Hanford-Derived Plutonium in Columbia River Sediments

Abstract

Mass spectrometry data on plutonium isolated from Columbia River sediments exhibit mean ratios of plutonium-240 to plutonium-242 consistent with those observed for integrated global fallout. Ratios of plutonium-240 to plutonium-239 show marked deviations from accepted fallout values, suggesting a second source of plutonium-239. This additional plutonium-239 arises from the decay of neptunium-239 produced in reactor effluent water from the old plutonium production reactors located on the Hanford Reservation. An estimated 20 to 25 percent of the total plutonium inventory in sediments behind McNary Reservoir, the first downriver site of fine sediment accumulation below the Hanford Reservation, is ascribed to reactor operations.