Cases of the staff unaccounted exposure during the construction of the protective shell for a new confinement at the ChNPP site.

OBJECTIVE: cytogenetic control of the staff radiation exposure level during the construction of the protective shell for a new confinement at the ChNPP site.

MATERIALS AND METHODS: A cytogenetic examination was carried out for 32 staff persons from the contracting organ izations involved into construction of the protective shell for a new confinement. Additionally, for the goal of com parison, 28 persons who did not have professional contacts with the radiation factors were inspected. The analyti cal method of the aberrations on preparations of uniformly stained chromosomes of the peripheral blood lympho cytes has been used. The frequency has been determined for the dicentrics and centric rings with an accompanying pair fragment for 100 analyzed metaphases. The staff chronic exposure absorbed doses are estimated by means of the linear part of the linear quadratic equations, which describe the calibration dose dependence of the unstable chromosomal exchanges yield in the acute irradiated blood samples in vitro.

RESULTS: Six staff persons from 32 investigated ones have the individual frequency of the recent exposure specific markers (unstable chromosomal exchanges with accompanying pair fragments) significantly higher than those for the comparison group and the population average spontaneous level. It indicates on the possibility of their exces sive irradiation during the work execution in the ChNPP zone. Single cells with two chromosomal exchanges were registered for three persons, while such cells were absent in the comparison group. This is the result of the incorpo ration of radionuclides, which are available in the air at the workplaces. The calculated averaged individual absorbed doses caused by the recent exposure of six staff persons lies in the range from 102.5 to 371.0 mGy.

CONCLUSION: The doses calculated from the frequency of unstable chromosomal exchanges with the accompanying pair fragment caused by the recent exposure of six staff persons are exceeding significantly the doses determined by the methods of physical dosimetry and the occupational exposure dose limits.