Assessment of Pre-irradiation SiC CMC Joint Performance in Representative Cladding Geometries

Silicon carbide fiber reinforced, silicon carbide matrix composites (SiC-SiC) offer strength at high temperatures, corrosion resistance, and stability during irradiation, and are being developed by General Atomics as cladding for accident tolerant fuel (ATF) applications and advanced reactor concepts. Advanced joining techniques capable of withstanding harsh reactor environments are key to enable GA's SiGA^tm SiC-SiC composite. The objective of this work is to obtain joint-specific material properties for assemblies in representative planar and cladding geometries that will allow for the generation of a material properties database and more accurate simulation of SiC joint behavior across a range of temperatures and irradiation conditions. To support this, three different joint formulations are being assessed for mechanical and thermal performance pre and post irradiation in the High Flux Isotope Reactor (HIFR) at ORNL. GA has previously identified its hybrid SiC (HSiC) joint as the most promising and best suited joining approach for cladding applications [1]. Additionally, oxide and trans-eutectic phase (TEP) joints are being investigated to make the material property database more comprehensive as these joints have previously shown strength resilience under irradiation in planar geometries [2]. The thermal and mechanical data obtained in this work will address vital knowledge gaps, enabling more accurate modeling of joints in SiC-based components for accelerated material qualification. The scope of work presented here focuses on the mechanical and thermal performance of the joint material prior to irradiation in HFIR. Endplug push-out (EPPO) testing to determine joint strength in tube geometries, and shear strength testing for planar geometries have provided a benchmark for pre-irradiation mechanical performance. These results show that all three selected joint methodologies result in cladding joints capable of withstanding the expected joint stresses in a LWR reactor environment [3]. This has been accompanied by He leak testing of the joint regions on tube specimens to assess the suitability of each joint methodology for cladding applications. Here, only the HSiC formulation consistently met critical leak rate requirements suggesting that other joining strategies require additional development. Finally, pre-irradiation thermal testing has been completed to establish a baseline for comparison after irradiation. Subsequent irradiation of these joints types in HFIR will provide further detail on joint material properties and their appropriateness for nuclear applications.