Improvement of heat-removal capability using heat conduction on a novel reactor cavity cooling system (RCCS) design with passive safety features through radiation and natural convection

A previously-reported concept of reactor cavity cooling system (RCCS) with passive safety features consists of two continuous closed regions: an ex-reactor pressure vessel region and a cooling region with a heat-transfer surface to ambient air. The RCCS uses a novel shape to efficiently remove the heat released from the reactor pressure vessel (RPV) through thermal radiation and natural convection. Employing air as a working fluid and ambient air as an ultimate heat sink, the novel RCCS design strongly reduces the possibility of losing the heat sink for decay-heat-removal during nuclear accidents including a station blackout. The RCCS could stably and passively remove the heat released from the RPV and the decay heat after reactor shutdown. The previously-reported heat-removal rate of the RCCS was approximately 3 (kW/m2). The heat flux from the RPV surface of the High Temperature engineering Test Reactor (HTTR) is almost in the same range; 1.23-2.46 (kW/m2). In this paper, the authors address an improvement of heat-removal capability by considering potential of heat leakage due to heat conduction through the RCCS wall aimed at increasing a thermal reactor power level. Under the assumption of doubling the RCCS wall heat transfer area, a heat-flux removed by the RCCS could be doubled, such as approximately 6.2 (kW/m2).