Asako Shimada

Radiochemical analysis of rubble and trees collected from Fukushima Daiichi Nuclear Power Station

To characterize the rubble and trees contaminated by radionuclides released by the recent accident at the Fukushima Daiichi Nuclear Power Station, the radiochemical analysis protocols were modified using those developed by the Japan Atomic Energy Agency for the waste generated by research, industrial, and medical facilities. The radioactivity concentrations of gamma-ray-emitting nuclides 60Co, 94Nb, 152Eu, and 154Eu, and beta-particle-emitting nuclides 14C, 129I, 36Cl, 79Se, and 99Tc were successfully applied by the modified analytical method. In contrast, the radioactivity concentrations of 3H, 90Sr, 137Cs, and alpha-particle-emitting nuclides were applied by the conventional method. Unfortunately, 36Cl, 94Nb, 129I, 152Eu, 154Eu, and alpha-particle-emitting nuclides were below the detection limit of the conventional method. The measured radioactivity concentrations, except for that of 3H, were not uniform in the area but depended on the reactor unit. Although the radioactivity concentrations were varied widely, this analysis successfully clarified the characteristics of the radioactivity concentrations of the rubble and trees.

Development of a separation method for molybdenum from zirconium, niobium, and major elements of rubble samples.

A method for separation of Mo from Zr, Nb, and other major elements of rubble samples from the Fukushima Daiichi Nuclear Power Station (FDNPS) was developed to enable 93Mo assay of the rubble samples. Although (93)Mo analysis has been reported in a few studies, the known separation method is tedious and time consuming, or the target is a simple material. Therefore, a simple and rapid protocol for the separation of a complex material, i.e., the rubble sample, was developed in this study. Firstly, loss of Mo during the digestion of simulated rubble samples was evaluated. Next, weight distribution coefficients (Kds) of Zr, Nb, and Mo between an extraction chromatographic resin (tetra valent actinide resin, TEVA resin) and acid solutions (HF-HCl and HF-HNO3 solutions) were determined to obtain suitable solution conditions for the separation of Mo from Zr and Nb. Based on the obtained Kds, a chromatographic separation scheme was designed and applied to the digested solution of the simulated rubble sample. Consequently, Mo was successfully separated from Zr, Nb and other major metal ions of the simulated rubble sample.

A new method to analyze 242mAm in low-level radioactive waste based on extraction chromatography and β-ray spectrometry.

A new method for identifying (242m)Am in low-level radioactive waste (LLW) using β-ray spectrometry is proposed. First, (152)Eu, (241+242m+243)Am, and (244)Cm in a digested solution of simulated LLW were separated from the major components of the digested solution and Pu using a transuranium element resin (TRU resin). Next, Am and Cm were separated from Eu using a tetravalent actinide element resin (TEVA resin). A β-ray spectrum of the fraction containing Am and Cm was recorded and the contribution of (239)Np, which is a daughter nuclide of (243)Am, was subtracted to determine the radioactivity of (242m)Am. Also mutual separation of Am, Cm, and Eu was carried out using a tertiary pyridine resin to determine (242m)Am by analyzing the increase of (242)Cm in the Am fraction just after separation of Am from Cm, which is the traditional method. The isotope ratio of (242m)Am/(241)Am determined by β-ray spectrometry agreed with that obtained by analyzing the traditional method.

Development of an extraction chromatography method for the analysis of 93Zr, 94Nb, and 93Mo in radioactive contaminated water generated at the Fukushima Daiichi Nuclear Power Station

A new mutual separation method was developed to enable the analysis of 93Zr, 94Nb, and 93Mo in radioactive contaminated water from the Fukushima Daiichi Nuclear Power Station (FDNPS). First, distribution coefficient (Kd) values between tetra valent actinide resin and HF, HF/HNO3, and HF/HCl solutions were obtained to select the conditions for chromatographic separation. The separation performance of the developed method was validated with samples containing potentially interfering elements of the measurement of 93Zr, 94Nb, and 93Mo. Finally, the chromatographic separation method was applied to the analysis of 93Zr, 94Nb, and 93Mo in contaminated water sampled at the FDNPS.

Development of a Rapid Analytical Method for 129I in the Contaminated Water and Tree Samples at the Fukushima Daiichi Nuclear Power Station

The separation conditions for iodine species were investigated to analyze 129I in contaminated water and tree samples generated from the Fukushima Daiichi Nuclear Power Station (FDNPS). Inorganic iodine species in the samples from FDNPS were thought to be iodide (I−) and iodate (IO3 −); therefore, the behaviors of these species during separation using a solid-phase extraction sorbent, Anion-SR, for water samples and combustion for tree sample were studied. When the amount of I was 1 μg and used within a few hours, I− was extracted with the Anion-SR in 3 M NaOH and diluted HCl (pH 2) solutions, whereas IO3 − was only slightly extracted in these solutions. In contrast, 15 ng I− with a larger amount of IO3 − (1 μg I) in the diluted HCl (pH 2) and allowed to stand for 1 day was only slightly recovered. It is possibly that I− was changed to another species in a day in this condition. Iodate was successfully reduced to I− with NaHSO3 in the diluted HCl solution and extracted with the Anion-SR. Consequently, the solution condition to analyze both I− and IO3 − using Anion-SR was observed to be the diluted HCl at pH 2 with a reductant. For the tree samples, a combustion method was applied and the rate of temperature increase was optimized to avoid anomalous combustion. Greater than 90 % recovery was obtained for both I− and IO3 −, and the chemical species in the trap solutions was observed to contain I−.