The si t uat i on of  Ag and Pu radi oi sot opes i nsoi l  rel eased f rom Fukushi ma Dai i chi  nucl earpower pl ant s
著者Ki mura Haruhi ko,  Uesugi  Masaki ,  Muneda A. ,Wat anabe R. ,  Yokoyama Aki hi ko,  Nakani shi  Takeo
j ournal  orpubl i cat i on t i t l e
J ournal  of  Radi oanal yt i cal  and Nucl earChemi st ry
vol ume303
number2
page range1469- 1471
year2014- 01- 01
URLht t p: //hdl . handl e. net /2297/41327
doi: 10.1007/s10967-014-3587-y
The situation of Ag and Pu radioisotopes in soil released from  
Fukushima Daiichi nuclear power plants 
H. Kimura 1, M. Uesugi2, A. Muneda3, R. Watanabe 1, A. Yokoyama 2, 
T. Nakanishi 4 
1Grad. School Nat. Sci. Tech., Kanazawa Univ., 2 Inst. Sci. Eng., Kanazawa 
Univ., 3Col. Sci. Eng., Kanazawa Univ.,  4Adv. Sci. Res. Cent., Kanazawa 
Univ. 
Corresponding author’s e-mail address: yokoyama@se.kanazawa-u.ac.jp 
1. Abstract 
Massive radionuclides were released into the environment due to the 
Fukushima Daiichi nuclear power plant (FDNPP) accident in March 2011. The 
concentrations of Pu and 110mAg in a soil sample that was collected in 
Futaba-cho located at 4km north-west of FDNPP were measured by 
α-spectrometry and γ-spectrometry, respectively. The analytical result 
suggests that Pu isotopes are deposited in the soil as particles with high 
radioactivity (hot particles), although the 110mAg isotope is deposited 
uniformly like as Cs isotopes in a soil sample.  
Keywords 
Pu, 110mAg, hot particle, soil, Fukusima Daiichi, α-ray spectrometry 
2. Introduction 
 Massive radionuclides were released into the environment due to the 
Fukushima Daiichi nuclear power plant (FDNPP) accident in March 2011. 
They were mainly volatile fission products such as 137Cs, 134Cs, 132I and 131I, 
but non-volatile radionuclides such as Pu and Ag isotopes were also emitted to 
a minor extent. The behavior of these released radionuclides changes in 
response to their chemical forms in the processes such as emission, diffusion, 
and deposition.  
The volatile fission products were found to be distributed in Fukushima and 
its adjacent prefectures [1]. On the other hand, the non-volatile radionuclides 
such as Ag and Pu isotopes were distributed in high pollution area including 
FDNPP [2,3]. It was quite unlikely for them to disperse into the atmosphere 
like volatile nuclides because the non-volatile nuclides have high boiling 
points. These non-volatile nuclides would disperse with particles not through 
vaporization process.  
The existence of such hot particles causes the radioactivity concentrations 
in soils to vary over a wide range, even if the samples are collected in one 
place [1]. Therefore, in this work, we focused the radioactive Cs, Ag and Pu, 
and decided to research for the dispersion behavior of Pu isotopes and 110mAg. 
Besides, we examined their chemical properties by dissolution experiments 
using with several kind of leaching solutions. 
3. Sample 
The following two samples were collected and prepared for the present work. 
Details of the samples are found elsewhere [4]. 
Soil 1 : 
This soil sample was collected in Futaba-cho located at 4km north-west of 
FDNPP. Firstly, the sample was agitated by hand hundred times and dried at 
105℃ overnight in a drying tumbler. Then it was crushed in a mortar and 
passed through a 2mm sieve. It was heated at 450℃ for 4 hours to 
decompose the organics in the soil sample.  
Soil 2 : 
 This soil sample was collected from a side ditch in Namie-cho located in 
24km northwest of FDNPP. The sample was subjected to drying, sieving and 
organics decomposition processes in the same way as above. 
