The Calculation, Presentation and Use of Collective Doses for Routine Discharges

Over recent decades concerns have been expressed about the way collective doses have been used. In particular, there is general agreement that using the fully aggregated collective dose masks a lot of useful information on levels of individual dose and their distribution over space and time, which decision makers may consider important. The International Commission on Radiological Protection has suggested a ‘collective dose matrix’ approach as a solution to this. A study has been carried out to explore some of the issues involved in the development and use of such matrices. In particular, practical issues regarding the disaggregation of collective dose in relation to individual dose rates and the temporal and spatial distribution of exposures have been addressed. Calculations have been undertaken to illustrate ways in which the estimated collective dose from routine discharges can be broken down. The nuclear site chosen was the Sellafield reprocessing plant but additional calculations were also undertaken for the Cap de La Hague reprocessing plant for comparative purposes. It was found that useful information on the temporal and spatial elements of collective doses can be obtained and that per-caput doses can be used to give an indication of the likely individual doses that make up the collective dose. At long times following discharges of radionuclides to the environment doses due to global circulation will dominate the collective dose and there is likely to be little requirement for obtaining information on individual dose distributions.