Computational Substantiation of Model Experiments for Studying the Occurrence Conditions of Condensation-Induced Water Hammers in the Injection Pipeline of a Pressurizer System

Abstract

During normal operation, the upper section of the injection pipeline of the pressurizer system in a reactor plants (RP) with VVER reactors contains steam and subcooled water induced by prescribed operating coolant leakages. To substantiate the safe operation of the RP, experimental studies of the conditions for the initiation of the condensation-induced water hammer (CIWH) are required. Such studies are needed to confirm the absence of CIWH events under steady-state conditions and to estimate potential impact loads during transients. The problem was formulated to perform preliminary calculations of the experiments to substantiate that the results obtained in a downscaled model made to 1 : 2 scale for all dimensions may be transferred to the conditions of a full-scale pipeline. The developed computational model, implemented in the Russian code KORSAR, is described. The paper presents the results of a computational study of thermohydraulic processes in a full-scale injection pipeline after a decrease in the water level in the pressurizer below the spray nozzles during heating of the reactor plant in the presence of the prescribed permanent coolant leakage through the pipeline. Critical flow rates at which steam does not enter the injection pipeline or fills only the section located in the pressurizer have been determined. Variant calculations were performed of a scaled pipeline with different values of the permanent leakage flowrate; flow rates were set as required to ensure similarity in terms of Reynolds, Mach, Froude, and homochronicity numbers. When comparing predictions for the full-scale and downscaled pipelines, the similarity was demonstrated of thermohydraulic processes at a model flowrate of permanent leakages, selected to obtain the same of Froude numbers, and the full-scale values of the steam pressure and the incoming water temperature.