Development of a Rapid Analytical Method for 129I in the Contaminated Water and Tree Samples at the Fukushima Daiichi Nuclear Power Station
Abstract 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, Iwas extracted with the Anion-SR in 3 M NaOH and diluted HCl (pH 2) solutions, whereas IO3was only slightly extracted in these solutions. In contrast, 15 ng Iwith 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 Iwas changed to another species in a day in this condition. Iodate was successfully reduced to Iwith NaHSO3 in the diluted HCl solution and extracted with the Anion-SR. Consequently, the solution condition to analyze both Iand IO3using 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 Iand IO3-, and the chemical species in the trap solutions was observed to contain I-.
Because of the accident, a large amount of radioactive waste was generated at the Fukushima Daiichi Nuclear Power Plants (FDNPP). To establish the waste management strategy, the radioactivity inventory has to be evaluated. Iodine-129 is one of the important nuclides of which the radioactivity has to be evaluated. Although Iis considered a major species of 129I generated in the reactor, IO3and I2 are possibly generated, depending on the reactor conditions . Furthermore, because seawater was introduced to the reactors for cooling down in the early phase of the accident and seawater contains the natural iodine species, 127IO3-, an isotope exchange reaction between 127IO3and 129Imay have occurred. Therefore, analytical conditions to determine total I content, in this case IO3and I-, in water and tree samples were investigated in the current work.
Presently, contaminated water is accumulating in the basement of the reactor and turbine buildings at FDNPP. The accumulated water-processing equipment was installed to decontaminate and to desalinate. Consequently, secondary waste such as spent zeolite and sludge is generated. To evaluate the radioactivity inventory of the waste indirectly, water samples were collected from the inflow and outflow of the apparatus . The contaminated water contains high levels of radioactivity of 137Cs, 90Sr, and other radionuclides. To limit radiation exposure of the analyst, rapid chemical separation of iodine species from these radionuclides is required. Chemical separation studies using the solid-phase extraction sorbent Anion-SR have been reported to rapidly separate Ifrom major fission products such as Cs and Sr in contaminated water samples . However, Anion-SR essentially extracts only Iand not IO3-. Therefore, reduction of IO3to Iis required to analyze total
I. In this study, NaHSO3 was used as the reductant and the solution conditions were studied to reduce IO3to I-.
Because of the hydrogen explosion of FDNPP, trees on the site were contaminated by the radionuclides. Many of the trees were cut down to provide space to install tanks storing the contaminated water. Consequently, approximately 40,000 m3 of trees were stored in the site as radioactive waste . A combustion method was used to analyze 129I in cement, ash, and soil samples [5, 6]. To apply a combustion method for the tree samples, there were some subjects: evaporation and deposition of the organic materials and anomalous combustion. Therefore, decomposition of organic material to CO2 and H2O using oxidant was examined. In addition, the rate of temperature increase was controlled to avoid anomalous combustion. Furthermore, the influence of the chemical species, IO3 or I , on recovery was studied.