Abstract
In the present study, 129I activities and 129I/127I atom ratios were measured in 60 soil samples contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The 127I concentrations, 129I activities, and 129I/127I atom ratios in dry-weight were observed to be 0.121–23.6 mg kg−1, 0.962–275 mBq kg−1, and (0.215–79.3) × 10−7, respectively. The maximum values of both 129I activities and 129I/127I atom ratios in Japanese soil increased about three orders of magnitude due to this accident. The equation logy = 0.877logx + 0.173 (Pearson’s r = 0.936; x, 129I concentration; y, 131I concentration; decay-corrected to March 11, 2011) instead of a simple constant may be a better way to express the relationship between 129I and 131I in Japanese soil affected by both global fallout and FDNPP accident fallout. In addition, a moderate correlation was observed between 129I and 135Cs (logy = 0.624logx + 1.01, Pearson’s r = 0.627; x, 129I activity; y, 135Cs activity). However, 129I presented larger fractionations with less volatile radionuclides, such as 236U, 239Pu, and 240Pu. These findings indicated 135Cs could be roughly estimated from 129I or 131I; this is advantageous as fewer 135Cs data are available and 135Cs/137Cs is being considered a promising tracer during radiocesium source identification.
Highlights
The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011 released massive amounts of radionuclides into the terrestrial environment, including both short-lived radionuclides (e.g. 133Xe, 5.2 d; 131I, 8.0 d; 133I, 20.8 h; 134Cs, 2.1 y) and long-lived radionuclides (e.g. 129I, 1.57 × 107 y; 135Cs, 2.3 × y; 236U, 2.342 × y; 239Pu, 24,110 y and 240Pu, 6,564 y)[1,2]
These long-lived radionuclides can be determined in environmental samples for a long time after a nuclear accident; they have great potential to act as proxies for short-lived radionuclides that are of greater radiological concern
We report data for 127I, 129I, and 131I in 60 soil samples, with heavy 134Cs contamination due to the FDNPP accident, that were collected immediately after this accident. For those soil samples without 131I activity data, 131I activities were reconstructed via deduced 129I-131I equation and measured 129I activities. Other radionuclides, such as 135Cs, 236U, 239Pu, 240Pu, were considered with regard to the differences and relevance among them in soil samples affected by the FDNPP accident fallout and global fallout, in order to see whether 129I can track other radionuclides (135Cs, 236U, 239Pu, and 240Pu) derived from the FDNPP accident fallout and global fallout
Summary
The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011 released massive amounts of radionuclides into the terrestrial environment, including both short-lived radionuclides (e.g. 133Xe, 5.2 d; 131I, 8.0 d; 133I, 20.8 h; 134Cs, 2.1 y) and long-lived radionuclides (e.g. 129I, 1.57 × 107 y; 135Cs, 2.3 × y; 236U, 2.342 × y; 239Pu, 24,110 y and 240Pu, 6,564 y)[1,2]. Conventional radiometric methods, such as γ spectrometry, are easier to apply as they do not have complicated procedures for sample treatment, chemical separation, and purification Those short-lived radionuclides with high radiation exposure risk, such as 131I and 134Cs, were extensively studied in the initial stage of the FDNPP accident. Initial reconstructions of the distribution of 131I deposition through the measurement of 129I were obtained, as it was known that there were strong correlations between 131I and 129I activities in the contaminated surface soil samples affected by both the Chernobyl accident[7] and the FDNPP accident[8,9,10,11] They are well-suited tracers with great potential for source identification. Other radionuclides (major long-lived ones), such as 135Cs, 236U, 239Pu, 240Pu, were considered with regard to the differences and relevance among them in soil samples affected by the FDNPP accident fallout and global fallout, in order to see whether 129I can track other radionuclides (135Cs, 236U, 239Pu, and 240Pu) derived from the FDNPP accident fallout and global fallout
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