CNL-25-098, Supplement to License Amendment Request to Revise Technical Specifications to Adopt Risk-Informed Completion Times TSTF-505, Revision 2, Provide Risk-informed Extended Completion Times - RITSTF Initiative 4b

Supplement to License Amendment Request to Revise Technical Specifications to Adopt Risk-Informed Completion Times TSTF-505, Revision 2, Provide Risk-informed Extended Completion Times - RITSTF Initiative 4b

ML25232A156
Person / Time
Site:	Watts Bar
Issue date:	08/20/2025
From:	Hulvey K Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
CNL-25-098, EPID L-2024-LLA-0175
Download: ML25232A156 (1)

Text

10 CFR 50.90 1101 Market Street, Chattanooga, Tennessee 37402 CNL-25-098 August 20, 2025 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Units 1 and 2 Facility Operating License Nos. NPF-90 and NPF-96 NRC Docket Nos. 50-390 and 50-391

Subject:

Supplement to License Amendment Request to Revise Technical Specifications to Adopt Risk-Informed Completion Times TSTF-505, Revision 2, Provide Risk-Informed Extended Completion Times -

RITSTF Initiative 4b (WBN-TS-19-29) (EPID L-2024-LLA-0175)

References:

1. TVA Letter to NRC, CNL-25-001, License Amendment Request to Revise Technical Specifications to Adopt Risk-Informed Completion Times TSTF-505, Revision 2, Provide Risk-Informed Extended Completion Times - RITSTF Initiative 4b, (WBN-TS-19-29), dated December 27, 2024 (ML24362A110) 2.

NRC electronic mail to TVA, RE: Audit Questions Requiring Inclusion in Supplement, dated August 1, 2025 In Reference 1, Tennessee Valley Authority (TVA) requested an amendment to the Watts Bar Nuclear Plant (WBN), Units 1 and 2, Facility Operating License Nos. NPF-90 and NPF-96. The proposed amendment would modify Technical Specification (TS) requirements to permit the use of Risk-Informed Completion Times in accordance with Technical Specifications Task Force (TSTF)-505, Revision 2, Provide Risk-Informed Extended Completion Times - RITSTF [Risk-Informed TSTF] Initiative 4b.

In Reference 2, the Nuclear Regulatory Commission (NRC) acknowledged TVAs proposal to supplement the license amendment request (LAR) in Reference 1 to address several of the NRC staffs questions posed during the July 2025 regulatory audit that was held in support of the LAR review. Enclosure 1 provides TVAs response to a selection of the NRC staffs regulatory audit questions. Enclosure 2 provides modifications to the Reference 1 LAR resulting from audit question responses.

U.S. Nuclear Regulatory Commission CNL-25-098 Page 2 August 20, 2025 This letter does not change the no significant hazard considerations or the environmental considerations contained in Reference 1. Additionally, in accordance with Title 10 of the Code of Federal Regulations 50.91(b)(1), TVA is sending a copy of this letter and the enclosures to the Tennessee Department of Environment and Conservation.

There are no regulatory commitments contained in this submittal.

Please address any questions regarding this submittal to Amber V. Aboulfaida, Senior Manager, Fleet Licensing, at avaboulfaida@tva.gov.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 20th day of August 2025.

Respectfully, Kimberly D. Hulvey General Manager, Nuclear Regulatory Affairs and Emergency Preparedness

Enclosures:

1.

Response to Selected Audit Questions

2.

Supplemental Changes to the LAR cc (w/Enclosures):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRC Project Manager - Watts Bar Nuclear Plant Director, Division of Radiological Health - Tennessee State Department of Environment and Conservation Digitally signed by Edmondson, Carla Date: 2025.08.20 10:49:47

-04'00' CNL-25-098 E1 1 of 17 Response to Selected Audit Questions Note: The Nuclear Regulatory Commission (NRC) staffs questions are in italics throughout this enclosure. The Tennessee Valley Authority (TVA) responses are in unitalicized font.

Probabilistic Risk Assessment Licensing Branch A Audit Questions QUESTION 02 - Consideration of Shared Systems in RICT Calculations Regulatory Guide (RG) 1.200, Revision 2, states, [t]he base PRA serves as the foundational representation of the as-built and as-operated plant necessary to support an application.

Table 1 of LAR enclosure 8 indicates the existence of cross-ties between units and identifies several systems that are shared. It is not clear to NRC staff how these systems are shared, whether they can support both units in an accident, and how the shared systems are credited for each unit in the PRA models. NRC staff notes that for certain events, such as dual unit events (e.g., loss of offsite power), it may be appropriate to only credit the shared systems for one unit. Therefore, address the following:

a.

Explain how shared systems are modeled in the Real Time Risk (RTR) model for each unit in a dual unit event demonstrating that shared systems are not over-credited in the RTR model.

OR b.

If the RTR model does not address the impact of events that can create a concurrent demand for the system shared by both units, then justify that this exclusion has an inconsequential impact the RICT calculations.

TVA Response Shared safety-related systems include the essential raw cooling water, component cooling water, fire protection, spent fuel cooling, fuel oil storage tanks, preferred and emergency electric power, chemical and volume control, radioactive waste, emergency gas treatment system, auxiliary control air system, control and Auxiliary Building ventilation systems, the auxiliary feedwater supply tank, and the FLEX equipment. Not all of these systems are modeled in the WBN Probabilistic Risk Assessment (PRA) model.

There are two condensate storage tanks at WBN. In the WBN PRA model, Tank A is dedicated to Unit 1 and Tank B is dedicated to Unit 2. There is also a 500,000-gallon auxiliary feedwater supply tank that can be lined up to either unit for long term water supply. This is only credited for long term heat removal in the WBN Fire PRA model.

The vital DC power system is shared to the extent that a few loads (e.g., the vital inverters) in one nuclear unit are energized by the DC power channels assigned primarily to power loads of the other unit. In no case does the sharing inhibit the safe shutdown of one unit while the other unit is experiencing an accident.

All shared systems are sized for all credible initial combinations of normal and accident states for the two units, with appropriate isolation to prevent an accident condition in one unit from CNL-25-098 E1 2 of 17 carrying into the other. There are several multi-unit initiators included in the WBN RTR model (e.g., loss of offsite power, loss of essential raw cooling water, internal flooding, internal fires, etc.). Multi-unit initiators affect components in both units simultaneously such that credit cannot be taken for equipment in the opposite unit if it is affected by the multi-unit initiator. In the WBN RTR model, power to a shutdown board in one unit can only be supplied from a diesel in the opposite unit if both diesels in the opposite unit are available.

The 3MW and 480 V FLEX diesels are the only FLEX equipment credited in the WBN PRA model. The A FLEX diesels are only credited for providing power for Train A power and the B FLEX diesels are only credited for providing power for Train B power. Since only one train of power is required to safely shutdown an accident unit and the 3MW diesels can only be aligned to one 6.9 kV shutdown board at a time (either Unit 1 or Unit 2), a single 3MW FLEX diesel will not be credited for providing power to more than one unit for multi-unit initiators. Similarly, since the 480 V diesels can only be aligned to one 480 V shutdown board at a time (either Unit 1 or Unit 2), a single 480 V FLEX diesel will not be credited for providing power to more than one unit for multi-unit initiators.

QUESTION 03 - Impact of Seasonal Variations The Tier 3 assessment in RG 1.177 stipulates that a licensee should develop a program that ensures that the risk impact of out-of-service equipment is appropriately evaluated prior to performing any maintenance activity. NEI 06-09-A and its associated NRC SE state that, for the impact of seasonal changes, either conservative assumptions should be made or the PRA should be adjusted appropriately to reflect the current (e.g., seasonal or time of cycle) configuration.

