Characteristics analysis of the natural circulation circuit with two-loop under rolling motion conditions

In the design of off-shore small nuclear reactor, it is necessary to consider the effect of ocean motion conditions on thermal and hydraulic characteristics. In this paper, additional inertia forces models are established, and the model is applied to the RELAP/SCDAP program, the system analysis program for ocean motion is obtained. The thermal and hydraulic characteristics of natural circulation loop under swing condition are analyzed by using modified RELAP program. The results show that the average flow rate under rolling conditions is less than that of the stationary conditions. The loop flow fluctuation lags behind the rolling motion and the cooling water temperature fluctuation lags behind the loop flow fluctuation. The fluctuation amplitude of the natural flow rate will increase as the rolling amplitude or frequency increases. When the rolling motion is severe enough, back-flow may occur in the loops. Increasing the heating power or increasing the height difference between cold and heat sources can increase the driving force of natural circulation of the system and reduce the influence of rolling motion on natural circulation. (authors)