Dynamic ballooning analysis of a generic PWR fuel assembly using the multi-rod coupled MATARE code

•Ballooning in PWR fuel assembly during reflooding phase was analysed with MATARE code.•Different fuel burn-ups, burnable poisons, guide thimbles inhibit coherent ballooning.•The levels of blockage observed do not impair the coolability of the fuel assembly.•The code is capable to simulate the deformation of wide regions of a fuel assembly.•MATARE results on PWR fuel assembly are in agreement with the experimental data.

A multi-rod representation of different zones of a typical PWR fuel assembly under post-LOCA reflooding conditions was analysed with the MATARE code. The MATARE (MAbel-TAlink-RElap) code is a multi-pin deformation analysis code created through the dynamic coupling between the thermal-hydraulic code RELAP5 and multiple instances of the single-pin thermal-mechanics code MABEL. The main aim is to predict the behaviour of the fuel rods under conditions leading to clad ballooning, and to investigate whether plausible inter-pin inhomogeneities inhibit coherent ballooning and consequent flow passage blockage. The inter-pin differences analysed included different fuel burn-ups, the presence of burnable poisons (gadolinium oxide), and the existence of the control rod guide thimbles. Three different fuel assembly zones were analysed.