ML24080A391
| ML24080A391 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 03/20/2024 |
| From: | Shilpa Arora NRC/NRR/DORL/LPL3 |
| To: | Frank E DTE Electric Company |
| References | |
| L-2023-LLA-0092 | |
| Download: ML24080A391 (9) | |
Text
From: Surinder Arora Sent: Wednesday, March 20, 2024 11:22 AM To: Eric Frank Cc: Jeff Whited
Subject:
Fermi 2 - Request for Additional Information for License Amendment Request Regarding Risk-Informed ECCS Strainer Performance Evaluation (FINAL) (L-2023-LLA-0092)
Eric Frank,
By letter dated June 13, 2023 (Agencywide Documents Access Management System (ADAMS) Accession No. ML23164A232), DTE Electric Company (the licensee) submitted, for the NRC staff review and approval, a license amendment request to use risk informed methodology to evaluate ECCS Strainer performance.
The U.S. Nuclear Regulatory Commission (NRC) staff is reviewing the above request and has determined, through the regulatory audit, that response to the following request for additional information (RAI) is needed to complete its review. The draft RAI was sent to you on March 13, 2024, to ensure that the NRC staffs questions are understandable, the regulatory basis is clear, and there is no proprietary information contained in the draft RAI. In response, your email dated March 19, 2024, confirmed that no clarification call was needed to discuss any questions in the draft RAI. Accordingly, I am providing below the final RAI with no change to the content.
Also, we have noted your request to allow DTE an RAI response time of 60 days instead of the default 30 days built in our standard review schedule. Considering this request and your previous request to suspend staffs regulatory audit until June7, 2024 conveyed in DTE letter dated February 6, 2024 (ADAMS Accession No. ML24037A189), we will provide you in a separate communication the revised review completion date and the estimated work hours for this licensing request.
Thank you,
Docket No. 50-341 EPID: L-2023-LLA-0092
Surinder Arora, P. E.
Project Manager, Fermi 2 and Dresden 2 & 3 NRR/DORL/LPL3 surinder.arora@nrc.gov 301-415-1421
REQUEST FOR ADDITIONAL INFORMATION LICENSE AMENDMENT REQUEST FOR A RISK INFORMED APPROACH TO ECCS STRAINER PERFORMANCE (EPID L-2023-LLA-0092)
FERMI 2 DTE ELECTRIC COMPANY DOCKET NO. 50-341
On June 13, 2023, DTE Electric Company (DTE, the licensee) requested, in accordance with the provisions of Title 10 Code of Federal Regulations (10 CFR) 50.90, an amendment to modify the Fermi 2 Updated Final Safety Analysis Report (UFSAR) to describe the methodology used to address the impact of potential debris sources from a postulated high-energy line break on the Emergency Core Cooling System (ECCS) suppression pool strainer performance. The proposed amendment would revise the licensing basis as described in the Fermi 2 UFSAR to allow the use of a risk-informed methodology to address potential debris sources beyond those currently evaluated in a deterministic methodology. The licensees submittal also requested exemptions to 10 CFR 50.46 and associated general design criteria.
10 CFR 50.46 requires that the ECCS be capable of performing its safety function considering the most challenging loss-of-coolant accidents (LOCAs). To assure that long -term core cooling (LTCC) is maintained, the NRC has concluded that the effects of debris on the ECCS must be considered as part of the analysis. The NRC has reviewed the information provided by the licensee and determined that the additional information requested below is required for the staff to make a regulatory decision regarding the request.
The RAIs included in this transmittal were discussed with the licensee during a regulatory audit.
The NRC staff and license e have discussed these issues during the audit and the licensee is familiar with the information requested via these RAIs. The licensee understands that the NRC requires information in response to these questions to complete its review of the license amendment request.
The NRC staff did not include RAIs that it determined could be affected by the licensees current effort to quantify the potential for additional Min-K to be generated or RAIs that could be affected by the related change in Min-K source term. Additional RAIs, if required, will be sent after the NRC reviews supplemental information submitted by the licensee. If the licensee believes that its additional work will affect the responses to some of the questions in this request, the responses to such questions may be submitted after the work regarding the Min -K source term is complete.
Request for Additional Information
(A) Technical Specification Branch (STSB) RAIs :
STSB-RAI-1
Provide revised exemption requests that are consistent with regulatory precedent. The exemptions should request exemption to 10 CFR 50.46(a)(1) which points to other properties sufficient to provide assurance that the most severe postulated loss-of-coolant accidents are calculated. The NRC considers the deterministic evaluation of sump performance to be one of the other properties. A quote from a previously approved exemption indicates NRC acceptance of this precedent - The NRC staff interprets the section 50.46(a)(1) requirement to calculate ECCS performance for o ther properties as requiring licensees to consider the impacts of debris generation and transport in containment. Consider discussing whether testing or further deterministic analysis had been evaluated as a potential way to resolve the issue instead of using the exemption process when evaluating special circumstances.
