ML23137A116

Draft Slides for Advisory Committee on Reactor Safeguards Subcommittee Meeting Regarding Use of Accident Tolerant Fuel Lead Test Assemblies

ML23137A116
Person / Time
Site:	Vogtle
Issue date:	06/02/2023
From:	Markley M Plant Licensing Branch II
To:	Southern Nuclear Operating Co
Shared Package
ML23137A114	List: ML23130A386 ML23137A116
References
EPID L-2022-LLA-0097
Download: ML23137A116 (1)

Text

NRC Staff Presentation Accident Tolerant Fuel (ATF)

Lead Test Assemblies (LTAs)

Vogtle, Units 1 and 2 June 21, 2023

OPENING REMARKS Joseph Donoghue, Director Division of Safety Systems Office of Nuclear Reactor Regulation

OPENING REMARKS - Continued

• NRC appreciates the opportunity to share these proposed changes with the ACRS.

• Member feedback is valuable.

• NRC does not require an ACRS letterreport to proceed but would greatly benefit from one.

• An ACRS letter report would inform expected future batch loading requests for higher enrichment and/or higher burnup.

3

PRESENTERS

• Licensing Actions

• John Lamb - DORL/NRR

• Chapter 15 Accident

• Charley Peabody -

Analysis, LOCA, & Non SNSB/DSS/NRR LOCA

• Code Analysis, Core

• Brandon Wise -

Physics, and Cladding SFNB/DSS/NRR

• Fuel Handling &

• Kent Wood - SFNB Storage

• Conclusion

• Joseph Donoghue, Director DSS/NRR 4

LICENSING ACTIONS

• SNC requested:

- Amendments to License Condition 2.D and TSs: (1)

TS 3.7.18, Fuel Assembly Storage in the Fuel Storage Pool, (2) TS 4.2.1, Fuel Assemblies, and (3) TS 4.3, Fuel Storage.

- Three Exemptions

• 10 CFR 50.46 and 10 CFR part 50, Appendix K to allow the use of coated AXIOM cladding, with ADOPT fuel pellets enriched up to 6 weightpercent U235.

• 10 CFR 50.68(b)(7) to allow greater than 5 weight percent U235 5

LICENSING ACTIONS - Continued

• Load four Westinghouse LTAs with advanced ATF features:

- Advanced Doped Pellet Technology (ADOPT) uranium dioxide (UO2) fuel,

- AXIOM cladding, chromium coating,

- four rods per LTA with up to 6 weightpercent enrichment U235.

• SNC is not requesting higher burnup greater than its current licensing basis of 60,000 MWd/MTU.

6

LTA DESIGN

• The LTAs are Westinghouse 17 x 17 PRIME Optimized Fuel Assembly design and each contain:

- Up to 132 rods with Westinghouse ADOPT UO2 pellets at maximum of 5 weightpercent enrichment and coated AXIOM cladding,

- 3 rods with Westinghouse ADOPT UO2 pellets at maximum of 6 weightpercent enrichment and coated AXIOM cladding,

- 1 rod with Westinghouse ADOPT UO2 pellets at maximum of 6 weightpercent enrichment and uncoated AXIOM cladding,

- All other rods will have UO2 pellets at maximum of 5 weightpercent enrichment, ZrB2 IFBA coated pellets and coated AXIOM cladding.

7

UFSAR CHAPTER 15 ACCIDENT ANALYSIS

• General Accident Analysis, Core Source Term, and Radiological Dose Consequences

- Most accidents, as well as source term, dose consequences, and design transients see negligible changes from placing 16 higher enriched LTA fuel rods into a core of 50,952 active rods.

- Avg enrichment of the core is only increased 0.0003% by 4 LTAs.

- Avg core enrichment remains ~ 4.4 - 4.6%.

8

UFSAR CHAPTER 15 ACCIDENT ANALYSIS - Continued

- This increase in enrichment is not a significant driver of increased source term, dose consequences, or cooling requirements, and is within the bounding assumptions and safety margins of the existing analyses which conservatively assume 5.00% enrichment for establishing source term and dose consequences.

