ML25324A367

Issuance of Amendment Nos. 254 and 256 Revision to Technical Specification 3.8.1 Using Risk-Informed Process for Evaluations

ML25324A367
Person / Time
Site:	Diablo Canyon
Issue date:	12/02/2025
From:	Samson Lee NRC/NRR/DORL/LPL4
To:	Gerfen P Pacific Gas & Electric Co
Lee S, 301-415-3158
References
EPID L-2025-LLA-0124 TS 3.8.1
Download: ML25324A367 (0)

Text

December 2, 2025 Ms. Paula Gerfen Senior Vice President, Generation and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 56, Mail Code 104/6 Avila Beach, CA 93424

SUBJECT:

DIABLO CANYON NUCLEAR POWER PLANT, UNITS 1 AND 2 - ISSUANCE OF AMENDMENT NOS. 254 AND 256 RE: REVISION TO TECHNICAL SPECIFICATION 3.8.1 USING RISK-INFORMED PROCESS FOR EVALUATIONS (EPID L-2025-LLA-0124)

Dear Ms. Gerfen:

The U.S. Nuclear Regulatory Commission (the Commission) has issued the enclosed Amendment No. 254 to Facility Operating License No. DPR-80 and Amendment No. 256 to Facility Operating License No. DPR-82 for the Diablo Canyon Nuclear Power Plant, Units 1 and 2, respectively. The amendments consist of changes to the Technical Specifications (TSs) in response to your application dated July 31, 2025.

The amendments revise TS 3.8.1, AC [Alternate Current] Sources - Operating, using the Risk-Informed Process for Evaluations (RIPE). Specifically, the revision adds an associated completion time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> that is applicable only to specific plant conditions.

A copy of the related Safety Evaluation is enclosed. Notice of Issuance will be included in the Commissions monthly Federal Register notice.

Sincerely,

/RA/

Samson S. Lee, Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323

Enclosures:

1. Amendment No. 254 to DPR-80

2. Amendment No. 256 to DPR-82

3. Safety Evaluation cc: Listserv

PACIFIC GAS AND ELECTRIC COMPANY DOCKET NO. 50-275 DIABLO CANYON NUCLEAR POWER PLANT, UNIT 1 AMENDMENT TO FACILITY OPERATING LICENSE Amendment No. 254 License No. DPR-80

1.

The Nuclear Regulatory Commission (the Commission) has found that:

A.

The application for amendment by Pacific Gas and Electric Company (the licensee), dated July 31, 2025, complies with the standards and requirements of the Atomic Energy Act of 1954, as amended (the Act), and the Commissions rules and regulations set forth in 10 CFR Chapter I; B.

The facility will operate in conformity with the application, the provisions of the Act, and the rules and regulations of the Commission; C.

There is reasonable assurance (i) that the activities authorized by this amendment can be conducted without endangering the health and safety of the public, and (ii) that such activities will be conducted in compliance with the Commissions regulations; D.

The issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public; and E.

The issuance of this amendment is in accordance with 10 CFR Part 51 of the Commissions regulations and all applicable requirements have been satisfied.

2.

Accordingly, the license is amended by changes to the Technical Specifications as indicated in the attachment to this license amendment, and paragraph 2.C.(2) of Facility Operating License No. DPR-80 is hereby amended to read as follows:

(2)

Technical Specifications The Technical Specifications contained in Appendix A and the Environmental Protection Plan contained in Appendix B, as revised through Amendment No. 254 are hereby incorporated in the license. Pacific Gas & Electric Company shall operate the facility in accordance with the Technical Specifications and the Environmental Protection Plan, except where otherwise stated in specific license conditions.

3.

This license amendment is effective as of its date of issuance and shall be implemented within 120 days of the date of issuance.

FOR THE NUCLEAR REGULATORY COMMISSION Tony Nakanishi, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

Attachment:

Changes to Facility Operating License No. DPR-80 and the Technical Specifications Date of Issuance: December 2, 2025 TONY NAKANISHI Digitally signed by TONY NAKANISHI Date: 2025.12.02 12:43:36 -05'00'

PACIFIC GAS AND ELECTRIC COMPANY DOCKET NO. 50-323 DIABLO CANYON NUCLEAR POWER PLANT, UNIT 2 AMENDMENT TO FACILITY OPERATING LICENSE Amendment No. 256 License No. DPR-82

1.

The Nuclear Regulatory Commission (the Commission) has found that:

A.

The application for amendment by Pacific Gas and Electric Company (the licensee), dated July 31, 2025, complies with the standards and requirements of the Atomic Energy Act of 1954, as amended (the Act), and the Commissions rules and regulations set forth in 10 CFR Chapter I; B.

The facility will operate in conformity with the application, the provisions of the Act, and the rules and regulations of the Commission; C.

There is reasonable assurance (i) that the activities authorized by this amendment can be conducted without endangering the health and safety of the public, and (ii) that such activities will be conducted in compliance with the Commissions regulations; D.

The issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public; and E.

The issuance of this amendment is in accordance with 10 CFR Part 51 of the Commissions regulations and all applicable requirements have been satisfied.

2.