4 Experimental 
4-1 Measurement of Pu radioactivity 
  Six aliquots of 10g were picked up from soil 1. After addition of 242Pu 
tracer, six aliquots of 10g soil were leached on a hot plate at 90-100℃ with 
40mL of 10 M HNO 3 -0.1M HF for 4 hours. Then, after isolation and 
purification of Pu through anion exchange procedure [4,5], they were 
electrodeposited on a steel plate and measured by α-spectrometry. 
4-2 Dissolution experiment of Pu with acids 
Each of two aliquots of 10g was picked up to a teflon beaker from soil 2. 
One sample was leached on a hotplate with 40ml of 8M HNO 3 and the other 
was leached with 40ml of 10M HNO 3 -0.1M HF for 2 hours, then they were 
filtered. The leaching operation was repeated.  
Conc. HNO 3  and conc. HF acids were added to the two residues until they 
were completely decomposed. After isolation and purification of Pu, the Pu 
were electrodeposited on a stainless steel plate and subjected to 
α-spectrometry [4,5]. 
4-3 Measurement of 110mAg radioactivity 
 Many aliquots were prepared and picked up to 25ml vial bottles. They were 
subjected to γ-spectrometry to determine their radioactivity.    
4-4 Dissolution experiments of 110mAg species 
We used a column (0.5φ×5 cm) filled with 1g soil sample. To perform 
dissolution experiments, leaching solvents were passed through the column. 
Leaching solutions were used with several concentrations acids of HCl and 
HNO 3 , pure water, seawater, conc. aqua ammonia, di-ammonium hydrogen 
citrate 25% solution, and 1M Na 2 S 2 O 3. These eluents were collected to 25ml 
vial bottles and measured by γ-spectrometry. Details of the chemical 
procedures are found elsewhere [4]. 
5. Results 
The concentrations of 238Pu and 137Cs are shown in Figure 1. The results 
were obtained through the measurements with duplication analysis of a soil 
sample.  
The 137Cs nuclides are generally suggested to be deposited uniformly in 10g 
of soil sample. The results of 137Cs radioactivity for six samples were within 
109-132Bq/g, and its standard deviation was 8.3. In the figure are also shown 
the concentrations of 238Pu for six samples with the ratios of 238Pu/ 239+240Pu 
as a table. These ratios of 238Pu/ 239+240Pu are larger than the averaged ratio for 
global fallout around 0.03. The radioactivity of 238Pu for one sample was 
clearly higher than the others and its ratio of 238Pu/ 239,240Pu was also higher as 
shown in the table with the figure. The existence of hot particles causes their 
radioactivity concentrations to vary over a wide range even if soil samples are 
well mixed. Therefore, these results suggest that the 238Pu isotopes were 
released from FDNPP as particles with high radioactivity. 
Tables 1 and 2 show the results of dissolution experiments. Rate of digestion 
with 10M HNO 3 -0.1M HF was higher than that with 8M HNO 3 for first 
digestion, but both of the methods digested more than 90 percent of Pu in soil 
as a total of the first and second digestions. It is often noted that sintered Pu 
dissolves sparingly in HNO 3 [6]. The result suggests unexpectedly that the Pu 
species are not sintered and dissolve in nitric acid. 
On the other hand, Fig. 2 shows a good correlation of concentrations of 
137Cs with 110mAg. The 110mAg isotope is deposited as same as the Cs isotopes. 
Table 3 shows the results of dissolution experiments. For soil 1, the 110mAg 
isotope was eluted from the soil column with conc. ammonia water and 
sodium thiosulfate solution. The dissolved Ag portions were 7 percent and 14 
percent from soil 1. The chemical form of Ag is supposed to be mixture of 
metal simple substances and oxides. 
6. Conclusion 
 It is suggested that the Pu isotopes have dissolvable chemical species in 
nitric acid and they are deposited in soil as hot particles. The Ag isotopes are 
suggested to be deposited with fine particles as same as the Cs isotopes in soil 
and their chemical forms may be a mixture of metal simple substances and 
oxides.  