9

LOCA ACCIDENT ANALYSES

• LOCA & Steam Line Break Mass and Energy Releases

- The containment response for these accidents is primarily impacted by RCS initial pressure and temperature conditions, as well as the break location and area parameters.

- Since these parameters are unchanged by the LAR, the analyses of record remain bounding for both short and longterm responses.

- Downstream containment and compartment responses are also not impacted.

10

LOCA ACCIDENT ANALYSES -

Continued

• Large and Small Break LOCA Analyses

- Large and Small Break LOCA Evaluation Model (EM) computer codes were re evaluated with LTA data.

- Both EMs demonstrated that 10 CFR 50.46 acceptance criteria for LOCAs continue to be met without any code modifications.

11

NON-LOCA ACCIDENT ANALYSES Vendor (Westinghouse) evaluated Steam Line Breaks, Locked Rotor, Loss of RCS Flow, and Control Rod Ejection

• No impact to computer codes, methodology, or acceptance criteria.

• LTA geometry, material properties, and reactivity feedback characteristics have no substantive impacts on the analyses and remain within existing margins.

• LTAs do not impact the departure from nucleate boiling ratio (DNBR) or peak clad temperatures (PCT).

12

NON-LOCA ACCIDENT ANALYSES - Continued Additional consideration for Control Rod Ejection event analysis

• Application and supplements designate that while LTAs may be placed in certain limiting core locations, the LTAs may only be utilized in such locations which are nonlimiting with respect to the control rod ejection analysis.

13

Neutronics

• SNC uses the PARAGON lattice physics code and NEXUS for neutronics calculations.

- There is no significant deviation in the neutron flux spectrum.

Therefore, there is reasonable assurance that these codes will adequately model the LTAs.

• PARAGON and NEXUS have been compared to the PARAGON2 code, which has been shown to be acceptable at enrichments greater than 5 wt% U-235.

- PARAGON2 has been shown to be acceptable to analyze the neutronic performance of new, unapproved fuel designs,

• No proposed changes to the nuclear design process.

14

CORE PHYSICS

• Flux spectrum will continue to be dominated by coresident fuel.

• Peaking factors remain less than what is assumed in the UFSAR.

• Differences between LTAs and coresident fuel are modeled explicitly.

• Neutronic impact of the LTAs are confined to the LTAs 15

THERMAL HYDRAULICS

• The codes and methods used by SNC for thermalhydraulic analyses are mostly unaffected by the LTAs.

• No changes to any thermalhydraulic related acceptance criteria are proposed and there is no expected loss of margin.

• Coated cladding is modeled as an increase in the outer diameter of the AXIOM cladding. This results in a negligible reduction in flow area due to the thin coating thickness.

16

AXIOM CLADDING

• WCAP18456P/NP approved December 16, 2022

• AXIOM cladding requires an exemption from the applicability requirements of 10 CFR 50.46 and Appendix K.

17

AXIOM CLADDING - Continued

• AXIOM cladding is a zirconium alloy which has demonstrated better inreactor performance compared to the Optimized ZIRLO alloy.

- The NRC staff expects AXIOM cladding to perform at least as well as Optimized ZIRLO cladding, which is used in the coresident fuel.

• The NRC staff determined that the use of AXIOM cladding in these LTAs is acceptable because there is no expected loss of safety margin or reduction in acceptance criteria.

18

CHROMIUM COATING

• Most fuel rods will have a thin chromium coating for increased corrosion resistance.

-SNC does not credit the chromium coating in its analyses.

19

CHROMIUM COATING - Continued

• There is no expected loss of safety margin associated with the chromium coating.

- ATFISG202001 states the reduced cladding emissivity is a potential adverse effect of a chromium coated rod that could increase PCT.

- SNCs analyses indicate that during LOCA conditions the difference in emissivity between coated and uncoated cladding has little effect on PCT.

20

HIGHER ENRICHMENT

• Four rods in each LTA will be enriched to a maximum of 6 weightpercent U235.

• Most codes and methods where fuel enrichment is a significant parameter have either been approved for use or contain data and models for enrichments greater than 5 weightpercent U235.

• The neutronic impact of the LTAs is expected to be small and confined to the LTA.

