F3, should be updated to for use with risk informed submittals or peer reviews, or justification should be included in the documentation for the interim quantification results detailing why elements of the previous quantification analysis still apply to the interim model results.
Serial No: 19-282B Docket No. 50-336 ATTACHMENT 6 EXTERNAL HAZARDS SCREENING DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 2
Serial No: 19-282B Docket No. 50-336 Attachment 6, Page 1 of 8 External Hazards Screening Airport hazard meets 1975 SRP requirements. Airports, military installations and flight corridors around MPS2 (including Groton Aircraft Impact y PS2 Airport) have been considered.
Evaluations of aircraft impact associated with these facilities find that it does not pose a significant hazard.
Not applicable to site because of topology. MPS2 is located on the y Long Island Sound with no hilly or Avalanche C3 mountainous terrain near the site.
Avalanches are not a viable external initiator.
Plant design accounts for biological growth. Slowly developing growth can be detected and mitigated by surveillance. The circulating water system intake structure incorporates several features to control biological fouling including Biological Event y C1, C5 trash racks and traveling screens, a cutoff wall to prevent ecologically rich surface water from entering the system, exit passages for fish are provided, vertical guides allow individual channels to be drained .
and a chlorination system for biocide treatments.
Slowly developing event can be Coastal Erosion y C5 detected and mitigated by surveillance.
Plant design eliminates drought as Drought y C1, C5 a concern and event is slowly developing. The Ultimate Heat Sink UHS is the Lon Island Sound
Serial No: 19-282B Docket No. 50-336 Attachment 6, Page 2 of 8 which is unaffected by drought since. it communicates with the Atlantic Ocean.
Offsite power is expected to be lost as a result of a storm surge that introduces external flooding risk to External Flooding y None MPS2. Consequently, there is no external flood risk impact associated with the proposed amendment request.
The wind loadings for all structures are based on American Society of Civil Engineers Paper 3269, "Wind Forces on Structures". The basic design wind velocity for MPS2 Class 1 structures is 115 mph with gusts up to 140 mph.
MPS2 structures are designed for tornados having a maximum rotational velocity of 300 mph and a maximum translational velocity of 60 mph. This design basis tornado has a frequency less than 1E-6/yr at MPS2.
Extreme Wind or y C1, PS4 Tornado Failure of a service water pump due to missile strike is bounded by 1E-6/yr. Failure of both diesels due to missile strike is bounded by 1E-6/yr.
Failure of the EOG Room ventilation due to tornado is bounded by 1E-6/yr. CDF due to tornado-induced failure of the East 480V Switchgear Room ventilation is bounded by 1E-6/yr. Control Room ventilation failure is not a significant contributor to risk because of alternate means of Control Room coolin and the
Serial No: 19-2828 Docket No. 50-336 Attachment 6, Page 3 of 8 ability to shut down outside the Control Room.
Fog can be a contributor to transportation accidents.
Transportation accidents meet the criteria of the 1975 SRP.
Deep draft boats must stay at least 2 miles offshore to avoid running Fog y PS2,C1 aground on Bartlett Reef.
Therefore, a boat that could cause significant damage to the Intake Structure is highly unlikely to collide with the Intake Structure and would, most likely, run aground first.
Site is cleared preventing fire from y propagating onto the site and is not Forest or Range Fire C3 located in forested or grassland area.
y Frost is covered under snow and Frost C4 ice hazards.
Loss of offsite power (LOOP) events associated with hail are addressed in the Internal Events PRA and the occurrence frequency Hail y C2 is enveloped by the frequency of weather-induced LOOP events.
Limited occurrence and bounded by other events for which the plant is designed.
Plant is designed for this hazard.
Ventilation systems provide High Summer conditioned air in the plant to cool y C1, C5 equipment. Weather-induced Temperature LOOP events are considered in the Internal Events PRA. Effects on the UHS are slow to develo if the
Serial No: 19-282B Docket No. 50-336 Attachment 6, Page 4 of 8 develop at all because of the size of the Long Island Sound.