LAR enclosure 8, section 3, on attributes of the RTR model, states, There are no seasonal variations included in the WBN OTMHM [one top multi hazard model]. It is not clear to NRC staff why no mechanism or criteria are used to determine when PRA adjustments need to be made in the RTR due to changes in Tennessee River water temperature, nor seasonal or time of cycle dependencies. Therefore, address the following to clarify the treatment of seasonal and time of cycle variations:

a. Discuss any PRA modeling adjustments made in the RTR to account for seasonal and time of cycle variations during a RICT evolution. Also, explain how these adjustments are made and how this approach is consistent with the guidance in NEI 06-09-A and its associated NRC SE.

b. Describe the criteria used to determine when PRA adjustments due to seasonal or time of cycle variations need to be made in the RTR and what mechanism initiates these changes.

c. Describe the number of emergency raw cooling water (ERCW) pumps that are required due to river water temperature throughout the year; and discuss the impact of the ERCW header temperature on the number of component cooling water (CCW) heat exchangers required to mitigate modeled events. Describe how the RTR conservatively models the success criteria of ERCW pumps and CCW heat exchangers for all seasons in order to have no seasonal variations included in the model.

CNL-25-098 E1 3 of 17 TVA Response

a. There are no PRA modeling adjustments made in the RTR model to the cooling water systems to account for seasonal and time of cycle variations during a Risk Informed Completion Time (RICT) evolution. The RTR model conservatively models cooling water systems such that systems can perform their function under the highest river water temperatures at the end of the cycle for the maximum decay heat load. Conservative assumptions were made in the thermal hydraulics analysis (supporting the success criteria and timing associated with human reliability) to account for changes in decay heat given the time in cycle.

b. There are no PRA modeling adjustments made in the RTR model to account for seasonal and time of cycle variations, so there are no criteria used to determine when PRA adjustments due to seasonal or time of cycle variations need to be made.

c. WBN has a total of 8 ERCW pumps. The minimum combined safety requirements for the ERCW system are met by two pumps in one plant train. Loss of either header or the loss of an entire emergency power train will not prevent safe shutdown. If one of the running pumps fails during operation, the operator must act to recover lost flow by manually starting a redundant standby ERCW pump. The operator action to manually start the standby pump is included in the RTR model.

QUESTION 04 - In-Scope LCOs and Corresponding PRA Modeling The NRC SE for NEI 06-09-A specifies that the LAR should provide a comparison of the TS functions to the PRA modeled functions to show that the PRA modeling is consistent with the licensing basis assumptions or to provide a basis for when there is a difference. LAR enclosure 1, table E1-1 identifies each TS LCO Condition proposed to be in the RICT program, describes whether the systems and components participating in the TS LCO are modeled in the PRA, and compares the design basis and PRA success criteria. For certain TS LCO Conditions, the table explains that the associated SSCs are not explicitly modeled in the PRAs but their unavailability will be represented using a surrogate event that fails the function performed by the SSC. For one LCO Condition, the LAR did not provide enough description for NRC staff to conclude that the PRA modeling will be sufficient for the proposed LCO Condition. Therefore, address the following:

a. LAR table E1-1 states for TS LCO 3.7.5 (Auxiliary Feedwater System) Condition B (One AFW [auxiliary feedwater] train inoperable in MODE 1, 2, or 3 for reasons other than Condition A) that the design basis success criterion is Two of three AFW pumps and the PRA success criterion is One of three AFW Pumps. The comment column for this entry states that limited accident scenarios, such as specific ATWS transients, do require two AFW pumps. It is not clear to NRC staff why the PRA success criteria is not conservatively modeled like the design success criteria to include all accident scenarios.

Therefore, address the following:

i.

Describe all accident scenarios that require two AFW pumps and justify why the PRA success criteria of one of three AFW pumps is adequate for these scenarios with respect to this application.

ii. Describe any adjustments of AFW success criteria made to the RTR model for emergent conditions similar to accident scenarios provided in response to (i) OR CNL-25-098 E1 4 of 17 provide a justification for why no changes are made to the RTR model for emergent conditions similar to accident scenarios provided in response to (i).

TVA Response:

a.i. The WBN PRA does not use auxiliary feedwater (AFW) success criteria of one of three pumps for all scenarios. The number of AFW pumps required for success changes in the PRA model depending upon the accident sequence. Detailed calculations were performed for representative accident scenarios using MAAP4 to determine the minimum number of AFW pumps required for the spectrum of accidents included in the WBN PRA model. These calculations showed that one AFW pump is adequate for removal of decay heat for all modeled scenarios except for those involving an Anticipated Transient Without SCRAM (ATWS). The ATWS scenarios require either the turbine driven pump, both motor driven pumps, or all three AFW pumps (depending on the availability of the primary system power operated relief valves). The PRA logic ensures that the correct number of required AFW pumps are selected based on the availability of the primary system power operated relief valves.

a.ii There are no adjustments of AFW success criteria made to the RTR model for emergent conditions since the logic already accounts for the need for more than one pump in ATWS scenarios as described above.

Probabilistic Risk Assessment Licensing Branch C (APLC) Audit Questions QUESTION 10 - Seismic PRA Model Peer Review In section 5 of enclosure 2 of the LAR, TVA states, The March 2016 WBN Units 1 and 2 Seismic Probabilistic Risk Assessment (SPRA) was peer reviewed against the requirements of ASME/ANS RA-Sa-2009, the American Society of Mechanical Engineers (ASME)/American Nuclear Society (ANS) Probabilistic Risk Assessment (PRA) Standard.

In section 3.2.3 of enclosure 1 of the previously approved WBN application to adopt 10 CFR 50.69, TVA states, ASME/ANS PRA Standard ASME/ANS RA-Sb-2013 [] is credited for the peer review performed on the WBN SPRA.

Please address the following:

a. Specify the PRA standard upon which the last full-scope peer review was completed for the SPRA.

b. If the last full-scope peer review of SPRA was conducted against the SPRA requirements in ASME/ANS RA-Sb-2013, justify that the use of this alternative approach to the NRC-endorsed approach addresses the technical elements for the development of a SPRA.

TVA Response

a. The last full-scope peer review completed for the WBN SPRA was against American Society of Mechanical Engineers (ASME)/American Nuclear Society (ANS) RA-Sb-2013.

(Reference 1). This is revised in Enclosure 2.

CNL-25-098 E1 5 of 17

b. The response to RAI APLB-02 in Reference 2 (CNL-19-035) also applies to Part b of NRC Question 10 for the WBN RICT LAR.

References

1.

ASME/ANS RA-Sb-2013, Addenda to ASME/ANS RA-S-2008 Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications, June 2013

2.

TVA letter to NRC, CNL-19-035, Response to Request for Additional Information Regarding Application for Technical Specification Change Regarding Risk-Informed Justification for the Relocation of Specific Surveillance Frequency Requirements to a Licensee Controlled Program (WBN-TS-18-14) (EPID L-2018-LLA-0279), dated May 7, 2019 (ML19127A323)

Electrical Engineering Branch (EEEB) Audit Questions General Design Criteria (GDC) 17 requires, in part, that both offsite and onsite electrical power systems should be provided to permit the functioning of systems, structures, and components (SSCs) important to safety. The safety function for each system, assuming other is not functioning, assures fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded, and the core is cooled, and containment integrity and other vital functions are maintained for postulated accidents.

