ML24043A046
| ML24043A046 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 02/16/2024 |
| From: | Kimberly Green Plant Licensing Branch II |
| To: | Tennessee Valley Authority |
| Green K | |
| Shared Package | |
| ML24043A047 | List: |
| References | |
| EPID L-2023-LRM-0003 | |
| Download: ML24043A046 (1) | |
Text
February 16, 2024 LICENSEE:
Tennessee Valley Authority FACILITY:
Browns Ferry Nuclear Plant, Units 1, 2 and 3
SUBJECT:
SUMMARY
OF JANUARY 22, 2024, PUBLIC MEETING WITH TENNESSEE VALLEY AUTHORITY TO DISCUSS USE OF RISK-INFORMED PROCESS EVALUATION (RIPE) FOR A PROPOSED LICENSE AMENDMENT REQUEST REGARDING ELIMINATION OF LIMITING CONDITION FOR OPERATION ACTIONS FOR THE ROD WORTH MINIMIZERS (EPID L-2023-LRM-0003)
On January 22, 2024, the U.S. Nuclear Regulatory Commission (NRC) staff held a 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) Limiting Conditions for Operation (LCO) 3.3.2.1, Control Rod Block Instrumentation, 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 LCO 3.1.6, Rod Pattern Control.
The meeting notice and agenda for this meeting, dated January 10, 2024, are available at ADAMS Accession No. ML24012A053. The licensees slides and handouts for the meeting are available at ADAMS Package Accession No. ML24019A097. A list of the meeting attendees is enclosed.
TVA stated that TS LCO 3.1.6 requires that control rods be in compliance with the banked position withdrawal sequence (BPWS). The BPWS, which are control rod patterns, prevent high worth control rods. The RWM is an automatic system that uses error lights and rod movement blocks to enforce BPWS control rod patterns. The RWM automatically blocks the continuous withdraw of an out of sequence control rod during reactor startup until the mispositioned control rod is moved to an allowed position. The RWM is required to be operable during reactor startup per TS 3.3.2.1 LCO and is functionally tested in startup during Mode 2 as required by TS Surveillance Requirement (SR) 3.3.2.1.2. TVA stated that this test delays startup, particularly if any repairs are needed.
When the RWM is inoperable during reactor startup, TS 3.3.2.1, Action C.2.1.1 allows reactor startup to continue if at least 12 control rods have been withdrawn. Action C.2.1.2 allows one reactor startup a year, if <12 control rods have been withdrawn. Action C.2.2 requires control rod movements to be independently verified to comply with BPWS requirements when the RWM is inoperable. TVA noted that having 12 rods withdrawn does not eliminate or reduce fuel damage from a control rod drop accident (CRDA).
TVA will propose to eliminate LCO 3.3.2.1 Actions C.2.1.1 and C.2.1.2 to allow reactor startup with the RWM inoperable provided control rod movements are independently verified to comply with BPWS. TVA stated that it plans to use the RIPE for the proposed change.
TVA described the CRDA analysis, which is performed each cycle to verify damaged fuel rods can be cooled and the source term from damaged fuel rods is bounded by that assumed in the radiological analysis for a CRDA. TVA stated that the results of the analysis demonstrate that unless the rod drop occurs in the highest worth control rod that there is margin in the CRDA analysis to absorb a misposition that would increase the worth of a dropped rod. TVA noted that the RWM is not modeled in the Browns Ferry probabilistic risk assessment (PRA), and the CRDA is not an initiator in the PRA since a design basis CRDA does not meet the PRA definition of core damage. Therefore, TVA performed a bounding calculation of the increase in core damage frequency (CDF) and large early release frequency (LERF) for when RWM is not functional and control rod movements are independently verified by assuming core damage occurs if the control rod(s) misposition is not detected by the independent verification.
TVA calculated that the increase in CDF from no longer crediting RWM is 2.13x10-8/year, which is less than the criterion for a RIPE submittal of <10-7/year. Additionally, the increase in LERF is 5.75x10-9/year, which is less that the criterion for a RIPE submittal of <10-8/year.
