DCL-06-079, CFR 50.46 Emergency Core Cooling System Evaluation Model Changes
| ML061810264 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 06/20/2006 |
| From: | Jacobs D Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-06-079 | |
| Download: ML061810264 (6) | |
Text
PacificGasand ElectricCompany' Donna Jacobs Diablo Canyon Power Plant Vice President P.0. Box 56 Nuclear Services Avila Beach, CA 93424 805.545.4600 June 20, 2006 Fax: 805.545.4234 PG&E Letter DCL-06-079 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-323, OL-DPR-82 Diablo Canyon Unit 2 10 CFR 50.46 Emergency Core Cooling System Evaluation Model Chanqes
Dear Commissioners and Staff:
Pursuant to 10 CFR 50.46, this letter provides a 30-day 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, Unit 2. These PCT margin allocations have been made due to two reactor vessel design changes, which have been implemented during the Unit 2 thirteenth refueling outage.
The Upflow Conversion (UC) design change converted the Unit 2 reactor vessel from a downflow barrel/baffle configuration to an upflow configuration, while the Upper Head Temperature Reduction (UHTR) design change reduced the upper head temperature to a value corresponding to the Reactor Coolant System cold leg temperature (Tcold). Because the absolute value of the sum of these new PCT margin allocations exceeds 50 0 F, they can be considered "significant" in accordance with 10 CFR 50.46. The UC design change resulted in a 170F and a 40OF decrease in the best estimate large-break loss-of-coolant accident (BELOCA) PCT results for the Reflood I period and the Reflood 2 period, respectively. The UHTR design change resulted in a 159 0 F and a 1240 F decrease in the BELOCA PCT results for the Reflood 1 period and the Reflood 2 period, respectively. These PCT changes are with respect to the last annual report submitted via Pacific Gas and Electric (PG&E) Letter DCL-05-086, dated July 25, 2005.
There has been no change in the Unit 1 BELOCA PCT results and the small-break loss-of-coolant accident (SBLOCA) PCT results for Units 1 and 2 also remain unchanged as presented in DCL-05-086. The summary of the updated Unit 2 PCT margin allocations and their bases are provided in the enclosure.
A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Catlaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
- South Texas Project
- Wolf Creek 0
Document Control Desk PG&E Letter DCL-06-079 June 20, 2006 Page 2 The new Unit 2 PCT values remain within the 2200°F limit specified in 10 CFR 50.46. The Unit 2 BELOCA PCT Margin Utilization Sheets are provided in Attachment A of the enclosure. The ECCS evaluation model changes that have resulted in the new PCT margin allocation are summarized in Attachment B.
As discussed in the enclosed report, PG&E has performed a plant-specific reanalysis for Unit 2 using the accepted methodology established in WCAP-12945-P-A, "Code Qualification Document for Best Estimate LOCA Analysis," dated 1998, and WCAP-1 6009-P-A, "Realistic Large-Break LOCA Evaluation Methodology Using the Automated Statistical Treatment Uncertainty Method (ASTRUM)," dated 2005. This reanalysis explicitly incorporates the Unit 2 reactor vessel design changes and has been submitted for NRC review in PG&E Letter DCL-06-006, "10 CFR 50.46 License Amendment Request 06-02 Revision to Technical Specification 5.6.5, 'Core Operating Limits Report (COLR),"' dated March 2, 2004. PG&E will update these DCPP Unit 2 BELOCA analysis-of-record PCT values after the Technical Specification revision is approved.
If there are any questions regarding this report, please contact Mr. Mark Mayer of my staff at (805) 545-4674 Sincerely, Donna acobs Vice Predent,NuclearServices ddm/2254/A0642916 Enclosure cc: Diablo Distribution cc/enc: Edgar Bailey, DHS Terry W. Jackson, NRC Senior Resident Inspector Bruce S. Mallett, NRC Region IV Alan B. Wang, NRR Project Manager A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde o South Texas Project
- Wolf Creek
Enclosure PG&E Letter DCL-06-079 30-DAY REPORT OF EMERGENCY CORE COOLING SYSTEM EVALUATION MODEL CHANGES THAT AFFECT PEAK CLADDING TEMPERATURE Pursuant to 10 CFR 50.46, this enclosure provides a 30-day report of changes in the Westinghouse emergency core cooling system (ECCS) evaluation model that affects peak cladding temperature (PCT) calculations for Diablo Canyon Power Plant (DCPP), Unit 2. This report is based on changes described in the following Westinghouse 10 CFR 50.46 notification letter:
Westinghouse Letter PGE-05-67, dated September 9, 2005, "Transmittals of Draft WCAP-1 6443-P and 10 CFR 50.46 Margin Tracking Sheets" Attachment A to this enclosure provides DCPP Unit 2 best estimate large-break loss-of-coolant accident (BELOCA) PCT Margin Utilization Sheets. These PCT margin allocations have been made due to two reactor vessel design changes, which have been implemented during the Unit 2 thirteenth refueling outage (2R13).
