Research on In-pile Performance of TRISO Particle under Multi-physics Field Coupling Condition

The tristructural isotropic (TRISO) coated fuel particle is the most important part for high temperature gas reactors (HTGR) fuel element and dispersed microencapsulation fuel. Multilayered TRISO particle possess excellent irradiation stability, fission production capacity and high temperature resistance. The inpile performance of TRISO particle can affect the safety of reactor. Thus, the simulation of TRISO particle inpile performance is important to forecast the safety of the particle. The performance of TRISO particle was calculated by employing the finite element software. 1/8 sphere characteristic unit was established, the diameter of UO2 kernel was 800 μm, and the thickness of buffer, inner pyrolytic carbon (IPyC) layer, SiC and outer pyrolytic carbon (OPyC) layers were set 100, 30, 40 and 30 μm respectively. Three sides of the characteristic unit were set as symmetry condition, and the temperature was set on the outer side surface of the particle. The effect of the power on the performance of the TRISO particle was studied by defining the power of UO2 kernel. Deformation, temperature gradient and fission product diffusion occur in TRISO particle due to the irradiationthermalmechanical coupling condition during operation process. In order to investigate the inpile performance in HTGR condition, the calculation method was established by setting boundary condition and defining the materials physical model. 3D finite element platform was employed to analyze the inpile performance. The result indicates that kernel temperature increases with power, and the temperature gradient distinction among the TRISO particles with different power is small. The gap occurs between IPyC layer and buffer layer, and the gap size at the end of life decreases with the increase of kernel power. IPyC layer suffers relatively high tensile stress, which may cause the broken of IPyC layer. SiC layer suffers tensile stress when the kernel power reaches high value, and the maximum value of tensile stress increases with the kernel power. The failure probability of SiC layer reaches to 2.2×10-6. SiC layer can resist the diffusion of the fission product such as 110Ag, 90Sr and 137Cs. None of fission product appears out of SiC layer at the end of life which proves the safety of TRISO particles. PyC layers exert pressure on the SiC layer which decreases the tensile stress of SiC layer and the failure probability of SiC layer decreases significantly. As mentioned above, SiC layer possesses low failure probability and the excellent fission production capacity, and TRISO particle has preferable security features.