Distribution and History of Nuclear Weapons Related Contamination in Sediments from the Ob River, Siberia as Determined by Isotopic Ratios of Plutonium Neptunium, and Cesium.

摘要

This thesis addresses the sources and transport of nuclear weapons related contamination in the Ob River region. The atom ratios 240Pu/239Pu, 237Np/239Pu, and 137Cs/240Pu, contained in sediments from the region and measured by magnetic-sector ICP-MS, are used to distinguish between global fallout and contamination derived from local sources. Data presented in this study demonstrate that non-fallout contamination has been transported the full length of the tributaries draining the nuclear facilities, Mayak, Semipalitinsk, and Tomsk-7. In some cases, contamination originating from one or more of these facilities has been transported as far as the Ob delta. Linear transport rate estimates (km yr-1) indicate that contaminated sediments transit between source tributaries and the Ob delta rapidly (i.e. 0 to 1 yr.), suggesting that a catastrophic release of contamination at fuel reprocessing facilities would result in measurable levels of contamination in the delta within 1-2 years. Sequential extraction experiments indicate that the majority of plutonium and neptunium (80 to 90 percent) are not truly refractory and likely associate with redox sensitive sedimentary components. Only a minor fraction of contamination is associated with acid leachable or acid degestible sedimentary phases.