RADIOACTIVE POLLUTION OF THE OB RIVER SYSTEM FROM URALS NUCLEAR ENTERPRISE MAJAK

The Techa river belongs to the Iset-Tobol-Irtysh-Ob rivet system. Arou nd 1950 the Techa was contaminated with medium and high level radioact ive waste from the MAJAK nuclear installation. The total discharge amo unted to 100 PBq; Sr-90 and Cs-137 contributed 11.6% and 12.2% respect ively. Presently the Techa contains about 0.3 TBq Sr-90, more than 6 T Bq Cs-137 and about 8 GBq Pu-239,Pu-240. The levels of the radionuclid es upstream are several orders of magnitude higher than those expected from global fallout The activity concentrations decrease exponentiall y or by power functions with distance. The study has shown that the co ntamination of the soil of the Techa flood plain is 15-85 times higher than global fallout levels. There is an unexplained radioactive conta mination in the Iset river after confluence with the Techa.