ABSTRACTSpent nuclear fuel will, by the radiation, split nearby water into oxidizing
and reducing compounds. The reducing compounds are mostly hydrogen that will
diffuse away. The remaining oxidizing compounds can oxidize the uranium
oxide of the fuel and make it more soluble. The oxidised uranium will
dissolve and diffuse away. The nuclides previously incorporated in the spent
fuel matrix can then be released and also migrate away from the fuel.A model is proposed where the produced oxidizing species compete for
reaction with the fuel and for escaping out of the system. The chemical
reaction rate of oxygen and fuel is taken from literature values based on
experiments. The escape rate of oxidants to a receding redox front in the
backfill is modelled assuming a redox reaction of oxidizing component and
reducing component in the surrounding. The rate of movement of the redox
front is determined from the rate of production of oxidants. This is
estimated using a previously devised model that has been calibrated to in
situ observed radiolysis.Three cases are modelled. In the first case it is assumed that the reducing
compound is insoluble and that the reaction between oxygen and reducing
mineral is very fast. In the second case it is assumed that the reducing
component has a known solubility and that it can migrate to meet the oxygen
and quickly react. In a third case a finite reaction rate is modelled
between the oxygen and the reducing species.The sample calculations show that if the reducing mineral has to be supplied
from the backfill a large fraction of the spent fuel could be oxidised. If
the corrosion products of a degraded steel canister can supply the reducing
species and the redox reaction is fast, very small amounts of the fuel could
be oxidised. Literature data indicate that the redox reaction rate may not
be so fast that it can be considered instantaneous and then a considerable
fraction of the fuel could be oxidised. The model gives a means of exploring
which mechanisms and data may be of most importance for radiolytic fuel
dissolution, but the realism of the data and the model must be tested
further. There is a lack of understanding and data on reaction rates,
heterogeneous as well as homogeneous. This is crucial to the results.
Cover Picture: Graphitic‐Based Solid‐State Supercapacitors: Enabling Redox Reaction by In Situ Electrochemical Treatment (Batteries & Supercaps 7/2020)