ML24088A008
| ML24088A008 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 03/27/2024 |
| From: | Thomas Wengert NRC/NRR/DORL/LPL4 |
| To: | Keele R Entergy Operations |
| Wengert T | |
| References | |
| L-2023-LLA-0052 | |
| Download: ML24088A008 (6) | |
Text
From:
Thomas Wengert Sent:
Wednesday, March 27, 2024 1:35 PM To:
Keele Jr, Riley D Cc:
REID, MARK; Jennie Rankin
Subject:
ANO-2 -- TSTF-505 Post-Audit Final RAI (L-2023-LLA-0052)
Attachments:
ANO-2 TSTF-505 Post-Audit Final RAI.pdf On March 18, 2024, the U.S. Nuclear Regulatory Commission (NRC) staff sent Entergy Operations, Inc. (Entergy) the draft Request for Additional Information (RAI) for Arkansas Nuclear One, Unit 2 (ANO-2) identified below. This RAI relates to the license amendment request to modify the ANO-2 technical specifications to permit the use of Risk-Informed Completion Times (RICT) in accordance with Technical Specification s Task Force (TSTF)-505, Revision 2, Provide Risk Informed Extended Completion Times - RITSTF Initiative 4b.
Subsequently, the licensee informed the NRC staff that a clarification of this RAI was not necessary. A publicly available version of this final RAI (attached with Draft removed) will be placed in the NRCs Agencywide Documents Access and Management System (ADAMS). As agreed, please provide the response to this RAI within 30 days of this correspondence.
From: Thomas Wengert Sent: Monday, March 18, 2024 1:01 PM To: REID, MARK <mreid1@entergy.com>
Cc: Keele Jr, Riley D <rkeele@entergy.com>; Jennie Rankin <Jennivine.Rankin@nrc.gov>
Subject:
ANO-2 -- TSTF-505 Post-Audit Draft RAI (L-2023-LLA-0052)
By letter dated April 5, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23095A281), as supplemented by letter dated January 11, 2024 (ML24011A293), Entergy Operations, Inc. (the licensee) submitted a license amendment request (LAR) to modify the ANO-2 technical specifications to permit the use of Risk-Informed Completion Times (RICT) in accordance with TSTF-505, Revision 2, Provide Risk Informed Extended Completion Times - RITSTF Initiative 4b.
The NRC staff has reviewed the submittals and has determined that additional information is required for the staff to complete its review of this application. This request for additional information (RAI) is identified as draft at this time to confirm your understanding of the information that the NRC staff needs to complete the evaluations.
Please contact me if you would like to set up a conference call with the NRC staff to clarify this request for information. In addition, lets discuss the timing for your response.
Tom Wengert Project Manager - Arkansas Nuclear One NRR/DORL/LPL4
(301) 415-4037
Hearing Identifier:
NRR_DRMA Email Number:
2442 Mail Envelope Properties (PH0PR09MB7403C1D0E93E4003F9A457218F342)
Subject:
ANO-2 -- TSTF-505 Post-Audit Final RAI (L-2023-LLA-0052)
Sent Date:
3/27/2024 1:34:53 PM Received Date:
3/27/2024 1:34:00 PM From:
Thomas Wengert Created By:
Thomas.Wengert@nrc.gov Recipients:
"REID, MARK" <mreid1@entergy.com>
Tracking Status: None "Jennie Rankin" <Jennivine.Rankin@nrc.gov>
Tracking Status: None "Keele Jr, Riley D" <rkeele@entergy.com>
Tracking Status: None Post Office:
PH0PR09MB7403.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 2259 3/27/2024 1:34:00 PM ANO-2 TSTF-505 Post-Audit Final RAI.pdf 135959 Options Priority:
Normal Return Notification:
No Reply Requested:
No Sensitivity:
Normal Expiration Date:
1 REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING LICENSE AMENDMENT REQUEST TO REVISE TECHNICAL SPECIFICATIONS TO ADOPT RISK-INFORMED COMPLETION TIMES TSTF-505, REVISION 2, PROVIDE RISK-INFORMED EXTENDED COMPLETION TIMES - RITSTF INITIATIVE 4B ENTERGY OPERATIONS, INC.
ARKANSAS NUCLEAR ONE, UNIT 2 DOCKET NO. 50-368 By letter dated April 5, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23095A281), as supplemented by letter dated January 11, 2024 (ML24011A293), Entergy Operations, Inc. (the licensee) submitted a license amendment request (LAR) to modify the ANO-2 technical specifications to permit the use of Risk-Informed Completion Times (RICT) in accordance with TSTF-505, Revision 2, Provide Risk Informed Extended Completion Times - RITSTF Initiative 4b.
