From the earliest days of the development of nuclear power, it has been recognised that nuclear reactors and other nuclear plant such as fuel manufacturing and reprocessing facilities, together termed fuel cycle facilities, have the potential to cause health risks to persons on and off the site as a consequence of radiations to which they may be exposed. It has therefore been axiomatic that the designers of the plant, and its subsequent operators, take the greatest care to minimise the exposure of persons to radiation.