ML24268A099
| ML24268A099 | |
| Person / Time | |
|---|---|
| Site: | Fermi  (NPF-043) |
| Issue date: | 10/01/2024 |
| From: | Shilpa Arora Plant Licensing Branch III |
| To: | Domingos C DTE Electric Company |
| Arora S | |
| References | |
| EPID L-2023-LLA-0092 | |
| Download: ML24268A099 (1) | |
Text
October 1, 2024 Christopher P. Domingos Site Vice President DTE Electric Company 6400 N. Dixie Highway Newport, MI 48166
SUBJECT:
FERMI 2 POWER PLANT - AUDIT
SUMMARY
FOR LICENSE AMENDMENT REQUEST AND REGULATORY EXEMPTIONS FOR A RISK-INFORMED APPROACH TO ADDRESS EMERGENCY CORE COOLING SYSTEM (ECCS) STRAINER PERFORMANCE (EPID L-2023-LLA-0092)
Dear Christopher Domingos:
By letter dated June 13, 2023 (Agencywide Documents Access Management System (ADAMS)
Accession No. ML23164A232), as supplemented by letters dated April 24, 2024, and May 30, 2024 (ML24115A095 and ML24151A173, respectively), DTE Electric Company (the licensee) submitted, for the NRC staff review and approval, a license amendment request to use risk informed methodology to evaluate the emergency core cooling system (ECCS) strainer performance pursuant to Title 10 of the Code of Federal Regulations (10 CFR) section 50.90, Application for amendment of license, construction permit, or early site permit.
Additionally, in accordance with the regulations in 10 CFR 50.12, Specific exemptions, the licensee requested exemptions from certain requirements of 10 CFR 50.46(a)(1), and appendix A, General Design Criteria for Nuclear Power Plants, to 10 CFR part 50, specifically, General Design Criterion (GDC) 35, and Emergency core cooling, GDC 38, Containment heat removal.
To support its review, the U.S. Nuclear Regulatory Commission (NRC) staff conducted a virtual regulatory audit between September 18, 2023, and September 4, 2024. An audit plan, describing the purpose of the audit was issued on September 7, 2023 (ML23248A224). The NRC staff reviewed documents uploaded on the internet-based audit portal and held discussions with members of DTE Electric Company and its contractors. The regulatory audit summary is enclosed with this letter.
If you have any questions, please contact me by telephone at (301) 415-1421 or by e-mail at Surinder.Arora@nrc.gov.
Sincerely,
/RA/
Surinder S. Arora, Project Manager Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-341
Enclosure:
Audit Summary cc: Listserv
Enclosure OFFICE OF NUCLEAR REACTOR REGULATION REGULATORY AUDIT
SUMMARY
FOR THE REGULATORY AUDIT IN SUPPORT OF LICENSE AMENDMENT REQUEST FOR A RISK-INFORMED APPROACH TO ADDRESS EMERGENCY CORE COOLING SYSTEM STRAINER PERFORMANCE DTE ELECTRIC COMPANY FERMI 2 POWER PLANT DOCKET NO. 50-341
1.0 BACKGROUND
By letter dated June 13, 2023 (Agencywide Documents Access Management System (ADAMS)
Accession No. ML23164A232) as supplemented by letters dated April 24, 2024, and May 30, 2024 (ML24115A095 and ML24151A173, respectively), DTE Electric Company (the licensee) submitted, for the NRC staff review and approval, a license amendment request (LAR) and exemption requests to use risk informed methodology to evaluate emergency core cooling system (ECCS) strainer performance for the Fermi 2 Power Plant. The amendment would modify the Fermi licensing bases, including the Updated Final Safety Analysis Report.
Specifically, the amendment would allow the use of a risk-informed approach to address safety issues associated with ECCS strainer performance in the presence of debris.
On September 7, 2023 (ML23248A224), the U.S. Nuclear Regulatory Commission (NRC) issued an audit plan, which provided the list of requested documents and other details pertaining to the audit. An audit team, consisting of NRC staff and two contractors from the Southwest Research Institute (SwRI), conducted a remote regulatory audit to support the review of the LAR from September 18, 2023, to September 4, 2024. The audit was conducted following the guidance in the Office of Nuclear Reactor Regulation (NRR) Office Instruction LIC-111, Revision 1, Regulatory Audits (ML19226A274).
