DCL-04-094, 10 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes

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10 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes
ML042160235
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 07/23/2004
From: Becker J
Pacific Gas & Electric Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-04-094
Download: ML042160235 (10)
v • d • e


Text

Pacific 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 23, 2004 805.545.3462 PG&E Letter DCL-04-094 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 Emergency Core Cooling System Evaluation Model Changes

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 a bounding 350 F increase in the small-break loss of coolant accident (SBLOCA) PCT results for DCPP Unit 1 since the last annual report submitted via PG&E Letter DCL-04-091, dated July 24,2003. The SBLOCA PCT results for Unit 2 remain unchanged.

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 approved by the NRC on March 11, 2004. PG&E intends to submit a license amendment request which would revise the Technical Specifications (TS) to incorporate the Westinghouse superposition step methodology into the licensing basis and establish a new BELOCA analysis of record. However, the superposition step methodology represents an appropriate emergency core cooling system evaluation model for the purpose of performing PCT assessments and updating the PCT margin allocations for both DCPP Units 1 and 2. In the interim period until the TS are revised and the Unit 2 analysis is completed, respectively, an appropriately conservative PCT margin is established by maintaining the current analysis of record PCT value for 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 two large-break 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 BELOCA methodology.

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

  • Comanche Peak
  • Diablo Canyon
  • Palo Verde
  • Wolf Creek 0

-y Document Control Desk PG&E Letter DCL-04-094 July 23,2004 Page 2 Small-Break LOCA Best Estimate Large-Break LOCA Reflood 1 Reflood 2 Unit 1: 1352 0F 1976 0F (no change) 1964 0F (no change)

Unit 2: 1306 0F (no change) 1976 0F (no change) 1964 0F (no change)

The new PCT values remain within the 2200 0F 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. Attachment C contains the updated PCT values using the Westinghouse superposition step methodology and is labeled "Pending Analysis of Record." PG&E will update these DCPP Unit 1 large break analysis-of-record PCT values after the TS revision is approved. In addition, as discussed in the enclosed report, PG&E will perform a plant-specific analysis for Unit 2 using the accepted methodology established in WCAP-1 2945-P-A, "Code Qualification Document for Best Estimate LOCA Analysis," Bajorek, S. M. et. al., 1998. This analysis will be completed prior to the Unit 2 thirteenth refueling outage, which is currently scheduled to begin in May 2006, as discussed in PG&E Letter DCL-04-017, "Supplement to 2003 10 CFR 50.46 Annual Report of Emergency Core Cooling System Evaluation Model Changes, Unit 2 BELOCA Analysis," dated March 2, 2004.

Sincerely, James R. ec r Vice President, DCPP Operationsand Station Director smg/A0587393/R0249062 Enclosure cc/enc: Bruce S. Mallett David L. ProuIx Girija S. Shukla Diablo Distribution

Enclosure PG&E Letter DCL-04-094 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 I and 2. This report is based on changes described in the following Westinghouse 10 CFR 50.46 notification letter:

Westinghouse Letter PGE-04-20, dated March 15, 2004, "Diablo Canyon Units 1 and 2,10 CFR 50.46 Annual Notification and Reporting for 2003."

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.

While the Unit 1 BELOCA PCT results remain unchanged, there has been a bounding 350F increase in the SBLOCA PCT results for DCPP Unit I since the last annual report submitted via PG&E Letter DCL-04-091, dated July 24, 2003.

Both the BELOCA and the SBLOCA PCT results for Unit 2 remain unchanged.

Per the commitment identified in PG&E Letter DCL-00-134, dated October 19, 2000, PG&E has performed a reanalysis for the BELOCA. The analysis was performed using the Westinghouse superposition step methodology, which was approved by the NRC in its Safety Evaluation dated March 11, 2004. PG&E intends to submit a license amendment request to revise the Technical Specifications (TS) to incorporate the Westinghouse superposition step methodology into the licensing basis and establish a new BELOCA analysis of record. Attachment C contains the updated PCT values using the Westinghouse superposition step methodology and is labeled "Pending Analysis of Record."

PG&E will update these DCPP Unit 1 large break analysis-of-record PCT values after the license amendment is issued.

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 past BELOCA analysis of record was 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. Based on the reanalysis results with several comparative cases showing Unit 2 PCTs exceeding those of Unit 1, PG&E determined that the bounding plant methodology was 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-1 2945-P-A, "Code Qualification Document for Best Estimate LOCA Analysis," Bajorek, S. M. et. al., 1998.