High Tide, Lake y High tide is covered by external C4 Level, or River Stage flooding considering storm surge.
y Hurricane is covered by external Hurricane C4 flooding and high winds or tornado.
Plant is designed against freezing temperatures. Protection against y ice blocking of roof penetrations will Ice Cover C1, C4 be demonstrated by Dominion. Ice blockage causing flooding is covered under external flooding.
Explosive hazard impacts and control room habitability impacts meet 1975 SRP requirements (RG
1. 78 and 1.91 ). Industrial facilities Industrial or Military y are too distant to pose a hazard to PS2 Facility Accident the safe operation of the plant.
Nearby military facilities do not conduct operations that could potentially pose a hazard to the safe operation of the plant.
MPS2 has an internal flooding PRA Internal Flooding N None model.
Addressed in Attachment 1 Section Internal Fire N None 4.4.
y Not applicable to the site because Landslide C3 of topography.
Lightning strikes causing loss of offsite power or turbine trip are contributors to the initiating event Lightning y C1, C4 frequencies for these events.
However, other causes are included. The impacts are no reater than those alread modeled
Serial No: 19-2828 Docket No. 50-336 Attachment 6, Page 5 of 8
. in the internal events PRA.
Additionally, MPS2 does not have a specific vulnerability to lightning and does not have unique features that would create a high likelihood of failing safety-related systems, structures, or components concurrent with a LOOP.
Not applicable to site because of location. MPS2 is located on the Low Lake Level or y C3 coast of the Long Island Sound River Stage which is virtually unaffected by lack of precipitation.
Plant is designed for this hazard.
Potential pipe freezing is addressed by a requirement for heat tracing Low Winter y C1, C5 operability during cold weather.
Temperature Impacts on the UHS are slow to develop, if it all, due to the size and salinity of the Long Island Sound.
Event occurrence frequency of meteorites greater than 100 lb.
striking the plant is 7E-9/yr. This frequency is very low in absolute Meteorite or Satellite y terms and lower than aircraft C2, PS4 Impact impacts. Aircraft impact damage envelops meteorite/satellite impact damage. Site is no more likely to be struck by meteorite/satellite than any other site.
y Pipelines are not close enough to Pipeline Accident C3 significantly impact plant structures.
Plant storage of chemicals meets 1975 SRP requirements (RG 1.78 Release of and 1.91 ). Control room habitability Chemicals in Onsite y PS2 during postulated chemical Storage releases has been evaluated and it has been determined that habitabilit is not threatened .b this
Serial No: 19-282B Docket No. 50-336 Attachment 6, Page 6 of 8 hazard.
Not applicable to the site because of location. There are no diversions River Diversion y C3 near MPS2. Cooling water is supplied directly from the Long Island Sound.
Not applicable to the site because Sand or Dust Storm y C3 of location. MPS2 is not subjectto sand or dust storms.
Not applicable to the site because of location. Seiche in the Long Island Sound or the discharge y basin was evaluated not to be a Seiche C3 hazard for these bodies of water because of their geometry and locations relative to seiche inducing phenomena.
Addressed in Attachment 1 Section Seismic Activity N None 4.4.
Event damage potential is less than other events for which the plant is Snow y C1, C4 designed. Potential flooding impacts covered under external flooding.
Plant is designed for this hazard.
The MPS2 UFSAR Chapter 2.7 describes the characteristics of the area geology, soil conditions, Soil Shrink-Swell y testing, foundations and backfill.
C1 Consolidation Allowable bearing pressures for soil-supported structures are greater than contact pressures as determined by backfill testing. The potential for this hazard is low.
Serial No: 19-282B Docket No. 50-336 Attachment 6, Page 7 of 8 y Storm surge is covered by external
Storm Surge C4 flooding.
Toxic gas is covered by industrial or military facility accident, release of chemicals in on-site storage, and transportation accident. Control Toxic Gas y C4 room habitability during postulated chemical releases has been evaluated and it has been determined that habitability is not threatened by this hazard.
