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The Effects of the Chemical and Radiolytic Degradation of Asphalt on Plutonium Solubility

  • B. F. Greenfield (a1), M. Ito (a2), M. W. Spindler (a1), S. J. Williams (a1) and M. Yui (a2)...

Abstract

The influence of alkaline degradation or radiolytic degradation of asphalt on plutonium solubility has been investigated. Asphalt has been contacted with water, sodium hydroxide solution or concrete leachate at 80°C for periods of up to approximately 2 years. Sodium nitrate was also present in some of the experiments. Plutonium solubilities were measured at pH 12 in the leachates and found to be less than 10-8 mol dm-3 for most degradations. Relatively low levels of Total Organic Carbon were measured in the leachates. Alpha radiolysis of asphalt in the presence of concrete and water has also been studied. Samples of asphalt were encapsulated in concrete after coating with the 238PuO2, crushed and leached at room temperature. The solubility of plutonium was measured in samples of the leachates after approximately 90 days and 180 days had elapsed. The results showed that the solubility of plutonium in the α-radiolysis leachates remained low and was in the range 2 × 10-11 to 8 × 10-9 mol dm-3. A consideration of these results, and data published elsewhere, suggests that chemical and radiolytic attack on asphalt or bitumen under anaerobic, alkaline conditions typical of a deep cementitious repository is unlikely to generate complexants for plutonium which are effective at high pH. Any enhancement of plutonium solubility is likely to be less significant than that arising from the degradation of some other organic materials.

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