Study on availability of TRACE code analysis for pool boiling under atmosphere condition

TRACE is an analytical code for calculating thermal hydraulics in nuclear power plants. We conducted sensitivity analyses to understand an applicability and functionality in low pressure and low speed fluid using the TRACE code. Firstly, it was showed that there is a large vibration of a void fraction near a water level in analyses for pool boiling at atmospheric pressure, which may be driven by the liquid phase velocity rather than the gas phase velocity or the liquid-gas interfacial drag. Secondly, in analyses for liquid water-non condensable gas mixed fluid in order to eliminate an influence of phase change, it was proved that the vibration tends to occur when density difference between liquid and gas is large, and that the liquid phase is dragged strongly by the gas phase rising which causes the vibration, furthermore it was showed to be able to suppress the vibration by adjusting friction loss on the liquid phase. (author)