The potentiostatic titration method is one of the effective methods for determining the total uranium assay in high-concentration uranium samples. A notable approach is the Devies-Grey titration method, which was first reported in 1964. In the U sample treatment process of this method, the reduction of U(VI) by Fe(II) is initially a non-spontaneous reaction based on the reduction potentials of the two half-reactions. However, in a high-concentration phosphoric acid medium, the reduction potential of Fe(II) is enhanced, simultaneously increasing the reduction potential of U(VI). As a result, the redox reaction becomes spontaneous due to these dual effects. On the other hand, the reaction kinetics can elucidate why nitric acid does not oxidize U(IV) during the oxidation of Fe(II) to Fe(III). Furthermore, the role of Mo(VI)/Mo(V) as a redox enhancer, employed alongside nitric acid, can be comprehended through electrochemical means. Similarly, the function of V(IV) as an electrochemical enhancer, aiding the action of the Cr(VI) titrant, becomes understandable. Grasping the various phenomena that manifest during the titration process is imperative for refining existing titration methods and pioneering new ones.

Measurement of oxide ion (O2-) concentration is a basic technology required in molten salt fields, from energy storage systems to electrolytic reduction of rare earth elements or spent nuclear fuels. In a molten salt reactor, O2- ions react with actinide elements to form their oxides or oxy-chlorides to induce actinide precipitation, and promote metal corrosion to cause a failure of structural material. For these reasons, removal of O2- ions and monitoring of the O2- concentration in molten salt reactors are essential. In this study, methods using chemical and electrochemical methods were investigated for measuring the concentration of O2- ions in a molten salts. The acid-base neutralization reaction was used as a chemical analysis method. And electrochemical methods using the O2- diffusion limit current and YSZ (yttria stabilized zirconia) indicator electrode were used for measuring the O2- concentration. Finally, a modified method using porous membrane electrode was applied to monitor the O2- concentration. The O2- concentration was measured up to about 2wt% of Li2O by the method using the O2- diffusion current, up to about 4wt% by the YSZ indicator electrode, and about 6wt% by the porous membrane electrode in LiCl molten salts.

Though many treatment technologies of contaminated water have been developed for a long time, it is still difficult to find a suitable method for large volumes of low radioactivity tritium-contaminated water. For this reason, most of the tritium-contaminated water been discharged to the biosphere or been stored in a special control area as radioactive waste. Activated carbon is a common material, but since there are few data on the treatment of tritium-contaminated water, its adsorption behavior to HTO is worth studied. In our study, for the tritium-contaminated water having a low radioactivity concentration (350-480 Bq/g), adsorption experiments were performed with activated carbon. The effects on the selective adsorption of HTO were investigated for temperature (5-55°C), hydrogen peroxide (1-10wt%) and activated carbon reuse (1-6 times) under non-equilibrium conditions. The treatment of activated carbon significantly reduced the radioactivity of tritium-contaminated water around 60 minutes of adsorption time. In order to clearly analyze the experimental results, positive factors and negative factors on the HTO selectivity were separately evaluated according to the adsorption time. Temperature and the reuse of activated carbon were evaluated as negative factors for HTO selectivity of activated carbon, whereas hydrogen peroxide (> 5wt%) was evaluated as a positive factor. By the evaluation method of separating the influencing factors into two types, the adsorption experimental results of HTO could be understood more clearly.

The effect of hydrogen peroxide on the electrochemical behavior of iron was investigated in perchlorate solutions. Iron showed four distinct behaviors in the perchlorate solutions of pH 3.0. First, the active dissolution regions of Fe with two current waves were observed in the potential range of −0.7 to 0 V (vs. SCE). Second, the stable passivation was found in the potential range between 0 and 0.3 V (vs. SCE). Third, unstable passivation region was observed in the potential range of 0.3 to 1.2 V (vs. SCE). Finally, pitting corrosion was observed at a potential above 1.2 V (vs. SCE). The pH increase stabilized the passivation process of iron, whereas the increase in temperature had a negative influence by enhancing the passivation and pitting behaviors of iron. The presence of hydrogen peroxide at the concentrations below 1.45 mM had an adverse effect on the formation of the passive layer. However, at concentrations above 1.45 mM, hydrogen peroxide affected a beneficial influence on the formation of stable iron oxide layer in the active dissolution region. In addition, regardless of the hydrogen peroxide concentration, the presence of hydrogen peroxide mitigated the pitting corrosion of iron.