2D(r,θ) Simulations of the HBC-4 Power-to-Melt Experiment with the Fuel Performance Code ALCYONE

Abstract

This paper presents 2D(r, θ ) simulations of the HBC-4 power-to-melt experiment performed with the fuel performance code ALCYONE. The HBC-4 experiment is one of the two test cases selected for the simulation exercise on past fuel melting experiments of the Power to Melt and Maneuverability (P2M) project. The ramp terminal level (RTL) at peak power node (PPN) has been estimated at 66 kW·m−1 by gamma scanning and 70 kW·m−1 based on online measurements of thermal fluxes. The fuel burnup at PPN was close to 60 GWd/tU−1. The cladding failed during the short holding time at a RTL of 40 s. Fuel melting took place at the pellet center, and in particular, in front of clad cracks. In this paper, simulations of the HBC-4 power-to-melt experiment are performed using an updated version of the 2D(r, θ ) scheme of ALCYONE where half of the fuel pellet is described. This configuration allows for the modeling of clad failure by iodine stress corrosion cracking and of its consequences on fuel pellet deformation. The modeling of fuel melting relies on thermochemical equilibrium calculations performed with the OpenCalphad Gibbs Energy Minimizer and the Thermodynamics of Advanced Fuels International Database. The simulation without clad failure indicates that the solidus is reached during the HBC-4 experiment but not the liquidus. The simulation with clad failure leads to a small increase in the fuel temperature that is sufficient to reach the liquidus at the pellet center, in agreement with postirradiation examination (PIE). The impact of water ingress in the rod and vaporization at the pellet surface is discussed, showing that it could explain the pronounced swelling of the fuel pellet reported from the PIE.