Fuel performance simulations of TRISO particle geometries derived from XCT

Abstract

The current AGR TRISO fuel specification effectively assumes that the layer thickness variations within a particle do not significantly affect particle performance. However, the limits of this assumption and their relevance for commercial TRISO production have not been established. In this work, a method was developed to generate 3D geometries of TRISO particles, including the spatial variation in layer thickness, from X-ray computed tomography for use in fuel performance modelling. Simulated irradiation of a demonstration particle found SiC hoop stress values peaking at 315 MPa in tension, significantly in excess of those from previous modelling studies with similar particle aspect ratios. Simulations with representative 2D axisymmetric geometries based on the demonstration particle predicted significantly lower stresses for the same simulated irradiation. 2D radial segments extracted with an arbitrarily oriented polar axis under-predicted the maximum SiC hoop stress by 315-400 MPa, while those extracted with the polar axis passing through the point of maximum SiC hoop stress in the 3D model under-predicted the maximum SiC hoop stress by 165-275 MPa. The 2D model produced using existing methods for generating a 2D flat-spot particle under-predicted the maximum SiC hoop stress by 215 MPa. These findings suggest that existing models may underestimate the stress caused by the asphericity of certain TRISO particle morphologies, and that the current AGR specification may not capture all of the geometric factors that contribute to particle failure probability.