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Locking up radiotoxicity
02 May 2008
International scientists are using computer simulations to give insights into the long-term safety of nuclear waste in deep geological repositories.
Under repository conditions, europium would regularly alternate with calcium and sodium cations
It is particularly important to retain actinides safely because they have such long radioactive half-lives. One way this is done is by forming thermodynamically stable solid solutions, where the solids' cations can be substituted by the actinides preventing them from leaching out. Victor Vinograd at the Institute of Geosciences, Frankfurt, Germany, Dirk Bosbach at the Institute of Nuclear Waste Disposal, Karlsruhe, Germany, and international collaborators have carried out computer simulations to try to understand the behaviour of one such solid solution based on powellite, a naturally occurring mineral, in which some calcium cations are substituted with sodium and europium.
'Europium has similar chemical behaviour to the actinides. Therefore, such simulations help us find the conditions under which radionuclides are stable in the repository system,' explains Vinograd. The team found that at temperatures typical for repository conditions, europium would regularly alternate with calcium and sodium in the powellite structure. Vinograd says that the results leave little doubt that at these temperatures, the formation of stable powellite solutions is possible only at specific calcium/lanthanide(actinide) ratios. The team hopes to move on to chemically more complex waste repository systems in the future, he says.
Link to journal article
Subsolidus phase relations in Ca2Mo2O8–NaEuMo2O8-powellite solid solution predicted from static lattice energy calculations and Monte Carlo simulations
Victor L. Vinograd, Dirk Bosbach, Björn Winkler and Julian D. Gale, Phys. Chem. Chem. Phys., 2008, 10, 3509
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