DCL-12-102, 10 CFR 50.46 30-Day Notification Report of Significant Emergency Core Cooling System Evaluation Model Changes That Affect Peak Cladding Temperature

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10 CFR 50.46 30-Day Notification Report of Significant Emergency Core Cooling System Evaluation Model Changes That Affect Peak Cladding Temperature
ML12293A096
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 10/18/2012
From: Allen B
Pacific Gas & Electric Co
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
DCL-12-102
Download: ML12293A096 (9)
v • d • e


Text

_ _ Pacific Gas and

~&~ Electric Company Diablo Canyon Power Plant PO. Box 56 Av ila Beach. CA 9342 4 800.545.6000 October 18, 2012 PG&E Letter DCL-12-1 02 u.s. Nuclear Regulatory Commission 10 CFR 50.46 ATTN: Docu ment 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 10 CFR 50.46 30-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. There have been no changes in the small-break loss-of-coolant accident (LOCA) PCT results for either Unit 1 or Unit 2 since our last annual update provided in PG&E Letter DCL-12-070, "10 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes for 2011," dated July 19, 2012.

The attachments to the enclosure provide a summary of the PCT margin allocations and their bases. Attachment A contains Unit 1 best-estimate large-break LOCA (BE LBLOCA) PCT Margin Utilization sheets. Attachment B furnishes the 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.

The PCT values remain within the 2200 degree Fahrenheit (F) limit specified in 10 CFR 50.46. However, because Unit 1 and Unit 2 BE LBLOCA have a total PCT margin allocation that is currently greater than 50 degrees F, and in order to coordinate with the 24-month fuel cycle project schedule, PG&E expects to complete the Unit 1 BE LBLOCA reanalysis and provide the updated PCT results to the NRC by December 2016, as stated in PG&E Letter DCL-11-082, "10 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes for 2010," dated July 19, 2011. Also, PG&E now expects to complete the Unit 2 BE LBLOCA reanalysis and provide the updated PCT results to the NRC by December 2016.

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-12-1 02 October 18, 2012 Page 2 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.

Sincerely,

~'? 5. A-tL---

Barry S. Allen Site Vice President wrl8/6980/50518974 Enclosure cc/enc: Elmo E. Collins, NRC Region IV Laura H. Micewski, Acting NRC Senior Resident Inspector Joseph M. Sebrosky, NRR Senior 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-12-1 02 10 CFR 50.46 30-DAY NOTIFICATION REPORT OF SIGNIFICANT ECCS EVALUATION MODEL CHANGES THAT AFFECT PCT On September 20, 2012, 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 (AOR). Because the absolute value of the sum of the temperature changes is greater than 50 degrees Fahrenheit (F), these changes are defined to be significant in accordance with 10 CFR 50.46. Accordingly, this 30-day notification report is submitted to the U.S. Nuclear Regulatory Commission (NRC) to describe the nature of the changes. This report is based on changes described in the following Westinghouse 10 CFR 50.46 notification letter:

Westinghouse Letter LTR-US-12-409, "Diablo Canyon Units 1 and 2, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown," dated September 20,2012 There has been no change or impact to the DCPP, Units 1 and 2, small-break LOCA (SBLOCA) evaluation model that affects PCT as reported in the latest annual report in PG&E Letter DCL-12-070, "10 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes for 2011 ," dated July 19, 2012.

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 contains the Unit 2 BE LBLOCA PCT Margin Utilization Sheets. Attachment C summarizes the 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 are listed below.

Best-Estimate LBLOCA Reflood 1 Reflood 2 Unit 1 2005 of 2095 of Unit 2 The PCT values remain within the 2200 degree F limit specified in 10 CFR 50.46.

