Sensitivity study of the unprotected loss-of-flow accident for the EFIT reactor

A sensitivity study has been performed on the Unprotected Loss-Of-Flow accident for a 400 MWth lead-cooled accelerator-driven system. The investigated design data parameters were the core pitch-to-diameter ratio, the core height, and the distance between thermal centres. The examined physical properties were the coolant's conductivity, the fuel's conductivity, the pump halving time and the heat transfer coefficient at the hottest fuel pin. The hottest inner clad temperature has been the reference output variable. The target of the study is to identify the input parameters that produce a stronger impact on the reference output variable. The statistical strategy followed in this study has been a two level fractional factorial design. Each factor (either design datum or physical property) is considered to take only two possible values, lower and upper, which are respectively the lower and upper values of the corresponding ranges. Since all possible combinations of the seven factors are not affordable from a computational point of view, a 'wise' selection of computer runs is done in a stepwise procedure. This procedure allows us to discard non-relevant parameters at early stages and to pay attention to actually important factors. Within the ranges and uncertainties considered, 3 design parameters were identified as the most influential parameters, the core pitch-to-diameter ratio being the most influential one by far. A slightly non-linear influence of this design parameter on the hottest inner clad temperature was uncovered by running the code at a central design point. (authors)