DCL-03-091, CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes

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CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes
ML032170651
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 07/24/2003
From: Becker J
Pacific Gas & Electric Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-03-091
Download: ML032170651 (9)
v • d • e


Text

Pacifc Gas and Electric Company James R. Becker Diablo Canyon Power Plant Vice President-Diablo Canyon PO. Box 56 Operations and Station Director Avila Beach, CA 93424 July 24, 2003 805.545.3462 Fax: 805.545.4234 PG&E Letter DCL-03-091 U.S. Nuclear Regulatory Commission 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 10 CFR 50.46 Annual Report of Emergence Core Cooling System Evaluation Model Chanaes

Dear Commissioners and Staff:

Pursuant to 10 CFR 50.46, this letter provides an annual report of changes in the Westinghouse emergency core cooling system evaluation models that affect peak cladding temperature (PCT) calculations for Diablo Canyon Power Plant (DCPP), Units 1 and 2. There has been no change in the small-break loss of coolant accident (SBLOCA) PCT results or evaluation model since the last annual report submitted via PG&E Letter DCL-02-089, dated July 26, 2002.

Per the commitment identified in PG&E Letter DCL-00-1 34, dated October 19, 2000, PG&E has performed a reanalysis for the best estimate large-break loss of coolant accident (BELOCA). The reanalysis was performed using the Westinghouse superposition step methodology, which is currently being reviewed (WCAP-12945 revision) by the NRC. The reanalysis will not be established as the analysis of record per 10 CFR 50.46 until after NRC acceptance of the methodology, which is anticipated later this year. However, the superposition step methodology represents an appropriate ECCS evaluation model for the purpose of performing PCT assessments and updating the PCT margin allocations for both DCPP Units 1 and 2.

The summary of the updated PCT margin allocations and their bases are provided in the enclosure, and the final net PCT values are listed below for each Unit.

It should be noted that two PCT values are reported for the BELOCA consistent with the current Westinghouse PCT tracking methodology. The 2 large-break PCT values are labeled Reflood 1 and Reflood 2, as they represent the 2 distinctive PCT peaks that occur during the reflood phase for the BELOCA methodology.

A member of the STARS (Strategic Teaming and Resource Sharing) Alliance CatLaway

  • Comanche Peak
  • Diablo Canyon
  • Palo Verde
  • Wolf Creek 4200

P _p Document Control Desk PG&E Letter DCL-03-091 A July 24, 2003 Faage 2 Small-Break LOCA Best Estimate Large-Break LOCA Reflood 1 Reflood 2 Unit 1 (no change): 1317 OF 1976 OF 1964 OF Unit 2 (no change): 1306 OF 1976 OF 1964 OF The PCT values remain within the 22000 F limit specified in 10 CFR 50.46. The Unit 1 SBLOCA and BELOCA PCT Margin Utilization sheets are provided in Attachment A of the enclosure. The Unit 2 SBLOCA and BELOCA PCT Margin Utilization Sheets are provided in Attachment B of the enclosure.

PG&E will update the DCPP Unit 1 large break analysis of record PCT value once the NRC acceptance of the Westinghouse superposition step reanalysis methodology is obtained. Since acceptance is anticipated later this year, PG&E is also providing a draft Unit 1 PCT margin allocation sheet for information. This Unit 1 PCT margin allocation sheet is labeled "Pending Analysis of Record" and is provided in Attachment C of the enclosure. In addition, as discussed in the enclosed report, PG&E will perform a plant specific BELOCA analysis for Unit 2 using the accepted methodology established in WCAP-12945-P-A, "Code Qualification Document for Best Estimate LOCA Analysis," Bajorek, S. M. et. al., 1998. This analysis will be completed to support design changes to be implemented during the Unit 2 twelfth refueling outage, which is currently scheduled for the fall of 2004.

Sincerely, James R. Becker Vice President, DCPP Operations and Station Director mjr/A0494471 E2/R0236364 Enclosure cc/enc: Thomas P. Gwynn David L. Prouix Girija S. Shukla 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-03-091 ANNUAL REPORT OF EMERGENCY CORE COOLING SYSTEM EVALUATION MODEL CHANGES THAT AFFECT 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 Diablo Canyon Power Plant (DCPP), Units 1 and 2. This report is based on changes described in the following Westinghouse 10 CFR 50.46 notification letters:

Westinghouse Letter PGE-03-16, dated March 11, 2003, "Diablo Canyon Units 1 and 2, 10 CFR 50.46 Annual Notification and Reporting for 2002."

