DCL-13-111, Thirty-Day Notification Report of Significant Emergency Core Cooling System Evaluation Model Changes That Affect Peak Cladding Temperature

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Thirty-Day Notification Report of Significant Emergency Core Cooling System Evaluation Model Changes That Affect Peak Cladding Temperature
ML13319A885
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 11/14/2013
From: Allen B
Pacific Gas & Electric Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-13-111
Download: ML13319A885 (9)
v • d • e


Text

Pacific Gas and Electric Company Barry S. Allen Diablo Canyon Power Plant Site Vice President Mail Code 104/6 P. O. Box 56 Avila Beach, CA 93424 805.545.4888 Internal: 691.4888 November 14,2013 Fax: 805.545.6445 PG&E Letter DCL-13-111 u.s. Nuclear Regulatory Commission 10 CFR 50.46 ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 and 2 Thirty-Day Notification Report of Significant Emergency Core Cooling System Evaluation Model Changes That Affect Peak Cladding Temperature

Dear Commissioners and Staff:

Pursuant to 10 CFR 50.46(a)(3)(ii), Pacific Gas and Electric Company (PG&E) is providing a 30-day notification report of significant changes in the Westinghouse emergency core cooling system (ECCS) evaluation models that affect peak cladding temperature (PCT) calculations for Diablo Canyon Power Plant, Units 1 and 2. The details of the changes are described in the enclosure.

The attachments to the enclosure provide a summary of the PCT margin allocations and their bases. Attachment A contains Diablo Canyon, Unit 1, best-estimate, large-break, loss-of-coolant accident (BE LBLOCA) PCT Margin Utilization sheets. Attachment B furnishes the Diablo Canyon, Unit 2, BE LBLOCA PCT Margin Utilization Sheets. Attachment C has a summary of ECCS evaluation model changes and PCT margin allocations that have occurred since the last annual report.

PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this letter.

If you have questions regarding this submittal please contact Mr. Steve Baker at 805-545-6742.

,SW~ Jo~

Barry S. Allen A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

  • Comanche Peak
  • Diablo Canyon
  • Palo Verde
  • San Onofre
  • Wolf Creek

Document Control Desk PG&E Letter DCL-13-111 November 14,2013 Page 2 dho6/6038/505887 52 Enclosure cc/enc: Marc L. Dapas, NRC Region IV Administrator Thomas R. Hipschman, NRC Senior Resident Inspector Jennivine K. Rankin, NRR Project Manager Diablo Distribution A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

  • Comanche Peak
  • Diablo Canyon
  • Palo Verde
  • San Onofre
  • Wolf Creek

Enclosure PG&E Letter DCL-13-111 THIRTY-DAY NOTIFICATION REPORT OF SIGNIFICANT EMERGENCY CORE COOLING SYSTEM EVALUATION MODEL CHANGES THAT AFFECT PEAK CLADDING TERMPERATURE On October 8, 2013, Pacific Gas and Electric Company (PG&E) received a letter from Westinghouse transmitting revised peak cladding temperature (PCT) margins for the Diablo Canyon Power Plant (DCPP), Units 1 and 2, best-estimate, large-break, loss-of-coolant accident (BE LBLOCA) analysis of record. Since the absolute value of the sum of the latest temperature changes is greater than 50°F, these changes are considered significant, and PG&E submits this report describing the nature of the changes. This report is based on changes describ~d in the following Westinghouse 10 CFR 50.46 notification letters:

Westinghouse Letter LTR-LlS-13-349, "Diablo Canyon Units 1 and 2, 10 CFR 50.46 Report for Revised Heat Transfer Multiplier Distributions,"

dated July 31, 2013 Westinghouse Letter LTR-LlS-13-473, "Diablo Canyon Units 1 and 2, 10 CFR 50.46 Reports for Changes to Grid Blockage Ratio and Porosity,"

dated October 4,2013 There has been no change or impact to the DCPP, Units 1 and 2, small-break, loss-of-coolant accident (SBLOCA) evaluation model that affects PCT as reported in the latest annual report, PG&E Letter DCL 13-077, "10 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes for Peak Cladding Temperature for 2012," dated July 30,2013.

A summary of the PCT margin allocations and their bases are provided in the enclosed attachments. Attachment A contains Unit 1 BE LBLOCA PCT Margin Utilization sheets. Attachment B furnishes the Unit 2 BE LBLOCA PCT Margin Utilization Sheets. Attachment C has a summary of emergency core cooling system (ECCS) evaluation model changes and PCT margin allocations that have occurred since the last annual report.

