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Potential environmental effects of radioactive isotopes are of great public concern. Fortunately most long-lived isotopes have strong affinities for solids and limited mobility under natural conditions. It recently has been proposed that some isotopes may form colloids that move with groundwater. The detection of plutonium in groundwater some 3400 m down Mortandad Canyon at the Los Alamos National Laboratory is cited widely as an example of such transport. The current work re-examines data from this canyon to evaluate the significance of such transport. 239Pu entering the canyon increased sharply in the early 1980s. Routine monitoring during this period shows that isotopically distinct plutonium appeared in one downgradient well before it appeared in wells closer to the source. If this is ignored, plutonium moved at least twice as fast as groundwater flow and easily outdistanced a tritium peak. Isotopically heavy plutonium arrived simultaneously in surface alluvium and groundwater, and the isotopic composition of plutonium in alluvium and groundwater are identical. Plutonium clearly did not move down-canyon via groundwater. The potential for plutonium movement through groundwater on colloids may be overstated at this and other sites.

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As part of the U.S. Department of Energy Advanced Accelerator Applications Program, a systems study was conducted to evaluate the transmutation performance of advanced fuel cycle strategies. Three primary fuel cycle strategies were evaluated: dual-tier systems with plutonium separation, dual-tier systems without plutonium separation, and single-tier systems without plutonium separation. For each case, the system mass flow and TRU consumption were evaluated in detail. Furthermore, the loss of materials in fuel processing was tracked including the generation of new waste streams. Based on these results, the system performance was evaluated with respect to several key transmutation parameters including TRU inventory reduction, radiotoxicity, and support ratio. The importance of clean fuel processing (~0.1% losses) and inclusion of a final tier fast spectrum system are demonstrated. With these two features, all scenarios capably reduce the TRU and plutonium waste content, significantly reducing the radiotoxicity; however, a significant infrastructure (at least 1/10 the total nuclear capacity) is required for the dedicated transmutation system.

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