Accordingly, the license is amended by changes to the Technical Specifications as indicated in the attachment to this license amendment, and paragraph 2.C.(2) of Facility Operating License No. DPR-82 is hereby amended to read as follows:

(2)

Technical Specifications (SSER 32, Section 8)* and Environmental Protection Plan The Technical Specifications contained in Appendix A and the Environmental Protection Plan contained in Appendix B, as revised through Amendment No. 256, are hereby incorporated in the license. Pacific Gas & Electric Company shall operate the facility in accordance with the Technical Specifications and the Environmental Protection Plan, except where otherwise stated in specific license conditions.

3.

This license amendment is effective as of its date of issuance and shall be implemented within 120 days of the date of issuance.

FOR THE NUCLEAR REGULATORY COMMISSION Tony Nakanishi, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

Attachment:

Changes to Facility Operating License No. DPR-82 and the Technical Specifications Date of Issuance: December 2, 2025 TONY NAKANISHI Digitally signed by TONY NAKANISHI Date: 2025.12.02 12:44:02 -05'00'

ATTACHMENT TO LICENSE AMENDMENT NO. 254 TO FACILITY OPERATING LICENSE NO. DPR-80 AND LICENSE AMENDMENT NO. 256 TO FACILITY OPERATING LICENSE NO. DPR-82 DIABLO CANYON NUCLEAR POWER PLANT, UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50-323 Replace the following pages of the Facility Operating License Nos. DPR-80 and DPR-82, and Appendix A Technical Specifications with the attached revised pages. The revised pages are identified by amendment number and contain marginal lines indicating the areas of change.

Facility Operating License No. DPR-80 REMOVE INSERT 3

3 Facility Operating License No. DPR-82 REMOVE INSERT 3

3 Technical Specifications REMOVE INSERT 3.8-2 3.8-2 3.8-2a 3.8-2b

Amendment No. 254 (4)

Pursuant to the Act and 10 CFR Parts 30, 40, and 70, to receive, possess, and use in amounts as required any byproduct, source or special nuclear material without restriction to chemical or physical form, for sample analysis or instrument calibration or associated with radioactive apparatus or components; and (5)

Pursuant to the Act and 10 CFR Parts 30, 40, and 70, to possess, but not separate, such byproduct and special nuclear materials as may be produced by the operation of the facility.

C.

This License shall be deemed to contain and is subject to the conditions specified in the Commissions regulations set forth in 10 CFR Chapter I and is subject to all applicable provisions of the Act and to the rules, regulations, and orders of the Commission now or hereafter in effect; and is subject to the additional conditions specified or incorporated below:

(1)

Maximum Power Level The Pacific Gas and Electric Company is authorized to operate the facility at reactor core power levels not in excess of 3411 megawatts thermal (100% rated power) in accordance with the conditions specified herein.

(2)

Technical Specifications The Technical Specifications contained in Appendix A and the Environmental Protection Plan contained in Appendix B, as revised through Amendment No. 254 are hereby incorporated in the license.

Pacific Gas & Electric Company shall operate the facility in accordance with the Technical Specifications and the Environmental Protection Plan, except where otherwise stated in specific license conditions.

(3)

Initial Test Program The Pacific Gas and Electric Company shall conduct the post-fuel-loading initial test program (set forth in Section 14 of Pacific Gas and Electric Companys Final Safety Analysis Report, as amended), without making any major modifications of this program unless modifications have been identified and have received prior NRC approval. Major modifications are defined as:

a.

Elimination of any test identified in Section 14 of PG&Es Final Safety Analysis Report as amended as being essential;

Amendment No. 256 (4)

Pursuant to the Act and 10 CFR Parts 30, 40, and 70, to receive, possess, and use in amounts as required any byproduct, source or special nuclear material without restriction to chemical or physical form, for sample analysis or instrument calibration or associated with radioactive apparatus or components; and (5)

Pursuant to the Act and 10 CFR Parts 30, 40, and 70, to possess, but not separate, such byproduct and special nuclear materials as may be produced by the operation of the facility.

C.

This License shall be deemed to contain and is subject to the conditions specified in the Commissions regulations set forth in 10 CFR Chapter I and is subject to all applicable provisions of the Act and to the rules, regulations, and orders of the Commission now or hereafter in effect; and is subject to the additional conditions specified or incorporated below:

(1)

Maximum Power Level The Pacific Gas and Electric Company is authorized to operate the facility at reactor core power levels not in excess of 3411 megawatts thermal (100% rated power) in accordance with the conditions specified herein.

(2)

Technical Specifications (SSER 32, Section 8)* and Environmental Protection Plan The Technical Specifications contained in Appendix A and the Environmental Protection Plan contained in Appendix B, as revised through Amendment No. 256, are hereby incorporated in the license.

Pacific Gas & Electric Company shall operate the facility in accordance with the Technical Specifications and the Environmental Protection Plan, except where otherwise stated in specific license conditions.

(3)

Initial Test Program (SSER 31, Section 4.4.1)

Any changes to the Initial Test Program described in Section 14 of the FSAR made in accordance with the provisions of 10 CFR 50.59 shall be reported in accordance with 50.59(b) within one month of such change.

• The parenthetical notation following the title of many license conditions denotes the section of the Safety Evaluation Report and/or its supplements wherein the license condition is discussed.

