PNNL

Abstract

Because of its importance to reconstructing radiation doses for ongoing epidemiological studies, a feasibility study was undertaken to determine if the source term of radioactive materials released to the Techa River from the Mayak Production Association, the first facility in the former Soviet Union for the production of plutonium, could be reconstructed from historical measurements made at a limited number of downriver locations. We used historically measured water flow rates and total-beta radioactivity measurements, and considered the processes of radioactive decay and of sorption/desorption. A simple radionuclide mass balance approach was used. To determine the rate of input of radionuclides to the Techa River system, it was depicted as a series of segments for which measurements are available. For each segment, a system of recurrent (with time) equations was compiled for radioactivity balance accounting for the radioactivity inflow, activity discharge with water, and the reduction of activity from radioactive decay. The equations change with time to account for the changing nature of the river regime. Effective sorption constants for Sr-90 and Cs-137, characterizing the transport of radionuclides among river system components (water and bottom sediments), were defined based on the inventory of these radionuclides deposited at each of the river segments, and data on water concentration and radioactive removal. All information on radioactive contamination of the river system components during the period 1949 - 1996 was used. The pilot study indicated that it is possible to determine the historical releases of a wider suite of radionuclides using the historical monitoring data from numerous locations along the river, rather than relying on a more uncertain reconstruction of quantities released at the point of discharge. Radionuclides include Sr-90, Ru-106, Cs-137, and Ce-144. Estimated concentrations of radionuclides at various times are presented.