RA-15-0012, Response to Request for Additional Information Regarding the Duke Energy Carolinas, LLC (Duke Energy) 10 CFR 50.46, 30-Day Report; Estimated Impacts to Peak Cladding Temperature Due to Fuel Pellet Thermal Conductivity Degradation
| ML15090A303 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 03/31/2015 |
| From: | Repko R Duke Energy Carolinas, Duke Energy Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA-15-0012, TAC MF5572, TAC MF5573, TAC MF5574 | |
| Download: ML15090A303 (7) | |
Text
( '-> DUKE ENERGY.
March 31, 2015 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Oconee Nuclear Station, Units 1, 2, and 3 Docket Numbers 50-269, 50-270, and 50-287 Renewed Operating License Nos. DPR-38, DPR-47, and DPR-55 Regis T. Repko 526 South Church Street Charlotte, NC 28202 Mailing Address:
Mail Code EC07H !P.O. Box 1006 Charlotte, NC28201-1006 704-382-4126 704-382-4541 fax RA-15-0012 10 CFR 50.46{a)(3)
Subject:
Response to Request for Additional Information Regarding the Duke Energy Carolinas, LLC (Duke Energy) 10 CFR 50.46 Day Report for Oconee Nuclear Station, Units 1, 2, and 3; Estimated Impacts to Peak Cladding Temperature due to Fuel Pellet Thermal Conductivity Degradation
References:
- 1.
Letter from Duke Energy (Ernest J. Kapopoulos, Jr.) to USNRC (Document Control Desk), "Duke Energy Carolinas, LLC (Duke Energy): 10 CFR 50.46 -
30-Day Report for Oconee Nuclear Station, Units 1, 2, and 3; Estimated Impacts to Peak Cladding Temperature due to Fuel Pellet Thermal Conductivity Degradation," dated December 17, 2014 (ML14353A214)
- 2.
Letter from USNRC (J. Whited) to Duke Energy (Scott Batson), "Oconee Nuclear Station, Units 1, 2, and 3, Request For Additional Information Re:
1 0 CFR 50.46 - 30 Day Report on Estimated Impacts to Peak Cladding Temperature Due to Fuel Pellet Thermal Conductivity Degradation {TAC NOS. MF5572, MF5573, AND MF5574)," dated March 2, 2015 (ML15056A357)
In Reference 1, Duke Energy Carolinas, LLC (Duke Energy) submitted a report describing a significant error identified in the emergency core cooling system (ECCS) evaluation model, and an estimate of the effect of the error on the predicted peak cladding temperature (PCT) for Oconee Nuclear Station (ONS) Units 1, 2, and 3. This report was submitted pursuant to 10 CFR 50.46(a)(3).
Reference 2 transmitted Requests for Additional Information (RAis) regarding the Reference 1 submittal. The responses to these requests are provided in Attachment 1.
The following commitment is made in this letter:
The Oconee Large Break LOCA reanalysis incorporating the Thermal Conductivity Degradation (TCD) error correction will be performed within 15 months after NRC approval of the supplement to BAW-10192P-A.
This commitment supersedes that made in Reference 1.
U.S. Nuclear Regulatory Commission March 31, 2015 Page 2 Should you have any questions regarding this request, please contact Art Zaremba at (980) 373-2062.
