Critical group identification via a radiological habit study of members of the public potentially exposed to radiation from the Koeberg Nuclear Power Station

Maree, Marc
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The Koeberg Nuclear Power Station is situated on the Cape West Coast, approximately 30 km north of Cape Town and is licensed by the National Nuclear Regulator of South Africa (NNR). The NNR authorises internationally acceptable annual discharges of radioactive effluent from the plant, under controlled conditions via approved liquid and gaseous effluent pathways. The radioactivity contained in effluent may migrate into the environment and directly and/or indirectly expose members of the public to radiation and result in public dose. One way of assessing the public dose is to identify the Critical Group, those members of the public who are the most highly exposed. A Critical Group is defined as a small group of people being reasonably homogeneous with respect to its exposure for a given radiation source and given exposure pathway. The identification of the Critical Group is motivated by the need to demonstrate compliance with international and national radiological safety requirements and to safeguard potentially exposed individuals in the vicinity of the Koeberg Nuclear Power Station. A radiological habit survey was designed and implemented. Data were obtained from members of the public relating to their eating and recreational habits which may result in potential exposure. Recent radiological environmental-surveillance data and radiological monitoring data were combined with the radiological habit survey data taking the aquatic, terrestrial, direct radiation and combined pathways into account in order to calculate Retrospective Public Doses. A pathway habit-profiling method was applied to derive profiles of habit rates for each pathway. Individuals with the highest consumption rates, occupancy or doses were identified and a “cut-off” method was applied to select the Critical Groups and Critical Group rates for each pathway. Habit profiles, source terms and dose rates measured during fieldwork were applied to calculate effective doses. The pathway which gave rise to the highest Critical Group dose was used to identify the Critical Group for the Koeberg Nuclear Power Station. The highest Critical Group dose was used for comparison with the national annual dose limit and dose constraint.