Assessment of CASMO-4 predictions of the isotopic inventory of high burn-up MOX fuel

The current paper presents an assessment of the depletion model in CASMO-4 based on highly-burnt MOX fuel data from the Programme ARIANE. Isotopic compositions calculated with CASMO-4 for a sample irradiated for 6 cycles in the Swiss PWR Beznau-1 have been compared with experimental data from the PSI and SCK.CEN radio-chemical laboratories. Both a 1-D pin-cell and a 2-D fuel-assembly model have been used, together with detailed and burn-up averaged irradiation histories. The results obtained (a) show that predictions for the most important actinides have errors below 10%, (b) highlight problems with Am and Eu isotopes, and (c) indicate experimental inaccuracies probably linked to the measurement techniques for 129I and some metallic fission products. Additional studies, focused on refined pin-cell treatment, have found that such modeling effects can be significant for the prediction of some actinides, e.g. Pu, Cm and Am. (authors)