A new plant for spent nuclear fuel reprocessing will be operated in near future at Rokkasho in the northernmost part of the Mainland of Japan. Iodine-129 is expected to be released from the plant to the environment. This 129I enters the environmental iodine cycle and changes the iodine isotopic abundances. Evaluation of the levels of 129I in environmental samples in Japan before its operation would contribute to studies on the migration behavior of iodine itself, radiological exposure by radioactive iodine and utilization of 129I as a tracer. Five sampling sites in Japan were selected at Hokkaido, Iwate, Akita, Hyogo and Ooita. Samples of soils, seaweeds and milk were collected from all the sampling sites. Soil samples were sliced into two sections: one is a surface-layer from 0 to 5 cm depth and the other is a deeper-layer from 5 to 20 cm depth. Sample preparation for soils and seaweeds was carried out with a combination of combustion and an anion exchange resin disk. Since the disk was clogged by milk fat, it was difficult for milk to penetrate into the disk. The sample preparation for milk, therefore, was carried out with a combination of the batch technique using an anion exchange resin and the solvent extraction method. Iodine in the samples was precipitated to the chemical forms of AgI and PdI2 for the measurements with an accelerator mass spectrometry (AMS) and a neutron activation analysis (NAA), respectively. Iodine-129 was measured by both AMS and NAA, and 127I by an inductively coupled plasma mass spectrometry (ICP-MS). The iodine isotopic ratios (129I / 127I) for some samples of surface and deep-layer soils, all of seaweeds and milk were below the NAA detection limit (129I / 127I = 10-9 - 10-10), but those for some soil samples were detected by NAA. For example, the iodine isotopic ratios obtained from AMS and NAA for the samples of surface-layer soils at Hokkaido were (2.4 ± 0.04) × 10-8 and (2.4 ± 0.26) × 10-8 , respectively. The results with the different measurement methods were in excellent agreement within the analytical errors. Our presentation will give the detailed results for the measurements by AMS and NAA, together with the discussion of iodine isotopic ratio in environmental samples.
See more of Poster Session I
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)