Previously, a reactor cavity cooling system (RCCS) has been reported with passive safety features comprising of two continuous closed regions, namely an ex-reactor pressure vessel region and cooling region with a heat-transfer surface to ambient air. The novel shape of the RCCS allows it to efficiently remove heat released from the reactor pressure vessel (RPV) via thermal radiation and natural convection. The RCCS design significantly reduces the possibility of losing the heat sink for decay heat-removal during nuclear accidents including a station blackout by employing air as a working fluid and ambient air as ultimate heat sink. RCCS has the potential to stably and passively remove heat released from the RPV and decay heat following a reactor shutdown. The RCCS achieved a heat-removal rate of approximately 3 kW/m2. On the contrary, the heat fluxes from the RPV surface of the high temperature engineering test reactor and commercial high temperature gas-cooled reactors are 1.23–2.46 kW/m2 and approximately 3.0 kW/m2, respectively. In the previous report, the authors changed the adiabatic boundary conditions and considered the heat dissipation effect from the RPV region to ground through the RCCS wall via heat conduction; therefore, the authors could improve the system's heat-removal capability to increase its thermal reactor power level. Moreover, considering the possibilities for doubling the heat-transfer areas and increasing the emissivities, heat flux removed by the RCCS could potentially reach 7.0 kW/m2. Herein, the authors conduct a comparative methodology between an actual RCCS and a downscaled heat-removal test facility.
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