ML20262A751
| ML20262A751 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 09/17/2020 |
| From: | Samson Lee NRC/NRR/DORL/LPL4 |
| To: | Joseph Turner Wolf Creek |
| References | |
| L-2020-LLA-0091 | |
| Download: ML20262A751 (6) | |
Text
From:
Lee, Samson Sent:
Thursday, September 17, 2020 3:27 PM To:
Josh Turner
Subject:
Requests for additional information: Wolf Creek amendment request to modify technical specification surveillance frequency consistent with TSTF-425 (EPID: L-2020-LLA-0091)
By letter dated April 27, 2020 (ADAMS Accession No. ML20119A873), Wolf Creek Nuclear Operating Corp. (WCNOC), submitted a license amendment request (LAR) regarding Wolf Creek Generating Station, Unit 1. The proposed amendment would modify the Wolf Creek TS by relocating specific surveillance frequencies to a licensee-controlled program with the implementation of NEI 04-10. The licensee states that the proposed changes are consistent with Nuclear Regulatory Commission (NRC) approved industry/Technical Specification Task Force (TSTF) Standard Technical Specifications (STS) change TSTF-425, Revision 3 (ADAMS Accession No. ML090850642).
The NRC staff has reviewed the LAR and determined that additional information is required to complete the review. The NRC staffs requests for additional information (RAIs) are listed below. The staff may have additional RAIs. The staff sent the draft RAIs to the WCNOC staff and held a clarification call on September 17, 2020. The WCNOC staff requested, and NRC agreed, to a RAI response by October 27, 2020.
The NRC staff considers that timely responses to RAIs help ensure sufficient time is available for staff review and contribute toward the NRCs goal of efficient and effective use of staff resources. Please note that if you do not respond to this request by the agreed-upon date or provide an acceptable alternate date, we may deny your application for amendment under the provisions of Title 10 of the Code of Federal Regulations, Section 2.108. If circumstances result in the need to revise the agreed upon response date, please contact me at (301) 415-3168 or via e-mail Samson.Lee@nrc.gov.
REGULATORY BASES AND GUIDANCE Title 10 of the Code of Federal Regulations (10 CFR) Part 50.36(c)(3), requires, in part, that Technical Specifications (TSs) include surveillance requirements. Surveillance requirements are requirements relating to test, calibration, or inspection to assure that the necessary quality of systems and components is maintained, that facility operation will be within safety limits, and that the limiting conditions for operation will be met.
Nuclear Energy Institute (NEI) guidance document NEI 04-10, Revision 1, Risk-Informed Technical Specifications Initiative 5b, Risk-Informed Method for Control of Surveillance Frequencies" (ADAMS Accession No. ML071360456), provides guidance for relocating the surveillance frequencies from the TSs to a licensee-controlled program by providing an NRC-approved methodology for control of the surveillance frequencies. The guidance in NEI 04-10, Revision 1, is acceptable for referencing in licensing actions to the extent specified and under the limitations delineated in NEI 04-10, and the NRC safety evaluation providing the basis for NRC acceptance of NEI 04-10 (ADAMS Accession No. ML072570267).
NEI 04-10 Step 5, RG 1.200 PRA Technical Adequacy, requires the probabilistic risk assessment (PRA) to be of sufficient technical capability and be subjected to a peer review process assessed against a standard or set of acceptance criteria that is endorsed by NRC Regulatory Guide (RG) 1.200, Revision 2,
An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed Activities (ADAMS Accession No. ML090410014).
NEI 04-10 Step 5 also states that plants implementing TSTF-425 shall evaluate their PRAs in accordance with RG 1.200. Further, it is stated that the RG specifically addresses the need to evaluate important assumptions that relate to key modeling uncertainties and the identified key sources of uncertainty serve as inputs to identifying appropriate sensitivity cases in [NEI 04-10] Step 14.
NEI 04-10 Step 5 also discusses how RG 1.200 provides attributes of importance for risk determinations relative to external events, seismic, internal fires, and shutdown. The RG specifically addresses the need to evaluate important assumptions that relate to key modeling uncertainties and the need to evaluate parameter uncertainties and demonstrate that calculated risk metrics (e.g., core damage frequency (CDF) and large early release frequency (LERF)) represent mean values.
