Chelating agents, such as EDTA, NTA, and citric acid, possess the capacity to establish complexes with radionuclides, potentially enhancing the migration of such radionuclides from the disposal sites. Hence, quantification of these chelating agents in radioactive wastes is required to ensure secure disposal protocols. The determination of chelating agents in radioactive wastes is mainly composed of two steps, e.g. extraction and detection. However, there are little information on the extraction of the chelators in various radioactive wastes. We endeavored to optimize the extraction conditions for citric acid (CA) found within concrete, a prevalent component in the context of dismantled waste materials. Given the inherent high solubility of CA in water, we applied an aliquot of deionized water to the concrete and conducted a one-hour ultrasonic leaching procedure to facilitate chelate extraction. Subsequently, following the preparation of the concrete leachate via vacuum filtration and centrifugation to yield a clarified solution, we quantified the concentration of CA within the solution using Ion Chromatography (IC). To enhance leaching efficiency, we examined the % recovery variation with respect to the pH of the leaching solution. The optimized extraction method will be applied to diverse chelating agents and radioactive waste categories.

Low- and intermediate-level radioactive waste for permanent disposal often contains organic complexing agents, so-called chelating agents. Organic complexing agents, which are polycarboxylic acids, can increase the mobility of radionuclides into the environment by forming water-soluble complexes with most heavy metals. Therefore, analyzing the complexing agents in radioactive waste is crucial for comprehensive management of nuclear wastes. According to regulatory guidelines, specifically Notice No. 2021-16 issued by the Nuclear Safety and Security Commission, the determination of chelating agent content in radioactive waste materials is required to ensure proper management and safe disposal. However, only a few methods are available to analyze the chelators in various matrices such as concrete, metals, soil, and mixed solid wastes like plastics, vinyl, and rubber. Recently, we found a UV-Vis method based on an enzymatic reaction is inadequate for analyzing citric acid in radioactive waste with a complex matrix like concrete. To address this, we developed a method to determine the contents of EDTA and NTA using a UV-Vis spectrophotometer and citric acid using ion chromatography. The results showed good validity and reliability to determine the chelating agents in various radioactive wastes.

Chelating agents, such as EDTA, NTA, and citric acid, can form radionuclide-chelate complexes that may enhance the migration of radionuclides from disposal sites. Therefore, the contents of these chelators in radioactive wastes are determined for the secured disposal. In this study, a rapid automated method using ion chromatography (IC) is described for analysis of chelating agents. The method enables direct use of a sample solution for the measurement unlike colorimetric or enzymatic methods. In these cases, lots of chemicals are consumed to convert the chelating agents to be UV-Vis-active compounds during the pretreatment process and finally, absorbance or transmittance are measured at specific wavelength using UV-Vis spectrophotometer. In particular, the enzymatic method for determination of citric acid, because of its strong dependence on experimental conditions including sample types and chemical reagents may produce inconsistent results. The automated system using IC allows a laboratory to directly measure the amount of citric acid while reducing total analysis time and increasing efficiency. In addition, this method is capable of detecting a trace amount of citric acid, thereby lowering LOD and LOQ values.