Concepts and methods of control of radioactive contamination on the soil-vegetation-milk food chain in the vicinity of nuclear plants

As a consequence of very restrictive radiation protection guides for the surroundings of light-water-cooled power reactors in the Federal Republic of Germany for surveillance of the food chain soil-plants-milk sensitive monitoring procedures are to be applied. For this purpose radiochemical mehtods with a limit of detection of <= 5 pCi/kg on fresh basis should be prescribed. Whereever possible a limit of detection of <= 1 pCi/kg should be approached. Sampling principles and sample handling are discussed. J 131 determinations in milk are of absolute priority. The limit of detection for this determination has been fixed at a level of 0.5 pCi/l. Corresponding methods have been published by the national authorities. By gamma spectrometry with Ge(Li)-detectors (> 15% relative efficiency) the long term development of radioactive contamination of plants and milk may be controlled very effectively. A limit of detection of <= 5 pCi/kg in wet matter for all relevant gamma emitting radioisotopes can be realized by measuring the ashes of plants and milk. Total beta activity measurements including those corrected for K 40 are critically discussed. They are believed to be not satisfactory for low level activity surveillance of biological materials. Total beta activities are usually impossible to interpret and the data should not be reported as numerical values. Instead of beta measurements Sr 89/Sr 90 analysis by the known methods are proposed. Eventually tritium determinations might be performed. (orig./HP)