On the Revision of Control Index Levels on the Ingestion of Food and Water in the Guidelines for Radiological Emergency Preparedness and Countermeasures in Japan

This paper describes the revised index levels of the control of food and water in the Nuclear Safety Commission guidelines, “Off-Site Emergency Planning and Preparedness for Nuclear Power Plants, etc.” Food and water are divided into five categories, and the consumption of each has been conjectured. For this purpose, a nationwide survey for nutrition in Japan by the Welfare Ministry and a survey on the food of infants and children in the coastal area of Ibaraki Prefecture by the National Institute of Radiological Sciences are considered. These categories are (1) drinking water, (2) milk and dairy products, (3) vegetables, (4) grain, and (5) meats, egg, fish, shellfish, and others. The radionuclides groups are then chosen in consideration of their potential importance in regard to food and water contamination. Those chosen were, (1) radio-iodine, (2) radioactive cesium and strontium, (3) uranium, and (4) plutonium and alpha-rayemitting transuranic radionuclides. The intervention dose levels of 5mSv of effective dose and 50mSv of committed equivalent dose to the thyroid for radio-iodine for a period of one year were adopted. The radioactivities of 131I, 132I, 133I, 134I, 135I, and 132Te are assumed to be proportional to the contents in nuclear fuel after a cooling time of 0.5 day, and the radioactivity of 131I is taken as a scale that represents the level of control on the ingestion of food and water. Based on doses to infants, whose exposure is highest, the levels of control are recommended to be 300Bq/kg or more for drinking water and milk and other dairy products, and 2, 000Bq/kg or more for vegetables, except edible roots and potatoes. It is assumed that radio-cesium released in the environment is accompanied by strontium radio-nuclides with a 90Sr/137Cs radioactivity ratio of 0.1, taking into account the past measurements of fallout. Radio-nuclides are assumed to contain 137Cs, 134Cs, 90Sr, and 89Sr with the same mixing ratio as that of the fuel in a nuclear reactor. The sum of radioactivity of 134Cs and 137Cs is used as a scale that represents the level of control, and the yearly average concentration in food and water is presumed equal to half the concentration of those in the peak term. It has then been recommended that the levels of control for radio-cesium should be 200Bq/kg or more for drinking water and milk and other dairy products, and 500Bq/kg or more for vegetables, grain, meat, eggs, and fish. Moreover, in special cases, measurements on radi