Modelling nuclear fuel behaviour with TAF-ID: Calculations on test VERDON-1, representative of a nuclear severe accident
Résumé
The chemical behaviour of the main chemical elements present in a PWR irradiated fuel sample (fission products Ba, Ce, Cs, Gd, I, La, Mo, Nd, Np, O, Pd, Pu, Rh, Ru, Sr, Tc, Te, UO2 fuel, and Zr clad) submitted to a nuclear severe accident type sequence (VERDON-1 test) has been investigated by thermodynamic calculations using the TAF-ID database. Particular emphasis has been placed on to the release of the fission products Ba, Cs, Mo, and Zr, and the interactions between the sample cladding and the UO2 matrix. Calculation results have been compared to experimental observations completed during (instantaneous release of fission products) and after (final chemical state of elements in the sample) the VERDON-1 experiment. TAF-ID calculations have described accurately the melting of the sample following the formation of a mixed (U,Zr)O2-x phase due to the interaction between the fuel and the cladding. The instantaneous released fractions observed for Ba and Mo during the test have been also explained as a function of the test atmosphere and temperature.