ML25127A214
| ML25127A214 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 05/22/2025 |
| From: | Tony Nakanishi Plant Licensing Branch IV |
| To: | Heflin A Arizona Public Service Co |
| Orders, William | |
| References | |
| EPID L-2024-LLR-0069 | |
| Download: ML25127A214 (1) | |
Text
May 22, 2025 Mr. Adam Heflin Executive Vice President/
Chief Nuclear Officer Mail Station 7605 Arizona Public Service Company P.O. Box 52034 Phoenix, AZ 85072-2034[
SUBJECT:
PALO VERDE NUCLEAR GENERATING STATION, UNITS 1, 2, AND 3 -
ALTERNATIVE REQUEST ALLOWING NORMALLY CLOSED VALVES WITH A SAFETY FUNCTION TO CLOSE TO BE EXERCISE TESTED ONCE PER REFUELING CYCLE (EPID L-2024-LLR-0069)
Dear Mr. Heflin:
By letter dated October 22, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24296B214), as supplemented by a letter dated March 6, 2025 (ML25065A267), Arizona Public Service Company (the licensee) submitted Alternative Request VRR-02 to the U.S. Nuclear Regulatory Commission (NRC) proposing the use of an alternative to specific inservice testing (IST) requirements in the 2012 Edition of the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code) for the fourth IST interval program at Palo Verde Nuclear Generating Station, Units 1, 2, and 3 (Palo Verde).
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1),
Acceptable level of quality and safety, the licensee proposed to implement Alternative Request VRR-02 on the basis that the alternative would provide an acceptable level of quality and safety in lieu of certain requirements in the ASME OM Code as incorporated by reference in 10 CFR 50.55a, Codes and standards, for specific valves at Palo Verde.
As described in the enclosed safety evaluation, the NRC staff has determined that Alternative Request VRR-02 submitted and supplemented by the licensee to extend the ASME OM Code required exercise interval for the 28 valves specified in the request for each Palo Verde unit provides an acceptable level of quality and safety in lieu of the ASME OM Code requirements for quarterly exercising of the subject valves. The NRC staff has also determined that the testing approach described in Alternative Request VRR-02 provides reasonable assurance that the subject valves will be operationally ready to perform their safety functions for the duration of the alternative request. Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements in 10 CFR 50.55a(z)(1). Therefore, the NRC staff authorizes Alternative Request VRR-02 for the duration of Palo Verde Nuclear Generating Station, Units 1, 2, and 3, fourth IST interval program, which is scheduled to end on January 14, 2028.
All other ASME OM Code requirements as incorporated by reference in 10 CFR 50.55a for which relief or an alternative was not specifically requested, and granted or authorized (as appropriate), in the subject request remain applicable.
If you have any questions, please contact the Palo Verde Project Manager, William Orders, at 301-415-3329 or by email at William.Orders@nrc.gov.
Sincerely, Tony Nakanishi, Chief Plant Licensing Branch LPL4 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-528, STN 50-529, and STN 50-530
Enclosure:
Safety Evaluation cc: Listserv TONY NAKANISHI Digitally signed by TONY NAKANISHI Date: 2025.05.22 12:12:58 -04'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ALTERNATIVE REQUEST VRR-02 PALO VERDE NUCLEAR GENERATING STATION, UNITS 1, 2, AND 3 ARIZONA PUBLIC SERVICE COMPANY DOCKET NOS. 50-528, 529, AND 530
1.0 INTRODUCTION
By letter dated October 22, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24296B214), as supplemented by a letter dated March 6, 2025 (ML25065A267), Arizona Public Service Company (the licensee) submitted Alternative Request VRR-02 to the U.S. Nuclear Regulatory Commission (NRC) proposing the use of an alternative to specific inservice testing (IST) requirements in the 2012 Edition of the American Society of Mechanical Engineers (ASME) Operation and Maintenance of Nuclear Power Plants, Division 1, OM Code: Section IST (OM Code) for the fourth IST interval program at Palo Verde Nuclear Generating Station, Units 1, 2, and 3 (Palo Verde).
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1),
Acceptable level of quality and safety, the licensee proposed to implement Alternative Request VRR-02 on the basis that the alternative would provide an acceptable level of quality and safety in lieu of certain requirements in the ASME OM Code as incorporated by reference in 10 CFR 50.55a, Codes and standards, for specific valves at Palo Verde.
