Investigations of surface state and stability of AM 316L SS components

Purpose and goal

The overall aim of the project is to pave the way for well-informed use of additively manufactured (AM) stainless steel in small modular reactors (SMRs), without compromising safety aspects, stress corrosion cracking (SCC) included. A little more specifically, the project has the following goals: 

- To understand the mechanisms of SCC in AM-produced and post-treated 316L (stainless steel) in SMR-relevant environments, and to compare this with conventionally produced 316L. 

- To understand how different process paths affect SCC in 316L components

Challenge

Stress corrosion in stainless steel is a known phenomenon to be aware of in nuclear power reactors. Microstructure and surface properties of AM materials differ from conventionally manufactured parts and affect the susceptibility to initiation of SCC.

Solution

Additive manufacturing is a new technology, which is pointed out as particularly interesting for small modular reactors. The use of AM in SMR opens up completely new possibilities with respect to component design, manufacturing lead times and availability of spare parts. For safe use, for example light water reactor (LWR) type SMRs, extensive verification of component properties is required.

Structure and expected outcome

The project will include a whole chain of processes, to contribute to a complete understanding of SCC mechanisms resulting from exposure in SMR/LWR environment to AM materials. AM 316L material will be manufactured with powder bed fusion laser beam (PBF-LB) and post processes applied (for example hot isostatic pressing (HIP)). These will be subjected to SCC initiation testing in the relevant SMR/LWR environment. To fully understand the mechanisms, the material will be characterized in detail, using techniques such as light optical microscopy (LOM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atom probe tomography (APT). All results will be carefully analyzed in connection with theory.