ML24204A271
| ML24204A271 | |
| Person / Time | |
|---|---|
| Site: | Technical Specifications Task Force |
| Issue date: | 08/01/2024 |
| From: | Shivani Mehta NRC/NRR/DSS |
| To: | |
| References | |
| EPID L -2019-PMP-0207 TSTF-576 | |
| Download: ML24204A271 (1) | |
Text
TSTF-576 SE Supplemental Information By letter dated September 13, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23256A266), the Technical Specifications Task Force (TSTF) submitted Traveler TSTF-576, Revision 3, Revise Safety/Relief Valve Requirements (TSTF-576), to the U.S. Nuclear Regulatory Commission (NRC). TSTF-576 proposed changes to the Standard Technical Specifications (STSs) for boiling-water reactor (BWR) designs under the consolidated line item improvement process (CLIIP).
There were statements made in TSTF-576 that were immaterial to the NRC staffs review of the traveler. Additionally, the NRC staff wanted to document background information related to the traveler, but the information wasnt within scope of the SE. These items are discussed below.
1.0 S/RVs lifting outside the allowable as-found technical specification (TS) limits As discussed in the SE of TSTF-576, S/RVs installed in boiling water reactors (BWRs) have at times lifted outside the allowable as-found TS limits. This resulted in many Licensee Event Reports (LERs), submitted pursuant to 10 CFR 50.73, wherein the licensees conclusion was that the reactor coolant system (RCS) safety limit (SL) for pressure would not have been challenged during design basis events. The NRC staff did not review the LER calculations as part of the traveler review, but based on its review of the LERs, the NRC staff understands these calculations are performed using best-estimate methods that use known previous cycle information. Although licensee analyses have shown there is not a significant safety concern, there is a regulatory compliance issue resulting from the valves frequently lifting outside the specified as-found TS limits. SR 3.0.1 requires that SRs shall be met during all modes or specified conditions in the applicability of the Limiting Condition for Operation (LCO). As demonstrated during testing, the S/RVs have been frequently found to lift outside the TS limits required by the as-found tolerance SR. Thus, the SR is not met at some point in time while the plant is operating in a specified condition in the applicability; however, testing of the S/RVs cannot determine the timing of the failure. Therefore, the S/RVs do not maintain a reasonable expectation of operability.
The NRC staffs long-term position has been to allow licensees to attempt to repair the S/RVs via modification and, in parallel, develop a traveler to revise the surveillance requirement (STS) to alleviate the regulatory concern and eliminate the excessive number of LERs, because this has been viewed as an issue that would not significantly degrade plant safety or result in harm to the public. The NRC staffs long-term position on treatment of this issue is documented in an analysis conducted by the NRC staff (ML18213A030). In that analysis, the NRC staff recommended that the BWR Owners Group (BWROG) continue to attempt to resolve the S/RV setpoint issue via hardware and licensing changes, and that the NRC staff provide appropriate regulatory oversight. The review also concluded that the NRC staff would explore and select appropriate regulatory options based on the BWROG proposed resolution. Since that time, the TSTF developed a proposal that resulted in this traveler, TSTF-576.
2.0 Existing STS alignment with regulations and SL The NRC staff notes that in several places within the traveler, including the model application, it is stated that the change is being made to align the overpressure protection requirements with the SLs, the specified safety function, and incongruent with the regulations. Those statements are factually incorrect. The NRC staff concludes that the existing STS are fully aligned with the regulations and provide assurance that the SL will not be challenged. However, the NRC staff recognizes that the regulations allow for different ways to assure compliance, and the proposed revision to the STS provides an acceptable alternative that will protect the SL and maintain alignment with the regulations. The flexibilities in the traveler reduce the regulatory burden associated with excessive LER submittals and the expectation of operability.
3.0 Lowest functional capability of the system The traveler states that the existing LCO does not represent the lowest functional capability required for safe operation as required by 10 CFR 50.36. The TSTFs basis for this assertion appears to be that the existing LCO places requirements separately on each valve (i.e.,
component) instead of establishing a requirement for RCS pressure considering the performance of all S/RVs (i.e., system). This is factually incorrect. 10 CFR 50.36 clearly requires LCOs both at the system and the component levels, as appropriate, because any structure, system or component that meets one of the 10CFR50.36(c)(ii) criteria would be required to have an LCO. The NRC notes that it is acceptable to formulate LCOs at the system level as was proposed in the traveler.
