Text

Emergency License Amendment Request- One Time Extension to Technical Specifications (TS) 3/4.8.1 Action a.3 Allowed Outage Time for an Inoperable Offsite Source
	ML24064A247
Person / Time
Site:	Seabrook
Issue date:	03/04/2024
From:	Catron S; NextEra Energy Seabrook
To:	; Office of Nuclear Reactor Regulation, Document Control Desk
References
	L-2024-032
	Download: ML24064A247 (1)
	v • d • e

NEXTera*

EN~

U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington DC 20555-0001 RE:

Seabrook Station Docket No. 50-443 Renewed Facility Operating License No. NPF-86 March 4, 2024 L-2024-032 10 CFR 50.90 10 CFR 50.91(a)(5)

Emergency License Amendment Request-One Time Extension to Technical Specifications (TS) 3/4.8.1 Action a.3 Allowed Outage Time for an Inoperable Offsite Source Pursuant to 10 CFR 50.90, NextEra Energy Seabrook, LLC (NextEra) hereby requests an amendment to Renewed Facility Operating License NPF-86 for Seabrook Nuclear Plant Unit 1 (Seabrook). The proposed changes are being requested on an emergency basis pursuant to 10 CFR 50.91 (a)(5).

The proposed one-time change modifies the Allowed Outage Time for Seabrook TS 3/4.8.1, "AC.

Sources - Operating," Action a.3 from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 30 days.

The enclosure to this letter provides NextEra's evaluation of the proposed changes. Attachment 1 to the enclosure provides the Seabrook TS pages marked-up to show the proposed changes.

This submittal was developed using the guidance provided in NUREG-0800 Standard Review Plan, Branch Technical Position 8-8.

NextEra has determined that the proposed license amendment does not involve a significant hazards consideration pursuant to 1 O CFR 50.92(c), and that there are no significant environmental impacts associated with the change. The Seabrook Onsite Review Group (ORG) has reviewed the enclosed amendment request. In accordance with 10 CFR 50.91 (b)(1 ), a copy of this license amendment request is being forwarded to the designee for the State of New Hampshire.

NextEra requests approval of this emergency License Amendment Request by March 8, 2024, to support the currently planned replacement of the 3B Reserve Auxiliary Transformer and restoration of the offsite source to Operable status.

Should you have any questions regarding this submission, please contact Mr. Kenneth Mack, Licensing Manager at (561) 904-3635.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on the !2!:/.__ day of March 2024.

tron and Regulatory Compliance Director - Nuclear Fleet Enclosure Attachm,ents NextEra Energy Seabrook, LLC P.O. Box 300, Lafayette Road, Seabrook, NH 03874

Seabrook Station Docket Nos. 50-443 cc:

USNRC Region I Administrator USNRC Project Manager USNRC Senior Resident Inspector Director Homeland Security and Emergency Management New Hampshire Department of Safety Division of Homeland Security and Emergency Management Bureau of Emergency Management 33 Hazen Drive Concord, NH 03305 Katharine Cederberg, Lead Nuclear Planner The Commonwealth of Massachusetts Emergency Management Agency 400 Worcester Road Framingham, MA 01702-5399 L-2024-032 Page 2 of 2

Seabrook Station Docket Nos. 50-443 Evaluation of the Proposed Changes Seabrook Station L-2024-032 Enclosure Page 1 of 14 Emergency License Amendment Request-One Time Extension to Technical Specifications (TS) 3/4.8.1 Action A.3 Completion Time for an Inoperable Offsite Source 1.0

SUMMARY

DESCRIPTION 2.0 DETAILED DESCRIPTION

3.0 TECHNICAL EVALUATION

4.0 REGULA TORY EVALUATION

5.0 ENVIRONMENTAL CONSIDERATION

6.0 REFERENCES

ATTACHMENT 1: Technical Specifications pages (markup)

ATTACHMENT 2: PRA Evaluation for 38 RAT Emergency LAR

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 2 of 14 1.0

SUMMARY

DESCRIPTION 2.0 Pursuant to 10 CFR 50.90, NextEra Energy Seabrook, LLC (NextEra) requests an amendment to Renewed Facility Operating License NPF-86 for Seabrook Nuclear Plant Unit 1 (Seabrook). The proposed changes are being requested on an emergency basis pursuant to 10 CFR 50.91 (a)(5).

The reason that this License Amendment Request (LAR) is being submitted on an emergency basis and the justification why this situation could not be avoided is discussed in Section 2.

The proposed change provides for a one-time modification of the Allowed Outage Time (AOT) for Seabrook TS 3/4.8.1, "AC. Sources - Operating," Action a.3 from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 30 days. This one-time extension is requested to facilitate replacement of the 38 Reserve Auxiliary Transformer.

NextEra requests approval of this emergency LAR by March 8, 2024, to support the currently planned replacement of the 38 Reserve Auxiliary Transformer and restoration of the offsite source to Operable status.

DETAILED DESCRIPTION 2.1 System Design and Operation The facility is interconnected to offsite power via three 345 kilovolt lines of the transmission system for the New England states. The normal preferred source of power for the unit is its own main turbine generator. The redundant safety feature buses of the unit are powered by two unit auxiliary transformers. A highly reliable generator breaker is provided to isolate the generator from the unit auxiliary transformers in the event of a generator trip, thereby obviating the need for a bus transfer upon loss of turbine generator power. In the event that the unit auxiliary transformers are not available, the redundant safety feature buses of the unit are powered by two reserve auxiliary transformers. Upon loss of offsite power, the unit is supplied with adequate power by either of two fast-starting, diesel-engine generators. Either diesel-engine generator and its associated safety feature bus is capable of providing adequate power for a safe shutdown under accident conditions with a concurrent loss of offsite power. A non-safety related supplemental emergency power system (SEPS) is available as a backup power source to either safety feature bus when one or both emergency diesel generators fail to start and load. SEPS is capable of providing adequate power for a safe shutdown under loss of offsite power condition. A constant supply of power to vital instruments and controls of each unit is assured through the redundant 125 volt direct current buses and their associated battery banks, battery chargers and inverters.

Basis of Current Design:

Two reserve auxiliary transformers (RATs) provide a second immediate access circuit from the preferred power supply (offsite source) to the onsite distribution system, providing power for all loads including all the engineered safety features loads. The transformers are three phase, three winding, outdoor type, oil filled, Class OA/FA/(FOA Future) transformers with wye connected 345 kV primary rated 27/36/(45 Future) MVA at 55°C and 30.24/40.32/(50.4 Future) MVA at 65°C; wye connected 13.8 kV secondary winding rated 18/24/(30 Future) MVA at 55°C and 20.16/26.88/(33.6 Future) MVA at 65°C, and delta connected 4300 volt tertiary rated 12/16/(20 Future) MVA at 55°C and 13.44/17.92/(22.4 Future) MVA at 65°C. Each transformer has the capacity to supply the power requirements of the connected load under all plant conditions.

The RATs are located on the north side of the Turbine Building heater bay. The pair of transformers are connected to the 345 kV switching station by SF6 gas insulated bus.

High voltage bushings are used to connect the transformer terminals to the SF6 gas-insulated bus.

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 3 of 14 2.2 2.3 2.4 The secondary winding of each reserve auxiliary transformer is connected to a 13.8 kV switchgear bus, and the tertiary winding is connected to one train of 4160 volt emergency switchgear and to one 4160 volt nonessential switchgear lineup. By this arrangement, a separate RAT feeds each emergency bus. Connections to both the 13.8 kV and the 4160 volt switchgear are made with three phase nonsegregated phase bus ducts. There is a contingency alignment where emergency diesel generator EDG-1A may be aligned to provide power to the RAT-3A tertiary winding.

Description of Events On March 1st, 2024, at approximately 0542, the Seabrook Station control room received alarms associated with 345kV breakers 695 and 52 opening and de-energizing the 38 Reserve Auxiliary Transformer and declared the 38 Reserve Auxiliary Transformer inoperable. Initial troubleshooting identified that 38 Reserve Auxiliary Transformer had two local alarms present: sudden pressure relay actuated along with low oil level. A low SF6 gas alarm was identified at 0652. The Outage Control Center was immediately staffed with around-the-clock coverage. Following inspection of the 38 Reserve Auxiliary Transformer, it was concluded that the maintenance activity would entail the replacement of the transformer.

Reason the Amendment is Requested on an Emergency Basis Seabrook entered TS LCO 3.8.1.1 Action a. at approximately 0542 on March 1, 2024.

The AOT of Action a.3 requires that Seabrook shutdown at 0542 on March 4, 2024, unless at least two offsite circuits are restored to Operable status. Restoration of the offsite circuit requires replacement of the 38 Reserve Auxiliary Transformer.

This change is needed sooner than can be issued under exigent circumstances because the Notice of Enforcement Discretion expires at 0542 on March 9, 2024, and this license amendment request is considered timely considering the unplanned nature of the event.

Reason Emergency Situation Has Occurred Based on the inspections and data collected, the most likely cause of this event is a catastrophic failure of the bushing porcelain, which allowed a flow path of SF6 gas from the SF6 gas compartment through the bushing internals into the transformer tank. This was most likely caused by the loss of insulating oil in the bushing resulting in a fault and creating an overpressure condition and arcing inside the transformer. Since this failure resulted in contamination of the transformer internals with porcelain fragments, and the inability to conclusively test and inspect for winding damage, it is prudent to replace the transformer.

2.5 Reason the Situation Could Not Have Been Avoided There were no prior indications of an imminent bushing failure that would have driven a proactive bushing replacement. Specifically, RAT bushing oil pressures are recorded on a weekly basis. The last pressure readings taken for the BRAT occurred on February 22, 2024, and were satisfactory. Review of the past data indicates stable readings with no adverse trend.

Doble testing of the RAT 38 bushings were conducted during the last refueling outage in April 2023. The results from the April 18, 2023, Doble tests were not outside of our acceptance criteria. This data was reviewed by both the Fleet Transformer group and Doble engineers and the data was determined to be acceptable for continued service. As

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 4 of 14 2.6 part of the failure investigation a review using the full historical data from the previous test data of the transformer bushings indicated changes in power factor values on the failed bushing that requires additional review for root cause.

Current Requirements/ Proposed Changes to TS 3/4.8.1 In Modes 1 through 4, TS Limiting Condition for Operation (LCO) 3.8.1.1 requires two physically independent circuits between the offsite transmission network and the onsite Class 1 E Distribution System and two separate and independent diesel generators.

a.

Action a.3 requires that if an offsite circuit is inoperable, it shall be restored to Operable status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months .

The proposed change requests a one-time extension of Action a.3 to restore the offsite circuit from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 30 days to return the inoperable offsite circuit to Operable status. This will be reflected as a footnote to TS LCO 3.8.1.1 Action a.3.

The proposed footnote will read as follows:

A one-time Allowable Outage Time (AOT) extension for an inoperable offsite circuit allows 30 days to restore the inoperable offsite circuit to OPERABLE status.

Compensatory measures within NextEra Energy Seabrook, LLC letter L-2024-032 dated March 4, 2024, shall be implemented and shall remain in effect during the extended AOT period. The one-time AOT extension shall expire upon completion of the maintenance to restore the offsite circuit to OPERABLE status not to exceed 30 days following issuance of the amendment authorizing the one-time AOT extension.

b. Action b. provides a one-time AOT extension for an inoperable diesel generator that has expired.

The proposed change permanently removes the footnote applicable to TS 3.8.1.1, ACTION b.2)(a), as denoted by a double-asterisk(**). The footnote authorized a one-time extension to TS 3.8.1.1, ACTION b.2)(a) that has since expired and is no longer required.

c. Action c. requires actions during the 30-day AOT requested in Action a.3 that cannot be met with one offsite circuit and one diesel generator inoperable, such as restoring at least two offsite circuits to Operable status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months from the time of initial loss.

The proposed change requests a one-time change to make Action c.3) not applicable to restore the offsite circuits and diesel generators during the 30-day AOT in Action a.3 to restore the offsite circuit. This will be reflected as a footnote to TS LCO 3.8.1.1 Action c.3).

The proposed footnote will read as follows:

- A one-time Allowable Outage Time (AOT) extension for an inoperable offsite circuit and diesel generator allows 30 days to restore the inoperable offsite circuit to OPERABLE status. Compensatory measures within NextEra Energy Seabrook, LLC letter L-2024-032 dated March 4, 2024, shall be implemented and shall remain in effect during the extended AOT period. The one-time AOT extension shall expire upon completion of the maintenance to restore the offsite circuit to OPERABLE status not to exceed 30 days following issuance of the amendment authorizing the one-time AOT extension.

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 5 of 14

d. Action e. requires actions with two required offsite AC. circuits inoperable, including Action e.3 that cannot be met to restore at least two offsite sources to Operable status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months from the time of initial loss.

The proposed change requests a one-time change to make Action e.3) not applicable to restore the offsite circuits during the 30-day AOT in Action e.3 to restore the offsite circuit. This will be reflected as a footnote to TS LCO 3.8.1.1 Action e.3).

The proposed footnote will read as follows:

A one-time Allowable Outage Time (AOT) extension for an inoperable offsite circuit allows 30 days to restore the inoperable offsite circuit to OPERABLE status.

Compensatory measures within NextEra Energy Seabrook, LLC letter L-2024-032 dated March 4, 2024, shall be implemented and shall remain in effect during the extended AOT period. The one-time AOT extension shall expire upon completion of the maintenance to restore the offsite circuit to OPERABLE status not to exceed 30 days following issuance of the amendment authorizing the one-time AOT extension.

3.0 TECHNICAL EVALUATION

3.1 Compliance with NUREG-0800 Standard Review Plan, Branch Technical Position 8-8 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," specifically discusses the defense-in-depth (DID) aspects for onsite power sources from a deterministic perspective for proposed Allowed Outage Time (AOT) extensions. No changes are being proposed to the current AOTs for the Seabrook emergency diesel generators. The following is a list of critical BTP 8-8 guidance and an explanation as to how Seabrook complies with the guidance 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).

