Thermal Performance Analysis of a Cooled-Vessel Design Using GAMMA+

GT-MHR adopts high-Cr materials, such as 2 1/4Cr-Mo or 9Cr-1Mo-V steel, for the reactor pressure vessel (RPV). However, there are still open issues when manufacturing and procuring high-Cr vessels. In order to avoid these open issues, Kim and Lee proposed a cooled-vessel concept as a promising option for the NHDD (Nuclear Hydrogen Development and Demonstration) system. A basic idea of the cooled vessel concept is to use the conventional RPV materials (e.g., SA-508 or 533) instead of high-Cr materials by reducing the RPV temperature below its operating structural limit. The reduction of the RPV temperature is achieved by a change of the coolant flow path and an additional vessel cooling system (VCS) if necessary. Based on the computational fluid dynamics (CFD) analysis and the system analysis, Kim et al. showed that the cooled-vessel design concept is feasible for a 600 MWth prismatic very high temperature reactor (VHTR). In this paper, parametric calculations are made to analyze the thermal performance of a cooled-vessel design with various design conditions by using the GAMMA+ code. For the two types of reactor cavity cooing systems (RCCS) (i.e., air-cooled or water-cooled RCCS), the effects of the reactor coolant system (RCS) inlet temperature and the location of the VCS injection nozzle are investigated. A 600 MWth prismatic VHTR under full power operating conditions is considered in this work