Plutonium partitioning to colloidal and particulate matter in an acidic, sandy sediment: implications for remediation alternatives and plutonium migration.

Plutonium partitioning within a bulk, freshwater sediment and to specific size fractions of the sediment was determined. Fission track analysis was used to observe the spatial heterogeneity of fissile isotopes of Pu and U in the sediment. For the bulk sediment, a six-step sequential extraction scheme was used to elucidate Pu partitioning. Although no direct Pu speciation is obtained from our sequential extraction scheme, this study demonstrates that the partitioning information obtained is more useful for evaluating ex-situ remediation treatments than information obtained from complete digestion and analysis of the bulk sediment. The majority of 238Pu and 239 + 240Pu appear to be partitioned in the oxidizable fraction, suggesting that Pu is primarily associated with organic matter in the bulk sediment or may exist as a discrete, oxidizable phase. By varying filter pore size used to separate the sequential extraction leachate solution from the remaining solid phase, a fraction of 238Pu associated with colloidal material was observed, and chemical evidence suggests that this colloidal material is relatively refractory. Pu partitioning to various size fractions of the bulk sediment was also compared to the percent organic carbon present in those size fractions. Interestingly, little correlation was observed between the percentage of organic carbon and concentrations of Pu isotopes in the various size fractions, although differences were observed in the distributions of 238Pu versus 239 + 240Pu in the size fractions. These results suggest that other sediment phases may also be important for Pu partitioning. Our observations are described in the context of feasibility of various remediation options.

In vitro dissolution characteristics of aged and recrystallised high-fired 232ThO2.

The dissolution characteristics of 232Th from ThO2 in the lung have been determined in an in vitro study. Two types of ThO2 were examined to determine if the age of the material had any effect; an aged high-fired ThO2 that had its progeny in secular equilibrium, and a recently recrystallised and high-fired ThO2 in disequilibrium. The results show the amount of 232Th that dissolved from the aged ThO2 was approximately 10 times greater than the amount that dissolved from the recrystallised and fired ThO2 which was the result of recoil damage to the crystal structure of the aged material. A model based on nuclear track theory was developed to relate the size of the observed rapidly soluble fraction of 232Th to the age of the material and its experimentally determined surface area.