The PCT values that are calculated in Attachment A remain within the 2200°F limit specified in 10 CFR 50.46. However, since the total PCT margin allocation is currently greater than 50°F, PG&E will perform a reanalysis in accordance with 10 CFR 50.46(a)(3)(ii). In order to coordinate and accommodate the upcoming regulation changes related to 10 CFR 50.46 that are still in development, PG&E will complete the BE LBLOCA reanalysis for Unit 1 (PG&E Letter DCL-11-082) and Unit 2 (PG&E Letter DCL-12-102) and provide the updated PCT results to the NRC by December 2016.

1

Attachment A PG&E Letter DCL-13-111 DCPP UNIT 1 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION BEST -ESTIMATE z LARGE-BREAK LOSS-OF-COOLANT ACCIDENT (LOCAl PG&E Letter1 Reflood Reflood 1 2 A. ANALYSIS OF RECORD 1900°F 1860°F DCL-05-146

~PCT ~PCT B. PRIOR 10 CFR 50.46 EMERGENCY CORE COOLING SYSTEM (ECCS)

MODEL ASSESSMENTS 2

1. Revised blowdown heatup 5°F 5°F DCL-05-086 uncertainty distribution.
2. HOTSPOT Fuel Relocation Error. 10°F O°F DCL-07-071
3. Replacement Steam Generators 75°F 71°F DCL-09-057
4. 230 kV Degraded Voltage Event O°F 39°F DCL-11-082
5. Performance and Design (PAD) -118°F -118°F DCL-12-102 4.0 Implementation
6. Fuel Thermal Conductivity 133°F 238°F DCL-12-102 degradation (TCD) and Peaking Factor Burndown C. 10 CFR 50.46 ECCS MODEL ASSESSMENTS THIS YEAR
1. Revised Heat Transfer Multiplier 5°F -35°F This Letter Distributions
2. Changes to Grid Blockage and 24°F 24°F This Letter Porosity D. SUM OF 10 CFR 50.46 CHANGES
1. Net Sum of peak cladding 134°F 224°F temperature (PCT) Changes
2. Absolute Sum of PCT Changes 370°F 530°F E. Analysis of Record PCT (Line A) +

Line D.1 Net Sum of 10 CFR 50.46 2034°F 2084°F PCT Changes For those issues that have been previously reported under 10 CFR 50.46, a PG&E letter number is listed.

2 Only permanent assessments of PCT margin are included. Temporary PCT allocations that address current LOCA model issues are not considered with respect to 10 CFR 50.46 reporting requirements.

A-1

Attachment A PG&E Letter DCL-13-111 The sum of the PCT from the most recent analysis of record using an acceptable evaluation model and the estimates of the net PCT effect for changes and errors identified since this analysis remains less than 2200°F.

A-2

Attachment 8 PG&E Letter DCL-13-111 DCPP UNIT 2 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION BEST -ESTIMATE 2 LARGE-BREAK LOSS-OF-COOLANT ACCIDENT {LOCAl PG&E Letter1 A. ANALYSIS OF RECORD PCT= 1872°F DCL-07-071

8. PRIOR 10 CFR 50.46 EMERGENCY CORE COOLING SYSTEM (ECCS) MODEL ASSESSMENTS 2
1. HOTSPOT Fuel Relocation Error. ~PCT= O°F DCL-07-071
2. 230 kV Degraded Voltage Event ~PCT= 16°F DCL-11-082
3. Fuel TCD and Peaking Factor ~PCT= 20goF DCL-12-102 Burndown C. 10 CFR 50.46 ECCS MODEL ASSESSMENTS THIS YEAR
1. Revised Heat Transfer ~PCT -17°F This Letter Multiplier Distribution
2. Changes to Grid Blockage and ~PCT 24°F This Letter Porosity D. SUM OF 10 CFR 50.46 CHANGES
1. Net Sum of 10 CFR 50.46 peak ~PCT= 232°F cladding temperature (PCT)

Changes

2. Absolute Sum of 10 CFR 50.46 ~PCT= 266°F PCT Changes E. Analysis of Record PCT (Line A) +

Line 0.1 Net Sum of 10 CFR 50.46 2104°F PCT Changes The sum of the PCT from the most recent analysis of record using an acceptable evaluation model and the estimates of the net PCT effect for changes and errors identified since this analysis remains less than 2200°F.

For those issues that have been previously reported under 10 CFR 50.46, a PG&E letter number is listed.

2 Only permanent assessments of peT margin are included. Temporary PCT allocations that address current LOCA model issues are not considered with respect to 10 CFR 50.46 reporting requirements.

