Consideration of Cr-doped UO2 fuel performance for a Fluoride-Cooled High Temperature Reactor concept

This work follows the AGR-like FHR ongoing research that proposes to adopt the British Advanced Gas cooled Reactor (AGR) geometry combined with the molten salt Fluoride-Cooled High Temperature Reactor (FHR) concept. This work presents the new models and material properties implemented in the TRANSURANUS code for Cr-doped UO2 fuel, which is one of the advanced technology fuels considered for light water reactors. For this purpose, we update the mechanistic model for fission gas behaviour in the code by means of a dedicated fission gas diffusion coefficient recently proposed by Cooper et al. on the basis of atomistic scale simulations to take into consideration the impact of the dopant on the point defects that control the fission gas diffusivity in various temperature regions of interest. In a consistent manner, we propose also a modified creep correlation based on the mechanistic model for standard oxide fuels. Furthermore, we analyse the effect of cracking observed in doped fuels subjected to power ramps and take into consideration the limited densification of the high-density fuel reported in the open literature. A subsequent parametric study pointed out the main factors affecting the integral fission gas release rate, which was shown to be a limiting factor in the AGR-like FHR under consideration. Finally, the improved performance of the advanced technology fuel is shown by means of the reduced inner gas pressure at end of life, as well as the reduced pellet cladding mechanical interaction during the postulated operational transient from the open literature for AGRs. As a result, the doped fuel is shown to be able to sustain higher power levels in the AGR-like FHR.