Comparison between new thermohydraulic one-channel models and experiments

Five different thermohydraulic one-channel models, COCHA, FRANCESCA, MARMITA, STASWR and THS, were tested bu experimentally checking two-phase flows along a boiling water reactor fuel element. As regards the evolution of the vapor content along the cooling channel, the agreement between all the programs and the measurements is satisfactory for small to middle entrance undercooling in the domain of undercooled boiling. For high undercooling, only the COCHA program gives satisfactory results. For the middle part of the cooling channel, all programs are satisfactory, while in the upper part, especially for increasing outlet vapor contents, the calculated values are generally too low for all programs, and especially for FRANCESCA.