Thermo-mechanical response of LMFBR fuel elements using EAC with emphasis on the TRANSURANUS module

The European Accident Code EAC is a multichannel modular computer code for simulating the initiation phase of low-probability whole-core accidents in LMFBRs, i.e. loss of flow (LOF) or transient overpower (TOP) events. The code presents itself as an informatic structure into which various stand-alone modules from the Joint Research Centre and from other laboratories have been included. Three phenomena mainly control the neutronic behaviour of the whole core, namely fuel pin behaviour, sodium thermohydraulics and fuel motion. Fuel behaviour, in particular, is computed by means of the TRANSURANUS program which is an advanced tool for fuel performance analysis, extensively used in both the LWR and the LMFBR areas. Because of the modular structure of EAC, the computation of these interacting phenomena proceeds necessarily in a sequential manner, not only channel-wise but also time-wise. The purpose of this paper is to illustrate how the EAC approach remedies the usual drawbacks of a weak coupling, in particular as far as the strong interaction between fuel pin and coolant channel is concerned. Numerical results will be presented on the basis of an international benchmark exercise dedicated to a hypothetical LOF accident in the irradiated core of the fictitious 700 MWe EUROPE reactor. (orig.)