An analysis of a contact between a kernel and a buffer of a TRISO-coated fuel particle

The kernel of a TRISO-coated fuel particle in a high temperature gas-cooled reactor (HTGR) starts to push the buffer and the coating layers of the particle outward when it swells with a neutron irradiation and contacts with the buffer. A contact model in which the buffer was assumed to be a spring was devised to explicitly express the contact pressure between a kernel and coating layers. Through mathematical modeling, a system of the first-order differential equations was constituted in order to calculate the stress and displacements of the coating layers of a TRISO particle. A kernel and coatings mechanical interactions (KCMI) analysis method was set up according to the open and closed states. The buffer was assumed to experience an elastic deformation and a thermal expansion in the KCMI analysis method. A computer program for the KCMI analysis method was created and inserted into a HTGR fuel performance analysis code COPA developed at the Korea Atomic Energy Research Institute (KAERI). For the open and closed contact states, the maximum tangential stresses of the coating layer were calculated and compared. The gas and contact pressures, kernel displacement, kernel swelling, and thermal expansion of the kernel and buffer were also calculated. (authors)