Nuclear Executive Update   
An EPRI Progress Report, September 2010
TECHNICAL HIGHLIGHTS
Revision to Materials Degradation Matrix Tackles Long-Term Operation Issues

The revision – and related updates to EPRI’s issue management tables – will guide materials research in strategic areas related to long-term operation, such as increased neutron fluence, fatigue, and fracture resistance.

EPRI has completed a revision of the Materials Degradation Matrix to address how extended plant operation beyond 60 years would impact materials degradation issues (report 1020987). Updates to the corresponding Issue Management Tables for boiling water and pressurized water reactors will be completed later this year. These revisions build on previous efforts to address extended operation to 60 years, and support industry commitments to actively manage materials aging degradation.

EPRI convened an expert panel in February 2010 to initiate the revision. This panel included leading materials experts from electric utilities, EPRI, academia and industry consultants. Regulatory and government observers also participated in the discussions.

Through this expert elicitation process, EPRI identified several strategic issues on materials degradation related to long-term operation:

  • Impacts of increase in the end-of-life neutron fluence
  • Increase in fatigue cycles
  • Late-in-life increase of cracking susceptibility
  • Long-term instability of surface stress improvement
  • Steam generator fouling and corrosion due to extended plant operation

The expert panel also stressed that industry should continue to work on resolving near-term concerns related to:

  • Environmental effects on fracture resistance, with growing evidence that the fracture properties of some structural materials can be degraded significantly after long-term exposure to hydrogenated high temperature water.
  • Stress corrosion cracking (SCC) of nickel-based alloys and austenitic stainless steels, including whether weld imperfections could lead to crack initiation in thick-walled Alloy 690 components or Alloy 52 / 152 weld overlays, secondary side cracking of Alloy 690TT tubing in the presence of lead, the cracking properties of thermally aged cast austenitic stainless steels in PWR pressure boundary components, and corrosion cracking of stainless steels in PWR primary water.

The Materials Degradation Matrix provides the basis for identifying and prioritizing R&D gaps for resolving materials aging issues in specific plant components. These gaps are reflected in the Issue Management Tables that guide research activities in EPRI’s materials programs.

For more information, contact TG Lian at 650.855.2405, tlian@epri.com