ML14219A412

10 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes for Peak Cladding Temperature for 2013

ML14219A412
Person / Time
Site:	Diablo Canyon
Issue date:	08/07/2014
From:	Allen B S Pacific Gas & Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-14-070
Download: ML14219A412 (10)

Text

Pacific Gas and Electric Company August7,2014 PG&E Letter DCL-14-070 Barry S. Allen Site Vice President Diablo Canyon Power Plant Mail Code 104/6 P. 0. Box 56 Avila Beach, CA 93424 805.545.4888 Internal:

691.4888 Fax: 805.545.6445 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 10 CFR 50.46 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 and 2 10 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes for Peak Cladding Temperature for 2013 Dear Commissioners and Staff: Pursuant to 10 CFR 50.46 , the enclosure to this letter is the annual report of changes in the Westinghouse emergency core cooling system evaluation models that affect peak cladding temperature (PCT) calculations for Pacific Gas and . Electric Company's (PG&E's) Diablo Canyon Power Plant, Units 1 and 2. The attachments to the enclosure provide a summary of the PCT margin allocations and their bases. PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this report. If you have questions regarding this submittal please contact Mr. Mark Sharp at 805-545-3031.

Sincerely, tr---ul-4.1 Barry S. Allen j813/4486/64093434/50640861

/50640862 Enclosure cc/enc: Peter J. Bamford, NRR Project Manager Marc L. Dapas, NRC Region IV Administrator Thomas R. Hipschman, NRC Senior Resident Inspector Diablo Distribution A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

• Comanche Peak

• Diablo Canyon

• Palo Verde

• Wolf Creek Enclosure PG&E Letter DCL-14-070 ANNUAL REPORT OF EMERGENCY CORE COOLING SYSTEM EVALUATION MODEL CHANGES FOR PEAK CLADDING TEMPERATURE Pursuant to 10 CFR 50.46, this enclosure provides an annual report of changes in the Westinghouse emergency core cooling system (ECCS) evaluation models that affect peak cladding temperature (PCT) calculations for Pacific Gas and Electric Company's (PG&E's) Diablo Canyon Power Plant, Units 1 and 2. This report is based on changes described in Westinghouse Letter L TR-LIS-14-94, "Diablo Canyon Units 1 and 2 10 CFR 50.46 Annual Notification and Reporting for 2013," dated March 17, 2014. Attachment A contains Unit 1 small-break loss-of-coolant accident (SBLOCA) and best-estimate, large-break loss-of-coolant accident (BELOCA) PCT margin utilization sheets. Attachment 8 contains the corresponding Unit 2 data. Attachment C has a summary of ECCS evaluation model changes and PCT margin allocations that have occurred since the last report. There have been no changes in the SBLOCA PCT results for either Unit 1 or Unit 2 since the last annual update. The last annual update was provided in PG&E Letter DCL-13-077, "1 0 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes for Peak Cladding Temperature for 2012," dated July 30, 2013. Subsequently a 30-day notification report was provided in PG&E Letter DCL-13-111, "Thirty-Day Notification Report of Significant Emergency Core Cooling System Evaluation Model Changes that Affect Peak Cladding Temperature," dated November 14, 2013. There have been additional changes in the Unit 1 and Unit 2 BELOCA PCT results in 2013 and the final net PCT values are listed below for each unit. Two PCT values are reported for the Unit 1 BELOCA results. The two BELOCA PCT values are labeled Reflood 1 and Reflood 2, as they represent the two distinctive PCT peaks that occur during the reflood phase for the Unit 1 BELOCA Code Qualification Document methodology.

The Unit 2 BELOCA reports only one PCT value consistent with the BELOCA ASTRUM methodology.

SBLOCA BELOCA Reflood 1 Reflood 2 Unit 1: 1391 oF (no change) Unit 2: 1288°F (no change) The PCT values remain within the 2200oF limit specified in 10 CFR 50.46. However, because Unit 1 and Unit 2 BELOCA have a total PCT margin allocation that is currently greater than 50°F, PG&E will complete the Unit 1 BELOCA reanalysis and provide the updated PCT results to the NRC by December 2016, 1 Enclosure PG&E Letter DCL-14-070 as stated in PG&E Letter DCL-13-111.