AC Sources - Operating 3.8.1 DIABLO CANYON - UNITS 1 & 2 Rev 14 Page 2 of 37 Tab_3!8u3r14 TS retyped.doc 0717.1310 ACTIONS (continued)

CONDITION REQUIRED ACTION COMPLETION TIME B.

One DG inoperable.

B.1 Perform SR 3.8.1.1 for the required offsite circuit(s).

1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AND Once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter.

AND

---

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

In MODE 1, 2, and 3, TDAFW pump is considered a required redundant feature.

B.2 Declare required feature(s) supported by the inoperable DG inoperable when its required redundant feature(s) is inoperable.

4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> from discovery of Condition B concurrent with inoperability of redundant required feature(s).

AND OR (continued) 3.8-2 Unit 1 - Amendment No. 135,166,215,245, Unit 2 - Amendment No. 135,167,217,247, 254 256

AC Sources - Operating 3.8.1 DIABLO CANYON - UNITS 1 & 2 Rev 14 Page 3 of 37 Tab_3!8u3r14 TS retyped with amendment numbers.doc 1126.1229 ACTIONS (continued)

CONDITION REQUIRED ACTION COMPLETION TIME B. (continued)

---

NOTES---------

1. Only applicable to one Centrifugal Charging subsystem train, one Safety Injection subsystem train, one Residual Heat Removal subsystem train, one Containment Spray train, one CFCU system, one vital CCW loop (not including CCW heat exchanger), one ASW train, one CRVS train, one ABVS train, or one inverter inoperable.

2. Not applicable if a required offsite circuit is inoperable.

24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> from discovery of Condition B concurrent with inoperability of applicable redundant required feature(s).

(continued) 3.8-2a Unit 1 - Amendment No. 254 Unit 2 - Amendment No. 256

AC Sources - Operating 3.8.1 Tab_3!8u3r14 TS retyped with amendment numbers.doc 1126.1229 ACTIONS (continued)

CONDITION REQUIRED ACTION COMPLETION TIME B.

(continued)

B.3.1 Determine OPERABLE DG(s) is not inoperable due to common cause failure.

OR 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> B.3.2 Perform SR 3.8.1.2 for OPERABLE DG(s).

AND 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> B.4 Restore DG to OPERABLE status.

14 days OR In accordance with the RICT Program (continued)

DIABLO CANYON - UNITS 1 & 2 3.8-2b Rev 14 Page 4 of 37 Unit 1 - Amendment No. 254 Unit 2 - Amendment No. 256

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 254 TO FACILITY OPERATING LICENSE NO. DPR-80 AND AMENDMENT NO. 256 TO FACILITY OPERATING LICENSE NO. DPR-82 PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT, UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50-323

1.0 INTRODUCTION

By application dated July 31, 2025 (Reference 1), Pacific Gas and Electric Company (PG&E, the licensee) submitted a license amendment request (LAR) for Diablo Canyon Nuclear Power Plant, Units 1 and 2 (Diablo Canyon).

The proposed amendments would use the Risk-Informed Process for Evaluations (RIPE) to modify Technical Specification (TS) 3.8.1, AC [Alternating Current] Sources - Operating.

Specifically, the proposed change would modify Required Action B.2 of TS 3.8.1 to add an associated completion time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> that is applicable only to specific plant conditions.

2.0 REGULATORY EVALUATION

2.1 Background

The Diablo Canyon Class 1E AC electrical power distribution system ensures reliable power to safety systems (engineered safety features (ESF)) through redundant offsite and onsite power sources. The offsite power system sources consist of two 230-kilovolt (kV) and three 500-kV transmission lines that feed into 230-kV and 500-kV switchyards. These lines supply power to 4.16-kV ESF buses via auxiliary and standby startup transformers. The onsite power system consists of three load groups per unit, each with two offsite power connections and one dedicated diesel generator (DG). TS 3.8.1 requires two qualified offsite circuits, three DGs and two diesel fuel oil transfer system trains, be operable in Modes 1 through 4. TS 3.8.1 Required Action B.2 stipulates that within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, any safety-related feature dependent on an inoperable DG must be declared inoperable if its associated redundant feature on a separate Class 1E power distribution subsystem is also inoperable.

2.2 Proposed Change to TS 3.8.1 Required Action B.2 The proposed change to Diablo Canyon TS 3.8.1 Required Action B.2 establishes a new, separate 24-hour completion time applicable when one required DG is inoperable, and one applicable redundant required feature is concurrently inoperable. New NOTE 1 is added to Required Action B.2 that specifies the applicable redundant required features as follows:

one Centrifugal Charging subsystem train one Safety Injection subsystem train one Residual Heat Removal subsystem train one Containment Spray train one Containment Fan Cooler Unit (CFCU) system one vital Component Cooling Water (CCW) loop (excluding CCW heat exchanger) one Auxiliary Saltwater (ASW) train one Control Room Ventilation System (CRVS) train one Auxiliary Building Ventilation System (ABVS) train one Inverter The 24-hour completion time does not apply if more than one of the above systems is inoperable. In such cases, the existing 4-hour completion time remains in effect. In addition, new NOTE 2 to Required Action B.2 states that the 24-hour completion time is not applicable if a required offsite power circuit is inoperable.

