RS-18-074, Supplement to License Amendment Request to Utilize Accident Tolerant Fuel Lead Test Assemblies
| ML18184A270 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 07/02/2018 |
| From: | Gullott D Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RS-18-074 | |
| Download: ML18184A270 (8) | |
Text
Exelon Generation RS-18-074 July 2, 2018 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Byron Station, Unit 2 Renewed Facility Operating License No. NPF-66 NRC Docket No. 50-455 2000 10 CFR 50.90
Subject:
Supplement to License Amendment Request to Utilize Accident Tolerant Fuel Lead Test Assemblies
Reference:
Letter from D. M. Gullatt (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission , 11 License Amendment Request to Utilize Accident Tolerant Fuel Lead Test Assemblies, 11 dated March 8, 2018 In the Referenced letter, 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, 11 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 (L TAs) during Byron Station Unit 2, Cycles 22, 23, and 24. The LTR design described in the March 8, 2018 EGC submittal states that the uranium silicide (U3Sb) pellets in each rod will be enclosed in a capsule within a sealed segmented rod of approximately one foot in length, and that the segmented rod is inserted into a standard fueled rod to make up part of the normal-length fuel rod. Subsequently the L TR design was changed to eliminate the capsule in order to improve safety and to reduce complexity of manufacturing and analysis.
Additionally, the make-up of the LTA containing the ADOPTŽ LTRs was revised to eliminate the use of the ADOPTŽ pellets with standard Optimized ZIRLOŽ clad and only use the ADOPTŽ pellets with the coated Optimized ZIRLOŽ clad. The technical analysis approach of the specific changes from the previous design and the associated core design impacts are provided in the attached supplement to the March 8, 2018 submittal.
EGC has reviewed the information supporting the No Significant Hazards Consideration and the Environmental Consideration that was previously provided to the NRC in the March 8, 2018 submittal.
The modification of the L TR 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 July 2, 2018 U.S. Nuclear Regulatory Commission Page 2 impact statement nor an environmental assessment needs to be prepared in support of the proposed amendment.
In accordance with 10 CFR 50.91, 11 Notice for public comment; State consultation, 11 paragraph (b), EGC is notifying the State of Illinois of this supplement to the March 8th 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. Once approved, the amendment shall be implemented within 30 days. Should you have any questions concerning this letter, please contact Ms. Rebecca L. Steinman at (630) 657-2831.
I declare under penalty of perjury that the foregoing is true and correct. Executed on the 2nd day of July 2018. Respectfully, David M. Gullatt Manager -Licensing 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 ATTACHMENT 1 Evaluation of L TR Modification on Proposed Change
Subject:
Supplement to License Amendment Request to Utilize Accident Tolerant Fuel Lead Test Assemblies 1.0
SUMMARY
DESCRIPTION 2.0 DETAILED DESCRIPTION 3.0 TECHNICAL EVALUATION
4.0 REGULATORY EVALUATION
5.0 ENVIRONMENTAL CONSIDERATION
6.0 REFERENCES
ATTACHMENT 1 Evaluation of L TR Modification on Proposed Change 1.0
SUMMARY
DESCRIPTION By letter dated March 8, 2018 (Reference 6.1) 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, 11 Additional Conditions, 11 of the Byron Station Unit 2 Operational License that authorizes the use of a limited number of Accident Tolerant Fuel (ATF) Lead Test Rods (L TRs) in two Lead Test Assemblies (L TAs) during Byron Station Unit 2, Cycles 22, 23, and 24. The L TR design described in Reference 6.1 states that the uranium silicide (U3Si2) pellets in each rod will be enclosed in a capsule within a sealed segmented rod of approximately one foot in length, and that the segmented rod is inserted into a standard fueled rod to make up part of the normal-length fuel rod. Continued development of the Byron Accident Tolerant Fuel (ATF) program has resulted in a modification to the rod design to improve safety and to reduce complexity of manufacturing and analysis.
In the modified L TR design, the uranium silicide pellets will be enclosed in a sealed Optimized ZIRLOŽ clad segment with the segment positioned between two solid Zircaloy bars to constitute the full-length rod. Additionally, the make-up of the L TA containing the ADOPTŽ L TRs was revised to eliminate the use of the ADOPTŽ pellets with standard Optimized ZIRLOŽ clad and only use the ADOPTŽ pellets with the coated Optimized ZI RLO TM clad 1* This change is due to the higher pellet density of the ADOPTŽ fuel which results in higher power when compared to uranium dioxide pellets. To minimize this power increase, all ADOPTŽ pellets will be placed in coated rods because chromium is a light neutron absorber.
