Report on “Radiation Disaster Recovery Studies”
Course: Radioactivity Environmental Protection
Name NGUYEN THANH HAI○Regarding“Radiation Disaster Recovery Studies”

In 2011, earthquakes, tsunamis and nuclear incidents in Fukushima Prefecture,
Japan made the whole world concerned. Once again Chernobyl disaster’s obsession
returned to humanity. From Vietnam, with little knowledge of radiation incidents, I
monitored the daily situation with anxiety about the development and disaster recovery
in Fukushima in media. Fortunately in 2013 I learned about the Phoenix Leader
Education program (Hiroshima Initiative) for Renaissance from Radiation Disaster (PLEP) and
was fortunate enough to be accepted to study Radioactivity Environmental Protection atHiroshima University.
At Phoenix Program, I have learned the knowledge related to radiation, radioactive
disaster and recovery after radiation disaster. More importantly, I learned not only inthe field of environmental protection after a nuclear disaster but also in social
rehabilitation and radiation disaster medicine. All three fields - environmental, socialand health are closely related and inseparable from the Radiation Disaster Recovery
study. My understanding of this correlation is increasingly strengthened through thePhoenix Program's first two-year subjects spread across the fields of environment,
society and medicine. Besides, I also participate in scientific seminars, short-term
training courses and field trips to research and management centers related to radiation
safety and nuclear power plants, disaster site locations, etc. Attending lectures byleading experts in the field of radioactive disaster research and attending meetings withpeople affected by the Fukushima radiation accident have given me a lot of knowledge
and experiences for my own study.
According to The Nuclear and Industrial Safety Agency (NISA) within the Ministryof Economy, Trade and Industry of Japan, the total discharge amounts to the air fromthe reactors of Fukushima Dai-ichi NNP were approximate 1.61017Bq for Iodine 131
and approximate 1.51016Bq for Cesium 1371). Fukushima before the 2011 tsunami was1

