Modeling of the thermal and mechanical fracture of the SiC layer in TRISO-coated particle fuel

Abstract

In recent, the investigation of High Temperature Gas-cooled Reactor (HTGR) as a high temperature heat source for hydrogen production plants is renovated. The hydrogen is world-widely in the limelight as the next energy carrier and their production methods are also being studied. Besides the advantage of supplying high temperature heat for hydrogen production plant, HTGR has a higher thermal efficiency for electricity generation and lower capital cost than light water reactors. Along with the development of HTGR system, many safety studies of HTGR are being performed. These studies are on how much fission products would be released from the kernel to eventually the environment. In this study, the integrity of Triisotropic (TRISO) coated fuel particle as fuel element of HTGR is investigated as the first step for safety assessment. There are 5 layers in TRISO; a kernel, a buffer layer, an inner pyro-carbon (IPyC), a silicon carbide (SiC), and an outer pyro-carbon (OPyC) layer. Among those barriers, a SiC layer whose thickness is around 25~30$\mu$m plays a major role of retaining fission product (FP) inside the TRISO due to its thermal and chemical toughness. After literature survey on previous models, a new method of stress analysis and failure assessment for SiC layer is developed, and computer code is achieved. Thermal and mechanical stress on SiC layer is calculated considering neutron irradiation. And the failure probability is assessed using Weibull theory. Developed model is evaluated by comparing the result of the model with the previous results. The comparison reveals that this new model is reliable, fast, easy to use, and correspond with other models. This mechanical analysis method can be applied to development of improved fuel particle. Even though the state of the art for TRISO coated fuel particles is well advanced now, development of optimized TRISO fuel is needed to expand the capabilities of HTGR.