QUESTION 13 - Electrical Discussion Topic

, table E1-1, shows the same number of 14 TS changes as in attachments 2.1and 2.2 including their individual wording for TS Conditions identified except for the following:

i.

TS 3.8.9, Condition A for Unit 2 is not shown, only the one for same TS and Condition for Unit 1 ii.

TS 3.8.9, Condition F for Unit 2 is not shown, only the one for same TS and Condition for Unit 1, table E1-2, shows the same 14 TS changes as in attachment 2.1 including their individual wording.

, table E1-3, shows the same 14 TS changes as in Attachment 2.2 including their individual wording except for the following:

i.

TS 3.8.9.A should be for Unit 2 AC [alternating current] shutdown boards ii.

TS 3.8.9.F should be for Unit 1 AC shutdown boards TVA Response Tables E1-1 (TS 3.8.9 Conditions A and F) and E1-3 are revised in Enclosure 2.

CNL-25-098 E1 6 of 17 QUESTION 15 - TS LCO 3.8.1, Condition E LCO 3.8.1.b requires four diesel generators (DGs) capable of supplying the onsite Class 1E

[alternating current] AC Electrical Power Distribution System to be operable. TS 3.8.1, Condition B, is for one required DG inoperable. The Required Action for that LCO condition requires restoration of DG.

UFSAR section 8.3.1 indicates onsite power system for either unit consists of the (1) standby AC power system, and (2) the 120 volts (V) vital AC system. The standby power ac system meets the requirements of GDC 17 for Class 1E onsite ac power system. The standby power system serving each unit is divided into two redundant load groups power trains. These power trains (Train A and Train B for each unit) provide power to all safety related equipment. The UFSAR further states that the four 6.9 kilovolt (kV) shutdown boards are arranged into four power trains (two per unit). Each 6.9 kV shutdown board is one train. UFSAR section 8.1.5.3 states that a single failure (loss of battery or loss of a DG) in the plant and an assumed loss of offsite power, sufficient engineered safety features (ESF) loads are still automatically available to the accident unit and to safely shut down the remaining unit. The shared safety systems are designed so that one load group (Train 1A & 2A or Train 1B & 2B) can mitigate a design-basis accident in one unit and accomplish an orderly shutdown of the other unit.

DSC in table E1-1 for TS LCO 3.8.1, Condition E appears inconsistent with the purpose of DSC of providing minimum SSCs for safe shutdown.

DSC indicates success is one qualified circuit between transmission network and the onsite 1E AC electrical power distribution systems or two DGs of a load group. The worst case is DGs of a load group available for safe shutdown with offsite power unavailable. Please clarify or explain why DSC, which should be the minimum SSCs to achieve a safe shutdown, does not address the worst case.

TVA Response The Design Success Criteria (DSC) in Table E1-1 for TS 3.8.1 Condition E is revised in.

QUESTION 16 - TS LCO 3.8.4, Conditions A and B LCO 3.8.4 requires Train A and Train B vital direct current (DC) electrical power subsystems to be operable. UFSAR section 8.3.2.1.1 indicates that 125 VDC vital power system has four redundant channels (designated as Channels I, II, III, and IV) and consists of four lead-acid-calcium batteries, eight battery chargers (including two pairs of spare chargers), four distribution boards, battery racks, and the required cabling, instrumentation and protective features. A channel has a battery charger to supply normal DC power, a battery for emergency DC power, and a battery board which facilitates load grouping and provides circuit protection. The UFSAR also indicates that each channel supplies the control circuits for a shutdown board. USFAR section 8.1.5.3 indicates that the Class1E DC power system has four redundant divisions. TS Bases B3.8.4, DC Sources - Operating - Background, indicates that the 125 VDC vital power system is composed of the four redundant channels (Channels I and III are associated with Train A and Channels II and IV are associated with Train B) and channel composition.

DSC appears inconsistent with the LCO, the UFSAR and TS Bases, and column 2 of TS 3.8.4, Condition A or B which refer to trains. Please clarify or explain the inconsistencies by DSC CNL-25-098 E1 7 of 17 stating the composition of a Power Train (e.g., Train A of Unit 1 and Train A of Unit 2 as a Power Train).

TVA Response Table E1-1 for TS 3.8.4 Conditions A and B is revised in Enclosure 2.

QUESTION 17 - TS LCO 3.8.4, Conditions D and E USFAR [sic] section 8.3.1.1 states that there is a DG battery subsystem for each DG. Each subsystem is comprised of a battery, battery charger, distribution center, and cabling. The battery provides control and field-flash power when the charger is unavailable. The charger, if 480 VAC is available, supplies the normal DC loads, maintains the battery in a fully charged condition, and recharges the battery while supplying the required loads regardless of the status of the plant. The batteries are physically and electrically independent. DSC appears inconsistent with the LCO which differentiates between vital DC and DG DC electrical power subsystems.

Please clarify or explain why table E1-1, column 2 and column 5, for TS 3.8.4 Conditions D and E apply to DC electrical power trains, but the LCO is for DG DC trains or subsystems.

TVA Response Table E1-1 for TS 3.8.4 Conditions D and E is revised in Enclosure 2.

QUESTION 18 - TS LCO 3.8.7, Condition A UFSAR section 8.3.1.1 indicates 125 VDC vital system supplies power for the 120 VAC system with there being four uninterruptible power systems (UPS) for ESF loads and four UPS for reactor protection system (RPS) loads. The UFSAR also indicates that the 120 V vital AC system consists of four identical power channels per unit (designated as Channels I, II, III and IV). Each channel for both units consists of an inverter and a distribution panel which facilitates load grouping and provides circuit protection.

DSC appears inconsistent with the LCO 3.8.7 which addresses inverters, and the DSC only requires ESF and RPS power divisions for safe shutdown. Please clarify or explain the inconsistency by, for instance, identifying number of inverters for those ESF and RPS power divisions.

TVA Response There is one 120 VAC vital instrument power board for each of the four channels in each unit for a total of eight 120 VAC vital instrument power boards. The inverters are the preferred source of power for the 120 vital instrument power boards because of the stability and reliability they achieve. There is one inverter for each of the four channels for each unit (eight normal inverters). There is also one spare inverter for each of the four channels that is shared between units making a total of twelve inverters in the plant.

The components in the reactor trip system (RTS) and the engineered safety feature actuation system (ESFAS) receive power from 120 VAC vital instrument power boards. Up to four channels of power are used for each of those systems for each unit. Table 3.3.1-1 of the CNL-25-098 E1 8 of 17 WBN technical specifications (TS) provides the number of required channels for the RTS.

Table 3.3.2-1 of the WBN TS provides the number of required channels for the ESFAS.

Table E1-1 for TS 3.8.7 Condition A is revised in Enclosure 2.

Instrumentation and Controls Branch (EICB) Audit Questions QUESTION 19 - Defense in Depth Evaluation for Protected Functions TSTF-505 Revision 2 (ML18183A493) states:

The description of proposed changes to the protective instrumentation and control features in TS Section 3.3, Instrumentation, should confirm that at least one redundant or diverse means (other automatic features or manual action) to accomplish the safety function (for example, reactor trip, SI, containment isolation, etc.) remains available during use of the RICT, consistent with the defense-in-depth philosophy as specified in RG 1.174 (Note that for each application, the staff may selectively audit the licensing basis of the most risk-significant functions with proposed RICTs to verify that such diverse means exists).

The LAR includes an evaluation to address the above; however, this evaluation is missing the table (typically supplied in TSTF-505 LARs) which systematically demonstrates, for each event in UFSAR Chapter 15 (that is mitigated by I&C subject to RICT), the credited means and the diverse means to initiate the protective function. Please provide this table for discussion during the audit.