In Alternative Request VRR-02, the licensee proposes to modify the quarterly stroke-time testing requirement in the ASME OM Code to require testing only once per refueling cycle for 19 air-operated valves (AOVs) and 9 solenoid-operated valves (SOVs) in each Palo Verde unit that are normally closed in their safety position, and under specific controls, when temporarily opened to their non-safety position to ensure their return to the closed safety position. The licensee asserts that the proposed alternative provides an acceptable level of quality and safety in accordance with 10 CFR 50.55a(z)(1).
2.0 REGULATORY EVALUATION
The regulations in 10 CFR 50.55a(f)(4), Inservice testing standards requirement for operating plants, state in part:
Throughout the service life of a boiling or pressurized water-cooled nuclear power facility, pumps and valves that are within the scope of the ASME OM Code must meet the inservice test requirements (except design and access provisions) set forth in the ASME OM Code and addenda that become effective subsequent to editions and addenda specified in [10 CFR 50.55a(f)(2) and (3)] and that are incorporated by reference in [10 CFR 50.55a(a)(1)(iv)], to the extent practical within the limitations of design, geometry, and materials of construction of the components.
The regulations in 10 CFR 50.55a(z), Alternatives to codes and standards requirements, state:
Alternatives to the requirements of paragraphs (b) through (h) of this section or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that:
(1) Acceptable level of quality and safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a compensating increase in quality and safety. Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
3.0 TECHNICAL EVALUATION
3.1 Licensees Alternative Request VRR-02 Applicable ASME OM Code Edition The applicable Code of Record for the fourth IST interval program at Palo Verde is the 2012 Edition of ASME OM Code, as incorporated by reference in 10 CFR 50.55a. The licensee applies ASME OM Code Case OMN-20, Inservice Test Frequency, as accepted with conditions in NRC Regulatory Guide (RG) 1.192, Operation and Maintenance Code Case Acceptability, ASME OM Code, Revision 5, March 2024 (ML23291A006), to test periods specified in the ASME OM Code.
Applicable ASME OM Code Components Tables 1-1 and 1-2 in the licensees submittal dated October 22, 2024, list the valves at Palo Verde within the scope of Alternative Request VRR-02. The scope includes 28 valves at each of the three Palo Verde units for a total of 84 valves at the Palo Verde site.
Applicable OM Code Requirements The IST requirements in the 2012 Edition of the ASME OM Code, as incorporated by reference in 10 CFR 50.55a, related to this alternative request are as follows:
ASME OM Code, subsection ISTC, Inservice Testing of Valves in Light-Water Reactor Nuclear Power Plants, paragraph ISTC-3510, Exercise Test Frequency, states, in part, that active Category A, Category B, and Category C check valves shall be exercised nominally every 3 months, except as provided by certain paragraphs in subsection ISTC.
Licensees Proposed Alternative For the valves listed in Alternative Request VRR-02 for Palo Verde, the licensee is requesting NRC authorization to perform exercise testing once per refueling cycle in lieu of the quarterly exercise test required by the ASME OM Code, subsection ISTC, paragraph ISTC-3510. The licensee asserts that this alternative to ISTC-3510 provides an acceptable level of quality and safety because the valves are designed, operated, and controlled to ensure that their safety functions are met. The licensee states that risk impacts from extending the specified valves to a once-per-cycle test period have been evaluated and are found to be acceptably small. The licensee considers that the maintenance and performance history demonstrates acceptable operation of the valves. The licensee notes that ASME Code Case OMN-20 will apply to the 18-month test period for the applicable valves in Alternative Request VRR-02.
Licensees Reason for Request The licensee proposes to perform once-per-refueling cycle exercise and stroke-time testing of the valves specified in Alternative Request VRR-02. At Palo Verde, the operating cycles are 18 months for each reactor unit, which exceeds the 3-month interval required by ISTC-3510.
Licensees Basis for Use of Proposed Alternative The NRC staff summarizes the basis provided by the licensee for Alternative Request VRR-02 in the following paragraphs:
With respect to design, the licensee states that the valves within the scope of Alternative Request VRR-02 are normally closed with an active safety function to close. These valves have no safety function in the open position and are designed to fail in the closed position. To meet these functions, the valves are designed to close through passive release of stored energy upon operation of control room hand switches. For an AOV, control solenoids deenergize to remove air pressure from the diaphragm and the main spring drives the valve closed. For an SOV, the main solenoid deenergizes allowing an internal spring to drive the valve closed. Therefore, based on valve design, the licensee asserts that every stroke of one of the subject valves validates the safety function to close and the ability to fail closed upon loss of power.
