2022-08617. Level 3 Probabilistic Risk Assessment Project Documentation (Volume 3x)

AGENCY:

Nuclear Regulatory Commission.

ACTION:

Draft report; request for comment.

SUMMARY:

The U.S. Nuclear Regulatory Commission (NRC) is issuing for public comment a draft report on the Level 3 Probabilistic Risk Assessment (PRA) project; specifically, “Volume 3x: Overview of Reactor, At-Power, Level 1, 2, and 3 PRAs for Internal Events and Internal Floods.”

DATES:

Submit comments by June 21, 2022. Comments received after this date will be considered if it is practical to do so, but the Commission is able to ensure consideration only for comments received on or before this date.

ADDRESSES:

You may submit comments by any of the following methods; however, the NRC encourages electronic comment submission through the Federal rulemaking website:

• Federal rulemaking website: Go to https://www.regulations.gov and search for Docket ID NRC-2022-0085. Address questions about Docket IDs in Regulations.gov to Stacy Schumann; telephone: [phone]; email: [e-mail]. For technical questions, contact the individual listed in the For Further Information Contact section of this document.

• Mail comments to: Office of Administration, Mail Stop: TWFN-7-A60M, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, ATTN: Program Management, Announcements and Editing Staff.

For additional direction on obtaining information and submitting comments, see “Obtaining Information and Submitting Comments” in the SUPPLEMENTARY INFORMATION section of this document.

FOR FURTHER INFORMATION CONTACT:

Alan Kuritzky, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, telephone: [phone], email: [e-mail].

SUPPLEMENTARY INFORMATION:

I. Obtaining Information and Submitting Comments

A. Obtaining Information

Please refer to Docket ID NRC-2022-0085 when contacting the NRC about the availability of information for this action. You may obtain publicly available information related to this action by any of the following methods:

• Federal Rulemaking Website: Go to https://www.regulations.gov and search for Docket ID NRC-2022-0085.

• NRC's Agencywide Documents Access and Management System (ADAMS): You may obtain publicly available documents online in the ADAMS Public Documents collection at https://www.nrc.gov/​reading-rm/​adams.html. To begin the search, select “Begin Web-based ADAMS Search.” For problems with ADAMS, please contact the NRC's Public Document Room (PDR) reference staff at 1-800-397-4209, 301-415-4737, or by email to [e-mail]. For the convenience of the reader, instructions about obtaining materials referenced in this document are provided in the “Availability of Documents” section.

• NRC's PDR: You may examine and purchase copies of public documents, by appointment, at the NRC's PDR, Room P1 B35, One White Flint North, 11555 Rockville Pike, Rockville, Maryland 20852. To make an appointment to visit the PDR, please send an email to [e-mail] or call 1-800-397-4209 or 301-415-4737, between 8:00 a.m. and 4:00 p.m. (ET), Monday through Friday, except Federal holidays.

B. Submitting Comments

The NRC encourages electronic comment submission through the Federal rulemaking website ( https://www.regulations.gov ). Please include Docket ID NRC-2022-0085 in your comment submission.

The NRC cautions you not to include identifying or contact information that you do not want to be publicly disclosed in your comment submission. The NRC will post all comment submissions at https://www.regulations.gov as well as enter the comment submissions into ADAMS. The NRC does not routinely edit comment submissions to remove identifying or contact information.

If you are requesting or aggregating comments from other persons for submission to the NRC, then you should inform those persons not to include identifying or contact information that they do not want to be publicly disclosed in their comment submission. Your request should state that the NRC does not routinely edit comment submissions to remove such information before making the comment submissions available to the public or entering the comment into ADAMS.

II. Discussion

As directed in SRM-SECY-11-0089, “Options for Proceeding with Future Level 3 Probabilistic Risk Assessment (PRA) Activities,” the staff is conducting a full-scope multi-unit site Level 3 PRA (Level 3 PRA project) that addresses all internal and external hazards; all plant operating modes; and all reactor units, spent fuel pools, and dry cask storage. The reference site for this study contains two four-loop Westinghouse PWRs with large dry containments. The objectives of the Level 3 PRA project are to (1) develop a Level 3 PRA, generally based on current state-of-practice methods, tools, and data, that (a) reflects technical advances since the last NRC-sponsored Level 3 PRAs (NUREG-1150), which were completed over 30 years ago, and (b) addresses scope considerations that were not previously considered ( e.g., low power and shutdown risk, multi-unit risk, other radiological sources); (2) extract new insights to enhance regulatory decision making and to help focus limited NRC resources on issues most directly related to the agency's mission to protect public health and safety; (3) enhance PRA staff capability and expertise and improve documentation practices to make PRA information more accessible, retrievable, and understandable; and (4) demonstrate technical feasibility and evaluate the realistic cost of developing new Level 3 PRAs.

The work performed under this project is being documented as a multi-volume report. This first batch of Level 3 PRA project reports provides a high-level discussion of the overall project technical approach (Volume 2) and describes the analyses and results for the reactor, at-power, Level 1, 2, and 3 PRAs for internal events and internal floods (Volume 3). Each set of Level 3 PRA project reports covering the Level 1, 2, and 3 PRAs for a specific site radiological source, plant operating state, and hazard group (or groups) is accompanied by an overview report. The overview reports summarize the results and insights from all three PRA levels.

The Level 3 PRA project analyses reflect the reference plant as it was designed and operated as of 2012. To provide results and insights better aligned with the current design and operation of the reference plant, the overview reports also provide a reevaluation of the plant risk based on a set of new plant equipment and PRA model assumptions and compare the results of the reevaluation to the original study results. This reevaluation reflects the current reactor coolant pump shutdown seal design at the reference plant, as well as the potential impact of FLEX strategies, both of which reduce the risk to the public.

The results of the original Level 3 PRA project analyses and the reevaluation both show that, when considering internal events and floods, the combination of this plant design and site location has substantial margin to the quantitative health objectives related to the NRC's safety goal policy. Even though these margins can vary for other plants due to variations in their design and siting, the estimates derived for the reference plant, when adjusted for siting and design variations, would provide useful qualitative risk insights for other U.S. operating plants.

III. Availability of Documents

The documents identified in the following table are available to interested persons through ADAMS, as indicated.

Document description	ADAMS Accession No.
SRM-SECY-11-0089, “Options for Proceeding with Future Level 3 Probabilistic Risk Assessment (PRA) Activities”	ML112640419
Level 3 PRA Project, Volume 3x: Overview of Reactor, At-Power, Level 1, 2, and 3 PRAs for Internal Events and Internal Floods; Draft Report for Comment	ML22067A210
Level 3 PRA Project, Volume 3a: Reactor, At-Power, Level 1 PRA for Internal Events, Part 1—Main Report	ML22067A211
Level 3 PRA Project, Volume 3a: Reactor, At-Power, Level 1 PRA for Internal Events, Part 2—Appendices	ML22067A212
Level 3 PRA Project, Volume 3b: Reactor, At-Power, Level 1 PRA for Internal Flooding	ML22067A213
Level 3 PRA Project, Volume 3c: Reactor, At-Power, Level 2 PRA for Internal Events and Floods	ML22067A214
Level 3 PRA Project, Volume 3d: Reactor, At-Power, Level 3 PRA for Internal Events and Floods	ML22067A215
Level 3 PRA Project, Volume 2: Background, Site and Plant Description, and Technical Approach	ML22067A232

Dated: April 19, 2022.

For the Nuclear Regulatory Commission.

John A. Nakoski,

Chief, Probability Risk Assessment Branch, Division of Risk Analysis, Office of Nuclear Regulatory Research.