Also, PG&E will complete the Unit 2 BELOCA reanalysis and provide the updated PCT results to the NRC by December 2016. 2 Attachment A PG&E Letter DCL-14-070 DIABLO CANYON POWER PLANT UNIT 1 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION SMALL-BREAK LOCA A. ANALYSIS OF RECORD B. PRIOR 10 CFR 50.46 Emergency Core Cooling System (ECCS) MODEL ASSESSMENTS 2 1. None C. 10 CFR 50.46 ECCS MODEL ASSESSMENTS THIS YEAR 1. None D. SUM OF 10 CFR 50.46 CHANGES 1. Net Sum of 10 CFR 50.46 PCT= ilPCT = ilPCT = PCT Changes ilPCT = OoF 2. Absolute Sum of 10 CFR 50.46 PCT Changes ilPCT = 0°F E. ANALYSIS OF RECORD PCT (Line A) + Line 0.1 Net Sum of 10 CFR 50.46 PCT Changes PG&E Letter 1 DCL-09-057 The sum of the peak cladding temperature (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. 2 For those issues that have been previously reported under 10 CFR 50.46, a PG&E letter number is listed. Only permanent assessments of PCT margin are included. Temporary PCT allocations that address current loss-of-coolant accident (LOCA) model issues are not considered with respect to 10 CFR 50.46 reporting requirements.

A-1 Attachment A PG&E Letter DCL-14-070 DIABLO CANYON POWER PLANT UNIT 1 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION Best-Estimate, Large-Break Loss-of-Coolant Accident PG&E Letter 1 Reflood 1 Reflood 2 A. ANALYSIS OF RECORD 1900°F 1860°F DCL-05-146 B. PRIOR 10 CFR 50.46 ECCS MODEL ASSESSMENTS 2 1. Revised blowdown heatup 5°F 5°F DCL-05-086 uncertainty distribution. 2. HOTSPOT Fuel Relocation 10°F OoF DCL-07-071 Error. 3. Replacement Steam 75°F 71°F DCL-09-057 Generators

4. 230 kV Degraded Voltage Event OoF 39°F DCL-11-082

5. Performance and Design 4.0 -118°F -118°F DCL-12-102 Implementation

6. Fuel Thermal Conductivity 133°F 238°F DCL-12-102 Degradation and Peaking Factor Burndown 7. Revised Heat Transfer Multiplier 5°F -35°F DCL-13-111 Distributions

8. Changes to Grid Blockage and 24°F 24°F DCL-13-111 Porosity C. 10 CFR 50.46 ECCS MODEL ASSESSMENTS THIS YEAR 1. Error in Burst Strain Application 15°F . 40°F This Letter D. SUM OF 10 CFR 50.46 CHANGES 1. Net Sum of PCT Changes 149°F 264°F 2. Absolute Sum of PCT Changes 385°F 570°F E. Analysis of Record PCT (Line A) + Line 0.1 Net Sum of 10 CFR 50.46 2049°F 2124°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. A-2 2 Attachment A PG&E Letter DCL-14-070 For those issues that have been previously reported under 10 CFR 50.46, a PG&E letter number is listed. 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-3 Attachment 8 PG&E Letter DCL-14-070 DIABLO CANYON POWER PLANT UNIT 2 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION Small-Break Loss-of-Coolant Accident PG&E Letter 1 A. ANALYSIS OF RECORD PCT= 1288°F DCL-08-061 B. PRIOR 10 CFR 50.46 Emergency Core Cooling System (ECCS) MODEL ASSESSMENTS 2 1. None 0°F C. 10 CFR 50.46 ECCS MODEL ASSESSMENTS THIS YEAR 1. None 0°F D. SUM OF 10 CFR 50.46 CHANGES 1. Net Sum of 10 CFR 50.46 PCT Changes 0°F 2. Absolute Sum of 10 CFR 50.46 PCT Changes OoF E. ANALYSIS OF RECORD PCT (Line A) + Line 0.1 Net Sum of 1288°F 10 CFR 50.46 PCT Changes The sum of the peak cladding temperature (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. 2 For those issues that have been previously reported under 10 CFR 50.46, a PG&E Letter number is listed. Only permanent assessments of PCT margin are included.

Temporary PCT allocations that address current loss-of-coolant accident (LOCA) model issues are not considered with respect to 10 CFR 50.46 reporting requirements.

