Compact buffer zone plate-fin IHX—The key component for high-temperature nuclear process heat realization with advanced MHR

Abstract

Based on ever-demanding environmental considerations, it is projected that, before the middle of the 21st Century, nuclear power will play an important role in the non-electric energy sector, particularly in the generation of hydrogen in a large quantity by means of high-temperature nuclear process heat (PH). The modular helium reactor (MHR) is the only type of nuclear plant that has this high-temperature capability. The key component in the primary circuit of the PH-MHR is the intermediate heat exchanger (IHX) since this facilitates transfer of the nuclear thermal energy to the process plant in a secondary helium loop. With an operating temperature of up to 1000°C, and perhaps even higher, the IHX requirements are demanding, the foremost being integrity (e.g. leaktightness), high compactness for integration in the steel pressure vessel and high performance. The major theme of this paper is that, for commercial PH-MHR service in the 21st Century, the IHX will be of plate-fin construction and be of a double-barrier construction to obviate both helium leakage and tritium diffusion into the secondary loop. This advanced type of IHX will replace first-generation units which are based on a single-barrier, low surface compactness, tubular, helical-bundle geometry, and are essentially a carry-over from steam generator technology used in earlier gas-cooled reactors. The use of very efficient offset fin surface geometries will give a compact IHX assembly that is compatible with installation in a steel vessel for a nuclear process heat source rated perhaps as high as 1200 MW(t). Included in this paper are discussions in the areas of IHX geometry/construction, materials considerations, development required, and the applicability of existing technology bases.