2.3 Regulatory Requirements The regulations in Title 10 of the Code of Federal Regulations (10 CFR) Section 50.36, Technical specifications, state that the TSs will include items in five specific categories. These categories include: (1) safety limits, limiting safety system settings, and limiting control settings; (2) limiting conditions for operation (LCOs); (3) surveillance requirements; (4) design features; and (5) administrative controls. In particular, 10 CFR 50.36(c)(2)(i) states, in part:

Limiting conditions for operation are the lowest functional capability or performance levels of equipment required for safe operation of the facility. 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.

Section 4.1, Applicable Regulatory Requirements/Criteria, of the enclosure to the licensees LAR dated July 31, 2025 (Reference 1), describes that Diablo Canyon licensing basis includes 10 CFR Part 50, Appendix A General Design Criterion (GDC) 17, Electric power systems.

GDC 17 requires that both onsite and offsite electric power systems are provided to permit the functioning of structures, systems and components (SSCs) that are important to safety. Each power system must provide sufficient capacity and capability to assure that: (1) fuel design limits and reactor coolant pressure boundaries are not exceeded during operational events, and (2) core cooling, containment integrity, and other vital functions are maintained during accidents.

The onsite electric power system must have independence, redundancy, testability, and supported safety functions must perform assuming a single failure. The offsite electric power system must include two physically independent circuits from the transmission network. Power systems must minimize the risk of losing remaining power sources due to loss of the nuclear unit power, transmission network failure, or an onsite power supply failure.

2.4 Regulatory Guidance Diablo Canyon submitted the license amendment request for review under the U.S Nuclear Regulatory Commission (NRC, the Commission) Risk-Informed Process for Evaluations (RIPE).

Diablo Canyon stated that the process used for the amendment was consistent with the process described in NRCs Guidelines for Characterizing the Safety Impact of Issues, Revision 2 (Reference 2). The NRC has revised the RIPE guidance, and the current guidance can be found in the Safety Impact Characterization Guidance for Implementing the Risk-Informed Process for Evaluations, (SIC) Revision 3 (Reference 3). Revision 3 of the SIC relaxed the risk acceptance criteria and added a discussion on performance monitoring strategies, but no substantial changes were made to the process for determining the safety impact of a proposed change.

The Office of Nuclear Reactor Regulation (NRR) temporary staff guidance (TSG) document TSG-DORL-2021-01, Revision 4 (Reference 4) provides the framework and guidance for NRR staff to implement the streamlined processing of license amendment requests submitted under RIPE. Use of this guidance is limited to issues for which the safety impact associated with an issue addressed by a license amendment request can be modeled using probabilistic risk assessment (PRA). The NRCs review is streamlined in that RIPE is based on the application of pre-existing risk informed criteria that allow for review and disposition of the submittal with minimal resources.

RIPE, as described in the SIC, is available to licensees that have a technically-acceptable PRA and have established an integrated decisionmaking panel (IDP). For the purposes of RIPE, having a technically-acceptable PRA must be demonstrated by having an approved and implemented license amendment for Technical Specifications Task Force (TSTF) Traveler TSTF-505, Provide Risk-Informed Extended Completion Times - RITSTF [Risk-Informed TSTF] Initiative 4b (Reference 5) or TSTF-425, Relocate Surveillance Frequencies to Licensee Control - RITSTF Initiative 5b (Reference 6). Under RIPE, an IDP may be established by having an approved and implemented 10 CFR 50.69, Risk-informed categorization and treatment of structures, systems and components for nuclear power plants, amendment or by establishing a RIPE IDP, as documented in the Nuclear Energy Institute (NEI) guidance, NEI Guidelines for the Implementation of the Risk-Informed Process for Evaluations Integrated Decision-Making Panel (Reference 7). Licensees that have implemented an NRC-approved amendment to adopt TSTF-505 or TSTF-425 and have established an IDP can leverage these initiatives to perform safety impact characterizations using RIPE and request licensing actions with the expectation that the NRC will use a streamlined review process if the issue is characterized as having a minimal safety impact.

Changes made under RIPE are reviewed by NRC staff in a manner consistent with the principles of risk-informed decision-making (RIDM) outlined in Regulatory Guide (RG) 1.174, Revision 3, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis (Reference 8), which includes ensuring that the proposed change meets current regulations (unless an exemption is requested), is consistent with the defense-in-depth philosophy, maintains sufficient safety margins, is consistent with the Commissions Safety Goal Policy Statement, and includes performance monitoring strategies.

For RIPE, as described in the SIC, all the following must apply in order to characterize an issue as having a minimal safety impact:

The issue contributes less than 5 x 10-7/year to core damage frequency (CDF) except on a case-by-case basis, with justification; The issue contributes less than 5 x 10-8/year to large early release frequency (LERF) except on a case-by-case basis, with justification; The issue has no safety impact or minimal safety impact in accordance with the SIC; and Cumulative risk is assessed based on plant-specific CDF and LERF. Cumulative risk is acceptable for the purposes of this guidance if baseline risk remains less than 1 x 10-4/year for CDF and less than 1 x 10-5/year for LERF once the impact of the proposed change is incorporated into baseline risk.

