Surface decontamination by photocatalysis

Currently in the nuclear industry, surface contamination in the form of radioactive metal or metal oxide deposits is most commonly removed by chemical decontamination, electrochemical decontamination or physical attrition. Physical attrition techniques are generally used on structural materials (concrete, plaster), with (electro)chemical methods being used to decontaminate metallic or painted surfaces. The most common types of (electro)chemical decontamination are the use of simple mineral acids such as nitric acid or cerium (IV) oxidation (MEDOC). Use of both of these reagents frequently results in the dissolution of a layer of the substrate surface increasing the percentage of secondary waste which leads to burdens on downstream effluent treatment and waste management plants. In this context, both mineral acids and MEDOC can be indiscriminate in the surfaces attacked during deployment, e.g. attacking in transit through a pipe system to the site of contamination resulting in both diminished effect of the decontaminating reagent upon arrival at its target site and an increased secondary waste management requirement. This provides two main requirements for a more ideal decontamination reagent: Improved area specificity and a dissolution power equal to or greater than the previously mentioned current decontaminants. Photochemically promoted processes may provide such a decontamination technique. Photochemical reduction of metal ion valence states to aid in heavy metal deposition has already been extensively studied [I], with reductive manipulation also being achieved with uranium and plutonium simulants (Ce) [2]. Importantly photooxidation of a variety of metals, including neptunium [3], has also been achieved. Here we report on the potential application of this technology to metal dissolution