Simulating sodium pool natural circulation in rvacs operation using CFD

Reactor vessel auxiliary cooling system (RVACS) has been developed to make diverse safety system for sodiumcooled fast reactor (SFR). In the loss of flow (LOF) accident condition, decay heat from the core is transferred to the reactor vessel by natural circulation inside of the sodium pool. The reactor vessel transfers its heat to the containment vessel by the conduction and radiation through the gap between the reactor vessel and the containment. Finally, the containment vessel releases its heat to the air flow from the atmosphere, which is the ultimate heat sink, by means of the RVACS. Although natural circulation of sodium is an important phenomenon because it determines the sodium boiling, it has not been sufficiently researched for the case of the RVACS. Therefore, in this study, natural circulation of the sodium in the LOF condition was analyzed experimentally to evaluate the maximum sodium temperature in the LOF. Water was used as a simulant for the sodium with the reduced scale. The experimental apparatus was scaled down about 1/25 by length, focusing on the modified Boussinesq number which represents the ratio of heat transfer by the natural circulation to the conduction. Because the modified Boussinesq number was the same with that of the actual reactor, overall temperature distribution in scale-downed apparatus with water would be similar to that of the sodium pool. Difference between the maximum and the minimum temperature of the water pool in the experiment was about 0.7oC, which corresponds to 5.1oC temperature difference of the sodium in LOF condition of an actual reactor with the operation of the RVACS. By comparing temperature difference