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
- 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
- MWe Megawatt-electric
- ASME American Society of Mechanical
- NEA Nuclear Energy Agency Engineers
- NWC Normal water chemistry
- BWR Boiling water reactor
- OECD Organization for Economic Co-operation
- BWRVIP Boiling Water Reactor Vessel and and Development Internals Project
- PWR Pressurized water reactor
- CGR Crack growth rate
- PWSCC Primary water stress corrosion cracking
- EPRI Electric Power Research Institute
- FT Fracture toughness
- HAZ Heat-affected zone
- SEM Scanning electron microscopy
- SMILE Studsvik Materials Integrity for Life Extension
- IASCC Irradiation-assisted stress corrosion
- SS Stainless steel cracking
- TEM Transmission electron microscopy
- WCAP Westinghouse Commercial Atomic Power
- K Applied stress intensity factor
- ZIRP Zorita Internals Research Project
- MRP Materials Reliability Program