Abstract
In order to examine the attenuation of radiation damage through the thickness of an irradiated reactor pressure vessel (RPV), four segments were acquired from the Zion Unit 1 power plant RPV after the plant was decommissioned. The Zion Unit 1 RPV Beltline Weld Segment 1 was cut into seven blocks, consisting of five base metal and two beltline welds from the high fluence region of the segment. Through-wall test specimens were machined and tested. Specimens included those used for Charpy impact, Master Curve fracture toughness testing, and chemical analysis. The observed through-thickness ductile-to-brittle transition temperatures in the beltline weld deviated significantly from the expected behavior based on the attenuation of fast fluence as a function of depth into the RPV. Beginning at the inside surface, the 41-J Charpy transition temperature was either flat or slightly increasing until the ¾ -T location. The results of a simple, model-based analysis of the Zion beltline weld material that included the irradiation conditions and material chemistry were generally consistent with industry trend curves and the standard attenuation model, rather than the observed data. Although there was no archive material from the RPV available to permit measurement of the unirradiated properties, fracture toughness specimens fabricated from archive surveillance weld were used to obtain an estimate of the initial through-thickness values of the Charpy transition temperature. The Charpy shifts obtained using this approach were similarly in disagreement with the predictions of the US NRC Regulatory Guide 1.99, Rev. 2. However, testing of irradiated Charpy specimens taken from the RPV following post-irradiation annealing (10 hr. at 500 °C) provided a quite different estimate of the unirradiated properties which improved the agreement between the inferred through-thickness Charpy shifts and exponential attenuation model included in Regulatory Guide 1.99/2. The analysis of the Zion data and data obtained in previous post-mortem examinations of decommissioned RPVs indicates that more work is needed to understand the through-thickness properties of RPV materials in order to properly assess through-wall damage attenuation.
| Original language | English |
|---|---|
| Article number | 156445 |
| Journal | Journal of Nuclear Materials |
| Volume | 623 |
| DOIs | |
| State | Published - Mar 2026 |
Funding
This research was sponsored by the U.S. Department of Energy, Office of Nuclear Energy, Light Water Reactor Sustainability Program Materials Research Pathway under contract DE-AC05-00OR22725 with UT-Battelle, LLC / Oak Ridge National Laboratory. The authors wish to thank Xiang (Frank) Chen and Igor Remec who reviewed the manuscript. We also would like to thank Bill Server for discussion and comments on the manuscript. Continuous support from Xiang (Frank) Chen and Thomas Rosseel, the current and former Pathway Leads of the Long-Term Performance Pathway of the Light Water Reactor Sustainability Program, is highly appreciated. The Zion Nuclear Generating Station in Zion, Illinois consisted of two Westinghouse 4-loop pressurized water reactors, with each unit capable of producing 1040 MWe. The units were commissioned in 1973, permanently shut down in 1998, and placed into SAFSTOR (a method of decommissioning where a nuclear facility is placed and maintained in a condition that allows the facility to be safely stored and subsequently decontaminated to levels that permit release for unrestricted use) in 2010. The decommissioning of these reactors presented a unique opportunity for developing a better understanding of materials degradation and other issues associated with extending the lifetime of existing nuclear power plants (NPPs) beyond 60 years of service. To support the current operation and extended service of the US nuclear reactor fleet, the Oak Ridge National Laboratory (ORNL) procured components from the decommissioned reactors, including multiple segments of the Zion Unit 1 Reactor Pressure Vessel (RPV). The effort was supported by the Department of Energy (DOE) Light Water Reactor Sustainability (LWRS) Program Long-Term Performance Pathway, and coordinated with Zion Solutions, LLC, a subsidiary of Energy Solutions (ES).
Keywords
- Charpy impact
- Damage attenuation
- Irradiation effects
- Master curve fracture toughness
- Mechanical properties
- Reactor pressure vessel