Effect of power excursion on the thermal characteristics of VVER-1200 reactor

Abstract

This work involved performing a thermal hydraulics calculation on VVER-1200 reactor. In this calculation, the thermal power of the reactor was varied in steps from 100 to 180 % power to determine its influence on the thermal-hydraulics parameters, especially the points of onset of nucleate boiling (ONB) and the onset of significant void (OSV) which is also referred to as point of net vapor generation (NVG). The exit coolant temperature, predicted coolant temperature at ONB, predicted coolant temperature at OSV, maximum heat flux, variation of linear heat generation rate along the heat channel, minimum point of critical heat flux (CHF) and the corresponding minimum departure from nucleate boiling ratio (MDNBR) were all noted for each power step. The result showed that at about 130 % power, the descending predicted coolant temperature at ONB crossed below the ascending exit coolant temperature, indicating an ONB, furthermore, at about 165 % power, the descending predicted coolant temperature at OSV crossed below the ascending exit coolant temperature, indicating an OSV. In this calculation, there were no variation in any other parameter of the reactor and the inlet enthalpy remained constant throughout the step variation of power.