HTGR Knowledge Base

Topical Article 1: Modular HTGR Technology

HTGR technology is once again receiving increasing interest in many countries around the world as a promising future energy option. HTGR research reactors are coming on line in Japan and China, and two power plant designs are being pursued as international development projects, and additional design studies are under way. The renewed interest is based primarily on modular design concepts that utilise unique properties of the technology to assure retention of radioactive fission products by inherent and passive means. This characteristic offers the promise of an economically competitive electricity generation option at modest unit size, suitable for construction and operation in both industrialised and developing countries. The high temperature capability and smaller unit size also offers the prospect of non-electrical applications for high temperature process heat, as well as low temperature energy supply through cogeneration.

While increasing interest in modular HTGR designs is a recent development, the concept is not new. These smaller, modular designs have been under development for twenty years, beginning with a design originating in Germany in 1979. The supporting HTGR technology has been under development for over forty years, with major programs in the UK, the US and Germany from the 1950's through the early 90's. Important milestones have been achieved in the design and successful operation of three steel vessel HTGRs during the 1960's and 70's, and in the production and demonstration of robust, high quality fuel and other key elements of the technology. The technology has developed along two distinct paths: pebble bed fuel consisting of ceramic spheres 6 cm in diameter with continuous refuelling, and prismatic fuel consisting of hexagonal blocks approximately 35 cm across the flats and 75 cm in height with periodic batch refuelling. Both fuel systems utilise ceramic coated microparticles (< 1 millimetre diameter) of similar design.