The Seabrook Supplemental Emergency Power System (SEPS) as specified in Section 3/4.8.1 of the TS Bases meets this criterion.

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 deterministic evaluation supports the proposed AOT and the power source has enough capacity to carry all LOOP loads to bring the unit to a cold shutdown.

TS 3.8.1.1 Action b.2.(a) extends the AOT for an inoperable EOG from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 14 days if SEPS is available, as specified in the TS Bases; therefore, SEPS meets this criterion.

c)

Multi-unit sites that have installed a single AAC power source for SBO cannot substitute it for the inoperable diesel when requesting AOT extension unless the AAC source has 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.

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 6 of 14 Seabrook is a single unit site that responds to Station Blackout (SBO) as an AC Independent plant relying only on the station batteries as a source of electrical power for the coping duration. When the SBO analysis was initially performed there were no alternate AC power sources to support response as an Alternate AC (AAC) plant.

SEPS was subsequently installed and meets this criterion, but is not credited as an AAC power source.

d) For plants using 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.

Seabrook does not have a credited AAC power source. DID is discussed in Section 3.3.

e)

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.

Seabrook does not have a credited AAC power source. DID is discussed in Section 3.3.

f)

To support the one-hour time for making this power source available, plants must assess their ability to cope with loss of all AC power for one hour independent of an AAC power source.

Seabrook does not have a credited AAC power source. DID is discussed in Section 3.3.

g)

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.

Seabrook does not have a credited AAC power source. DID is discussed in Section 3.3.

h)

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.)

NextEra is requesting a temporary one-time 30-day AOT. It is estimated that up to 30 days is required to complete preparation of the spare transformer and implement the replacement. The duration of the requested 30 days AOT is justified.

i)

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

TS 3.8.1.1 Action b.2.(a) extends the AOT for an inoperable EDG from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 14 days if SEPS is available, as specified in the TS Bases. Section 3/4.8.1 of the TS Bases states that prior to exceeding the 72-hour AOT the SEPS must be available in accordance with Technical Requirement (TR) 31, which requires an operational readiness status check. The operational readiness status check is specified in TR 31 and consists of: (1) verifying the SEPS is operationally ready for automatic start and

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 7 of 14 Energization of the selected emergency bus; (2) verifying 24-hour onsite fuel supply; and (3) verifying alignment to the selected 4160 volt emergency bus and associated 480 volt bus.

j)

The availability of AAC or supplemental AC source shall be checked every 8-12 hours (once per shift). If the AAC or supplemental power source becomes unavailable any time during extended AOT, the unit shall enter the LCO and start shutting down within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months . This 24-hour period will be allowed only once within any given extended EOG AOT.

Section 3/4.8.1 of the TS Bases states the operational readiness status check must continue to be performed at least once every 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months following the initial SEPS availability verification. Section 3/4.8.1 of the TS Bases also states that should the SEPS become unavailable during the 14-day AOT and cannot be restored to available status, the EDG AOT reverts back to 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . The 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months begins with the discovery of the SEPS unavailability, not to exceed a total of 14 days from the time the EDG initially became inoperable.

The total connected load necessary for SEPS is 4371 kW. Each of the two SEPS Generators has a capacity of 2700 kW per unit, for a combined total of 5400 kW.

Therefore, the SEPS Generators have sufficient capacity to power the connected loads.

The total fuel consumption required by SEPS to reach 200 degrees Fahrenheit is 8675.8 gallons. Each SEPS generator has a fuel tank containing 6085 gallons for a total of 12170 gallons available storage. Procedural requirements include a minimum of 4775 gallons of fuel per engine, for a total on hand supply of 9550 gallons.

Therefore, sufficient fuel is available to achieve 200 degrees Fahrenheit, even at the minimum allowable fuel level.

Based on the above information, SEPS has the capacity (including the required fuel oil) to bring the unit to cold shutdown in the event of a LOOP concurrent with a failure of EDG A, while EDG B is unavailable.

The SEPS does not automatically connect to either emergency bus during a LOOP.

Were an EDG not available during a LOOP event, control room operators would respond using plant procedures to re-energize the emergency bus utilizing SEPS by closing the SEPS feeder breaker from the Main Control Board (MCB) to repower the affected emergency bus. The Emergency Power Sequencer would sequence loads onto the emergency bus.

In this scenario, the approximate time to repower the affected emergency buses by SEPS would be 5 - 15 minutes. This task is not an assigned Time Critical Task or a Time Sensitive Task, and timing runs have not been performed for the purpose of establishing an expected response time.

k)

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 and bus.

The planned one-time extended 30-day AOT will be used once to support replacement of the 38 Reserve Auxiliary Transformer.

I)

The preplanned maintenance will not be scheduled if severe weather conditions are anticipated.

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 8 of 14 Replacement of the 38 Reserve Auxiliary Transformer cannot be preplanned due to the emergent nature of the event.

In the event of severe weather, all work associated with the equipment impacted by the changes proposed in the emergency LAR will be suspended and the station procedures for severe weather will be used to control work processes.

m) 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.

NextEra Operations will notify the grid operator (Load Dispatcher) to request maintenance and switching activities be restricted to emergency operations only on the following lines:

Newington / Timber Swamp Line #3 Scobie Pond Line #2 Ward Hill / West Amesbury Line #1 Additionally, the grid operator (Load Dispatcher) will be contacted once per day during the extended 30-day AOT to ensure no significant grid disturbances are expected during the extended 30-day AOT.

n)

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 switch yard maintenance will be performed.

NextEra will not conduct any discretionary testing or maintenance, which can increase the likelihood of a plant transient (unit trip) or LOOP, on safety systems and important non-safety equipment in the offsite power systems while in the extended 30-day AOT. In addition, no discretionary switchyard maintenance will be performed on guarded equipment. OP-AA-102-1003, "Guarded Equipment," will be used to guard equipment that has been identified as being necessary to support nuclear safety.

o)

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.

OP-AA-102-1003 will be used to guard equipment that has been identified as being necessary to comply with TS LCOs and to support nuclear safety.

p)

Steam-driven emergency feed water pump(s) in case of PWR units, and Reactor Core Isolation Cooling and High Pressure Coolant Injection systems in case of BWR units, will be controlled as "protected equipment."

Seabrook is a PWR whose auxiliary feedwater system consists of the emergency feed water system (EFW) and the startup feedwater pump (SUFP). The EFW system consists of two 100% capacity pumps (one motor-driven and one steam turbine-driven). The SUFP provides redundant pumping capability. OP-AA-102-1003 will be used to guard the steam turbine-driven emergency feed water pump during the extended 30-day AOT.

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 9 of 14 3.2 3.3 3.4 Evaluation of Risk Impact provides the evaluation of risk impact for the proposed AOT extension, including a discussion of PRA scope, technical adequacy, modeling and insights. The evaluation determined that the ICCDP and the ICLERP for the proposed AOT extension are below the RG 1.177 threshold of 1.0E-6 per year ICCDP and 1.0E-07 ICLERP, respectively.

Defense-in-Depth Onsite Power System

Description:

The onsite power system is comprised of the 4160V Emergency Distribution System, including the standby diesel generators and the 4160-volt connections from the unit and reserve auxiliary transformers, the 480V Emergency Distribution System, the 120V Vital Instrumentation and Control Power System and the 125V DC Distribution System including the batteries and battery chargers. The Supplemental Emergency Power System (SEPS) also provides a non-safety related, diesel generator backed, power supply to one of the emergency buses when one or both emergency diesel generators fail to start and load.

Under normal operating conditions, the main generator supplies electrical power via isolated phase bus ducts to the utility grid through the generator step-up transformers and to the plant through the unit auxiliary transformers. The main generator is connected to the generator step-up and unit auxiliary transformers through a generator circuit breaker. During startup and shutdown, auxiliary power may be taken from the 345-kV system in one of two ways:

a.

Back-fed through the generator step-up transformers and unit auxiliary transformers when the generator circuit breaker is open.

b. From the reserve auxiliary transformers.

The principal feature of this system is the two redundant diesel generators which are connected to two groups of redundant emergency buses and loads when a loss of all offsite power sources occurs. Each redundant emergency bus and associated load group has sufficient redundancy, independence and testability to assure that the safety functions are performed. SEPS provides a non-safety related, diesel generator backed, power supply to the emergency buses if there is a loss of all offsite power and one or both emergency diesel generators fail to start and load.

Compensatory Actions Guarding of the following equipment:

o Both Emergency Diesel Generators o

The Supplemental Emergency Power System (SEPS) o The 345 Kv Switchyard, including the Breaker Enclosure building o

Generator Step Up Transformers o

Unit Auxiliary Transformers o

Reserve Auxiliary Transformer 3A o

Relay Room o

B and D Battery Chargers o

B and D Battery Room o

Steam turbine-driven emergency feed water pump

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 10 of 14 Note: Guarding of these areas will ensure that no unapproved work occurs in those areas that could threaten any of the electrical power supplies and subsequently reduce the current allowed outage time to a lesser allowed outage time. Operations will perform SRO walkdown of the guarded equipment per shift.

Current scheduled work is being reviewed to ensure no work is performed that could threaten offsite and onsite power sources.

Any scheduled work that is a threat to generation is being moved.

Any online scheduled work is being reviewed to ensure no impact to AC power sources.

ISO will provide daily updates to validate future grid work that could put the station under further ISO contingency actions.

Hourly fire watches will be performed in high fire risk areas.

Just In Time Training (JITT) will be performed with Licensed Operators prior to placing reserve auxiliary transformers in service and will include potential faults to aid in operator response and overall proficiency. In addition, Licensed Operators will perform a r.eview of the following procedures at the beginning of each shift rotation period (day shift; peak shift; mid shift): OS1246.02, Degraded Vital AC Power; E-0, Reactor Trip or Safety Injection; and ECA-0.0, Loss of All AC Power.

Note: Validation of the current work schedule for the next several weeks will ensure availability of equipment for operators to respond to any initiating events, as well as eliminate the possibility of an initiating event occurring due to work in areas that are currently guarded or protected.

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements/Criteria 10 CFR 50.36(c)(2)(i) states that when a limiting condition for operation of a nuclear reactor is not met, the licensee shall shut down the reactor or follow any remedial action permitted by the technical specifications until the condition can be met.

1 O CFR 50.63 states that light-water-cooled nuclear power plants licensed to operate be able to withstand for a specified duration and recover from an SBO.

10 CFR 50.65 states, in part, that the licensee shall assess and manage the increase in risk that may result from the proposed maintenance activities and that they must be sufficient to provide reasonable assurance that SSCs are capable of fulfilling their intended functions.

GDC 17 of 10 CFR 50, Appendix A, states an onsite 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 the other system is not functioning) shall be to provide sufficient capacity and capability to assure that (1) specified acceptable fuel design limits 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.

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 11 of 14 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 system 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 the other offsite electric power circuit, to assure that 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. Provision 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 of power from the transmission network, or the loss of power from the onsite electric power supplies.

The proposed license amendment complies with the requirements of 10 CFR 50.36(c),

10 CFR 50.63, 10 CFR 50.65(a)(4), and GDC 17 of 10 CFR 50, Appendix A. All regulatory requirements and applicable guidance will continue to be satisfied as a result of the proposed license amendment.

4.2 Precedents 4.3 4.2.1 Letter from NRC to Palo Verde Nuclear Generating Station, Unit 3, Issuance of Amendment Regarding Revision to Technical Specification 3.8.1, "AC

[Alternating Current] Sources - Operating" (Emergency Circumstances), dated December 23, 2016 (ADAMS Accession Number ML16358A676) 4.2.2 Letter from NRC to Brunswick Steam Electric Plant, Units 1 and 2, Issuance of Amendments for Technical Specification 3.8.1, "AC [Alternating Current] Sources

- Operating" One-Time Extension of Emergency Diesel Generator Completion Times and Suspension of Surveillance Requirements (Emergency Circumstances), dated November 26, 2017 (ADAMS Accession Number ML173286072) 4.2.3 Letter from NRC to Quad Cities Nuclear Power Station, Units 1 and 2, Issuance of Amendments Nos. 298 and 294 Regarding Increase Completion Time in Technical Specification 3.8.1.B.4 (Emergency Circumstances), dated December 17, 2023 (ML23349A162)

No Significant Hazards Consideration The proposed license amendment requests a one-time change to the Allowed Outage Time (AOT) for Seabrook Technical Specification (TS) 3/4.8.1, "AC. Sources -

Operating," Action a.3 from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 30 days to facilitate replacement of the 38 Reserve Auxiliary Transformer and associated one-time changes to Action c. and Action

e. to reduce risk.

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 12 of 14 As required by 10 CFR 50.91 (a), NextEra evaluated the proposed changes using the criteria in 10 CFR 50. 92 and determined that the changes do not involve a significant hazards consideration. An analysis of the issue of no significant hazards consideration is presented below:

(1)

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

Response: No The proposed change involves a one-time extension to the AOT for TS 3/4.8.1 Action a.3 to allow necessary time to replace the 3B Reserve Auxiliary Transformer and associated one-time changes to Action c. and Action e. to reduce risk.

With 3B Reserve Auxiliary Transformer out of service for non-elective maintenance as an initial condition the only accident with a changed probability of occurrence is the Loss of Nonemergency AC Power to the Plant Auxiliaries (Loss of Offsite Power). In this case, multiple faults would be required on the redundant offsite circuit and an additional fault on the offsite circuit supported by the 3B Reserve Auxiliary Transformer to result in a loss of offsite power (LOOP).

The use of compensatory measures such as guarding both Emergency Diesel Generators (EDGs), the Supplemental Emergency Power System, the 345 Kv Switchyard, including the Breaker Enclosure building, the Generator Step Up Transformers, Unit Auxiliary Transformers, 3A Reserve Auxiliary Transformer, and the Relay Room will preclude a significant increase in the probability of total loss of the offsite power source. The proposed amendment has no effect on the consequences of a LOOP because the EDGs provide power to safety related equipment following a LOOP. The design and function of the EDGs are not affected by the proposed change.

