The challenges associated with high burnup, high temperature and accelerated irradiation for TRISO-coated particle fuel

Fuel service conditions proposed for the very high temperature reactor will be challenging. All major fuel-related design parameters (burnup, temperature, fast neutron fluence, power density, particle packing fraction) exceed the values that were qualified in the successful German UO2 coated particle fuel development program in the 1980s. Of particular concern are the high burnup and high temperatures expected in the very high temperature reactor. In this paper, the challenges associated with high burnup and high temperature are evaluated quantitatively by examining the performance of the fuel in terms of different known failure mechanisms. Potential design solutions to ameliorate the negative effects of high burnup and high temperature are discussed. Also of concern are the effects of accelerated irradiation on coated fuel that often occur during irradiation testing. These effects are evaluated in this paper and recommendations concerning allowable levels of accelerations are presented.