21

ADOPT FUEL PELLETS

• WCAP18482P/NP approved June 13, 2022

-Licensees must demonstrate that CRE models, methods, and acceptance criteria are applicable to fuel designs containing ADOPT fuel pellets 22

ADOPT FUEL PELLETS - Continued

• ADOPT fuel pellets contain small amounts of chromia and alumina and have higher density than standard UO2 pellets.

- ADOPT fuel pellets have a greater quantity of fissile material and may be more sensitive to reactivityinitiated accidents, such as a rod ejection accident (REA).

- SNC has stated that the LTAs will not be placed in positions that limiting with respect to REAs.

23

FUEL HANDLING & STORAGE

• SNC needs an exemption to 10 CFR 50.68 Paragraph (b)(7) for the fuel rods enriched above a maximum of 5.0 weightpercent U235

• Each LTA is limited to four rods at a maximum of 6.0 weightpercent U235.

24

FUEL HANDLING & STORAGE-Continued

• Those four rods add 0.015% more U235 to the fuel assemblies relative to the Vogtle New Fuel Storage Rack (NFSR) analysis of record (AOR) and Vogtle Spent Fuel Pool (SFP) AOR maximum enrichment of 5.0 weightpercent U235.

• That is less than a third of the U235 enrichment manufacturing uncertainty of 0.05%

25

FUEL HANDLING & STORAGE -

Continued

• Higher Theoretical Density (TD) in the ADOPT pellets adds more U235 to the fuel assemblies than the four fuel rods enriched to a maximum of 6 wt/%.

- Vogtle NFSR AOR used 96% TD.

- Vogtle SFP AOR used 97.5% TD.

- ADOPT TD of 98.3% is limited to 136 rods per LTA.

( half)

- Increased TD adds 1.185% more U235 to LTAs relative to NFSR AOR and 0.412% more U235 to LTAs relative to SFP AOR.

26

FUEL HANDLING & STORAGE -

Continued

• The total increase in U235 for the Vogtle NFSR and SFP relative to the AORs is 1.2% and 0.427% respectively.

-The relative increase in U235 content is determined to aid in evaluating the potential impact on reactivity in the NFSR and SFP.

27

FUEL HANDLING & STORAGE -

Continued

• New Fuel Storage Racks

- Exemption credits the IFBA in the LTAs whereas the Vogtle NFSR AOR does not.

- SNC estimated the LTAs 128 IFBA rods at 1.5x Boron 10 loading provide substantial reactivity hold down relative to its current AOR for the NFSR

• 0.12 keff for fully flooded

• 0.10 keff for optimum moderation 28

FUEL HANDLING & STORAGE -

Continued

• New Fuel Storage Racks Continued

-NRC staff reviewed the estimates and believes the substantial reactivity margin provided by the IFBA provides reasonable assurance 10 CFR 50.68 Paragraphs (b)(2) [NFSR fully flooded]

and (b)(3) [NFSR optimum moderation]

will be met.

29

FUEL HANDLING & STORAGE -

Continued

• Spent Fuel Pool Storage Racks

- Exemption limits SFP storage to two Unit 2 storage configurations

- The twooutoffour (2oo4) configuration,

• a repeating 2x2 array of alternating fresh unburned and unpoisoned fuel assemblies with empty storage cells, and 30

FUEL HANDLING & STORAGE -

Continued

• Spent Fuel Pool Storage Racks Continued

- allcell (4oo4) configuration,

• a repeating 2x2 array with each storage cell filled with a fuel assembly meeting the specified burnup/enrichment requirements

- No storage in any other Unit 2 storage configuration is allowed.

- No storage in Unit 1 SFP is allowed.

31

FUEL HANDLING & STORAGE -

Continued

• Twooutoffour (2oo4) configuration

-Exemption credits the IFBA in the LTAs whereas the Vogtle SFP AOR does not.

• Similar to NFSR 32

FUEL HANDLING & STORAGE -

Continued

• Twooutoffour (2oo4) configuration Continued

- SNC estimated the LTAs 128 IFBA rods at 1.5x B10 loading provide substantial reactivity hold down relative to its current AOR for the SFP

• 0.15 keff

- That margin will decrease but remain substantial relative to a fresh unpoisoned fuel assembly.

