A new Approach to Assess the Doses to the Population in the 30 km-Zone after the Chernobyl Accident

INTRODUCTION Very few data are available to assess the exposure of the population within the 30 km exclusion zone around the NPP Chernobyl. While gamma dose rate measurements were performed at regular intervals in most villages within the exclusion zone, virtually no measurements of the total activity concentration in air or the concentration of individual radionuclides relevant to the inhalation exposure were carried out due to lack of monitoring capacity. Also practically no data on activity concentration in foodstuffs are available to evaluate the exposure by ingestion of contaminated foodstuff in the various settlements. An estimate of the internal exposure of persons living in the settlements of this zone during the time of the accident and evacuated thereafter, therefore, is not possible on the basis of measured activity concentrations in air and foodstuffs for the calculations. For some evacuees measurements of the thyroid were performed, but they cover only a limited number of individuals and therefore are representative only for certain settlements. They also comprise only I-intake and do not take into account other radionuclides some of which may deliver a significant contribution both to the inhalation and the ingestion dose, especially when the close distance to the Nuclear Power Plant is considered. Therefore, to reconstruct the exposure in the various settlements for epidemiological purposes, in particular with regard to the internal exposure, a new approach had to be developed. For that purpose the fact was used that, apart from dose rate measurements in each settlement, the deposition of Cs was extensively determined in the various settlements at a later stage after the accident. Also the radionuclide vector in deposition on ground is available from a number of measurements and for very few measurements also in air. Considering the fact that there was practically only dry deposition within the 30 km zone during the main fallout period, the integrated activity concentration in air of Cs and the other radionuclides may be derived from ground deposition and thus the activity concentration integral in air as the basis of dose estimates reconstructed. In the following the methodology and the problems associated with the reconstruction of some of the required parameters will be described and discussed.