1.1. INTRODUCTION/OBJECTIVES

In the early days of nuclear power development, many different reactor types were considered and indeed prototypes were built. These included light water, heavy water, gas reactor and liquid metal-cooled fast reactor systems. The majority of the reactors in operation in the world today are light water reactors (LWRs) but there is also a sizeable fraction of heavy water reactors. Most of these reactors were built in the 1970s and 80s; only a few new reactors have been built during the last decade. Regarding other types, gas reactors continue to operate in the UK. There are only one or two prototype fast reactors still in operation, although interestingly both gas and fast systems are now starting to be reconsidered for next generation plants. These will be described in the succeeding chapters. Details will be given on the latest designs that are being proposed.

This is an introductory chapter to summarise briefly and review the designs of currently operating reactor systems. It presents the achievements of the technologies to date. It covers the principal reactors in operation today including light, heavy water, gas and other reactor types that have operated successfully, e. g. liquid metal-cooled reactors. The chapter defines the starting point for discussion of future designs in subsequent chapters. Thus, only the main features of the various reactor designs are highlighted below. Detailed descriptions of these reactors are included in a number of sources, see Leclercq (1986), Ramsey and Modarres (1998), Hewitt and Collier (2000) and Mounfield (1991).

The scale of current nuclear power plant operation worldwide is given in Table 1.1, which shows International Atomic Energy Agency (IAEA) data for 2002. This indicates that in 2002, there were a total of 441 units in operation in 30 countries, generating 358,661 MWe (Net) of electricity.