RS-18-147, To License Amendment Request to Utilize Accident Tolerant Fuel Lead Test Assemblies
| ML18352B117 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 12/18/2018 |
| From: | Gullott D Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RS-18-147 | |
| Download: ML18352B117 (3) | |
Text
Exelon Generation RS-18-147 4300 W111f1elcl Roacl Warrenville. IL 60555 630 657 2000 Office 10 CFR 50.90 December 18, 2018 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Byron Station, Unit 2 Renewed Facility Operating License No. NPF-66 NRC Docket No. 50-455 Supplement #2 to License Amendment Request to Utilize Accident Tolerant Fuel Lead Test Assemblies
References:
- 1.
Letter from D. M. Gullatt (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission, "License Amendment Request to Utilize Accident Tolerant Fuel Lead Test Assemblies," dated March 8, 2018
- 2.
Letter from D. M. Gullatt (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission, "Supplement to License Amendment Request to Utilize Accident Tolerant Fuel Lead Test Assemblies," dated July 2, 2018 In Reference 1, Exelon Generation Company, LLC, (EGC) requested an amendment to Renewed Facility Operating License No. NPF-66 for Byron Station, Unit 2. The proposed change would add a License Condition to Appendix C, "Additional Conditions," of the Byron Station Unit 2 Operational License that authorizes the use of a limited number of Accident Tolerant Fuel (ATF) Lead Test Rods (LTRs) in two Lead Test Assemblies (LTAs) during Byron Station Unit 2, Cycles 22, 23, and 24.
Reference 2 describes an L TR design change that eliminated the uranium silicide pellet capsule originally described in Reference 1 to improve safety and to reduce complexity of manufacturing and analysis. Additionally, the make-up of the L TA containing the ADOPT' L TRs was revised in Reference 2 to eliminate the use of the ADOPT' pellets with standard Optimized ZIRLO' clad and only use the ADOPT' pellets with the coated Optimized ZIRLO' clad 1*
The license condition requested in Reference 1 explicitly states that the two LT As containing a limited number of Westinghouse Encore and ADOPT' accident tolerant fuel rods may be 1 Encore, ADOPT, and Optimized ZIRLO are trademark or registered trademark of Westinghouse Electric Company LLC, its affiliates and/or its subsidiaries in the United States of America and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners.
December 18, 2018 U.S. Nuclear Regulatory Commission Page 2 placed in nonlimiting Byron Station Unit 2 core regions during Cycles 22, 23 and 24. It also states "Impact on any aspect of reactor operation or safety will be negligible since the core design and reactor performance (during both normal and abnormal I accident operations) will be dominated by currently approved fuel types." These positions are consistent with the L TA provision of Technical Specification (TS) 4.2.1 which states "A limited number of lead test assemblies that have not completed representative testing may be placed in nonlimiting core regions."
While completing the power distribution limits confirmation computations for the Byron Station Unit 2 Cycle 22 ATF core models, it was found that the standard U02 linear heat generation rate (LHGR) reload limit, documented in the cycle specific Non-LOCA Reload Safety Analysis Checklist (RSAC), was exceeded for the blanket region of the ADOPT' L TRs. Specifically, the results of the reload analysis demonstrated that during a Condition II boron dilution transient, with rods in manual control, at the burnup step of 150 MWD/MTU, the ADOPT' L TRs are predicted to operate at higher power than the remainder of the core. This condition occurs during the dilution transient only and is not at steady state power. This condition does not exceed TS Safety Limit 2.1.1.3.
The standard U02 LHGR limit used in Westinghouse reload analyses is a constant value based on end of cycle (EOC) burnup conditions. The accident tolerant features of the ADOPT' fuel rods, such as the doping of the pellets and use of a coating, are not causing the exceedance of the RSAC LHGR limit based on this EOC burnup condition; the exceedance of the limit results from the use of fully enriched blanket regions. In the case of Cycle 22 for Byron Station Unit 2, the resident fuel in the remainder of the core is fabricated with lower enriched blankets than the ADOPT' rods causing the L TRs to be operating at a higher power than the bulk of the core at the elevation of the blanket pellets.
The nuclear industry has historically operated with fully enriched blankets. Designing with this feature is well understood and capable of being explicitly modeled. Consistent with current Westinghouse reload methods, if a cycle-specific reload analysis results in a value in excess of this RSAC limit, a more accurate burnup-dependent limit can be developed to demonstrate that the intent of the RSAC LHGR limit, i.e., that no centerline melt occurs, is met. In the case of the ADOPT' L TRs, the burnup-dependent limit is developed using PAD-ATF.
Except for the boron dilution event result described above, analyses completed to date have confirmed that the rods are placed in nonlimiting core regions with respect to the resident fuel.
Should another instance occur that a reload analysis shows the ADOPT' L TRs are not bounded by the other assemblies in the core, additional analyses will be performed to confirm that all surveillance and limiting conditions of operation are met and that all fuel licensing design bases remain satisfied prior to loading the L TRs into the Cycle 22 core at Byron Station Unit 2.
The reload analyses, supplemented as described above, will confirm that even with the ADOPT' rods leading the boron dilution event, the L TA program will have negligible impact on any aspects of reactor operation or reactor safety. Therefore, the overall conclusion that two LTAs containing a limited number of Westinghouse Encore and ADOPT' accident tolerant fuel rods will have a negligible impact on any aspect of reactor operations or reactor safety remains valid.
December 13, 2013 U.S. Nuclear Regulatory Commission Page 3 EGC has reviewed the information supporting the No Significant Hazards Consideration and the Environmental Consideration that was previously provided to the NRC in Reference 1. The original No Significant Hazards Consideration conclusions were based on the L TRs being bounded by the resident fuel in the core. As stated previously, in cases where the ADOPT' L TRs are not bounded by the remainder of the fuel in the core, explicit analysis will be performed to ensure that all surveillance and limiting conditions of operation are met and that all fuel licensing design bases remain satisfied. As a result, the Condition II analysis result described in this submittal does not affect the conclusion that the proposed license amendment does not involve a significant hazards consideration. This additional information also does not affect the conclusion that neither an environmental impact statement nor an environmental assessment needs to be prepared in support of the proposed amendment.
In accordance with 10 CFR 50.91, "Notice for public comment; State consultation,"
paragraph (b), EGC is notifying the State of Illinois of this supplement to the March 3th application for license amendment by transmitting a copy of this letter and its attachment to the designated State of Illinois official.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this letter, please contact Ms. Rebecca L. Steinman at (630) 657-2331.
I declare under penalty of perjury that the foregoing is true and correct. Executed on the 13th day of December 2013.
David M. Gullatt Director - Licensing and Regulatory Affairs Exelon Generation Company, LLC
Attachment:
Evaluation of L TR Modification on Proposed Change cc:
NRC Regional Administrator, Region Ill NRC Senior Resident Inspector, Byron Station Illinois Emergency Management Agency - Division of Nuclear Safety