The evaluation contained in this supplement discusses the impact of the modified L TR design on the previous technical justification and regulatory basis supporting the conclusion that inserting the subject LT As, including the described modifications, into the Byron Unit 2 core during Cycles 22, 23, and 24 can be conducted in a safe manner. It is expected that all applicable limits (e.g., fuel thermal mechanical limits, core thermal hydraulic limits, Emergency Core Cooling Systems limits, nuclear limits such as Shutdown Margin, transient analysis limits and accident analysis limits) associated with the L TAs remain bounded by the current analysis of record. 2.0 DETAILED DESCRIPTION The L TR design described in the March 8, 2018 EGC submittal states that the uranium silicide (U3Sb) pellets in each rod will be enclosed in a capsule within a sealed segmented rod of approximately one foot in length, and that the segmented rod is inserted into a standard fueled rod to make up part of the normal-length fuel rod. The modified L TR design eliminates the capsule so that the uranium silicide pellets will be loaded directly into the approximately one foot long sealed Optimized ZIRLOŽ clad rod segment. The fueled segment will utilize a thicker clad compared to the other rods in the assembly.
The modified design also includes solid Zircaloy 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. Page 2 of 6 ATTACHMENT 1 Evaluation of L TR Modification on Proposed Change bars in the remainder of the normal full-length rod, rather than fuel. As a result of this design, the conservative thermal margin cutback is based on the peak power of this one-foot axial segment, rather than integral rod power. The modified LTR design change affects only the four (4) uranium silicide L TRs (EnCore) and two of the ADOPTŽ L TRs. There is no change to the ADOPTŽ fuel pellets or the coated Optimized ZIRLOŽ cladding.
The L TA make-up is revised to reflect the uranium silicide L TR modification as well as to eliminate the use of the ADOPTŽ uranium dioxide fuel pellets with the standard Optimized ZIRLOŽ clad and only use the ADOPTŽ pellets with the coated Optimized ZIRLOŽ clad. The revised composition of the two LTAs, which will continue to contain up to a combined total of 20 L TRs, is as follows: L TA #1 is a Westinghouse VANTAGE+ Optimized Fuel Assembly design containing:
- Up to four rods with uranium silicide (U3Si2) pellets and Optimized ZIRLOŽ cladding.
The U3Si2 pellets will be enclosed in a sealed clad segment with the segment positioned between two solid Zircaloy bars.
- Up to four rods with standard uranium dioxide (U02) pellets and coated Optimized ZIRLOŽ cladding
- All other rods in LT A #1 will have standard uranium dioxide pellets and standard Optimized ZIRLOŽ cladding LTA #2 is a Westinghouse VANTAGE+
Optimized Fuel Assembly design and contains:
- Up to eight rods with standard uranium dioxide pellets and coated Optimized ZIRLOŽ cladding
- Up to four rods with Westinghouse ADOPTŽ uranium dioxide pellets and coated Optimized ZIRLOŽ cladding
- All other rods in LT A #2 will have standard uranium dioxide pellets and standard Optimized ZI RLOŽ cladding There are no other differences compared to the existing resident VANT AGE+ fuel assembly design. 3.0 TECHNICAL EVALUATION 3.1 Nuclear Safety and Design Impacts The behavior of the core continues to be dominated by the currently approved fuel. The core, including the LTAs, will be designed to ensure that the Technical Specification 4.2.1 "Fuel Assemblies" requirement to place the L TAs in non-limiting core regions continues to be met. The core design criteria used to ensure this requirement is met are as follows: Page 3 of 6 ATTACHMENT 1 Evaluation of L TR Modification on Proposed Change a. The L TRs will be designed to be at a lower power than the lead rod power (i.e., 5% for uranium silicide L TRs, 2% for Coated Clad and ADOPTŽ L TRs). b. The L TRs containing the uranium silicide within the LT A will be designed with a smaller pellet diameter relative to the U02 rods. They are not expected to be neutronically similar to the symmetric uranium dioxide rods as the new design is only a segment which cannot be compared to a full rod. c. The safety parameters related to peaking factors/thermal limits will be analyzed with the uranium silicide, ADOPTŽ pellets, and chromium coating explicitly modeled in the neutronic calculations.
- d. The LT As will not be placed in rodded locations considered in the Rod Ejection Accident analyses.
