Derivation of Working Limits for Continuous Release Rates of 90Sr and 137Cs to Atmosphere in a Milk Producing Area

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Abstract
This assessment is based on information gained mainly by analysis of fallout data on the transfer to milk of 90Sr and 137Cs deposited on grass. The amount of each nuclide transferred is related to the current rate of deposition and to the cumulative deposit in soil; these relationships are expressed primarily in terms of annual average values applicable to the United Kingdom as a whole. These values are used to derive basic working limits for continuous release rates corresponding to working limits in milk of 800 pc 90Sr/g Ca and 2 × 104 pc 137Cs/l. The former is based on the limit, specified by the British Medical Research Council, of 200 pc 90Sr/g Ca in bone as an annual average, and the latter on a maximum permissible annual dose of 0.5 rem. Basic working limits for release rates are subject to modifying factors, regarding, for example, agricultural variations, which may, and in some cases must, be applied when considering releases in given situations. These factors are discussed. A short-term averaging period of 1 week is recommended. Modified working limits suggested as provisional guides for purposes of planning and design, for example, are 0.4 c 90Sr/week and 10 c 137Cs/week for a stack of 50 m effective height at 300 m from the nearest pasture in a given situation of extreme (or unknown) agricultural characteristics in Great Britain. Basic working limits for a number of stack heights and distances are shown graphically.

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