The probability of other previously evaluated accidents is not affected since initiation of these events is not dependent on changes in status of the electrical power supply.

Therefore, the proposed license amendments would not involve a significant increase in the probability or consequences of an accident previously evaluated.

(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 involves replacement of the 3B Reserve Auxiliary Transformer that provides power to safety-related equipment for accident mitigation. The proposed change does not alter the design, physical configuration, or mode of operation of any other plant structure, system, or component. No physical changes are being made to any other portion of the plant (i.e., no new or different type of equipment will be installed) or a change in the method governing normal plant operation; therefore, no new accident scenarios, failure mechanisms, or limiting single failures are introduced as a result of this change. The proposed change to the AOT for TS 3/4.8.1 Action a.3 to allow replacement of the 3B Reserve Auxiliary Transformer does not result in any new mechanisms that could initiate damage to the reactor or its principal safety barriers since all design and performance criteria will continue to be met

Seabrook Station Docket Nos. 50-443 L-2024-032 Enclosure Page 13 of 14 and the nuclear unit will continue to be operated within the limits of its licensing basis.

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

(3)

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

Response: No The proposed amendment increasing the AOT for TS 3/4.8.1 Action a.3 for replacement of the 38 Reserve Auxiliary Transformer reduces the margin of safety for accident mitigation by removing redundancy in the offsite power source (i.e., only one emergency power bus may be supplied from offsite sources during this maintenance window). As stated previously, the reduction in margin is not significant due to compensatory measures that will be in place during the extended completion time.

Therefore, the proposed license amendment would not involve a significant reduction in the margin of safety.

Based upon the above analysis, NextEra concludes that the proposed amendment does not involve a significant hazards consideration under the standards set forth in 10 CFR 50.92(c}, and accordingly, a finding of no significant hazards consideration is justified.

4.4 Conclusion In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

5.0 ENVIRONMENTAL CONSIDERATION

The proposed license amendment modifies a regulatory requirement with respect to the installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or changes an inspection or surveillance requirement. However, the proposed license amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluents that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed license amendment meets the eligibility criterion for categorical exclusion set forth in 1 O CFR 51.22(c)(9). Therefore, pursuant to 1 O CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed license amendment.

6.0 REFERENCES

6.1 Seabrook Technical Specifications 6.2 Seabrook Technical Specifications Bases

Seabrook Station Docket Nos. 50-443 6.3 Seabrook Technical Requirement 31 L-2024-032 Enclosure Page 14 of 14 6.4 Seabrook UFSAR Section 8.4, Compliance with 10 CFR 50.63, Loss of all Alternating Current Power (Station Blackout) 6.5 Seabrook UFSAR Section 15.2.6, Loss of Nonemergency AC Power to the Plant Auxiliaries (Loss of Offsite Power) 6.6 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" 6.7 OP-AA-102-1003, "Guarded Equipment"

ATTACHMENT 1 PROPOSED TECHNICAL SPECIFICATION PAGES (MARKUP)

(7 pages follow)

3/4.8 ELECTRICAL POWER SYSTEMS 3/4.8.1 A.C. SOURCES OPERATING LIMITING CONDITION 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 1 E Distribution System, and

b.

Two separate and independent diesel generators, each with:

1)

A separate day fuel tank containing a minimum fuel volume fraction of 3/8 (600 gallons),

2)

A separate Fuel Storage System containing a minimum volume of 62,000 gallons of fuel,

3)

A separate fuel transfer pump,

4)

Lubricating oil storage containing a minimum total volume of 275 gallons of lubricating oil, and

5)

Capability to transfer lubricating oil from storage to the diesel generator unit.

APPLICABILITY: MODES 1, 2, 3, and 4.

ACTION:

NOTE-------------------------------------

LCO 3.0.4.b is not applicable to the diesel generators.

a. With an offsite circuit of the above required A.C. electrical power sources inoperable:

1. Perform Surveillance Requirement 4.8.1.1.1.a for the OPERABLE offsite circuit within 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months and at least once per 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months thereafter;

2.

Add new Within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months from discovery of no offsite power to one train concurrent with inoperability of redundant required feature(s), declare required feature(s) with no offsite power available inoperable when its redundant required feature(s) is footnote denoted by asterisk (*)

3.

inoperable; and

!Add asterisk '-sv Restore at least two offsite circuits to OPERABLE status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

SEABROOK - UNIT 1 3/4 8-1 Amendment No. W a4, 80, 114, ffl.:t.

INSERT A

A one-time Allowable Outage Time (AOT) extension for an inoperable offsite circuit allows 30 days to restore the inoperable offsite circuit to OPERABLE status.

Compensatory measures within NextEra Energy Seabrook, LLC letter L-2024-032 dated March 4, 2024, shall be implemented and shall remain in effect during the extended AOT period. The one-time AOT extension shall expire upon completion of the maintenance to restore the offsite circuit to OPERABLE status not to exceed 30 days following issuance of the amendment authorizing the one-time AOT extension.

ELECTRICAL POWER SYSTEMS A.C. SOURCES OPERATING LIMITING CONDITION FOR OPERATION 3.8.1.1 (Continued)

ACTION:

b.

With a diesel generator inoperable:

1) Demonstrate the OPERABILITY of the remaining A.C. sources by performing Specification 4.8.1.1.1 a within 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months and at least once per 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months thereafter.

Perform ACTION d. Demonstrate the OPERABILITY of the remaining diesel generator by performing Specification 4.8.1.1.2a.5) within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months .*

2) Restore at least two diesel generators to OPERABLE status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months , unless the following condition exists:

(a)

(b)

The requirement for restoration of the diesel generator to OPERABLE status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months may be extended to 14 days if the Supplemental Emergency Power System (SEPS) is availabl, s specified in the Bases, and Remove double-asterisk (**)

If at any time the SEPS availability cannot be me,

PS to available status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months (not to exceed 14 days from the time the diesel generator originally became inoperable), or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

The OPERABILITY of the remaining diesel generator need not be verified if it has been successfully operated within the last 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months , or if currently operating, or if the diesel generator became inoperable due to:

1.

Preplanned preventive maintenance or testing,

.------, 2.

An inoperable support system with no potential common mode failure for the remaining diesel generator, or Remove

3.

An independently testable component with no potential common mode failure for the remaining diesel generator.

- A one-time allowed outage time (AOT) extension for an inoperable diese gene at r Ila s 3 d ys to restore the associated diesel generator to OPERABLE status. Compensatory measures within NEE Letters SBK-L-20068 dated July 13, 2020, and SBK-L-20117 dated September 23, 2020, will remain in effect during the extended AOT period. The one-time AOT extension shall expire upon completion of the maintenance or 90 days after the issuance of the amendment, whichever comes first. In addition, SEPS availability will be checked prior to entering the 30-day extended AOT, and subsequently once per shift during the 30-day extended AOT. If SEPS becomes unavailable any time during the extended AOT, restore SEPS to available within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months . This 24-hour period will be allowed only once within any given extended EOG AOT.

SEABROOK - UNIT 1 3/4 8-2

ELECTRICAL POWER SYSTEMS A.C. SOURCES OPERATING LIMITING CONDITION FOR OPERATION 3.8.1.1 (Continued)

ACTION:

NOTE--------------------------------------------------

Enter applicable ACTIONS of LCO 3.8.3.1, "Onsite Power Distribution -

Operating," when ACTION c is entered with no AC power to any train.

c.

With one offsite circuit and one diesel generator of the above required A.C.

electrical power sources inoperable:

1)

Demonstrate the OPERABILITY of the remaining A.C. source by performing Specification 4.8.1.1.1 a. within 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months and at least once per 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months thereafter. Perform ACTION d. Demonstrate the OPERABILITY of the remaining diesel generator by performing Specification 4.8.1.1.2a.5) within 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months .*

2)

Restore at least one of the inoperable sources to OPERABLE status within 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months or be in at least HOT STANDBY within the next 6 Add double hours and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

asterisk (**)

3) least two o site circuits and two diesel generators to Add new footnote denoted by double asterisk (**)

OPERABLE status wit I ours from the time of initial loss or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months , unless the following condition exists:

(a)

The requirement for restoration of the diesel generators to OPERABLE status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months may be extended to 14 days if the Supplemental emergency Power System (SEPS) is available, as specified in the Bases, and (b)

If at any time the SEPS availability cannot be met, either restore the SEPS to available status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months (not to exceed 14 days from the time the diesel generator originally became inoperable), or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

The OPERABILITY of the remaining diesel generator need not be verified if it has been successfully operated within the last 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months , or if currently operating, or if the diesel generator became inoperable due to:

1.

Preplanned preventive maintenance or testing,

2.

An inoperable support system with no potential common mode failure for the remaining diesel generator, or

3.

An independently testable component with no potential common mode failure for the

~

remaining diesel generator.

SEABROOK-UNIT 1 3/4 8-2a Amendment No. 30, 80, 97,"'ffi.:l

. INSERT B

- A one-time Allowable Outage Time (AOT) extension for an inoperable offsite circuit and diesel generator allows 30 days to restore the inoperable offsite circuit to OPERABLE status. Compensatory measures within NextEra Energy Seabrook, LLC letter L-2024-032 dated March 4, 2024, shall be implemented and shall remain in effect during the extended AOT period. The one-time AOT extension shall expire upon completion of the maintenance to restore the offsite circuit to OPERABLE status not to exceed 30 days following issuance of the amendment authorizing the one-time AOT extension.

ELECTRICAL POWER SYSTEMS A.C. SOURCES OPERATING LIMITING CONDITION FOR OPERATION 3.8.1.1 ACTION:

(Continued)

Add new footnote denoted by asterisk (*)

d.

With one diesel generator inoperable in addition to ACTION b. or c. above, verify that:

1.

All required systems, subsystems, trains, components, and devices that depend on the remaining OPERABLE diesel generator as a source of emergency power are also OPERABLE, and

2.

When in MODE 1, 2, or 3, the steam-driven emergency feedwater pump is OPERABLE.

If these conditions are not satisfied within 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

e.

With two of the above required offsite AC. circuits inoperable Add astrisk

1.

Within 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months from discovery of two offsite circuit noperable concurrent with inoperability of redundant required feature(, declare required feature(s) inoperable when its redundant required featur: {s) is inoperable;

2.

Restore at least one of the inoperable offs*

sources to OPERABLE status within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months or be in at least HOT S NOBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months .

3.

With only one offsite source restore estore at least two offsite circuits to OPERABLE status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months om time of initial loss or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

f.

With two of the above required diesel generators inoperable:

1)

Demonstrate the OPERABILITY of two offsite AC. circuits by performing Specification 4.8.1.1.1 a. within 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months and at least once per 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months thereafter.

2)

Restore at least one diesel generator to OPERABLE status within 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months ,

3)

Restore at least two diesel generators to OPERABLE status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months from the time of initial loss or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months , unless the following condition exists:

(a)

The requirement for restoration of the diesel generators to OPERABLE status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months may be extended to 14 days if the Supplemental Emergency Power System (SEPS) is available, as specified in the Bases, and (b)

If at any time the SEPS availability cannot be met, either restore the SEPS to available status within 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months (not to exceed 14 days from the time the diesel generator originally became inoperable), or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

SEABROOK - UNIT 1 3/4 8-2b Amendment No. 30, 80, 97, 161

INSERT C

A one-time Allowable Outage Time (AOT) extension for an inoperable offsite circuit allows 30 days to restore the inoperable offsite circuit to OPERABLE status.

Compensatory measures within NextEra Energy Seabrook, LLC letter L-2024-032 dated March 4, 2024, shall be implemented and shall remain in effect during the extended AOT period. The one-time AOT extension shall expire upon completion of the maintenance to restore the offsite circuit to OPERABLE status not to exceed 30 days following issuance of the amendment authorizing the one-time AOT extension.

ATTACHMENT 2 PRA Evaluation for 38 RAT Emergency LAR (26 pages follow)

Section Table of Contents Title SBK-1 FJR-24-006 Revision O Page 2 of 27 Page 1.0 Purpose........................................................................................................................... 3 2.0 Methodology................................................................................................................... 3 3.0 PRA Quality.................................................................................................................... 4 4.0 Assumptions.................................................................................................................. 5 5.0 Common Cause Evaluation........................................................................................... 5 6.0 Evaluation....................................................................................................................... 6 7.0 Results............................................................................................................................ 6 7.1 Quantification.............................................................................................................................. 6 7.2 Importance Measures.................................................................................................................. 7 7.3 Configuration Management........................................................................................................ 8 8.0 External Events.............................................................................................................. 8 9.0 Summary and Recommendations................................................................................. 8 10.0 References...................................................................................................................... 9 11.0 Appendices................................................................................................................... 10 Appendix A: Model Quantification Settings.......................................................................... 11 Appendix B: Seabrook PRA Open Peer Review Issues....................................................... 11 Appendix C: Seabrook Fire PRA Open Peer Review lssues................................................ 14 Appendix D: Sensitivity Assessment for Common Cause Impacts to Both RATs............. 27

1.0 Purpose SBK-1 FJR-24-006 Revision O Page 3 of 27 This document provides a Probabilistic Risk Assessment of a proposed license amendment to permanently modify the Seabrook Station Technical Specifications (TS) by extending the Completion Time (CT) of the inoperable 3B Reserve Auxiliary Transformer (RAT), ED-X-3-B, from 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 30 days, which is the subject of Technical Specification Limiting Condition of Operation 3.8.1.1.

The offsite circuits receive power from three 345,000 volt transmission lines which terminate in a common termination yard, which is then fed to the switchyard. The switchyard is arranged through circuit breakers and transformers to form the two qualified circuits. Each ESF bus is capable of being supplied by the offsite circuits either through the unit auxiliary transformer (UAT) or reserve auxiliary transformer (RAT). The UAT is the preferred power supply and the RAT is the alternate power supply. For two independent offsite sources, each emergency bus must (1) be energized from its UAT, and (2) have its RAT supply available via fast transfer capability.

