Colloidal Products and Actinide Species in Leachate from Spent Nuclear Fuel

Abstract

Two well-characterized types of spent nuclear fuel (ATM-103 and ATM-106) were subjected to testing under potential unsaturated conditions with simulated groundwater at 90 °C. The actinides present in the leachate were determined at the end of two successive periods of ~60 days. A vessel acid strip was done at the end of the second period. Both colloidal and soluble actinide species were detected in the leachate which had pHs ranging from 4 to 7. The uranium phases identified in the colloids by transmission electron microscopy were schoepite and soddyite. The actinide release behavior of the two fuels appeared to vary. Both the total amount of material released and the relative amount of each isotope released was different for the two fuels.

Colloid-Associated Radionuclide Concentration Limits: ANL

“…Transport of radionuclide contaminants at numerous waste sites have been underestimated by models when compared to the field data where measurable concentrations of radionuclides have been detected migrating as colloids from the waste (McCarthy and Degueldre 1993). Most importantly, waste form corrosion can lead to the formation of another type of colloid known as primary or waste form colloids (Buck and Bates 1999;Finn et al 1994a;Fortner et al1997a). The formation of such colloids may allow actinide concentrations in solution that are significantly higher than achievable with real or pseudo colloids.…”

“…Data used in these analyses include at least ten years of testing for the static glass tests (Ebert 1995;Buck and Bates 1999; DTN: LL991110251021.099), over ten years of testing for the glass drip tests Fortner et al 1997aFortner et al , 1997b; DTN: LL000205551021.118), and over four years of testing for the spent fuel tests (Finn et al 1994a(Finn et al , 1994b; DTN: LL991001251021.090). The methods employed for colloid characterization in this section are TEM and filtration (analysis of filtrates with inductively coupled plasma-mass spectrometry (ICP-MS) or alpha spectroscopy).…”

“…Air was flushed through the lines to force water left in the lines onto the fuel. Further details on the tests can be found elsewhere (Finn et al 1994a). …”

“…Partially crystalline uranium silicate colloids ( Figure 18) were identified in the sample. Selected area electron diffraction (SAED) analysis and x-ray EDS compositional data identified the colloid as soddyite, a uranyl silicate with a U/Si ratio of 1:1 (Finn et al 1994a). December 2000…”

“…The particles were polycrystalline uranium-bearing phases with a high concentration of silicon (Finn et al 1994a; DTN: LL991110251021.099, pp. 67-69).…”