In normally operating nuclear power plants, the main exposure route for workers is external radiation originating from the reactor itself, from activated components and from stored fuel or waste. The potential for intakes of radioactive material by inhalation and ingestion usually only occurs during maintenance operations. At the same time, in planning for radiation protection, it has to be recognized that there is a risk of accidents in the operation of nuclear power plants, which could lead to significant radiation doses to workers and the public.

Radiation doses to workers should be kept as low as reasonably achievable taking into account a range of factors including the scheduling and management of different tasks related to the operation of the facility and trade-offs between doses to workers and the public related to decisions over radioactive waste management (IAEA, 2000a). Dose reduction in the workplace can be achieved through careful design in relation to both the generation of radioactive material and build-up of such material. For example, at the design stage of a nuclear power plant, consideration should be given to the choice of materials to minimize the formation of activated corrosion products while, during operation, techniques such as flushing, washing and decontamination should be employed to remove radioactivity from circuit components.

As a result of improved nuclear power plant designs and operating procedures, the average radiation exposure of workers employed at nuclear power plants worldwide has decreased in recent decades. Data from UNSCEAR indicate a world wide steady decline in the collective dose per unit power generation from 11 man Sv/GW y in the period 1975-1979 to 3.9 man Sv/GW y in the period 1990-1994 (UNSCEAR, 2000).

Small amounts of radionuclides are released by stack or pipeline into the atmospheric and aquatic environments respectively as part of the normal operation of nuclear power plants. Typical released radionuclides are tritium and the noble gases, Kr-85 and Xe-133; smaller amounts of fission products may also be released. The discharged radionuclides are dispersed and diluted in the atmospheric or aquatic environments. People living near to the power plant may be exposed to radiation as a result of the discharges. The amounts released must therefore be controlled and limited (by filters and separators) so that the radiation doses to the public are kept as low as reasonably achievable and below dose constraints (IAEA, 2012a). For this purpose, environmental assessment models are used to evaluate the transfer of radionuclides to persons living in the vicinity of the nuclear power plant via all possible pathways of exposure. Together with the results of environmental monitoring, the modelling assessment is used to confirm that the releases are acceptable and that doses to the representative person (formerly critical group) are within the dose constraints (IAEA, 2000b). In practice, radiation doses from the normal operation of nuclear power plants are low and usually they are well below the dose constraints set by national regulators (UNSCEAR, 2010).

To provide for the protection of workers under accident conditions, an assessment should be made at the design stage of the potential sources of radiation exposure that would exist during and after accidents. All potential accident scenarios, including severe accidents, should be considered in this assessment. The design should be such that the operator can ensure the safety of all persons on the site in the event of an accident or radiological emergency (IAEA, 2005a).

To address the protection of the public under accident conditions, the possible consequences of design basis accidents and severe accidents should be evaluated. In cases where the safety analysis shows that the established reference levels are not met, additional protective features should be incorporated into the design or operational measures should be developed to provide assurance that the reference levels will be met (IAEA, 2005a).

In the post-Chernobyl era, ‘safety culture’ has come to be recognized as an essential element of operational nuclear safety. In this context, a key international requirement is set out as follows: ‘A policy on safety shall be developed by the operating organization and applied by all site personnel. This policy shall give safety the utmost priority at the plant, overriding if necessary the demands of production and project schedules. The policy shall include a commitment to excellent performance in all activities important to safety and shall encourage a questioning attitude’ (IAEA, 2000c).