Potential hazards meet the 1975 SRP requirements. The hazards resulting from potential transportation accidents (i.e.,
highway, waterway, railroad, and air) were found to not contribute significantly to plant risk.
Highway - The distance to the nearest highway exceeds the RG 1.91 safe distance criterion.
Waterway - Most ships passing MPS2 are deep draft and must remain at least 2 miles offshore to Transportation y avoid running aground.
PS2,C4 Accident Railroad - Hazardous materials are transported about 0.25 miles from the protected area. Most of the transported hazardous materials (chlorine, anhydrous ammonia, carbon dioxide and carbon disulfide) meet the RG 1.78 screening criterion for low transport frequency. The remaining transported hazardous material (propane) presents negligible potential for damage due to explosion and is not a threat to control room habitabilit due to
Serial No: 19-2828 Docket No. 50-336 Attachment 6, Page 8 of 8 toxic gas plume.
Air - Covered under aircraft impact.
Tsunami y C4 Covered under external flooding.
Bounding analysis is used to show Turbine-Generated y PS4 CDF for turbine generated missiles Missiles is less than 1E-6/yr.
Not applicable to the site because Volcanic Activity y C3 of location. There are no volcanos within the vicinity of MPS2.
y Waves are covered under external Waves C4 flooding.
Note a - See Attachment 7 for descriptions of the screening criteria.
Serial No: 19-282B Docket No. 50-336 ATTACHMENT 7 PROGRESSIVE SCREENING APPROACH FOR ADDRESSING EXTERNAL HAZARDS DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 2
Serial No: 19-2828 Docket No. 50-336 Attachment 7, Page 1 of 2 Progressive Screening Approach for Addressing External Hazards NUREG/GR-2300 Initial Preliminary G1* Event damage and ASME/ANS potential is < events for Screening which plant is designed. Standard RA-Sa-2009 G2. Event has lower mean NUREG/GR-2300 frequency and no worse and ASME/ANS consequences than other Standard RA-Sa-events analyzed. 2009 NUREG/GR-2300 G3. Event cannot occur and ASME/ANS close enough to the plant Standard RA-Sa-to affect it.
2009 NUREG/GR-2300 Not used to G4. Event is included in and ASME/ANS screen. Used only the definition of another Standard RA-Sa- to include within event.
2009 another event.
G5. Event develops ASME/ANS slowly, allowing adequate Standard RA-Sa-time to eliminate or 2009 mitigate the threat.
PS1. Design basis hazard ASME/ANS Progressive cannot cause a core Standard RA-Sa-Screening
damage accident. 2009 PS2. Design basis for the NUREG-1407 and event meets the criteria in ASME/ANS the NRG 1975 Standard Standard RA-Sa-Review Plan (SRP). 2009 PS3. Design basis event NUREG-1407 as mean frequency is < 1E- modified in 5/y and the mean ASME/ANS conditional core damage Standard RA-Sa-probability is < 0.1. 2009 NUREG-1407 and PS4. Bounding mean GDF ASME/ANS is< 1E-6/y. Standard RA-Sa-2009
Serial No: 19-282B Docket No. 50-336 Attachment 7, Page 2 of 2 Screening not successful.
NUREG-1407 and PRA needs to meet ASME/ANS Detailed PRA requirements in the Standard RA-Sa-ASME/ANS PRA 2009 Standard.
Serial No: 19-282B Docket No. 50-336 ATTACHMENT 8 RESPONSES TO NRC NON-ACCEPTANCE ITEMS AND OTHER ITEMS FOR CONSIDERATION DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 2
Serial No: 19-2828 Docket No. 50-336 Attachment 8, Page 1 of 4 By letter dated August 14, 2019, Dominion Energy Nuclear Connecticut (DENG) submitted a proposed license amendment request (LAR) in accordance with 10 CFR 50.90 to revise Technical Specification (TS) 3.8.1.1, "A. C. Sources - Operating," to add a permanent Required Action (a.3) that provides an option to extend the allowed outage time (AOT) from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 10 days for one inoperable offsite circuit at Millstone Power Station Units 2 (MPS2) to the Nuclear Regulatory Commission (NRC). A one-time exception to the new proposed Required Action a.3 was also requested that would allow replacement of the Millstone Power Station Unit 3 (MPS3) 'A' RSST, its associated equipment, and other 345 kV south bus switchyard components that are nearing the end of their dependable service life. The NRC staff determined that the information provided in the LAR is not of sufficient detail to enable the NRC staff to proceed with its detailed technical review regarding the acceptability of the proposed LAR.