4.0 Methods of Review for other analysis While the proposed changes in the traveler ensure that the S/RV settings will adequately protect the overpressure SL, the NRC staff identified that the traveler does not provide specific review methods for, or NRC staff review of, other analyses. Currently, when the S/RV as-found settings are changed, the NRC staff reviews the changes to assure that all affected analyses remain acceptable. To support a generic change from +/-1% to +/-3%, General Electric developed Topical Report (TR) NEDC-31753P, BWROG In-Service Pressure Relief Technical Specification Revision Licensing Topical Report, dated February 1990. While that TR specifies details regarding the parameters to be examined when increasing the as-found tolerance, it does not provide a specific methodology on how to perform these analyses. The NRC staff SE on the TR (non-public1) provides limitations and conditions on the acceptable use of the TR. The NRC staff found the TR to be an acceptable framework to demonstrate that the increased as-found tolerances and associated analyses remained valid; however, the TR SE required plant-specific analyses to be submitted to the NRC for review to assure that the specific analyses were conducted adequately.
The traveler does not include the NRC staff review of the other or related analyses. Instead, it states that the requirements in 10 CFR 50.59, Changes, tests, and experiments, will ensure adequate evaluation of all potentially affected analysis except for the overpressure analysis. The RCS overpressure analysis will continue to be conducted using NRC staff-approved methods providing confidence that it is conducted acceptably.
1 The ADAMS Accession number of the non-public SE is ML20126E038.
STS Section 5.6.3.c states, "The core operating limits shall be determined such that all applicable limits (e.g., fuel thermal mechanical limits, core thermal hydraulic limits emergency core cooling system (ECCS) limits, nuclear limits such as shutdown margin, transient analysis limits, and accident analysis limits) of the safety analysis are met." The NRC staff interprets this requirement, as applied to the traveler, as a requirement for each licensee to evaluate all analyses in the Final Safety Analysis Report (FSAR), in addition to the RCS overpressure analysis, that could be affected by changes in the tolerances contained in the Core Operating Limits Report (COLR) and to ensure that these other analyses are not adversely affected by the SR/V setpoint tolerance changes.
As proposed in TSTF-576, STS 5.6.3, Core Operating Limits Report, would require that the overpressure analysis for S/RV setting values controlled in the COLR be performed using an NRC-approved method. Additionally, pursuant to 10 CFR 50.90, STS 5.6.3.c requires that when a licensee evaluates whether an S/RV tolerance change can be made without a license amendment, that the licensee must consider all related analyses described in the FSAR (as updated), such as those identified above, in determining whether any of the criteria in 10 CFR 50.59(c)(2) are met. These analyses must be completed prior to making changes to the as-found tolerances that are being moved to, or contained in, the COLR. Licensees must evaluate all of the effects of S/RV setpoint changes on the facility as described in the FSAR.
These changes must be evaluated in accordance with 10 CFR 50.59 as required by the regulation.
By comparison, the traveler indicates that methods used to perform other analyses of record, such as containment or S/RV piping integrity, or high-pressure injection system capability, may also be affected, but will not be listed in the STS or the COLR. The traveler indicates that a licensee may not have such an NRC-approved methodology in their licensing and design basis for a particular evaluation. To the extent such evaluations are a part of the facility as described in the FSAR (as updated), any changes to these analyses would be subject to the requirements of 10 CFR 50.59.
To summarize the discussion above, the NRC staff identified two requirements that are applicable to other analyses such as thrust load and high-pressure injection system requirements when revising the S/RV as-found tolerances:
- 1. As identified within the traveler, the TS COLR requires the licensee to assure that all applicable limits of the safety analysis are met, meaning that the licensee must also consider effects on other analyses resulting from the new limits, and
- 2. Any changes that would be needed to the facility as described in the FSAR (as updated) resulting from a change in S/RV as-found lift setpoints would be subject to the requirements of 10 CFR 50.59.
As required by 10 CFR 50.59(c)(2)(viii), a licensee must obtain a license amendment if, for example, a change to the facility as described in the FSAR (as updated) would result in a departure from a method of evaluation described in the FSAR (as updated) used in establishing the design bases or in the safety analysis. The definition of such a departure set forth in 10 CFR 50.59(a)(2) includes (i) changing any of the elements of the method described in the FSAR (as updated) unless the results of the analysis are conservative or essentially the same, or (ii) changing from a method described in the FSAR to another method unless that method has been approved by NRC for the intended application.
To the extent that the methods used to perform a particular evaluation are described in the FSAR, the licensee needs to determine whether the departure from a method of evaluation criterion applies. Based on these considerations, the NRC staff determined that there is reasonable assurance that, even though the methods used to perform evaluations supporting increased S/RV as-found lift setpoints (outside the overpressure analyses) may not be submitted for NRC staff review or performed using methods described in an NRC-approved TR, they will be performed using methods that are consistent with those described in the licensing basis or otherwise approved by the NRC staff for the intended application. If the methods used by the licensee result in a departure from the methods described in the FSAR, 10 CFR 50.59 requires prior NRC approval be requested via a LAR.
