ML23345A036

ATWS Uet December 11, 2023 Pre-submittal Meeting Slides

ML23345A036
Person / Time
Site:	Byron, Braidwood
Issue date:	12/11/2023
From:	Constellation Energy Generation
To:	Joel Wiebe NRC/NRR/DORL/LPL3
Wiebe J
References
EPID L-2023-LRM-0099
Download: ML23345A036 (1)

Text

Braidwood and Byron ATWS UET December 11, 2023

Agenda

• Purpose

• LAR Scope

• Reason for the Change

• Analyses and Preliminary Results

• Defense in Depth

• Key Milestones

• Summary 2 Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023

Purpose

• Constellation Energy Generation (CEG) proposes to delete Technical Specification (TS) 5.6.5.b.5. This specification is one of the Core Operating Limits Report (COLR) references. This Technical Specification is one of many analytical methods and limitations on the parameter Moderator Temperature Coefficient, Technical Specification 3.1.3.

• To solicit feedback from the NRC on the information presented and gain insight on NRC's information needs and review schedule considerations.

3 Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023

License Amendment Request Scope

• CEG proposes only to delete Technical Specification 5.6.5.b.5. This specification limits the most positive / least negative Moderator Temperature Coefficient (MTC) in the fuel cycle. This limit improves Anticipated Transient Without SCRAM (ATWS) Risk.

• After implementing this change, the cycle specific limits and confirmations associated with COLR Reference 5.6.5.b.5 will no longer be applied by CEG. The Moderator Temperature Coefficient will continue to be limited by Technical Specification Figure 3.1.3-1 and will be confirmed to be acceptable with all other COLR references listed in Technical Specification 5.6.5.b.

• After implementing the proposed change, Byron and Braidwood will continue to meet the ATWS Rule, 10 CFR 50.62, and continue to meet all other licensing basis commitments related to ATWS including those from NRC Generic Letter 83-28, Required Actions Based on Generic Implication of Salem ATWS Events.

• The proposed change may result in core designs with higher Hot Full Power Critical Boron concentrations and less negative MTCs. The effects of those changes are within the limits of existing regulations and licensing bases.

4 Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023

Reason for the change Fuel Cycle Length: CEG is evaluating 24 month cycles for Byron and Braidwood. The MTC limits for the longer cycles would significantly affect fuel cycle cost and feasibility.

Fuel Cycle Analytical Methods: The methodology prescribed by Technical Specification 5.6.5.b.5 is proprietary to Westinghouse, and CEG is pursuing alternative suppliers. The other fuel suppliers do not have this methodology or a practical alternative.

5 Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023

Analyses

• CEG will evaluate the changes in Risk for eliminating this limit using Regulatory Guide 1.174, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis.

• The CEG Evaluation will consider both CDF and LERF from both the Internal Events and External Events Probabilistic Risk Assessments (PRAs)

• The CEG PRA model is technically acceptable for the following applications

• Risk Informed Completion Times

• 50.69

• Surveillance Frequency Control Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023 6

Preliminary Results CDF / CDF: 5 E-5 / 5 E-7 LERF / LERF: 2 E-6 / 2 E-10 7 Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023

Unfavorable Exposure Time (UET) in PRA UET in Current Licensing Basis (Tech UET in CEG PRA:

Spec 5.6.3.b.5): MTC favorable (Y/N) with complex conditions based on MTC Favorable (<-8pcm/°F) (Y/N) o Rod Insertion {y,n}

2 Pressurizer PORVs o Aux Feedwater Trains {1,2}

2 Trains Auxiliary Feedwater o Pressurizer Safeties {3}

NO Auto or Manual Control Rod o Pressurizer PORVs {0,1,2}

Insertion The CEG Evaluation will determine The conditions above must the CDF and LERF between the demonstrate ATWS peak Pressure < current split fractions and 100% UET.

3200 psi for 95% of the fuel cycle.

Realistically, the UET is shifting from

< 5% to <50%

8 Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023

Large Early Release Frequency

• Some studies (WCAP-15831-P-A, WOG Risk-Informed ATWS Assessment and Licensing Implementation Process, August, 2007) conservatively assumed that RCS overpressure >3584 psid would lead to a large early release.

• CEG PRA does not automatically default to Large Early Release

• The high pressure induced steam generator tube rupture results in limited fuel failure (DNB) with significant scrubbing (steam generator secondary water inventory) and plating (steam generator and steam line surfaces) 9 Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023

Initiating Events Defense In Depth Automatic SCRAM Train A

- High Pressurizer Pressure

- Over Temperature Delta-T Automatic SCRAM Train B

- Low Steam Generator Level Manual SCRAM Train A

- UnderVoltage Trip

- Shunt Trip Manual SCRAM Train B Automatic Rod Insertion Favorable MTC Manual Start Motor Driven FW Pump AMSAC 10 Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023

Proprietary Key Milestones

• Pre-Submittal Meeting - December 11, 2023

• Expected Submittal Date - April 30, 2024

• Requested Approval Date - June 30, 2025 11 Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023

Summary

• CEG proposes only to delete Technical Specification 5.6.5.b.5. This specification limits the most positive / least negative MTC in the fuel cycle.

• MTC upper and lower limits for all other Design Basis events is unchanged.

• ATWS rule commitments unchanged

• Preliminary results demonstrate Region III in Reg Guide 1.174 evaluation 12 Byron-Braidwood Fuel Transition Project - ATWS UET Pre-submittal Meeting 12/11/2023

Questions 13