Volume Reduction Of Radioactive Waste Research Articles

Understanding of electrochemical behaviors of niobium in molten LiCl–KCl eutectic for pyrochemical decontamination process

In this study, the electrochemical behaviors of niobium were examined with 1.0 wt% of NbCl5 in the molten LiCl–KCl at 450 °C via different electrochemical techniques. A chronoamperometry was performed to prepare solutions containing the selected oxidation state of the Nb ion, and the color of the solution was compared to the literature data. Cyclic voltammetries were performed with a combination of different scan ranges and scan rates using an electrochemical cell prepared by LiCl–KCl–NbCl5 salt mixture and an inert tungsten electrode. Five oxidation and four reduction peaks were found, and possible redox reactions attributing to each peak were identified based on the rate of change of the current density as a function of the scan rate. It was found that Nb(V) can be deposited as a metallic Nb via Nb(IV), Nb(III), and Nb(II), and the deposition of the metallic Nb is perturbed by the formation of insoluble nonstoichiometric Nb chloride compounds on the electrode surface. Three irreversible oxidation peaks were caused by the oxidation of metallic Nb and insoluble Nb chlorides, which competed with each other, but the dissolution of metallic Nb became dominant as the scan rate increased. X-ray diffraction analysis was performed to examine the possibility of a chemical reduction of Nb(V) to Nb(IV), but no evidence was found, which indicated the initial concentration of Nb(V) was preserved in all the experiments. It was also found that the different pyrochemical processes would desirable to separate Nb for the purpose of salt purification as well as volume reduction of radioactive waste, depending on the electrochemical behaviors for other elements that can be simultaneously dissolved with Nb.

Polymeric coatings for surface decontamination and ecofriendly volume reduction of radioactive waste after use

A magnet-sensitive and strippable polymeric coating that consists of a magnetic adsorbent with 137Cs adsorption properties using a polyacrylamide (PAAm)/alginate(Alg)-based hydrogel with highly elastic properties was developed for surface decontamination. The aqueous polymeric solution of PAAm and Alg containing adsorbent could be easily applied to 137Cs-contaminated surfaces via the brush method. The simple addition of calcium ions on the surface induced the formation of an adsorbent/PAAm-Alg hydrogel film that could easily peel away from decontaminated surfaces due to its high elasticity. This polymeric coating displayed a good removal efficiency of 96.53% and a decontamination factor (DF) of 28.85 for 137Cs-contaminated surfaces due to the presence of the adsorbent, which had a large distribution coefficient for Cs (3.34 × 104 mL/g), and the large amount of Cs chelating groups in the Alg and PAAm, such as carboxyl and amine groups. The generated volume of the radioactive wastes after surface decontamination was simply reduced due to the magnetic separation of the adsorbent from the used polymeric coating. Furthermore, this new ecofriendly volume reduction method for radioactive waste demonstrated the reusability of PAAm and Alg for further surface decontamination because almost all of the 137Cs (99.838%) captured in the used polymeric coating was removed by magnetic separation of the adsorbent. Therefore, the adsorbent/PAAm-Alg-based polymeric coating system has excellent potential as a new cost-effective surface decontaminant.

Present Situation of Fukushima and Possibility of Decontamination Technology by Superconducting Magnetic Separation System

SUMMARYA large amount of radionuclides were spread by the accident of Fukushima Daiichi nuclear power plant in 2011. The situation of surrounding area of nuclear power plant is momentarily changing. In order to consider for decontamination or volume reduction of radioactive wastes, it is necessary taking into account not only the technical needs but also feelings of inhabitants, reduction of environmental load, reduction of the radiation exposure on workers, and efficiency and cost of decontamination work. In this paper, the application possibility of superconducting magnetic separation system for decontamination and volume reduction was discussed compared with other technologies from above multidirectional viewpoint.

207 炉内空冷式焼却炉を用いた汚染廃棄物の減容化(焼却・溶融技術)

207 炉内空冷式焼却炉を用いた汚染廃棄物の減容化(焼却・溶融技術)

Nano-aggregates of hexacyanoferrate (II)-loaded magnetite for removal of cesium from radioactive wastes

Nano-sized magnetic sorbents can be promising candidate materials for treatment of low-level effluents resulting in effective decontamination and very high volume reduction of radioactive wastes. Preparation of magnetite-hexacyanoferrate composite was based upon wet-dispersion and in situ precipitation for synthesizing coatings on magnetite. Superior magnetic properties were rendered to potassium nickel (II) hexacyanoferrate (II), a sorbent with high specificity for cesium uptake, by loading to magnetite. The magnetic complex showed same apparent sorption capability for cesium as potassium nickel (II) hexacyanoferrate (II). Transmission electron microscope revealed a particle size distribution of 8–30 nm for these magnetic particles. Large moment possessed by particles was responsible for high uptake of magnetic separator column at low background magnetic field. Low residual magnetism favored magnetic filter regeneration parameter requirement.