Therefore, the NRC staff determined that the use of methods included in the COLR References to perform the overpressure analysis, but not to use such methods to perform any downstream evaluations, is acceptable.
5.0 Removal of the lower as-found tolerance The proposed change in TSTF-576 removes the as-found low tolerance pressure limit from the STS. The low tolerance is not an assumption in the overpressure analysis and is not needed to protect the overpressure SL. One purpose of the lower as-found setpoint tolerance is to ensure sufficient margin exists between the normal operating pressure of the system and the point at which the S/RVs actuate in the safety mode. The difference between normal operating pressure and the lowest opening pressure of relief valves is referred to as the simmer margin. If the opening pressure of an S/RV drifts too low, it could open during normal operation or a minor transient, thus initiating a transient or increasing the consequences of a transient. In response to NUREG-0737, Clarification of TMI [Three Mile Island] Action Plan Requirements, (ML102560051) General Electric concluded that the occurrence of stuck open relief valves can be reduced by increasing S/RV simmer margins.
If during testing, a licensee determines that an as-found lift pressure is higher than that established in the COLR, it must evaluate the overpressure analysis and all other analyses that may be affected by the increased lift pressure. The licensee must use methods consistent with the plant licensing basis and evaluate all analyses that may be affected by the higher lift setting.
The NRC staff understands that licensees may be able to make a determination regarding some or all of the other analyses using information already available to them or by using simplified methods. When assigning new as-found limits, including simplified evaluations or determinations, licensees are required to review potential effects for all affected analyses, not just overpressure, using the criteria in 10 CFR 50.59, including careful consideration of the criteria regarding departure from a method of evaluation described in the FSAR (as updated) used in establishing the design bases or in the safety analyses. If S/RVs are found to lift outside of the established as-found limits, then the licensee is required to evaluate the potential effects on all related plant analyses, not just RCS overpressure.
6.0 Recommendations for licensees adopting TSTF-576 The model application for TSTF-576 lists Attachment 4, Example Updated Core Operating Limits Report - For Information Only. The traveler does not include a depiction of the example COLR. The NRC staff considers it important for each licensee to include, as Attachment 4 to their submittal, an example page, or pages of their plant-specific COLR as they expect it to be revised to include the S/RV as-found limits. If the licensee does not follow the example COLR markup as provided in Appendix A of the traveler, the licensees submittal may not be reviewed under the CLIIP.
When considering potential alternatives to ASME OM Code requirements for valve population expansion, the NRC staff notes that it is not a good practice to base valve test population expansion on values that allow tolerances greater than those specified in the current TS. The NRC conclusion for this is because the proposed change is being made to address issues with setpoint drift. Therefore, reducing the number of valves tested by increasing the tolerance has the potential to reduce the reliability of the system.
To reduce the potential for delays in implementation and associated resource expenditures, a licensee choosing to adopt TSTF-576 is strongly encouraged to engage with the NRC staff prior to implementation to determine whether a 10 CFR 50.55a(z) alternative request is necessary, as there are overlapping regulatory requirements in this area. As noted on page 15 of Section 3 in the traveler, engagement with the NRC will be necessary when more than one inservice testing (IST) acceptance criteria is proposed, because the ASME OM Code requirements incorporated in 10 CFR 50.55a for S/RV setpoint testing can no longer be followed. TSTF-576 addresses TS requirements, but 10 CFR 50.55a still controls the regulatory requirements for IST.
7.0 Values for a-found lift tolerances in the COLR are used to determine operability TSTF-576 contains an example that implies that the values for as-found lift tolerances in the COLR will not directly determine Operability and/or reportability. Instead, it states: If an evaluation of the deficient condition performed under the Corrective Action Program determines that the affected S/RVs did not satisfy the SR while the plant was operating within the Applicability, an LER is required documenting that the TS were not followed. To prevent any confusion between the cited example and the requirement when determining Operability based on as-found values, the COLR values are the values that must be met to demonstrate operability. This is consistent with the current TS in that the values listed in the SR determine Operability. Any test result outside the COLR limits implies that the system is/was inoperable.
Failure to meet the SR due to exceeding any as-found lift tolerance in the COLR would require an LER per 10 CFR 50.73(a)(2)(i)(B). Having the values in the COLR provides flexibility to the licensee for establishing these values. The values in the COLR at the time that the S/RVs are removed from service for testing are the values used to determine operability. Failure to meet the SR due to exceeding the as-found lift tolerances in the COLR would require an LER per 10 CFR 50.73(a)(2)(i)(B).