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.