Sincerely,
~~-
Regis T. Repko Senior Vice President Governance, Projects, and Engineering
Attachment:
- 1)
Response to Request for Additional Information Regarding the Duke Energy Carolinas, LLC (Duke Energy) 1 0 CFR 50.46 Day Report for Oconee Nuclear Station, Units 1, 2, and 3; Estimated Impacts to Peak Cladding Temperature due to Fuel Pellet Thermal Conductivity Degradation
U.S. Nuclear Regulatory Commission March 31, 2015 Page 3 xc:
V. M. McCree, Region II Administrator U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Avenue NE, Suite 1200 Atlanta, Georgia 30303-1257 James A. Hall, Project Manager (ONS)
U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852-2738 Jeffrey A. Whited, Project Manager (by electronic mail only)
U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation 11555 Rockville Pike, Mailstop: 0-881A Rockville, MD 20852 Eddy L. Crowe USNRC Resident Inspector - ONS
RA-15-0011 Page 1 of 4 Response to Request for Additional Information Regarding the Duke Energy Carolinas, LLC (Duke Energy) 10 CFR 50.46 Day Report for Oconee Nuclear Station, Units 1, 2, and 3; Estimated Impacts to Peak Cladding Temperature due to Fuel Pellet Thermal Conductivity Degradation
RA-15-0011 Page 2 of 4 Response to Request for Additional Information Regarding the Duke Energy Carolinas, LLC (Duke Energy) 10 CFR 50.46-30-Day Report for Oconee Nuclear Station, Units 1, 2, and 3; Estimated Impacts to Peak Cladding Temperature due to Fuel Pellet Thermal Conductivity Degradation NRC Request #1 The letter dated December 17, 2014, stated that 11AREVA's recommendation to Duke Energy with respect to aLB [large break] LOCA [Loss of Coolant Accident] reanalysis for Oconee is to perform an explicit analysis of the limiting PCT [peak cladding temperature] case. COPERNIC2 will be used to obtain the appropriate uncertainty factors with TCD [Thermal Conductivity Degradation] effects considered... II The letter also documents a regulatory commitment to perform this reanalysis.
The NRC has determined that the TAC03/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 [emergency core cooling system] EM [evaluation model] requires the use of NRC-approved fuel thermal-mechanical models. Although the COPERNIC code has been approved by the NRC, as documented in BAW-1 0231 P-A, the NRC staff does not consider the application of COPERNIC-based uncertainty values to TACO-based fuel performance methods, for application within the BWNT-LOCA ECCS evaluation model, to be accordant with NRC-approved methodology.
Regarding calculated emergency core cooling performance evaluation (i.e., LOCA analysis),
1 0 CFR 50.46 states, in part, 11ECCS cooling performance must be calculated in accordance with an acceptable evaluation model... II The change in fuel temperature uncertainty 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 this new uncertainty, would remain acceptable.
In light of the fact that the proposed TACO and GDTACO fuel temperature uncertainty values have not been previously reviewed and approved by the NRC, explain how Duke 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).
Duke Energy Response AREVA plans to submit a supplement to BAW-10192P-A for NRC review and approval which will describe appropriate fuel temperature uncertainty values, based on the COPERNIC2 code, which will be applied to the TAC03 and GDTACO initial fuel temperatures. The COPERNIC2 code has been approved by the NRC, and explicitly models fuel pellet thermal conductivity degradation. Following NRC approval of the supplement to BAW-10192P-A, a LBLOCA reanalysis will be performed for Oconee using the acceptable LBLOCA evaluation model which will include the NRC-approved TCD error corrections.
RA-15-0011 Page 3 of 4 NRC Request #2 Based on previous reports submitted to the NRC pursuant to 10 CFR 50.46 requirements, the NRC staff understands that the TCD-related model changes will be incorporated into a version of the BWNT LOCA ECCS EM that corrects for an error previously reported, concerning the nodalization of column weldments above the core. Altogether, these model changes will significantly change the predicted emergency core cooling performance for ONS.
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 whether the implementation of the changes described above will affect the predicted emergency core cooling performance for the spectrum of break sizes, locations, and other properties, such that the existing, most limiting LOCA event analyzed remains the most severe hypothetical loss-of-coolant accident.
Since the December 17, 2014, letter indicates that a "reanalysis for the highest PCT case at Middle-of-Life for Oconee Nuclear station... " will be performed, explain how this analysis will address the requirement identified above, regarding assurance that the most severe hypothetical loss-of-coolant accidents are calculated.
