Heat Transfer Distribution for Reactor Cavity Cooling System Riser Considering Thermal Conduction

The reactor cavity cooling system (RCCS) is the safety grade system for a very high temperature reactor (VHTR). The main role of the RCCS is the heat removal from the reactor vessel. The verification of the performance of the passive RCCS is a key objective for the construction of demonstration plant. Korea Atomic Energy Research Institute (KAERI) is considering the air-cooled RCCS under natural convection operation for a PMR200. Bae et al. studied scaling of PMR200 RCCS prior to the experimental verification of the RCCS. The cavity radiation number and temperature ratio number were selected as controlling non-dimensional group. The heat transfer in the riser is one of the key phenomena to predict the performance of the prototype RCCS. The riser absorbs heat from the reactor vessel, through radiative heat transfer, and from the reactor cavity, through convective heat transfer. The absorbed heat is removed by convective heat transfer in the riser. CFD results showed that thermal conduction through the RCCS riser was not negligible. Because the material of the riser duct was carbon steel, the thermal conduction effect was comparable even with a small duct thickness to the convective heat transfer by air flow. It is strongly recommended that the heat transfer in RCCS should go with consideration on the thermal conduction of the RCCS riser duct