ML21253A090

Supplemental Information Needed for Acceptance of Requested Licensing Actions License Amendment and Regulatory Exemption for a Risk-Informed Approach to Address GSI-191 (EPIDs L-2021-LLA- 0152 and L-2021-LLE-0039)

ML21253A090
Person / Time
Site:	Wolf Creek
Issue date:	09/23/2021
From:	Samson Lee Plant Licensing Branch IV
To:	Reasoner C Wolf Creek
Lee S, 301-415-3168
References
EPIDs L-2021-LLA- 0152 and L-2021-LLE-00
Download: ML21253A090 (5)

Text

September 23, 2021 Mr. Cleveland Reasoner Chief Executive Officer and Chief Nuclear Officer Wolf Creek Nuclear Operating Corporation P.O. Box 411 Burlington, KS 66839

SUBJECT:

WOLF CREEK GENERATING STATION, UNIT 1 - SUPPLEMENTAL INFORMATION NEEDED FOR ACCEPTANCE OF REQUESTED LICENSING ACTIONS RE: LICENSE AMENDMENT AND REGULATORY EXEMPTION FOR A RISK-INFORMED APPROACH TO ADDRESS GENERIC SAFETY ISSUE 191 AND RESPOND TO GENERIC LETTER 2004-02 (EPID L-2021-LLA-0152 AND EPID L-2021-LLE-0039)

Dear Mr. Reasoner:

By letter dated August 12, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21224A118), Wolf Creek Nuclear Operating Corporation (the licensee) submitted an application requesting a license amendment that would revise the licensing basis as described in the Wolf Creek Generating Station Updated Safety Analysis Report to allow the use of a risk-informed approach to address potential issues discussed in Generic Safety Issue (GSI)-191, Assessment of Debris Accumulation on PWR [Pressurized-Water Reactor] Sump Performance, and respond to Generic Letter 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors (ADAMS Accession No. ML042360586). Additionally, the licensee requested an exemption from certain requirements in Section 50.46(a)(1) of Title 10 of the Code of Federal Regulations (10 CFR) in accordance with the provisions of 10 CFR 50.12, Specific exemptions. The licensees application was submitted following the guidance in Regulatory Guide 1.174, Revision 3, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis (ADAMS Accession No. ML17317A256).

The purpose of this letter is to provide the results of the U.S. Nuclear Regulatory Commission (NRC) staffs acceptance review of the application. The acceptance review was performed to determine if there is sufficient technical information in scope and depth to allow the NRC staff to complete its detailed technical review. The acceptance review is also intended to identify whether the application has any readily apparent information insufficiencies in its characterization of the regulatory requirements or the licensing basis of the plant.

Consistent with 10 CFR 50.90, an application for an amendment to a license (including the technical specifications) must fully describe the changes requested, and following as far as applicable, the form prescribed for original applications. Section 50.34 of 10 CFR addresses the content of technical information required. This section stipulates that the submittal addresses the design and operating characteristics, unusual or novel design features, and principal safety considerations.

C. Reasoner Consistent with 10 CFR 50.12, the Commission may, upon application by any interested person or upon its own initiative, grant exemptions from the requirements of the regulations of this part, which are authorized by law, will not present an undue risk to the public health and safety, and are consistent with the common defense, and security. The Commission will not consider granting an exemption unless special circumstances are present, as specified in 10 CFR 50.12(a)(2).

The NRC staff has reviewed the application and concluded that the information delineated in the enclosure to this letter is necessary to enable the NRC staff to make an independent assessment regarding the acceptability of the application in terms of regulatory requirements for the protection of public health and safety and the environment.

In order to make the application complete, the NRC staff requests that the licensee supplement the application to address the information requested in the enclosure by October 12, 2021. This will enable the NRC staff to assess the acceptability of the application for its detailed review. If the information responsive to the NRC staffs request is not received by the above date, the application will not be accepted for review pursuant to 10 CFR 2.101, and the NRC will cease its activities associated with the application. If the application is subsequently accepted for review, you will be advised of any further information needed to support the NRC staffs detailed technical review by separate correspondence.

The information requested and associated timeframe in this letter were discussed with the licensees staff on a September 23, 2021, clarification call.

If you have any questions, please contact me at 301-415-3168 or via e-mail at Samson.Lee@nrc.gov.

