会議発表用資料 Transuranic elements in soil samples from Fukushima Prefecture collected in March 2011

R.KIEREPKO  ,  S.K.Sahoo

2016-08-30
内容記述
The gigantic tsunami in the northeast Japan region (11 March 2011) caused serious damage to Fukushima Dai-ichi nuclear power plant (FDNPP). As a result, large amount of fission products dispersed across a large area of northern Japan. This work, focus on the estimation of radioactivity level by determination of transuranic isotopes (Pu , 241Am, U) and/or the activity ratios in the surface soil samples collected during a few days after accident (17 – 19 March 2011) from the Fukushima prefecture. All samples were dried at temperature of 1050 C overnight and passed through 2 mm mesh sieve. Subsequently, samples were placed in the polypropylene cylindrical containers for gamma spectrometric measurements. The measurement time was fixed during 1h. Results clearly showed contamination of all samples by aerosols related to FDNPP accident (activity ratio of 134Cs/137Cs was found almost to unit). After that, samples were homogenized and about 10 g of each powdered samples were ashed at a temperature of 6000 C. The soil samples were decomposed and dissolved by strong acids. Subsequently, radiochemical separation and purification of plutonium, americium and uranium isotopes were measured by α- spectrometry. Radionuclides and their isotopes ratios have been used as tracer of anthropogenic activity. The relation between them can provide an idea about the source/sources of an investigated contamination. The activity concentration of 239+240Pu in samples ranged between <0.006 Bq kg-1 and 0.216 Bq kg-1 with an average value of 0.052 Bq kg-1. Obtained level was lower than average activity concentration of Pu in soil (0.15 Bq kg-1 ) from Japan (before FDNPP accident) reported by IAEA . The explanation of that difference could be fact that investigated samples originated from cultivated area (before accident). We could notice 238Pu only in three samples and the values were usually close to MDC (0.005 Bq kg-1). The activity ratios of 238Pu/239+240Pu in two samples coincided with global fallout and were comparable with reported value. There was no strong correlation between high activity concentration of volatile radioisotopes (134Cs, 137Cs) with Pu. Results of Am and U isotopes and their interpretation will be presented at the conference.
NINTH INTERNATIONAL CONFERENCE ON NUCLEAR AND RADIO CHEMISTRY-NRC9

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