2.0 Methodology The current Internal Events & Fire PRA models for the Seabrook station were used for this evaluation. The current internal events PRA model, SBK23, was obtained from Ref. 3, and the current fire PRA model, SBK21, was obtained from Ref 5. Each model was quantified using the default truncation limits demonstrated for convergence for that respective model.

Regulatory Guide (RG) 1.177, "An Approach for Plant-Specific, Risk Informed Decision-making:

Technical Specifications" [Ref. 1 ]. RG 1.177 describes acceptable methods for assessing the nature and impact of proposed T.S. changes, including AOT extensions, by considering engineering issues and applying risk insights.

Reg. Guide 1.177 directly addresses the PRA-based risk metric requirements for permanent TS changes, as reproduced below:

"The staff provides the following TS acceptance guidelines specific to permanent CT changes for evaluating the risk associated with the revised CT, in addition to those acceptance guidelines in RG 1.174:

a. The licensee has demonstrated that the TS CT change has only a small quantitative impact on plant risk. An ICCDP of less than 1x10-6 and an ICLERP of less than 1x10-7 are considered small for a single TS condition entry {Tier 1 ).

b. The licensee has demonstrated that there are appropriate restrictions on dominant risk-significant configurations associated with the change (Tier 2).

c. The licensee has implemented a risk-informed plant configuration control program, including procedures to use, maintain, and control such a program (Tier 3)."

Based on the available quantitative guidelines for other risk-informed applications, it is judged that the criteria shown in Table 1 represent a reasonable set of acceptance guidelines. For the purposes of this evaluation, these guidelines demonstrate that the risk impacts are acceptably low. This, combined with effective compensatory measures (for planned TS entries) to maintain lower risk, will ensure that the TS change meets the intent of small risk increases consistent with the Commission's Safety Goal Policy Statement. This document addresses Tier 1 of the risk associated with the change; Tiers 2 and 3 are addressed in Section 3.4 in the LAR enclosure.

Table 1: Proposed Risk Acceptance Guidelines Risk Acceptance Guideline Basis SBK-1 FJR-24-006 Revision O Page 4 of 27 ICCDP is an appropriate metric for assessing ICCDP < 1E-6 risk impacts of out of service equipment per RG 1.177. This guideline is specified in Section 2.4 of RG 1.177.

ICLERP is an appropriate metric for ICLERP < 1 E-7 assessing risk impacts of out of service equipment per RG 1.177. This guideline is specified in Section 2.4 of RG 1.177 The ICCDP associated with each OOS configuration for a new CT is given by ICCDPrnx3B= (CDFEoX3B - CDFBASE) x CT NEW [Eq. 1]

Where, CDFEoX3B= the annual average CDF calculated for configuration with equipment OOS CDFBASE = baseline annual average CDF with average unavailability for all equipment.

This is the CDF result of the baseline PRA CT NEW= the new extended CT (in units of years)

NOTE: ICCDP is a dimensionless probability and ICLERP is quantified similarly.

3.0 PRA Quality The ASME / ANS PRA Standard (ASME/ANS RA-Sa-2009), [Ref. 6], has technical elements, high-level requirements (HLRs), and detailed supporting requirements (SRs). NRC Regulatory Guide 1.200 Revision 2, "An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk Informed Activities" [Ref. 4], endorses the standard with minor clarifications.

The Seabrook PRA has undergone peer review against the ASME PRA Standard, Parts 1 (configuration control), 2 (internal events), and 3 (internal flood events).

Peer reviews have been conducted against internal event supporting requirements as follows:

In 1999, a review of all technical elements was performed using the industry PSA Certification process, the precursor to the PRA Standard.

In 2005, a focused peer review was performed for the elements AS, SC, and HR, as well as configuration control. This review was done to PRA Standard ASME RA-Sa-2003.

In 2009, a focused peer review was performed for all elements of Part 3, Internal Flooding. This review was done to PRA Standard ASME/ANS RA-Sa-2009.

In 2012, a focused peer review was performed for the element LE. This review was done to PRA Standard ASME/ANS RA-Sa-2009.

SBK-1 FJR-24-006 Revision O Page 5 of 27 In 2019, a focused peer review was performed on all elements upgraded by the conversion from Riskman to CAFTA. This review was done to PRA Standard ASME/ANS RA-Sa-2009.

Four self-assessments against the internal event SRs in the PRA standard were performed in 2005 (ASME RA-Sa-2003), 2007 (ASME RA-Sb-2005), 2010 (ASME/ANS RA-Sa-2009) and 2011 (ASME/ANS RA-Sa-2009). The first three self-assessments considered all internal events technical elements. The SA-2011 addressed only the open findings against specific SRs.

In October 2017, all resolved findings were reviewed to Appendix X to NEI 05-04, NEI 07-12, and NEI 12-13, "Close-out of Facts and Observations" (F&Os) as accepted by the NRC staff in their May 3, 2017, memorandum (ML17079A427).

Following the findings closure review, the 2019 focused scope peer review identified additional findings. Appendix B provides a listing of the remaining open findings and the status of their resolution as well as an assessment of the impact on this evaluation. Overall, the open findings do not have an impact on the results and conclusions of this LAR.

The Seabrook Fire PRA model has undergone a peer review conducted in 2023. This review was done against the requirements of Part 4 of the PRA Standard ASME/ANS RA-Sa-2009.

A self-assessment against the requirements of Part 4 of the PRA Standard ASME/ANS RA-Sa-2009 was completed in 2023 and represents the most current status of the Seabrook Fire PRA model. This assessment reviewed the results of the 2023 peer review on the Seabrook Fire PRA model.

Appendix C includes the open findings as a result of the 2023 peer review on the Fire PRA model and the status of their resolution as well as an assessment of the impact on this evaluation. Overall, the open findings do not have an impact on the results and conclusions of this LAR.

4.0 Assumptions

1. Only the 38 RAT, is considered OOS for the allowed outage time. The 3A RAT is considered available for service during the period of 38 RAT replacement even though during the 38 RAT replacement activity there will be intermittent out of service coincident conditions to support danger tagouts of work control boundaries.

2. No compensatory measures are credited in this assessment.

3. Flooding risk is considered to be bounded by Internal Events. The North Yard area, which includes the UATs and RATS, was screened from internal flooding hazard risk per Ref. 2.

5.0 Common Cause Evaluation The 38 RAT experienced an internal pressure fault and requires a full replacement. The 3A RAT initial inspections indicate this is not a common mode failure, therefore there is no extent of condition. Inspections conducted on the remaining two bushings of RAT 38 indicated no signs of degradation and proper oil pressure. Inspections of the RAT 3A bushing oil pressure indicates satisfactory results; therefore, this evaluation does not examine CCF or the risk impact of a failure of the 3A RAT also. However, a Full Power Internal Events (FPIE) sensitivity was performed for internal events considering both RA Ts failed with results shown in attachment D

'Both RATs Failed Sensitivity'. This is considered a bounding sensitivity since no CCF is

SBK-1 FJR-24-006 Revision 0 Page 6 of 27 modeled for these large transformers as there is no industry related common cause failure data for large transformers.

6.0 Evaluation There are 2 Reserve Auxiliary Transformers which provide back-up power to the station's emergency buses. 3A RAT provides backup power to Train A bus 5 emergency bus whereas 38 RAT provides backup power to Train B bus 6 emergency bus. These buses can also be powered from their respective EDGs. Failure of the 38 RAT fails the backup power for the Train B bus 6 which is normally powered from the UAT-28. For Train A bus 5 it is UAT-2A. The high degree of redundancy for these emergency buses leads to the expectation that the risk significance of the RAT failure will be low.

7.0 Results 7.1 Quantification The internal events PRA quantification was performed on the Ref. 3 internal events PRA model with a CDF truncation of 1 E-12 and LERF truncation of 1 E-13. Table 2 shows the results of the internal events PRA model quantification.

Table 2: Results for FPIE Delta Risk Calculation Case CDF (/yr)

Delta CDF (/yr)

LERF (/yr)

Delta LERF (/yr)

Baseline 2.45E-06 1.0SE-07 ED-X-3-B Unavailable 2.46E-06 1.00E-08 1.0SE-07 O.OOE-00 As noted in Assumption 3, the flooding risk increase is assumed to be equivalent to the Internal Events change in risk. This assumption is a conservative assumption as there are no unscreened flooding scenarios in the North Yard area so no flooding events are analyzed that would result in a loss of all transformers. The Internal Events PRA model does however still have these failures, such as a loss of offsite power, so the change in risk that is calculated would bound any change in risk from the unscreened internal flooding scenarios.

The fire PRA quantification was performed on the Ref. 5 model with a CDF truncation of 1 E-12 and LERF truncation of 1 E-13. Table 3 shows the results of the fire PRA model quantification.

Table 3: Results for Fire Delta Risk Calculation Case CDF (/yr)

Delta CDF (/yr)

LERF (/yr)

Delta LERF (/yr)

Baseline 2.95E-5 6.22E-7 ED-X-3-B Unavailable 3.10E-5 1.SOE-6 6.25E-7 3.00E-9 The contribution to change in risk for the 38 RAT out of service was then summed to determine the total contribution from internal events, flood, and fire in Table 4.

SBK-1 FJR-24-006 Revision 0 Page 7 of 27 Table 4: Conditional Risk Calculations for Internal Events, Flood, and Fire PRA Metric CTnew (yrs)

Delta CDF (LERF) 30 Day ICCDP

(/yr) (IE +IF+ FR)

(ICLERP)

CDF 0.082 (30 days) 1.52E-06 1.25E-07 LERF 0.082 (30 days) 3.00E-09 2.46E-10 7.2 Importance Measures Because support systems and other modeled events could underpin these events, model importance measures were further reviewed. Risk insights regarding the dominant risk contributors are obtained via a review of initiating event frequencies, component, and operator action importance measures.

The ratio of configuration-specific Risk Achievement Worth (RAW) and baseline model RAW was considered a noteworthy figure. If a RAW value increases significantly between the baseline and configuration-specific models, it would be potentially noteworthy in terms of plant configuration control.

Table 5 shows the ratio of configuration-specific Risk Achievement Worth (RAW) to baseline model RAW (RAWEox3s/RAWsase) for the five CDF events with the highest ratio.

As expected, the top changes in event importances are failures of the unit auxiliary transformer (Train B), the generator step-up (GSU) transformers, and the Switchyard GSU Motor-Operated Disconnect. The top change in importance for initiating events is the loss of vital 4.16KV Bus ES (Train A). No operator action was identified as significantly increasing in importance as a result of the 3B RAT OOS.

When reviewing LERF importance measures, no additional components were identified with an increase beyond those from CDF.

The importance measures for fire were also reviewed to identify additional changes in risk. The results of this review mirrored the results of the Internal Events review. In summary, the review of importance values demonstrated that, as expected, the UAT and GSU transformers become more important in the event the 3B RAT is out of service.

Table 5: Comparison of Importance Measures Basic Event BE Description CDF RAW Ratio EDX2B.FX UAT B fault 7.38 EDX1A.FX GSU Phase A fault 2.89 EDX1B.FX GSU Phase B fault 2.89 EDX1C.FX GSU Phase C fault 2.89 SYMODG106.TO Switchyard GSU Motor-Operated Disconnect Transfer Open 2.24

SBK-1 FJR-24-006 Revision O Page 8 of 27 The Fire PRA model was reviewed to identify fire scenarios with the largest risk increase associated with 38 RAT unavailability. These scenarios are shown below in Table 6.

Table 66: Dominant Fire Scenarios Fire Compartment Description Scenario Description SY Transformers PLT_FC_3_0 FCB: SY Transformers DG Building - Engine Room - Train A DG_FC_2A_A Oil Scenario Damaging all targets in DG FC 2A A PLT_FC_3_0_FS1 1-ED-X-1-A:GSU Phase A SY Transformers PL T_FC_3_0_FS2-0 1-ED-X-1-B:GSU Phase B PLT FC 3 0 FS3-0 1-ED-X-1-C:GSU Phase C 7.3 Configuration Management In terms of risk significance of plant configurations, RG 1.177 requires reasonable assurance that risk-significant plant equipment outage configurations will not occur when specific plant equipment is out of service consistent with the proposed change.

As documented in Appendix D, the common cause failure sensitivity analysis demonstrates that with the 38 RAT out of service, any maintenance on the emergency diesels shall be restricted.

8.0 External Events The purpose of this portion of the assessment is to evaluate the spectrum of external event challenges to determine which external event hazards should be explicitly addressed as part of the risk assessment. Internal events, including internal flooding, and fire are quantitatively addressed as described in the previous sections. The impact due to seismic, high winds, external floods, shutdown operation, and other hazard groups are addressed here.

Seismic Seabrook does not have a seismic PRA. However, the increase in risk during a seismic event is deemed negligible. The seismic risk is typically governed by the initiating event frequency, as a "cliff-edge" effect occurs in that all offsite power transformers would tend to be highly reliable up to a certain ground motion, and then all offsite power would fail past this point. Given the seismic event frequency is not changing, the change in seismic risk is less likely than the change in risk due to internal events.

Other External Events Seabrook does not explicitly evaluate any other external event hazards (e.g., external flooding) in the probabilistic modeling. Per Ref. 7, S8K-PRAE-15-010, these external hazards were screened for analysis per the ASME/ANS Standard. Given this condition does not increase the frequency of these external events hazards the change in risk is considered negligible.

9.0 Summary and Recommendations Extension of the 38 RAT allowed outage time of 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months to 30 days has a minor impact on the PRA results and the increase is within NRC limits established by Reg. Guide 1.177.