The regulatory audit is a planned license or regulation-related activity that includes the examination and evaluation of primarily non-docketed information. The regulatory audit is conducted with the intent to gain understanding, to verify information, and/or to identify information that will require docketing to support the basis of a licensing or regulatory decision.
Performing a regulatory audit of the licensees information is expected to assist the NRC staff in efficiently conducting its review or gain insights on the licensees processes or procedures.
Information that the NRC staff relies upon to make the safety determination must be submitted on the docket. However, the NRC staff may review supporting information retained as records under Title 10 of the Code of Federal Regulations (10 CFR) section 50.71, Maintenance of records, making of reports, and/or 10 CFR 54.37, Additional records and recordkeeping requirements, which, although not required to be submitted as part of the licensing action would help the NRC staff better understand the licensees submitted information.
2.0 AUDIT ACTIVITIES The NRC audit team consisted of the following NRC staff members and the contractors from SwRI. The NRC audit team held an entrance meeting on Tuesday, August 10, 2021, with the licensees staff and contractors. The list of Ameren participants is provided in Attachment 1.
During the remainder of the audit, the NRC audit team participated in technical discussions with the licensee based on discipline according to section 3.0 of the audit plan.
List of NRC Participants Division Branch NRC staff Division of Safety Systems Technical Specifications Branch Steve Smith Andrea Russell Division of Risk Assessment Probabilistic Risk Assessment Licensing Branch B Daniel Ju Jay Robinson Division of New and Renewed Licenses Vessels and Internals Branch John Tsao Division of Operating Reactor Licensing Plant Licensing Branch III Surinder Arora SwRI Contractor Osvaldo Pensado John Bickel 3.0 RESULTS OF THE AUDIT Technical discussions were focused on the following major areas (Attachment 2 provides the summary of the technical discussions):
- 1.
General Information and Licensing Bases
- 2.
Debris Generation/Zone of Influence (Excluding Coatings)
- 3.
Transport
- 4.
Head Loss
- 5.
Risk-Informed Basis
- 6.
Defense in Depth and Safety Margin
- 7.
LAR, Exemption Request, and Performance Monitoring Program The NRC audit team participated in an audit exit meeting with the licensee on Tuesday, September 4, 2024, where the NRC staff provided a brief summary of the technical discussion conclusions.
The NRC staff provided a brief conclusion of the audit objectives that were met and details on the path forward. There were no open items in the discussion and no deviation from the audit plan. The licensee agreed to provide a supplement to the application to address audit discussion points.
Additional information needed to support the LAR review, as necessary, will be formally communicated by the licensee via a supplement to the LAR.
Attachments:
- 1. List of DTE Electric Company Participants
- 2. Summary of Discussions
LIST OF DTE ELECTRIC COMPANY PARTICIPANTS Roxanne Vonhabsburg - Supervisor, Licensing and Compliance Derek Corrin - Licensing Engineer Michael Koenemann - PRA Engineer Christopher Vukonich - Supervisor Design Engineering Mechanical Bruce Letellier - Nuclear Services Manager (Serco)
Andrew Roudenko, Project Manager - Quality Assurance (Serco)
Eric Peterson, Senior Engineer - Risk Quantification (Serco)
SUMMARY
OF DISCUSSIONS In addition to the items discussed below, the NRC staff reviewed the information as discussed in section 3.0 of the audit plan, dated September 7, 2023 (ML23248A224), regarding an LAR and exemption request proposing to use a risk-informed evaluation for addressing the effects of debris on ECCS strainer performance. The request was submitted by DTE Electric Company (the licensee) for the Fermi 2 Power Plant (Fermi). These reviews contributed to the NRC staff understanding of the issues discussed during the audit.