The U.S. Nuclear Regulatory Commission (NRC) staff have reviewed the licensees submittals and concluded that additional information, as discussed below, is required to complete its review:
PRA Licensing Branch A (APLA) RAI 01 - Sources of PRA Model Uncertainty Regulatory Basis Regulatory Guide (RG) 1.200, An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed Activities, Revision 3, states, in part, NRC [U.S. Nuclear Regulatory Commission] reviewers, [will] focus their review on key assumptions and areas identified by peer reviewers as being of concern and relevant to the application. The NRC staff evaluates the acceptability of the probabilistic risk assessment (PRA) for each new risk-informed application and as discussed in RG 1.174, recognizes that the acceptable technical adequacy of risk analyses necessary to support regulatory decision-making may vary with the relative weight given to the risk assessment element of the decision-making process. The NRC staff notes that the calculated results of the PRA are used directly to calculate a risk informed completion time (RICT), which subsequently determines how long structures, systems, and components (SSCs) -- both individual SSCs and multiple, unrelated SSCs -- controlled by technical specifications can remain inoperable. Therefore, the PRA results are given a very high weight in the staffs review of a TSTF-505 license amendment request (LAR). This is consistent with the guidance in Item 10 of Section 2.3.4, PRA Technical Adequacy of NEI 06-09, Risk Informed Technical Specifications Initiative 4b; Risk Managed Technical Specifications (RMTS) Guidelines, Revision 0-A (ML122860402), which states, in part:
For LCOs [limiting conditions for operation] in which it is determined that identified uncertainties could significantly impact the calculated RICT, sensitivity studies should be performed for their potential impact on the RICT calculations.
2 (Reference EPRI-1009652 [ ] for one method to determine key uncertainties.)
Insights obtained from these sensitivity studies should be used to develop appropriate compensatory risk management actions.
Issue In Audit Question 07.b the NRC staff noted that LAR Enclosure 9 Section 4, Assessment of Level 2 Epistemic Uncertainty Impacts, states that no key sources of uncertainty for the RICT program were identified for the Level 2 PRA. However, in Table 8.4-3 of the ANO-2 key assumptions and sources of uncertainty analysis report provided on the audit portal, it is reported for the sensitivity study on the conditional steam generator tube rupture (SGTR) probability of burst (POB) that the RICT for LCO 3.7.1.5, which concerns main steam isolation valve operability, is very sensitive to this parameter (i.e., a 55 percent reduction in the RICT).
Based on this sensitivity study result it appears to the NRC staff that the conditional POB is a key source of uncertainty for the RMTS application.
In its response to this audit question provided in the LAR supplement dated January 11, 2024, the licensee explains that the conditional POB used in the ANO-2 PRA model is based on plant-specific steam generator tube inspection data obtained under the Steam Generator Integrity Program and is calculated utilizing methods developed by the Electric Power Research Institute (EPRI). It is further explained that the conditional POB value used in the sensitivity study is not a plant-specific value but rather a generic value developed by the NRC staff in NUREG-0844, NRC Integrated Program for the Resolution of Unresolved Safety Issues A-3, A-4, and A-5, Regarding Steam Generator Tube Integrity (ML082400710). However, while the response acknowledges that there is uncertainty in the conditional POB, no information is provided to show that the conditional POB has an inconsequential impact on the RICT calculations.
Request for Additional Information Justify that the conditional POB has an inconsequential impact on the RICT calculations.
If, in response to part a), the licensee cannot justify that the conditional POB has an inconsequential impact on the estimated RICTs, then identify potential additional contingencies or actions that can compensate for this uncertainty.
APLA RAI 02 - FLEX Fire PRA Update of Failure Probabilities Regulatory Basis Item 10 of Section 2.3.4 of NEI 06-09 states, in part: PRA modeling (i.e., epistemic) uncertainties shall be considered in application of the PRA base model results to the RMTS program. The NRC safety evaluation for NEI 06-09 states that this consideration is consistent with Section 2.3.5 of RG 1.177, An Approach for Plant-Specific, Risk-Informed Decisionmaking:
Technical Specifications, Revision 1, (ML100910008).
NRC staff memorandum dated May 6, 2022, Updated Assessment of the Industry Guidance for Crediting Mitigating Strategies in Probabilistic Risk Assessments (ML22014A084), provides the staffs assessment of challenges in incorporating Diverse and Flexible Mitigation Strategies (FLEX) equipment and strategies into a PRA model in support of risk-informed decisionmaking in accordance with the guidance of RG 1.200.
3 Conclusion 6, concerning FLEX equipment failure data, in the May 6, 2022, NRC memorandum, instructs that licensees should not use failure rates of permanently installed equipment to represent portable equipment, even if sensitivity analyses are performed.
Issue In response to APLA Question 08 in the LAR supplement dated January 11, 2024, the licensee stated that the Fire PRA is being updated using PWROG-18042-N failure rates and is to be completed to support the RICT program implementation. The NRC staff notes that this planned future action by the licensee appears to be an implementation item for this application, however no implementation item was provided in the LAR supplement.
Request for Additional Information Propose a mechanism, such as an implementation item, that provides reasonable assurance to the NRC staff that the Fire PRA model will be updated using the FLEX equipment failure rates in PWROG-18042-N prior to implementing the RICT program.