ML20346A104
| ML20346A104 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 12/11/2020 |
| From: | Blake Purnell NRC/NRR/DORL/LPL3 |
| To: | Taken J Exelon Generation Co |
| References | |
| L-2020-LLA-0017 | |
| Download: ML20346A104 (5) | |
Text
From:
Purnell, Blake Sent:
Friday, December 11, 2020 11:26 AM To:
Taken, Jason C.:(Exelon Nuclear)
Cc:
David Gullott (David.Gullott@exeloncorp.com); Salgado, Nancy; Kusumawatimurray, Putri:(Exelon Nuclear)
Subject:
LaSalle County Station, Units 1 and 2 - Request for Additional Information Regarding the License Amendment Request to Adopt 10 CFR 50.69 (EPID L-2020-LLA-0017)
- Jason, By letter dated January 31, 2019 (ADAMS Accession No. ML20031E699), Exelon Generation Company, LLC (EGC) submitted a license amendment request to allow implementation Section 50.69, Risk-informed categorization and treatment of structures, systems and components for nuclear power reactors, of Title 10 of the Code of Federal Regulations (10 CFR) at LaSalle County Station, Units 1 and 2.
By letters dated October 1 and October 16, 2020 (ADAMS Accession Nos. ML20275A292 and ML20290A791, respectively), EGC submitted supplemental information in response to a request for additional information (RAI) from the U.S. Nuclear Regulatory Commission (NRC) staff.
The NRC staff has reviewed EGCs submittals and the staff in the NRCs Probabilistic Risk Assessment Licensing Branch C (APLC) has identified the need for additional information to complete its review. The NRC staff requests that a response to the RAI below be provided within 45 days of the date of this email.
- Thanks, Blake Purnell, Project Manager Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/BC NRR/DRA/APLC/BC NAME BPurnell NSalgado SRosenberg DATE 12/11/20 11/23/20 12/7/20
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SECOND ROUND REQUEST FOR ADDITIONAL INFORMATION RELATED TO LICENSE AMENDMENT REQUEST TO ADOPT 10 CFR 50.69, RISK-INFORMED CATEGORIZATION AND TREATMENT OF STRUCTURES, SYSTEMS, AND COMPONENTS FOR NUCLEAR POWER REACTORS EXELON GENERATION COMPANY, LLC
LASALLE COUNTY STATION, UNITS 1 AND 2 DOCKET NOS. 50-373 AND 50-374 APLC 50.69-ROUND 2 RAI NO. 01-01:
To support the U.S. Nuclear Regulatory Commission (NRC) staffs regulatory finding on Title 10 of the Code of Federal Regulations (CFR) 50.69 (e) for the proposed alternative seismic approach, Probabilistic Risk Assessment Licensing Branch C (APLC) Request for Additional Information (RAI) No. 01 (ADAMS Accession No. ML20240A218) requested an explanation of statements made by the licensee in Section 3.2.3 of the enclosure to the license amendment request (LAR; ADAMS Accession No. ML20031E699).
These statements related to the licensee assessing the need to update, as appropriate, the structure, system, and component (SSC) categorization for the proposed alternative seismic approach in accordance with 10 CFR 50.69(e) if the LSCS [LaSalle County Station] seismic hazard changes from medium risk (i.e., Tier 2) at some future time.
In its response to APLC RAI No. 01 (ADAMS Accession No. ML20275A292), the licensee stated that for the case where the seismic hazard is reduced such that it meets the criteria for the Tier 1 approach in Electric Power Research Institute (EPRI) Report 3002012998, if categorization changes are warranted, they will be implemented. Further, the licensee stated that seismic considerations for subsequent system categorization activities will be performed in accordance with the guidance in EPRI 3002012988 Section 2.2, Low Seismic Hazard/High Seismic Margin Sites.
Similarly, in the response to APLC RAI No. 01, the licensee stated that for the case where the seismic hazard increases such that a seismic probabilistic risk assessment (SPRA) becomes necessary to demonstrate adequate seismic safety, if categorization changes are warranted, they will be implemented. Further, the response states that seismic considerations for subsequent system categorization activities will follow the guidance be performed [sic] in accordance with NEI 00-04 criteria, as recommended in EPRI 3002012988 Section 2.4, High Seismic Hazard/Low Seismic Margin Sites.