NEI 04-10 Step 14, Perform Sensitivity Studies states that, Additional sensitivity cases should also be explored for particular areas of uncertainty associated with any of the significant contributors to the CDF and LERF results or if there are open Gap Analysis items when compared to the ASME Standard Capability Category II [CC-II] that would impact the results of the assessment. Step 14 also calls for ensuring that there is not an undue reliance on key assumptions and causes of uncertainty.
RG 1.177, Revision 1, An Approach for Plant-Specific, Risk-Informed Decisionmaking: Technical Specifications, (ADAMS Accession No. ML100910008), outlines the staff position in performing sensitivity and uncertainty analyses in support of surveillance frequency changes to technical specifications.
RG 1.200, Revision 2, Section 2.2, provides regulatory guidance regarding peer reviews and the staff regulatory position on NEI 00-02, Probabilistic Risk Assessment (PRA) Peer Review Process Guidance (ADAMS Accession No. ML061510619), NEI 05-04 Process for Performing Follow-On [Internal Events]
PRA Peer Reviews Using the American Society of Mechanical Engineers (ASME)/American Nuclear Society (ANS) PRA Standard (ADAMS Accession No. ML083430462), and NEI 07-12 Fire Probabilistic Risk Assessment (FPRA) Peer Review Process Guidelines (ADAMS Accession No. ML102230070).
Attachment II Section 2 of the LAR states that the PRA models have been developed in accordance with the requirements of RG 1.200, Revision 2, subjected to peer review and the Facts and Observations (F&O) independent assessment process.
REQUESTS FOR ADDITIONAL INFORMATION The following requests for additional information (RAIs) are needed to enable the staff to complete its review of the licensees application:
RAI 1
The finding (F&O 3-8) pertaining to supporting requirement QU-F4, located in Table 3-1 of Attachment II, WCGS Open PRA Peer Review Findings observes that there was a lack of a clear method for identification and characterization of key plant-specific assumptions and sources of uncertainty. The resolution for this F&O states, in part: The quantitative characterization process is now being consolidated and more clearly documented.
- a. Confirm that this activity is complete or whether it will be completed prior to implementation of the Surveillance Frequency Control Program (SFCP).
- b. Provide details of any sensitivity analyses done to close out this F&O.
RAI 2
The resolution for F&O 6-8 states, in part: The one exception that prevented this F&O from being formally closed was that the Electric Power System Engineer Interview had not yet taken place.
Confirm that the interview has taken place, or that it will be completed prior to implementation of the SFCP.
RAI 3
In Section 4.0 of Attachment II of the LAR, the licensee states that, [T]he NEI 04-10 methodology recognizes that a key area of uncertainty for this application is the standby failure rate utilized in the determination of the STI [Surveillance Test Interval] extension impact. Therefore, the methodology requires the performance of selected sensitivity studies on the standby failure rate of the component(s) of interest for the STI assessment. The licensee furthermore states that, [t]he results of the standby failure rate sensitivity study plus the results of any additional sensitivity studies identified during the performance of the reviews as outlined in Section 3.2 above for each STI change assessment will be documented and included in the results of the risk analysis that are presented to the (IDP) [Independent Decision-making Panel]. This will include, for each STI change assessment, additional sensitivity studies that are identified through a review of identified gaps to CC-II and a review of identified sources of uncertainty as required by NEI 04-10, Steps 5 and 14. It is not clear to the staff of the details on how the licensee will resolve the balance between time-related and standby failures of test-limited risk commensurate with the guidance of RG 1.177, section 2.3.3 and NEI 04-10, Step 8.
- a. Describe the approach used to address test-limited risk and whether and how it follows the guidance of RG 1.177 and NEI 04-10.
- b. Alternatively, provide a detailed description with justification of the proposed adopted approach.
RAI 4
NEI 04-10, Step 12, Evaluate Total and Cumulative Effect on CDF and LERF describes details of various aspects of calculating revised STIs. Specifically, test strategies, sensitivity studies, and Common Cause Failure (CCF) treatment are addressed.
- a. Describe the approach to performing sensitivity analysis the licensee will use.
- b. How will the impact of various test strategies be evaluated in determining revised STIs?
- c. How will CCF be addressed in performing these calculations?
RAI 5
NEI 04-10, Revision 1, states that external events risk impact may be considered quantitatively or qualitatively. The NRC staffs safety evaluation on NEI 04-10, Revision 1 states that a qualitative
screening analysis may be used when the surveillance frequency impact on plant risk can be shown to be negligible or zero.