The safety impact must be characterized as none or minimal for the submittal to qualify for the NRC streamlined RIPE review. In addition, the RIPE LAR must include defense-in-depth and safety margin considerations assessed by the IDP.

3.0 TECHNICAL EVALUATION

TS LCO 3.8.1 requires two qualified offsite circuits, three DGs, and two diesel fuel oil transfer system trains to be operable in Modes 1 through 4. TS 3.8.1 Condition B is in effect when one DG is inoperable. Required Action B.2 stipulates that within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, any safety-related feature dependent on an inoperable DG must be declared inoperable if its associated redundant feature on a separate Class 1E power distribution subsystem is also inoperable.

The proposed change would add Note 1 to TS 3.8.1 Required Action B.2 to establish a new completion time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> when one required DG is inoperable, and one specified applicable redundant required feature is concurrently inoperable. Section 2.3, Proposed Technical Specifications Changes, of the enclosure to the licensees LAR (Reference 1) identifies that the configuration resulting from one inoperable DG, and any one of the above specified inoperable features (listed in section 2.2 above), is a low-risk plant configuration. In particular, section 2.4, Reason for the Proposed Change, of the enclosure to the licensees submittal states that the Diablo Canyon PRA model for the CCW system credits the CCW loop independent of the CCW heat exchanger. This PRA modeling construct was adopted to preclude the higher risk configuration resulting from concurrent modeling of the CCW loop and the CCW heat exchanger.

In addition, NOTE 2 is added to Required Action B.2 prohibiting the allowance of the 24-hour completion time if a required offsite circuit is inoperable. This restriction on the proposed TS completion time extension precludes the possibility of redundant vital equipment, such as the 120-Volt (V) AC inverters, being inoperable for an extended period of time.

The NRC staff reviewed the licensees justification and determined that the proposed TS 3.8.1 Required Action B.2 completion time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> includes appropriate restrictions to preclude unacceptable inoperable equipment combinations and maintains low risk plant configurations.

The preceding sections of this safety evaluation confirm that the safety impact associated with the proposed change is minimal. Therefore, the NRC staff concludes that the proposed completion time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for the stipulated plant configurations is acceptable.

3.1 Conformance with RIPE Minimal Safety Impact Criteria The licensee considered the RIPE screening questions contained in sections 4.1 and 4.2 of the NRCs SIC Revision 2 (Reference 2), and concluded that the requested license amendments involve adverse safety impacts, but that these impacts had a minimal impact on safety. The RIPE screening questions are unchanged in the revised RIPE guidance in Safety Impact Characterization Guidance for Implementing the Risk-Informed Process for Evaluations, (SIC)

Revision 3 (Reference 3). Considerations for each of the five RIPE screening questions are discussed below.

3.1.1 Does the issue result in more than a minimal increase in the frequency of occurrence of a risk significant accident initiator or result in a new risk-significant accident initiator?

Enclosure attachment 1, Evaluation of Screening Impact, of the licensees submittal describes that under TS 3.8.1 Condition B, when one DG is inoperable:

Required Action B.1 mandates verification of the operability of the required offsite power circuit(s) within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> of entering the condition and at 8-hour intervals thereafter.

Required Action B.2 requires declaring the safety-related features supported by the inoperable DG as inoperable within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> if their redundant features are also inoperable.

Table A.1-1 in enclosure attachment 1 to the licensees LAR presents a list of accident initiator categories that were evaluated for risk significance. The licensee stated that inoperability of a single required DG does not constitute an accident initiator, as the DG serves an accident mitigation function. Furthermore, the required actions under Condition B do not necessitate a change in the units operating mode or condition. New accident initiators are not introduced nor is the likelihood of existing initiators increased with the proposed change to extend the TS 3.8.1 Required Action B.2 completion time from 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for the allowed component configurations. Therefore, the proposed change would not result in an adverse impact on the frequency of occurrence of an accident initiator or result in a new accident initiator. The NRC staff reviewed the licensees consideration of this screening element and agrees with the licensees conclusion of no adverse impact because the DG serves an accident mitigation role and not an initiator such that the inoperability of a single DG does not introduce new accident initiators or increase their frequency.

3.1.2 Does the issue result in a more than minimal decrease in the availability, reliability, or capability of SSCs or personnel relied upon to mitigate a risk significant transient, accident, or natural hazard?

The licensees review of this RIPE screening question in enclosure attachment 1 of the LAR determined that extending the completion time for TS 3.8.1 Required Action B.2 from 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> introduces the potential for a temporary reduction in the availability of SSCs relied upon to mitigate transients, accidents, or natural hazards while one DG is inoperable, particularly in Modes 1 and 2. This extension could increase the duration before a required Mode 3 entry or prolong the inoperability of a required feature, which may adversely affect the availability of the DGs or supported features during a design-basis accident (DBA). However, the proposed change does not alter the number of required operable DGs or their functional requirements, and the DGs remain fully automatic, requiring no short-term operator action. The change introduces no new operator actions, does not affect emergency operating procedures, and does not alter established response times. In the event of a loss of preferred power, the ESF loads are automatically transferred to the DGs in time to ensure safe shutdown and accident mitigation.