TVA stated that RIPE is an acceptable approach for the proposed TS change to LCO 3.3.2.1 because:
The safety impact can be quantified using a bounding PRA analysis, since a low power PRA model is not available.
The PRA model used for the RIPE LAR is technically acceptable because it was used for Browns Ferry Technical Specification Task Force (TSTF) traveler TSTF-505, Provide Risk-Informed Extended Completion Times - RITSTF [Risk-Informed TSTF]
Initiative 4b, amendments.
The integrated decision-making panel (IDP) reviewing and approving the safety impact of the change is the same IDP used for implementation of the Browns Ferry amendments for Title 10 of the Code of Federal Regulations (10 CFR), Section 50.69, Risk-informed categorization and treatment of structures, systems and components for nuclear power reactors.
The change has no or minimal safety impact as demonstrated by the answers to the five RIPE screening questions. The change meets the RIPE quantitative criteria.
TVA also addressed the defense-in-depth considerations that the NRC staff previously posed to Arizona Public Service for an LAR for Palo Verde. The NRC staff reinforced the importance of including detailed information regarding defense-in-depth considerations in the LAR.
The NRC staff questioned the use of the RIPE process for the proposed LAR. The staff explained that because the event (i.e., RWM is not functional) is not modeled in the PRA, the proposed LAR would not meet the acceptance criteria for RIPE. TVA explained that because it used a bounding analysis, it believed it was meeting the guidance (i.e., Guidelines for Characterizing the Safety Impact of Issues, Revision 2 (ML22088A135)). The guidance states that where PRA models are not available, conservative or bounding analyses may be performed to quantify the risk impact (e.g., external events, low power and shutdown). The NRC staff explained that the intent of the statement in the guidance was that the bounding analysis would be used in the licensees previously NRC-reviewed PRA model. The staff also pointed out that section 4.3 of the guidance states that the issue has to be completely within the scope of the licensees PRA model to use RIPE or be bounded using surrogates, and that surrogates are limited to the use of basic events associated with the initiating event, mitigating system, or function of the issue being investigated.
TVA stated that it would consider the NRCs feedback but noted that it still plans to submit the LAR, possibly using a deterministic approach. TVA offered to support another public meeting prior to submittal of the LAR. TVA plans to 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
Enclosure LIST OF ATTENDEES JANUARY 22, 2024 PUBLIC MEETING WITH TENNESSEE VALLEY AUTHORITY REGARDING USE OF RISK-INFORMED PROCESS EVALUATION (RIPE) FOR A PROPOSED LICENSE AMENDMENT REQUEST REGARDING ELIMINATION OF LIMITING CONDITION FOR OPERATION ACTIONS FOR THE ROD WORTH MINIMIZERS 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 Camille Peres NRC Ravi Grover NRC Vic Cusumano NRC Charley Peabody NRC Lauren Bryson NRC David Wrona NRC Reinaldo Rodriguez NRC Lou McKown NRC Kevin Pfeil NRC Atonio Zoulis NRC Beau Eckermann Tennessee Valley Authority (TVA)
Bill Williamson TVA Chris Carey TVA Stuart Rymer TVA Andy Taylor TVA Bradley Dolan TVA Mark Nicholson TVA Jesse Baron TVA Greg Preston TVA Brett Titus Nuclear Energy Institute (NEI)
Andrew Mauer NEI Cheryl Gayheart Southern Nuclear Company (SNC)
Jason Douglas SNC Wes Sparkman SNC David Enfield SNC Jeff Gromansky Enercon Bob Post Enercon Dennis Earp Duke Energy Vicken Khatchadourian EPM Sarah Kane Arizona Public Service Mary Miller Dominion Energy Jana Bergman Curtiss-Wright
Package: ML24043A047 Meeting Summary: ML24043A046 Meeting Notice: ML24012A053 Slides: ML24019A097 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 2/12/24 02/15/24 02/15/24 02/16/24