With respect to operation, the licensee states that the valves within the scope of Alternative Request VRR-02 remain closed unless they are taken out of their safety position for testing or plant control. The valves are only operated under procedural control, either for testing or to achieve a specific plant control evolution. To perform exercise testing, the valves are taken out of their safety position to establish test conditions and then tested in the closing direction. After testing, the valves remain in their normally closed safety position. To perform plant operations such as containment depressurization and safety injection tank level maintenance, operators open the valves via established operating procedures and close the valves again once the evolution is complete. Procedures are written to return the valves to their normally closed position in accordance with the Palo Verde status control program. Any failure to return the valve to its normal position violates the status control program and is dispositioned in accordance with the corrective action program.
The licensee states that use of the subject valves varies depending on plant status and operational needs at Palo Verde. The licensee reviewed valve position data from the second quarter of 2024 (April, May, and June) to assess the frequency and duration for which the subject valves are out of their safety position. No valve was open for more than 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> with a unit online. During the Unit 3 refueling outage, some valves were open for multiple days or had no position data available. Before returning a valve to service, the licensee notes that performance is reconfirmed through formal exercise testing as required by the IST program. The licensee considers that post-maintenance and periodic testing in refueling outages provides confidence in each valves ability to perform its safety function during the next operating cycle.
Similarly, the licensee asserts that each successful valve closure performed to support operational activities validates a valves ability to close and meet its safety function to fail-safe in the closed position.
The licensee notes that the out-of-safety-position durations observed in the second quarter of 2024 are consistent with their active classification under ASME OM Code and NRC guidance.
NUREG-1482, Guidelines for Inservice Testing at Nuclear Power Plants: Inservice Testing of Pumps and Valves and Inservice Examination and Testing of Dynamic Restraints (Snubbers) at Nuclear Power Plants, Revision 3, July 2020 (ML20202A473), section 2.4.2, Valves, which states that passive valves open for days, weeks or months are expected to be classified as active, whereas passive valves removed from their safety position temporarily under administrative control need not be classified as active. The guidance indicates that duration in the out of safety position is a key input to active/passive determination. The licensee states that the subject valves are classified as active in the IST program with the active valve test methodology continued to be applied.
With respect to control, the licensee states that administrative controls ensure the subject valves are returned to their closed safety position after each use. Valves with remote position indication must meet ASME OM Code, subsection ISTC, paragraph ISTC-3700, Position Verification Testing. The licensee states that it complies with paragraph ISTC-3700 and the supplemental indication requirements of 10 CFR 50.55a(b)(3)(xi), OM condition: Valve Position Indication, to provide reasonable assurance that control room indication correctly reflects valve position for valves in the IST program. When the expected closed indication is not displayed after valve use, operators are trained to enter the condition into the corrective action program and follow the technical specification actions.
With respect to risk evaluation, the licensee asserts that extending valve exercise testing to 18 months from quarterly produces an acceptably small increase in risk. Nine of the 28 valves within the scope of this request in each unit are in the Palo Verde probabilistic risk assessment (PRA) model. These valves contribute to changes in core damage frequency (CDF) and large early release frequency (LERF). Based on the test period extension, the total change in CDF is 5.2 x 10-10 per year while the total change in LERF is 1.63 x 10-8 per year. These are less than permitted in RG 1.174, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis, Revision 3, January 2018 (ML17317A256). RG 1.174 specifies risk increases to remain less than 1 x 10-6 per year for CDF and less than 1 x 10-7 per year for LERF. Nineteen of the 28 valves within the scope of this request in each unit are not in the PRA model, because the licensee states that they have negligible risk impact. The licensee asserts that the change in risk from extending to an 18-month test frequency is acceptably small for each of the 28 valves within the scope of this request in each unit. Nine of the 28 valves produce a total change in CDF and LERF that remains less than allowed under RG 1.174, while the remaining 19 valves are considered to have negligible risk impact.
