Overview of the high-temperature gas-cooled reactor technology

The high-temperature gas-cooled nuclear reactors (HTGRs) technology was developed in the 1960s and 1970s and five reactors were built in the US, the UK and Germany. These reactors had advantageous inherent safety features and they adopted the Rankine thermodynamic power cycle. Unfortunately, the concepts turned out to be too expensive and these prototype reactors were closed prematurely. During the recent years interest for HTGRs has increased. One reason is the advances in the gas turbine technology, which makes possible to use closed Brayton cycle in HTGRs. This improves the efficiency of HTGRs from 40% to almost 50% and has great cost benefits. The current development work is concentrated in two main concepts. The South African Pebble Bed Modular Reactor (PBMR) has reached the status that, assuming shareholders approval and Government consent, preliminary construction activities could commence by mid 2001. The Gas Turbine Modular Helium Reactor (GT-MHR) project, which i s based on the technology and development work of General Atomics (GA) at US, continues as an international project. One main objective of this reactor is to burn the excess military plutonium in Russia. The HTGRs have, in it's new form, all necessary characteristics to become a relevant alternative for conventional power plants in the domain of medium-power thermal or electrical energy production units. This has become possible through combining the advancements of gas-fired power plants and the inherent safety features of the HTRs. The use of a direct cycle thermodynamic system (Brayton cycle) improves the efficiency of the plant close to 50% and eliminates the accidents due to leaking steam generator tubes. The modular design and the inherent safety features of the relative small-size modules eliminate the needs for complicated engineering safety system. This brings additional cost savings through smaller material costs, reduced construction time of the plant and less mainten ance and testing. The possibility to use different type of fuels and to achieve high discharge burnup brings additional cost savings. Due to the small size of the new HTGRs, it could become an attractive power generation alternative for small countries. The small investment costs, the possibility for combined power and heat production and the possibility to easily increase the power of the unit, by constructing more modules, makes it also a flexible and competitive alternative for the liberalised European or U.S energy markets.