In this research, when the hydrothermal behavior at the time of LOCA in PWRs is forecast with high accuracy by the optimal forecast code based on a two-fluid model, there are some problems in the accuracy of forecast of low velocity two-phase flow, therefore, the subjects related to it were studied. The subjects are the forecast using the multi-dimensional optimal forecast code of the heat transfer acceleration phenomena in high power output fuel assemblies originating in the radial power distribution in a core in the reflooding period at the time of LOCA, the evaluation of the applicability of the hydrothermal model in a core in reflooding period which was developed for 15 x 15 type fuel assemblies to 17 x 17 type fuel assemblies, the grasping of the mechanism of opposite flow limiting phenomena in hot leg, the elucidation of the scale effect of channels and the development of a model which is applicable up to actual reactor scale. The studies carried out on these subjects and the conclusions of respective studies are reported. (K.I.) 79 refs.
Ohnuki, Akira 
- Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment