ML063560346

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November 30, 2006 NRC Presentation Slides: Wolf Creek Flaw Evaluation
ML063560346
Person / Time
Site: Wolf Creek Wolf Creek Nuclear Operating Corporation icon.png
Issue date: 11/30/2006
From:
Office of Nuclear Reactor Regulation
To:
Mensah T
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Download: ML063560346 (13)


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NRC Wolf Creek Flaw Evaluation November 30, 2006

NRC Analysis of Wolf Creek Flaws

  • NRC analysis of Wolf Creek flaws to determine:

- Time from initiation 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 U.S. Nuclear Regulatory Commission 2

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 644oF.

- 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.

U.S. Nuclear Regulatory Commission 3

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)

U.S. Nuclear Regulatory Commission 4

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 U.S. Nuclear Regulatory Commission 5

Surge Nozzle: Results 1.2Y K-driven (WRS) 1.5Y K-driven (No WRS)

NRC Constant 9:1 (WRS)

Constant 9:1 (No WRS) 6:1 MRP 10:1 20:1 Initiation to Current Size Current time Current time Current Size to Leakage to Rupture to Rupture (Normal Op.) (Faulted) 10/00 10/03 10/06 10/09 10/12

-6 0 6 Time (years)

  • Last Volumetric Examination: 1993 U.S. Nuclear Regulatory Commission 6
  • 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 the NRCs leakage flaw size.

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)

U.S. Nuclear Regulatory Commission 7

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 U.S. Nuclear Regulatory Commission 8

Relief Nozzle: Results 0-3M K-driven (WRS) 0-4M 5-14M K-driven (No WRS) 6-15M NRC Constant 21:1 (WRS)

Constant 21:1 (No WRS) 6:1 MRP 10:1 20:1 Initiation to Current Size Current time Current time Current Size to Leakage to Rupture to Rupture (Normal Op.) (Faulted) 10/99 10/06 10/13

-7 0 7 Time (years)

  • Last Volumetric Examination: 2000 U.S. Nuclear Regulatory Commission 9
  • 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 the NRCs leakage flaw size.

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)

U.S. Nuclear Regulatory Commission 10

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 U.S. Nuclear Regulatory Commission 11

Safety Nozzle: Results 0-9M K-driven (WRS) 0-10M 4-5Y K-driven (No WRS)

NRC Constant 8:1 (WRS)

Constant 8:1 (No WRS) 6:1 MRP 10:1 20:1 Initiation to Current Size Current time Current time Current Size to Leakage to Rupture to Rupture (Normal Op.) (Faulted) 10/97 10/06 10/15

-9 0 9 Time (years)

  • Last Volumetric Examination: 2000 U.S. Nuclear Regulatory Commission 12
  • 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 the NRCs leakage flaw size.

Conclusions

  • Range of numerical results dependent upon assumptions.
  • Timeframes to leakage for Surge and Relief lines range from 1-21/2 years; 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 resolve the differences in the NRC and MRP analyses, e.g. the assumptions and models that drive the results.

U.S. Nuclear Regulatory Commission 13