Westinghouse Letter PGE-03-33, dated June 6, 2003, "Diablo Canyon Unit 1 BELOCA Reanalysis Final Engineering Report."

Attachment A to this enclosure provides DCPP Unit 1 small-break loss of coolant accident (SBLOCA) and best estimate large-break loss of coolant accident (BELOCA) PCT Margin Utilization Sheets. Attachment B to this enclosure provides DCPP Unit 2 SBLOCA and BELOCA PCT Margin Utilization Sheets.

There has been no change in the SBLOCA PCT results or evaluation model since the last annual report submitted via PG&E Letter DCL-02-089, dated July 26, 2002.

Per the commitment identified in PG&E Letter DCL-00-1 34, dated October 19, 2000, PG&E has performed a reanalysis for the BELOCA. The reanalysis was performed using the Westinghouse superposition step methodology, which is currently being reviewed (WCAP-12945 revision) by the NRC. The reanalysis will not be established as the analysis of record per 10 CFR 50.46 until after NRC acceptance of the methodology, which is anticipated later this year. However, the superposition step methodology represents an appropriate ECCS evaluation model for the purpose of performing PCT assessments and updating the PCT margin allocations for both DCPP Units 1 and 2.

PG&E will update the Unit 1 large-break analysis of record PCT value once the NRC acceptance of the Westinghouse superposition step reanalysis methodology is obtained. Since acceptance is anticipated later this year, PG&E is also providing a draft Unit 1 PCT margin allocation sheets for NRC information.

This Unit 1 PCT margin allocation sheet is labeled "Pending Analysis of Record" and is provided as Attachment C to this enclosure.

It should also be noted that during the BELOCA reanalysis, Westinghouse identified that due to ECCS model changes, the Unit 2 PCT exceeded that of Unit 1 for several comparative cases. The current BELOCA analysis of record is based on a bounding plant methodology that established Unit 1 as the limiting plant, and the Unit I PCT results as bounding when applied to Unit 2.

ENCLOSURE PG&E Letter DCL-03-091 Based on the reanalysis results with several comparative cases showing Unit 2 PCTs exceeding those of Unit 1, PG&E has determined that the bounding plant methodology is no longer appropriate for establishing the Unit 2 BELOCA analysis of record. Therefore, PG&E will perform a plant-specific BELOCA analysis for Unit 2 using the accepted methodology established in WCAP-12945-P-A, "Code Qualification Document for Best Estimate LOCA Analysis," Bajorek, S. M. et. al., 1998.

The Unit 2 BELOCA analysis will be completed in support of design changes to be implemented during the Unit 2 twelfth refueling outage. This outage is currently scheduled for the fall of 2004. These Unit 2 design changes include modifying the reactor vessel internals to provide baffle region core bypass flow in the upward direction instead of the current downward direction, and reducing the reactor coolant temperature in the upper head region.

In the interim period until the NRC approves the Westinghouse superposition step reanalysis methodology and the Unit 2 analysis is completed, an appropriately conservative PCT margin is established by maintaining the current analysis of record PCT value for DCPP Units 1 and 2. This is conservative since the comparative case results generated as part of the Unit 1 reanalysis show a significant decrease in the overall PCT values relative to the current analysis for both DCPP Units 1 and 2 when the appropriate code corrections and ECCS model changes are implemented. The Unit 1 final PCT at the ninety-fifth percentile is significantly reduced compared with the current value (1900 OF, reanalysis vs. 1976 OF, original analysis). The Unit 2 comparative case results indicate that the revised Unit 2 PCT at the ninety-fifth percentile will be comparably reduced. Therefore, the PCT results of the current analysis of record remain conservative for both DCPP Units 1 and 2.

The final net PCT values that are reflected in Attachments A and B are listed below. It should be noted that two PCT values are reported for the BELOCA consistent with the current Westinghouse PCT tracking methodology. The 2 large-break PCT values are labeled Reflood 1 and Reflood 2, as they represent the 2 distinctive PCT peaks that occur during the reflood phase for the BELOCA methodology.

