Poster

FZJ-2013-06165

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Uptake of Radium during barite recrystallization

Brandt, F. (Corresponding author)FZJ* ; Klinkenberg, M.FZJ* ; Breuer, U.ZEA-3*FZJ* ; Rozov, K.FZJ* ; Bosbach, D.FZJ*

2013

Please use a persistent id in citations: http://hdl.handle.net/2128/5674

Abstract: In recent safety assessments for the direct disposal of spent nuclear fuel, Ra has been identified as a main contributor to dose after 100,000 years [1]. Due to the likely presence of BaSO4 which is formed by a reaction of Ba present as a fission product and sulfate ubiquitous in ground waters, it is expected that Ra will form a RaxBa1-xSO4 solid solution via recrystallization, which would lower the Ra concentration in solution significantly. However, due to a lack of reliable data, this solid solution system is currently not considered in long term safety assessments for nuclear waste repositories. For instance, the solubility of the pure RaSO4 endmember is not well defined. Furthermore, available literature data for the interaction parameter a0, which describes the non-ideality of the solid solution, vary by about one order of magnitude [2, 3]. The final Ra concentration in solution in this system is extremely sensitive to the amount of barite present, the difference in the solubility products of the end-member phases, and the degree of non-ideality of the solid solution phase. The EU-funded SKIN project investigates slow processes in close-to-equilibrium conditions for radionuclides in water/solid systems of relevance to nuclear waste management. Within the SKIN project we have combined a macroscopic experimental approach with ToF-SIMS and thermodynamic modelling to study in detail how a Ra containing solution will equilibrate with solid BaSO4 under repository relevant conditions. Batch experiments at close to equilibrium conditions show a final Ra concentration which is several orders of magnitude lower than the solubility of pure RaSO4. For the first time, the spatial distribution of Ra and Ba within the recrystallized barite powders - analysed using an ION-TOF TOF-SIMS - confirms the uptake of Ra into the solid. Solid-solution aqueous-solution equilibrium calculations were carried out for the BaSO4 – RaSO4 – H2O system with the GEMS – PSI code [4] in combination with the NAGRA – PSI thermodynamic database [10]. Thermodynamic modelling fits the experimental data best with an interaction parameter a0 = 0.6 and a solubility product KRaSO4 = -10.41.[1] Norrby, S.; Andersson, J.; Dverstorp, B.; Kautsky, F.; Lilja, C.; Sjöblom, R.; Sundström, B.; Toverud, Ö. & Wingefors, S. SKB 1997[2] Zhu, C. Geochimica et Cosmochimica Acta, 2004, 68, 3327-3337[3] Curti, E.; Fujiwara, K.; Iijima, K.; Tits, J.; Cuesta, C.; Kitamura, A.; Glaus, M. & Müller, W. Geochimica et Cosmochimica Acta, 2010, 74, 3553-3570[4] Wagner, T.; Kulik, D.; Hingerl, F. & Dmytrieva, S. Canadian Mineralogist, 2012, 50, 701 - 723[5] Hummel, W.; Berner, U.; Curti, E.; Pearson, F. J. & Thoenen, T.; Nagra technical report 02-16 2002

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Contributing Institute(s):

1. Nukleare Entsorgung und Reaktorsicherheit (IEK-6)
2. Analytik (ZEA-3)

Research Program(s):

1. 142 - Safety Research for Nuclear Waste Disposal (POF2-142) (POF2-142)
2. SKIN - Slow processes in close-to-equilibrium conditions for radionuclides in water/solid systems of relevance to nuclear waste management (269688) (269688)

Appears in the scientific report 2013

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Database coverage:

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