STSB-RAI-2
Update the FSAR markup to describe the risk-informed analysis methodology and how it relates to the design basis deterministic requirements for Fermi. The description should clearly explain the design basis for the strainers including the debris limits and how they affect operability. The markup should clearly describe what the risk analysis presented in the LAR is used for, what debris is covered, and how it supplements the deterministic design requirements. The acceptance criteria for the risk analysis should be included. For example, the risk results must remain in Region III of RG 1.174. If the risk analysis will be used to evaluate debris source discoveries that may exceed these design basis values, the markup should outline how such an analysis would be performed and specify the acceptance criteria that will be used. Alternately, if it is intended that the risk analysis be used only to evaluate the present condition, that should be stated. A one-time use of the analysis would not obviate the need to monitor the plant to assure that the risk results remain valid even after changes that may occur in the plant.
STSB-RAI-3
Update the FSAR markup to specify the key aspects, or methods, of the risk-informed analysis that cannot be changed without prior NRC approval.
STSB-RAI-4
Update the FSAR markup to define the acceptance criteria for the effects of debris on strainer performance. Define the conditions under which the strainers are considered operable. List the design basis requirements. Provide a clear definition of the deterministic limits beyond which a risk analysis is required. Define the debris that is evaluated by the risk-informed analysis and any other limitations on its use. Describe how any discovered new potential debris must be addressed.
STSB-RAI-5
The FSAR markup, Insert 2, should be revised from change in risk to the risk-informed analysis that must meet the 5 Key Principles of RG 1.174.
STSB-RAI-6
Provide a justification for the 1/8-inch bed thickness criteria used in the risk-informed analysis.
The justification should be based on plant-specific debris loads and design basis strainer testing and evaluation for Fermi. For example, describe how the design basis testing and analysis that was used to qualify the strainer demonstrates that a fibrous debris bed 1/8-inch thick is acceptable. On page 82 of 94 of Attachment 3 of the LAR, SERCO-REP-DTE-22609-02, Revision 1 (Serco calculation) (PDF pg. 154) the submittal discusses the assumptions for RHR strainers in service. It states that the loads are calculated assuming one RHR strainer and one CS strainer in SPC mode. This was also stated in the audit responses. In response to audit questions regarding whether the 1/8-inch debris bed limit for the risk-informed analysis was bounded by the design basis, a bed thickness was calculated assuming that 3 strainers were in service. Based on the NRC understanding, the GE strainer loading limits based on testing and analysis assumed two strainers in service. To maintain consistency with the design basis loading for the strainer it appears that the discussion regarding the risk-informed 1/8-inch debris bed limit should be based on debris collecting on two strainers. Note that this should result in greater margin than reported during the audit. However, this NRC observation is a simplification based on an equal distribution of debris across two strainers, while actual debris distribution in the risk-informed analysis is based on the flow through each strainer. It is unclear to the NRC what the assumptions were for debris distribution when the limits were established by GE.
Provide a comparison between the risk-informed debris bed limit and the maximum fiber bed thickness resulting from the GE limiting strainer tests and evaluation. Discuss why 3 strainers were assumed in the risk-informed baseline case when the design basis case appears to credit only two strainers.
STSB-RAI-7
Identify the material types of the non-RMI insulation shown as blue spheres in figures 2 -5 and 2-6 of Attachment 3 (Serco Calculation). Clarify whether this material is accounted for in the existing deterministic debris loads or if this material was newly discovered. Identify the material of the vertical red lines in the torus in figure 2-5 or confirm that they are not debris sources.
STSB-RAI-8
Describe how it is determined that closed check valves that are credited for system isolation for debris generation are holding pressure. Describe how the assumption in the analysis that the MS drain valves are shut and verified shut is implemented operationally.
STSB-RAI-9
Describe the current design basis for area occluded by miscellaneous debris, and the updated design basis amount for the miscellaneous debris identified in the containment. In the response, provide the limit associated with strainer qualification (likely 6 ft2 of sacrificial circumscribed area), the amount of labels discovered in the containment that may transport to the strainer, and any updated deterministic limit (increase to the 6 ft2 of sacrificial circumscribed area) if applicable. Clearly state how any increase above the strainer design value is evaluated by deterministic and/or risk informed methods. Describe how any updated design limit above the design value of 6 ft2 of sacrificial circumscribed area is defined and controlled in the plant.
Provide the basis for using 100 ft2 of sacrificial area in the risk informed analysis and how this value relates to the area of labels that will be the plant design limit following implementation of the LAR. Use consistent terms in the response. For example, use either sacrificial strainer area or total label area in descriptions (overlapped or not overlapped debris area). If necessary, describe how these values are assumed to be correlated to each other and the circumscribed area design limit. It may add clarity if this information is provided in tabular format. Provide the circumscribed and total strainer areas used to determine the strainer surface area assumed to be blocked by miscellaneous debris in the strainer calculations.
