Preliminary experimental validation of multi-loop natural circulation model based on RELAP5/SCDAPSIM/MOD 4.0

Passive safety systems mostly working on the principles of natural circulation are given much priority in increasing the reliability of reactors’ inherent safety features. In view of this, many researchers carry out numerical and experimental studies in single-loop natural circulation model to study the natural circulation behaviors. In the present study, the experimental loop consists of three loops; two of which operate on natural circulation while the third on forced circulation. The experimental loop has successfully established natural circulation under different pressure conditions and the experimental results obtained are compared with those of the RELAP5 code simulation for validating the multi-loop natural circulation RELAP5 model. Single-phase natural circulation flow rates and temperatures at various locations give reasonable agreements between the code and the experiment. The results show that height difference between the heat source and the heat sink is more influential than system pressure in increasing natural circulation flow rate. The system pressure maintains the stability of the system, thus keeping it within single-phase region with increase in heat. In addition, temperature difference in the first loop being higher than that of the second loop at all pressures, did not influence the first loop flow rate to be higher due to the advantage of height difference in the second loop. However, extending the conditions beyond those of the experiment, that is higher power and system pressure, the first loop flow rate increased more than that of the second loop as predicted by the RELAP5 code.