ML063560346

November 30, 2006 NRC Presentation Slides: Wolf Creek Flaw Evaluation

ML063560346
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Site:	Wolf Creek
Issue date:	11/30/2006
From:	Office of Nuclear Reactor Regulation
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NRC Wolf Creek Flaw Evaluation NRC Wolf Creek Flaw EvaluationNovember 30, 2006 2U.S. Nuclear Regulatory Commission NRC Analysis of NRC Analysis of Wolf Creek Flaws Wolf Creek Flaws

• NRC analysis of Wolf Creek flaws to determine:-Time from initiati on to current size.-Time from current size to leakage.-Time from leakage to rupture*Normal operating condition*Faulted condition.

• Results broken down by nozzle type-Surge/Relief/Safety 3U.S. Nuclear Regulatory Commission Analysis Assumptions Analysis Assumptions

• Assumptions:-Time to leakage = time to reach 100% through wall.-Time to rupture = time to reach critical flaw size.-Aspect ratio for growing crack:

• K-driven: governed by K-solution at both surface and deepest point shape; i.e. semi-elliptical shape.

• Constant c/a: growth in depth direction driven by K, length is set by original c/a ratio.-MRP-115 crack growth rate for Alloy 182 adjusted to 644 o F.-For initiation: back calculated crack growth to 0.04" crack depth.

-No flaw interactions for surge line.-Weld Residual Stresses (WRS) as identified for each case.

4U.S. Nuclear Regulatory Commission Surge Nozzle: Assumptions Surge Nozzle: Assumptions

• Assumptions:-WRS evaluated:*Repair WRS = 15%ID repair -FE analysis

• No Repair WRS

• No WRS-Loading conditions:*Leakage analysis used normal operating loads that include:-Deadweight

-Pressure

-Thermal Expansion (no stratification)*Rupture analysis evaluated both:-Normal operating condition

-Faulted loading condition (Normal operating + SSE) 5U.S. Nuclear Regulatory Commission Surge Nozzle: Results Surge Nozzle: Results

• Three Circumferential Flaws-4" ~31% Through Wall (9:1)-2.2" ~25% Through Wall (5:1)-0.8" @ inner surface (2:1)

• Weld Length = 38"

• Weld ID = 12" / OD = 15"

• Extensive Repair History

• Last Volumetric Examination: 1993 6U.S. Nuclear Regulatory Commission Surge Nozzle: Results Surge Nozzle: Results-606Time (years)Constant 9:1 (WRS)K-driven (WRS)6:1NRCMRP10/0010/0610/1210/0310/09Constant 9:1 (No WRS)10:120:1*Last Volumetric Examination: 1993Initiation to Current SizeCurrent Size to LeakageCurrent time to Rupture (Normal Op.)Current time to Rupture (Faulted)K-driven (No WRS)1.2Y1.5Y* MRP defines time to rupture as the time from a 1gpm leakage flaw to grow to the critical flaw size, which is significantly smaller than theNRC'sleakage flaw size.

7U.S. Nuclear Regulatory Commission Relief Nozzle: Assumptions Relief Nozzle: Assumptions

• Assumptions:-WRS evaluated:*ASME WRS based on 30ksi yield

• ASME WRS based on 40ksi yield

• No WRS-Loading conditions:*Leakage analysis used normal operating loads that include:-Deadweight

-Pressure

-Thermal Expansion (no stratification)*Rupture analysis evaluated both:-Normal operating condition

-Faulted loading condition (Normal operating + SSE) 8U.S. Nuclear Regulatory Commission Relief Nozzle: Results Relief Nozzle: Results

• One Circumferential Flaw-7.7" ~26% Through Wall (21:1)

• Weld Length = 16.3"

• Weld ID = 5.17" / OD = 8"

• Extensive Repair History

• Last Volumetric Examination: 2000 9U.S. Nuclear Regulatory Commission Relief Nozzle: Results Relief Nozzle: Results-707Time (years)Constant 21:1 (WRS)K-driven (WRS)6:1 NRCMRP10/9910/0610/13Constant 21:1 (No WRS)10:120:1*Last Volumetric Examination: 2000Initiation to Current SizeCurrent Size to LeakageCurrent time to Rupture (Normal Op.)Current time to Rupture (Faulted)K-driven (No WRS)0-3M0-4M5-14M6-15M* MRP defines time to rupture as the time from a 1gpm leakage flaw to grow to the critical flaw size, which is significantly smaller than theNRC'sleakage flaw size.

10U.S. Nuclear Regulatory Commission Safety Nozzle: Assumptions Safety Nozzle: Assumptions

• Assumptions:-WRS evaluated:*ASME WRS based on 30ksi yield

• ASME WRS based on 40ksi yield

• No WRS-Loading conditions:*Leakage analysis used normal operating loads that include:-Deadweight

-Pressure

-Thermal Expansion (no stratification)*Rupture analysis evaluated both:-Normal operating condition

-Faulted loading condition (Normal operating + SSE) 11U.S. Nuclear Regulatory Commission Safety Nozzle: Results Safety Nozzle: Results

• One Circumferential Flaw-2.5" ~23% Through Wall (8:1)

• Weld Length = 16.3"

• Weld ID = 5.17" / OD = 8"

• No known repair history

• Last Volumetric Examination: 2000 12U.S. Nuclear Regulatory Commission Safety Nozzle: Results Safety Nozzle: Results-909Time (years)Constant 8:1 (WRS)K-driven (WRS)6:1 NRCMRP10/9710/0610/15Constant 8:1 (No WRS)10:120:1*Last Volumetric Examination: 2000Initiation to Current SizeCurrent Size to LeakageCurrent time to Rupture (Normal Op.)Current time to Rupture (Faulted)K-driven (No WRS)0-9M0-10M4-5Y* MRP defines time to rupture as the time from a 1gpm leakage flaw to grow to the critical flaw size, which is significantly smaller than theNRC'sleakage flaw size.

13U.S. Nuclear Regulatory Commission Conclusions Conclusions

• Range of numerical results dependent upon assumptions.

• Timeframes to leakage for Surge and Relief lines range from 1-21/2years; Safety line timeframes longer.

• More conservative assumptions and calculations show no time between leakage and rupture.

• More realistic calculations show timeframes between leakage and rupture range from a few months to a year.

• Important to understand and reso lve the differences in the NRC and MRP analyses, e.g. the assumptions and models that drive the results.