SPECIFIC OF THERMOHYDRAULIC CALCULATIONS OF CORE PRESSURIZED WATER SMALL MODULAR REACTORS IN CASE NATURAL CIRCULATION OF THE COOLANT

The article has been devoted to the study of the main features of pressurized water small modular reactors and an analysis of the influence of the specified features on the thermohydraulic calculation of the core. Special attention is given to small modular reactors with natural circulation of the coolant. It was determined that in the calculation of the core, natural circulation affects the determination of pressure losses and the heat transfer coefficient. When determining pressure losses, the difference between natural and forced coolant circulation lies in the components of pressure losses that need to be considered. In the determination of the heat transfer coefficient, the key factor is the determination of the Nusselt number, where the circulation flow regime affects determining criteria. The issue of determining the critical heat flow using the CHF LOOK UP TABLET method is also considered for the further determination of the departure from nuclear boiling, which serves to assess the safety of operation of the installation. As an example, during the study, a thermohydraulic calculation of the core of the small modular reactor Holtec SMR-160, as one of the advanced representatives of this type of reactor, was performed. As a result of the conducted calculation, the value of pressure losses, the distribution of the heat transfer coefficient and the minimum departure from nuclear boiling were obtained. The study shows the departure from nuclear boiling obtained as a result of the calculation is close to the minimum allowable value, but it is quite acceptable considering the characteristics of natural coolant circulation. However, it necessitates further analysis during the assessment of the reactor facility's safety.