ML24236A703

Pre-Submittal Meeting Slides to Support August 29, 2024 Aps/Westinghouse Thermal Design Procedure (Wtdp) Meeting

ML24236A703
Person / Time
Site:	Palo Verde
Issue date:	08/22/2024
From:	Arizona Public Service Co
To:	William Orders NRC/NRR/DORL/LPL4
References
Download: ML24236A703 (1)

Text

Westinghouse Thermal Design Procedure (WTDP)

Pre-Submittal Meeting August 29, 2024 Agenda

• Introduction

• Case for Action

• Background

• DNBR Limit

• Fuel Failure Analysis

• Setpoint Methodology

• Proposed Changes

• Proposed Schedule

• Questions & Feedback

2 Case for Action

The proposed Palo Verde license amendment adopts advanced Westinghouse methodology to modernize reactor core reload design

- WCAP-18240-P-A, Westinghouse Thermal Design Procedure (WTDP) (2020)

• Applicable to Westinghouse and Combustion Engineering Pressurized Water Reactors (PWRs)

- Palo Verde is lead plant for licensing application

- Submittal will address both Westinghouse and Framatome fuel

• Westinghouse CE16NGF (2018, ML17319A103 and ML17319A107)

• Framatome CE16HTP (2020, ML20031C947 and ML20031C968)

3

Background

WCAP-18240-P-A, Westinghouse Thermal Design Procedure (WTDP)

- Methodology for Departure from Nucleate Boiling Ratio (DNBR)

Specified Acceptable Fuel Design Limit (SAFDL)

• ANSI N18.2 Conditions I (normal operation) and II (moderate frequency events)

- Methodology for rods-in-DNB fuel failure analysis

• ANSI N18.2 Conditions III (infrequent events) and IV (limiting faults), except Loss of Coolant Accidents (LOCAs)

- Methodology for Core Protection Calculator System (CPCS) and Core Operating Limit Supervisory System (COLSS) setpoints

4

Background

WCAP-18240-P-A, Westinghouse Thermal Design Procedure (WTDP)

- Evolutionary change relative to current methods

• WCAP references Palo Verde Updated Final Safety Analysis Report (UFSAR)

- Leverages improvements in computational resources and automation

• More efficient core reload analysis process

- Reduces DNBR SAFDLs

- May reduce cycle-specific fuel failure predictions for non-LOCA accidents

5 DNBR Limit

Current Methodology

- Technical Specification (TS) 5.6.5, Core Operating Limits Report (COLR)

• Combustion Engineering CEN-356(V)-P-A, Modified Statistical Combination of Uncertainties (MSCU)

• Related methodologies

- Thermal-hydraulic analysis codes

- Critical heat flux (CHF) correlations

- Core inlet flow distribution

- NRC Information Notice 2014-01, Fuel Safety Limit Calculation Inputs Were Inconsistent with NRC-Approved Correlation Limit Values

6 DNBR Limit

Current Methodology

- MSCU statistically combines uncertainties associated with system parameters and state parameters to determine CPCS/COLSS setpoints and overall uncertainty factors

• System parameters - Related to fuel type (for example, fuel rod pitch, fuel rod outside diameter, CHF correlations)

• State parameters - Related to plant operating conditions (for example, core power distribution, reactor coolant pressure, core inlet flow)

7 DNBR Limit

Current Methodology

- MSCU involves numerous thermal-hydraulic simulations to evaluate the effects of parameter perturbations

- Statistical analysis yields a DNBR probability density function (pdf) and SAFDL

• DNBR pdf - Probability of fuel failure vs. DNBR

• DNBR SAFDL - At least a 95% probability, at a 95% confidence level, that the hot fuel rod in the core does not experience DNBR during normal operation or Anticipated Operational Occurrences (AOOs)

8 DNBR Limit

Current Methodology

- First use of MSCU was Palo Verde Unit 1 Cycle 2 (1987, ML021690079)

• Number of simulations constrained by computational resources and costs

• Proprietary conservative biases reduced the number of required simulations

- Fuel type analytical limits

• CE16STD: DNBR SAFDL = 1.34

- TORC with CE-1 (2001, ML010880411)

• CE16NGF: DNBR SAFDL = 1.25

- VIPRE with WSSV and ABB-NV (2018, ML17319A103 and ML17319A107)

• CE16HTP: DNBR SAFDL = 1.27

- VIPRE with BHTP (2020, ML20031C947 and ML20031C968)

