ML22143A842
| ML22143A842 | |
| Person / Time | |
|---|---|
| Issue date: | 05/25/2022 |
| From: | Matthew Hiser, Pat Purtscher, Robert Tregoning NRC/RES/DE |
| To: | |
| Kalikian R, 301-415-5590 | |
| Shared Package | |
| ML22143A408 | List: |
| References | |
| Download: ML22143A842 (14) | |
Text
RIL 2022-05: NRC Technical Assessment of Zorita Materials Testing Results Matthew Hiser, Patrick Purtscher, Robert Tregoning NRC Office of Nuclear Regulatory Research May 25-26, 2022 Annual NRC-Industry Materials Exchange Meeting
Summary
- EPRI led a cooperative effort to harvest reactor internals from a decommissioning plant in Spain known as the Zorita reactor
- Effort included NRC and other international participants
- Materials harvested from Zorita included:
- Baffle plate materials with fluences up to ~50 displacements per atom (dpa)
- Core barrel weld and heat-affected zone (HAZ) materials with fluences up to ~2 dpa
- NRC technical assessment of Zorita materials testing results was recently published: RIL 2022-05 2
Zorita Background and Context
- Zorita reactor internals characteristics:
- 160 MWe Westinghouse-designed single loop PWR
- Operated for 26.4 effective full-power years
- Internals fabricated with Type 304 austenitic stainless steel (SS)
- Operated at a fairly low temperature for a PWR (<330°C max compared to
>360°C at many PWRs)
- Fabrication records for the internals could not be found
- Compositional and microstructural analysis of weld and plate show expected results for 304 SS plate and 308 SS weld metal
- Highly representative of the SS internals in operating U.S. plants
- Based on design, aging conditions, and known fabrication information
Overview of Zorita Research Programs
Key Takeaways from Zorita Testing
- Baffle plate materials
- Very low amount of observed void swelling
- Repeated observations of high crack growth rate (CGR) during irradiation-assisted stress corrosion cracking (IASCC) CGR testing
- Tensile, crack initiation, and fracture toughness (FT) data as expected based on literature data
- Core barrel weld materials
- Very low FT values observed in multiple tests
- Tensile and CGR data as expected based on literature data
Void Swelling Results
Void Swelling Takeaways
- Swelling results correlate more strongly with temperature than fluence, consistent with literature data
- Results are an encouraging sign that void swelling may not progress rapidly in LWRs
- Due to lower temperature (<330°C), Zorita results do not conclusively eliminate the potential for significant void swelling, particularly at higher temperatures
- Additional LWR-irradiated materials at higher temperatures should be studied to more confidently assess void swelling for extended plant operation
High Fluence IASCC CGR Results
High Fluence IASCC CGR Takeaways
- NRC staff have carefully analyzed the Zorita plate CGR results
- Conditions leading to high CGRs are K > 15 MPam and fluence >25 dpa
- High CGR data are representative of the IASCC susceptibility at elevated fluence
- NRC staff have proposed a condition on ASME Code Case N-889 to limit applicability to <20 dpa
- Other factors to consider:
- Zorita data likely from one heat of material - heat-to-heat variability
- Low operating stresses and irradiation-induced stress relaxation
- Additional data from SMILE should help improve understanding
SS Weld Fracture Toughness Results
SS Weld Fracture Toughness Takeaways
- BWRVIP-100, Rev. 1-A criteria for irradiated SS FT are not bounding of the Zorita weld data or data from ANL on a cancelled BWR core shroud
- Zorita HAZ data are approximately bounded by the BWRVIP-100 criteria
- Regulatory Activities
- In March 2021, EPRI notified the NRC of a Part 21 notification about the potential nonconservatism in BWRVIP-100, Revision 1-A (ML21084A164)
- In November 2021, NRC released a LIC-504 assessment of the BWRVIP-100 non-conservatism issue (ML21312A543) finding no immediate safety issue
SS Weld Fracture Toughness Takeaways
- SS weld materials (including Zorita) show strong resistance to IASCC crack growth
- Low weld FT most relevant to pre-existing fabrication flaws or slowly growing SCC flaws
- Zorita data remain approximately bounded by BWRVIP-100, Rev. 1-A criteria
- Operating experience shows flaws are more likely to form in this region
- Additional data from SMILE and other potential harvesting should help improve understanding
Future Work
- Seeking additional data on harvested irradiated SS materials in key areas:
- Low dose (<2 dpa) SS weld to validate Zorita FT results
- Higher dose (2-20 dpa) SS weld to assess FT and IASCC performance at higher fluences
- High dose (>20 dpa) and high temperature (~360°C) SS plate to assess CGR and void swelling behavior
- SMILE project will help to address each of these interests:
- SS weld material above and below 2 dpa
- SS plate material up to ~50 dpa at a higher temperature than Zorita
Acronym List ANL Argonne National Laboratory ASME American Society of Mechanical Engineers BWR Boiling water reactor BWRVIP Boiling Water Reactor Vessel and Internals Project CGR Crack growth rate EPRI Electric Power Research Institute FT Fracture toughness HAZ Heat-affected zone HWC Hydrogen water chemistry IASCC Irradiation-assisted stress corrosion cracking INL Idaho National Laboratory K
Applied stress intensity factor MRP Materials Reliability Program MWe Megawatt-electric NEA Nuclear Energy Agency NWC Normal water chemistry OECD Organization for Economic Co-operation and Development PWR Pressurized water reactor PWSCC Primary water stress corrosion cracking RPV Reactor Pressure Vessel SCC Stress corrosion cracking SEM Scanning electron microscopy SMILE Studsvik Materials Integrity for Life Extension SS Stainless steel TEM Transmission electron microscopy WCAP Westinghouse Commercial Atomic Power ZIRP Zorita Internals Research Project