posted on 2019-05-31, 00:00authored bySebastien N. Kerisit, Zhizhang Shen, Micah P. Prange, Eugene S. Ilton
The
effects of radiation fields present in nuclear waste tanks
on the structure and reactivity of Al-bearing phases, a major component
of the solid waste inventory, and their implications for nuclear waste
processing remain poorly understood. While H2 release from
irradiated Al-(oxy)hydroxide phases can be measured experimentally,
the mechanisms that lead to its formation and the fate of other radiolytic
species are not known. Density functional theory calculations were
therefore performed to determine the energetics of radiolytic species
(O– and H0) across the interface between
water and both the (010) and (101) facets of boehmite (γ-AlOOH),
the two surfaces that dominate the morphology of boehmite particles
at alkaline pH values relevant to tank waste. The DFT calculations
employed semilocal and hybrid exchange-correlation functionals and
consisted of a combination of energy minimizations and ab initio molecular
dynamics simulations. The calculations showed that the release of
H0 radicals from boehmite into the liquid phase was highly
exothermic, whereas the O– radicals remained trapped
at the surface of boehmite particles. The solid–water interface
is therefore the locus of separation of radiolytic species, and the
accumulation of O– radicals under irradiation could
lead to significant changes in particle reactivity.