Multi-pin ballooning during LOCA transient: A three-dimensional analysis

Computational predictions concerning ballooning of multiple fuel pins during a loss of coolant accident (LOCA) with a final reflood phase are now more than ever of interest amongst the design basis accidents in pressurized water reactors (PWR). Difficulties for such studies are twofold. Firstly, modeling has to take into account many coupled phenomena as thermics (heat generation, radiation, convection and conduction), hydraulics (multi-dimensional one-to-three phase flow and shrinkage) and mechanics (thermal expansion, creep and embrittlement) but also chemistry (oxidation, hydriding, etc.). Secondly, there exists only a few experimental investigations to validate the complex coupled modeling enabling such predictions. This paper deals with the new computational 3D tool named DRACCAR which models the deformations of rods within a bundle (from one rod to a full fuel assembly) during LOCA transients including the water reflood phase.