Although the extension could theoretically reduce SSC availability, the licensee stated that the impact is considered minimal due to the infrequency of entries into TS 3.8.1 Required Action B.2. The licensees review of plant operating history from 2008 to 2025 identified only three valid entries into this condition, resulting in a low annual frequency of 0.0882. These results support the conclusion that the proposed change has a minimal impact on overall plant safety. During entries into Required Action B.2, the required features remain powered by the operable offsite AC source, ensuring continued functionality and high reliability.

The NRC staff reviewed the licensees consideration of this screening element and concluded that the evaluation supported a conclusion of a not more than minimal adverse impact for this screening element. Given the automatic nature of the DGs, the absence of new operator actions, and the low historical frequency of TS 3.8.1 Required Action B.2 entries. The NRC staff concludes that the proposed extension does not result in more than a minimal decrease in the availability, reliability, or capability of SSCs or personnel relied upon to mitigate a transient, accident, or natural hazard.

3.1.3 Does the issue result in more than minimal increase in the consequences of a risk significant accident sequence?

The evaluation for adverse impact on the consequences of an accident sequence described in enclosure attachment 1 of the licensees LAR determined that the proposed TS changes do not result in a more than minimal increase in the consequences of a risk significant accident sequence because the assumptions and methodologies used of the accident dose consequences are not impacted by proposed change. The NRC staff reviewed the licensees consideration of this screening element and concluded that the determination of not more than minimal adverse impact is reasonable given that the Diablo Canyon TS LCO requirements remain unchanged, and dose consequences are unaffected.

3.1.4 Does the issue result in more than minimal decrease in the capability of a fission product barrier?

The licensees review of this RIPE screening question in enclosure attachment 1 of the licensees LAR determined that the proposed change did not result in an adverse impact on the capability of a fission product barrier. Diablo Canyon employs multiple fission product barriers (fuel cladding, the reactor coolant system (RCS) pressure boundary, and containment) to ensure radiological protection. TS 3.8.1 Required Action B.2 is designed to maintain the safety function of critical systems in the event of a loss of offsite power while a DG is inoperable. The required features referenced in this action include redundant systems, subsystems, trains, components, and devices that rely on DGs for emergency power. Failures of required redundant features refer to inoperable components associated with the Class 1E AC electrical power distribution subsystem that is redundant to the one linked to the inoperable DG. While in TS 3.8.1 Condition B, these required features remain powered by at least one operable offsite AC source and retain their ability to perform their safety functions. As a result, the DBA analysis credited capabilities of these features to cool the fuel, maintain RCS pressure boundary integrity, and preserve containment are not compromised by extending the completion time for Required Action B.2 from 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

The NRC staff reviewed the licensees consideration of this screening element and concluded that at least one train of redundant features associated with SSCs credited in the Diablo Canyon DBA analysis would remain operable during the proposed completion time extension. Therefore, the NRC staff finds that that the proposed change is determined to have a minimal impact on overall plant safety and does not result in more than a minimal decrease in the capability of the fuel cladding, RCS pressure boundary, or containment to function as effective fission product barriers.

3.1.5 Does the issue result in more than minimal decrease in defense-in-depth capability or safety margin?

The licensees review of this RIPE screening question in enclosure attachment 1 of its LAR determined that extending the completion time for TS 3.8.1 Required Action B.2 from 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, introduces the potential for an adverse impact on defense-in-depth capability. The proposed change introduces the potential for a longer duration during which a DG or its associated features may be inoperable. This extension could adversely affect the plants defense-in-depth strategy. However, the licensees evaluation described in enclosure attachment 1 determined that the principles of defense-in-depth remain preserved such that this change does not result in a more than minimal decrease in defense-in-depth capability or safety margin. The licensees evaluation reflected the guidance provided in Regulatory Guide (RG) 1.174, Revision 3 (Reference 8), Key Principle 2, which addresses maintaining the defense-in-depth philosophy. The licensees evaluation assessed the seven considerations for evaluating such changes as described in section C.2.1.1.2 of RG 1.174.

The licensees assessment describes that the proposed extension does not introduce a new allowable plant equipment configuration under the TS and does not compromise the plants ability to prevent failures of critical safety barriers such as the fuel cladding, reactor vessel, or containment. The design and functionality of the AC offsite sources and redundant ESF features remain unaffected by the proposed change and these systems continue to fulfill their role in mitigating severe accidents. Diablo Canyon also maintains an NRC-approved Emergency Plan, which includes provisions for public protection through sheltering or evacuation in the event of a radiological release.

The NRC staff concludes that the licensees assessment demonstrates that the proposed change preserves essential elements of plant design, including hazard survivability, accident mitigation, and public protection. In addition, the balance among the layers of defense-in-depth is maintained, and the combined safety barriers (fuel cladding, RCS pressure boundary, and containment) retain their effectiveness as fission product barriers. Thus, the defense-in-depth philosophy remains intact, as the change does not lead to more than a minimal decrease in the plants layered safety approach. Therefore, the NRC staff concludes that the proposed change does not result in a more than minimal degradation of defense-in-depth or safety margins.

