PREDICTIONS OF TRANSURANIC MOVEMENT IN SOILS Attempts have been made to describe the movement of transSuranics through soils on a mathematical basis. Lester et al. (1974) investigated the hypothetical band and 239,240bu (pCi/g), 225U and 258U (ug/g) l (that column which follows the ground water flow path) to a surface water body from an underground geologic nuclear waste disposal site. Numerical resolutions of analytical (mathematical) solutions revealed that differences in adsorption characteristics between soluble chain members, axial disper- sion, and radioactive decay all act to reduce radionuclide discharge rates at the exit of the soil column. This method draws on a uniform, one-dimensional model and requires evaluation cf the distribution co- 3 efficient, Kg. for each soil-radionuclide combination. Thus, this technique has limited application to predicting movement of transuranics in terrestrial soils where radionuclide Kg values can vary over wide ranges along the transport path. Other mathematical models to predict the distribution of radionuclides in soils have been presented by Cohen (1975) and Aleksakhin (1963). A direct application of predicting transuranic distributions 13. jt tt LL Distribution of Area L1-A Soil 1 239,240 (Adapted a aera £5 td Pu, 2355, in a soil profile was presented by Jakubick (1976), who attempted to reconstruct plutonium concentrations in soils of south-west Germany. By correlating the few 733+?"°py measurements available in Germany with the fallout data from Ispra, Italy, the probable history of plutonium fallout was reconstructed. From these datathe plutonium input Funetion in the vicinity of Heidelberg was derived. The plutonium distribution in a soil column from fallout in the United States was used in conjunction T N 30 Fig. 0.1 oO SOIL DEPTH (cm) 0]0.01 impulse releases of transuranic parent- daughter chains through a soil column with the calculated cumulative fallout input function to predict the and 2 from Essington 3 By in NTS et al., plutonium distribution and turnover rate in Heidelberg soils. 1976). of this study imply that the migration of Results fallout plutonium takes place completely, or to a great extent, in the form of discrete particles probably weakly aggregated to soil particles. The removal of fallout plutonium particles (analogous to plutonium oxide particles) from a given soil layer seemed to obey an exponential law, with a characteristic turnover time of 5-6 years for a 5 cm thick partially saturated soil layer. . DISCUSSION This review has pointed out that there are many and diverse observations of transuranic distributions in soils; however, almost ali of the observations are limited to plutonium. Some information on the distribution of americium has been produced, but generally only at nuclear weapons testing areas. Measurements on the distributions of the other 69 68