Silicon dissolution and morphology modification of NITE SiC/SiC claddings in pressurized flowing water under neutron irradiation

Claddings of silicon carbide (SiC)-based composites for light water reactors are expected to be a key component of accident-tolerant fuel technology for enhancing nuclear safety. Muroran Institute of Technology has developed technologies for producing SiC/SiC claddings by a nano-infiltration and transient eutectic phase (NITE) method in the MEXT-funded project named “SCARLET.” As part of this program, neutron irradiation experiments were performed in a pressurized cooling water flow at the Halden Reactor in Norway. During the irradiation experiments, silicon dissolution from the SiC/SiC specimens was measured, and the relationship among the dissolution, properties of SiC/SiC claddings and reactor operating conditions was studied. The morphology of the SiC/SiC claddings was not significantly modified by the irradiation experiments; however, the joint parts were corroded and suffered damage. Observation of irradiated specimens and a rough estimate of the SiC dissolution rate under each irradiation condition indicated that the NITE SiC/SiC composite has potential as a structural material for pressurized water reactors (PWRs) that are operated under hydrogen water chemistry conditions. It is also shown that chemical-vapor-deposited (CVD)-SiC and other coating techniques are necessary for the realization of SiC reactor core. Joining and coating technologies were also tested, but appropriate methods could not be identified experimentally; thus, joining and coating techniques should be further developed.