an important agricultural area in Japan. Therefore, the task of assessing the impact ofradioactive pollution on rice in Fukushima is very important. After the FDNPP disasteroccurred, the top concern of the people (not just farmers in Fukushima) is that theagriculture produces is safe? For government authorities, the issue of assessing the levelof radioactive contamination in the soil, even after decontamination, evaluating thelevel of radiation safety in local agricultural products has become urgent. The study ofrecovery from radioactive disasters is not only a matter of natural science but also
covers the socio-economic and health issues. For example, how long does it take to ban
farm produces in Fukushima to be eligible for sale? There are many studies onradioactive contamination in rice and the mechanisms of spreading cesium radioactivity
to rice were published2-6). The effect of potassium on the absorption of radioactive
cesium into rice plant has been shown; however, there are some points which deviate
from the correlation7). In order to clarify these above, we conducted a study on four rice fields inFukushima City, 60 km northwest of the FDNNP. From 2014 to 2018, we sampled soil and rice plant,
analyzed soil particle size, analyzed radioactive Cesium 134, Cesium 137 and Potassium 40 with Ge
semiconductor detector (GEM 30-70, ORTEC). We also used the 57Fe Mӧssbauer spectroscopy tostudy soil oxidation/reduction properties in the soil through the relative area of FeII. From which
many important conclusions are drawn such as: The change of the circumference aroundthe rice field may affect the uptake of radioactive cesium into rice. The effect of fallowing
field to downstream fields should be monitored for years to consider more. It has alreadybeen shown that some factors such as the concentration of potassium and grain size
distribution in soils contribute the appearance of contaminated rice, however, ourresults suggest that dynamics of soil among the neighboring fields should be explored infuture studies.
In conclusion, after being trained in the PLEP, my personal awareness of the natureand processes in the radiation disaster has changed drastically. The most important
thing that I have learnt from the PLEP is related to radiation disaster, the recovery
itself not only in the approaching of environmental field but strongly connect with social
recovery, and the preparedness of medicine supply and prevent and healing the damage
caused by radioactivity to human. The recovery is a long-term process and it takes lot ofresources, not only time, finances. Our research has contributed a small part to raisingpeople's awareness of radioactive environmental pollution in Fukushima prefecture,especially the spread of radioactive cesium in soil and rice. These perceptions areimportant to people who work in management, policy making and people living
in/outside areas affected by radiation incidents. The Radiation Disaster Recovery
Studies does not only apply to disasters caused by nuclear power plants but also
includes research for possible disaster risks for all other areas of life that are related tothe use of radioactive energy.
2References:
1) Nuclear Emergency Response Headquarters Government of Japan, Report ofJapanese Government to the IAEA Ministerial Conference on Nuclear Safety- TheAccident at TEPCO's Fukushima Nuclear Power Stations, June 2011.
2) Philip J. White and Martin R. Broadley, Mechanisms of caesium uptake by plants,Sciences, E., 113, 241–256 (2000).
3) Endo, S., Kajimoto, T., and Shizuma, K.: Paddy-field contamination with 134Cs and137Cs due to Fukushima Dai-ichi Nuclear Power Plant accident and soil-to-rice transfer
coefficients, J. Environ. Radioact., 116, 59 - 64. (2013).
4) Nakanishi, M., T. and Kobayashi, I., K.: Radioactive cesium deposition on rice, wheat,peach tree and soil after nuclear accident in Fukushima, J. Radioanal. Nucl. Chem., 296,985-989 (2013).
5) Ohmori, Y., Inui, Y., Kajikawa, M., Nakata, A., Sotta, N., Kasai, K., Uraguchi, S.,
Tanaka, N., Nishida, S., Hasegawa, T., Sakamoto, T., Kawara, Y., Aizawa, K., Fujita, H.,Li, K., Sawaki, N., Oda, K., Futagoishi, R., Tsusaka, T., Takahashi, S., Takano, J.,
Wakuta, S., Yoshinari, A., Uehara, M., Takada, S., Nagano, H., Miwa, K., Aibara, I.,Ojima, T., Ebana, K., Ishikawa, S., Sueyoshi, K., Hasegawa, H., Mimura, T., Mimura, M.,
Kobayashi, I., N., Furukawa, J., Kobayashi, D., Okouchi, T., Tanoi, K., and Fujiwara, T.:
Difference in cesium accumulation among rice cultivars grown in the paddy field inFukushima Prefecture in 2011 and 2012, J. Plant Res., 127, 57-66 (2014).
6) Nihei, N., Tanoi, K., and Nakanishi, M., T.: Inspections of radiocesium concentrationlevels in rice from Fukushima Prefecture after the Fukushima Dai-ichi Nuclear PowerPlant accident, Sci. Rep., 5, 8653 (2015).
7) T. Saito, S. Ohkoshi, S. Fujimura, K. Iwabuchi, M. Saito, T. Nemoto, M. Sato, K.
Yoshioka and H. Tsukada , Effect of potassium application on root uptake of radiocesiumin rice, Proceedings of Int. Symp Environmental Monitoring and Dose Estimation ofResidents after Accident of TEPCO's Fukushima Daiichi Nuclear Power Stations. Part
3–5, Kyoto Univ. Res. Reactor Inst. 2012.

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○Title of Doctoral Thesis

Properties of the Soil in Rice Fields and Transfer of Cesium to Rice Plants○Summary of Doctoral Thesis

