Jei-Won Yeon

The Oxidation Behavior of Iodide Ion Under Gamma Irradiation Conditions

Abstract The oxidation behavior of iodide ion (I−) was investigated in aqueous solutions under a high dose rate of gamma irradiation in the range of 0 to 10 kGy·h−1. In particular, we investigated the formation of tri-iodide ion (I3−), the pH change of the solution, and the behavior of iodine species after the irradiation. As the gamma dose and the irradiation time increased, both the formation rate and the amount of I3− correspondingly increased. While I3− is not present above pH 10 due to its disproportionation reaction even without gamma irradiation, with irradiation, I3− does not exist above pH 6.4 because the H2O2 acts as a reductant above pH 5.4. At relatively high concentrations of I−, I3− was the major oxidation species of the gamma irradiation. However, as the irradiation progressed, the concentration of I3− decreased gradually, and eventually, I2 was left as the only species.

Effect of water-droplet sizes and radiation-field exposure on the transfer of I2 and CH3I gases adsorbed in water

Experimental findings on the transfer of I2 and CH3I gases adsorbed in water were accomplished according to different water-droplet sizes with or without exposure to a radiation field, using two different analysis methods: quantitative analyses based on ultraviolet-visible light and gas chromatography-mass spectroscopies. The amount of transferred volatile iodine was strongly influenced by the existence of water, and a little larger amount of I2 or CH3I was transferred with bigger sized water droplets than smaller ones when the same amount of water was applied. The decomposition effect was superior to the charging effect under a γ-radiation field in our experimental condition, and the relationship between transferred volatile iodine concentrations and water-droplet sizes in the presence of radioactive sources was following the trend of the absence of radioactive sources.

Formation of CH 3 I in a NaI and methyl alkyl ketone solution under gamma irradiation conditions

We investigated the effects of concentrations of NaI and methyl alkyl ketone on the formation of methyl iodide under gamma irradiation conditions. Without irradiation, the formation of methyl iodide does not occur. For the formation of methyl iodide, the solution pH should be brought to lower than 6 by radiolytic decomposition of ketones and air. At a pH below 6, the iodide was oxidized into iodine, allowing for the formation of CH3I from the reaction of iodine and the CH3 radical. When the concentrations of NaI and methyl alkyl ketone were similar, the concentration of methyl iodide was generally at its highest, and as the gamma dose increased, the concentration of methyl iodide increased.

Volatility of radioactive iodine under gamma irradiation: effects of H2O2 and NaOH on the decomposition rate of volatile molecular iodine dissolved in aqueous solutions

The decomposition of molecular iodine by hydrogen peroxide and sodium hydroxide was kinetically studied in aqueous solutions at ambient temperature. To obtain an effective decomposition rate constant under experimental conditions, the concentration of triiodide ions was measured over time instead of that of molecular iodine. Overall, sodium hydroxide was regarded as a more effective decomposer than hydrogen peroxide. As demonstrated in the present study, existing methodologies can be simplified by grouping relevant reaction steps in order to estimate iodine volatility under a severe accident condition for a nuclear power plant.

Introduction of 6th Asian-Pacific Symposium on Radiochemistry (APSORC17)

The Asia-Pacific Symposium on Radiochemistry 2017 (APSORC17) was the sixth of a series of quadrennial conferences started in 1997 in Kumamoto (Japan). APSORC has taken place at Fukuoka (Japan) in 2001, Beijing (China) in 2005, Napa (CA, USA) in 2009, and Kanazawa (Japan) in 2013. Since the announcement in 2013 of hosting the APSORC17 in Korea, our institution, Korea Atomic Energy Research Institute (KAERI), has taken a role as the main organizer in cooperation with Korea Nuclear Society (KNS). Over the past two decades, we have seen the growth of APSORC and noted that it has provided an excellent platform for the exchange of scientific knowledge in diverse fields in radiochemistry. In these areas KAERI also has played a central role in incubating and expanding radiochemistry in Korea, as it celebrates its 60th anniversary next year. Recently, we have invested greater efforts into resolving key issues such as nuclear non-proliferation and the safe disposal of high-level radioactive wastes originating from the progress and maturity of Korean nuclear energy production. In this respect, the local organizing committee (LOC) agreed to host APSORC17 under the theme ‘‘Radiochemistry for Peaceful Prosperity.’’ As my colleagues and I expected, it became the first comprehensive international symposia covering various fields of radiochemistry in Korea. The conference was held in Jeju Island during 17–22 September 2017 with great success. We selected 326 abstracts in total and about 370 persons registered for the conference. After being reviewed by the scientific committee, the abstracts were assigned for presentation including 6 plenary lectures, 40 invited lectures, and 140 oral and 140 poster presentations. There were 10 exhibitors who displayed their products in relation to radioanalytical techniques. At the conference 335 participants (including 15 accompanying persons) representing 21 countries around the world attended five plenary sessions, 39 oral sessions, and two poster sessions (Fig. 1). There was plenty of time for discussion between sessions and at social programs (Fig. 2). In APSORC17 most traditional technical areas dealt with in the previous series of the conferences were covered as well as a special session of (1) Nuclear Non-proliferation. A total of twelve technical sessions were arranged, and the remaining were as follows: (2) Severe Accident & Environmental Remediation Issues, (3) Nuclear Chemistry, (4) Nuclear Energy Chemistry, (5) Nuclear Analytical Techniques, (6) Separation Chemistry, (7) Actinide Chemistry, (8) Nuclear Forensics, (9) Environmental Radiochemistry and Radioecology, (10) Radiopharmaceutical Chemistry, (11) Application of Nuclear and Radiochemical Techniques, and (12) Education in Nuclear and Radiochemistry. In a special session arranged for the Hevesy Medal Award (HMA) Prof. Amares Chatt of the JRNC Board of the Hevesy Award announced the winner of HMA 2017: Prof. Pavel P. Povinec. He presented his award lecture on New ultra-sensitive radioanalytical technologies for new sciences following the medal award ceremony with Dr. Kwang Yong Jee, the chair of APSORC17 LOC. The six invited speakers in plenary sessions held each morning made huge contributions to the success of this conference by providing comprehensive reviews and perspectives in different areas of radiochemistry. I would like to give my special thanks to the speakers for the following lectures: Actinide Chemistry relevant to the Long-term Safety of Nuclear Waste Disposal by Jae-Il Kim (former director of KIT-INE, Germany); Limitations on Containment of Nuclear Programs by Olli Heinonen (senior advisor of SNF-DD, USA); Superheavy Elements of the Mendeleev’s Periodic Table: Present Status and Future by Sergey Dmitriev (director of FLNR-JINR, Russian Federation); Chemistry of the Heaviest Elements by Yuichiro Nagame (deputy director of ASRC-JAEA, Japan); New & Kwang Yong Jee nkyjee@kaeri.re.kr