Sincerely,

/RA/

Samson S. Lee, Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-482 Enclosure Supplemental Information Needed cc: Listserv

SUPPLEMENTAL INFORMATION NEEDED LICENSE AMENDMENT REQUEST AND EXEMPTION REQUEST FOR A RISK-INFORMED APPROACH TO ADDRESS GENERIC SAFETY ISSUE-191 AND RESPOND TO GENERIC LETTER 2004-02 WOLF CREEK NUCLEAR OPERATING CORPORATION WOLF CREEK GENERATING STATION, UNIT 1 DOCKET NO. 50-482 By letter dated August 12, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21224A118), Wolf Creek Nuclear Operating Corporation (the licensee) submitted an application requesting a license amendment that would revise the licensing basis as described in the Wolf Creek Generating Station Updated Safety Analysis Report to allow the use of a risk-informed approach to address potential issues discussed in Generic Safety Issue (GSI)-191, Assessment of Debris Accumulation on PWR [Pressurized-Water Reactor] Sump Performance, and respond to Generic Letter 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors (ADAMS Accession No. ML042360586). Additionally, the licensee requested an exemption from certain requirements in Section 50.46(a)(1) of Title 10 of the Code of Federal Regulations in accordance with the provisions of 10 CFR 50.12, Specific exemptions. The licensees application was submitted following the guidance 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 (ADAMS Accession No. ML17317A256).

REGULATORY BASIS Section 2.4, Acceptance Guidelines of RG 1.174, Revision 3, states in part:

if there is an indication that the CDF [core damage frequency] may be considerably higher than 10-4 per reactor year, the focus should be on finding ways to decrease rather than increase it.

and if there is an indication that the LERF [large early release frequency] may be considerably higher than 10-5 per reactor year, the focus should be on finding ways to decrease rather than increase it.

and In applying these guidelines, it is particularly important to recognize that the risk metrics calculated using PRA [probabilistic risk assessment] models are a function of the assumptions and approximations made in the development of those models. This is particularly important when the results from PRA models for multiple hazard groups are Enclosure

combined, since the results from some hazard groups, depending on the state of practice, may be conservatively or nonconservatively biased.

INFORMATION INSUFFICIENCIES During its acceptance review of the application the U.S. Nuclear Regulatory Commission (NRC) staff noted that Table 1, Baseline CDF and LERF Values in Attachment VII Overview of Risk-Informed Approach, of the application provides the plants baseline CDF as 5.69E-04 per year and baseline LERF as 1.34E-05 per year. In the same attachment the licensee states only that (1) the fire PRA model has not yet been finalized or peer reviewed, and (2) the CDF and LERF values are expected to decrease. In addition, the plants baseline CDF and LERF values reported in the application indicate the potential erosion of margins to the Commissions Safety Goals for the Operations of Nuclear Power Plants (51 FR 28044; August 4, 1986, and republished in 51 FR 30028; August 21, 1986) embedded in the 10-4 per reactor year and 10-5 per reactor year guidelines for CDF and LERF, respectively. Information is unavailable in the application justifying why this is not the case. Further, the NRC staff noted that Table 3, GSI-191 Risk Quantification Results, in Attachment VII of the application shows the change in CDF and LERF from various hazards. The application states that these values are not added together because bounding methods were used in the calculation of the values. While a licensee has the option of selecting the approach for determining the change in risk from different contributors, the application does not provide sufficient information to support not aggregating the change in risk and, therefore, the claim that the base case change in risk is within Region III of RG 1.174.

SUPPLEMENTAL INFORMATION NEEDED To support the continuation of the acceptance review for this application, the NRC staff requests the licensee to supplement the application with the following information:

1. Justification supporting the claim that the CDF and LERF values are expected to decrease, including the anticipated extent of the decrease, details of the existing fire PRA model conservatisms and non-conservatisms on the PRA results as presented in the application, any plant modifications affecting potential fire risk, and details of the new fire PRA model, current status, and schedule for finalization.

2. Discussion of whether ways to reduce baseline CDF and LERF, consistent with the guidance in RG 1.174, have been identified, and the associated implementation schedule, or justification why such steps are unnecessary.

3. Justification that the margins from the Commissions Safety Goals embedded in the 10-4 per reactor year and 10-5 per reactor year guidelines for CDF and LERF in RG 1.174, respectively, are maintained based on the baseline CDF and LERF values described in the application. Provide any actions and an implementation schedule to maintain the margins if necessary.

4. Justification that the total change in risk remains within Region III of RG 1.174 after aggregating the change in risk from the different contributors listed in Table 3 of the application.

ML21253A090 OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA NRR/DRA/APLB/BC NAME SLee PBlechman JWhitman DATE 9/9/2021 9/10/2021 9/9/2021 OFFICE NRR/DORL/LPL4/BC NRR/DORL/LPL4/PM NAME JDixon-Herrity SLee DATE 9/10/2021 9/23/2021