Biogeochemical behaviour of 137Cs and 90Sr in the artificial reservoirs of Mayak PA, Russia

The Mayak Production Association PA. in the southern Urals, Russia was the site of the first weapons-grade plutonium production reactor complex in Russia. The site and surrounding area have been significantly contaminated by direct discharges of radionuclides for over 40 years, the Techa River alone having received more than 100 PBq of waste in the period 1949]1956. The aim of this study was to consider the levels of 90Sr and 137Cs in water, sediment and biota samples for two industrial reservoirs in the Mayak PA area, thus allowing a biogeochemical assessment of the behaviour of radionuclides in the system. Four sediment cores were collected and sectioned along with four water samples and seven fish samples pike, perch and roach.. Samples were analysed using i. standard gamma-spectro- metric techniques HPGe and NaI Tl. detectors. for 137Cs determination; and ii. radiochemical separation and beta-counting low-background, anti-coincidence and Geiger]Muller counters. for 90Sr determination. Maximum specific activities dry weight. of 3350 kBq kgy1 137Cs and 720 kBq kgy1 90Sr were measured in sediments from Reservoir 10. Activity levels of sediment-bound radionuclides in Reservoir 11 were 403 kBq kgy1 137Cs and 670 kBq kgy1 90Sr. Water concentrations in Reservoir 10 were as high as 100 Bq ly1 137Cs and 8.4]14 kBq ly1 90Sr. A dramatic decrease in 137Cs concentrations was observed in Reservoir 11, i.e. 1.1]1.5 Bq ly1, but 90Sr levels fell to a lesser extent, i.e. 1.9]2.4 kBq ly1. Sediment and water activity data allowed the calculation of distribution coefficients Kd values.. This parameter fluctuated for both radionuclides reflecting the heterogeneous nature of the sediment deposits in the reservoirs. Caesium-137 Concentration Factors CFs. as high as 1400 l kgy1 were calculated for pike from Reservoir 10. A pronounced ‘trophic level’ effect was evident in Reservoir 11 pike CFs1000, roach CFs240..