By letter dated October 7, 2019, the NRC formally provided DENG an opportunity to supplement the proposed LAR as follows:
NRC INFORMATION REQUEST NO. 1-a
1. In Section 3.9 of the LAR, "MPS2 FLEX Strategy," the licensee states that "during the proposed permanent TS Required Action and one-time exception, DENG will utilize the FLEX diesel generators as a supplemental power source to the-inoperable offsite power source. The technical evaluation to support this approach is provided in Section 4.0."
In Section 4.2 of the LAR, "Supplemental Power Source (SPS) for Extended AOTs
[Allowed Outage Times]," the licensee states, "DENG proposes to use the onsite 480 V FLEX diesel generators as the supplemental power source for the inoperable offsite circuit, to mitigate a postulated LOOP [Loss of Offsite Power]
event. The FLEX _diesel generators are selected as the supplemental power -
source because the MPS2 EDGs [emergency diesel generators] (which are the first line of defense) cannot be credited."
. In Section 4.2.2 of the LAR, "Initial Conditions - Electrical Power Configuration (for 1O-Day/35-Day AOTs), the licensee lists as one of the initial conditions: "FLEX 4160 V portable generators are stored offsite but are available for connection to MPS2 4160 V bus 240."
In Section 4.3 of the LAR, "Assessment Against Branch Technical Position [BTP] 8-8," the licensee states the f~llowing:
l'Two 4160 V generators are stored offsite in the NSRC [National SAFER Response Center] storage facility. These 4160 V generators would be used (as requested) to allow operators to place the unit in cold shutdown, if the alternative actions are unable to restore power. Therefore, the intent of this criterion is met. [ ... ]"
The deployment of the 480 V FLEX diesel generator and re-powering 480 V bus 22F within the timeline described in Table 1-3 will allow operators (as directed by the appropriate FSG [FLEX Support Guideline] procedure) to restore power to recharge the battery prior to depletion and to maintain reactor coolant system inventory. However, the onsite 480 V FLEX diesel generator
Serial No: 19-282B Docket No. 50-336
Attachment 8, Page 2 of 4 will be connected to MPS2 480 V bus 22F within 13 hours1.50463e-4 days 0.00361 hours 2.149471e-5 weeks 4.9465e-6 months rather than one hour
[emphasis added]. Stripping of non-required DC [direct current] and vital 120 V instrument loads shows that battery life is extended to 29 hours3.356481e-4 days 0.00806 hours 4.794974e-5 weeks 1.10345e-5 months (Reference 1-37), well beyond the time battery charging will be restored via repowering 480 V bus 22F."
The staff finds that the application as submitted does not include information demonstrating that the proposed change meets the intent of the *criteria identified in BTP 8-8. Specifically:
a. The supplemental power source, must demonstrate that it has enough capacity to carry all LOOP [loss-of-offsite power] loads to bring the unit to a cold shutdown without any load shedding.
DENC RESPONSE The LAR has been supplemented to credit the Millstone Power Station Unit 3 (MPS3)
Station Blackout (SBO) diesel generator rather than the Millstone Power Station (MPS)
FLEX generators. The MPS3 SBO diesel generator can bring MPS2 to cold shutdown without load shedding. Additional detail has been provided in Attachment 1, Section 4.2.5, and Section 4.3 bullet a) of the LAR Supplement.
NRC INFORMATION REQUEST NO. 1-b
b. To support the one-hour time for making this power source available, plants must assess their ability to cope with loss of all AC [alternating current] power for one hour independent of an alternate alternating current (AAC) power source. The plant should have formal engineering calculations for equipment sizing and protection and have approved procedures for connecting the AAC or supplemental power sources to the safety buses.
Based on the above, the staff requests the licensee to provide technical justification to demonstrate how it meets the applicable criteria in BTP 8-8.
DENC RESPONSE The LAR has been supplemented to credit the MPS3 SBO diesel generator rather than the MPS FLEX generators. Discussion related to the ability to cope with loss of all AC power for one hour has been provided in Section 3.7, Section 4.2.4, and Section 4.3, bullet a) of the LAR Supplement. Additional detail related to engineering calculations for equipment sizing has been included in Attachment 1, Section 4.2.5 and Section 4.3 e) of the LAR Supplement.