Regulatory Position C.9 of RG 1.201, Revision 1 (ADAMS Accession No. ML061090627), states, in part:
As part of the NRCs review and approval of a licensees or applicants application requesting to implement §50.69, the NRC staff intends to impose a license condition that will explicitly address the scope of the PRA and non-PRA methods used in the licensees categorization approach. If a licensee or applicant wishes to change its categorization approach and the change is outside the bounds of the NRCs license condition (e.g., switch from a seismic margins analysis to a seismic PRA), the licensee or applicant will need to seek NRC approval, via a license amendment, of the implementation of the new approach in their categorization process.
Section 2.3, Description of the Proposed Change, of the enclosure to the LAR proposes the addition of a condition to the renewed operating license of LSCS, Units 1 and 2, to document the NRC's approval of the use of 10 CFR 50.69 for the licensee. The proposed license condition explicitly identifies the proposed alternative seismic approach, and states, prior NRC approval, under 10 CFR 50.90, is required for a change to the categorization process specified above (e.g., change from a seismic margins approach to a seismic probabilistic risk assessment approach).
The licensees response to APLC RAI No. 01 appears to be inconsistent with the licensees proposed license condition because the statements made by the licensee in the response indicate that the
licensee will start to and continue to use process(es) outside the bounds of the proposed alternative seismic approach (i.e., the Tier 2 approach), such as the Tier 1 approach and SPRA, without prior review and approval by the NRC staff.
Confirm that the licensee will request prior NRC approval, consistent with the proposed license condition, if the licensees feedback process determines that a process different from the proposed alternative seismic approach is warranted for seismic risk consideration in categorization under 10 CFR 50.69. Alternatively, provide details of all the approaches, with the corresponding bases and justifications, that the licensees proposed 10 CFR 50.69 program will use for seismic risk consideration, and provide the associated conforming modifications to the proposed license condition.
APLC 50.69-ROUND 2 RAI NO. 4E-01:
The staff requested information through APLC 50.69 RAI No. 4e (ADAMS Accession No. ML20240A218) to support its finding on 10 CFR 50.69 (b)(2)(ii) for the proposed alternative seismic approach. APLC 50.69 RAI No. 4e requested information on the use of failure probabilities other than the 1E-4 value and how the use of the other value would be accepted by the NRC staff. In its response in supplement dated October 16, 2020 (ADAMS Accession No. ML20290A791), the licensee states that more realistic seismic-induced failure probabilities may be developed for the surrogates. Step 7 in Attachment 2 to the licensees supplement dated October 16, 2020 also states that other appropriately justified values may be used for the failure probability used in the surrogate sensitivity.
In its response to APLC 50.69 RAI No. 4b, the licensee provided justification for the 1E-4 failure probability for the surrogate event. Specifically, the licensee explained that the 1E-4 failure probability for the surrogate event was actually based on the occurrence frequency for seismically induced loss-of-offsite power (LOOP). The licensees justification included convolution of the hazard and LOOP fragility from three plants. The licensees justification, as noted in the response to APLC 50.69 RAI No. 4b, is only for the 1E-4 failure probability for the surrogate event. Further, the example demonstration of the categorization results from the proposed alternative seismic approach in response to APLC 50.69 RAI No.
4d also used only 1E-4 as the failure probability for the surrogate event.
The licensees response to APLC 50.69 RAI No. 4e did not address how the proposed approach provides the NRC staff with the ability to review and approve the justification for any failure probability other than 1E-4. Further, the licensees response to APLC 50.69 RAI No. 4e overlooks the justification that the failure probability is coupled to the seismically induced LOOP occurrence frequency. As a result, use of failure probabilities other than the 1E-4 value can potentially challenge or negate the licensees justification for the 1E-4 value provided in response to APLC 50.69 RAI No. 4b as well as APLC 50.69 RAI No. 4d and therefore, the basis for the staffs decision on the acceptability of the proposed alternative seismic approach.
