Analysis on coolant flow in the reactor cavity under external reactor vessel cooling

As part of a study on thermal hydraulic behavior in a reactor cavity under external reactor vessel cooling in the APR 1400, preliminary analyses of the steady state for future large scale experiments using the air injection method and for the actual plant of the APR 1400 have been performed to investigate the coolant circulation mass flow rate between the reactor vessel and the insulation material using the RELAP5/MOD3 computer code. The RELAP5/MOD3 results of the preliminary analysis for the large-scale air injection experiment have shown that the coolant circulation mass flow rate of the air injection case is four times higher than that of the same heat flux boundary condition case, because of the inlet velocity vector of the air, steam condensation, and the density difference between the air and the steam. Increases in the coolant inlet, upper coolant outlet, and lower coolant outlet areas lead to an increase in the coolant circulation mass flow rate. As the lower coolant outlet moves to a lower position, the coolant circulation mass flow rate increases but the increasing rate is gradual. In the preliminary analysis of the APR 1400, the change of the lower coolant outlet to a lower position affects the coolant circulation mass flow rate, but the variation trend is not the same as the air injection experimental case