However, because Unit 1 and Unit 2 BE LBLOCA have a total PCT margin allocation that is currently greater than 50 degrees F, and in order to coordinate with the 24-month fuel cycle project schedule, PG&E expects to complete the Unit 1 BE LBLOCA reanalysis and provide the updated PCT results to the NRC by December 2016, as stated in PG&E Letter DCL-11-082, 1

Enclosure PG&E Letter DCL-12-1 02 "10 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes for 2010," dated July 19, 2011. Also, PG&E now expects to complete the Unit 2 BE LBLOCA reanalysis and provide the updated PCT results to the NRC by December 2016.

2

Attachment A PG&E Letter DCL-12-1 02 DCPP UNIT 1 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION BEST-ESTIMATE 2 LARGE-BREAK LOCA PG&E Letter1 Reflood Reflood 1 2 A. AOR 1900°F 1860°F DCL-05-146

~PCT ~PCT 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 Error. 10°F OaF DCL-07-071

3. Replacement Steam Generators 75°F 71°F DCL-09-057
4. 230kV Degraded Voltage Event OaF 39°F DCL-11-082 C. 10 CFR 50.46 ECCS MODEL ASSESSMENTS THIS YEAR
1. Performance and Design (PAD) -118°F -118°F This Letter 4.0 Implementation
2. Fuel thermal conductivity 133°F 238°F This Letter degradation (TCD) and Peaking Factor Burndown D. SUM OF 10 CFR 50.46 CHANGES
1. Net Sum of PCT Changes 105°F 235°F
2. Absolute Sum of PCT Changes 341°F 471°F E. AOR PCT - Line A + Line 0.1 Net Sum of 10 CFR 50.46 PCT Changes 2005°F 2095°F The sum of the PCT from the most recent AOR 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 degrees 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 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 B PG&E Letter DCL-12-1 02 DCPP UNIT 2 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION BEST-ESTIMATE 2 LARGE-BREAK LOCA PG&E Letter1 A. AOR PCT= 1872°F DCL-07-071 B. PRIOR 10 CFR 50.46 ECCS MODEL ASSESSMENTS 2

1. HOTSPOT Fuel Relocation Error. i1PCT= OaF DCL-07-071
2. 230kV Degraded Voltage Event i1PCT= 16°F DCL-11-082 C. 10 CFR 50.46 ECCS MODEL ASSESSMENTS THIS YEAR
1. Fuel TCD and Peaking Factor i1PCT 20goF This Letter Burndown D. SUM OF 10 CFR 50.46 CHANGES
1. Net Sum of 10 CFR 50.46 PCT i1PCT=

Changes

2. Absolute Sum of 10 CFR 50.46 i1PCT=

PCT Changes E. AOR PCT - Line A + Line 0.1 Net Sum of 10 CFR 50.46 PCT Changes The sum of the PCT from the most recent AOR 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 degrees 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 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-1

Attachment C PG&E Letter DCL-12-1 02 CURRENT EMERGENCY CORE COOLING SYSTEM MODEL CHANGES AND ERRORS Unit 1 Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown

Background

Fuel pellet TCD and peaking factor burndown were not explicitly considered in the DCPP Unit 1 BE LBLOCA AOR. NRC Information Notice 2011-21 notified addressees of recent information obtained concerning the impact of irradiation on fuel thermal conductivity and its potential to cause significantly higher predicted PCT results in realistic ECCS evaluation models. This evaluation provides an estimated effect of fuel pellet TCD and peaking factor burndown on the PCT calculation for the DCPP Unit 1 BE LBLOCA AOR.

Affected Evaluation Model 1996 Westinghouse BE LBLOCA Evaluation Model Estimated Effect A quantitative evaluation was performed to assess the PCT effect of fuel pellet TCD and peaking factor burndown on the DCPP Unit 1 BE LBLOCA analysis. For 10 CFR 50.46 reporting purposes, the analysis concluded that the estimated PCT impact is 133 degrees F for Reflood 1 and 238 degrees F for Reflood 2. The peaking factor burndown included in the evaluation is provided in Table 1 and is conservative for the current cycle. PG&E and Westinghouse jointly use processes which ensure that the LOCA analysis input values conservatively bound the as-operated plant values for those parameters and will be validated as part of the reload design process.