STSB-RAI-10
Miscellaneous debris (tags and labels) that may cover greater area than the original design assumption can affect the areal density of non-fibrous debris types (other than Nukon or LDFG) that may collect on the strainer. Describe how the increase in the areal density of debris is evaluated. Discuss whether the change in the areal density of the other debris types is bounded by the design basis analysis. Discuss how any increased bed thickness or increased velocity though the debris bed is considered in the evaluation.
STSB-RAI-11
Describe the pump operating combinations and flow rates over time as they were considered in the risk-informed analysis.
STSB-RAI-12
The baseline configuration assumed for the risk-informed analysis is the single train runout case. This case appears to represent an unlikely scenario that may result in earlier scenario failure but also result in lower risk values than the more likely single train suppression pool cooling (SPC) case. The submittal states that the SPC case is the design basis case and that it results in higher risk than the baseline (single train runout) case. Justify using the runout case as the baseline in the risk-informed analysis instead of the more likely SPC mode. Justify using the risk values from the single train runout case for comparison against the regulatory acceptance criteria or provide CDF values for the SPC and baseline cases including pump failure probabilities.
STSB-RAI-13
In the description of the torus cooling mode on page 39 of 94 of the Serco calculation (PDF pg. 111) it is stated that the flow rate is 10,000 gpm rated. Explain what rated means in this case. What flow rates for torus cooling mode are considered in design basis analyses?
Provide a discussion that demonstrates that the design basis conditions are adequately evaluated by the risk-informed analysis.
STSB-RAI-14
On Page 75 of 94 (PDF pg. 147) of the Serco calculation a discussion regarding the defense-in-depth-philosophy is provided. The discussion does not include the information specified in the guidance of RG 1.174. Provide a defense-in-depth discussion that follows the guidance of RG 1.174 or an equivalent alternate discussion.
(B) Vessels and Internals Branch (NVIB) RAIs:
NVIB-RAI-1
The Serco calculation, page 25, (PDF pg. 97) states that 1103 welds were selected as the possible LOCA locations in the risk-informed application of CASA Grande. The licensee further stated that The review further identified a subset of 924 welds that are considered active LOCA locations given the at-power plant configurationA subset of only 921 welds represents potentially active LOCA locationsThe plant configuration provides fo r auto-isolation of 37 welds that reduce the number of welds to 887 unique locations The licensee further reduced the LOCA location to 884 welds.
Discuss how 1103 welds were reduced to 924 welds although the licensee did state that the 924 welds are considered active LOCA locations. Explain why 179 welds (1103-924) were eliminated from consideration. (2) Clarify whether 884 welds or 921 welds are included in the risk analysis. (3) Discuss whether every one of the 884 welds has been ultrasonically examined at least once. (4) Clarify whether 884, 924, 921, or 1103 welds are considered in the scope of the license amendment request (i.e., in-scope welds).
NVIB-RAI-2
Section 6.5 of the Serco Calculation, page 83 (PDF pg.155), states that All Class I welds at Fermi are either Category A, welds with no known cracks that are made from materials that are considered resistant to IGSCC, or Category B, welds made from material that is considered susceptible to IGSCC but have been mitigated by stress improvement prior to two cycles of operation.
Discuss whether Category A welds have recorded indications from the ultrasonic examinations performed during inservice inspection (ISI) intervals even though the report states the welds have no known cracks (i.e., difference between an indication and a crack). (2) Discuss any degradation occurred in the Category B welds after mitigation. If degradation was identified, discuss the corrective actions. (3) Discuss whether Class 2 welds in the drywell/containment are considered as in-scope welds (i.e., are they part of the risk analysis). If not, clarify why the Class 2 welds in the containment are not included in the risk analysis.
NVIB-RAI-3
Section 6.5 of the Serco Calculation, page 83 (PDF pg. 155), states that Pre ssure retaining welds are inspected in accordance with ASME Code Case N-716-1 Alternative Classification and Examination Requirements. This Code Case prioritizes inspection of risk significant welds and welds potentially susceptible to a degradation mechanism, such as Intergranular Stress Corrosion Cracking (IGSCC) or thermal fatigue Ten percent of Class I welds are examined over a ten-year interval...
Discuss whether the in-scope welds have been examined per the ASME Code,Section XI. (2)
Discuss whether the same ten percent of the Class 1 welds are examined per Code Case N-716-1 during every 10-year ISI interval or different population of welds are examined in different 10-year ISI intervals. (3) Discuss the percent of in-scope welds that have not been inspected and will not be inspected to the end of the license renewal period. (4) For the in-scope welds that will never be inspected, discuss whether the higher probability of failure value was used for these welds than for the inspected welds in the risk analysis.
