ML20212L870

Request for Additonal Information Review of License Amendment Requests Regarding Riskinformed Categorization and Treatment of Structures, Systems and Components (L-2019-LLA-0290)

ML20212L870
Person / Time
Site:	Nine Mile Point
Issue date:	07/30/2020
From:	Marshall M Plant Licensing Branch 1
To:	Reynolds R Exelon Generation Co, Exelon Nuclear
Marhsall M, NRR/DORL/LPL, 415-2871
References
EPID L-2019-LLA-0290, L-2019-LLA-0290
Download: ML20212L870 (3)

Text

From: Marshall, Michael To: [Licensee] Ron Reynolds (Exelon)

Cc: Danna, James

Subject:

NINE MILE POINT NUCLEAR STATION, UNIT 2 - REQUEST FOR ADDITONAL INFORMATION RE: REVIEW OF LICENSE AMENDMENT REQUESTS REGARDING RISKINFORMED CATEGORIZATION AND TREATMENT OF STRUCTURES, SYSTEMS AND COMPONENTS (L-2019-LLA-0290)

Date: Thursday, July 30, 2020 1:13:00 PM Hello Ron, By letter dated December 26, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19360A145), Exelon Generation Company, LLC (Exelon, the licensee) requested that the NRC modify the Licensing Basis, of Renewed Facility Operating License No. NPF-69 for Nine Mile Point Nuclear Station, Unit 2 (Nine Mile Point 2). Exelons proposed license amendment request would modify Nine Mile Point 2 licensing basis to allow for the implementation of the provisions of Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 69 (50.69), Risk-Informed Categorization and Treatment of Structures, Systems and Components [SSCs] for Nuclear Power Reactors. The proposed changes are based on NEI 00-04, 10 CFR 50.69 SSC Categorization Guideline, Revision 0 dated July 2005 (ADAMS Accession No. ML052910035).

The NRC staff has reviewed the information provided in the license amendment request and has determined that additional information is needed to complete its review. Below is the NRC staffs request for additional information. The request for additional information was discussed with you on July 30, 2020, and it was agreed that Exelons response would be provided within 30 days from the date of this email.

Requests for Additional Information

1. NEI 00-04, Section 7.1 provides guidance related to categorizing components supporting multiple functions. The guidance states: "the SSC, or part thereof, should be assigned the highest risk significance for any function that the SSC or part thereof supports."

Section 4 of NEI 00-04 addresses categorization of SSCs that serve an interface between two or more components, stating:

[] there may be circumstances where the categorization of a candidate low safety-significant SSC within the scope of the system being considered cannot be completed because it also supports an interfacing system. In this case, the SSC will remain uncategorized until the interfacing system is considered.

Section 4 of NEI 00-04 also addresses system boundary assignment stating:

All components and equipment within the defined boundaries of the chosen system should be included. However, care should be taken in extending beyond system boundaries to avoid the introduction of new systems and functions. [] The system boundary should be defined such that any components from another system only support the safety function of the primary system of interest.

The NEI guidance states that the interfacing system should be considered. The LAR does not explain how the interfacing system will be considered. In this context, the definition of

system boundaries may become important for the categorization. Given these observations, address the following:

a. Describe, with examples, how system boundaries are defined to ensure that the interfacing SSCs are assigned to the right system to support a correct categorization outcome.

b. Describe and justify with examples, how the licensee intends to address the guidance in NEI 00-04 for interfacing SSCs. If an interface SSC is categorized before categorizing all the systems that it interfaces address the following:

i. Describe how it is ensured that the sub-set of all the interfacing system functions associated with the interfacing component can and will be correctly and comprehensively identified without fully categorizing the interfacing system.

ii. Confirm that interface components will only be categorized if interface component failure cannot prevent performance of any interface system functions.

2. Section 5.3 of NUREG-1855, Revision 1, Guidance on the Treatment of Uncertainties Associated with PRAs in Risk-Informed Decisionmaking, Final Report, dated March 2017 (ADAMS Accession No. ML17062A466), presents guidance on the process of identifying, characterizing, and qualitative screening of model uncertainties. Discussion of the PRA model uncertainty process is provided in LAR Section 3.2.7. The LAR states that the process for identifying key assumptions and sources of uncertainties for the internal events and the fire PRAs was performed using the guidance in NUREG-1855, Revision 1. It further states that the internal events and the fire PRA models and notebooks were reviewed for plant-specific key assumptions and sources of uncertainty.

Further, the LAR states that generic sources of uncertainty for the internal events PRA were identified from Electric Power Research Institute (EPRI) Technical Report (TR)-1016737, Treatment of Parameter and Modeling uncertainty for Probabilistic Risk Assessments and for the fire PRA from EPRI TR-1026511, Practical Guidance of the Use of Probabilistic Risk Assessment in Risk-informed Applications with a Focus on the Treatment of Uncertainty. The LAR does not describe the process and the criteria used to identify, from the initial comprehensive list of assumptions and sources of uncertainty in the base PRA model(s) (including those associated with plant-specific features, modeling choices, and generic industry concerns), the specific key assumptions and sources of uncertainties presented in the LAR.

Describe, separately for the internal events, internal flooding and the fire PRAs, the process used to identify and evaluate key assumptions and sources of model uncertainty. Address the following in the response:

a. Discuss how a comprehensive list of plant-specific and generic industry key assumptions and sources of uncertainty were identified as a starting point for this evaluation.

b. Explain how the comprehensive list of key assumptions and sources of uncertainty sources was screened to a list of uncertainties that were specifically evaluated for their impact on the 50.69 application.

c. Explain what criteria, qualitative or quantitative, or what additional analysis were used to evaluate the impact of the key assumptions and sources of uncertainty on the 50.69 application.

Best Regards, Michael L. Marshall, Jr., Senior Project Manager Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-410