Small-Break LOCA Best Estimate Large-BreakBLOCA Reflood 1 Reflood 2 Unit 1 (no change): 1317 OF 1976 OF 1964 OF Unit 2 (no change): 1306 OF 1976 OF 1964 OF

ATTACHMENT A PG&E Letter DCL-03-091 DCPP UNIT I PEAK CLADDING TEMPERATURE MARGIN UTILIZATION SMALL-BREAK LOCA PG&E Letter' A. ANALYSIS OF RECORD PCT= 13040F DCL-99-096 B. PERMANENT 10 CFR 50.46 ECCS MODEL ASSESSMENTS 2

1. NOTRUMP Mixture Level APCT = 130 F DCL-00-107 Tracking/Region Depletion Errors C. 10 CFR 50.59 AND 10 CFR 50.92 SAFETY EVALUATIONS
1. None APCT = 0F D. OTHER MARGIN ALLOCATIONS
1. None APCT = 0F LICENSING BASIS PCT + MARGIN ALLOCATION PCT = 1317 0 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-I

ATTACHMENT A PG&E Letter DCL-03-091 DCPP UNIT 1 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION BEST ESTIMATE LARGE-BREAK LOCA PG&E Lefter' Reflood Reflood 1 2 A. ANALYSIS OF RECORD 19760 F 19640 F DCL-00-1 07 APCT APCT B. PERMANENT 10 CFR 50.46 ECCS MODEL ASSESSMENTS 2

1. None OOF 0F C. 10 CFR 50.59 AND 10 CFR 50.92 SAFETY EVALUATIONS
1. None OOF OOF D. OTHER MARGIN ALLOCATIONS
1. None 0F OOF LICENSING BASIS PCT + MARGIN 1976 0F 1964 0F ALLOCATION PCT 1 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-2

f ATTACHMENT B PG&E Letter DCL-03-091 DCPP UNIT 2 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION SMALL-BREAK LOCA PG&E Letter' A. ANALYSIS OF RECORD PCT = 1293 0F DCL-99-096 B. PERMANENT 10 CFR 50.46 ECCS MODEL ASSESSMENTS 2

1. NOTRUMP Mixture Level APCT = 13 OF DCL-00-1 07 Tracking/Region Depletion Errors C. 10 CFR 50.59 AND 10 CFR 50.92 SAFETY EVALUATIONS
1. None APCT = 0 OF D. OTHER MARGIN ALLOCATIONS
1. None APCT = 0 OF LICENSING BASIS PCT + MARGIN ALLOCATION PCT = 1306 0F 1 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 B PG&E Letter DCL-03-091 DCPP UNIT 2 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION BEST ESTIMATE LARGE-BREAK LOCA PG&E Letter' Reflood Reflood 1 2 A. ANALYSIS OF RECORD 19760F 19640 F DCL-00-1 07 APCT APCT B. PERMANENT 10 CFR 50.46 ECCS MODEL ASSESSMENTS 2

1. None 0F 0F C. 10 CFR 50.59 AND 10 CFR 50.92 SAFETY EVALUATIONS
1. None 0F 0F D. OTHER MARGIN ALLOCATIONS
1. None 0F 0F LICENSING BASIS PCT + MARGIN 19760 F 19640 F ALLOCATION PCT 1 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-2

I e ATTACHMENT C PG&E Letter DCL-03-091 Pending Analysis of Record DCPP UNIT I PEAK CLADDING TEMPERATURE MARGIN UTILIZATION BEST ESTIMATE LARGE-BREAK LOCA Reflood Reflood 1 2 A. ANALYSIS OF RECORD 1900OF 18600 F Reference 1 APCT APCT B. PERMANENT 10 CFR 50.46 ECCS MODEL ASSESSMENTS 2

1. None 0F 0F C. 10 CFR 50.59 AND 10 CFR 50.92 SAFETY EVALUATIONS
1. None 0F 0F D. OTHER MARGIN ALLOCATIONS
1. None 0F 0F LICENSING BASIS PCT + MARGIN 1900 0F 1860 0F ALLOCATION PCT Reference 1: Westinghouse Letter PGE-03-33, 'Diablo Canyon Unit I BELOCA Reanalysis Final Engineering Report," June 6, 2003 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.

C-1

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