Effects of the mesostructures and irradiation conditions on the thermo-mechanical coupling behaviors in LWR-used fully ceramic-microencapsulated fuel pellets

Abstract

Fully ceramic microencapsulated (FCMTM) fuels, proposed as an accident tolerant fuel in light water reactors (LWRs), consists of tri-structural isotropic (TRISO) fuel particles and silicon-carbide ceramic matrix. To ensure the in-pile service safety with improving the fuel economy simultaneously, FCM fuels should be optimally designed. The effects of TRISO particle volume fraction, particle distribution pattern and irradiation conditions on the thermal–mechanical behavior in FCM fuel pellets are investigated via the self-developed code TMAIMF(Thermo-mechanical Analysis of Inert Matrix Fuels). The evolution results of temperature, deformation and stress fields with the increase of burnup indicates that (1) when the particle volume fraction increases from ∼ 15 % to ∼ 43 %, the central temperature gives a rise of ∼ 10 % at 19 % FIMA (fissions per initial heavy metal atoms); the radial size increment will be shortened; while, the maximum tensile stresses of each coating layer of the TRISO particles are slightly varied; (2) the results of temperature, deformation and maximum tensile stress have weak correlations with the fuel particle distribution pattern; (3) the integrity of FCM pellets can be maintained at high fission rate conditions and extended burnup levels; (4) the finite element models with the axial displacement constrained are representative, which can obtain more conservative analysis results than the free-end models. The numerical simulation results demonstrate that the TRISO-particle-based fuel pellets could be flexibly optimized to satisfy the demands of economy and safety.

Keywords

• FCM fuel
• Dispersion nuclear fuel
• TRISO particle
• Thermal–mechanical coupling behavior
• Optimization