TVA Response The requested table is provided below. It tabulates the instrumentation functions that are proposed for a RICT, the Updated Final Safety Analysis (UFSAR) Chapter 15 events they are designed to provide protection for and provides which primary RTS and ESFAS instrumentation functions can provide diverse protection. The results of this table are based on a review of the TS Bases, and Chapters 7 and 15 of the WBN UFSAR. While the functions in the right-hand column represent a diverse means of performing the protective action, they are not necessarily analyzed as providing equivalent protection. This table should be considered additive to LAR, Section 4.

RICT Function UFSAR Chapter 15 Event Diverse Functions RTS Instrumentation

1. Manual Reactor Trip Available for all events requiring a reactor trip N/A 2.a Power Range Neutron Flux - High Uncontrolled Rod Cluster Control Assembly Bank Withdrawal from a Subcritical Condition Power Range Neutron Flux - Low Power Range Neutron Flux Rate - High Intermediate Range Neutron Flux Source Range Neutron Flux Manual Reactor Trip CNL-25-098 E1 9 of 17 RICT Function UFSAR Chapter 15 Event Diverse Functions Uncontrolled Rod Cluster Control Assembly Bank Withdrawal at Power Overtemperature T Overpower T Pressurizer Pressure - High Pressurizer Water Level - High Manual Reactor Trip Excessive Heat Removal Due to Feedwater System Malfunctions Power Range Neutron Flux - Low Overtemperature T Overpower T Source Range High Neutron Flux Trip Manual Reactor Trip Excessive Load Increase Incident Overtemperature T Overpower T Pressurizer Pressure - Low Manual Reactor Trip Rupture of a Control Drive mechanism Housing (Rod Cluster Control Assembly Ejection)

Power Range Neutron Flux - Low Power Range Neutron Flux Rate - High Positive Rate Manual Reactor Trip 2.b Power Range Neutron Flux - Low Uncontrolled Rod Cluster Control Assembly Bank Withdrawal from a Subcritical Condition Power Range Neutron Flux - High Power Range Neutron Flux Rate - High Intermediate Range Neutron Flux Source Range Neutron Flux Manual Reactor Trip Excessive Heat Removal Due to Feedwater System Malfunctions Power Range Neutron Flux - High Overtemperature T Overpower T Source Range High Neutron Flux Trip Manual Reactor Trip Rupture of a Control Drive mechanism Housing (Rod Cluster Control Assembly Ejection)

Power Range Neutron Flux - High Power Range Neutron Flux Rate - High Positive Rate Manual Reactor Trip 3.a Power Range Neutron Flux Rate -

High Positive Rate Uncontrolled Rod Cluster Control Assembly Bank Withdrawal from a Subcritical Condition Power Range Neutron Flux - High Power Range Neutron Flux -Low Intermediate Range Neutron Flux Source Range Neutron Flux Manual Reactor Trip Rupture of a Control Drive mechanism Housing (Rod Cluster Control Assembly Ejection)

Power Range Neutron Flux - High Power Range Neutron Flux - Low Manual Reactor Trip

6. Overtemperature T

Uncontrolled Rod Cluster Control Assembly Bank Withdrawal at Power Power Range Neutron Flux - High Overpower T Pressurizer Pressure - High Pressurizer Water Level - High Manual Reactor Trip CNL-25-098 E1 10 of 17 RICT Function UFSAR Chapter 15 Event Diverse Functions Uncontrolled Boron Dilution Source Range Neutron Flux - High Manual Reactor Trip Loss of External Electrical Load and/or Turbine Trip Pressurizer Pressure - High Pressurizer Water Level - High Steam Generator Water Level - Low Low Turbine Trip Manual Reactor Trip Excessive Load Increase Power Range Neutron Flux - High Over Power T Trip Pressurizer Pressure - Low Manual Reactor Trip Major Rupture of a Main Feedwater Pipe (Unit 1)

Pressurizer Pressure - Low Pressurizer Pressure - High Pressurizer Water Level - High Steam Generator Water Level - Low Low Safety Injection Signal Actuation Trip Manual Reactor Trip Excessive Heat Removal Due to Feedwater System Malfunctions Power Range Neutron Flux - High Power Range Neutron Flux - Low Overpower T Source Range High Neutron Flux Trip Manual Reactor Trip Single Rod Cluster Control Assembly Withdrawal at Full Power Manual Reactor Trip Steam Generator Tube Rupture Pressurizer Pressure - Low Manual Reactor Trip Accidental Depressurization of the Reactor Coolant System Pressurizer Pressure - Low Manual Reactor Trip

7. Overpower T Uncontrolled Rod Cluster Control Assembly Bank Withdrawal at Power Overtemperature T Power Range Neutron Flux - High Pressurizer Pressure - High Pressurizer Water Level - High Manual Reactor Trip Excessive Heat Removal Due to Feedwater System Malfunctions Power Range neutron Flux - High Power Range Neutron Flux - Low Overtemperature T Source Range High Neutron Flux Trip Manual Reactor Trip Accidental Depressurization of the Main Steam System Pressurizer Pressure - Low Safety Injection Signal Actuation Trip Manual Reactor Trip CNL-25-098 E1 11 of 17 RICT Function UFSAR Chapter 15 Event Diverse Functions Excessive Load Increase Power Range Neutron Flux - High Over Temperature T Trip Pressurizer Pressure - Low Manual Reactor Trip Major Rupture of a Main Steam Line Pressurizer Pressure - Low Safety Injection Signal Actuation Trip Manual Reactor Trip 8.a Pressurizer Pressure - Low Excessive Load Increase Power Range Neutron Flux - High Over Temperature T Trip Overpower T Trip Manual Reactor Trip Accidental Depressurization of the Reactor Coolant System Over Temperature T Trip Manual Reactor Trip Accidental Depressurization of the Main Steam System Overpower T Safety Injection Signal Actuation Trip Manual Reactor Trip Inadvertent Operation of Emergency Core Cooling System Manual Reactor Trip Loss of Reactor Coolant from Small Ruptured Pipes or From Cracks in Large Pipes Which Actuate ECCS Manual Reactor Trip Major Reactor Coolant Pipe Ruptures (LOCA)

Manual Reactor Trip Major Rupture of a Main Steam Line Overpower T Safety Injection Signal Actuation Trip Manual Reactor Trip Major Rupture of a Main Feedwater Pipe Over Temperature T (Unit 1)

Pressurizer Pressure - High Pressurizer Water Level - High Steam Generator Water Level - Low Low Safety Injection Signal Actuation Trip Manual Reactor Trip Steam Generator Tube Rupture Over Temperature T Manual Reactor Trip 8.b Pressurizer Pressure - High Uncontrolled Rod Cluster Control Assembly Bank Withdrawal at Power Overtemperature T Power Range Neutron Flux - High Overpower T Pressurizer Water Level - High Manual Reactor Trip CNL-25-098 E1 12 of 17 RICT Function UFSAR Chapter 15 Event Diverse Functions Loss of External Electrical Load and/or Turbine Trip Overtemperature T Pressurizer Water Level - High Steam Generator Water Level - Low Low Turbine Trip Manual Reactor Trip Major Rupture of a Main Feedwater Pipe Over Temperature T (Unit 1)

Pressurizer Pressure - Low Pressurizer Water Level - High Steam Generator Water Level - Low Low Safety Injection Signal Actuation Trip Manual Reactor Trip

