Chelating agents like ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and nitrilotriacetic acid (NTA) find extensive application in the removal of residual substances due to their high stability constants with a wide range of metal ions. They also play a crucial role in nuclear decontamination operations aimed at eliminating metallic radionuclides such as 60Co, 90Sr, and 239Pu. However, improper disposal of chelated radioactive waste can lead to significant increases in radionuclide migration rates from disposal sites. Therefore, it is imperative to comprehend the behavior of chelating agents under varying conditions, including pH, temperature, and metal ion concentrations. In this study, we present the results of a pH-dependent composition analysis of nickel-chelate complexes using UV-Vis spectrophotometry. Nickel (Ni) serves as an ideal metal ion for investigating its interactions with chelating agents due to its solubility over a wide pH range and high stability constants with all three chelating agents mentioned earlier. Initially, UV-Vis spectra of Ni-EDTA, Ni-DTPA, and Ni-NTA complexes were recorded at various pH levels. We assigned absorption maxima and compared our findings with existing literature on each Ni-chelate complex. Furthermore, we examined mixed samples of all three complexes, varying the pH to monitor changes in composition. The results and their implications will be presented in our poster presentation.

As existing nuclear power plants reach the end of their lifespan, 22 nuclear power plants in korea are scheduled to be permanently shut down and decommissioned by 2050. Chelates are used as decontamination agents during nuclear power plant operation and decommissioning, and as a result, decommissioning waste contains chelates. Chelates contained in radioactive waste are complexed with radionuclides and increases their mobility. So, qualitative and quantitative analysis of chelates contained in radioactive waste is necessary. However, the spectroscopic method (UVVis), previously used for chelate analysis in Korea takes too much time for analysis and cannot analyze two or more chemically similar chelates at the same time. Due to these problems, new methods for analyzing chelate must be developed. Overseas, many cases of chelate analysis using advanced analysis equipment have been reported. CEA in France has developed a chelate analysis method for application to radioactive waste using HPLC-MS (J. Chromatogram. A, 1276, 20-25, 2013). In this method, the existing method of measuring EDTA using a complex of Fe and EDTA was improved to measuring a complex of Ni and EDTA. Based on such overseas cases, we would like to develop an analysis method for chelates in radioactive waste. For this purpose, we will verify similar overseas papers and develop pretreatment methods for mixtures of chelates (EDTA, DTPA, NTA) and metals (Fe, Ni, Cu, etc.) in various media. Finally, we will develop a separation analysis technology for multi-component chelates in nuclear decommissioning waste based on LCMS.