ML24142A515

April 22, 2024, Summary of Public Mtg with Tennessee Valley Authority to Discuss Use of Risk-Informed Process Evaluation for a Proposed License Amendment Request Elimination of Limiting Condition for Operation Actions for the Rod Worth Mini

ML24142A515
Person / Time
Site:	Browns Ferry
Issue date:	05/28/2024
From:	Kimberly Green Plant Licensing Branch II
To:	Tennessee Valley Authority
Green K
References
EPID L-2024-LRM-0059
Download: ML24142A515 (1)

Text

May 28, 2024

LICENSEE: Tennessee Valley Authority

FACILITY: Browns Ferry Nuclear Plant, Units 1, 2 and 3

SUMMARY

OF APRIL 22, 2024, PUBLIC MEETING WITH TENNESSEE VALLEY AUTHORITY TO DISCUSS USE OF RISK-INFORMED PROCESS EVALUTION (RIPE) FOR A PROPOSED LICENSE AMENDMENT REQUEST REGARDING ELIMINATION OF LIMITING CONDITION FOR OPERATION ACTIONS FOR THE ROD WORTH MINIMIZER (EPID L-2024-LRM-0059)

On April 22, 2024, the U.S. Nuclear Regulator y Commission (NRC) staff held a second public teleconference with representatives of the Tennessee Valley Authority (TVA, the licensee) to discuss the use of Risk-Informed Process Evaluation (RIPE) for a proposed license amendment request (LAR) for Browns Ferry Nuclear Plant (Browns Ferry), Units 1, 2, and 3. The proposed LAR would modify Browns Ferry Technical Specification (TS) 3.3.2.1, Control Rod Block Instrumentation, to eliminate Required Actions C.2.1.1 and C.2.1.2 to allow reactor startup with rod worth minimizer (RWM) inoperable provided control rod movements are independently verified to be in compliance with banked position withdrawal sequence, as required by limiting condition for operation (LCO) 3.1.6, Rod Pattern Control. The meeting notice and agenda for this meeting, dated April 10, 2024, are available at Agencywide Documents Access and Management System (ADAMS) Accession No. ML24101A135. The licensees slides for the meeting are available at ADAMS Accession No. ML24113A096. A list of the meeting attendees is enclosed.

During the first public meeting, held on January 22, 2024, the NRC staff explained to TVA that the planned approach would not meet the acceptance criteria for RIPE because the initiating event (i.e., RWM is not functional) is not modeled in the probabilistic risk assessment (PRA) model that was previously evaluated by the NRC. A meeting summary for the first public meeting, including a description of the RWM, can be found at ADAMS Accession No. ML24043A046. TVA requested the second public meeting to present its revised risk evaluation of the proposed change to address the NRC staff s comments at the previous meeting and to obtain additional NRC feedback and concerns regarding the revised approach.

TVA recalled the proposed TS change, which will elim inate TS LCO 3.3.2.1, Actions C.2.1.1 and C.2.1.2, to allow an unrestricted number of reactor startup with the RWM inoperable provided control rod movements are independently verified to comply with banked position withdraw sequence (BPWS). The BPWS are control rod patterns that prevent high-worth control rods.

This limits the reactivity insertion in a control rod drop accident (CRDA), thereby limiting the power excursion in a CRDA and, consequently, eliminates or limits fuel rod damage.

TVA stated that the RWM is not modeled in the Browns Ferry PRA, and the CRDA is not considered an initiating event in the Browns Ferry PRA. TVA explained that even without BPWS compliance, the drop of a high-worth control rod does not damage enough fuel rods to meet the PRA definition of core damage. As such, even when the RWM does not enforce BPWS compliance, the outcome of a CRDA is likely that an automatic or manual scram will occur with

subsequent probabilistic equipment failures and/or operator errors that result in a loss of core cooling and subsequent core damage. TVA determined that it could assess risk from a CRDA by adjusting the reactor scram initiating event frequency in the Browns Ferry PRA. TVA reasoned that in low power operation the plant has the same equipment that is important for preventing core damage as it has during full power operation; therefore, the Browns Ferry full power PRA model can provide a bounding risk assessment for lower power operation. TVA stated that under the current TS requirement, onl y a select set of CRDAs will result in fuel damage, but not core damage, and those CRDAs will likely result in an automatic or manual reactor scram. Under the proposed TS requirement, the RWM is, worst-case, not going to be functional for most reactor startups; therefore, there will be an increase in the number of CRDAs that result in fuel damage and increase in the frequency of an automatic or manual reactor scram. The NRC staff asked if a reactor scram is being used as a surrogate for a CRDA. TVA confirmed that this is the approach being used.