9. Pressurizer Water Level - High Uncontrolled Rod Cluster Control Assembly Bank Withdrawal at Power Overtemperature T Power Range Neutron Flux - High Overpower T Pressurizer Pressure - High Manual Reactor Trip Loss of External Electrical Load and/or Turbine Trip Overtemperature T Pressurizer Pressure - High Steam Generator Water Level - Low Low Turbine Trip Manual Reactor Trip Major Rupture of a Main Feedwater Pipe Over Temperature T (Unit 1)

Pressurizer Pressure - Low Pressurizer Pressure - High Steam Generator Water Level - Low Low Safety Injection Signal Actuation Trip Manual Reactor Trip

10. Reactor Coolant Flow - Low Partial Loss of Forced Reactor Coolant Flow Undervoltage RCPs Underfrequency RCPs Manual Reactor Trip Complete Loss of Forced Reactor Coolant Flow Undervoltage RCSs Underfrequency RCPs Manual Reactor Trip Reactor Coolant Pump Locked Rotor Manual Reactor Trip

11. Undervoltage RCPs Complete Loss of Forced Reactor Coolant Flow Reactor Coolant Flow - Low Underfrequency RCPs Manual Reactor Trip Partial Loss of Forced Reactor Coolant Flow Reactor Coolant Flow - Low Underfrequency RCPs Manual Reactor Trip

12. Underfrequency RCPs Complete Loss of Forced Reactor Coolant Flow Reactor Coolant Flow - Low Undervoltage RCPs Manual Reactor Trip Partial Loss of Forced Reactor Coolant Flow Reactor Coolant Flow - Low Undervoltage RCPs Manual Reactor Trip CNL-25-098 E1 13 of 17 RICT Function UFSAR Chapter 15 Event Diverse Functions 14.a/b Turbine Trip

- Low Fluid Oil Pressure/Turbine Stop Valve Closure Loss of External Electrical Load and/or Turbine Trip Pressurizer Pressure - High Overtemperature T Pressurizer Water Level - High Steam Generator Water Level - Low Low Manual Reactor Trip

15. SI Input from ESFAS Accidental Depressurization of the Main Steam System Overpower T Pressurizer Pressure - Low Manual Reactor Trip Major Rupture of a Main Steam Line Overpower T Pressurizer Pressure - Low Manual Reactor Trip Major Rupture of a Main Feedwater Pipe Over Temperature T (Unit 1)

Pressurizer Pressure - Low Pressurizer Pressure - High Steam Generator Water Level - Low Low Pressurizer Water Level - High Manual Reactor Trip

17. Reactor Trip Breakers N/A - This function is a design feature of the RTS system required for operability in support of any trip signal.

N/A

18. Reactor Trip Breaker Undervoltage and Shunt Trip Mechanisms N/A - This function is a design feature of the RTS system required for operability in support of any trip signal.

N/A

19. Automatic Trip Logic N/A - This function is a design feature of the RTS system required for operability in support of any trip signal.

N/A ESFAS Instrumentation 1.a Safety Injection Manual Initiation Design feature available for all accidents where SI is credited.

N/A 1.b Safety Injection Automatic Actuation Logic and Actuation Relays Design feature available for all accidents where SI is credited.

N/A 1.c Safety Injection Containment Pressure - High Steam Line Break Inside Containment Pressurizer Pressure - Low Steam Line Pressure - Low Manual Initiation CNL-25-098 E1 14 of 17 RICT Function UFSAR Chapter 15 Event Diverse Functions Accidental Depressurization of Main Steam System Pressurizer Pressure - Low Steam Line Pressure - Low Manual Initiation Major Rupture of a Main Feedwater Line Steam Line Pressure - Low Pressurizer Pressure - Low Manual Initiaition Loss-of-Coolant Accident Pressurizer Pressure - Low Manual Initiation 1.d Safety Injection Pressurizer Pressure - Low Accidental Depressurization of Main Steam System Containment Pressure - High Steam Line Pressure - Low Manual Initiaition Accidental Depressurization of Reactor Coolant System Manual Initiation Major Rupture of a Main Feedwater Line Steam Line Pressure - Low Containment Pressure - High Manual Initiaition Steam Generator Tube Rupture Manual Initiation Steam Line Break Containment Pressure - High Steam Line Pressure - Low Manual Initiation Loss-of-Coolant Accident Containment Pressure - High Manual Initiation 1.e Safety Injection Steam Line Pressure - Low Accidental Depressurization of Main Steam System Containment Pressure - High Pressurizer Pressure - Low Manual Initiaition Major Rupture of a Main Feedwater Line Containment Pressure - High Pressurizer Pressure - Low Manual Initiaition Steam Line Break Pressurizer Pressure - Low Containment Pressure - High Manual Initiation 2.a Containment Spray Manual Initiation Design feature available for all accidents where Containment Spray is credited.

N/A 2.b Containment Spray Automatic Actuation Logic and Actuation Relays Design feature available for all accidents where Containment Spray is credited.

N/A 3.a/b.(1)

Containment Isolation Phase A/B Isolation - Manual Initiation Design feature available for all accidents where Containment Isolation is credited.

N/A CNL-25-098 E1 15 of 17 RICT Function UFSAR Chapter 15 Event Diverse Functions 3.a/b.(2)

Containment Isolation Phase A/B Isolation -

Automatic Actuation Logic and Actuation Relays Design feature available for all accidents where Containment Isolation is credited.

N/A 4.a. Steam Line Isolation - Manual Initiation Design feature available for all accidents where Steam Line Isolation is credited.

N/A 4.b. Steam Line Isolation -

Automatic Actuation Logic and Actuation Relays Design feature available for all accidents where Steam Line Isolation is credited.

N/A 4.d.(1) Steam Line Isolation Steam Line Pressure - Low Steam Line Break Containment Pressure - High High Steam Isolation Negative Rate - High Manual Initiation 4.d.(2) Steam Line Isolation Negative Rate - High Steam Line Break Containment Pressure - High High Steam Line Pressure - Low Manual Initiation 5.a Turbine Trip and Feedwater Isolation

- Automatic Actuation Logic and Actuation Relays Available for all accidents where Turbine Trip and Feedwater Isolation is credited.

N/A 5.b Turbine Trip and Feedwater Isolation

- SG Water Level -

High High Excessive Heat Removal Due to Feedwater System Malfunction Manual Initiation 5.d Turbine Trip and Feedwater Isolation

- North MSVV Room Water Level High Main Feedwater Line Break in North MSVV Room Manual initiation 5.e Turbine Trip and Feedwater Isolation

- South MSVV Room Water Level High Main Feedwater Line Break in the South MSVV Room Manual initiation 6.a Auxiliary Feedwater -

Automatic Actuation Logic and Actuation Relays Design feature available for all accidents where Auxiliary Feedwater is credited.

N/A CNL-25-098 E1 16 of 17 RICT Function UFSAR Chapter 15 Event Diverse Functions 6.b Auxiliary Feedwater SG Water Level - Low-Low Loss of Normal Feedwater Loss of Offsite Power Trip of All Main Feedwater Pumps SI Signal Manual Initiation Major Rupture of a Main Feedwater Line Loss of Offsite Power SI Signal Trip of All Main Feedwater Pumps Manual Initiation 6.d Auxiliary Feedwater - Loss of Offsite Power Loss of Non-Emergency AC Power to the Station Auxiliaries SG Water Level - Low Low Trip of All Main Feedwater Pumps SI Signal Manual Initiation Loss of Normal Feedwater SG Water Level - Low Low Trip of All Main Feedwater Pumps SI Signal Manual Initiation Major Rupture of a Main Feedwater Line SG Water Level - Low Low Trip of All Main Feedwater Pumps SI Signal Manual Initiation 6.f Auxiliary Feedwater -

Auxiliary Feedwater Pump Suction Transfer on Suction Pressure - Low Design feature available for all accidents where Auxiliary Feedwater is credited.

