Long term prediction of population exposure in the areas contaminated after the Chernobyl accident

In order to proceed to the recovery phase after an accident, it is necessary to guarantee the resumption of normal living conditions for the population in the contaminated area. As a criterion for determining such conditions, the USSR National Committee for Radiation Protection recommends a lifetime effective dose equivalent of 0.35 Sv. The evaluation of the lifetime dose includes two components: the dose for the first four years after the accident, determined from actual data, and the dose for the remaining period calculated from models. The main contributions to exposure in the recovery phase are external exposure from the soil surface and internal exposure from the intake of radionuclides with food products. The main radionuclides are 137Cs and, to some extent, 134Cs. The contribution of intake through inhalation during this period is negligible. The density of 137Cs contamination of the area and the content of 137Cs in milk in the year preceding the recovery phase, i.e. in 1989, are used as initial calculation parameters. In estimating the external exposure, the following data taken from each population centre were used: the dynamics of the change in the dose rate in open areas for a period of four years, the radionuclide composition of the fallout and direct measurements of the individual external exposure of various population groups. The internal exposure for the period of 1986-1989 was calculated on the basis of direct measurements of the caesium radionuclide body burden in various population groups. The main intake of caesium into the body (up to 90%) was through the consumption of milk and milk products. It is assumed that the reduction in milk contamination as of 1990 will proceed in such a way that it will effectively be reduced by one half over a period of 14 years; this is the average time obtained for the USSR for the global fallout of products from nuclear explosions. 1 tab