Dose assessment for the Metlino and Muslyumovo populations who lived along the Techa river from 1949 to 1954.

In the period from 1949 to 1956, liquid radioactive waste was routinely and accidentally discharged by the Mayak Production Association, Southern Urals, Russia, into the Techa river. Based on a novel approach, the contamination of the Techa river water, the bottom sediments and the adjacent flood plains was modelled, and internal and external doses were estimated for two villages located downstream of the site of liquid radioactive waste release. Altogether, 11 radionuclides that occurred in the liquid radioactive waste were included in the calculations. The results suggest significantly higher doses than previously assumed, with the major contribution in the year 1951. Radionuclides with half-lives of less than 1 year, such as 89Sr, 131I, 95Zr+95Nb, 103Ru+103mRh, 140Ba+140La, and 144Ce+144Pr, represent the major sources and, in contrast, long-lived radionuclides, such as 90Sr and 137Cs that have so far been assumed to be most important, did not dominate the doses. For adults from the village Metlino, located 7 km downstream of the site of liquid radioactive waste discharge, the committed effective doses due to intake of radionuclides were calculated to be about 2.3 Sv, while the external doses were between about 1.2 Sv and 6.9 Sv. On the other hand, for adults from Muslyumovo, located 75 km downstream, the committed effective doses due to intake of radionuclides were calculated to be about 0.5 Sv, while the external doses were between 0.5 Sv and 2.0 Sv. The values for the skin doses to the Metlino and Muslyumovo populations were about 7.1 Sv and 1.3 Sv, respectively. It is concluded that the current dose estimates for the residents of the Techa river need, therefore, reevaluation.

Reconstruction of the radionuclide spectrum of liquid radioactive waste released into the Techa river in 1949-1951.

The major part of the liquid radioactive waste released by the Mayak Production Association (PA) radiochemical plant into the Techa river occurred in 1949-1951, but there is information on only one single radiochemical analysis of a water sample taken on 24 and 25 September 1951. These data are here used to assess the spectrum of radionuclides that were released between 1949 and 1951. For this purpose, details of the radiochemical methods of radionuclide extraction and radiometric measurements of beta-activity used at Mayak PA in the 1950s have been taken into account. It is concluded that the data from the radiochemical measurements agree with the theoretical composition of fission products in uranium after exposure times in the reactor (120 days) and subsequent hold times (35 days) that were typical for the procedures at that time. The results of the analysis are at variance with assumptions that underlie the current Techa river dosimetry system. They confirm the conclusion that the external doses to the Techa river residents in the critical period up to 1952 were predominantly due to short-lived fission products.

A reconsideration of the external dose assessment for the Techa river population.

A new methodology is employed to infer the time course of the external dose rate that affected the Techa riverside population. This was accomplished using information on the radionuclide composition of released radioactive waste and from earlier and current data on the degree of the river floodplain contamination with (137)Cs. The new approach is proposed for use in the dose reconstruction. Compared to current assumptions it indicates a considerably higher dose contribution due to short-lived fission products from the predominant peak of contamination in 1951. Relative to the present Techa river dosimetry system (TRDS-2000) this information may increase the external dose estimates several fold and correspondingly reduce the solid cancer risk estimate.