N/A 7.a Automatic Switchover to Containment Sump Automatic Actuation Logic and Actuation Relays Design feature available for all accidents where Automatic Switchover to Containment Sump is credited.

N/A 8.a ESFAS Interlocks Reactor Trip, P-4 Design feature available for all accidents where Reactor Trip is credited.

N/A Technical Specifications Branch (STSB) Audit Questions QUESTION 20 - Technical Specification 5.7.2.24 In attachment 4, cross reference table for TSTF-505, for the RICT program, page A4-10 of 10, it identifies it as Section 5.5.20 in the column of the table for WBN TS/RA. NRC staff notes that the RICT program for WBN is TS 5.7.2.24. NRC staff also notes that the Programs and Manuals CNL-25-098 E1 17 of 17 heading for WBN is listed as TS Section 5.5 in the table, when it is TS Section 5.7. Confirm and correct.

TVA Response TVA confirms that the Attachment 4 Programs and Manuals heading should be 5.7 for the RICT Program Description and that WBN TS/RA entry should be 5.7.2.24. This is revised in.

QUESTION 21 - Technical Specification 3.8.9 In attachment 5, cross reference table for TSTF-439, page A5-2 of 2, for TS 3.8.9 RA A.1, staff notes in the variation reference column that it refers to The WBN Condition B instead of The WBN Condition A. Confirm and correct, if needed.

TVA Response TVA confirms that the Attachment 5 Attachment 1 Variation Reference column entry for the first row under Distribution Systems - Operating should refer to WBN Condition A, not Condition B. This is revised in Enclosure 2.

QUESTION 22 - Technical Specification 3.6.8 In table E1-1, for 3.6.8 Condition B, for one containment region with no OPERABLE hydrogen ignitor, the DSC states one region without an operable ignitor. Should it say, one region with an operable ignitor?

TVA Response TVA confirms that the Design Success Criteria for TS 3.6.8 Condition B should be One region with an operable ignitor. This is revised in Enclosure 2.

QUESTION 23 - Technical Specification Bases B.1 In attachment 3, bases markup, B 3.3.2.B.1, B.2.1, and B.2.2 on page B 3.3-84, it shows removing actions B.2.1 and B.2.2 but the heading doesnt reflect this removal. Consider revising the heading to match the removal of these actions and reflecting only B.1 in the heading.

TVA Response TVA confirms that the heading to Bases Page B 3.3-84 should only have B.1 and that B.2.1, and B.2.2 should be deleted. This is revised in Enclosure 2.

CNL-25-098 Supplemental Changes to the LAR (13 pages)

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2024 and concluded in May of 2024. The final report of this FSPR concluded that 100 percent of the SRs reviewed met CC II or better and no new finding level F&Os were issued.

As a result of the closure review and the FSPR, the WBN FPRA model has no open finding level F&Os, does not utilize any methods that have not been peer reviewed, and all applicable SRs of the ASME standard are met at CC II or better.

5 Technical Acceptability of the Seismic PRA Model The March 2016 WBN Units 1 and 2 Seismic Probabilistic Risk Assessment (SPRA) was peer reviewed against the requirements of ASME/ANS RA-Sa-2009, the American Society of Mechanical Engineers (ASME)/American Nuclear Society (ANS) Probabilistic Risk Assessment (PRA) Standard.[7] This peer review was performed using the process defined in Nuclear Energy Institute (NEI) guidelines NEI-12-13.[] This peer review resulted in 74 finding level F&Os.

An F&O Closure Review Independent Assessment was performed on the WBN SPRA in April of 2017. The purpose was to perform an assessment in accordance with Appendix X of NEI 12-13 to review TVAs proposed close out of Finding level F&Os of record from the June 2019peer review (discussed above) against the ASME/ANS RA-Sa-2009 PRA Standard and toassess whether closure action resulted in a PRA upgrade.

Following completion of the Independent Assessment, all of the Finding level F&Os were closed and no longer considered applicable to the WBN SPRA. With the closure of all peer review findings, the SPRA model of record meets the requirements for PRA technical acceptability for this application. No upgrades were required as a part of the F&O closure review. No F&Os were generated during this review.

6 Credit for Flex Equipment in the PRA Models The WBN PRA Models (Internal Events and Internal Flooding, Fire, and Seismic) include the two 480V FLEX Diesel Generators (DGs) permanently installed on the Auxiliary Building roof, the two 6.9KV 3 MW FLEX DGs installed in the WBN FLEX Building and the associated ventilation and fuel supply systems. There are no automatic starts modeled for any of the FLEX DGs. The FLEX Diesels are only credited for station blackout conditions where there is adequate time to align the diesels to the corresponding safety-related boards.

The 480V FLEX DGs are installed with an integral protected day tank to provide a maximum of ten hours of operation before fuel makeup is required. Refueling of the 480V DG day tank is achieved using the fuel oil transfer pump taking suction from the seven day tank. The fuel for the 6.9KV 3 MW FLEX DGs is initially supplied from a day tank with makeup from the seven day tank via the fuel oil transfer pump. The 480V FLEX DGs are secured inside rooms located on the AB roof where the maximum calculated temperature with the DGs on standby is within the design temperature.

Therefore, no ventilation is modeled for the 480V FLEX DGs.

The FLEX Building ventilation system is capable of adequate cooling of the 6.9KV 3MW FLEX DG radiators and other skid mounted equipment. The sliding door is required to be open when a 6.9KV FLEX DG is running to allow sufficient supply of aspirating and cooling air. Airflow through the FLEX Building to support 6.9KV FLEX DG operation is provided by the DG radiator fans and exhaust fans.

Operator actions to start and maintain (including refueling) the DGs are included in the PRA models.

The WBN PRA models do not credit portable FLEX equipment for core damage or release mitigation.

CNL-25-001 E24 of 7 CNL-25-098 E2-1 of 13 RA-Sb-2013

Reference:

Response to Question 10

Table E1-1: In Scope TS/LCO Conditions to Corresponding PRA Functions TS LCO/Condition SSCs Covered by TS LCO Condition SSCs Modeled in PRA?

Function Required by TS LCO Condition Design Success Criteria PRA Success Criteria Other Comments TS 3.8.9, Distribution System - Operating Two independent trains each consisting of Two 6.9 kV Shutdown Boards and four 480 V Shutdown Boards Yes Supply required AC electrical power to required loads One train of AC electrical power distribution (one Unit 1 6.9 kV shutdown board, one Unit 2 6.9 kV shutdown board, and associated 480 V shutdown boards)

Same as design criteria SSCs are modeled consistent with the TS scope and can be directly included in the CRMP tool for the RICT program.

(Unit 1 Only)

Condition A One or more AC electrical power distribution subsystems inoperable due to one or more Unit 1 AC shutdown boards inoperable.

(Unit 2 Only)

Condition A One or more AC electrical power distribution subsystems inoperable due to one or more Unit 2 AC shutdown boards inoperable CNL-25-098 E2-2 of 13 (Unit 2 Only)

Condition A One or more AC electrical power distribution subsystems inoperable due to one or more Unit 2 AC shutdown boards inoperable Unit 1 Only)

Added

Reference:

Response to Question 13 each

Table E1-1: In Scope TS/LCO Conditions to Corresponding PRA Functions TS LCO/Condition SSCs Covered by TS LCO Condition SSCs Modeled in PRA?