The Upflow Conversion (UC) design change converted the Unit 2 reactor vessel from a downflow barrel/baffle configuration to an upflow configuration, while the Upper Head Temperature Reduction (UHTR) design change reduced the upper head temperature to a value corresponding to the Reactor Coolant System (RCS) cold leg temperature (T.od). The UC design change resulted in a 170 F and a 40°F decrease in the BELOCA PCT results for the Reflood 1 period and the Reflood 2 period, respectively. The UHTR design change resulted in a 159°F and a 124 0 F decrease in the BELOCA PCT results for the Reflood 1 period and the Reflood 2 period, respectively. These PCT changes are assessments against the PCT values contained in the last annual report submitted in Pacific Gas and Electric (PG&E)
Letter DCL-05-086, dated July 25, 2005. There has been no change in the Unit I BELOCA PCT results, and the small-break loss-of-coolant accident (SBLOCA) PCT results for Unit 1 and Unit 2 also remain unchanged from the information presented in DCL-05-086. A detailed summary of the ECCS evaluation model changes that have resulted in this new PCT margin allocation are summarized in Attachment B.
PG&E has performed a plant-specific reanalysis for Unit 2 using the accepted methodology established in WCAP-1 2945-P-A, "Code Qualification Document for Best Estimate LOCA Analysis," dated 1998, and WCAP-1 6009-P-A, "Realistic Large-Break LOCA Evaluation Methodology Using the Automated Statistical Treatment Uncertainty Method (ASTRUM)," dated 2005. This re-analysis explicitly incorporates the Unit 2 reactor vessel design changes and has been submitted for NRC review in the PG&E Letter DCL-06-006, "10 CFR 50.46 License Amendment Request 06-02 Revision to Technical Specification 5.6.5, 'Core Operating Limits Report (COLR),"' dated March 2, 2004. PG&E will update these DCPP Unit 2 BELOCA analysis-of-record PCT values after the Technical Specification revision is approved.
Enclosure PG&E Letter DCL-06-079 The final net Unit 2 BELOCA PCT values that are reflected in Attachments A 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 BELOCA PCT values are labeled Reflood 1 and Reflood 2, as they represent the two distinct PCT peaks that occur during the reflood phase.
Best Estimate Large-Break Loss-of-coolant Accident Reflood 1 Reflood 2 Unit 2: 1805°F 1805°F
ATTACHMENT A PG&E Letter DCL-06-079 DCPP UNIT 2 PEAK CLADDING TEMPERATURE MARGIN UTILIZATION BEST ESTIMATE LARGE-BREAK LOCA PG&E Letter1 Reflood Reflood 1 2 A. ANALYSIS OF RECORD 1976 0 F 1964 0 F DCL-00-1 07 APCT APCT B. PERMANENT 10 CFR 50.46 2 ECCS MODEL ASSESSMENTS
- 1. Revised blowdown heatup 50 F 5 0F DCL-05-086 uncertainty distribution
- 2. Upflow Conversion (UC) -17 0 F -40OF
- 3. Upper Head Temperature -159°F -1240F Reduction (UHTR)
C. 10 CFR 50.59 AND 10 CFR 50.92 SAFETY EVALUATIONS
- 1. None 0OF 0OF D. OTHER MARGIN ALLOCATIONS
- 1. None 0OF 0OF LICENSING BASIS PCT + MARGIN 1805°F 1805°F ALLOCATION PCT 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.
ATTACHMENT B PG&E Letter DCL-06-079 BEST ESTIMATE LARGE-BREAK LOSS-OF-COOLANT ACCIDENT (BELOCA)
Upflow Conversion (UC) and Upper Head Temperature Reduction (UHTR)
Evaluations The impact of the reactor vessel internals changes performed prior to Cycle 14 operation (prior to the Unit 2 thirteenth refueling outage) on the current licensing basis BELOCA analysis for Diablo Canyon Power Plant (DCPP) Unit 2 has been identified. The WCOBRAITRAC input deck used in the Unit 2 analysis of record was modified first to model the conversion of the Unit 2 barrel baffle region to the upflow configuration. The detailed thermal hydraulic parameters associated with the modified barrel baffle region flow were modeled, and the reference transient was then executed using the current approved version of WCOBRA/TRAC. The Unit 2 input deck was then further modified to model the reduction in the upper head temperature to the Tco.d condition, and again the reference transient was executed.
In this way the impact of each plant modification was evaluated individually for the DCPP Unit 2 10 CFR 50.46 peak cladding temperature (PCT) margin utilization sheet.
The current DCPP Unit 2 licensing basis PCT 95 9 is reduced due to each of these plant changes. The UC leads to a 170F decrease in the PCT during the Reflood 1 period, and the UHTR produces an additional 159 0 F decrease in the PCT during the Reflood I period. In addition, the conversion of the barrel baffle region to an upflow configuration leads to a 40°F decrease in the PCT during the Reflood 2 period, and the UHTR produces an additional 124 0 F decrease in the PCT during the Reflood 2 period.