Effects of the key parameters of TRISO particle buffer layer on in-pile thermo-mechanical behavior in FCM fuel pellets

Abstract TRISO particle buffer layer is a critical functional part in FCM fuels. A skeleton stress model for buffer layer is proposed, dependent on the current porosity, the maximum macroscale tensile stress and the pore pressure, which is incorporated into the self-developed code of Thermo-mechanical Analysis of Inert Matrix Fuels (TMAIMF). Deeper insight is gained from the simulated thermo-mechanical variables in FCM fuel pellets, and the effects of buffer layer porosity and creep coefficient are investigated. This research indicates that (1) the macroscale maximum tensile stresses in the particle coating layers of buffer, IPyC and OPyC as well as the SiC matrix exhibit a significant decrease except those in SiC coating layers, when the initial porosity and creep coefficient of buffer layer increase; (2) with a rise of PyC creep coefficient, the maximum tensile stress of buffer layer skeleton and the buffer/IPyC interfacial tensile stresses will decrease heavily under irradiation conditions of LWRs, which gives an explanation for the no-cracking phenomenon in irradiated FCM surrogate pellets. Optimization of the microstructure of buffer layer and the creep performance of PyC materials might make the integrity and high heat transfer capability of FCM fuels maintained during a long irradiation cycle in LWRs.