8-1 Attachment B PG&E Letter DCL-14-070 DIABLO CANYON POWER PLANT UNIT 2 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION Best-Estimate, Large-Break Loss-of-Coolant Accident PG&E Letter 1 A. ANALYSIS OF RECORD PCT= 1872°F DCL-07-071 B. PRIOR 10 CFR 50.46 ECCS MODEL ASSESSMENTS 2 1. HOTSPOT Fuel Relocation Error. 11PCT= ooF DCL-07-071

2. 230 kV Degraded Voltage Event. 11PCT= 16oF DCL-11-082

3. Fuel Thermal Conductivity 11PCT= 209°F DCL-12-102 Degradation and Peaking Factor Burndown 4. Revised Heat Transfer Multiplier 11PCT= -17oF DCL-13-111 Distribution

5. Changes to Grid Blockage and 11PCT= 24°F DCL-13-111 Porosity C. 10 CFR 50.46 ECCS MODEL ASSESSMENTS THIS YEAR 1 . Error in Burst Strain Application 11PCT= 21oF This Letter D. SUM OF 10 CFR 50.46 CHANGES 1. Net Sum of 10 CFR 50.46 PCT 11PCT= *253oF Changes 2. Absolute Sum of 10 CFR 50.46 11PCT= 287°F PCT Changes E. ANALYSIS OF RECORD PCT 2125°F (Line A) + Line 0.1 Net Sum of 10 CFR 50.46 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. 2 For those issues that have been previously reported under 10 CFR 50.46, a PG&E letter number is listed. 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.

B-2 Attachment C PG&E Letter DCL-14-070 CURRENT EMERGENCY CORE COOLING SYSTEM MODEL . CHANGES AND ERRORS Unit 1 . Error in Burst Strain Application Background An error in the application of the burst strain was discovered in HOTSPOT. The equation for the application of the burst strain is given as Equation 7-69 in WCAP-16009-P-A and in WCAP-12945-P-A.

The outer radius of the cladding after burst occurs should be calculated based on the burst strain, and the inner radius of the cladding should be calculated based on the outer radius. In HOTSPOT, the burst strain is applied to the calculation of the cladding inner radius. The cladding outer radius is then calculated based on the inner radius. As such, the burst strain is incorrectly applied to the inner radius rather than the outer radius, which impacts the resulting cladding geometry at the burst elevation after burst occurs. Correction of the erroneous calculation results in thinner cladding at the burst node and more fuel relocating into the burst node, leading to an increase in the peak cladding temperature (PCT) at the burst node. This issue has been evaluated to estimate the impact on existing best-estimate, large-break loss-of-coolant accident (BELOCA) analysis results. Affected Evaluation Model 1996 Westinghouse BELOCA Evaluation Model Estimated Effect A representative Diablo Canyon Power Plant Unit 1 case was run using HOTSPOT versions which only differ in the burst strain application.

Based on the change in the 95th percentile results, estimated PCT effects of 15°F for Reflood 1 and 40°F for Reflood 2 have been established for 10 CFR 50.46 reporting purposes for Diablo Canyon Power Plant Unit 1. C-1 Unit2 Error in Burst Strain Application Background Attachment C PG&E Letter DCL-14-070 An error in the application of the burst strain was discovered in HOTSPOT. The equation for the application of the burst strain is given as Equation 7-69 in WCAP-16009-P-A and in WCAP-12945-P-A. The outer radius of the cladding after burst occurs should be calculated based on the burst strain, and the inner radius of the cladding should be calculated based on the outer radius. In HOTSPOT, the burst strain is applied to the calculation of the cladding inner radius. The cladding outer radius is then calculated based on the inner radius. As such, the burst strain is incorrectly applied to the inner radius rather than the outer radius, which imp , acts the resulting cladding geometry at the burst elevation after burst occurs. Correction of the erroneous calculation results in thinner cladding at the burst node and more fuel relocating into the burst node, leading to an increase in the PCT at the burst node. This issue has been evaluated to estimate the impact on existing BELOCA analysis results. Affected Evaluation Model 2004 Westinghouse Realistic BELOCA Evaluation Model Using ASTRUM Estimated Effect The issue described above was evaluated based on the results of executing the most limiting plant-specific HOTSPOT runs for similar plants with a HOTSPOT version that includes the correction of this error. This resulted in an estimated PCT impact of 21 oF for Diablo Canyon Power Plant Unit 2. C-2