ML24236A703
| 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
2 Agenda Introduction Case for Action
Background
DNBR Limit Fuel Failure Analysis Setpoint Methodology Proposed Changes Proposed Schedule Questions & Feedback
3 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)
4 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
5 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
- May reduce cycle-specific fuel failure predictions for non-LOCA accidents
6 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
7 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)
8 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 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)
9 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
- TORC with CE-1 (2001, ML010880411)
- VIPRE with WSSV and ABB-NV (2018, ML17319A103 and ML17319A107)
- VIPRE with BHTP (2020, ML20031C947 and ML20031C968)
10 DNBR Limit WTDP Methodology
- Removes conservative biases from current MSCU methodology
- 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
11 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
12 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
13 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
14 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)
15 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
16 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
17 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
- Use of CETOP-D or VIPRE in setpoint methodology
18 Proposed Changes
19 Proposed Changes
20 Proposed Schedule October 2024:
License Amendment Request (LAR) submittal October 2025:
Request completion of NRC review 2025-2026:
Palo Verde implementation
Questions & Feedback