Table 7:Conditional Risk Calculation PRA Metric Incremental Probability for 30 Day AOT ICCDP ICLERP Internal Events 8.21E-10 O.OOE+OO Internal Floods 8.21 E-10 O.OOE+OO Fire 1.23E-07 2.46E-10 External Events Negligible Negligible Total 1.25E-07 2.46E-10 Acceptance Criteria 1.00E-06 1.00E-07 SBK-1 FJR-24-006 Revision 0 Page 9 of 27 Based on the model insights and sensitivities, the compensatory measures (i.e., Risk Management Actions - RMAs) for operational consideration:

Fire watches Restricted maintenance on the emergency diesels 10.0 References

1. USNRC, Regulatory Guide (RG) 1.177, "An Approach for Plant-Specific, Risk Informed Decision-making: Technical Specifications," Revision 2, (ADAMS Accession No. ML20164A034).

2. SSPSS-2019 "Seabrook Station Probabilistic Safety Study" Revision 0, September 2019.

3. GDOC SBK-1 FJR-23-006 Rev. 1, "Seabrook Internal Events Model", August 2023.

4. Regulatory Guide 1.200, "An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk Informed Activities," Revision 2, March 2009.

5. GDOC SBK-BFJR-23-042 Rev. 1, "Seabrook Unit 1 At-Power Fire PRA, Qualitative Screening, Quantification, and Uncertainty Analysis Notebook", December 2023.

6. ASME PRA Standard RA-Sa-2009, Addenda to ASME/ANS RA-S-2009 Standard for Level 1 / Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications, February 2009.

7. GDOC SBK-PRAE-15-010 Rev. 0 "Seabrook Station PRA Capability Assessment",

November 2015.

8. GDOC SBK-BFJR-23-034 Rev. 1 "Seabrook Unit 1 At-Power Fire PRA, Plant Partitioning Notebook", December 2023.

9. GDOC SBK-BFJR-23-036 Rev. 1 "Seabrook Unit 1 At-Power Fire PRA, Cable Notebook",

December 2023.

10. GDOC SBK-BFJR-23-037 Rev. 1 "Seabrook Unit 1 At-Power Fire PRA, Fire Risk Model Notebook", December 2023.

11. GDOC SBK-BFJR-23-038 Rev. 1 "Seabrook Unit 1 At-Power Fire PRA, Ignition Frequency Notebook" December 2023.

SBK-1 FJR-24-006 Revision 0 Page 10 of 27

12. GDOC SBK-BFJR-23-039 Rev. 1 "Seabrook Unit 1 At-Power Fire PRA, Fire Scenario Selection Notebook", December 2023.

13. GDOC SBK-BFJR-23-040 Rev. 1 "Seabrook Unit 1 At-Power Fire PRA, Main Control Room Analysis Notebook", December 2023.

14. GDOC SBK-BFJR-23-041 Rev. 1 "Seabrook Unit 1 At-Power Fire PRA, Fire HRA Notebook", December 2023.

15. GDOC SBK-BFJR-23-042 Rev. 1 "Seabrook Unit 1 At-Power Fire PRA, Qualitative Screening, Quantification, and Uncertainty Analysis Notebook", December 2023.

16. GDOC SBK-BFJR-23-044 Rev. 0 "Seabrook Unit 1 At-Power Fire PRA, Seismic-Fire Interactions Notebook", December 2023.

11.0 Appendices Appendix A:

Model Quantification Settings Appendix B:

Seabrook PRA Open Peer Review Issues Appendix C:

Seabrook Fire PRA Open Peer Review Issues Appendix D:

Sensitivity Assessment for Common Cause Impacts to Both RA Ts

Appendix A: Model Quantification Settings

ED-X-3-B OUT OF SERVICE (OOS) FLAG EDX3B.FX PROB 1.0 EDX3B.FX.YR PROB 1.0 Appendix B: Seabrook PRA Open Peer Review Issues Supporting Issue Requirement The Seabrook PRA uses all operating experience when performing the Bayesian update. The use of all operating experience in the Bayesian update can provide non-conservative results for component failure probabilities.

DA-D4-01 For example, if a component has been replaced, previous operating experience is no longer applicable for DA-E2-02 that component.

The Bayesian reasonableness check does not discuss any criteria for when there are O failures in the plant-specific experience. For these cases, none of the checks will pass the specified criteria.

The following documentation issues were identified:

1) Table 13.6-1 of the Data Analysis shows the Bayesian validation of the Seabrook type codes. It is noted that the Bayesian update equations used for Beta distributions are incorrect. The equation used to update the beta parameter of the beta distribution should be B_prior +

n_exposures - n_failures. The current equation used is B_prior + n_exposures. Note that the current equation used is not consistent with the CAFTA Bayesian update DA-E1-01 tool.

2) Section 13.6.2 of the Data Analysis discusses three conditions for checking the reasonableness of the Bayesian update. In the description of the conditions it should be stated '... 5th percentile and less than the 95th percentile of the generic/posterior distribution.'

3) Section 13.6.2 states that the parameters of interest in the reasonableness check are the: mean values, 5th percentile value, and 95th percentile value. Table 13.6-1 does not provide the mean values.

The following documentation issues were identified:

1) A review of the CAFTA database shows that there are 6 common cause groups making use of the MGL method: BUSFX, BUSFL, LINES, LINES.YR, LINESMNT, and LINESMNT.YR. A search of the System Analysis notebook states that for BUS56FX 'Note that MGL CCF parameters are used in the 2019 update DA-E2-01 because the 2015 update to NUREG/CR-5497 did not have information on switchgear CCF failure data.' This statement does not provide a reference to the data source used, and the data notebook does not provide this information either.

2) There is no discussion regarding the selection of staggered or non-staggered testing schemes and the use of these calculation methods for the CCF groups.

1 )Self-assessment identifies limitations with manpower QU-C2-01 I HR-G?-01 requirements and there still appear to be gaps with HRAC specific inputs for manpower. Additionally, execution locations are also not identified for all actions.

SBK-1 FJR-24-006 Revision O Page 11 of 27 Evaluation Section 1.0 of the Seabrook PRA Notebook 13, Data Analysis, was revised (to Rev. 2) to provide additional information. No impact on application.

The Data Notebook was revised to address this documentation-only finding.

No impact on application.

The Data Notebook was revised to address this documentation-only issue.

No impact on application.

The Human Reliability Analysis (HRA) was revised in support of the 2022 Seabrook model update. The three items identified were all addressed in Revision

Supporting Issue Requirement 2)Not being able to reproduce results. Recreating the dependency analysis using the same cutsets that were used and creating a combination event recovery rule file resulted in 860 combinations versus the documented 505 combinations in the Section 11 HR document Section 11.8.1.3.

3)Manual combination and dependency overrides lacked sufficient justification for assigned dependency levels.

For example, combination of HH.OFLOCW.FL and HH.OFL 1 CW.FA, the current justification taken is for larger timing separation between actions, however, the override taken is equivalent to intervening success. This isn't sufficient justification for the override taken.

Section 3.0 of Section 11, Human Actions Analysis, discusses methodology and references PRA-106 "PRA Model Guidelines", Section 106E Methodology for AS-C1-01 / DA-E1-02 /

Human Reliability Analysis. PRA-106 is the modeling information for RISKMAN. No discussion could be found HR-11-01 / SY-C1-01 for dependency analysis methodology in the conversion report.

Similar issue was found to exist in Systems Analysis, Data Analysis, HRA, and Accident Sequence.

There are instances where the information from Appendix 11.1A does not match the HRAC. See example below.

HH.OHSB1.FA Tcog 5 minutes versus Appendix 11.A1 HR-E4-01 Tcog of 20-30 minutes.

Also, Operator interview Insights in HRAC for HH.OAL T1.FL don't seem to match the interview documentation. This appears to be a systemic problem as there were other instances found.

Logic flags have not been set to TRUE or FALSE for all flags prior to the generation of cutsets. The current QU-89-01 methodology sets logic flags to TRUE in the recovery rules which occurs after the generation of cutsets.

Additional cutsets have been generated in the final results that should not exist as they are non-minimal.

SOKC is not accounted for in some type codes that use identical data sets. One example is for the type codes NICB1 C and NICB10. Both of these type codes use the QU-E3-01 / QU-A3-01 same data set, but since they are different type codes UNCERT does not take the same sample for both distributions. This appears to be a common approach when the generic data doesn't delineate between the different failure modes of a component.

1) The FTREX.ini file was not documented. This is necessary to quantify the model and is significant because the default method is not used.

2) The criteria establishing convergence is based on

<=5% change when compared to the next decade. The example in the standard uses a <5% final change. The final change is interpreted as calculating the percent QU-F2-01 change at the current truncation level with respect to the previous decade truncation level not the next. The criteria used is adequate, but there is no documentation of definition used to establish convergence.

3)There is no discussion of the top basic events and why they make logical sense. A general statement that notes that basic events importance's were reviewed to ensure they make logical sense is not sufficient evidence for the actual review taking place.

SBK-1 FJR-24-006 Revision O Page 12 of 27 Evaluation 2 ofSBK-1FJR-19-041, "Seabrook Human Reliability Analysis - Internal Events." Execution locations were added to the HRA Calculator, the method for performing dependency analysis was documented and reproducible, and dependency overrides were justified. No impact on application.

This issue is documentation only. The methods used for performing HRA and dependency analysis are documented in Rev. 2 of SBK-1 FJR-19-041. No impact on application.

This issue was resolved with Rev. 2 of SBK-1 FJR-19-041. Operator interviews were re-performed in support of the report revision and updated in the HRA Calculator. No impact on application.

This issue was resolved by flag file changes in the 2022 model update. No non-minimal cutsets were identified in the model update. No impact on application.

This issue was resolved with the 2022 model update. Type codes that shared data sets were revised to ensure functionality with UNCERT. No impact on application.

This issue is documentation only. No impact on application.

Supporting Issue Requirement

4) There is no documentation of how the circular logic is broken. A demonstration was performed that identified a couple examples of where in the model circular logic was broken. This identification and modeling technique needs to be documented.

Component importance measures were not identified.

QU-06-01 The supporting requirement specifically requires the identification of significant SSCs.

SBK-1 FJR-24-006 Revision 0 Page 13 of 27 Evaluation This issue was resolved with the 2022 model update. Component importance measures were identified in the model update report. No impact on application.

Appendix C: Seabrook Fire PRA Open Peer Review Issues SBK-1 FJR-24-006 Revision O Page 14 of 27 The open findings as a result of the 2023 peer review on the Fire PRA are included in the table below. An evaluation of the findings has been completed as part of a 2023 self-assessment and the resolutions have been applied to the current Fire PRA model. Therefore, the open findings do not have an impact on the results and conclusions of this LAR.

Supporting Issue Evaluation Requirement Description NAH-FIRE-TR-RM-000001 (SBK-BFJR-Areas outside the protected area were improperly included as23-034) and associated GPAB fire compartments attachment was revised to remove the PAUs outside the protected area that PP-A1 Basis have no potential adverse effect such as PAUs such as the warehouses outside the protected area have MISCEXPA.

no potential to adversely affect any equipment or cable item to This issue was resolved in Revision 1 of be credited in the Fire PRA. This has the potential to dilute the SBK-BFR-23-034; therefore, no impact transient weighting factors.

on this application.

Description The FSS Database (SBK-BFJR-23-035)

Review of power supplies and interlocks for inclusion in ES.

Tbl_import_Equip_List was revised to add columns for whether a power supply Basis was required, the required power supply Section 5. 7 of the ES notebook indicates that any additional and the power supply modeling in the power supplies, interlocks, and other dependencies that are PRA logic model. The power supply ES-A2 / ES-B4 /

identified in the CS notebook are either considered sub-logic was confirmed in the model. The PRM-B9 components on the main component, and thus the associated interlocks were explicitly identified in the cables are included with the main component, or are added to cable selection table and the FPRA equipment list. A complete listing of the interlocks by confirmatory notes added.

equipment functional state does not appear to be included in This issue was resolved in Revision 1 of the CS notebook, and no systematic review of power supplies SBK-BFR-23-035; therefore, no impact and interlocks appears to have been made and documented in on this application.

the ES notebook. It is unclear if this review has been completed.

Description The Fire PRA Equipment List Cables should be mapped to basic events RCPCV456A(B].RS "tbl_import_Equip_List" was revised to (PORV A[B] fails to reseat).

model the reseat basic events. The cable selection was updated to map Basis cables to the reseat basic events In 'tbl_import_Equip_List', basic events RCPCV456A[B].RS identified for modeling.

ES-B1 (PORV A[B] fails to reseat) are screened out as Screening 'A' This issue was resolved in Revision 1 of with the Note 'type code NIVR3C - PORV, ASDV - fail to SBK-BFR-23-035; therefore, no impact reseat; no electrical dependency'. Since the PORVs can fail to on this application.

close due to a spurious hot short, cables should be mapped to these events. Note that cables are mapped to basic events RCPCV456A[B].TO, but these events are used in different places in the CAFTA logic.

Description The fire PRA Equipment List Corrections to Table 'tbl_import_Equip_List'.

"tbl_import_Equip_List" was reviewed.

"tbl_import_Equip_List" was revised to Basis change the disposition of basic events to Basic event CSHCV123.TO (CS Valve CS-HCV-123 transfers "N/A" if screened and confirm all basic open) is dispositioned in 'tbl_import_Equip_List' as 'I' (always events have one box checked ES-D1 failed), but the box for 'Modeled' is checked. Note that all other (screened, modeled, always failed).

entries in 'tbl_import_Equip_List' dispositioned as 'I' (always Confirmed CSHCV123.TO is modeled failed) are included in 'tbl_fq_FRANX_Zone_to_Raceway' Zone with N/A for Screen_Basis. Confirmed "AlwaysFailed'. Also, in 'tbl_import_Equip_List', basic event Screened was checked for SWAF192.PL.YR (CT Pump Room Intake FILTER F192 fails SWAF192.PL.YR.

due to plugging) is screened as disposition 'A', but the box for This issue was resolved in Revision 1 of

'Screened' is not checked. Confirm this is correct.

