Chemical Approaches to Understanding the Environmental Behavior of Pu, Np, and Tc

Some topics discussed are as follows: speciation behavior of Pu, Np, and Tc; thermodynamic and radiochemical behavior; sorption studies with soils; Pu oxidation states in fresh water; Np oxidation states in soils; effect of oxidation state of Tc on environmental transport predictions; and thermodynamic calculations of Tc speciation. (HLW

Mobile Species of Pu, Np, Cm, Am and Tc in the Environment

This paper will describe field and laboratory findings on the nature of soluble species of plutonium, neptunium, curium, americium, and technetium and demonstrate the importance of oxidation state and complexing ligands on migration potential. Both of these geochemically-influenced variables are difficult to incorporate into models, yet significantly influence actual migration if it occurs

Technetium behavior in sulfide and ferrous iron solutions

Pertechnetate oxyanion (/sup 99/TcO/sub 4//sup -/), a potentially mobile species in leachate from a breached radioactive waste repository, was removed from a brine solution by precipitation with sulfide, iron, and ferrous sulfide at environmental pH's. Maghemite (..gamma..-Fe/sub 2/O/sub 3/) and geothite (..cap alpha..-FeOOH) were the dominant minerals in the precipitate obtained from the TcO/sub 4//sup -/-ferrous iron reaction. The observation of small particle size and poor crystallinity of the minerals formed in the presence of Tc suggested that the Tc was incorporated into the mineral structure after reduction to a lower valence state. Amorphous ferrous sulfide, an initial phase precipitating in the TcO/sub 4//sup -/-ferrous iron-sulfide reaction, was transformed to goethite and hematite (..cap alpha..-Fe/sub 2/O/sub 3/) on aging. The black precipitate obtained from the TcO/sub 4//sup -/-sulfide reaction was poorly crystallized technetium sulfide (Tc/sub 2/S/sub 7/) which was insoluble in both acid and alkaline solution in the absence of strong oxidents. The results suggested that ferrous- and/or sulfide-bearing groundwaters and minerals in host rocks or backfill barriers could reduce the mobility of Tc through the formation of less-soluble Tc-bearing iron and/or sulfide minerals

Aerodynamic Size Associations of Natural Radioactivity With Ambient Aerosols

The aerodynamic size of /sup 214/Pb, /sup 212/Pb, /sup 210/Pb, /sup 7/Be, /sup 32/P, /sup 35/S (as SO/sub 4//sup 2 -/), and stable SO/sub 4//sup 2 -/ was measured using cascade impactors. The activity distribution of /sup 212/Pb and /sup 214/Pb, measured by alpha spectroscopy, was largely associated with aerosols smaller than 0.52 ..mu..m. Based on 46 measurements, the activity median aerodynamic diameter of /sup 212/Pb averaged 0.13 ..mu..m (sigma/sub g/ = 2.97), while /sup 214/Pb averaged 0.16 ..mu..m (sigma/sub g/ = 2.86). The larger median size of /sup 214/Pb was attributed to ..cap alpha..-recoil depletion of smaller aerosols following decay of aerosol-associated /sup 218/Po. Subsequent /sup 214/Pb condensation on all aerosols effectively enriches larger aerosols. /sup 212/Pb does not undergo this recoil-driven redistribution. Low-pressure impactor measurements indicated that the mass median aerodynamic diameter of SO/sub 4//sup 2 -/ was about three times larger than the activity median diameter /sup 212/Pb, reflecting differences in atmospheric residence times as well as the differences in surface area and volume distributions of the atmospheric aerosol. Cosmogenic radionuclides, especially /sup 7/Be, were associated with smaller aerosols than SO/sub 4//sup 2 -/ regardless of season, while /sup 210/Pb distributions in summer measurements were similar to sulfate but smaller in winter measurements. Even considering recoil following /sup 214/Po ..cap alpha..-decay, the avervage /sup 210/Pb labeled aerosol grows by about a factor of two during its atmospheric lifetime. The presence of 5 to 10% of the /sup 7/Be on aerosols greater than 1 ..mu..m was indicative of post-condensation growth, probably either in the upper atmosphere or after mixing into the boundary layer

