| Summary: | A central question to be addressed by the international sub-seabed radioactive waste disposal program is the mobility of radionuclides through sediments, which are the most important barrier to the transfer to the ocean and eventually to man. The major component of high-level radioactive waste is uranium. Here we report the measurement of low uranium concentrations in composite pore-water samples from the uppermost 20-30 m of deep-sea abyssal plain sediments from the Great Meteor East and Southern Nares Abyssal Plains Area. Many values are between 0.1 and 0.5 p.p.b. (parts per 10 9 ) which are the lowest uranium concentrations ever measured in the pore waters of deep-sea sediments. Our lowest value, 0.05±0.01 p.p.b., is orders of magnitude lower than the predicted solubility of UO 2 or U 4 O 9 , probably indicating solubility control of U(IV) by an adsorbed phase. The uranium concentrations obtained from both sites correlate closely with measured redox potentials ( E h ) in the sediments. The low mobility of uranium in pore waters from turbiditic deep-sea abyssal plain sediments, which can be deduced from these measurements, has important implications for the sub-seabed disposal of high-level radioactive waste, and for marine geochemistry of uranium.
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