References 
[1] Environment monitoring database for the distribution of radioactive 
substances released by TEPCO Fukushima Daiichi NPP accident (2014) 
Nuclear Regulation Authority, Ministry of Environmental, Japan, 
https://mapdb.jaea.go.jp/mapdb/portals/3/ Accessed 25 April 2014 
[2] Environment monitoring database for the distribution of radioactive 
substances released by TEPCO Fukushima Daiichi NPP accident (2012) 
Nuclear Regulation Authority, Ministry of Environmental, Japan, 
https://mapdb.jaea.go.jp/mapdb/portals/201012/  Accessed 25 April 2014 
[3] Yamamoto M, Takada T, Nagao S, Koike T, Shimada K, Hoshi M, 
Zhumadilov K, Shima T, Fukuoka M, Imanaka T, Endo S, Sakaguchi A, 
Kimura S (2012) An early survey of the radioactive contamination of soil due 
to the Fukushima Dai-ichi Nuclear Power Plant accident, with emphasis on 
plutonium analysis, Geochem J 46:341-353 
[4] Kimura H, Uesugi M, Muneda A, Watanabe R, Yokoyama A, Nakanishi T 
(2013) Particulates of Pu radioisotopes released from Fukushima Daiichi 
nuclear power plants, Proceedings of the 14th Workshop on Environmental 
Radioactivity :344-349 
[5] The Pu analysis (1991) Japan’s Ministry of Education, Culture, Sports, 
Science and Technology, 
http://www.kankyo-hoshano.go.jp/series/main_pdf_series_12.html 
 (In Japanese) Accessed 25 April 2014 
[6] Vajda N, Kim CK (2011) Determination of transuranium isotopes (Pu, Np, 
Am) by radiometric techniques: a review of analytical methodology, Anal 
Chem 83:4688-4719  
Fig.1 
050100150
Pu-238 [mBq/g] 
 Cs-137 [Bq/g] 
Note: The Pu ratio for global fallout is around 0.03. 
Table 1  Dissolution of Pu in soil 2 with 8M HNO 3   
Sample 
238Pu 
(Bq/kg) 
239+240Pu 
(Bq/kg) 
238Pu/ 239+240Pu 
Dissolution 
First 
digestion 
8.0±0.3 3.5±0.2 2.3±0.4 87 
Second 
digestion 
1.1±0.1 0.46±0.04 2.3 ±0.6 12 
Complete 
Decomposition 
0.07±0.01 0.038±0.005 2.0±0.7 1 
Table 2  Dissolution of Pu in soil 2 with 10M HNO 3 -0.1M HF 
Sample 
238Pu 
 (Bq/kg) 
239+240Pu 
 (Bq/kg) 
238Pu/ 239+240P
Dissolution 
ratio（％） 
First 
digestion 
1.02±0.04 0.47±0.03 2.2 ±0.5 93 
Second 
digestion 
0.077±0.007 0.025±0.004 3.1 ±1.0 5 
Complete 
Decomposition 
0.033±0.005 0.012±0.003 2.8 ±1.3 2 
Fig. 2 
0100200300
Ag-110m[Bq/g] 
Cs-137 [Bq/g] 
Table 3  Elution of 110mAg from soils  
Sample 
Water 
water 
Ammonia 
water 
Ammonium 
citrate soln. 
1M Sodium 
thiosulfate 
HNO 3 
Soil 1 − − ○(7 %) − 〇(14 %) ○ ○ 
Soil 2 × × × × ○ ○ ○ 
○: eluted, ×: not eluted, −: not applied 
Figure captions 
Fig.1  Correlation of 238Pu and 137Cs activities in soil 1 
Fig.2  Correlation of 110mAg and 137Cs activities in soil 1 
Table captions 
Table 1  Dissolution of Pu in soil 2 with 8M HNO 3 
Table2  Dissolution of Pu in soil 2 with 10M HNO 3 -0.1M HF 
Table 3  Elution of 110mAg from soils 