TVA estimated the increase in reactor scrams under the proposed TS change based on the number of reactor startups Browns Ferry experiences per year, which is less than two, multiplied by the probability that the control rods are not in compliance with BPWS. This estimated increase in reactor scrams is added to the scram initiating event frequency in the Browns Ferry PRA. As an example, TVA calculated the increase in core damage frequency (CDF) for Browns Ferry, Unit 1, to be less than 10 -7 per year, and the increase in large early release frequency (LERF) to be less than 10 -8 per year. Because the risk model is based on the full power PRA model, the reactor scram frequency is used as a surrogate in the risk evaluation, and the CDF and LERF are bounding metrics for characterizing the impact of the proposed TS change, TVA concluded that RIPE is an acceptable approach for the proposed TS change.

TVA discussed its proposed answers to each of the RIPE screening questions for any impact and the minimal impact RIPE screening questions for which an impact was identified as presented in the slides. The NRC staff noted that the responses to the screening questions for any impact should be broad and include all potential impacts. If the response identifies an impact, a justification as to why the impact is less than minimal should be provided. The staff noted that if a response to a screening question for any impact is NO, but the staff disagreed, it would be difficult to accept the LAR because the RIPE review process does not usually allow for any requests for additional information. The staff encouraged TVA to provide additional details to demonstrate that defense-in-depth is not more than minimally impacted by the proposed change. Also, the staff stated that TVA should include information in the LAR about any operator actions used for defense in depth, including the procedures used, how operators are trained in accordance with those procedures, and that changes to the procedures are controlled under its procedure change control program.

The NRC staff noted that it recently issued Revision 3 to the Safety Impact Characterization Guidance for Implementing the Risk-Informed Process for Evaluations (ML23354A152), which includes criteria for assessing performance monitoring strategies. Because TVAs presentation did not include any information about performance monitoring, the NRC staff informed TVA that it should include information regarding performance monitoring in its LAR.

TVA stated that it would consider the NRCs feedback. Although it did not provide a firm timeframe for its planned submittal, TVA stated that it might submit the LAR by the end of November.

No regulatory decisions were made at this meeting.

No comments or public meeting feedback forms were received.

Please direct any inquiries to me at 301-415-1627 or Kimberly.Green@nrc.gov.

/RA/

Kimberly J. Green, Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

Docket Nos. 50-259, 50-260, and 50-296

Enclosure:

List of Attendees

cc: Listserv LIST OF ATTENDEES APRIL 22, 2024, TELECONFERENCE WITH TENNESSEE VALLEY AUTHORITY REGARDING USE OF RISK-INFORMED PROCESS EVALUTION (RIPE) FOR A PROPOSED LICENSE AMENDMENT REQUEST REGARDING THE ROD WORTH MINIMIZER FOR BROWNS FERRY NUCLEAR PLANT, UNITS 1, 2 AND 3

Name Organization Kim Green U.S. Nuclear Regulatory Commission (NRC)

John Hughey NRC Michelle Kichline NRC Antonios Zoulis NRC Ravi Grover NRC Charley Peabody NRC Jason Drake NRC Zach Turner NRC Shamica Billups NRC Beau Eckermann Tennessee Valley Authority (TVA)

Bill Williamson TVA Christopher Carey TVA David Renn TVA Andy Taylor TVA Bradley Dolan TVA Mark Nicholson TVA Jesse Baron TVA Shawna Hughes TVA Gordon Williams TVA Fernando Ferrante EPRI Carol Trull EPRI Tony Brown Nuclear Energy Institute (NEI)

Andrew Mauer NEI Sara Scott Xcel Energy Jeff Gromatzky Enercon Mary Miller Dominion Energy Deann Raleigh Curtiss-Wright Jana Bergman Curtiss-Wright Tom Gazda

Enclosure

Meeting Pkg ML24143A002 Meeting Summary ML24142A515 Meeting Notice ML24101A135 Slides ML24113A096 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME KGreen ABaxter DWrona KGreen DATE 05/21/24 05/24/24 05/28/24 05/28/24