With respect to maintenance and performance history, the licensee states that the subject valves routinely demonstrate acceptable testing performance. The licensee reports that valve stroke time performance trends since 2020 show normal performance variation with no degrading trends. The licensee provided a summary of the maintenance history showing few corrective maintenance work orders from quarterly IST testing. Based on its review, the licensee asserted that Palo Verde walkdowns, maintenance, and operational activities are identifying component issues at a lower threshold than required by OM Code test criteria.
In summary, the licensee proposes that the NRC authorize this request to perform once-per-refueling cycle exercise testing of the subject valves in lieu of the 3-month requirement in ISTC-3510. The licensee asserts that a once-per-refueling cycle test for these valves provides an acceptable level of quality and safety because the valves are designed, operated, and controlled such that their safety functions are routinely met and verified. The licensee also considers the risk evaluation to show that the changes in CDF and LERF are acceptably small from the proposed alternative. Performance and maintenance history shows the valves are managed effectively because issues are identified and resolved before they can be detected by OM Code testing. The licensee states that the proposed alternative will be used for the duration of Palo Verdes fourth IST program interval, which is scheduled to end January 14, 2028. The licensee considers this to be a sufficient basis to support the alternative request per 10 CFR 50.55a(z)(1).
3.2
NRC Staff Evaluation
The 2012 Edition of the ASME OM Code, subsection ISTC, paragraph ISTC-3510, as incorporated by reference in 10 CFR 50.55a, requires that active Category A, Category B, and Category C check valves shall be exercised nominally every 3 months, except as provided by certain paragraphs in subsection ISTC. In Alternative Request VRR-02, the licensee requested the NRC to authorize exercise testing of specific valves at Palo Verde once per refueling cycle in lieu of the quarterly exercise testing. The licensee asserts that this alternative provides an acceptable level of quality and safety in accordance with 10 CFR 50.55a(z)(1).
The NRC staff reviewed the justification provided by the licensee in Alternative Request VRR-02 in support of its proposal to extend the ASME OM Code required exercise interval for the 28 valves specified in the request for each Palo Verde unit. The staff evaluated the licensees justification related to design, operation, control, risk evaluation, and maintenance and performance history for the proposed extension of the exercise interval to refueling outages for the valves within the scope of the request.
With respect to design, the valves within the scope of Alternative Request VRR-02 in each Palo Verde unit consist of 19 AOVs and 9 SOVs that are normally closed with an active safety function to close and no safety function to open. With respect to operation, the valves within the scope of Alternative Request VRR-02 remain closed in their safety position unless they are taken out of their safety position for testing or plant control. With respect to control, the licensee states that administrative controls ensure the subject valves are returned to their closed safety position after each use. With respect to risk evaluation, the licensee asserts that extending valve exercise testing to 18 months from quarterly produces an acceptably small increase in risk. With respect to maintenance and performance history, the subject valves routinely demonstrate acceptable testing performance with stable performance and no degrading trends.
Alternative Request VRR-02 indicates that the normally closed valves within the scope of the request might be repositioned from their closed safety position to their open non-safety position for an unspecified amount of time. NUREG-1482, Revision 3, provides guidance for passive valves (such as sample valves) that may be stroked to their non-safety position from their normal safety position for a short period of time when under positive administrative control. In a request for additional information (RAI) dated February 10, 2025 (ML25041A286), the NRC staff requested that the licensee describe the procedural controls that will be in place for the specific valves within the scope of Alternative Request VRR-02, including instances where the valve might remain in its open non-safety position beyond one reactor operator shift period.
In its RAI response dated March 6, 2025, the licensee stated that the Palo Verde normal operating procedures (NOPs) and shift turnover process ensure the valves within the scope of Alternative Request VRR-02 are returned to their safety position following plant activities. For example, Palo Verde Procedure 40DP-9OP09, System Status Control, states:
NOPs are formatted such that a standard section establishes a normal configuration wherein normal is the Full Power, Mode 1 system line-up. For each section that places a system in other than a normal configuration, a subsequent section exists to restore the normal configuration.
As an example of this process, the licensee references Palo Verde Procedure 40OP-9CP01, Containment Purge System, which is used to open and close valves CPAUV0004B and CPBUV0005B for containment venting. Specifically:
Section 6.2, Venting Containment, opens the valves to start the venting process.
Section 6.6, Stopping Containment Vent, closes the valves to end the venting process.