SBK-BFR-23-035; therefore, no impact on this application.

Supporting Issue ReQuirement Description Coordination for 120V AC or 125V DC buses/panels has been assumed and not reviewed.

Basis Section 4.3.1.1.3 and Attachment 3 of the CS/CF notebook analyzes and confirms coordination for 4160V and 480V buses and MCCs. However the notebook does not discuss or confirm CS-B1 that coordination exists for voltages less than 480V (e.g., 120V AC or 125V DC buses/panels), and rather assumes that a correct coordination exists. After speaking with the Peer Review support team, additional coordination calculations were presented that confirm coordination for the remaining buses.

These additional calculations were only listed as References in the CF/CS notebook, with no discussion or point to the additional references. Experience indicates that this level of voltage historically has issues with proper coordination.

Description Review of interlocks and other dependencies not documented.

Basis The methodology in Section 4.3.1.1.3 of the CS/CF notebook (NAH-FIRE-TR-RM-000003) does not provide sufficient detail CS-C1 or guidance to identify interlocks and other dependencies during the cable selection process. The section solely discusses power supplies, which are documented in. After discussing with the peer review support team, it seems that cables supporting interlocks were included in the cable selection, however the process and results for this review are not documented in the CS/CF or ES notebooks.

Description Coordination analysis for 480V MCCs lack sufficient technical basis.

Basis of the CS/CF notebook evaluates the coordination of select 480V MCCs (E511, E512, E513, E514, CS-C4 E515, E611, E612, E613, E614, E615) by analyzing only the largest load (motor and non-motor). However, it could not be confirmed that this could be applied to all loads on these MCCs. Additionally, Section 4.3.1.1.3 includes a statement that discusses evaluation and assumption of short circuit current at the end of cables connected to MCC-E511. Sufficient information or a calculation could not be found to support this statement.

Description Unpopulated HRA Calculator Tables that Impact Dependency Analysis Basis This Finding is consistent with previous Internal Events F&O HR-6-1. There are 26 combinations that are currently assessed by HRA Calculator [SBK_HRA_DAF.daf] as 2 - Complete PRM-B2 / HRA-Dependency, which implies Sufficient Staffing and C1 Simultaneous Timing. Since no overrides were assigned, it is not clear if or how well these combinations were reviewed for appropriateness. But the quantification was done with no Crew Composition table filled out in HRA Calculator file SBK-21 Rev 2_Fire DIT-004, which is the basis for the dependency analysis staffing evaluation. While the 2-CD dependency evaluation could be considered conservative since it leads to a high(er)

Joint HEP, it is not technically correct in evaluating SR HR-G7

- availability of resources. This is a potential concern since to the Fire HRA Notebook, NAH-FIRE-TR-RM-SBK-1 FJR-24-006 Revision 0 Page 15 of 27 Evaluation NAH-FIRE-TR-RM-000003 (SBK-BFJR-23-036) was revised consistent with the possible resolution. The coordination of 120V AC and 125 V DC panels/buses has been analyzed and included in tables 4&5 of Attachment 3. Text in Sections 4.3.1.1.4 & 4.4.1 has been modified.

The Cable Notebook (SBK-BFJR 036) was revised to include documentation regarding the identification of interlocks and dependencies during cable selection process.

This issue was resolved in Revision 1 of SBK-BFR-23-036; therefore, no impact on this application.

NAH-FIRE-TR-RM-000003 (SBK-BFJR-23-036) and associated attachments were revised consistent with the possible resolution for MCCs. Text in Section 4.3.1.1.3 has been modified to justify the resolution of this F&O.

This issue was resolved in Revision 1 of SBK-BFR-23-035; therefore, no impact on this application.

The Internal Events HRA Calculator was revised and delivered through DIT-005.

This was incorporated into the Fire HRA Notebook (SBK-BFJR-23-041 ).

Confirmed execution PSFs included located such as "A/B Train Switchgear Rooms SEPS Switchgear Room" for HH.SEPE5XFR.FA.

This issue was resolved in Revision 1 of SBK-BFR-23-041 ; therefore, no impact on this application.

Supporting Issue Requirement 000008, the Fire PRA Operator Interview Summary, Section 3.0, states that "The Fire Brigade is made up of the FB leader and four of the five NSOs." (NSOs are Aux Operators in the field, so if there are two or more local actions happening simultaneously in a short timeframe, there is a question of whether there are sufficient personnel available.) In addition, the Execution Location information in HRA Calculator is not always populated, although it has been identified and documented for ex-MCR actions in Fire HRA Notebook Table 4.3-1. While this information omission does mainly involve Level 2 actions, there are local actions credited in the Fire PRA (e.g., HH.OFCRL3.REC and HH.SEPE5XFR.FA) that are impacted and may not be evaluated properly in the dependency analysis.

Description Some non-credited operator actions are inadvertently being credited in the Fire PRA quantification.

Basis Section 5.5.1 (Table 5.5-1) of the ES notebook identifies operator actions that are screened from the FPRA, with the basis that the accident sequences to which they apply are not caused by fire-induced failures. Specifically, the Level 2 HFEs which were screened, which are not ANDed with their specific initiator (%SGTR LOOPX, %ALMFW, %AMFW, %ALOSP, %ASLOC, etc). One PRM-B11 of these events (HH.OCl1A.FA) first appears in cutset #35, and has a FV of 0.0025 Description Set Internal Events flag to FALSE in Fire PRA quantification.

Basis Internal Events PRA quantification appears to require flag event FL-INTERNAL set to TRUE or 1.0 (and initiator %FIRE set to FALSE or 0.0). For Fire PRA it may be advisable to set FL-INTERNAL to FALSE to ensure internal events HFEs are not inadvertently credited.

Description Possible detrimental actions in the fire procedures should be considered in the Fire PRA.

Basis HRA Notebook Table 4.3-6 lists several prompt disablement actions that are taken by the operators (dependent on the fire PRM-B11 / HRA-location) that may be detrimental to the safe shutdown of the B2 plant. For example, if the PORV block valves are closed (based on OS1200.00 Step 5) and then all steam generator cooling is failed due to the fire or random failures, bleed and feed cooling could not be credited unless the PORV block valves are re-opened, which would require a new operator action.

Description Disposition of Internal Events F&O 5-1 is incomplete.

Basis PRM-C1 According to PRM-B2, the peer review exceptions and deficiencies for the Internal Events PRA are required to be dispositioned, it is also required that the disposition does not adversely affect the development of the Fire PRA plant response model." For F&O 5-1, NAH-FIRE-TR-RM-000004, SBK-1 FJR-24-006 Revision 0 Page 16 of 27 Evaluation The Fire PRA updated the flag file (SBK-Master-Flag - No Flood.fig) to set to actions not credited in the Fire PRA to TRUE for quantification.

This issue was resolved in Revision 1 of SBK-BFR-23-042; therefore, no impact on this application.

The Fire PRA updated the flag file (SBK-Master-Flag - No Flood.fig) to set FL-INTERNAL to FALSE for quantification.

This issue was resolved in Revision 1 of SBK-BFR-23-042; therefore, no impact on this application.

The Fire PRA was updated to review the fire procedures such as OS1200.00, OS1200.01 and OS1200.02 and model any prompt actions which may be detrimental. Appendix G was added to the PRM Notebook (SBK-BFJR-23-037) for the required model updates. was added to the Fire HRA Notebook (SBK-BFJR-23-041) for review of detrimental impact from prompt disablement actions.

This issue was resolved in Revision 1 of SBK-BFR-23-037 and SBK-BFJR 041; therefore, no impact on this application.

The disposition of Internal Events F&O 5-1 was revised in NAH-FIRE-TR-RM-000004 (SBK-BFJR-23-037) to confirm the updates were completed in Internal Events prior to Fire PRA.

This issue was resolved in Revision 1 of SBK-BFR-23-037; therefore, no impact on this application.

Supporting Issue Requirement Appendix E, Table E-1 states "The 2019 data update covers the period of July 1, 2013 through August 31, 2018, not all of Seabrook's operating experience. Considering the very small fraction of components in the database replaced during this time, the impact on failure rates is negligible." With respect to F&O 5-1, the fraction of components that were replaced over this time period is irrelevant if a Fire PRA component is risk significant due to its random failure probability. Updating the random failure probability basic event based on plant data may be inappropriate if the component has been replaced. An inappropriate change in random failure probability of a risk significant basic event could result in a change in fire risk. The Seabrook team provided additional information during the review that documented closure of F&O 5-1. However, NAH-FIRE-TR-RM-000004 has not been updated to reflect this closure.

Description There are no fire scenarios developed for Fire Compartment FCMISCEXPA.

Basis This ID is identified as a fire compartment in the PP Notebook FSS-A1 as the group of buildings/structures outside of the Protected Area, however, there is no fire ignition frequency or fire scenario assigned to this fire compartment.

Description The MGR Analysis does not specifically model the MCB scenarios for control room abandonment due to habitability and the FSS Spreadsheet screens MCBs based on a review of Control Room fire events in the Fire events Database (FEDB) reveals that none of the Control Room fires affected items much beyond the point of ignition.

Basis The potential for MCB scenarios to result in main control room FSS-B2 abandonment is not included in the Seabrook Fire PRA.

Description The MGR Analysis does not consider the potential for a transient fire within the MCB horseshoe impacting the open, exposed MCB panels. The MGR Analysis does not consider the potential for propagation and/or damage to MCB panels across the horsehoe corridor to the open, exposed cables in FSS-C1 the MCB panels.

Basis The MCB and transient scenarios could result in damage to additional MCB back/front panels due to the open configuration.

SBK-1 FJR-24-006 Revision O Page 17 of 27 Evaluation This is inter-related with 06-012. The PP Notebook was revised to remove fire compartment FCMISCEXPA therefore ignition frequency was not assigned to a location removed from GPAB. All documentation for FCMISCEXPA was removed from Ignition Frequency (SBK-BFJR-23-038), FSS (SBK-BFJR-23-039) and Quantification Notebook (SBK-BFJR-23-042).

This issue was resolved in Revision 1 of SBK-BFR-23-038, SBK-BFJR-23-039 and SBK-BFJR-23-042; therefore, no impact on this application.

The MGR Notebook (SBK-BFJR-23-040) and FSS (SBK-BFJR-23-039) attachments (for scenario development) were revised to assess the MCB scenarios for habitability criteria. The MCB HRR was documented and justification provided to assign abandonment probability. Section 4.3.8.5 of the FSS Notebook documents the application of MCB fire progression event tree. CFAST previously included the appropriate HRR for open cabinets and FSS documentation reflects the assumed MGR abandonment for propagation beyond single panel.

This issue was resolved in Revision 1 of SBK-BFR-23-040 and SBK-BFJR 039; therefore, no impact on this application.

The FSS Notebook (SBK-BFJR-23-039) was revised to include documentation about transients within the MCB which include single and multiple panel damage within the MCB. FSS attachments (for scenario development) were revised to model single panel and multiple panel damage within the MCB based on the layout of the MCB and transient 201. Scenarios are identified by CB_FC_3A_A-T-MCB* or CB_FC_3A_A-TFWC-MCB* with the node, panel, or panels impacted.

Supporting Issue Requirement Description The fire modeling does not postulate fire spread to adjacent cabinets for electrical panels (non-switchgear and MCCs).

Basis The fire modeling currently models all electrical panels as single fire scenarios with no propagation to the adjacent section of the cabinet or adjacent cabinets.

Description There is no specific documentation provided that confirms that the fire rated conduit is not subject to mechanical damage or direct flame impingement from a high-hazard ignition source.

FSS-C8 Basis This SR requires confirmation that the credited fire wrap will not be subject to either mechanical damage or direct flame impingement from a high-hazard ignition source.

Description The top CDF and LERF contributors contain known conservatisms that are not addressed. The Quantification Notebook includes a sensitivity analysis which indicates that the fire PRA is sensitive to MCA scenarios. MCA scenarios DG_FC_3AB_Z-CB_FC_2B_A and DG_FC_3AB_ZDG_FC_2A_A are included in the top 20 CDF scenarios. Based on the current results, several fire scenarios among the top contributors are utilizing conservative modeling approaches and including larger than realistic target sets. The Seabrook Fire PRA model has not refined the detailed fire scenarios to remove the modeling conservatisms in several of these top scenarios FSS-D3 / FSS-G6 Basis

/ FQ-E1 The two SWGR and Cable spreading rooms are at the top of the list for risk relevant fire compartments. For LERF in particular, the cable spreading room contributes 95% of the risk. For CDF these three fire compartments make up 46% of the risk. There are known conservatisms in the fire modeling within these locations and based on this, there is potential masking of significant contributors taking place. MCA scenarios are risk significant based on the Quantification Notebook sensitivity analysis and some MCA scenarios are included in the top 20 CDF scenarios. Risk significant fire scenarios such as the Cable Spreading Room transient fires are failing a large amount of targets in the compartment. Walkdown of this compartment indicates fire modeling refinements are available to reduce these impacts.

Description An initial ambient temperature of 25°C was utilized in the fire modeling calculations for several fire scenarios. This ambient temperature does not appear to be appropriate for areas that are not temperature controlled such as the PAB, Turbine FSS-D4 Building, Service Water Pumphouse, DG Buildings, etc.

Basis The use of a higher initial ambient temperature could impact the required HRR, damage time, and therefore, the severity factors and non-suppression probabilities.

SBK-1 FJR-24-006 Revision 0 Page 18 of 27 Evaluation Section 4.3.5.8 was added to FSS Notebook (SBK-BFJR-23-039).

The target sets assigned to electrical cabinet modeled with detailed fire modeling were reviewed and revised as needed to either justify why propagation cannot occur or revise the target sets to reflect propagation to adjacent electrical sections.

