This paper deals with the modeling of the degradation of a B4C control rod during a PWR severe accident. In the first part of the paper, the modeling of this degradation as implemented in the ICARE/CATHARE code, developed and used at IRSN, is described. It is stressed on the modeling of the B4C oxidation process, and, especially on the justification of the simplifying assumptions as well as on the preliminary validation of the model. On this purpose, the model is assessed against separate effect tests and against the integral Quench-09 test. The validation work carried out up to now, has shown that the model considered here is quite efficient to compute the B4C oxidation taking into account the main overall parameters, namely, the temperature, the steam partial pressure and the total pressure.
Moreover, in the second part of the paper, an illustration of the operability of the modelling of the whole control rod degradation is provided, by means of the pre-test calculation of the PHEBUS FPT3 test. The degradation process, as modelled in the ICARE/CATHARE code is precisely described and analysed in order to assess the physics consistency in the results. In particular, this calculation demonstrated the pertinence of the coupling between the B4C control rod degradation, the Zircaloy claddings oxidation and the thermalhydraulics modelling. Finally, it can be kept in mind, regarding the FPT3 test, that according to the calculation, the expected amount of B4C oxidized is more than half of the initial inventory, whereas a forth is dissolved and relocated.