Radionuclides in transport in the Columbia River from Pasco to Vancouver, Washington

Abstract

The radionuclide discharges in the cooling-water effluent of the reactors on the U.S. Atomic Energy Reservation at Hanford, Wash., were formed by neutron activation of: (1) impurities in the Columbia River water used to cool the reactors, (2) corrosion products from the reactor components, and (3) chemicals used in the water-treatment process. Until all the eight reactors that were cooled by once-through flow were shut down, their cooling-water effluents were the main source of dissolved and particulate radionuclides in the Columbia River. Concentrations and discharges of 13 dissolved and particulate radionuclides were observed at Pasco and Vancouver, Wash., for all or parts of the period from January 1964 to September 1966, and at Umatilla, Oreg., from May 1965 to September 1966. A time-series analysis of concentrations and discharges of eight of the 13 particulate and dissolved radionuclides at Pasco and Vancouver showed a progressive decrease in the concentrations and discharges of many radionuclides during the study period. The decrease was mainly attributable to a decrease in the number of operating reactors. Concentrations and discharges of the radionuclides varied seasonally in separate patterns that were used to categorize the particulate and dissolved radionuclides into five classes. Concentrations of radionuclides in classes 1, 2, and 4 varied seasonally in accord with seasonal variations in dissolved parent materials in the river water used to cool the reactors. The seasonal variations of concentrations of class-3 radionuclides exhibited characteristics of dilution by the river discharge of a source with constant strength. Concentrations of class-5 radionuclides varied seasonally in close accord with the seasonal variation in water discharge at Vancouver, Wash.; this evidence indicates that, after transport far enough downstream, the variability in concentrations of many radionuclides in the Columbia River tended to lose dependency on its variability at the source and became dependent upon the variability in the water discharge. Specific activities of zinc-65 and chromium-51 at Vancouver varied inversely with concentration of suspended sediment. Seasonal variations in the discharges of dissolved and particulate radionuclides depended on seasonal variations in their concentrations and the seasonal variation in the water discharge. For the generally anionic chromium-51 and the anionic and uncharged antimony-124, the ratio of dissolved-radionuclide discharge to the total discharge averaged 93 and 96 percent, respectively, at the river stations, and varied little in time at a river station or among the river stations. The average percentages dissolved for the generally cationic cobalt-58, cobalt-60, zinc-65, manganese-54, scandium-46, and iron-59 were generally much lower than that for the anionic radionuclides and depended on the radionuclide. The percentages dissolved for the cationic radionuclides generally varied greatly in time at a station and among the stations. The hydrodynamic and sedimentation characteristics of the Columbia River and the chemical characteristics of the radionuclides were found to be important factors affecting the disposition of the radionuclides discharged at Pasco in the PascoVancouver reach.