NSUF 24-4965: Impact of re-irradiation on strain-induced structure in heavy irradiated austenitic steel

The objective of this work is to understand and quantify the interaction between localized plastic deformation and solute precipitation in a radiation environment. We will examine the hypothesis that boundaries of dislocation channels and deformation twins, formed while in service, can serve as preferential solute precipitation locations during following re-irradiation, enhancing, irradiation-assisted stress corrosion cracking (IASCC) susceptibility. Localized deformation and solute segregation are two of the primary drivers of IASCC in austenitic stainless steels in nuclear reactor internal components1. Irradiation changes the deformation mechanism in austenitic alloys to localized dislocation channels; it produces dislocation glide obstacles like dislocation loops and precipitates which increase the stress needed to move dislocations and thus dislocation glide takes place locally in channels where the stress locally is enough to glide2. Radiation-induced Ni and Si solute precipitation and grain boundary segregation also play a role in IASCC through increasing the susceptibility to grain boundary oxidation2. However, the direct interplay between Ni/Si precipitation and dislocation channels has received less attention. Earlier, post proton-irradiation tensile testing of 304 stainless steel revealed that the formation of dislocation channels resulted in the dissolution of Ni/Si-rich precipitates within the dislocation postchannel3, as shown in Figure 1a. Recently as part of the Light Water Reactor Sustainability program, characterization was performed on a baffle former bolt (BFB) made of 316 stainless steel (SS), which had been in service for ~40 years in a pressurized water reactor (PWR), resulting in a damage dose of ~41 dpa at a temperature of ~300°C. Post-irradiation evaluation revealed the presence of dislocation channels at the intersection between the bolt head and bolt shank indicative of loading at a stress level close to yield stress at least once while in service. Microstructural analysis showed the development of Ni/Si-rich precipitates along the edges of the in-service formed channels, as shown in Figure 1b/c. Primary Ni/Si precipitates were destroyed during dislocation channel formation, and secondary Ni/Si precipitates formed along the dislocation channel edges during the continued irradiation. Complex chemistry inside the defect-free channel may influence localized corrosion, material long-term performance, and safety. The results demonstrate a potentially new phenomenon – secondary precipitation along the dislocation channel or twin formed while in service. As such, this proposal seeks to capture this behavior in a controlled experiment as that observed in the harvested material to determine its mechanisms. In this work, small-scale SS-Tiny specimens cut from unstrained regions in the bolt mid-shank of the BFB #44124,5 and tensile tested using digital image correlation (DIC) followed by heavy ion irradiation. The outcome of this work will provide quantitative analysis of the irradiated microstructure including dislocation loops, dislocation channel evolution, and radiation-induced segregation/precipitation to the mechanical deformation defects. If successful, the results will inform the interaction of radiation effects and mechanical deformation and how it may affect IASCC on components in service.

추가 정보

필드	값
Award Announced Date	2024-05-28T17:08:33.323
Awarded Institution	Oak Ridge National Laboratory
Facility Tech Lead	Kory Linton, Lin Shao
Irradiation Facility	Accelerator Laboratory
PI	Soyoung Kang
PI Email	[email protected]
Project Type	RTE
RTE Number	None