The reduced diameter of the uranium silicide pellets obviates the need for reducing the enrichment of these pellets, as was previously described in Reference 6.1. The design basis limits/criteria described in Reference 6.1 are unchanged by the L TR changes described in this document but the above core design restrictions supersede the initial restrictions described in Sections 3.3 and 4.1 of Reference 6.1. 3.2 Technical Analysis Impacts The L TR design change described in Section 2 of this document affects the four (4) uranium silicide L TRs and two of the ADOPTŽ L TRs. There is no change to the design of the ADOPTŽ fuel pellets or the coated Optimized ZIRLOŽ cladding, only an increase in the number of ADOPTŽ rods using the coated Optimized ZIRLOŽ from two to four rods. Since there is limited impact on the make-up of the two LT As, it is expected that there will be no impact to the LOCA; non-LOCA; thermal-hydraulic; fuel handling, storage, and shipping; BEACON core monitoring system; or alternative source term methodologies described in Reference 6.1. Impacts to the other technical evaluations are described below. Mechanical Design Methodology To ensure a conservative deployment of the new uranium silicide fuel type, a segmentation strategy will be employed for these four L TRs. The uranium silicide pellets will be loaded directly into a sealed Optimized ZIRLOŽ rod segment of approximately one foot in length with a thicker clad. The uranium silicide fueled segment will be placed between fuel assembly spacer grids, thus eliminating the risk of grid-to-rod failure and debris fretting failure. The thicker clad will also increase corrosion margin and pellet-clad mechanical interaction margin. The segment will utilize Optimized ZIRLOŽ cladding in all four LTRs. The uranium silicide L TRs will be lighter than the standard fuel rods because they have less fuel; however, no vibration-related impact on reactor performance is anticipated.
Page 4 of 6 ATTACHMENT 1 Evaluation of L TR Modification on Proposed Change Seismic The impact of the uranium silicide rod design change will be negligible.
The change in LT A weight associated with the L TR modification is not expected to have any detrimental impact on fuel assembly seismic characteristics.
Westinghouse will evaluate the grid deformation analysis to ensure adequate margin is maintained and that the ability to maintain a coolable geometry is not impacted.
Core Physics For conservatism, the primary design criterion is to maintain the uranium silicide L TR power peaking at least 5% below the core power peaking. The associated LT A will also be one of the lower enrichment reload batch assemblies.
The associated design criteria for the fueled and the coated Optimized ZIRLOŽ LTRs will be to maintain the power peaking at least 2% below the core maximum power peaking. Note that the 5% and 2% power suppression will be design criteria utilized when creating the core loading pattern and will not be monitored during plant operation.
The L TRs will not be designed to lead the core in power peaking at any time during planned operation.
Westinghouse fuel design and core design methods can accommodate the unfueled Zircaloy bars on the top and bottom of the uranium silicide segment, and there will be no significant increase in uncertainty or risk introduced by the unfueled inert regions. Fuel Rod Design No adverse effects are anticipated from the modified uranium silicide L TR design. The uranium silicide rods will not have uranium on their extremities which negates comparison to a full-length symmetric partner's rod average burnup. A comparison is feasible of the unique uranium silicide segment design to 1 foot segments of U02 fueled rods in similar locations in the core. The standard U02 rods in the LT A will meet all applicable limits, including those related to burnup, throughout all cycles of operation.
The overall core design will continue to meet all applicable design criteria using approved methodologies, standard loading pattern strategies, and monitoring of rod burnup at the core design level. The L TRs with uranium silicide, including the thicker cladding and unfueled remainder of the segmented rod, are being analyzed with the developmental PAD-ATF fuel performance code. Preliminary results indicate that the segment has increased margin to most key fuel rod performance criteria due to operating at a lower fuel temperature due to its higher thermal conductivity.
4.0 REGULATORY EVALUATION
EGC has reviewed the information supporting the No Significant Hazards Consideration that was previously provided to the NRC in Reference 6.1. The modification of the L TRs described in this supplement does not affect the conclusion that the proposed license amendment does not involve a significant hazards consideration.
5.0 ENVIRONMENTAL CONSIDERATION EGC has reviewed the information supporting the Environmental Consideration that was previously provided to the NRC in Reference 6.1. This modification of the L TRs described in Page 5 of 6 ATTACHMENT 1 Evaluation of L TR Modification on Proposed Change this supplement does not affect the conclusion that neither an environmental impact statement nor an environmental assessment need to be prepared in support of the proposed amendment.
6.0 REFERENCES
6.1 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, ADAMS Accession No. ML18067A431 6.2 Byron/Braidwood Stations, Updated final Safety Analysis Report, Section 4.2, "Fuel System Design" 6.3 Byron Station Technical Specification 4.2.1, "Fuel Assemblies" Page 6 of 6