The fundamental requirement in controlling the radia­tion exposure of operating staff during normal opera­tion of the power station is to ensure that doses re­ceived by operators are kept below the limits recom­mended by ICRP and, further, to keep those doses as low as reasonably practicable (ALARP). An annual target figure for the effective dose-equivalent for in­dividual members of the power station staff resulting from normal operation of the power station was chosen by the CEGB to be equal to 10 mSV (1 rem), in the belief that this represents the lower limit of what is reasonably achievable. In addition to the individual dose target a station collective dose-equivalent of 2 man-mSv (0.2 man-rem) per MW(E) installed capacity was also specified.

When the CEGB safety criteria were first developed, the target for the maximum dose to any member of the public from routine liquid and gaseous effluent discharges and direct radiation, was arbitrarily set at 0.25 mSv (0.025 rem). However, this was later changed to 0.17 mSv (0.017 rem) which is one-thirtieth of the ICRP limit for the general public, with a target of 0.05 mSv (0ЮО5 rem) dose from direct radiation.