Thermohydraulic Test of a Model of a High-Pressure Mixing Heater

The thermal cycle of the secondary circuit at an NPP with a BREST-OD-300 reactor includes a mixing feed water heater (MFWH) to heat the feedwater at the steam generator’s inlet to a minimum of 340°C (to keep the lead coolant temperature above the lead pour point in the shell side of the steam generator) under all operating conditions. To substantiate the design solutions and finalize the procedure for thermohydraulic design of the MFWH at an operating pressure as high as 15 MPa, NPO CKTI conducted bench tests on an MFWH model in versions with one or two heating stages with water distribution by gravity. The experiments have confirmed that the feedwater can be heated as required in a full-scale heater. Generalization of the experimental data has demonstrated the advantage of the droplet model in describing the thermohydraulic processes in the MFWH over the jet model used to calculate the low-pressure mixing heaters (LPMH). The dependences for calculating the average diameter of water droplets and their fall velocity in a steam environment have been updated. It has been established that, at a pressure of 5–15 MPa, the time to heat droplets depends mainly on their size and the thermal conductivity of water in them. The minimum height of the heating section (the zone of free fall of water droplets in a steam environment) in the MFWH should be 0.7 m, which will provide the subcooling of water to the steam saturation temperature of less than 1°C in a heater with two heating stages.