The NRC staff completed its initial review of the LAR and developed a list of information to be reviewed to support its regulatory finding. The licensee posted requested information in its audit portal for the NRC to review. After reviewing the additional information, the NRC staff identified issues to discuss with the licensee to gain additional clarity into the methods used in its evaluation. The issues were discussed with the licensee during two meetings, one on November 2, 2023, and another on November 16, 2023. Due to issues identified by the NRC during its review, the licensee requested that the audit be suspended until June 7, 2024, in a letter dated February 6, 2024 (ML24037A189). This requested was made because the licensee required an extended time to perform additional analyses and was delayed due to a planned outage.
Based on the audit discussions, the NRC staff developed requests for additional information (RAIs) and sent them to the licensee on March 20, 2024 (ML24080A391). The licensee was able to complete some of the RAI responses relatively quickly because the answers were not dependent on the new analyses. These responses were transmitted to the NRC on April 24, 2024 (ML24115A095). After finalizing its analysis, the licensee provided a second set of responses on May 30, 2024 (ML24151A173).
After reviewing the two sets of RAI responses, the NRC staff identified additional items that required clarification discussions as part of the audit. These questions were developed after reviewing the new evaluation that was performed by the licensee. The NRC met with the licensee on September 4, 2024, to discuss the issues. As a result of the meeting, the NRC staff determined that some of the issues did not require further information on the docket for the NRC to make its regulatory finding. However, a few issues that require further information on the docket were identified. These issues are listed below. For the Category 1 issues the NRC staff gained adequate insights and information from the licensees docketed material and audit clarifications such that no further information is required to make a regulatory decision. For the Category 2 items additional information, as stated in the list, is required.
The NRC staff did not reach any regulatory conclusions during the audit. Regulatory decisions will be based on information that has already been received on the docket or a future licensee supplement to the LAR.
Category 1 Issues - No further Information Needed
- 1) The NRC understands the response to question P1 and does not need further information on the docket. The licensee stated that penetration Min-K is not included in the latest revision of DC-5979. The information is currently available in SERCO-REP-DTE-22929-02, R0. This issue is documented in the plants corrective action program and the information will be included in a future revision of the calculation.
- 2) For questions P3, P4, and P5, further information is not required on the docket to make as safety determination for the LAR. NRC staff will state in its safety evaluation (SE) that its conclusions are made regardless of the issues discussed during the audit.
- 3) Further information regarding questions F4 and F5 is not required on the docket. The NRC understands that modeling of the guard pipes is based on plant drawings. The NRC also understands that hydraulic pipes are not modeled as robust barriers in any of the debris generation calculations. The hydraulic pipes (and other factors) are qualitatively credited for reductions in penetration Min-K debris generation for some cases, including the modified baseline case in LAR, Attachment 4 (RAI response).
Penetration Min-K was not considered in the initial debris calculations in the LAR (Attachment 3), so no Min-K reductions are applied there. In addition, discussions during the audit clarified the definitions of the various cases for the NRC staff. However, the NRC staff notes that renaming final baseline case in Attachment 4 (modified baseline) as simply the baseline case, and labeling other cases as sensitivity studies, could reduce confusion regarding the analysis.
- 4) The NRC does not require further information regarding the effects of strainer area blocked by miscellaneous debris and associated risk due to Min-K. The NRC will document its findings for this issue in the SE. Independent NRC calculations confirm minor changes in the CDF after alternative approaches to quantify the effect of miscellaneous debris strainer surface blockage on Min-K debris loading.
Category 2 Issues - Further Information Needed on Docket
- 1) The response to P2 is acceptable. The NRC understands that the Final Safety Analysis Report markup will be revised to clarify that the design basis applies to the conditions described in the LAR and allows up to 100 ft2 of miscellaneous debris but does not allow intentional introduction of any type of debris into containment.
- 2) The responses to questions F1, F2, and F3, are acceptable. The NRC staff understands that the exemptions will be revised to clarify that all of the three key elements of the exemption must be present for the exemption to apply to the plant condition. The response stated that the exemptions will be revised to clarify the implementation. In addition, the exemptions will be revised to remove the request that the exemptions be approved within 1 year because of the delays incurred during the review of the LAR.
