Partitioning of Plutonium between Glass, Secondary Phases, and Contact Refractories
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bottom of the melter. Crystalline Phases can have a wide range of compositions and can be either more or less dense than the molten glass. Refractory Phasesare formed within the refractory lining of the melter and are generally rather immobile. In all of these cases, the secondary phase tends to sequester and concentrate specific components from the glass melt, and for this and other reasons their formation is undesirable. In a plutonium system it is essential to know the extent to which such phases could accumulate plutonium if they should form. In this study small-scale batch melts were made using waste simulants that included plutonium spikes. Secondary phases were forced to form and their plutonium concentrations relative to the glass were determined. This initial study addresses only three of the above four phases (salt phase, crystal phases, and refractory phases). EXPERIMENTAL METHODS The development of glass formulations for the AMWTP is reported elsewhere [1], as is also the demonstration and testing of those formulations in a small-scale continuously-fed joule-heated melter system [2]. The same glass formulations were used in this work, and most experiments described herein used glass actually produced in those small-scale melter tests. Overview Fifty milligrams (200 gCi) of 242pu was procured from the Oak Ridge National Laboratory Isotope Distribution Office for this work. The longer half-life of this isotope permits greater mass for a given activity, which affords increased analytical sensitivity for the tests that were conducted. A dedicated micro-scale (a few grams capacity) glass melting furnace was set up inside a glove box for this work. Samples of the non-radioactive AMWTP glasses were ground and remelted with the requisite quantity of plutonium nitrate solution to yield glasses containing 0.5 wt% PuO9 ; this is about 100 times the overall average concentration expected in the AMWTP glass product [I]. The higher plutonium concentration was used to enhance effects and to ensure analytical detection. Glass Preparation Two non-radioactive base glasses of similar composition were used in this study, one (AMWTP3 1B) that was produced during the melter tests [2] and included cerium, which was used as a surrogate for plutonium in those tests, and one (AMW9CeO) without cerium that was produced as a 300 g crucible melt. The measured composition of AMWTP3IB is shown in Table I together with measured compositions after refractory corrosion tests to be described later. The radioactive glasses were produced in two steps. First, the parent glass was melted in a platinum-gold crucible at 1200'C for 90 minutes with mechanical stirring of the melt for the final 60 minutes, cooled rapidly by pouring it onto a graphite plate, and then ground to 100 ýtm powder. The second step was performed in a glove box. Two to three grams of 100 Im glass powder were 242 placed in a platinum-gold crucible and sufficient plutonium nitrate solution (10 mg pu/ml) added to produce 0.5 wt% PuO2 in the glass product. The crucible was the
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