In Section 5.0 of Attachment II to the LAR the licensee stated that Wolf Creek is currently developing a seismic PRA, but it has neither been completed nor peer reviewed. A Seismic Margins Assessment (SMA) was performed with a review level earthquake at 0.3g peak ground acceleration (PGA) during the IPEEE.
The licensee proposed to assess SSCs impacted by frequency changes in the proposed program against the SMA in accordance with NEI 04-10 guidance.
The SMA in the licensees IPEEE, completed in 1995, concluded that only a few instances are required for a detailed review to screen equipment anchorages to a high confidence of a low probability of failure (HCLPF) of at least 0.3g PGA. The licensees recent seismic hazard and screening report (ADAMS Accession No. ML14097A020) shows that the ground motion response spectrum (GMRS) for the Wolf Creek site peaks at 0.73g (12.5 Hz) and the GMRS is higher than the safe shutdown earthquake (SSE) at a frequency of about 5 Hz or higher. It is unclear to the NRC staff whether the licensees IPEEE SMA continues to be appropriate for use in the proposed program. It is also unclear whether updated information about the seismic hazard will be used in the proposed program.
Discuss how the licensees IPEEE SMA, including the success paths and corresponding SSCs, continues to be appropriate for use in the proposed program given recent information on the re-evaluated seismic hazard at the site. Include a description of how recent seismic hazard information is included in the licensees proposed program or justify its exclusion.
RAI 6
NEI 04-10, Revision 1, states that external events risk impact may be considered quantitatively or qualitatively. The NRC staffs safety evaluation on NEI 04-10, Revision 1 states that a qualitative screening analysis may be used when the surveillance frequency impact on plant risk can be shown to be negligible or zero.
In Section 5.0 of Attachment II to the LAR, the licensee stated that Wolf Creek has developed a high winds PRA model and conducted an external events screening assessment in accordance with Parts 6 and 7 of the ASME/ANS PRA Standard. However, given that the high winds PRA model still has outstanding F&Os that need to be addressed, the licensee proposed to utilize the IPEEE analysis for high winds for the STI change evaluations. It is unclear to the NRC staff whether the licensees IPEEE information and evaluation continues to be appropriate for use in the proposed program. It is also unclear whether updated information about high winds will be used in the proposed program.
Discuss how the licensees IPEEE evaluation for high winds continues to be appropriate for use in the proposed program given the insights from the licensees high winds PRA model and other recent relevant high wind studies, if available. Include a description of how recent high winds related information is included in the licensees proposed program or justify its exclusion.
RAI 7
NEI 04-10, Revision 1, states that external events risk impact may be considered quantitatively or qualitatively. The NRC staffs safety evaluation on NEI 04-10, Revision 1 states that a qualitative
screening analysis may be used when the surveillance frequency impact on plant risk can be shown to be negligible or zero.
In Section 5.0 of Attachment II to the LAR the licensee stated that other external hazards, including external flooding, were determined in the IPEEE to be negligible contributors to overall plant risk. In the licensees Flood Hazard Reevaluation Report (ADAMS Accession No. ML14077A281), the licensee determined that the current design basis flood levels do not bound the reevaluated hazard elevations for the local intense precipitation (LIP) hazard. It is unclear to the NRC staff whether the licensees IPEEE information and evaluation for external flooding continues to be appropriate for use in the proposed program. It is unclear to the NRC staff how the updated external flooding information for the site will be used in the proposed program.
Discuss how the licensees IPEEE evaluation for external flooding continues to be appropriate for use in the proposed program given recent information on the external flooding hazard at the site. Include a description of how recent external flooding information for the site is included in the licensees proposed program or justify its exclusion.
Hearing Identifier:
NRR_DRMA Email Number:
791 Mail Envelope Properties (DM8PR09MB61835FA10B5D5B0B9FD9ADF79A3E0)
Subject:
Requests for additional information: Wolf Creek amendment request to modify technical specification surveillance frequency consistent with TSTF-425 (EPID: L-2020-LLA-0091)
Sent Date:
9/17/2020 3:27:06 PM Received Date:
9/17/2020 3:27:06 PM From:
Lee, Samson Created By:
Samson.Lee@nrc.gov Recipients:
"Josh Turner" <Josh.Turner@evergy.com>
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