8-1

Attachment C PG&E Letter DCL-13-111 CURRENT EMERGENCY CORE COOLING SYSTEM MODEL CHANGES AND ERRORS Unit 1 Revised Heat Transfer Multiplier Distributions

Background

Several changes and error corrections were made to WCOBRAITRAC and the impacts of these changes on the heat transfer multiplier uncertainty distributions were investigated. During this investigation, errors were discovered in the development of the original multiplier distributions, in the grid locations specified in the WCOBRAITRAC models for the G2 Refill and G2 Reflood tests, and in processing test data used to develop the reflood heat transfer multiplier distribution.

Therefore, the blowdown heatup, blowdown cooling, refill, and reflood heat transfer multiplier distributions were redeveloped. For the reflood heat transfer 'multiplier development, the evaluation time windows for each set of test experimental data and each test simulation were separately defined, based on the time at which the test or simulation exhibited dispersed flow film boiling heat transfer conditions characteristic of the reflood time period. The revised heat transfer multiplier distributions have been evaluated for impact on existing analyses.

Affected Evaluation Model 1996 Westinghouse best-estimate, large-break, loss-of-coolant accident (BE LBLOCA) Evaluation Model Estimated Effect A plant transient calculation representative of Diablo Canyon, Unit 1, transient behavior was performed with the latest version of WCOBRAITRAC. Using this transient, HOTSPOT calculations were performed with both the original and revised heat transfer multiplier distributions. Based on the change in the 95th percentile results, estimated peak centerline temperature effects of plus 5°F for Reflood 1 and minus 35°F for Reflood 2 have been established for 10 CFR 50.46 reporting purposes for Diablo Canyon, Unit 1.

Changes to Grid Blockage Ratio and Porosity

Background

A change in the methodology used to calculate grid blockage ratio and porosity for Westinghouse fuel resulted in a change to the grid inputs used in the Diablo Canyon, Unit 1, LBLOCA analysis. Grid inputs affect heat transfer in the core during a LBLOCA.

C-1

Attachment C PG&E Letter DCL-13-111 Affected Evaluation Model 1996 Westinghouse BE LBLOCA Evaluation Model Estimated Effect The updates to the methodology to calculate grid blockage ratio and porosity used as input in Westinghouse LBLOCA models resulted in degraded heat transfer in the core for the fuel type used in Diablo Canyon, Unit 1. The estimated penalty associated with the changes is 24°F for both Reflood 1 and Reflood 2 for 10 CFR 50.46 reporting purposes.

Unit2 Revised Heat Transfer Multiplier Distributions

Background

Several changes and error corrections were made to WCOBRAITRAC and the impacts of these changes on the heat transfer multiplier uncertainty distributions were investigated. During this investigation, errors were discovered in the development of the original multiplier distributions, including errors in the grid locations specified in the WCOBRAITRAC models for the G2 Refill and G2 Reflood tests, and errors in processing test data used to develop the reflood heat transfer multiplier distribution. Therefore, the blowdown heatup, blowdown cooling, refill, and reflood heat transfer multiplier distributions were redeveloped. For the reflood heat transfer multiplier development, the evaluation time windows for each set of test experimental data and each test simulation were separately defined based on the time at which the test or simulation exhibited dispersed flow film boiling heat transfer conditions characteristic of the reflood time period. The revised heat transfer multiplier distributions have been evaluated for impact on existing analyses.

Affected Evaluation Model 2004 Westinghouse Realistic LBLOCA Evaluation Model Using ASTRUM Estimated Effect A plant transient calculation representative of Diablo Canyon, Unit 2, transient behavior was performed with the latest version of WCOBRAITRAC. Using this transient, a matrix of HOTSPOT calculations was performed to estimate the effect of the heat transfer multiplier distribution changes. Using these results and considering the heat transfer multiplier uncertainty attributes from limiting cases for Diablo Canyon, Unit 2, an estimated PCT effect of minus 17°F has been established for 10 CFR 50.46 reporting purposes for Diablo Canyon, Unit 2.

C-2

Attachment C PG&E Letter DCL-13-111 Changes to Grid Blockage Ratio and Porosity

Background

A change in the methodology used to calculate grid blockage ratio and porosity for Westinghouse fuel resulted in a change to the grid inputs used in the Diablo Canyon, Unit 2, LBLOCA analysis. Grid inputs affect heat transfer in the core during a LBLOCA.

Affected Evaluation Model 2004 Westinghouse Realistic LBLOCA Evaluation Model Using ASTRUM Estimated Effect The updates to the methodology to calculate grid blockage ratio and porosity used as input in Westinghouse LBLOCA models resulted in degraded heat transfer in the core for the fuel type used in Diablo Canyon, Unit 2. The estimated penalty associated with the changes is 24°F for 10 CFR 50.46 reporting purposes.

C-3

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