IRSN R and D Studies on Fuel Behaviour under LOCA Conditions

The most important safety principle in case of a loss of coolant accident (LOCA) is to preserve the long term coolability of the core. The associated safety requirements are to ensure the resistance of the fuel rods upon quench and post-quench loads and to maintain a coolable geometry in the core. These requirements are formalised in safety criteria, associated with limiting values, mainly expressed through a maximum cladding temperature (PCT) and an equivalent cladding reacted ratio (ECR) with the aim of ensuring a residual ductility of the cladding. In order to prepare acceptance criteria reassessment, IRSN recently conducted an extensive State-of-the-art review relative to fuel behaviour under LOCA conditions. The main pending questions can be summarised under three topics: i) loss of cladding integrity upon quench and post-quench loads, ii) relocation of fuel fragments, iii) flow blockage and core coolability. To address these issues, IRSN is conducting a R and D programme that consists in experiments and code developments. (author)