UNDERSTANDING VARIATION IN PARTITION COEFFICIENT, Kd ...

In a similar comparison of sorption databases for use in performance assessments of radioactive
waste repositories, Stenhouse and Pöttinger (1994) list “realistic” K d values (ml/g) for uranium in
crystalline rock/water systems of 1,000 (NAGRA), 5,000 [Svensk Kärnbränslehantering AB
(Nuclear Fuel and Waste Management Company), Sweden; SKB], 1000 (TVO), and 6 (Canadian
Nuclear Fuel Waste Management Programme, CNFWM). For bentonite/groundwater systems,
they list 5,000 (NAGRA), 3,000 (SKB), and 500 (TVO). The reader should refer to sources cited
in Stenhouse and Pöttinger for details regarding the source, derivation, and measurement of these
values.
Thibault et al. (1990) [also summarized in Sheppard and Thibault (1990)] updated a compilation
of soil K d values that they published earlier (Sheppard et al., 1984). The compilations were
completed to support the assessment(s) of a Canadian geologic repository for spent nuclear fuel in
Precambrian Shield plutonic rock. Thibault et al. collected K d values from other compilations,
journal articles, and government laboratory reports for important elements, such as uranium, that
would be present in the inventory associated with Canada’s nuclear fuel wastes. Because Thibault
et al. (1990) and Sheppard and Thibault (1990) are frequently cited, their derived uranium K d
values are reported here for the sake of completeness. The K d values for each element were
categorized according to 4 soil texture types. These included sand (i.e., contains $70 percent
sand-size particles), clay (i.e., contains $35 percent clay-size particles), loam (i.e., contains an
even distribution of sand-, clay-, and silt-size particles, or #80 percent silt-size particles), and
organic (i.e., contains >30 percent organic matter and are either classic peat or muck sediments,
or the litter horizon of a mineral sediment). Based on their previous evaluations, Thibault et al.
ln-transformed and averaged the compiled K d values to obtain a single geometric mean K d value
for each element for each soil type. The K d values for each soil type and the associated range of
K d values listed for uranium by Thibault et al. (1990) are given in Table J.3.
Table J.3. Geometric mean uranium K d values derived by Thibault et al. (1990) for
sand, loam, clay, and organic soil types.
Soil Type
Geometric
Mean K d
Values (ml/g)
Observed Range of
K d Values (ml/g)
J.18
Number of
K d Values
Sand 35 0.03 - 2,200 24
Loam 15 0.2 - 4,500 8
Clay 1,600 46 - 395,100 7
Organic 410 33 - 7,350 6