Analysis of the MT-3 clad ballooning reflood test using the multi-rod coupled MATARE code

If PWR fuel rods balloon in a co-located fashion following a large break LOCA, it is possible that an un-coolable region could be formed. The MT-3 test was one of the few large-scale experiments performed to investigate this. In this paper we report the analysis of this experiment using a novel combined thermal-hydraulic and structural mechanics model, able to model multiple distinct rods in a coupled fashion. The sensitivity of the behaviour to (in particular) the channel droplet distribution makes a full ‘first principles’ validation impractical, but good agreement is achieved between observed and predicted blockage fractions, and the observed incoherence of ballooning is reproduced well.