Mitigation of radionuclide deposition in contaminated water: effects of pH on coprecipitation of Cs(I) and Sr(II) with Fe(III) in aqueous solutions

In the present study, the amounts of caesium and strontium were quantified in the precipitates formed in solutions of sodium hydroxide and iron(III), caesium, and strontium chlorides in the pH range of 7–13. At pH 8 or lower, less caesium and strontium were found in the precipitates. It was verified that for water radioactively contaminated after a severe accident at a nuclear power plant, both iodine volatilization and metal coprecipitation with iron(III) hydroxide can be minimized at ambient temperature by maintaining the water pH near 7.

Spectroscopic Studies of Lanthanides Ion in High-Temperature Molten Salt

Abstract Spectroscopic studies for lanthanide elements in molten salt media performed using absorption, fluorescence, infrared, Raman, electron spin resonance spectroscopy (EPR), and Mössbaur spectroscopy were reviewed in an effort to understand the effect of structural change and chemical behavior of lanthanides on the temperature increase and the matrix change. The absorption spectroscopic studies revealed electronic energy levels of the transitions with the general structural information of the lanthanide elements, whereas the laser-induced fluorescence studies revealed more detailed information on lanthanide elements such as the lifetime behavior, structural changes, and hypersensitive transition. Infrared and Raman spectroscopy also provided structural details of molecule containing lanthanides, and the EPR and Mössbaur spectroscopy provided supporting information for the spontaneous reduction of trivalent lanthanides, such as Eu(III). The recent development of X-ray spectroscopy such as extended X-ray absorption fine structure (EXAFS) also provided detailed information for lanthanide halide in a molten salt medium. The characteristics of f-d as well as f-f transitions of the lanthanide elements were reviewed and the structural changes depending on the media, lanthanides element, and temperature were discussed in detail.

Dispersion Properties of B4C Microparticles as Emergency Neutron Absorbers in Spent-Fuel Pool Water

Abstract The dispersion properties of boron carbide (B4C) microparticles in aqueous media were investigated by measuring the particle size distribution, the dispersibility, and the zeta potential as these properties relate to their application as neutron absorbers in fuel-storage pool water. The B4C powder is composed of particles with a narrow size distribution, with a d50 (mean diameter) of 0.65 μm. The amount of B4C particles dispersed decreased exponentially with increasing dispersion time. The dispersibility of B4C particles increased with an increase in the loading of B4C particles and reached a maximum value at 12.91 wt%. The zeta potential of the B4C suspension was measured as a function of pH and temperature. The B4C suspension has a negative zeta potential value in the pH range between 2 and 12. The dispersion of B4C particles was not greatly influenced by the addition of boric acid (H3BO3). The absolute value of the zeta potential decreased with increasing temperature.

Introduction to a New Real‐Time Water Chemistry Measurement System

In reactor water chemistry, there are three major chemical parameters: pH, redox potential, and electrical conductivity. The pH is conventionally evaluated by measuring Li and B concentrations. Instead of redox potential, the concentration of dissolved hydrogen is generally measured to evaluate the redox condition. The conductivity data provide the information on the concentration of impurities. Until now, these methods have been used for measuring chemical parameters in nuclear power plants (NPPs). However, these methods have inherent limitations as real-time monitoring means, because they are normally applied at room temperature. In order to overcome this limitation, we developed a water chemistry measurement system for enhancing the accuracy of chemistry monitoring. We adopted a ceramic-based pH electrode as a pH sensor. A Pt electrode was used to measure the redox condition. Also, using a potential transient technique, the Pt electrode was also used for measuring the concentration of corrosive species.

The Fundamentals of Reduction of UO 2 2+ Ions on a Pt Electrode and Methods for Improving Reduction Current Efficiency

This review article considered the electrochemical reduction of uranyl ions on a Pt surface. Specifically, we focussed on the improvement in its reduction current efficiency. First, this article briefly explained the fundamentals of the reduction of uranyl () ions on a Pt surface. Namely, they involved the electrochemical behaviour of uranium species, and electrochemical cell configurations for the reduction of ions. In addition, the effects of adsorbed hydrogen atoms were investigated on the reduction of ions. Finally, this article presented the methods for improving current efficiency of the reduction of ions on a Pt surface. Three different kinds of methods are introduced, which include electrochemical surface treatments of Pt electrode involving hydrogenation and anodisation, the use of catalyst poisons, and formation of thin mercury film on a Pt electrode. Moreover, this article provided some clues about how hydrogenation and catalyst poisons work on the reduction of ions.