Mobility of U, Np, Pu, Am and Cm from Spent Nuclear Fuel into Bentonite Clay

Abstract

The mobility of uranium, neptunium, plutonium, americium and curium from spent nuclear fuel (U0 2 ) into compacted bentonite was studied. Pieces of spent BWR U0 2 fuel was embedded in a compacted bentonite clay/low saline synthetic groundwater system. After a contact time of six years the bentonite was sliced into 0.1 mm thick slices and analysed for its content of actinides. Radiometric as well as inductively coupled plasma mass spectrometry (ICP-MS) were used for the analysis. The influence on the mobility by the addition of metallic iron, metallic copper and vivianite (Fe(II)-mineral) to the bentonite clay was investigated. The results show a low mobility of actinides in bentonite clay. Except for uranium the mobility of the other actinides could, after six years of diffusion time, only be detected less than 1 mm from the spent fuel.

Diffusion and sorption of U(VI) in compacted bentonite studied by a capillary method

“…There is little difference in the evaluated apparent diffusion coefficients, D a , for two different contact times. The values of D a in our experiments are very close to the data reported by Yu and Neretnieks [3], where D a of U(VI) diffusion in compacted bentonite at ρ = 1000 ± 50 kg/m 3 are (2.0 ± 1.0) × 10 −12 m 2 /s; about one order of magnitude higher than the values reported by Ramebäck et al [9], where D a of U(VI) diffusion ranges from 1.6 × 10 −14 to 1.9 × 10 −13 m 2 /s for contact times ranges from 3 to 74 months. The difference in D a values may be attributed to the difference of bentonite density, particle sizes of bentonite and contact time.…”

“…The plausible reason is an effect of slow kinetics in some part of the system (e.g. redox and surface reactions and/or chemical changes in the bentonite-water system), causing a higher D a for shorter diffusion time than for prolonged time [9]. It is worth noting that there is no difference in the D a values for contact time between 48 and 85 days in this work.…”

“…It is possible that apparent diffusivities for U(VI) derived after diffusion time Table 2. shorter than some years may give overestimated diffusivities, since the system may not be in the equilibrium [9]. In Fig.…”

“…The difference in D a values may be attributed to the difference of bentonite density, particle sizes of bentonite and contact time. Ramebäck et al [9] reported that the diffusion time had an influence on the apparent diffusion coefficient of U(VI) in compacted bentonite; the D a value decreases with increasing contact time. The plausible reason is an effect of slow kinetics in some part of the system (e.g.…”

Experimental values for 241Am and 239+240Pu Kd's in French agricultural soils

“…Due to their high chemical reactivity, the chemistry of transuranides is particularly complex (Silva and Nitsche, 1995;Choppin and Morgenstern, 2001;Neck and Kim, 2001;Haschke and Oversby, 2002). Soil-solution partition processes include adsorption on clays, a process that is pH dependant (Vyas and Mistry, 1981;Degueldre et al, 1994), or association with colloids (Ramebaeck et al, 1998;Takahashi et al, 1998;Alonso and Degueldre, 2003), as well as the formation of various complexes, notably with organic molecules; indeed soil organic matter plays a significant role on americium and plutonium behaviour (Olofsson and Allard, 1983;Livens and Singleton, 1991;Lee and Lee, 2000;Roussel-Debet et al, 2000;Hakem et al, 2001). Actinides complex with humic and fulvic acids and with low molecular weight organic acids.…”