Table 1: Peaking Factors Assumed in the Evaluation of TCD Rod Burnup (MWD/MTU) FdH (1)(2)(3) FQ Transient (1) (4) FQ Steady~State(4) 0 1.700 2.700 2.100 30,000 1.700 2.700 2.100 60,000 1.400 1.929 1.500 62,000 1.400 1.929 1.500 (1) Includes uncertainties.

(2) Hot assembly average power follows the same burndown, since it is a function of FdH.

(3) Nuclear Enthalpy Rise Hot Channel Factor (FdH)

(4) Heat Flux Hot Channel Factor (FQ)

C-1

Attachment C PG&E Letter DCL-12-1 02 Unit 1 PAD 4.0 Implementation

Background

The BE LBLOCA AOR for DCPP Unit 1 used fuel rod design inputs from PAD Version 3.4. To isolate the effect of fuel rod design input from PAD code version differences, the impact of using fuel rod design input from PAD Version 4.0 was estimated prior to explicitly considering fuel rod design input which includes fuel pellet TCD and peaking factor burndown and is based on the PAD Version 4.0 code.

The implementation of PAD Version 4.0 into the 1996 Westinghouse BE LBLOCA Evaluation Model was implemented by Westinghouse as a forward-fit, Discretionary Change. The plant-specific implementation of PAD Version 4.0 into the BE LBLOCA AOR for DCPP Unit 1 is considered a design input change into the BE LBLOCA analysis. PG&E and Westinghouse jointly utilize processes which ensure that the LOCA analysis input values conservatively bound the as-operated plant values for those parameters and will be validated as part of the reload design process.

Affected Evaluation Model 1996 Westinghouse BE LB LOCA Evaluation Model Estimated Effect A qualitative evaluation was performed to estimate a PCT effect resulting from a change in fuel rod design input parameters from Version 3.4 and PAD Version 4.0.

For 10 CFR 50.46 reporting purposes, the evaluation concluded that the estimated PCT impact is -118 degrees F for Reflood 1 and Reflood 2.

C-2

Attachment C PG&E Letter DCL-12-1 02 Unit2 Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown

Background

Fuel pellet TCD and peaking factor burndown were not explicitly considered in the DCPP Unit 2 BE LBLOCA AOR. NRC Information Notice 2011-21 notified addressees of recent information obtained concerning the impact of irradiation on fuel thermal conductivity and its potential to cause significantly higher predicted PCT results in realistic ECCS evaluation models. This evaluation provides an estimated effect of fuel pellet TCD and peaking factor burndown on the PCT calculation for the DCPP Unit 2 BE LBLOCA AOR.

Affected Evaluation Model 2004 Westinghouse Realistic LBLOCA Evaluation Model Using ASTRUM Estimated Effect A quantitative evaluation was performed to assess the PCT effect of fuel pellet TeO and peaking factor burndown on the DCPP Unit 2 BE LBLOCA analysis. For 10 CFR 50.46 reporting pu rposes, the analysis concluded that the estimated PCT impact is 209 degrees F. The peaking factor burndown included in the evaluation is provided in Table 1 and is conservative for the current cycle. PG&E and Westinghouse jointly use processes which ensure that the LOCA analysis input values conservatively bound the as-operated plant values for those parameters and will be validated as part of the reload design process.

Table 1: Peaking Factors Assumed in the Evaluation of TCD Rod Burnup (MWD/MTU) FdH (1) (2) (3) FQ Transient (1) (4) FQ Steady-State(4) 0 1.700 2.700 2.100 30,000 1.700 2.700 2.100 60,000 1.400 1.929 1.500 62,000 1.400 1.929 1.500 (1) Includes uncertainties.

(2) Hot assembly average power follows the same burndown, since it is a function of FdH.

(3) Nuclear Enthalpy Rise Hot Channel Factor (FdH)

(4) Heat Flux Hot Channel Factor (FQ)

C-3

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