To address long-term valve repositioning, the licensee states that when plant activities take longer than one reactor operator shift, the operators use the shift turnover process to communicate valve status to the on-coming shift crew. The licensee indicates that Procedure 40DP-9OP33, Shift Turnover, controls this process with position-specific checklists, person-to-person communication, and documentation to ensure the on-coming control room staff understand the status of plant equipment. The process requires operators to review the control board indications, discuss plant activities controlled by NOPs, and explain the reason for any valve out of its normal position. The valves within the scope of Alternative Request VRR-02 have control room indications and are included in this review. The NRC staff agrees that the Palo Verde NOPs and the shift turnover process provide assurance that the subject valves are returned to their normally closed safety position following plant activities.
Alternative Request VRR-02 indicates that each valve within its scope will be verified to return to its closed safety position from the open non-safety position. In an RAI, the NRC staff requested the licensee to describe its plans to provide reasonable assurance that each valve returns to its closed safety position. In its RAI response dated March 6, 2025, the licensee stated that Palo Verde reactor operators will assess the operational readiness of each valve within the scope of Alternative Request VRR-02 by adhering to station requirements to monitor stroke performance, look for abnormal or erratic action, and verify successful closure. The licensee indicates that the Palo Verde operational provisions apply to the opening and closing strokes of all safety-related valves, regardless of test frequency. The licensee intends that these provisions will continue to apply to the valves within the scope of Alternative Request VRR-02, consistent with the requirements of ASME OM Code, which requires responding to any abnormality or erratic action during valve operation.
Also in its RAI response, the licensee stated that Palo Verde operating procedures for exercising the valves within the scope of Alternative Request VRR-02 are performed in compliance with plant procedures on Conduct of Operations (40DP-9OP02), Procedure and Work Instruction Use and Adherence (01DP-0AP09), and Condition Reporting Process (01DP-0AP12). These procedures require:
Using established procedures for all plant manipulations (Procedure 40DP-9OP02).
Reading each procedure step and understand the expected plant response before taking action (Procedure 01DP-0AP09).
Observing and verifying the expected response after each action (Procedure 01DP-0AP09).
Documenting in a condition report (and reporting to on-shift management) any abnormal or erratic action that would challenge full closure of a valve (Procedure 01DP-0AP12).
The licensee stated that the Condition Reporting Process procedure (01DP-0AP12) ensures valve performance deviations are incorporated into the corrective action program. The Operations Department Practices guidance (ODP-1) further reinforce the importance of operator engagement to identify deviations in valve operation, including system flows, levels, or pressures, that could indicate seat leakage or failure to fully close.
The licensee states that these procedures and practices are consistent with the ASME OM Code, subsection ISTC, paragraphs ISTC-5131(d) and ISTC-5151(d), which require recording any abnormality or erratic action during valve strokes. The licensee emphasizes that it is not seeking an alternative to these provisions of the ASME OM Code.
The licensee states that seat leakage testing requirements in ASME OM Code, subsection ISTC, paragraph ISTC-3600, Leak Testing Requirements, will continue to be met as applicable for OM Category A valves within the scope of Alternative Request VRR-02. All 15 Category A valves are containment isolation valves tested in accordance with Palo Verde Procedures 73ST-9CL01, Containment Leakage Type B and C Testing, and 73ST-9CL07, Containment Ventilation Purge Isolation Valves (8-Inch) - Penetration 78 and 79, per Appendix J to 10 CFR Part 50, Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors.
For OM Category B valves within the scope of Alternative Request VRR-02, reactor operators will continue to apply Palo Verde Procedure ODP-1 to obtain system indications of full closure. If evidence of leakage is identified for an OM Category B valve, reactor operators will enter this finding in the corrective action program per Procedure 01DP-0AP12.
The Risk Evaluation section of Alternative Request VRR-02 indicates that 9 of the 28 valves for each Palo Verde unit within the scope of the request are included in the Palo Verde PRA model, and the remaining 19 of the 28 valves are not modeled in the PRA. PRA studies typically assume that valves are returned to their highest availability following quarterly exercising. The NRC staff evaluated the risk insights in extending the quarterly testing interval out to refueling outages (every 18 months) compared to the PRA reset of the availability of these valves by quarterly testing. For example, NUREG-0677, The Probability of Intersystem LOCA [Loss-of-Coolant Accident]: Impact Due to Leak Testing and Operational Changes, May 1980 (ML19323E667), indicates the benefits of resetting the availability with periodic testing and highlights very small changes in failure rate probabilities between biennial and annual testing.
