ML15061A155
| ML15061A155 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 02/27/2015 |
| From: | Andrea George Plant Licensing Branch IV |
| To: | David Bice, Clark R Entergy Nuclear Operations |
| References | |
| TAC MF5545 | |
| Download: ML15061A155 (5) | |
Text
1 NRR-PMDAPEm Resource From:
George, Andrea Sent:
Friday, February 27, 2015 1:49 PM To:
'CLARK, ROBERT W'; 'BICE, DAVID B (ANO)'
Cc:
'PYLE, STEPHENIE L'
Subject:
Requests for Additional Information - ANO-1 Report Regarding Changes in Peak CLadding Temperature ECCS LOCA Analysis (per 10 CFR 50.46 and 10 CFR 50.73) - TAC No.
MF5545 Attachments:
MF5545 - RAIs.pdf Mr. Clark and Mr. Bice, By letter dated December 22, 2014 (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML14357A098), Entergy Operations, Inc. (Entergy, the licensee), submitted a report describing a significant error identified in the emergency core cooling system (ECCS) loss of coolant accident (LOCA) evaluation model, and an estimate of the effect of the error on the predicted peak cladding temperature (PCT) for Arkansas Nuclear One, Unit 1 (ANO-1). The errors identified in the ECCS LOCA evaluation model, and more specifically, the uranium thermal conductivity models, do not account for the thermal conductivity degradation that occurs as a function of the fuel burnup. This report was submitted by the licensee pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.46(a)(3) and 10 CFR 50.73.
In the course of its review, the NRC staff has determined that additional information is required to complete its evaluation. The formal requests for additional information (RAIs) are attached to this email. A public meeting regarding this topic and these RAIs was held on Wednesday, February 25, 2015 with all Babcock & Wilcox operating plants, AREVA, and the NRC staff. It was agreed via phone on Thursday, February 26, 2015, that a response to these RAIs would be provided by March 30, 2015. If you foresee any issues with meeting this date, please let me know.
Sincerely, Andrea George Project Manager Division of Operating Reactor Licensing U.S. Nuclear Regulatory Commission 301-415-1081
Hearing Identifier:
NRR_PMDA Email Number:
1910 Mail Envelope Properties (6F9E3C9DCAB9E448AAA49B8772A448C502460E696580)
Subject:
Requests for Additional Information - ANO-1 Report Regarding Changes in Peak CLadding Temperature ECCS LOCA Analysis (per 10 CFR 50.46 and 10 CFR 50.73) - TAC No. MF5545 Sent Date:
2/27/2015 1:48:38 PM Received Date:
2/27/2015 1:48:00 PM From:
George, Andrea Created By:
Andrea.George@nrc.gov Recipients:
"'PYLE, STEPHENIE L'" <SPYLE@entergy.com>
Tracking Status: None
"'CLARK, ROBERT W'" <RCLARK@entergy.com>
Tracking Status: None
"'BICE, DAVID B (ANO)'" <DBICE@entergy.com>
Tracking Status: None Post Office:
HQCLSTR01.nrc.gov Files Size Date & Time MESSAGE 1606 2/27/2015 1:48:00 PM MF5545 - RAIs.pdf 83431 Options Priority:
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Recipients Received:
REQUEST FOR ADDITIONAL INFORMATION REPORT REGARDING SIGNIFICANT CHANGE IN PEAK CLADDING TEMPERATURE FOR ECCS LOCA ANALYSIS PUSUANT TO 10 CFR 50.46 AND 10 CFR 50.73 ENTERGY OPERATIONS, INC.
ARKANSAS NUCLEAR ONE, UNIT 1 DOCKET NO. 50-313 BACKGROUND By letter dated December 22, 2014 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML14357A098), Entergy Operations, Inc. (Entergy, the licensee),
submitted a report describing a significant error identified in the emergency core cooling system (ECCS) loss of coolant accident (LOCA) evaluation model, and an estimate of the effect of the error on the predicted peak cladding temperature (PCT) for Arkansas Nuclear One, Unit 1 (ANO-1). This report was submitted pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.46(a)(3) and 10 CFR 50.73.