Function Required by TS LCO Condition Design Success Criteria PRA Success Criteria Other Comments TS 3.8.9, Distribution System - Operating Two independent trains consisting of Two Unit 1 120 V AC vital power boards and two Unit 2 120 V AC vital power boards Yes Supply required AC electrical power to required loads One train of AC electrical power distribution (one Unit 1 6.9 kV shutdown board, one Unit 2 6.9 kV shutdown board, and associated 480 V shutdown boards)

Same as design criteria SSCs are modeled consistent with the TS scope and can be directly included in the CRMP tool for the RICT program.

(Unit 1 Only)

Condition F Kne or more AC electrical power distribution subsystems inoperable due to one or more Unit 2 AC shutdown boards inoperable for reasons other than Condition E (Unit 2 Only)

Condition F Kne or more AC electrical power distribution subsystems inoperable due to one or more Unit 1 AC shutdown boards inoperable for reasons other than Condition E CNL-25-098 E2-3 of 13 (Unit 2 Only)

Condition F Kne or more AC electrical power distribution subsystems inoperable due to one or more Unit 1 AC shutdown boards inoperable for reasons other than Condition E

Reference:

Response to Question 13 Added (Unit 1 Only)

Table E1-3: Example RICT Calculations for Unit 2 TS LCO Condition RICT Estimate (Days) 3.8.9.A Distribution Systems - Operating - One or more AC electrical power distribution subsystems inoperable due to one or more Unit 2 AC shutdown boards inoperable 0.9 3.8.9.F Distribution Systems - Operating -One or more AC electrical power distribution subsystems inoperable due to one or more Unit 1 AC shutdown boards inoperable for reasons other than Condition E 15.9 CNL-25-098 E2-4 of 13 Revised

Reference:

Response to Question 13 Unit 2 Unit 1

Table E1-1: In Scope TS/LCO Conditions to Corresponding PRA Functions TS LCO/Condition SSCs Covered by TS LCO Condition SSCs Modeled in PRA?

Function Required by TS LCO Condition Design Success Criteria PRA Success Criteria Other Comments TS 3.8.1, AC Sources - Operating Condition E Two required offsite circuits inoperable Two qualified circuits between the offsite transmission network and the onsite 1E AC Electrical Power Distribution System.

Yes Provide power from offsite transmission network to onsite Class 1 buses Two DGs of the same load group Same as design criteria SSCs are modeled consistent with the TS scope and can be directly included in the CRMP tool for the RICT program.

CNL-25-098 E2-5 of 13 Two DGs of the same load group Revised

Reference:

Response to Question 15

Table E1-1: In Scope TS/LCO Conditions to Corresponding PRA Functions TS LCO/Condition SSCs Covered by TS LCO Condition SSCs Modeled in PRA?

Function Required by TS LCO Condition Design Success Criteria PRA Success Criteria Other Comments TS 3.8.4, DC Sources - Operating Condition A Operating - One or two required vital battery charger(s) on one subsystem inoperable Eight battery chargers (including one primary charger for each vital battery board and two pairs of spare chargers)

Yes Ensure availability of required DC power to shut down the reactor and maintain it in a safe condition One vital DC electrical power Train A (channels I and III for Unit 1 or channels II and IV for Unit 2) or Train B (channels II and IV for Unit 1 or (channels I and III for Unit 2) with each channel having one vital battery charger (2 vital battery chargers total)

Same as design criteria SSCs are modeled consistent with the TS scope and can be directly included in the CRMP tool for the RICT program.

CNL-25-098 E2-6 of 13 Eight battery chargers (including one primary charger for each vital battery board and two pairs of spare chargers)

One vital DC electrical power Train A (channels I and III for Unit 1 or channels II and IV for Unit 2) or Train B (channels II and IV for Unit 1 or (channels I and III for Unit 2) with each channel having one vital battery charger (2 vital battery chargers total)

Reference:

Response to Question 16 Revised

Table E1-1: In Scope TS/LCO Conditions to Corresponding PRA Functions TS LCO/Condition SSCs Covered by TS LCO Condition SSCs Modeled in PRA?

Function Required by TS LCO Condition Design Success Criteria PRA Success Criteria Other Comments Condition B One vital DC electrical power subsystem inoperable for reasons other than Condition A The vital 125 VDC system is divided into 4 channels and consists of four lead-acid-calcium batteries, four distribution boards, battery racks, and the required cabling, instrumentation and protective features.

(Channels I and III are associated with Train A and Channels II and IV are associated with Train B)

Yes Ensure availability of required DC power to shut down the reactor and maintain it in a safe condition Two 125 V vital battery boards on the same load group are capable of providing power to its associated loads Same as design criteria SSCs are modeled consistent with the TS scope and can be directly included in the CRMP tool for the RICT program.

CNL-25-098 E2-7 of 13 The vital 125 VDC system is divided into 4 channels and consists of four lead-acid-calcium batteries, four distribution boards, battery racks, and the required cabling, instrumentation and protective features.

(Channels I and III are associated with Train A and Channels II and IV are associated with Train B)

Reference - Response to Question 16 Revised Two 125 V vital battery boards on the same load group are capable of providing power to its associated loads

Table E1-1: In Scope TS/LCO Conditions to Corresponding PRA Functions TS LCO/Condition SSCs Covered by TS LCO Condition SSCs Modeled in PRA?

Function Required by TS LCO Condition Design Success Criteria PRA Success Criteria Other Comments TS 3.8.4, DC Sources - Operating Condition D One or two DG DC battery charger(s) on one train inoperable Four DG DC dual battery charger assemblies.

Yes Ensure availability of required DC power to shut down the reactor and maintain it in a safe condition One of the two battery chargers in each dual battery charger assembly is required to support the associated DG for one load group.

Same as design criteria SSCs are modeled consistent with the TS scope and can be directly included in the CRMP tool for the RICT program.

Condition E One DG DC train inoperable for conditions other than Condition D Four DG battery subsystems, one per DG. Each subsystem includes a

battery, distribution center, cabling, and cable ways.

The battery chargers are covered by Condition D.

Yes Ensure availability of required DC power to shut down the reactor and maintain it in a safe condition Control power is provided for one load group.

Same as design criteria SSCs are modeled consistent with the TS scope and can be directly included in the CRMP tool for the RICT program.

CNL-25-098 E2-8 of 13

Reference:

Response to Question 17 Revised Four DG DC dual battery charger assemblies.

One of the two battery chargers in each dual battery charger assembly is required to support the associated DG for one load group.

Four DG battery subsystems, one per DG. Each subsystem includes a

battery, distribution center, cabling, and cable ways.

The battery chargers are covered by Condition D.

Control power is provided for one load group.

Table E1-1: In Scope TS/LCO Conditions to Corresponding PRA Functions TS LCO/Condition SSCs Covered by TS LCO Condition SSCs Modeled in PRA?

Function Required by TS LCO Condition Design Success Criteria PRA Success Criteria Other Comments TS 3.8.7, Inverters - Operating Condition A One inverter in one channel inoperable.

Two unit inverters and one spare inverter per channel, each capable of supplying its associated AC vital instrument power boards, with 12 total inverters Yes Provide reliable AC power to vital instrument power boards Two inverters powering two 120V AC vital instrument power boards for one load group.

Same as design criteria SSCs are modeled consistent with the TS scope and can be directly included in the CRMP tool for the RICT program.

CNL-25-098 E2-9 of 13 Two inverters powering two 120V AC vital instrument power boards for one load group.