This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

Section 4.3.5.7 of NAH-FIRE-TR-RM-000006 (SBK-BFJR-23-039) was revised to include documentation similar to what was provided during responses during peer review for the impact of high hazards and HEAF on fire wrapped conduits.

This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

The Fire PRA was updated to address F&Os and additional refinements were performed as necessary to remove conservatisms. The risk insights represent the as-built as-operated plant condition. MCA scenarios have been refined and additional detailed fire modeling was completed.

This issue was resolved in Revision 1 of SBK-BFR-23-042; therefore, no impact on this application.

NAH-FIRE-TR-RM-000006 (SBK-BFJR-23-039) was revised to document the review of ambient temperatures for the plant. The FSS spreadsheet (and downstream calculations for HGL formation) were revised to incorporate the revised ambient temperatures in DATA worksheet of Attachment 2 to FSS Notebook.

Supporting Issue Requirement Description The FSS Notebook does not include the review of the the automatic detection systems for outlier behavior relative to system unavailability to justify the use of the generic estimate FSS-D7 for detection unavailability.

Basis This review is needed to confirm that the generic unavailability values assigned are bounding for the automatic detection systems.

Description Specific features of physical analysis unit and fire scenario under analysis (e.g., pocketing effects, blockages that might impact plume behaviors or the 'visibility' of the fire to detection and suppression systems, and suppression system coverage) are not included in the detailed fire modeling to ensure effectiveness of suppression and detection with respect to specific fire scenarios. The FSS Spreadsheet does not assess FSS-D8 the time to detector activation for fire scenarios, instead an automatic detection system probability is assigned if installed but assumes a 15-minute detection.

Basis There is a potential to credit detector or sprinkler actuation that will not be effective for an individual scenario based on the specific configuration. Automatic detection is credited in scenarios involving lower HR Rs without assessment of the detection actuation timing and effectiveness for the specific scenario and fire size.

Description There is no criteria provided or justified in the exposed structural steel analysis for structural collapse in terms of fire FSS-F2 generated conditions.

Basis There is no criteria to confirm which fire scenarios will result in exposed structural steel damage and structural collapse.

Description MCA Scenario CP-FC-1-0-TB_FC_1234_Z is included in the FSS Spreadsheet, however, CP-FC-1-0 is not a separate fire compartment and the Plant Partitioning Notebook lists CP-FC-1-0 as a fire zone within TB_FC_ 1234_2. Also, there is a typo in the compartment ID for scenarios in the Service Water Pumphouse in the FSS Database.

FSS-G6 Basis CP-FC-1-0-TB_FC_ 1234_2 MCA scenario is between a fire zone located within a Fire Compartment and is not a compartment boundary. Compartment IDs SW FC 1C A and SW_FC_ 1 C-A are used for the same compartment-and there is an issue with the two separate IDs in quantifying the MCA scenarios.

Description The FSS Notebook includes discussions of the basis for the FSS-H2 Thermoset damage criteria and lack of self-ignited cable fires as the cable type being qualified to IEEE-383.

Basis SBK-1 FJR-24-006 Revision 0 Page 19 of 27 Evaluation This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

Section 4.3.3.2.1 was revised to add a statement about assumed unavailability based on FP 3.1 and review of maintenance rule function failures.

This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

Section 4.3.3.2.3 was added to NAH-FIRE-TR-RM-000006 (SBK-BFJR 039) to document the review of fire detection and suppression system effectiveness on a scenario specific basis. The results of the detailed calculation are shown in the DATA worksheet of the FSS Spreadsheet to track the review and conclusions.

Smaller HRR were confirmed to not activate the detection or activate at later time than larger HRR or fires in the same configuration.

This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

NAH-FIRE-TR-RM-000006 (SBK-BFJR-23-039) Section 4.3.5.5 documentation was revised to document and justify the criteria for structural steel collapse due to fire-generated conditions.

This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

NAH-FIRE-TR-RM-000006 spreadsheet (SBK-BFJR-23-039) and database MCA was reviewed and revised to ensure the MCA scenarios are based on fire compartments.

NAH-FIRE-TR-RM-000006 spreadsheet (SBK-BFJR-23-039) and database MCA were reviewed and revised as needed to ensure there are no typos and the fire compartments are accurate and mapping targets in FRANX (see SW_FC_ 1 C_A vs. SW_FC_ 1 C-A).

This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

NAH-FIRE-TR-RM-000006 ( SBK-BFJR-23-039) Section 4.3.5.1 was revised to remove statements about IEEE-383 and replaced with the UFSAR reference and information on thermoset cables

Supporting Issue Requirement There are inconsistencies in the documentation that consider IEEE-383 qualified is equivalent to Thermoset cable.

Description A large number of MCA scenarios have a 1 E-1 5 fire frequency in FRANX with no basis for the frequency.

FSS-H8 Basis These MCA scenarios are screening due to the lack of hot gas layer and apply a default frequency value of 1 E-15 in FRANX.

Description There are multiple cases where the counting of ignition sources is inconsistent with the documented methodology as well as consistency across all fire compartments.

Basis Bin 16.2 (iso phase bus duct) counting is not consistent with the documented approach as discussed in Table 4-2. The document suggests that all frequency is allocated to the Turbine Building only. However, the PRA Model team has identified that the allocated count and documentation is incorrect and needs to be updated. During the walkdown it was identified that there are discrepancies in the counting of small cabinets, specifically wall mounted cabinets. In general, these types of cabinets were included in the component count as IGN-A7 found in Attachment 3 of NAH-FIRE-TR-RM-000005. However, as examples, there were some wall mounted cabinets that are located in the EOG room (DG_FC_2B_A) that are similar in design and size that were screened from the count with no justification provided why these were screened. During the walkdown it was identified that the remote shutdown panel count was a "1 ". However, based on the physical size of the cabinet compared to other similar cabinet sizes, the count is applied inconsistently. The remote shutdown panel includes 3 doors, which based on other counted panels, would be considered a count of 3. Bin 35, TGO, is another example of this discrepancy. Table 4-2 suggests that this Bin was equally split among the three locations that contain the TGO; Turbine Oil Tank Room, Lube Oil Reservoir Room, and the Main Turbine Building. However, Attachment 3 shows that the entire frequency associated with Bin 35 has been applied to the Turbine Building.

Description The transient weighting factors are inconsistently applied across the fire compartments within plant locations.

Basis Application of transient weighting factors used a 3 for almost all locations. Ductbanks used a O for occupancy but still had hot work, maintenance, and storage. During the walkdown it was noted that the non-essential SWGR room NES_FC_ 1A_Z had IGN-A9 a fair amount of storage (compared to similar type fire compartments) which appeared to be there during normal operation. This fire compartment is characterized as "average" for storage, this seems to be low given what was found. The SW pump house area (SW_FC_1E_Z) is also characterized as "average" for storage. However, during the walkdown, it was identified that there is a significant amount of storage located in this area. The Cable Spreading Room, which also has a "3",

had very"little to no storage In the area during the walkdown.

Compared to other areas, this rating may be considered high.

SBK-1 FJR-24-006 Revision O Page 20 of 27 Evaluation included in other parts of the Fire PRA documentation.

This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

NAH-FIRE-TR-RM-000006 ( SBK-BFJR-23-039) was revised to document the MCA screening and HGL formation results in new table within Section 4.3.4 Multi-Compartment Analysis.

This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

NAH-FIRE-TR-RM-000005 (SBK-BFJR-23-038) was revised to implement consistent counting of ignition sources and provide justification or document any assumptions performed during counting to ensure the frequency can be maintained and updated with the provided documentation through the expansion of information included in. The count of remote shutdown panels (MM-CP-108 A/ B) were revised in Attachment 3.

Consistency in ignition source counting is demonstrated with documentation in which was populated based on prior walkdown data and supporting plant information. Table 4-2 was revised to document the approach for Bin 16.2 and Bin 35.

This issue was resolved in Revision 1 of SBK-BFR-23-038; therefore, no impact on this application.

NAH-FIRE-TR-RM-000005 (SBK-BFJR-23-038) Attachment 3 weighting factors within Transient Survey Results worksheet were revised to reflect the plant experience. Ductbanks occupancy was revised to 0.3, NES_FC_ 1A_Z storage was revised to 10 based on similar compartments. SW_FC_ 1 E_Z storage was revised to 1 O based on FLEX equipment storage. Cable Spreading (CB_FC_2A_A) was revised to 1 with Notes added for justification.

The notes within "Transient Survey Result"" document the clarification when revisions were made beyond what was communicated through survey results.

Supporting Issue Requirement Description The following inconsistencies in the ignition source apportioning documentation were observed:

1) In Attachment 3 of NAH-FIRE-TR-RM-000005, there is a table that identifies those sources that have been screened or removed from the analysis. There are some sources that do not provide a justification for screening or removal.

2) There are some ignition source bins discussed in Table 4-2 of NAH-FIRE-TR-RM-000005 that are incorrectly stating how the actual counting is being applied.

3) Plant walkdowns were performed initially in 2015.

Subsequent walkdowns were performed in 2022 and 2023 but only in select fire compartments.

4) The non-PRA Junction Boxes are all included in a pseudo, fire compartment""UN"

Basis

1) Any ignition source that has been identified and subsequently screened or removed (and identified as such) should contain a basis for its removal. For example, ignition source 0-SY-CP-TMBR-SWMP in fire compartment IGN-83 TB_FC_1C_Z is listed as being screened with no basis.

2) Table 4-2 Bin 8 states that there are two EDGs at Seabrook.

However, a review of Attachment 3 indicated that there are actually 4 sources identified as part of Bin 8. The Fire PRA model team has confirmed that there are in fact 4 EDGs at the plant. Table 4-2 Bin 16.1 states that the segmented bus ducts are counted by the number of transition points. However, a review of Attachment 3 and as observed by the walkdowns, the count of the bus duct is based on number of bus duct runs for a given fire compartment. The Fire PRA model team has confirmed that the intended counting methodology is to follow what was done. However, the documentation does not accurately reflect this approach.

3) During this period of time, a number of plant changes have taken place where pieces of equipment were added and/or removed. These updates could have taken place in fire compartments that were not walkdown in 2022 and 2023. The Fire PRA model team acknowledged that the utility did perform a review of engineering changes for applicability to the Fire PRA. This was reviewed and transmitted to the Fire PRA model team in reference DIT 002-PRA.

4) The ignition frequency associated with this fire compartment Description Not all Potentially Challenging fires identified were dispositioned to confirm that the event can be screened from the Bayesian update process.

IGN-84 Basis There are 3 events identified in Attachment 1 that have no basis for excluding from the Bayesian update.

Description The mean and statistical representation of the uncertainty IGN-85 intervals is documented for most ignition source bins. However, some Bins are missing data.

Basis SBK-1 FJR-24-006 Revision 0 Page 21 of 27 Evaluation This issue was resolved in Revision 1 of SBK-BFR-23-038; therefore, no impact on this application.

1) Attachment 3 of the IGN Notebook (SBK-BFJR-23-038) was revised to remove the Screened Ignition Sources. was expanded to include explicit notes for inclusion/exclusion of all electrical nodes in EDISON.

2) Table 4-2 was revised and Section 4.3.2.1 was added to provide additional counting clarifications.

3) NAH-FIRE-TR-RM-000005 (SBK-BFJR-23-038) was revised to explicitly document the conclusions from the review of the plant design changes for impact on the Fire PRA in Attachment 6 (newly added).

4) NAH-FIRE-TR-RM-000005 (SBK-BFJR-23-038) Attachment 3 was revised to map JS-REMAINING to FCMISC.

Section 4.3.7.6 of NAH-FIRE-TR-RM-000006 (SBK-BFJR-23-039) was revised to clarify the modeling approach for the non-PRA junction boxes and approach for maintenance of the scenarios.

This issue was resolved in Revision 1 of SBK-BFR-23-039 and SBK-BFJR 038; therefore, no impact on this application.

NAH-FIRE-TR-RM-000005 (SBK-BFJR-23-038) Attachment 1 was revised to document the Bayesian Update Disposition in a new column. No additional Bayesian updates were performed based on the added dispositions.

This issue was resolved in Revision 1 of SBK-BFR-23-038; therefore, no impact on this application.

NAH-FIRE-TR-RM-000005 (SBK-BFJR-23-038) was revised to remove the uncertainty terms and provide a reference to worksheet IGN contained within Attachment 2 of the FSS Notebook.

Supporting Issue Requirement The uncertainty terms for Bin 15 are missing. On an ignition source level, Bin 24 results in an""erro"" since there is no 5th and 951h percentile. However, Attachment 2 of the FSS calculation contains all the necessary data.

Description Discrepancy between CF notebook and FSS database.

Basis Upon performing a sample review of conditional probabilities in of the CS/CF notebook (NAH-FIRE-TR-RM-000003) and the FSS database (NAH-FIRE-TR-RM-000006 ), a data discrepancy was found for cables attached to basic event RCP1 CBKR. FTO (Equipment 1-RC0 CF-A1 BKR-1-C). Certain cables for this BE were listed in table tbl_import_CFMLA with conditional probabilities, however the cables were not identified in Attachment 2 of the CS/CF notebook. After consulting with the peer review support team, the missing cables were determined to be not required for this BE. Review of Attachment 1 of the CS/CF notebook and table tbl_import_Cables_Selection confirmed that the missing cables are not required for the subject BE. Similar discrepancies were found on cables for other RC-BKR equipment.

Description Application of Disablement Action beyond Fire Procedure Direction Basis Fire PRA staff indicated [per response to Question EC-02] that HRA-B2 the one disablement action modeled at this time is HH.OISPV1FR.FA, Close PORV Block Valve to Isolate Stuck-Open PORV (SLOCA)- FIRE. This HFE is being applied to fire areas beyond those specified in Table 4.3-6 of the Fire HRA Notebook (which cites relevant fire procedure steps) Fire PRA staff clarified that HH.OISPV1 FR.FA is directed by E-0 Step 7 and uses the timing based on E-0 instead of prompt disablement action timing.