9 DNBR Limit

WTDP Methodology

- Removes conservative biases from current MSCU methodology

• CE16NGF: New DNBR SAFDL = 1.20

• CE16HTP: New DNBR SAFDL = 1.20

• DNBR pdf differs between the two fuel types

- CE16STD DNBR SAFDL of 1.34 will remain in CPCS/COLSS

• Same approach used when licensing CE16NGF and CE16HTP for Palo Verde

• Plant hardware limitations mentioned in TS Bases 2.1.1, Reactor Core Safety Limits (SLs)

• Setpoint methodology establishes relationship between plant hardware and cycle-specific core reload design

10 Fuel Failure Analysis

Current Methodology

- TS 5.6.5, Core Operating Limits Report (COLR)

• Combustion Engineering CENPD-183-A, C-E Methods for Loss of Flow Analysis (statistical convolution technique)

- Fuel rod power census

- DNBR pdf

- MSCU methodology for derivation of the DNBR pdf is analogous to that used for the SAFDL, but considers Condition III and Condition IV accident scenarios with a coincident Loss of Offsite Power (LOP)

• Lower reactor coolant flow rates

• Lower DNBRs

11 Fuel Failure Analysis

WTDP Methodology

- Statistical convolution technique analogous to CENPD-183-A

- More computationally efficient than current MSCU methodology when performing Palo Verde cycle-specific analyses

• Fewer thermal-hydraulic simulations required

• One DNBR pdf may be used for both DNBR SAFDL verification and fuel failure predictions

12 Fuel Failure Analysis

WTDP Methodology Example

- Limiting infrequent event (UFSAR Appendix 15E)

• Composite event assumes an initiating occurrence degrades thermal margin and brings the reactor core to the DNBR SAFDL

• While at the DNBR SAFDL, a LOP causes a coincident loss of forced reactor coolant flow

• Acceptance criterion is a small fraction (10%) of 10 CFR Part 100 limits

- WTDP methodology reduces cycle-specific fuel failure predictions

• Cycle-specific core reload analyses typically predict several thousand fuel rod failures for the postulated limiting infrequent event

• CE16NGF: Unit 1 Cycle 24 fuel failure reduced by ~100 fuel rods

• CE16HTP: Unit 2 Cycle 25 fuel failure reduced by ~200 fuel rods

13 Setpoint Methodology

Current Methodology

- TS 5.6.5, Core Operating Limits Report (COLR)

• Westinghouse WCAP-16500-P-A, Revision 0, CE 16x16 Next Generation Fuel Core Reference Report

- COLR includes Supplement 1, Application of CE Setpoint Methodology for CE 16x16 Next Generation Fuel (NGF)

- Setpoint methodology application at Palo Verde addressed in previous license amendments

• Westinghouse CE16NGF (2018, ML17319A103 and ML17319A107)

• Framatome CE16HTP (2020, ML20031C947 and ML20031C968)

14 Setpoint Methodology

Current Methodology

- Addresses use of MSCU where the CHF correlation within the CPCS and COLSS differs from the CHF correlations that are applicable to a specific fuel type

- Addresses the potential for different fuel types to introduce undesirable biases

• Temperature-dependent

• Pressure-dependent

• Flow-dependent

• Axial Shape Index (ASI)-dependent

15 Setpoint Methodology

WTDP Methodology

- Limitation/condition in NRC Safety Evaluation for WCAP-18240-P-A

• The use of an approved subchannel code (e.g., VIPRE-W) in lieu of CETOP-D must be consistent with the CE-NSSS setpoint methodology as defined in WCAP-16500-P-A, Supplement 1, Application of CE Setpoint Methodology for CE 16x16 Next Generation Fuel, Revision 1

- Palo Verde may choose to utilize this option in the future for selected analysis work

• Palo Verde TS 5.6.5 includes WCAP-16500-P-A, VIPRE-W, and VIPRE-01

• The faster CETOP-D code is desirable for time-critical circumstances

16 Proposed Changes

• Revise TS 5.6.5, Core Operating Limits Report (COLR), to add WCAP-18240-P-A

• Revise TS Bases 2.1.1, Reactor Core Safety Limits (SLs)

- Reduce CE16NGF DNBR SAFDL to 1.20

- Reduce CE16HTP DNBR SAFDL to 1.20

• Conforming changes to UFSAR

- New topical report

- Revised DNBR SAFDLs

- Use of CETOP-D or VIPRE in setpoint methodology

17 Proposed Changes

18 Proposed Changes

19 Proposed Schedule

• October 2024: License Amendment Request (LAR) submittal

• October 2025: Request completion of NRC review

• 2025-2026: Palo Verde implementation

20 Questions & Feedback