Improving the RELAP5 code modeling of the siphon break effect in a pool type research reactor

Abstract

The pool water of a research reactor is used for emergency cooling of the reactor core. Siphon breakers are installed in the lines of the Core Cooling System to stop the loss of water from the pool due to the siphon effect during an accident involving piping ruptures. Previous studies discuss the effectiveness of siphon breakers based on the air inlet area and question the ability of one-dimensional thermo-hydraulic codes to model the siphon break devices. By means of comparison with experimental results, this work demonstrates the ability of the RELAP5/MOD3.3 code to model the performance of the siphon breaker. There was satisfactory agreement between the numerical and experimental results, showing that, as the air intake areas of the siphons decrease, their effectiveness also decreases, resulting in greater drainage of the pool water. For smaller air intake areas, the RELAP5/MOD3.3 code showed conservative results, overestimating the reactor pool water losses.