Development of numerical simulation method for molten fuel falling behavior based on detailed two-phase analysis code TPFIT

In order to improve the safety of the BWR, it is required to evaluate the behavior of the plant when a severe accident occurred as seen at the Fukushima Daiichi NPPs. The objective of this study is to develop the evaluation method of the characteristics of molten core jet including the effects of the complicated structures in the BWR lower plenum. In this development, we are developing a simulation method to estimate the behavior of molten core jet falling down to the lower plenum of the BWR based on interface tracking method code TPFIT. In this paper, to validate the applicability of the modified TPFIT to the jet breakup phenomena, numerical results were compared with experimental results in detail. As a results, it was confirmed that the applicability of the modified TPFIT to the interface shape of the tip at initial stage of jet breakup, and atomization occurring at the interfaces. (author)