Application of the Porous Medium Heat transfer model of ICARE/CATHARE code against debris bed and “bundle” “ experiments

ICARE/CATHARE code is developed by the “Institut d e Radioprotection et de Sûreté Nucléaire” to simula te Nuclear Reactor behaviour during the course of a Loss of Co oling accident up to the core melting. The assessme nt of the heat transfer model in porous medium has been performed against experim ents performed in ACRR (SNL-USA) and in Phebus reac tors (at Cadarache – France). Calculation versus experiment results indi cate a good agreement for the thermal behaviour. Th e heat transfers inside solid debris bed can be well predicted using the Imura-Ya gi correlation to calculate the debris bed equivale nt thermal conductivity in a wide range of particles size. In the case of “Rod l ike geometry” calculations, the fuel rod assembly was modelled assuming several rings of fuel rods, with heat transfer including ra di tive phenomena using view factors between rods. An alternative modelling has been used considering the fuel rods as a porous med iu with with pure UO2 spherical particles of 1 cm diameter and a total porosity representative of the fuel bundle inside a cylindrical shroud. With this approach (heat excha nges accounted for with the Imura-Yagi correlation), the radial gradient calcul ated in a small bundle was significantly increased, from a few degrees (with the previous modelling) to about 150/200K at 2273K. Thi s modelling has been recently improved, to account for the heat transfer inside a fuel rod bundle, by a specific model based on an electrical analogy, considering the porous medium a s a cluster of true cylinders.