New reactor cavity cooling system having passive safety features using novel shape for HTGRs and VHTRs

Abstract

A new, highly efficient reactor cavity cooling system (RCCS) with passive safety features without a requirement for electricity and mechanical drive is proposed for high temperature gas cooled reactors (HTGRs) and very high temperature reactors (VHTRs). The RCCS design consists of continuous closed regions; one is an ex-reactor pressure vessel (RPV) region and another is a cooling region having heat transfer area to ambient air assumed at 40 ( o C). The RCCS uses a novel shape to efficiently remove the heat released from the RPV with radiation and natural convection. Employing the air as the working fluid and the ambient air as the ultimate heat sink, the new RCCS design strongly reduces the possibility of losing the heat sink for decay heat removal. Therefore, HTGRs and VHTRs adopting the new RCCS design can avoid core melting due to overheating the fuels. The simulation results from a commercial CFD code, STAR-CCM+, show that the temperature distribution of the RCCS is within the temperature limits of the structures, such as the maximum operating temperature of the RPV, 713.15 (K) = 440 ( o C), and the heat released from the RPV could be removed safely, even during a loss of coolant accident (LOCA). When the RCCS can remove 600 (kW) of the rated nominal state even during LOCA, the safety review for building the HTTR could confirm that the temperature distribution of the HTTR is within the temperature limits of the structures to secure structures and fuels after the shutdown because the large heat capacity of the graphite core can absorb heat from the fuel in a short period. Therefore, the capacity of the new RCCS design would be sufficient for decay heat removal.

An Overview of Non-LWR Vessel Cooling Systems for Passive Decay Heat Removal (Technical Letter Final Report)

“…With the same novel RCCS design, Takamatsu et al, 2018 [18] continued to investigate the heat leakage due to the heat conduction through the RCCS wall. In the previous study [16], [17], the reported heat-removal rate was approximately 3 kW/m 2 . Under the assumption that the RCCS wall heat-transfer area can be doubled, a heat flux removed by the RCCS could also be doubled at an increased thermal reactor power level.…”

“…A typical RCCS includes forced water cooling which may become unavailable during accidents. Using the HTTR in Japan as an example, Takamatsu and Hu [16], [17] proposed a new highly efficient reactor cavity cooling system (RCCS) having passive safety features without any requirement of electricity and mechanical drive, Figure 76. The RCCS design consists of two continuous closed regions: one ex-reactor RPV region and another ambient air cooling region.…”

“…To validate the U-bend effect, the authors also performed a simulation using the CFX code, which captured the centrifugal effect of the bend that shifts the maximum of the axial velocity toward the outer wall. Takamatsu and Hu [16], [17] proposed a new highly efficient reactor cavity cooling system (RCCS) having passive safety features without any requirement of electricity and mechanical drive, using the HTTR in Japan as an example. They performed modeling of this new concept using commercial code Star-CCM+, showing that the temperature distribution of the RCCS is within the temperature limits of the structures and the heat released from the RPV could be removed safely even during a loss of coolant accident (LOCA).…”

New reactor cavity cooling system (RCCS) with passive safety features: A comparative methodology between a real RCCS and a scaled-down heat-removal test facility

“…A new RCCS with a novel shape has been proposed for implementation in the HTTR (Takamatsu and Hu, 2015). The RCCS has air as its heat transport medium.…”

“…Thus, this work proposes a new air-cooled RCCS design that does not use the chimney (stack) effect and rely on emergency power generators (Takamatsu and Hu, 2015). The design concept and analysis results are presented in the following sections.…”