ML21217A302

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02B - NRC - Matl Tech Exchg - BWRVIP-100
ML21217A302
Person / Time
Issue date: 08/09/2021
From: Michael Benson, Ching Ng, David Rudland
NRC/NRR/DNRL
To:
Hiser A
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ML21217A247 List:
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Download: ML21217A302 (7)


Text

NRC Perspective on BWRVIP-100 Nonconservatism Michael L. Benson, Ching Ng, and David Rudland Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Industry/NRC Materials Programs Technical Information Exchange August 10, 2021

History of Core Shroud Cracking

  • Relatively severe cracking discovered in the 1990s

- Available via websearch

- Summary of the cracking experience

- Summary of industry response, included inspection and repair activities Industry/NRC Materials Programs Technical Information Exchange 2

Aging Management of Core Shroud

- proprietary

- proprietary

  • Inspection and flaw evaluation guidelines for the core shroud
  • ASME Code,Section XI inspection requirements for Core Support Structures

BWRVIP-100 Nonconservatism

  • Affects toughness and fluence threshold assumptions
  • Actual toughness could be lower than currently assumed in licensee calculations
  • Failure mode could transition from ductile to brittle earlier in life than previously assumed in licensee calculations
  • Licensee inspection frequencies for the core shroud could be too long Industry/NRC Materials Programs Technical Information Exchange 4

Staff Flaw Evaluation

  • Conservative assumptions

- Shroud wall thickness

- Crack size (through-wall and 360° surface flaw)

- Loading conditions (i.e., accident conditions)

  • Staff calculations indicate that the shroud can tolerate a relatively severe flaw Industry/NRC Materials Programs Technical Information Exchange 5

Risk-Informed Decision Making

  • NRRs LIC-504 process for dispositioning emergent safety concerns
  • Applies key principles of risk-informed decision-making
  • Staff weighs options for NRC management consideration

- Immediate action

- Longer-term action

- No action

  • The staff does not recommend immediate action Industry/NRC Materials Programs Technical Information Exchange 6

Conclusions

  • Licensees should update their inspection programs to account for the new information
  • LIC-504 document describes complete NRC risk-informed evaluation of the significance

- Flaw analysis and risk analysis

- Currently under internal review

- May be made public in the future

  • NRC is currently assessing options for appropriate oversight of industry actions on this matter Industry/NRC Materials Programs Technical Information Exchange 7