With respect to the test period extension, Palo Verde notes that the total change in CDF is 5.2x10-10 per year and total change in LERF is 1.63x10-8 per year for the 9 modeled valves in the PRA; and the remaining 19 valves are excluded from the PRA because they have negligible risk impact. The NRC staff confirmed the risk impact due to the modification meets the acceptance guidelines presented in RG 1.174, Revision 3. In addition, the NRC staff reviewed the PRA quality information provided by Palo Verde in its license amendment request titled License Amendment Request to Revise Technical Specifications to Adopt TSTF-505-A
[Technical Specifications Task Force (TSTF) Traveler TSTF-505-A], Revision 1, Risk-Informed Completion Times, dated July 31, 2015 (ML15218A300) and associated supplemental information to determine the Palo Verde PRA model is commensurate with the alternative request and demonstrates reasonable assurance of technical adequacy. The NRC staff further concludes that the results of the licensees risk analysis indicate that the proposed changes do not create special circumstances described in appendix D, Use of Risk Information in Review of Non-risk-informed License Amendment Requests, of NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR [Light-Water Reactor]
Edition, Section 19.2 Review of Risk Information used to Support Permanent Plant-Specific Changes to the Licensing Basis: General Guidance, June 2007 (ML071700658). Therefore, the NRC staff finds the risk implications of the proposed alternative request acceptable.
In summary, the NRC staff evaluated the justification provided by the licensee in Alternative Request VRR-02 (as supplemented) in support of the proposal to extend the ASME OM Code required exercise interval for the 28 valves specified in the request for each Palo Verde unit. In particular, the staff evaluated the licensees justification related to design, operation, control, risk evaluation, and maintenance and performance history for the proposed extension of the exercise interval to refueling outages for the valves within the scope of the request. For example, the applicable 19 AOVs and 9 SOVs in each Palo Verde unit are normally closed in their safety position, and under specific controls when temporarily opened to their non-safety position to ensure their return to the closed safety position. The NRC staff has determined that the testing approach described in Alternative Request VRR-02 provides reasonable assurance that the subject valves will be operationally ready to perform their safety functions for the duration of the alternative request. Based on its review, the staff has determined that the proposed exercise interval for the 28 valves specified in the request for each Palo Verde unit provides an acceptable level of quality and safety in lieu of the ASME OM Code requirements for quarterly exercising of the subject valves. Therefore, the staff finds that Alternative Request VRR-02 meets the requirements of 10 CFR 50.55a(z)(1).
4.0 CONCLUSION
As described above, the NRC staff has determined that Alternative Request VRR-02 submitted and supplemented by the licensee to extend the ASME OM Code required exercise interval for the 28 valves specified in the request for each Palo Verde unit provides an acceptable level of quality and safety in lieu of the ASME OM Code requirements for quarterly exercising of the subject valves. For example, the applicable 19 AOVs and 9 SOVs in each Palo Verde unit are normally closed in their safety position, and under specific controls when temporarily opened to their non-safety position to ensure their return to the closed safety position. The NRC staff has also determined that the testing approach described in Alternative Request VRR-02 provides reasonable assurance that the subject valves will be operationally ready to perform their safety functions for the duration of the alternative request. Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements in 10 CFR 50.55a(z)(1).
Therefore, the NRC staff authorizes Alternative Request VRR-02 for the duration of Palo Verde Nuclear Generating Station, Units 1, 2, and 3, fourth IST interval program, which is scheduled to end on January 14, 2028.
All other ASME OM Code requirements as incorporated by reference in 10 CFR 50.55a for which relief or an alternative was not specifically requested, and granted or authorized (as appropriate), in the subject request remain applicable.
Principal Contributors: Thomas G Scarbrough, NRR Nicholas Hansing, NRR Date: May 22, 2025
- concurrence via eConcurrence OFFICE NRR/DORL/LPL4/PM* NRR/DORL/LPL4/LA* NRR/DRA/APLA/BC* NRR/DEX/EMIB*
NAME WOrders PBlechman RPascarelli SBailey DATE 05/05/2025 5/13/2025 05/19/2025 05/21/2025 OFFICE NRR/DORL/LPL4/BC*
NAME TNakanishi DATE 05/22/2025