NSUF 25-5296: Inter-Phase Localized Fracture: A New Mechanism for RPV Embrittlement

The objective of this project is to understand inter-phase localized fracture, a non-hardening irradiation embrittlement mechanism not previously considered in reactor pressure vessel (RPV) steels. Irradiation embrittlement of RPV steels is one of the most crucial challenges facing continued operation of light water reactors, and is categorized as hardening-type or non-hardening embrittlement. Most studies have focused on the former, ascribing hardening embrittlement to dislocation pinning on loops and nanoclusters. On the other hand, non-hardening embrittlement is typically attributed to P radiation-induced segregation causing grain boundary decohesion. However, a new form of non-hardening embrittlement recently identified in dual-phase low-alloy steels (e.g., RPV steels) is localized fracture caused by stress concentrations at ferrite/bainite inter-phase boundaries – this mechanism has never before been considered in RPV steels. Because the ferrite phase fraction in RPV steel increases with irradiation, we hypothesize that inter-phase localized fracture will be exacerbated, playing a significant role in the overall irradiation embrittlement. We will conduct scanning electron microscopy (SEM) in situ uniaxial and triaxial straining with subsequent characterization of regions of interest, enabling us to directly visualize inter-phase localized fracture. Work will focus on as-received control specimens and proton irradiated specimens of SA508 RPV steel, intentionally selected to encompass a range of ferrite phase fractions. We have already characterized the dislocation loops, nanoclusters, and estimated irradiation embrittlement in these specimens through our ongoing NSUF program. By leveraging these previous results, the proposed project can have heightened impact by enabling us to develop a unified mechanism that captures both hardening-type and non-hardening type embrittlement in RPV steels.

Additional Info

Field	Value
Award Announced Date	2025-08-06T10:10:14.407
Awarded Institution	University of Illinois at Urbana-Champaign
Facility Tech Lead	Kory Linton, Lin Shao
Irradiation Facility	Accelerator Laboratory
PI	Elliot Marrero
PI Email	[email protected]
Project Type	RTE
RTE Number	None