The 1990 recommendations of the International Commission on Radiological Protection introduced the concept of the dose constraint. The concept of a generalised derived constraint (GDC) was introduced in the NRPB response to the recommendations.
GDCs apply to discharges of radionuclides to the environment and have been calculated for discharges to atmosphere, rivers and sewers for the radiologically significant isotopes of polonium, lead, radium and uranium. Those presented here are intended as convenient reference levels against which proposed discharges can be compared.
GDCs are calculated using deliberately cautious assumptions and in terms of annual discharges, assuming that the releases to the environment are continuous. If a proposed discharge is greater than about 30% of the GDC, the doses should be examined more closely, taking account of site-specific factors.