Serial No: 19-2828 Docket No. 50-336 Attachment 8, Page 3 of 4 NRC INFORMATION REQUEST NO. 2-a
2. Additionally, the NRG staff noted the following items for the licensee to consider when evaluating its response to the above acceptance review items and supplementing its LAR as appropriate:
a. The proposed TS markups do not discuss the compensatory measures and risk management actions taken during extended AOT. Since the NRG staff's review of the amendment considers the adequacy of compensatory measures and risk* management actions, it is the staff's expectation that these items would be referenced in the TS markup.
DENC RESPONSE The proposed TS markup provided in the LAR Supplement, Attachment 2 has been updated to state that "The risk management actions contained in DENG letter 19-282B, Attachment 4 (also provided. in TS Bases 3/4.8), shall remain in effect during the 10-day AOT." .
NRC INFORMATION REQUEST NO. 2-b b.. The LAR and the proposed TSs do not discuss information concerning the proposed actions to be taken, should severe weather conditions be anticipated prior to the scheduled transformer maintenance and replacement activities or if a severe thunderstorm warning or tornado warning is issued after entering TS Required Action a.3.
DENC RESPONSE The LAR Supplement, Attachment 1, Section 4.3 bullet j) discussion has been expanded to describe proposed actions that would be taken in response to severe weather.
NRC INFORMATION REQUEST NO. 2-c
c. The LAR states that the proposed activities for the permanent 10-day and the one-time 35-day offsite power AOT extensions are completed when Unit 3 is in Mode 5, 6, or defueled. However, the proposed Unit 2 TS markup does not indicate Unit 3 mode(s) for entry into Required Action a.3 of TS 3.8; 1.1.
DENC RESPONSE The proposed TS markup provided* in the LAR Supplement, Attachment 2 has been updated to specify that the 10-day and 35-day AOTs can only be entered when MPS3 is
. in MODE 5, 6 or defueled.
Serial No: 19-282B Docket No. 50-336 Attachment 8, Page 4 of 4 NRC INFORMATION REQUEST NO. 2-d
d. In several instances, the LAR references NRG draft Revision 1 of BTP 8-8 dated March 2018, and provides discussion of how the proposed change meets the proposed draft staff positions. The NRG staff has not issued the revised BTP as approved guidance for generic use. While the NRG staff's safety evaluation of the LAR will consider the plant-specific justifications provided by the licensee, it will not be evaluated against a draft (unapproved) update to the generic guidance.
DENC RESPONSE The citations of the draft Revision 1 of BTP a-8, dated March 2018, have been removed from LAR Supplement Attachment 1.
NRC INFORMATION REQUEST NO. 2-e
e. In Tables 1-1 and 1-2 of the LAR, the licensee provided the duration (in days) for the various work/preventative maintenance activities and contingencies supporting both the proposed permanent 10-day and one-time 35-day AOTs.
However, the licensee did not provide justification for the duration of the requested AOT (actual hours plus margin) based on plant-specific past operating experience.
DENC RESPONSE Discussion has been added in the LAR Supplement, Attachment 1, Sections 4.1.1 and 4.1.2, to provide more detail on how plant-specific past operating experience was used in deriving the permanent 10-day and one-time 35-day AOT durations.
While developing the LAR Supplement, additional review of the activities and durations comprising the 35-d~y AOT was performed. Some minor changes to the activity descriptions and durations were identified and incorporated in LAR Attachment 1, Table 1-2. The changes did not significantly impact the expected overall duration of the MPS3 RSST replacement project.

v t e Letter Sequence Supplement
EPID:L-2019-LLA-0177, TSTF-425, TSTF-425 (Approved, Closed)
Initiation Request, Request Acceptance, Acceptance Supplement, Supplement Administration Questions 23 December 2019 23 January 2020 19 February 2020 Answers 3 October 2019 11 February 2020 19 March 2020 Results Approval Other: ML20028C195
MONTHYEAR2019-09-26 [Table View]

ML19304A294

Text

SUMMARY

4.0 TECHNICAL EVALUATION

5.0 REGULATORY EVALUATION

6.0 ENVIRONMENTAL CONSIDERATION

7.0 REFERENCES

SUMMARY

4.0 TECHNICAL EVALUATION

5.0 REGULATORY EVALUATION

6.0 ENVIRONMENTAL CONSIDERATION

7.0 REFERENCES

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