Main Features of the Reactor Cavity Cooling System for the Framatome SC HTGR

The ability of modular high temperature reactor (HTR) concepts such as the SC HTGR to maintain acceptable core temperatures using passive heat removal without active systems, without electrical power, and even without reactor coolant is well established. This capability is the result of many factors in the design of a typical modular HTR including the core configuration and power level, the selection of reactor materials, and the heat removal path from the reactor cavity outside the reactor vessel. In the Framatome Steam Cycle High Temperature Gas Cooled Reactor (SC HTGR), the Reactor Cavity Cooling System (RCCS) provides the normal heat removal path from the reactor cavity in the Reactor Building to the outside environment. The RCCS is of particular interest, since it is the only safety related heat removal system available for residual heat removal. This paper describes the main features of the SC HTGR RCCS including the overall system configuration and the main subsystems and components. The SC HTGR RCCS is a water cooled system. RCCS panels with integral water tubes are located on the reactor cavity wall surrounding the reactor vessel, and a natural circulation water loop carries heat from these panels to water storage tanks during all operating modes including normal power operation, accident conditions, and shutdown modes. This system performance can be monitored on a continuous basis. During normal operation, heat is removed from the water storage tanks and discharged to the atmosphere by a separate active water loop. However, if the separate active water loop is unavailable for any reason (e.g., during an accident), the rejected heat is dissipated by the heat capacity and latent heat of vaporization of the water in the storage tank. The storage tanks are sized to provide several days of cooling for decay heat removal following an accident from full power reactor operation. A key consideration of the RCCS design is the performance of the system during different operating modes. This paper discusses the different operating modes and the expected performance during those operating modes. Finally, the paper discusses ongoing work to verify the expected system performance. (author)