Ken-ichiro Ishimori

Radionuclide release to stagnant water in the Fukushima-1 nuclear power plant1

After the severe accident at the Fukushima-1 nuclear power plant, large amounts of contaminated stagnant water have accumulated in turbine buildings and their surroundings. This rapid communication reports calculation of the radionuclide inventory in the core, collection of measured inventory in the stagnant water, and estimation of radionuclide release ratios from the core to the stagnant water. This evaluation is based on data obtained before 3 June 2011. The release ratios of tritium, iodine, and cesium were several tens of percent, whereas those of strontium and barium were smaller by one or two orders of magnitude. The release ratios in the Fukushima accident were equivalent to those in the accident of the Three Mile Island, Unit 2 (TMI-2).

Carbon-14 analysis in solidified product of non-metallic solid waste by a combination of alkaline fusion and gaseous CO2 trapping

In order to establish a simple and rapid analytical method for (14)C in solidified products made from non-metallic low-level radioactive solid wastes such as concrete, mortar and glass by melting treatment, a radiochemical analysis in combination with alkaline fusion as a sample decomposition method was examined. A simulated solidified product containing (14)C, which was prepared by using nuclear reaction (14)N(n, p)(14)C with thermal neutron irradiation, was analyzed by the present method to compare with a conventional radiochemical analysis using oxidizing combustion. The reproducible and quantitative recovery of (14)C from the simulated solidified product indicates that the present method is more efficient for (14)C analysis in solidified products than the conventional method using oxidizing combustion.

Synergistic Extraction of Am(III) and Eu(III) by Tris(2‐pyridylmethyl)Amine with Various Anions in 1,2‐Dichloroethane

The extraction equilibria of Am(III) and Eu(III) by using a tripodal ligand, tris(2‐pyridylmethyl)amine (tpa), with various lipophilic anions have been investigated. The extractability of both Am(III) and Eu(III) was increased by the combination of tpa and counteranions due to a synergistic effect. The separation factors between Am(III) and Eu(III) were also increased from 7.6 to 49 by the combination of counteranions and organic solvents. The extraction equilibria of Am(III) and Eu(III) with tpa in 1,2‐dichloroethane were determined by slope analysis. It was found that three anions and one molecule of the ligand coordinated to Am(III) and Eu(III) was extracted regardless of the anions.

Safe and rapid development of capillary electrophoresis for ultratrace uranyl ions in radioactive samples by way of fluorescent probe selection for actinide ions from a chemical library

After the serious nuclear accident at the Fukushima Daiichi Nuclear Power Plant caused by the Great East Japan Earthquake in 2011, the development of feasible, safe, and highly sensitive analytical methods (in terms of low levels of radiation exposure and radioactive waste generation) for radioactive samples, especially actinide (An) ions, represents an important challenge. Here we propose a methodology for selecting appropriate emissive probes for An ions with very low consumption and emission of radioactivity by capillary electrophoresis-laser-induced fluorescence detection (CE-LIF), using a small chemical library of probes with eight different chelating moieties. It was found that the emissive probe L1, which possesses the tetradentate chelating moiety 1,10-phenanthroline-2,9-dicarboxylic acid (PDA), was suitable for detecting uranyl ions. The detection limit for the uranyl-L1 complex using CE-LIF combined with dynamic ternary complexation and on-capillary concentration techniques was determined to be 2.9 × 10-12 M (0.7 ppt). No interference from the large excess of matrix metal ions was observed. This method was successfully applied to real radioactive liquid samples collected from nuclear facilities, including the Fukushima Daiichi Nuclear Power Plant. This strategy not only permitted the development of a safe and rapid analytical method but also provided insight into the coordination chemistry of An ion complexes. Specifically, the PDA structure provided substantial kinetic inertness to its uranyl complex; the formation of a ternary complex between uranyl-L1 and carbonate was revealed; and unusual interactions were observed between the π-electron systems of uranyl and the phenanthroline ring, which stabilized the uranyl-PDA interaction.

Preparation of Reference Materials on Radiochemical Analysis for Low-Level Radioactive Waste Generated From Japan Atomic Energy Agency

In order to prepare simulated reference materials of solidified products using a laboratory-scale electric furnace instead of a plasma heating device, melting tests of miscellaneous simulated solid wastes were conducted. Over 90% of Cs was remained in the solidified product by keeping the basicity (CaO wt%/SiO2 wt%) to be 0.05. Under the optimum melting conditions, reference materials containing α-ray emitting nuclides (237 Np, 241 Am and 244 Cm) or γ-ray emitting nuclides (60 Co, 137 Cs and 152 Eu) were prepared. For reference materials containing β-ray emitting nuclides such as 14 C and 36 Cl, a preparation method with nuclear reaction 14 N(n, p)14 C or 35 Cl(n, γ)36 Cl by thermal neutron irradiation was attempted. The radioactivity concentrations of the reference materials were evaluated from radiochemical analysis. It was confirmed that the reference materials could be successfully prepared on the present preparation methods.Copyright