1

Enclosure PG&E Letter DCL-04-094 The Unit 2 BELOCA analysis will be completed prior to the Unit 2 thirteenth refueling outage, as discussed in PG&E Letter DCL-04-017. This outage is currently scheduled to begin in May 2006 during which a design change will be implemented which involves 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 TS are revised and the Unit 2 analysis is completed, respectively, 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 I 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 I final PCT at the ninety-fifth percentile is significantly reduced compared with the current value (1900 0F, reanalysis vs. 1976 0F, 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 two large-break PCT values are labeled Reflood I and Reflood 2, as they represent the two distinctive PCT peaks that occur during the reflood phase for the BELOCA methodology.

Small-Break LOCA Best Estimate Large-Break LOCA Reflood 1 Reflood 2 Unit 1: 13520 F 19760 F (no change) 19640 F (no change)

Unit 2: 13060 F (no change) 19760 F (no change) 19641F (no change) 2

ATTACHMENT A ATTACHMENT A PG&E Letter DCL-04-094 DCPP UNIT I PEAK CLADDING TEMPERATURE MARGIN UTILIZATION SMALL-BREAK LOCA PG&E Letter1 A. ANALYSIS OF RECORD PCT = 13040 F 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
2. NOTRUMP Bubble Rise/Drift APCT = 350 F Flux Model Inconsistency Corrections C. 10 CFR 50.59 AND 10 CFR 50.92 SAFETY EVALUATIONS
1. None APCT = 0F D. OTHER MARGIN ALLOCATIONS
1. None APCT = OOF LICENSING BASIS PCT + MARGIN ALLOCATION PCT = 13520 F 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 peak cladding temperature (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

A1TACHMENTA ATTACHMENT A PG&E Letter DCL-04-094 DCPP UNIT 1 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION BEST ESTIMATE LARGE-BREAK LOCA PG&E Letter' Reflood Reflood 1 2 A. ANALYSIS OF RECORD 19760 F 19640 F DCL-00-107 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 I 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 peak cladding temperature (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-2

ATTACHMENT ATTACHMENT B PG&E Letter DCL-04-094 DCPP UNIT 2 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION SMALL-BREAK LOCA PG&E Letter' A. ANALYSIS OF RECORD PCT = 1293 0 F 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= 0OF LICENSING BASIS PCT + MARGIN ALLOCATION PCT = 13060 F I 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 peak cladding temperature (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.

B-1

ATTACHMENT PG&E Letter DCL-04-094 DCPP UNIT 2 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION BEST ESTIMATE LARGE-BREAK LOCA PG&E Letter1 Reflood Reflood 1

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 O0 F C. 10 CFR 50.59 AND 10 CFR 50.92 SAFETY EVALUATIONS
1. None O0 F OOF D. OTHER MARGIN ALLOCATIONS
1. None O0 F OOF LICENSING BASIS PCT + MARGIN 19760 F 19640 F ALLOCATION PCT I For those issues that have been previously reported under 10 CER 50.46, a PG&E letter number is listed.

2 Only permanent assessments of peak cladding temperature (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.

B-2

ATTACHMENT C PG&E Letter DCL-04-094 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 1 BELOCA Reanalysis Final Engineering Report," June 6, 2003 Only permanent assessments of peak cladding temperature (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.

C-1

ATTACHMENT D PG&E Letter DCL-04-094 CURRENT EMERGENCY CORE COOLING SYSTEM MODEL CHANGES AND ERRORS

1. NOTRUMP Bubble Rise/Drift Flux Model Inconsistencies NOTRUMP was updated to resolve inconsistencies in several drift flux models as well as the nodal bubble rise/droplet fall models. These changes include:
  • Bubble rise and droplet fall model calculations were made consistent with flow link calculations
  • Corrections were made to limits employed in the vertical counter-current flooding models
  • Checking logic was added to correct situations where drift flux model inconsistencies could result (i.e., prevent liquid flow from an all-vapor node and vapor flow from an all-liquid node)
  • A more rigorous version of the Yeh Drift Flux Model was implemented since the previous version of this model was incorrectly restricted to a 50 percent void fraction limit The changes identified above affect the 1985 Westinghouse small-break loss of coolant accident evaluation model with NOTRUMP. Representative plant calculations using the NOTRUMP code demonstrate that the implementation of these corrections leads to a bounding 350 F increase of the calculated peak cladding temperature for Unit 1 and a conservative estimate of 0F effect for Unit 2.

D-1

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