Destruction of Organic Matter from Radioactively Contaminated Water of Nuclear Power Plants Equipped with VVER (Analytical Review)

The literature review provides a critical analysis of the current experimental and practical use of oxidative methods for the destruction of organometallic complexes present in liquid radioactive waste (LRW) of nuclear power plants with water-cooled reactors. The main LRW organic complexes (containing ethylenediaminetetraacetate and oxalic acids) and methods of their oxidation by ozonation, addition of potassium permanganate and hydrogen peroxide are considered. The article outlines the results of combined oxidation (ultraviolet and ozone, supercritical oxidation in the presence of hydrogen peroxide, discharge cavitation combined with ozonation) and the processes of sediment formation (secondary waste) from the oxidative decomposition of organic compounds, which result in formation of highly dispersed amorphous Fe (oxy)hydroxide-based sediments. It is shown that ozonation is one of the most efficient methods for the destruction and removal of organic components from aqueous solutions of LRW since ozone has a higher oxidizing power compared to potassium permanganate and hydrogen peroxide. Currently, ozonation technologies are used at a number of nuclear facilities in the Russian Federation (Kursk, Kalinin and Leningrad NPPs). At the same time, the process of ozone production is highly energy-intensive and time-consuming, which is caused by its low solubility in aqueous solutions. Besides, ozone is a toxic, inflammable and explosive substance that requires special conditions during its production. Despite the fact that oxidation of LRW with potassium permanganate can reduce their activity, the process of destruction of organic complexes with this method leads to formation of significant volumes of manganese dioxide sediments (secondary waste). Also, complete oxidation of organic complexes cannot be achieved even using high concentrations of potassium permanganate. Oxidation of LRW using hydrogen peroxide has several advantages compared to other oxidative methods of water treatment — low cost, possibility to store regardless of the temperature, unlimited solubility in water, and simplicity. However, the efficiency of LRW oxidation with hydrogen peroxide is relatively low due to its selectivity for dissolved substances, which slows down the oxidation of a number of organic compounds. It is established that one of the most promising methods for the destruction of the organic components in LRW is the combined oxidation by physical methods in the presence of an additional oxidizing agent, which promotes the formation of hydroxyl radicals with a high reactivity towards oxidation.