The reported error concerned the BWNT LOCA ECCS evaluation model (EM), which is documented in Volume I of the NRC-approved licensing topical report (LTR) BAW-10192P-A, BWNT Loss-of-Coolant Accident Evaluation Model for Once-Through Steam Generator Plants, Volume I - Larger Break. The error relates to the ability of upstream fuel performance analysis codes to provide accurate predictions of the fuel pin initial temperature. The TACO3 code documented in NRC-approved LTR BAW-10162P-A, TACO3 - Fuel Pin Thermal Analysis Computer Code, and the GDTACO code documented in NRC-approved LTR BAW-10184P-A, GDTACO - Urania Gadolinia Fuel Pin Thermal Analysis Code, use uranium thermal conductivity models that do not account for the degradation of the thermal conductivity that occurs as a function of the fuel burnup.
Correction for this error caused a significant increase in the PCT predicted for ANO-1. Most notably, for postulated LOCAs that initiate at middle of life (MOL) or end of life (EOL) core conditions, thermal conductivity degradation (TCD) causes the predicted PCT to increase significantly. Because fuel at the beginning of life (BOL) does not experience appreciable TCD, the effects of the error at BOL conditions are much less significant. Similarly, EOL fuel operates at a non-limiting local heating rate (LHR), and remains generally non-limiting even when corrected for TCD. Therefore, TCD effects are most significant at MOL conditions.
During the course of its review of the licensees report dated December 22, 2014, the U.S.
Nuclear Regulatory Commission (NRC) staff has determined that additional information is required to complete its evaluation. In particular, 10 CFR 50.46(a)(3)(ii) states, for significant errors, that licensees shall provide this report within 30 days and include with the report a proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with § 50.46 requirements. In light of the significant model changes required to correct for this error, it is not clear to the NRC staff how the licensees indication, in the report, that a reanalysis would be provided on an NRC agreed-upon schedule will show compliance with 10 CFR 50.46 requirements.
REQUESTS FOR ADDITIONAL INFORMATION SNPB RAI-1) The report dated December 22, 2014, indicates that Entergy will correct for the TCD deficiency in a future LOCA analysis on an NRC agreed-upon schedule.
The NRC has determined that the TACO3/GDTACO fuel temperature uncertainty values are explicitly reflected in the NRC-approved fuel performance methodology documented in BAW-10162P-A and BAW-10184P-A. In addition, the BWNT LOCA ECCS EM requires the use of NRC-approved fuel thermal-mechanical models. It is not clear how a potential revision to the fuel temperature modeling provided by these thermal mechanical codes would remain compliant with the NRC-approved methodology.
Regarding calculated emergency core cooling performance evaluation (i.e.,
LOCA analysis), 10 CFR 50.46 states, in part, ECCS cooling performance must be calculated in accordance with an acceptable evaluation model The change in fuel performance modeling discussed above has not been submitted to the NRC staff for generic review and approval; therefore, it is not possible for the NRC staff to conclude that the evaluation model, once updated to incorporate the effects of TCD, would remain acceptable.
In light of the fact that TCD-corrected versions of the TACO3 and GDTACO fuel performance models have not been previously reviewed and approved by the NRC, explain how Entergy will ensure that the corrected ECCS evaluation is performed in accordance with an acceptable evaluation model, pursuant to 10 CFR 50.46(a)(1)(i).
SNPB RAI-2) The report dated December 22, 2014, indicates that the TCD-related model changes will be incorporated into a version the BWNT LOCA ECCS EM. This model revision will significantly change the predicted ECCS performance for ANO-1.
Regarding the evaluation of ECCS performance, 10 CFR 50.46(a)(1)(i) states, in part, that ECCS cooling performance 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. It is unclear how, or whether, the reanalysis suggested in the December 22, 2014, report would address this requirement.
Explain how the re-analysis will address the requirement identified above, regarding assurance that the most severe hypothetical loss-of-coolant accidents are calculated.
SNPB RAI-3) ANO1 TS 5.6.5, Core Operating Limits Report, states that the analytical methods used to determine the core operating limits shall be those previously reviewed and approved by the NRC, and specifies a list of those approved methods, includng Babcock & Wilcox LTR BAW-10179P-A, Safety Criteria and Methodology for Acceptable Cycle Reload Analyses.
As discussed in RAI 1, above, the updated fuel temperature uncertainty value does not appear consistent with the NRC-approved BWNT LOCA ECCS Evaluation Model. The application of COPERNIC-based fuel temperature uncertainties to TACO3 and GDTACO evaluation models is not consistent with NRC-approved fuel performance methodology. Furthermore, it is not clear that the proposed TCD correction is consistent with the discussion contained in Section 9.2.3 of BAW-10179P-A.
Explain how Entergy will ensure that the reanalysis referenced in the December 22, 2014, letter, will adhere to this TS requirement.