Substantial interest has been generated in advanced reactors over the past few years. This interest is motivated by the view that new nuclear power reactors will be needed to provide low carbon generation of electricity and possibly hydrogen to support the future growth in demand for both of these commodities. Some governments feel that substantially different designs will be needed to satisfy the desires for public perception, improved safety, proliferation resistance, reduced waste and competitive economics. This has motivated the creation of the Generation IV Nuclear Energy Systems programme in which ten countries have agreed on a framework for international cooperation in research for advanced reactors. Six designs have been selected for continued evaluation, with the objective of deployment by 2030. One of these designs is the very high temperature reactor (VHTR), which is a thermal neutron spectrum system with a helium-cooled core utilising carbon-based fuel. The pebble bed modular reactor (PBMR), being developed in South Africa through a worldwide international collaborative effort led by Eskom, the national utility, will represent a key milestone on the way to achievement of the VHTR design objectives, but in the much nearer term. This paper outlines the design objectives, safety approach and design details of the PBMR, which is already at a very advanced stage of development.

Most of the development in nuclear power in the past 30 years has gone into water-cooled reactors. As government funding has dwindled, development of promising alternative systems has lapsed in most countries. Although gas-cooled reactors have had a very good safety record, many have not been able to compete on economic grounds, mainly because of poor operating records and/or high infrastructure costs. Since broad-based construction has not been achieved, gas-cooled reactors have not benefited from cost reductions in the learning curve. The realization that nuclear energy will need to contribute to future power production expansion and the reduction of greenhouse gases has led to the resurgence of interest in safer and more economical ways to produce nuclear energy. One of these alternatives is the high-temperature gas-cooled reactor, as exemplified by the pebble-bed modular reactor (PBMR) being developed in South Africa. This direct-cycle, low power density design is based on clustering modules of modest power output into flexible power plants. Economic targets can be met through simplification by dispensing with the need for extensive back-up safety systems and high plant availability due to on-power refuelling and low-maintenance equipment.

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