Metallic core internals of the modular HTR

Abstract

Abstract In a modular high temperature reactor (HTR) the ceramic reflector surrounding the core is completely enclosed by metallic core internals. These comprise the cylindrical core barrel, the bottom structure supporting the ceramic internals, and the top thermal shield which locates the ceramic internals in the axial direction and provides a shield between the top head of the reactor pressure vessel (RPV) and the core. Radial location of the ceramic internals is provided by supports installed over the entire height of the core barrel and arranged according to the column-type design of the ceramic reflector. The nozzle for attachment of the hot gas duct is located below the core to the side of the hot gas plenum. This nozzle is connected to both the core barrel and the ceramic internals. Part of the nozzle is therefore made of graphite. Loads from the metallic as well as the ceramic internals are transmitted to the bottom head of the RPV. It is here that the core barrel is supported, thus allowing it to undergo axial thermal expansion in the upward direction. The barrel is sealed off at the top in order to permit access to the RPV top head for maintenance purposes when the reactor has been shut down. A system of expansion joints located above the top thermal shield provides a seal between the core barrel and the RPV.