ICRP CRITICAL GROUP CONCEPT IN RELATION TO WINDSCALE SEA DISCHARGES

The application of the recently recommended I.C.R.P. concept of a critical exposure group to the limiting human radiation exposure pathway arising as a result of the Windscale sea discharges, is discussed in the light of recent surveys of the supply of Porphyra seaweed for the laverbread industry of South Wales, and the production, distribution and consumption of the critical material laverbread. Factors leading to the reduction of exposure rates assessed on the basis of the radioactivity levels in the raw seaweed are evaluated and suggestions for incorporating them in a critical group model for the Windscale situation are made. The radiation exposure to the critical organ (lower large intestine) is estimated for both children and the critical group of adults: children are shown to experience a lover dose. The critical group contains adults of both sexes and has a median rate of laverbread consumption of 160 g per day. Based on the conservative assumption that pure Cumberland derived laverbread is consumed then the application of the model leads to estimated doses of 0.4–0.7 rem/yr to the lower large intestine during the period 1962–67. These may be compared with the I.C.R.P. recommended dose limit for members of the public of 1.5 rems/yr. © 1969 Health Physics Society.