Test Article Development to Support Materials Surveillance Technology for High-Temperature Reactors

Operational environments in generation IV reactors involve corrosive and irradiative conditions at elevated temperatures. Typical reactor operations consist of transients which imposes cyclic loads on reactor components. These cyclic loads, combined with corrosive and irradiative environments, result in synergistic degradation of component materials. However, limited data exists on the coupled damage effects on materials for reactor environments. While the surrogate material surveillance concept has been used in Light Water Reactors to assess irradiation damage, existing material surveillance technologies are not suitable for in-situ monitoring of coupled material degradation. Materials surveillance program focuses on material degradation management and estimating of remaining life of reactor components through surveillance test article. This paper presents the design and analysis methodology of a bi-metal surveillance test article, which uses difference in thermal expansion coefficient between two metals to induce in-situ cyclic loads. In this paper, Alloy 617 and stainless steel 316H are used, where A617 serves as the driver to induce thermal mismatch, while 316H is used as material to surveil. The design approach followed a two-step procedure; the first step involved simplified analysis using four-bar model to determine initial test article dimensions, and the second step conducted detailed analysis using finite element model to refine local geometries. The surveillance test articles were fabricated using welded designs. These test articles were tested by applying temperature cycles with peak temperature of 700C through tabletop furnace. The strain history was measured using Digital Image Correlation technique and compared against the simulated response. The results, conclusions and directions for future work are discussed in the paper.