3.2 Implementation of an IDP The licensee has been approved to adopt 10 CFR 50.69 by letter dated December 11, 2024 (Reference 9). The licensee established a multi-disciplinary IDP to evaluate the proposed license amendments to the TS 3.8.1 Required Action B.2 completion time from 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The IDP membership was comprised of plant personnel experienced in operations, design and systems engineering, safety analysis, and PRA risk assessment. Therefore, the NRC staff concludes that Diablo Canyon utilized an acceptable IDP in support of the proposed license amendments per the RIPE guidance. The IDP deliberated the five adverse safety impact screening questions contained in the SIC and concluded that the proposed completion time change is acceptable because the revised completion time only applies to low risk plant configurations when a DG is inoperable and it continues to provide adequate assurance of safe plant operation. The IDP evaluation is included in enclosure attachment 3 of the licensees LAR.

3.3 Use of an Acceptable/Approved PRA Model The NRC staff approved the Diablo Canyon risk-informed completion time license amendments by letter dated May 29, 2024 (Reference 10), adopting TSTF-505. In section 3.2, Technical Adequacy of the Probabilistic Risk Assessment, of the LAR enclosure, the licensee describes that the Diablo Canyon PRA model used to support the TSTF-505 and 10 CFR 50.69 license amendments includes internal and external events, fires, and seismic hazards. In addition, the submittal states that implementing procedures for the approved 10 CFR 50.69 license amendment have been completed. Therefore, the NRC staff concludes that Diablo Canyon utilized a technically-acceptable PRA model in support of the proposed exemption request per the RIPE guidance.

3.4 Evaluation of PRA Results The Diablo Canyon PRA model of record was utilized to evaluate all relevant scenarios involving DGs being out of service simultaneously with equipment powered by an alternate train of vital power, as defined within the scope of the proposed TS change. The PRA analysis credited the availability of power from an offsite electrical circuit, and the most limiting configuration among these combinations was identified and used as the bounding case for risk assessment purposes. The ABVS is not explicitly represented in the Diablo Canyon PRA model.

However, the licensee determined the ABVS to be of low-risk significance due to the extended room heatup times (exceeding 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) for PRA-relevant equipment that relies on ABVS for cooling. As a result, the licensee considered the bounding scenario used in the risk evaluation to be appropriate for extending the completion time for the ABVS in addition to all other components within the scope of the proposed TS change. The NRC staff notes that the SIC states RIPE is limited to proposed changes for which the safety impact associated with the issue can be modeled using PRA. While ABVS is not explicitly modeled in the Diablo Canyon PRA, the NRC staff finds that the risk impact of the ABVS is adequately bounded by the provided PRA results because the ABVS impacts equipment cooling, the associated risk-significant equipment is modeled in the PRA, and the affected equipment will not be impacted during the PRA mission time (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) due to extended room heatup times.

The licensee stated that the bounding risk increase was determined to be 5.61 x 10-8/year for CDF and 1.26 x 10-9/year for LERF. These results satisfy the RIPE criteria of contributing less than 5 x 10-7/year to CDF and 5 x 10-8/year to LERF. The NRC noted that the licensees risk results included a reduction in CDF and LERF to account for the low annual frequency of entry into TS 3.8.1 of.0882, as discussed in section 3.1.2 above. The SIC states that the change in CDF and LERF will be calculated as the difference in plant risk with the proposed change and without the proposed change. The NRC staff notes that the change in CDF and LERF without the reduction due to the low annual frequency of entry into TS 3.8.1 would increase the change in CDF to 6.36 x 10-7/year and LERF to 1.43 x 10-8/year, which exceeds the RIPE risk acceptance criteria for increase in CDF. However, the SIC states that exceedance of the risk acceptance criteria is acceptable on a case-by-case basis with justification. The NRC staff finds exceedance of the RIPE risk acceptance criteria acceptable in this case because only the most bounding risk results out of the various configurations modeled were above the acceptance criteria and the licensees review of operating experience determined that assuming entry into this TS every year would be conservative.

The addition of the calculated increase in risk associated with extending TS 3.8.1 Required Action B.2 completion time to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> does not appreciably alter the Diablo Canyon baseline risk for Unit 1 or Unit 2. Therefore, cumulative risk for Diablo Canyon remains less than the RIPE criteria of 1.0 x 10-4/year for CDF and 1.0 x 10-5/year for LERF. The NRC staff concludes that these results satisfy the RIPE criteria for a minimal increase in risk for the proposed license amendments.

3.5 Evaluation of the Need for Risk Management Actions Evaluation of the RIPE screening questions and the PRA results discussed above confirm that the proposed license amendments result in a minimal safety impact. Therefore, the guidance in TSG-DORL-2021-01 (Reference 3) states that risk management actions should be considered.

In section 3.4, Plant-Specific Risk Assessment Results, of the enclosure to LAR, the licensee describes several elements of the risk assessment to maintain low risk configurations associated with the proposed TS change. The associated redundant features applicable to the increased completion time are restricted to low-risk combinations including preclusion of the higher risk configuration resulting from concurrent modeling of the CCW loop and the CCW heat exchanger in the PRA modeling. Additionally, Note 2 is included in the proposed TS change to preclude the possibility of redundant vital equipment being inoperable for an extended period of time. In enclosure attachment 1 to the LAR, the licensee stated that compensatory measures are put in place by plant procedures to mitigate risk when a DG is inoperable and that these proceduralized compensatory measures are based on insights from the PRA model. Based on the licensees inclusion of specific elements in the risk assessment to maintain low risk configurations and existing proceduralized compensatory measures, the NRC staff concluded that no new risk management actions are required.