- 3) For questions F6, F7, F8, F9, and F10, no additional information, besides that stated in the responses to these questions, is required on the docket. The NRC understands how breaks contribute to the number of scenario failures and the associated risks. The NRC staff also understands that the discussions regarding the need for a thin fiber bed to allow Min-K to develop significant head loss will be revised in a supplement. The licensee included margin in the Min-K strainer qualified limit when making a correction in the density of Min-K. Based on audit discussions and review of debris generation calculations the NRC staff agrees that the original strainer design did not include Min-K from penetrations even though it was recognized that some Min-K was present in the penetrations. The NRC understands the logic behind the choice of the flow case for the baseline and crediting the availability of two divisions and operator actions to respond as described.
- 4) The NRC understands that Fermi will revise Attachment 4 to replace the constant CDF value for isolable welds in the arithmetic mean aggregation sensitivity case and update other values as a result of the change.
- 5) The NRC understands that Fermi will provide a supplement that includes a rationale for why the relatively high risk calculated for the arithmetic mean aggregation sensitivity is consistent with the overall conclusion of very small risk. NRC requires this information to include supplemental public references in its SE, supporting the overall conclusion of very small risk.
- 6) The NRC determined that the computation of the CDF to account for the 25 percent reduction in Min-K from penetrations have some minor inconsistencies. Provide estimates of risk contributions from (i) breaks solely exceeding 1/8-in fibrous debris bed thickness, (ii) breaks solely exceeding the Min-K design basis, and (iii) breaks exceeding both failure criteria, accounting for 25 percent reduction of penetration Min-K.
Summarize any changes made in the calculational methodology. The NRC understands that the overall risk clearly decreases after considering a decrease in penetration Min-K but is concerned that the computation methodology should be clearly presented.
The basis for question (6) is detailed below:
The following text is from Attachment 4 to NRC-24-0033, page 9:
The value 1.39x106 1/yr is the contribution from breaks that exceed the Min-K design basis load; and there are no remaining questions on how this value was computed. The contributions 3.10x107 1/yr and 3.11x107 1/yr to the CDF in the equation above came from Cases 2A and 3A, respectively, from breaks that exceed only the fibrous debris bed 1/8-in thickness limit, and assuming 0% reduction in Min-K. These contributions are slightly larger for the case of 25%
reduction in Min-K; however, the LAR assumes (in the above equation) these contributions to be the same, independent of the extent of reduction in penetration Min-K.
The following scatter plots were prepared considering Case 2A, which is very similar to Case 3A, considering different extent of reduction in penetration Min-K. The computations used data from the Excel file with CASA Grande results. The horizontal axes represent data from the Excel column labeled "Total Fiber Incl. Penetrations" and the vertical axes represent data from the column labeled "Total Min-K," without any modification to facilitate visual comparison to the case 0 percent reduction in penetration Min-K.
Yellow triangles: breaks that exceed solely the Min-K design basis load Blue circles: breaks that exceed both the Min-K DB load and 1/8-inch fiber bed thickness Green diamonds: breaks that exceed solely 1/8-inch fiber bed thickness limit Red squares: breaks not causing strainer failure In the equation above, the value 1.39x106 1/yr is the total contribution from the yellow triangles and blue circles for the case 0% reduction in Min-K, and the value 3.10x107 1/yr is the contribution from the green diamonds for the same case. The plots below show that the number of green diamonds increases with more reduction in penetration Min-K; therefore, there is an error in assuming that the 3.10x107 1/yr contribution is constant, independently of the reduction in penetration Min-K.
The NRC agrees that the risk decreases with reduction in penetration Min-K (i.e., number of yellow, green, and blue points decrease with reduction in Min-K), and that the error of assuming a constant value 3.10x107 1/yr is minor for the case 25 percent reduction in penetration Min-K, but it can be more substantial for cases crediting more reduction.
ML24268A099 OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL4/LA NRR/DSS/STSB/BC NAME SArora SRohrer SMehta DATE 9/23/2024 9/24/2024 9/26/2024 OFFICE NRR/DNRL/NCSG/BC NRR/DNRL/NVIB/BC NRR/DRA/APLB/BC NAME SBloom ABuford EDavidson DATE 9/27/2024 9/27/2024 10/1/2024 OFFICE NRR/DORL/LPL3/BC NRR/DORL/LPL3/PM NAME JWhited SArora DATE 10/1/2024 10/1/2024