• NUREG/CR6760, Study of the Effect of Integral Burnable Absorbers for PWR Burnup Credit 33

FUEL HANDLING & STORAGE -

Continued

• Fouroutoffour (4oo4) configuration

- Exemption credits burnup in the LTAs.

• The AOR burnup requirement is about 40 GWd/MTU and a 64 GWd/MTU LTA burnup limit provides a 24 GWd/MTU or greater than 8% in keff margin for the LTAs.

- Slightly more than a 5 weightpercent fuel assembly would require.

34

FUEL HANDLING & STORAGE -

Continued

• Fouroutoffour (4oo4) configuration Continued

- SNC set a requirement for the LTAs to have 64 GWd/MTU of burnup.

- NRC staff used Vogtles SFP AOR to estimate a fuel assembly with all fuel rods at 6 weightpercent would require 53 GWd/MTU.

- SNCs burnup requirement provides substantial margin.

35

FUEL HANDLING & STORAGE -

Continued

• SFP Accident

- SNC determined a multiple miss loading event that collocated the unburned LTAs was the limiting accident.

• Multiple misloadings are typically the limiting accident.

- SNC estimated the collocated LTAs would be < 0.95 keff with the TS Soluble Boron requirement of 2000 ppm.

• This estimate did not have substantial margin to preclude a detailed analysis.

36

FUEL HANDLING & STORAGE -

Continued

• SFP Accident Continued

-The SNC estimate did not include credit for the IFBA.

-The twooutoffour (2oo4) evaluation showed the IFBA provides significant margin.

37

FUEL HANDLING & STORAGE -

Continued

• SFP Conclusion

- SNC exemption request contains substantial margin for the twooutoffour and fouroutof four storage configurations.

- When the IFBA is considered in the multiple misloading accident there is considerable margin.

- Therefore, the NRC staff believes there is reasonable assurance that 10 CFR 50.68 Paragraph (b)(4) will be met.

38

CONCLUSION

• The NRC staff determined that there is reasonable assurance that the health and safety of the public will not be endangered by allowing SNC the use of four ATF LTAs for up to two cycles operation in Vogtle, Unit 2.

• The NRC staff welcomes an ACRS letter report.

39

ITEMS FOR DISCUSSION AT ACRS FULL COMMITTEE

• July 14 - ACRS Full Committee Meeting

• Licensing Action - Amendment and Exemptions to 10 CFR 50.68(b)(7), 10 CFR 50.

46, and 10 CFR Part 50, Appendix K

• Technical areas of emphasis requested by ACRS Subcommittee members 40

ACRONYMS

• ATF - Accident Tolerant Fuel

• LTAs - Lead Test Assemblies

• NRC - U.S. Nuclear Regulatory Commission

• ACRS - Advisory Committee on Reactor Safeguards

• SNC - Southern Nuclear Operating Company

• NRR - Office of Nuclear Reactor Regulation

• DSS - Division of Safety Systems

• DORL - Division of Operating Reactor Licensing

• SNSB - Nuclear Systems Performance Branch

• SFNB - Nuclear Methods & Fuel Analysis Branch 41

ACRONYMS - Continued

• TS - Technical Specification

• CFR - Code of Federal Regulations

• U235 - Uranium 235

• UO2 - Uranium Dioxide

• MWd - MegawattDay

• MTU - Metric Ton Uranium

• ZrB2 - Zirconium Diboride

• IFBA - Integral Fuel Burnable Absorber

• LOCA - LossofCoolant Accident

• EM - Evaluation Model

• RCS - Reactor Coolant System

• DNBR - Departure from Nucleate Boiling Ratio 42

ACRONYMS - Continued

• PCT - Peak Cladding Temperature

• REA - Rod Ejection Accident

• TD - Theoretical Density

• NFSR - New Fuel Storage Rack

• SFP - Spent Fuel Pool

• AOR - Analysis of Record

• 2oo4 - Two out of Four Configuration

• 4oo4 - AllCell Configuration

• B10 - Boron 10

• ppm - Parts Per Million 43