In addition, the licensees response to APLC 50.69 RAI No. 4e adds new information to its proposed alternative seismic approach that was not present in the LAR or the EPRI report supporting the LAR. The new information, added to step 5c in the EPRI report, states that the proposed alternative seismic approach was modified to include clarification that instead of screening SSCs out, the SSC may remain in the modified full power internal events (FPIE) model but with a seismic-induced failure probability from a plant-specific fragility analysis. The response does not provide any details on the purpose of and justification for this addition. In response to APLC 50.69 RAI No. 7, the licensee provided justification for not retaining changes to the FPIE PRA arising from the surrogate sensitivity due to the system-based
categorization and impacts on importance measures. It is unclear how the proposed modification to the licensees alternative seismic approach that SSC may remain in the modified FPIE model but with a seismic-induced failure probability is consistent with the licensees justification in APLC 50.69 RAI No. 7.
- a. Confirm that the licensee will only use a failure probability of 1E-4 for the surrogate event in its proposed alternative seismic approach, and that the discussion on the use of more realistic seismic-induced failure probabilities does not apply to the licensees proposed alternative seismic approach. If the licensee intends to use values other than 1E-4 for the surrogate event in its proposed alternative seismic approach, identify the value(s) and provide justification for that value(s) addressing APLC 50.69 RAI No. 4b and APLC 50.69 RAI No. 4d.
- b. Clarify whether the licensees alternative seismic approach will use the new guidance for step 5c in Section 2.3.1 of the EPRI report. If the licensee will use the new guidance, provide justifications for the modification to the licensees alternative seismic approach in step 5c (i.e., instead of screening SSCs out, the SSC may remain in the modified FPIE model but with a seismic-induced failure probability) and for its consistency with the licensees response to APLC 50.69 RAI No. 7.
APLC 50.69-ROUND 2 RAI NO. 4F-01:
The staff requested information through APLC 50.69 RAI No. 4f (ADAMS Accession No. ML20240A218) to support its finding on 10 CFR 50.69 (b)(2)(ii) for the proposed alternative seismic approach. APLC 50.69 RAI No. 4f requested justification for the use of the risk achievement worth (RAW) value of 20 to determine the categorization outcome from the surrogate sensitivity study. In its response in supplement dated October 16, 2020 (ADAMS Accession No. ML20290A791), the licensee cited the discussion of common-cause failures in NEI 00-04, Section 5.1, and stated that RAW values for correlated events and interaction events are by definition RAW values of common cause events.
Interaction events can include instances where only a single SSC is impacted rather than multiple SSCs or SSCs in different trains of a system. These cases are not known beforehand and the proposed alternative seismic approach, via the walkdown, can identify such cases during the categorization process. For such cases, the statement in NEI 00-04, Section 5.1, that a set of components or an entire system was made unavailable and therefore, the RAW value for common cause events appears to be inappropriate. For such cases, use of a RAW value of 20 appears to be a deviation from the endorsed NEI 00-04 guidance (i.e., the use of RAW value of 2 for single SSC failures). The licensees response to APLC 50.69 RAI No. 4f does not discuss such cases or justify the use of RAW value of 20 for such cases.
Confirm that the RAW value for single component failures in NEI 00-04 will be used in the proposed alternative seismic approach for interaction failures that do not impact either multiple SSCs or SSCs in separate trains of a system (including SSCs in a single train system). Alternately, justify the apparent deviation from NEI 00-04 for the proposed alternative seismic approach in the use of the common cause events RAW value for interaction failures that do not impact either multiple SSCs or SSCs in separate trains of a system (including SSCs in a single train system).
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Hearing Identifier:
NRR_DRMA Email Number:
930 Mail Envelope Properties (BLAPR09MB6481819CC390147D149B6B54E6CA0)
Subject:
LaSalle County Station, Units 1 and 2 - Request for Additional Information Regarding the License Amendment Request to Adopt 10 CFR 50.69 (EPID L-2020-LLA-0017)
Sent Date:
12/11/2020 11:25:49 AM Received Date:
12/11/2020 11:25:49 AM From:
Purnell, Blake Created By:
Blake.Purnell@nrc.gov Recipients:
"David Gullott (David.Gullott@exeloncorp.com)" <David.Gullott@exeloncorp.com>
Tracking Status: None "Salgado, Nancy" <Nancy.Salgado@nrc.gov>
Tracking Status: None "Kusumawatimurray, Putri:(Exelon Nuclear)" <Putri.Kusumawatimurray@exeloncorp.com>
Tracking Status: None "Taken, Jason C.:(Exelon Nuclear)" <Jason.Taken@exeloncorp.com>
Tracking Status: None Post Office:
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