One of the aims of the PHEBUS FPT3 test was to investigate the effect of boron carbide on fuel degradation in low steam flow rate situation, leading to steam starvation conditions during cladding oxidation phase.
Starting the calculations with the initial data set which served to the test definition, it has been shown that in looking closely to the experimental outputs, subsequent modifications of the initial data set can lead to very satisfying results with ICARE2 V3mod1.4, using mainly the new recommended default options.
The validation process has been decomposed in three parts:
First, the study of the thermal results. In order to better reproduce the temperature evolutions given by all the available TC, an adjustment of the power injected in the bundle has been mandatory.
Then, the study of the gas release due to oxidation processes. Using the “best-fitted” correlation for the oxidation of the zircaloy claddings gives very satisfying results if the inner side oxidation of the failed claddings is not allowed, in accordance with the b.e. calculations of the PHEBUS test FPT2.
For the oxidation of the B4C, 65% of the B4C inventory have been oxidised at the end of the test, leading to an amount of hydrogen of 15% of the whole H2 content.
Finally, the code fails to calculate any relevant degradation of the bundle at the end of the test. Fuel dissolution seems to be due to interactions between (B, C, SS) mixtures and fuel rods which are not yet modelled in the code.
Further investigations are needed and will be done in the frame of the Source Term Program with the BECARRE separate-effect-tests performed by IRSN.