A model of water thermal-hydraulics during depressurization of a vessel filled with water under saturation conditions

This paper discusses results obtained during the simulation of water dynamics and heat transfer during sudden depressurization of a vessel filled with water under the saturation conditions. Validated prediction of the thermal-hydraulics during the depressurization is important by virtue of wide implementation of pressurized vessels in chemical and power engineering. Particular emphasis was put on the implementation of the vessel in the field of steam storage and as the reactor pressure vessel of the boiling water reactor design. In both cases, the vessel is filled up to a certain level with saturated liquid water. The rest of the vessel is occupied by saturated steam. In case of the pressure decrease e.g. due to discharging of the steam from the vessel or due to the loss of coolant accident in a nuclear power plant, the liquid water evaporates abruptly, being a reason, thereby, of strong transients in the vessel. These transients and the sudden emergence of void in the region occupied at the beginning by liquid, cause elevation of the two-phase mixture. Prediction of this elevation - called the water level swell - is important from the view point of safe operation of the device. In this work, a model calculating liquid water collapse level and two-phase level swell is presented and validated against experimental data. The comparison of the model with the reference shows a good agreement.