NVIB-RAI-4
Discuss any in-scope welds that are fabricated with nickel-based Alloy 82/182. (2) Discuss whether these in-scope welds have been mitigated to reduce their susceptibility to stress corrosion cracking. (3) Discuss whether any in-scope nickel-based Alloy 82/182 welds that have not been mitigated. (4) For those unmitigated in-scope welds, discuss how they are being inspected to monitor their structural integrity. (5) Discuss whether the failure probability value in the risk analysis is increased to account for the unmitigated nickel-based Alloy 82/182 welds.
NVIB-RAI-5
Discuss the number of austenitic stainless steel welds that are susceptible to intergranular stress corrosion cracking (IGSCC) and are included in the risk analysis. (2) Discuss whether these in-scope austenitic stainless steel welds have been mitigated to reduce their susceptibility to IGSCC (excluding the improvement in primary system water chemistry). (3) For those in-scope unmitigated austenitic stainless steel welds, discuss the corrective actions (excluding water chemistry improvements). (4) Discuss whether the failure probability value in the risk analysis is increased to account for the unmitigated austenitic stainless steel welds that are susceptible to IGSCC.
NVIB-RAI-6
BWR owners have implemented inspection guidance of BWRVIP-75-A, BWR Vessel and Internals Project Technical Basis for Revisions to Generic, Letter 88-01 Inspection Schedules.
Discuss whether inspection guidance of BWRVIP-75-A has been implemented for the inservice inspection of in-scope welds at Fermi. (2) If affirmative, discuss how inspections of in-scope welds are carried out per the BWRVIP-75-A. (3) If the topic report is not implemented, discuss the reason.
NVIB-RAI-7
Discuss whether failure of flanges and bolts of a piping system, nozzle penetrations to the reactor vessel such as control rod drive mechanisms and standby liquid control system are considered as potential LOCA locations and included in the risk analysis.
NVIB-RAI-8
The Serco Calculation, page 33 (PDF pg. 105), Table 2-1 shows the failure probability for feedwater is 1.57E-4. Explain why this failure probability is lower than other piping in the table such as main steam and RWCU.
(C) Probabilistic Risk Assessment Licensing Branch B (APLB) RAI
APLB-RAI-1
In Attachment 3 (Serco calculation) of the license amendment request (LAR) on page 51 of 94 (PDF pg. 123), the double ended guillotine break (DEGB) model is represented as the baseline model. The NRC staff noted that partial breaks were not considered in the sensitivity analysis of the change in Core Damage Frequency (CDF). In accordance with NEI 04-07, Pressurized Water Reactor Sump Performance Evaluation Methodology, Revision 0, December 2004, (ADAMS Accession No. ML050550156), to assure defense in depth is maintained, mitigative capability must be maintained through all break sizes up through DEGB. Also, LARs in response to GL 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors, for PWRs have traditionally computed the CDF considering both the continuum break model (where pipes are assumed to exhibit partial breaks) and the DEBG-only model in sensitivity analyses. NUREG-0800, Standard Review Plan, Section 15.6.5, Loss-Of-Coolant Accidents Resulting from Spectrum of Postulated Piping Breaks Within the Reactor Coolant Pressure Boundary, (ADAMS Accession No. ML070550016), discusses the staff performing an evaluation on whether the entire break spectrum (break size and location) has been addressed and demonstrating compliance with requirements of 10 CFR 50.46. 10 CFR 50.46 requires that ECCS cooling performance must be calculated in accordance with an acceptable evaluation model and must be calculated for a number of postulated loss-of-coolant accidents of different sizes, locations, and other properties sufficient to provide assurance that the most severe postulated loss-of-coolant accidents are calculated. Understanding that partial hemispherical breaks occurrence affects the CDF, the NRC staff is requesting that the licensee provide justification for considering only DEGB in its analysis.
Hearing Identifier: NRR_DRMA Email Number: 2436
Mail Envelope Properties (BY3PR09MB8225EB188D559AEC95A7E85894332)
Subject:
Fermi 2 - Request for Additional Information for License Amendment Request Regarding Risk-Informed ECCS Strainer Performance Evaluation (FINAL) (L-2023-LLA-0092)
Sent Date: 3/20/2024 11:22:23 AM Received Date: 3/20/2024 11:22:00 AM From: Surinder Arora
Created By: Surinder.Arora@nrc.gov
Recipients:
"Jeff Whited" <Jeffrey.Whited@nrc.gov>
Tracking Status: None "Eric Frank" <eric.frank@dteenergy.com>
Tracking Status: None
Post Office: BY3PR09MB8225.namprd09.prod.outlook.com
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