A new RCCS (Reactor Cavity Cooling System) using a novel shape is proposed to be implemented in HTTR (High Temperature engineering Test Reactor). The RCCS has air as the heat transport medium. The reactor cavity of the RCCS is enlarged, including two regions, such as an ex-RPV (Reactor Pressure Vessel) region and a cooling region attached to the top of the RPV region.
From the RPV, it flows upward to the cooling region, the heat transfer area of which is large, and the air is cooled by exchanging heat with the ambient air. The large temperature difference between the coolant and ambient air facilitates heat removal.
The cooling regions feature two or three heat transfer areas, such as the interior, outside and top surfaces. Moreover, the heat transfer areas can easily be increased by machining surfaces or adding fins; therefore, the height of the RCCS can be decreased despite the small heat transfer coefficient on the RCCS outer surface without the chimney effect or the stack effect.
The simulation results show that the temperature distribution of the RCCS could be lower than the maximum temperature limits of the structures, such as the maximum operating temperature of the RPV, 713.15 (K) = 440 (oC), and that the heat released from the RPV could be safely removed. Thus, the capacity of the RCCS design is sufficient for decay heat removal.
The RCCS can passively remove 800 (kW) in the HTTR. The 800 (kW) discharged from the RPV is equivalent to 2.67 (%) of the decay heat of the rated operation of 30 (MW) at the elapsed time of 40 – 100 (sec) after reactor shutdown. It is therefore confirmed that the decay heat and the stored heat (in the fuel and the large amount of graphite in the core) of the HTTR after reactor shutdown can be removed by the proposed RCCS for a long time.
Moreover, when the RCCS can remove 600 (kW) smaller than 800 (kW) of the rated nominal state even during LOCA (Loss-of-coolant accident), 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.
Featured Authors information
In 1997, Dr. Takamatsu began doctoral studies in cryogenic engineering of Helium at Kyusyu University in Japan. His dissertation was completed in 2000, and the Ph.D. After that, he joined at the high temperature engineering test reactor (HTTR) built by Japan Atomic Energy Agency (JAEA).
He is a Nuclear Engineer and has experiences with operation and maintenance for 4 years, as well as reactor kinetics, reactor dynamics, reactor instrumentation and thermal-hydraulics for 12 years at the HTTR.
Figure legend: Temperature distribution of a new RCCS using a novel shape having passive safety features.
Kuniyoshi Takamatsu1, Rui Hu2. Annals of Nuclear Energy, Volume 77, March 2015, Pages 165-171.[expand title=”Show Affiliations”]
- Japan Atomic Energy Agency, 4002 Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki-ken 311-1393, Japan
- Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, United States
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 (°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 (°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.