Validation of the Porous Medium Heat transfer model of ICARE/CATHARE code to debris bed and bundle "in pile" experiments

Titre du congrès :Eurotherm81 Ville du congrès :Albi Date du congrès :04/06/2007

ICARE/CATHARE code is developed by the "Institut de Radioprotection et de Sûreté Nucléaire" to simulate Nuclear Power Plants behaviour during the course of a severe accidents. The assessment of the heat transfer model in porous medium has been performed against "in pile" experiments performed in ACRR (SNL-USA) and in Phebus reactor. Calculation versus experiment results indicate a good agreement for the thermal behaviour. The heat transfers inside solid debris bed can be well predicted using the Imura-Yagi correlation to calculate the debris bed equivalent thermal conductivity in a wide range of particles size. In the case of the Phebus ICARE2 standard calculations, the bundle was modelled assuming several rings of fuel rods, with heat transfer including radiative phenomena using view factors. An alternative modelling has been used considering the 21 fuel rods as a porous medium with mean particle diameter of 1 cm and a total porosity representative of the fuel bundle inside a cylindrical shroud. With this approach (heat exchanges accounted for with the Imura-Yagi correlation), the radial gradient in the bundle calculated was significantly increased, from a few degrees (with the previous modelling) to about 150/200K at 2273K. This modelling has been recently improved, to account for the heat transfer inside a fuel rod bundle, by a specific module based on an electrical analogy, considering the porous medium as a cluster of true cylinders.