Description Procedure Path for HFEs Credited for Fire Basis The primary Fire AOP OS1200.00, RESPONSE TO FIRE OR FIRE ALARM ACTUATION, specifically states up front that E-0 should not be entered if a fire induced transient causes a HRA-B3 reactor trip. There are two fire HFEs HH.FWP37BMSFR.FA, and HH.OISPV1 FR.FA that have E-0 cited as their primary Procedure in HRA Calculator. Responses to Questions EC-09 and DK-08 stated that Fire AOP OS12000.00 precautions that E-0 should not be entered until Step 9 of the procedure is processed. Based on the feedback from Seabrook operations where there is no transition out, the EOPs and Fire AOP procedures are implemented in parallel.

Description Lack of Fire HEP Consistency and Reasonableness Check along with Risk-Significant HFEs Quantified with Screening Values Basis HRA-C1 SR HR-G6 from Part 2 of the PRA Standard requires a consistency and reasonableness check of the HEPs relative to each other and given the scenario and context. This was not done. Attachment 5, Basic Event Importance Measures, of the FQ Notebook (NAH-FIRE-TR-RQ-000001, Rev. 0) was reviewed against the Fire HFE list from the Fire HRA Calculator SBK-1 FJR-24-006 Revision 0 Page 22 of 27 Evaluation This issue was resolved in Revision 1 of SBK-BFR-23-038; therefore, no impact on this application.

The FSS database""tbl_import_CFML""

was reviewed and revised to remove cables not required per Attachments 1 and 2 of NAH-FIRE-TR-RM-000003 (SBK-BFJR-23-036).

This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

The Fire HRA Notebook was revised to add the suggested paragraph as stated in the Possible Resolution.

This issue was resolved in Revision 1 of SBK-BFR-23-041; therefore, no impact on this application.

HH.FWP37BMSFR.FA and HH.OISPV1FR.FA were reviewed in the HRA Calculator to clarify the basis from operator insights for the modeled procedure path and timing. This is documented in Procedure and Training Notes within the HRA Calculator and documentation was added to Section 4.3.3.3 of the Fire HRA Notebook (SBK-BFJR-23-041).

This issue was resolved in Revision 1 of SBK-BFR-23-041; therefore, no impact on this application.

The Fire HRA Notebook (SBK-BFJR 041) was revised to add Attachment 4 listing the Fire HFEs and HEP along with discussion on the reasonableness including a comparison with the other Fire HFEs.

This issue was resolved in Revision 1 of SBK-BFR-23-041 ; therefore, no impact on this application.

Supporting Issue Requirement file SBK-21 Rev 2_Fire DIT-004. There are four HFEs and three combinations including HFEs that have FV>0.005 for CDF and are based on screening value HEPs:

HH.ODEP4.FA HH.OSIG2FR.FA HH.OSIG3FR.FA HH.SWCTSURVFR.FA COMBINATION_104 COMBINATION_ 135 COMBINATION_ 148 Description MCR Abandonment HFEs not credited in Fire PRA Model Basis Seven (7) fire HFEs are identified in the Fire HRA Notebook with a basic event name suffix of.REC and involve recovery HRA-D1 actions to restore specific systems at the RSS due to a CR fire in a specific MCR panel. However, Fire PRA staff stated (response to Question EC-02) that""The actions developed at the RSS are discussed in the HRA notebook (.REC actions).

Note that the current Seabrook MCR abandonment scenario does not credit any of the recovery actions at the RSS after MCR abandonment'"'

Description Documentation Issues within HRA Calculator Basis This Finding is consistent with F&O 20-9 from the November 2016 Fire PRA Peer Review documented in PWROG-16042-P Rev. 0, which identified an issue to Adjust the HFE timings used for two scenarios: 1) Spurious actuation of containment spray impacts on operator action for sump recirculation, 2)

HRA-E1 Loss of Main Feedwater impacts on Bleed & Feed actions. A new fire HFE with specific timing was developed for the first case, but notes in the HRA Calculator indicated for the Bleed &

Feed case that while an approximation was used, a new MAAP run was needed. Fire PRA staff stated [Question EC-08) that during the development of the updated IE HRA analysis, the approximation for an additional 2 minutes to transition from 30% wide range to 20% wide range was determined to be appropriate. However, the documentation in the timing analysis for the HFEs in question was not fully updated to reflect this change either in the IE or the Fire HRA.

Description NAH-FIRE-TR-RM-000009 does not specifically address diversion of suppressants from areas where they might be needed for those fire suppression systems associated with a SF-A2 common suppressant supply.

Basis SF-A2 requires assessment of the potential for diversion of suppressants from areas where they might be needed for those fire suppression systems associated with a common suppressant supply.

Description Other than a reference to the IPEEE walkdowns that were SF-A3 performed in 1992 and a statement that the associated fire PRA walkdowns also did not identify any concerns for seismic induced common cause failure of multiple fire suppression SBK-1 FJR-24-006 Revision 0 Page 23 of 27 Evaluation Section 5.3.2 of PRM Notebook (SBK-BFJR-23-037) was revised to document the model changes to credit operator actions for MCR abandonment. The Fire HRA Notebook (SBK-BFJR-23-041) includes the operator actions.

This issue was resolved in Revision 1 of SBK-BFR-23-041 ; therefore, no impact on this application.

This issue is documentation only. No impact on application.

This F&O is related to Seismic Fire Interaction which is a qualitative assessment, therefore this F&O does not impact this application.

Supporting Issue Requirement systems, no qualitative assessment for the potential was provided.

Basis SR SF-A3 requires the assessment of the potential for common-cause failure of multiple fire suppression systems due to the seismically induced failure of supporting systems such as fire pumps, fire water storage tanks, yard mains, gaseous suppression storage tanks, or building standpipes.

Description No discussion of the fire brigade training is described.

SF-AS Basis Part (a) of the SR requires that the extent to which training has prepared firefighting personnel to respond to potential fire alarms.

Description To support the fire quantification all required cables must be included in the FRANX data.

Basis FQ-A1 There are a number of cables (E3C-F36/1 and F36-P89 as examples) that are listed as""require'"' in Attachment 1 of NAHFIRE-TR-RM-000003. However, these cables are not found in the FSS Database (Attacment 1 of NAH-FIRE-TR-RM-000006). Not having these cables in the FSS Database could lead to an underestimation of the risk.

Description The top CDF and LERF contributors contain known conservatisms that are not addressed.

The Quantification Notebook includes a sensitivity analysis which indicates that the fire PRA is sensitive to MCA scenarios.

MCA scenarios DG_FC_3AB_Z-CB_FC_2B_A and DG_FC_3AB_ZDG_FC_2A_A are included in the top 20 GDF scenarios.

Based on the current results, several fire scenarios among the top contributors are utilizing conservative modeling approaches and including larger than realistic target sets. The Seabrook Fire PRA model has not refined the detailed fire scenarios to remove the modeling conservatisms in several of these top scenarios FQ-E1 Basis The two SWGR and Cable spreading rooms are at the top of the list for risk relevant fire compartments. For LERF in particular, the cable spreading room contributes 95% of the risk. For CDF these three fire compartments make up 46% of the risk. There are known conservatisms in the fire modeling within these locations and based on this, there is potential masking of significant contributors taking place.

MCA scenarios are risk significant based on the Quantification Notebook sensitivity analysis and some MCA scenarios are included in the top 20 CDF scenarios.

Risk significant fire scenarios such as the Cable Spreading Room transient fires are failing a large amount of targets in the compartment. Walkdown of this compartment indicates fire modeling refinements are available to reduce these impacts.

SBK-1 FJR-24-006 Revision O Page 24 of 27 Evaluation This F&O is related to Seismic Fire Interaction which is a qualitative assessment, therefore this F&O does not impact this application.

The FSS database'"'tbl_import_Cable_Selectio""

was reviewed and revised to ensure consistent with Attachment 1 of NAH-FIRE-TR-RM-000003 (SBK-BFJR 036). ErrorCheck_RequiredCables added to FSS database to confirm with future updates.

This issue was resolved in Revision 1 of SBK-BFR-23-039; therefore, no impact on this application.

The Fire PRA was updated to address F&Os and additional refinements were performed as necessary to remove conservatisms. The risk insights represent the as-built as-operated plant condition. MCA scenarios have been refined and additional detailed fire modeling was completed.

Supporting Issue Requirement Description The non significant cutset reviews do not sufficiently document a review of each cutset.

Basis and 7 of NAH-FIRE-TR-RQ-000001 document the review of randomly selected cutsets. These tables include all cutsets not included in the top 100 and only a small number of cutsets actually include a review. The process used to select these reviewed cutsets is not clear as there are very few cutsets actually documented. In discussion with the PRA model team, it was acknowledged that many of the insights were the same or similar. However, it is not clear from a reviewers FQ-F1 standpoint that this is the case. This was reviewed as part of Part 2 SR QU-D5.

Description of NAH-FIRE-TR-RQ-000001 provides a table of the basic event importances for both CDF and LERF.

Basis The tables in Attachment 5 do not provide sufficient basis for the relative importance of events. There is no documentation supporting the various types of importances relative to operator action, CCF events, joint HFEs (combinations), components as examples. This was reviewed as part of Part 2 SR QU-F3.

Description The CAFTA.rr database provided to the peer review team prior to the peer review team does not contain parameter distribution types or the error factors for the scenarios. Another database was provided during the review that did contain some error factors for scenarios (not all) but did not contain the distribution types. There are inconsistencies between the model and the UNC-A1 documentation with respect to some of the uncertainty distributions.

Basis Without the distribution type in the.rr database, the error factor will be ignored by UNCERT code so the uncertainty in the ignition frequency is not evaluated. In the documentation of the human failure events, it is stated that the distribution type is lognormal. However, in the.rr database, lognormal and beta distributions are used.

Description The state of knowledge correlation (SOKC) is not specifically addressed in the Seabrook documentation.

Basis Back referenced SR QU-E3 requires taking into account the UNC-A2 state-of-knowledge correlation. The Seabrook model does take into account the SOKC through the use of type codes to address the parametric uncertainties, but the documentation does not address it specifically.

SBK-1 FJR-24-006 Revision 0 Page 25 of 27 Evaluation NAH-FIRE-TR-RQ-000001 (SBK-BFJR-23-042) was revised to enhance the documentation for the nonsignificant cutset review completed in Section 5.3.2.

This issue was resolved in Revision 1 of SBK-BFR-23-042; therefore, no impact on this application.

This is tracked in the open Item section of NAH-FIRE-TR-RQ-000001 (SBK-BFJR-23-042). There is no planned update to add details to Attachment 5 of the Importances in this revision.

There is no impact to this application since this is documentation only.

The Fire PRA added a CAFTA.rr database to the NAH-FIRE-TR-RQ-000001 (SBK-BFJR-23-042 ) which is specific for UNCERT with the distribution types and uncertainty parameters populated. The documentation was reviewed and revised as necessary to align with the modeled distribution types.

This issue was resolved in Revision 1 of SBK-BFR-23-042; therefore, no impact on this application.

Section 5.5.19.3 was revised in the Quantification Notebook, SBK-BJFR 042, to include statements about how SOKC is addressed.

This issue was resolved in Revision 1 of SBK-BFR-23-042; therefore, no impact on this application.

Supporting Issue Requirement Description Case 1 Sensitivity Study: Always Failed includes two results: 1) case where cutsets contain HEPCOMB2 and 2) case where HEPCOMB2 cutsets are excluded. HEPCOMB2 is a combination of any 2 HFEs that were not included in the dependency analysis, but appeared in the sensitivity case cutsets. For this sensitivity case, the dependency analysis should have been expanded to include the unanalyzed combinations.

Basis The cutsets containing HEPCOMB2 have combinations of events that have not been analyzed. The use of this method masked the sensitivity study performed for always failed components such that its importance cannot be assessed.

Description CAFTA.rr database contains legacy items that are no longer used.

Basis The peer team believed that the documentation was inconsistent from the CAFTA.rr database because some hot short probabilities contained uncertainy distributions types (lognormal) that did not match the distribution type discussed in the documentation (beta).

SBK-1 FJR-24-006 Revision O Page 26 of 27 Evaluation The documentation for Case 1 sensitivity case was enhanced to describe the insights gained by the existing analysis.

This issue was resolved in Revision 1 of SBK-BFR-23-042; therefore, no impact on this application.

The.rr database was purged prior to the final updates to remove unused basic events and gates.

This issue was resolved in Revision 1 of SBK-BFR-23-042; therefore, no impact on this application.

SBK-1 F JR-24-006 Revision O Page 27 of 27 Appendix D: Sensitivity Assessment for Common Cause Impacts to Both RA Ts As noted in the Common Cause Evaluation discussion it is unlikely for there to be a common failure mechanism between the two RA Ts; however, a sensitivity was performed on the Internal Events model to identify any potential risk insights. Using the following flag file, the Internal Events PRA model was run at the 1 E-12 for CDF and 1 E-13 for LERF.

ED-X-3-B and ED-X-3-A OUT OF SERVICE (OOS) FLAG EDX3B.FX PROB 1.0 EDX3B.FX.YRPROB 1.0 EDX3A.FX PROB 1.0 EDX3A.FX.YRPROB 1.0 As shown in Table D-1 there is a small increase in risk for CDF (1.30E-07). In reviewing the risk insights from this assessment, the dominant contributors to this increase are from cutsets where either of the Emergency Diesel Generators are unavailable. Since this configuration is unlikely to be entered into for the duration of the RAT work the assumption that common cause does not exist between the two transformers is not a key assumption and does not impact the risk insights for this application.

Table D-1: Sensitivity Results Case CDF (/yr)

Delta CDF (/yr)

LERF (/yr)

Delta LERF (/yr)

ED-X-3-B Unavailable 2.46E-06 1.05E-07 ED-X-3-B & ED-X-3-A 2.59E-06 1.30E-07 1.05E-07 O.OOE+OO Unavailable

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