ANALYSIS AND PROGNOSIS OF RADIATION EXPOSURE FOLLOWING THE ACCIDENT AT THE SIBERIAN CHEMICAL COMBINE TOMSK-7

On April 6 1993 at 12.58 at the radiochemical plant of the Siberian Ch emical Combinat (Tomsk-7), a set-up for treatment of the uranium solut ion prior to extraction was damaged and part of the activity was relea sed into the environment. The release occurred through the collapsed w all and then standard ventilation system. The paper presents results o btained by Roshydromet divisions in assessing the magnitude of the acc ident and predicting its consequences. The meteorological data suggest ed that the most probable direction of the radioactive trail was north -east, towards the village of Georgievka. The preliminary sampling all owed the radionuclide composition of the release to be identified as R u-103, Ru-106, Zr-95, Nb-95 and Pu-239. Based on the results of the ae rial gamma survey conducted by specialists of Roshydromet and ''Berezo vgeologiya'', an area of increased gamma background (>10 mu R/hour) wa s outlined. In addition, measurements were made across the radioactive trail using equipment on vehicles. The activity release was estimated on the basis of the theoretical relationship between gamma dose and i sotopic activity. By calculations, 720 Ci of activity was released int o the environment. The criterium of correctness was the condition of m inimum deviation of the calculated gamma held from the measured one. F or calculation of Pu-239 depositions, the relationship (PuZr)-Pu-239-Z r-95 = (1 - 3.5) X 10(-3) was used. Based on data of depositions and h ydrological predictions, estimates were made for possible contaminatio n of the Samus-ka and Tom' rivers due to the surface run-off of radion uclides from the catchment area. For the village of Georgievka, respir ation individual dose was calculated which may result from wind resusp ension and uplift of radioactive dust containing Pu-239. The paper als o includes results of the actual aerial spectrometric gamma survey whi ch confirm the preliminary estimates of the activity release.