Дослідження процесів озонолізу органічних компонентів модельних розчинів рідких радіоактивних відходів реакторів ВВЕР

Abstract

The article highlights the problem of reprocessing of liquid radioactive waste (LRW) from the Ukrainian nuclear power plants with VVER reactors. The main method of these LRW treatment is distillation (evaporation) and ion exchange sorption. The final products of LRW processing by distillation are distillation residues, spent sorbents and sludges, and salt melt with significant radioactivity accumulated in large volumes, which do not meet the long-term storage and disposal criteria. So, it is necessary to develop a new, more efficient LRW treatment scheme that can solve the problems of large volumes of LRW and transfer waste to a state suitable for long-term storage and disposal. One of the important and challenging problems of LRW treatment is the presence of organic components (ethylenediaminetetraacetic acid (EDTA), oxalic acid, synthetic surfactants (SPAR) in the waste, since these substances complicate removal of radionuclides from the LRW. The results of investigation of ozonolysis conditions of LRW organic components are presented on the example of a model solution with imitated solutions of disodium salt of ethylenediaminetetraacetic acid and ethane diacid. It was established, that ozonation of organic components of LRW results in decreasing of pH value, which causes reduction of their destruction efficiency. Control of the pH values at the initial level (11−12 units) by permanent alkalifying can increase the ozonolysis efficiency of LRW organic components in 30%. EDTA is better destructed by ozone than ethane diacid. Destruction of LRW organic components progresses in two stages: the first is fast and second is low. The maximum of EDTA destruction degree, in the experimental conditions, was 86%; destruction degree of ethane diacid — 51%; maximum of LRW model solution organic components (EDTA, ethane diacid, synthetic surface-active reagent) destruction degree was 67%. Due to co-precipitation and adsorption during the solution ozonizing, decrease in Mn concentration in LRW model solution reaches 94.3%, 137Cs activity decreases by 26%, and 90Sr — 15.7%, concentration of Co decreases only by 6%.