Duke Energy Response The existing Oconee LBLOCA analysis has already incorporated a column weldment model as part of a partial reanalysis needed to address a separate error correction, as described in a 30-Day 10 CFR 50.46 report submitted by Duke Energy to the NRC on December 16, 2013 (Reference 1). That reanalysis did not account for the recent TCD error.
During AREVA's presentation to the NRC on February 25, 2015, AREVA stated that, for those plants which have existing analyses performed with up-to-date evaluation models prior to the TCD change, previous sensitivity studies can be used to determine the most severe case.
As part of the supplement to BAW-10192P-A, AREVA intends to confirm that the TCD error correction does not alter the conclusion of existing sensitivity studies. AREVA also intends to perform demonstration analyses to show how the revised evaluation model would be used in a licensing analysis. AREVA has indicated that the demonstration analysis to be included in the supplement to BAW-10192P-A will utilize the Oconee LBLOCA model.
For the Oconee TCD reanalysis effort, the middle-of-life (MOL) time in life is expected to remain limiting with respect to PCT, since TCD is not expected to affect the beginning-of-life (BOL) cases. For the Oconee reanalysis, the number of MOL cases to be analyzed, at particular axial core elevations, will be sufficient to ensure that the limiting break scenario has been calculated with an acceptable evaluation model, which includes the TCD error corrections to be described in the supplement to BAW-10192P-A. Also, an end-of-life (EOL) case at the 2.506 foot core elevation will be evaluated to ensure that EOL remains non-limiting with respect to PCT.
RA-15-0011 Page 4 of 4 NRC Request #3 ONS TS 5.6.5, "Core Operating Limits Report," Section b., requires that the "analytical methods used to determine the core operating limits shall be those previously reviewed and approved by the NRC for use at ONS," including BAW-10192P-A, "BWNT LOCA-BWNT Loss of Coolant Accident Evaluation Model for Once-Through Steam Generator Plants."
Explain how Duke will ensure that the reanalysis performed in fulfillment of the commitment provided in the December 17, 2014, letter, will remain consistent with the latest approved revision to BAW-10192P-A.
Specifically, 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 TAC03 and GDTACO evaluation models is not consistent with NRC-approved fuel performance methodology.
Duke Energy Response As noted in the response to NRC Request #1, a LBLOCA reanalysis will be performed for Oconee using the supplemented version of BAW-10192P-A, which will include the NRC-approved TCD error corrections.
As discussed with the NRC on February 25, 2015, the Oconee Large Break LOCA reanalysis will be performed after NRC approval is obtained for the supplement to BAW-1 0192P-A. The Oconee Large Break LOCA reanalysis incorporating the TCD error correction will be performed within 15 months after NRC approval of the supplement to BAW-10192P-A. This commitment supersedes that made in Reference 2.
As part of implementation of the Oconee Large Break LOCA reanalysis, the cycle-specific Core Operating Limits Report (COLA) will be updated to contain the complete identification for Topical Report BAW-10192P-A, including the NRC-approved supplement for the TCD error correction. Per Oconee Technical Specification 5.6.5, the COLA contains the complete identification for each of the Technical Specifications referenced topical reports used to prepare the COLA (i.e., report number, title, revision number, report date or NRC SER date, and any supplements).
References
- 1.
Letter from Duke Energy (Garry D. Miller) to USNRC (Document Control Desk), "30-Day Report Pursuant to 10 CFR 50.46, Changes to or Errors in an Evaluation Model," dated December 16, 2013 (ML13353A137)
- 2.
Letter from Duke Energy (Ernest J. Kapopoulos, Jr.) to USNRC (Document Control Desk), "Duke Energy Carolinas, LLC (Duke Energy): 10 CFR 50.46 Day Report for Oconee Nuclear Station, Units 1, 2, and 3; Estimated Impacts to Peak Cladding Temperature due to Fuel Pellet Thermal Conductivity Degradation," dated December 17, 2014 (ML14353A214)