3.6 Assessment of Performance Monitoring Strategies The regulation at 10 CFR 50.65, Requirements for monitoring the effectiveness of maintenance at nuclear power plants, requires that unacceptable performance is addressed and corrected for SSCs credited for design basis accident prevention and mitigation. In addition, section 3.2 of the enclosure to the LAR states that implementing procedures for the approved 10 CFR 50.69 license amendment have been completed. The regulation at 10 CFR 50.69(e)(1) requires periodic review of any changes to the plant, operational practices, and relevant operational experience and update of the PRA and the categorization and treatment processes for categorized SSCs, as appropriate. The NRC staff concluded that existing regulations and plant processes will provide acceptable performance monitoring such that the minimal safety impact of the proposed TS change will remain valid.

3.7 Technical Conclusion Based on its review of the LAR, the NRC staff finds that the licensee has demonstrated that the proposed license amendments are low risk, represent minimal safety impact, and maintain adequate defense-in-depth and safety margins. Therefore, the NRC staff finds that the proposed changes to the Diablo Canyon TSs to modify TS 3.8.1 Required Action B.2 to establish a new, separate 24-hour completion time applicable when one required DG is inoperable, and one applicable redundant required feature is concurrently inoperable, are acceptable.

4.0 STATE CONSULTATION

In accordance with the Commissions regulations, the California State official was notified of the proposed issuance of the amendments on September 8, 2025. The State official had no comments.

5.0 ENVIRONMENTAL CONSIDERATION

The amendments change requirements with respect to installation or use of facility components located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, published in the Federal Register on September 30, 2025 (90 FR 46933), and there has been no public comment on such finding. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.

6.0 CONCLUSION

The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) there is reasonable assurance that such activities will be conducted in compliance with the Commissions regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.

7.0 REFERENCES

1.

Rogers, J. E., Pacific Gas and Electric Company, letter to U.S. Nuclear Regulatory Commission, Diablo Canyon Units 1 and 2 Docket No. 50-275, OL-DPR-80 Docket No.

50-323, OL-DPR-82, License Amendment Request 25-04, Revision to Technical Specification 3.8.1 Required Action B.2 Completion Time Using Risk-Informed Process for Evaluations, dated July 31, 2025 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25212A192).

2.

U.S. Nuclear Regulatory Commission, Guidelines for Characterizing the Safety Impact of Issues, Revision 2, May 2022 (ML22088A135).

3.

U.S. Nuclear Regulatory Commission Safety Impact Characterization Guidance for Implementing the Risk-Informed Process for Evaluations, Revision 3, May 2024 (ML23354A152).

4.

U.S. Nuclear Regulatory Commission, NRR Temporary Staff Guidance Risk-Informed Process for Evaluations, TSG-DORL-2021-01, Revision 4, dated May 1, 2024 (ML23354A150).

5.

Technical Specifications Task Force, Transmittal of TSTF-505, Revision 1, Provide Risk-Informed Extended Completion Times - RITSTF Initiative 4b Errata, dated June 14, 2011, and Proposed Revision to the Model Application for TSTF-505, Revision 1, Provide Risk-Informed Extended Completion Times - RITSTF Initiative 4b, dated January 31, 2012 (Package ML120330410).

6.

Technical Specifications Task Force (TSTF) Improved Standard Technical Specifications Change Traveler TSTF-425, Revision 3, Relocate Surveillance Frequencies to Licensee Control-RITSTF Initiative 5b, dated March 18,2009 (Package ML090850642).

7.

Nuclear Energy Institute, NEI Guidelines for the Implementation of the Risk-Informed Process for Evaluations Integrated Decision-Making Panel, August 2020 (ADAMS Accession No. ML20245E147).

8.

U.S. Nuclear Regulatory Commission, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis, Regulatory Guide 1.174, Revision 3, January 2018 (ML17317A256).

9.

Lee, S. S., U.S. Nuclear Regulatory Commission, letter to P. Gerfen, Pacific Gas and Electric Company, Diablo Canyon Nuclear Power Plant, Units 1 and 2 - Issuance of Amendment Nos. 247 and 249 Re: Adoption of 10 CFR 50.69, Risk-Informed Categorization and Treatment of Structures, Systems and Components for Nuclear Power Reactors. (EPID L-2023-LLA-0137), dated December 11, 2024 (ML24269A083).

10.

Lee, S. S., U.S. Nuclear Regulatory Commission, letter to P. Gerfen, Pacific Gas and Electric Company, Diablo Canyon Nuclear Power Plant, Units 1 and 2 - Issuance of Amendment Nos. 245 and 247 Re: Revision to Technical Specifications to Adopt TSTF-505, Revision 2, Provide Risk-Informed Completion Times - RITSTF Initiative 4b (EPID L-2023-LLA-0100), dated May 29, 2024 (ML24099A219).

Principal Contributors: John Hughey Michelle Kichline Date: December 2, 2025

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