Revised

Reference:

Response to Question 18 CNL-25-001 A4-10 of 10 TSTF-505 TS Section Title/

Section/

Condition Description TSTF-505 TS/RA WBN TS/RA Disposition Justification Inverters - Operating 3.8.7 3.8.7 A. One [required] inverter inoperable.

A.1 A.1 Added RICT to RA A.1 WBN Condition wording is slightly different than STS (see AV-1)

Distribution Systems -

Operating 3.8.9 3.8.9 A. One or more AC electrical power distribution subsystems inoperable.

A.1 A.1 Added RICT to RA A.1 WBN Condition A is comparable to STS Condition A although the wording is different (see AV-1).

B. One or more AC vital buses inoperable.

B.1 B.1 Added RICT to RA B.1 WBN Condition and RA wording is slightly different from STS (see AV-1).

C. One or more DC electrical power distribution subsystems inoperable.

C.1 D.1 Added RICT to RA D.1 WBN Condition D and RA D.1 is comparable to STS Condition C although the wording is different (see AV-1).

N/A N/A F.1 Added RICT to RA F.1 No analogous STS Condition (see TV-5)

Programs and Manuals 5.5 5.5 Risk Informed Completion Time Program 5.5.18 5.5.20 Added Program Description TS numeric difference between STS and WBN (see AV-1). Revised paragraph e from PRA methods used to support this license amendment to PRA methods approved for use with this program. (see AV-14)

CNL-25-098 E2-10 of 13 Change to "5.7" Change to 5.7.2.24

Reference:

Response

to Question 20 CNL-25-001 A5-2 of 2 TSTF-439-A NUREG-1431 Affected TS TSTF-439-A Action WBN Disposition Variation Reference AC Sources - Operating 3.8.1 3.8.1 A. One [required] offsite circuit inoperable.

Deleted second CT from RA A.3.

Deleted second CT from RA A.3.

No variation B. One [required] DG inoperable.

Deleted second CT from RA B.4.

N/A Deleted second CT from RA B.5.

Deleted second CT from RA C.4 Administrative Variation - The WBN and NUREG-1431 RAs are numbered differently but have the same content.

Administrative Variation - WBN TS 3.8.1 contains Condition C, Two DGs in Train A inoperable OR Two DGs in Train B inoperable.

WBN TS LCO 3.8.1 - b requires four Operable DGs. This is based on WBN being a two-unit site. The DGs are organized as Train A (which contains one WBN Unit 1 DG and one WBN Unit 2 DG) and Train B (which contains one WBN Unit 1 DG and one WBN Unit 2 DG). STS is based on a single unit reference plant.

Accordingly, STS RA B.4 is functionally equivalent to WBN RA C.4 in that there will only be a maximum of one DG inoperable in each unit.

Distribution Systems -

Operating 3.8.9 3.8.9 A. One or more AC electrical power distribution subsystems inoperable.

Deleted second CT from RA A.1.

Deleted second CT from RA A.1.

Administrative Variation - The WBN Condition B is worded differently from NUREG-1431, but deletion of the second CT is equally applicable.

B. One or more AC vital buses inoperable.

Deleted second CT from RA B.1.

Deleted second CT from RA B.1.

Administrative Variation - The WBN Condition B is worded slightly differently from NUREG-1431, but the deletion of the second CT is equally applicable.

C. One or more DC electrical power distribution subsystems inoperable.

Deleted second CT from RA C.1.

Deleted second CT from RA D.1.

Administrative Variation - The WBN Condition D is worded slightly differently from NUREG-1431, and the RAs are numbered differently, but the deletion of the second CT is equally applicable.

CNL-25-098 E2-11 of 13 Should be "Condition A"

Reference:

Response to Question 21 CNL-21-026 E1-17 of 3

Table E1-1: In Scope TS/LCO Conditions to Corresponding PRA Functions TS Condition TS Condition Description SSCs Covered by TS LCO Condition SSCs Modeled in PRA?

Function Required by TS LCO Condition Design Success Criteria PRA Success Criteria Other Comments 3.6.8.B HMS - One containment region with no OPERABLE hydrogen ignitor.

Two HMS trains with ignitors Yes Controlled burn of hydrogen to prevent buildup following a degraded core accident One region without an operable ignitor One of two trains Individual regions are not modeled in the PRA. Loss of both HMS trains used as a conservative surrogate.

3.6.11.A Air Return System (ARS)

- One ARS train inoperable Two ARS 100%

capacity trains Yes Rapid return of air from upper to lower containment compartment after initial blowdown following a DBA One ARS train Same as design criteria 3.7.2.A MSIVs - One MSIV inoperable in Mode 1 MSIVs Yes Isolate Main Steam Lines One MSIV closure per steam generator Same as design criteria 3.7.5.A AFW System -

Turbine driven AFW train inoperable due to one inoperable steam supply OR One turbine driven AFW pump inoperable in MODE 3 Turbine Driven AFW Train (valves, flowpath, pump)

Yes Supply feedwater to SGs to remove decay heat from the RCS One train of AFW Same as design criteria CNL-25-098 E2-12 of 13 Should read "with" an operable ignitor

Reference:

Response to Question 22

ESFAS Instrumentation B 3.3.2 BASES (continued)

Watts Bar-Unit 1 B 3.3-84 Revision 200 ACTIONS B.1, B.2.1 and B.2.2 (continued)

Condition B applies to manual initiation of:

x SI; x

Containment Spray; x

Phase A Isolation; and x

Phase B Isolation.

Condition B also applies to the Auxiliary Feedwater Pump Suction Transfer on Suction Pressure - Low.

For the manual initiation Functions, this action addresses the train orientation of the SSPS for the functions listed above. For the AFW System pump suction transfer channels, this action recognizes that placing a failed channel in trip during operation is not necessarily a conservative action. Spurious trip of this function could align the AFW System to a source that is not immediately capable of supporting pump suction. If a channel or train is inoperable, 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> is allowed to return it to an OPERABLE status. Note that for containment spray and Phase B isolation, failure of one or both channels in one train renders the train inoperable. Condition B, therefore, encompasses both situations.

For the manual initiation Functions, the specified Completion Time is reasonable considering that there are two automatic actuation trains and another manual initiation train OPERABLE for each Function, and the low probability of an event occurring during this interval. For the AFW System pump suction transfer channels, the specified Completion Time is reasonable considering the nature of this Function, the available redundancy, and the low probability of an event occurring during this interval. If the channel or train cannot be restored to OPERABLE status, the plant must be placed in a MODE in which the LCO does not apply.

This is done by placing the plant in at least MODE 3 within an additional 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> (54 hours6.25e-4 days <br />0.015 hours <br />8.928571e-5 weeks <br />2.0547e-5 months <br /> total time) and in MODE 5 within an additional 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> (84 hours9.722222e-4 days <br />0.0233 hours <br />1.388889e-4 weeks <br />3.1962e-5 months <br /> total time). The allowable Completion Times are reasonable, based on operating experience, to reach the required plant conditions from full power conditions in an orderly manner and without challenging plant systems. For the AFW System pump suction transfer channels, aligning the RHR System for decay heat removal, so that the steam generators are not relied on for heat removal, places the plant in a MODE in which the LCO no longer applies. Therefore, per LCO 3.0.2, completion of the Required Action to place the unit in MODE 5 is not required.

Alternatively, a Completion Time can be determined in accordance with the Risk Informed Completion Time Program.

CNL-25-098 E2-13 of 13 Delete ", B.2.1 and B.2.2" B.1, B.2.1 and B.2.2 B.1, B.2.1 and B.2.2 B.1, B.2.1 and B.2.2

Reference:

Response to Question 23