Study of the Effects of Physicochemical Factors during Corrective Treatment of Reactor Bleed-off Water at Nuclear Power Plants to Ensure That Conditioned Radioactive Waste Meets Regulatory Requirements

The results of studies on the decomposition of surfactants in reactor bleed-off water by corrective treatment with hydrogen peroxide followed by heating are presented. A method for determining the type and concentration of surfactants in aqueous solutions based on high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS) is proposed. The dependences of the purification efficiency of the solution on initial surfactant concentration, treatment time and temperature, and the presence of an additional contaminant (potassium permanganate) are investigated. It is shown that, in order to satisfy regulatory document requirements under a conservative approach, surfactant removal efficiency should be at least 81% when evaporating the bottoms before cementing to 150 g/L and at least 95% when evaporating to 450 g/L. It is demonstrated that dosing hydrogen peroxide into aqueous solutions leads to the decomposition of complexing agents during processing at temperatures between 80–100°C. At temperatures of 80°C and above, the surfactant concentration reaches 62%, which corresponds, without a conservative approach, to the surfactant content in the bottoms not exceeding 1% after 4 h of treatment. Dosing potassium permanganate into the water to be purified makes it possible to remove almost 100% of surfactants without resorting to heating the water to the boiling point. The efficiency of surfactant removal down to the level of complexing agents in the bottoms below 1% is achieved by dosing potassium permanganate 70 min after the start of the experiment, and when heating to 100°C, in less than 40 min. The results obtained can be used to justify the safety of radioactive waste management technologies used in the nuclear power industry.