Recent Field Studies of Dry Deposition to Surfaces in Plant Canopies

A variety of field techniques were used to assess the dry deposition of sulfur. In a deciduous forest canopy in eastern Tennessee, inert petri plates and adjacent chestnut oak leaves showed similar SO/sub 4//sup -2/ deposition velocities of about 0.1 cm s/sup -1/. In the same forest, statistical analysis of throughfall yielded a deposition velocity of 0.48 cm s/sup -1/ for total sulfur (SO/sub 4//sup -2/ plus SO/sub 2/). The throughfall technique appears useful for scaling individual surface measurements to larger spatial and temporal scales. On a grassy field in Illinois, flat Teflon plates, petri dishes, and dustfall buckets were exposed side by side. Measured sulfate deposition increased with increasing rim height on the collection surface, and deposition velocities ranged from 0.14 to 0.70 cm s/sup -1/. Much of the deposition to these surfaces can be attributed to large-particle SO/sub 4//sup -2/. Dry season (summer) deposition velocities of /sup 7/Be in California were found to be similar to dry deposition velocities of /sup 212/Pb in Tennessee, ranging from 0.18 to 0.35 cm s/sup -1/. These natural radionuclides attach to submicron aerosols in the atmosphere and may be useful tracers of submicron SO/sub 4//sup -2/ deposition. 9 references, 5 figures, 4 tables

Nonproliferation Alternative Systems Assessment Program (NASAP): preliminary environmental assessment of thorium/uranium fuel cycle systems

This report presents a preliminary assessment of the quality of existing information available for the evaluation of potential environmental impacts resulting from large-scale implementation of a thorium-based fuel cycle. The report's purpose includes (1) assistance in the development of a hazard assessment policy for the Nonproliferation Alternative Systems Assessments Program (NASAP) sponsored by the Department of Energy, and (2) identification of areas in which further research is necessary to allow detailed evaluation of the environmental hazards associated with thorium fuel cycles in general. Both the hazard assessment data base and the available assessment methodology are evaluated. While this report does not present coverage of all issues pertaining to practical thorium fuel cycles and pertinent literature, it is an attempt to specify those issues likely to appear to be significant during an exhaustive hazard analysis

Transfer of /sup 131/I and /sup 95m/Tc from pasture to goat milk

Field measurements were made in 1983 on the transfer of /sup 131/I and /sup 95m/Tc from spray-contaminated pasture to goat's milk. The transfer of /sup 131/I to milk was similar to that used for mathematical models in US Nuclear Regulatory Commission Regulatory Guide 1.109, which was derived from stall-feeding experiments using capsulized doses. Compared to /sup 131/I, the /sup 95m/Tc transferred to milk was about 5600 times less. The lower transfer resulted from both immobilization of technetium on pasture prior to ingestion as well as reduced gastrointestinal absorption. The results show that the food chain transfer of technetium to milk is much less than that previously expected based on inferences made from metabolism studies. 6 references, 4 figures, 1 table

Plant uptake of americium, curium, and the chemical analog neodymium. [/sup 241/Am, /sup 244/Cm, /sup 147/Nd]

The plant uptake from several bulk soils has been determined for neodymium, a chemical analog to the transuranium elements americium and curium, and several other native rare earth elements as well. These investigations have demonstrated that neodymium, which has very similar chemical properties to americium and curium and should have a similar environmental behavior, does behave indistinquishably under both laboratory and field conditions. The uptake of the weathered or mobile forms of these elements from soils is expected to be governed primarily by their identical oxidation states and nearly identical ionic radii. This hypothesis is strongly supported by the chondritic (primordial) normalized rare earth element patterns in several plants. In these samples, the entire series of rare earth elements behaves as a smooth function of the REE ionic radii, as is also seen in the contiguous soils. This behavior suggests that the plant uptake of other ions with similar chemical properties (i.e., americium and curium) would also be governed by ionic size and charge