Analysis of the PHEBUS FPT3 core degradation using severe accidents codes ICARE/CATHARE, ATHLET-CD, MELCOR)

Titre du congrès :American Nuclear Society : 2008 Annual Meeting
Ville du congrès :Anaheim
Date du congrès :08/06/2008

The aim of the Phebus FP experimental program is to study the degradation phenomena and the behaviour of the fission products (FP) released in the reactor coolant system and the containment building. The program consists of four in-pile bundle tests (FPT0, FPT1, FPT2 and FPT3), performed under different conditions concerning the thermal hydraulics and the environment of fuel rods, in particular the amount of steam (strongly or weakly oxidizing atmosphere). The last test of this program, FPT3, has been performed in November 2004 in Cadarache. During the FPT3 experiment, boron carbide was used as absorber material for the first time instead of Ag-In-Cd, which was used in all the previous tests. Boron carbide is used in nuclear power plants like western type PWR, EPR, BWR and VVER, which shows the importance to assess its effects on the main degradation phenomena, as well as the gas release, and the impact on the fission products behaviour. This paper is focused on the FPT3 preliminary analyses, and in particular on the B4C control rod behaviour using Severe Accident Codes, i.e. ATHLET-CD, ICARE/CATHARE, MELCOR. The first part deals with an overview of the experimental results (boundary conditions, temperature evolutions, hydrogen and carbon compounds releases coming from the oxidation of the zircaloy claddings and the B4C absorber, as well as bundle degradation). The second part proposes a summary of the code modelling used in the different code applications, in particular those regarding the absorber rod degradation and oxidation process. The third part summarizes the code results with comparisons regarding some important experimental parameters (thermal behaviour, gas releases (H2, CO, CO2) and bundle degradation). The conclusion will be focused on the preliminary synthesis of the Severe Accident Code capabilities to simulate the control rod behaviour in a fuel rod assembly during the course of severe accident transient