Confinement of volatile fission products in the crystalline organic electride Cs+(15C5)2•e−

Abstract

The efficacy of filters to trap volatile radiotoxic nuclear fission products depends on the thermodynamic stability of these species within the filter material. Using atomic scale modeling based on density functional theory together with a dispersion correction, we predict the structures and energies of volatile fission product atoms and molecules trapped by a crystalline organic electride Cs+(15C5)2•e−. Endothermic encapsulation energies indicate that Kr and Xe are not captured by this electride. Conversely, encapsulation is very strong for Br, I, and Te, with respect to atoms and dimers as reference states, leading to the formation of trapped Br−, I−, and Te− ions. While both Rb and Cs are encapsulated exothermically (without significant charge transfer), their encapsulation is markedly weaker than that calculated for Br, I, and Te. Encapsulation of homonuclear dimers (Br2, I2, and Te2) as anionic molecular species is thermodynamically favorable, though they will disproportionate if sufficient encapsulation sites are available. Conversely, encapsulation of heteronuclear dimers (Rb–Br, Rb–I, Cs–Br, and Cs–I) is unfavorable with respect to their bulk solids as reference states.