On 11th March 2011, The Great East Japan Earthquake of magnitude 9.0 and the following
15 m tsunami hit the Tohoku area. This led to the cause of Fukushima Dai-ichi Nuclear Power Plant(FDNPP) accident, where 134Cs and 137Cs were released to the air and made land and rice fields
contaminated. As Phoenix student, I learnt the radiation disaster and restoration from the disaster inFukushima Prefecture. After the accident, the food safety has emerged as a very important problem.
Contaminated rice from paddy fields was observed in Fukushima City. How the contaminated rice isreduced was the basis for my doctoral dissertation. Although there are many studies concerning thecontamination of radioactive cesium and the transfer of radioactive cesium from soil to ears of rice inthe paddy fields of the Fukushima after the FDNPP accident has been carried out, the mechanism of
the up-taking of cesium into rice, the migration of cesium and the factors that affect are still required.
An investigation in 2013 showed the concentration of radioactivity of 137Cs and 134Cs in rice which
was collected from one of neighbor rice fields was relatively high. This study aims to investigate thecontamination of radiocesium in rice and paddy field’s soil, and the factors that affect thecontamination and the transfer of 137Cs and 134Cs into rice. In order to understand the factors, the soil
samples were collected, and the radioactive concentrations, the depth distribution, the soil size
distribution were investigated and the oxidative/reductive atmosphere in the paddy field wasinvestigated using 57Fe Mӧssbauer spectroscopy. Background and objective of the research are given
in Chapter 1.
The chapter 2 shows the method. Our study performs in 4 paddy fields (which are named as A,B, C, and D) in Fukushima City, which are 60 km Northwest far from Fukushima Dai-ichi Nuclear
Power Plant. We monitored the fields from 2014 to 2018. The paddy fields are irrigated by a nearby
pond and partial water from Abukuma River. Four fields were cultivated in 2013 and 2014, although
the upper two fields were not cultivated from 2015. The samples were taken from 4 paddy fields with
5 sample sites for each field. The samples were contained in U-8 vessels and the radioactivity wasmeasured by Ge semiconductor detector (GEM 30-70, ORTEC). The radioactivity was calibratedusing MX033U8PP source set (Japan Radioisotope Association). 57Fe Mӧssbauer spectroscopic
measurement was performed at room temperature with a 57Co (Rh) radiation source moving in aconstant acceleration mode on Wissel MB-500. The Mӧssbauer parameters were obtained byleast-squares fitting to Lorentzian peaks. The spectra were calibrated by the six lines of α-Fe, thecenter of which was taken as zero isomer shift.
Chapter 3 is the study about depth distribution of radioactive cesium in soil after cultivating
and the difference by the year of the uptake of radioactive cesium in rice in these fields. The averagevalue of five points in each field was compared to each other. The 137Cs concentration decreased4depending on the depth. The same trend was also observed in the depth dependence of 134Cs
concentration. The ratio of radioactivity concentration of 134Cs to 137Cs was 0.373. This value
corresponds well with the expected ratio (0.376) on the sampling day declined according to reductionof 134Cs by shorter half-life than that of 137Cs, given that the same amount of radioactivity of 137Cs
and 134Cs was released from the FDNPP reactor. These fields were cultivated, ploughed and irrigatedbefore transplanting rice seedlings in 2013. Nevertheless, the concentrations of 137Cs and 134Cs insoils were not uniform and there was depth dependency in 2014. It is expected that small particles
such as clay include a large amount of radioactive cesium. One of the possibilities is that bigger
particles fell down quickly but the small particles such as clay fell down slowly in the sedimentation
process after ploughing and irrigating, although the soils were mixed. There is a difference between
Fields A, B and Fields C, D. The radioactivity of 137Cs and 134Cs for 0-5 cm depth was higher inFields C and D than in Fields A and B, while the radioactivity for 5-10 cm was lower in Fields C andD than in Fields A and B. Relatively higher radioactivity of 137Cs and 134Cs was found at greater
depth in Fields A and B than in Fields C and D.
In Chapter 4 the 57Fe Mӧssbauer spectroscopy was used to determine the oxidative/reductive
characteristic of soil samples. The iron concentration variation was also investigated based on soil
size distribution. It was thought that Fields A, C, and D are in relatively in reductive atmosphere,while Field B is in relatively oxidative atmosphere. It was suggested that the oxidative/reductive
condition of iron state may reflect the features of the soils and then affect the solubility of potassiumand radioactive cesium in the field. We checked the change of 57Fe Mӧssbauer absorption dependingon the soil size. Consequently, the iron in the larger size soil is much abundant in Fields A and B
compared with that in Fields C and D. It is known that the small sized soil includes clay much. And
the radioactive cesium is adsorbed strongly to the clay. It is also thought that the cesium adsorbed tolarge sized soil is relatively easily desorbed and absorbed to rice body. The amount of iron may affectdesorption of radioactive cesium from large sized soil. One of the possibilities is that the iron works
as catalyst to dissolve radioactive cesium from soil. In conclusion, oxidative atmosphere and inparticular more abundant iron in larger size soil may affect the transfer of radioactive cesium fromsoil to rice grain.
Chapter 5 shows the change in the characters of soil of Fields A-D. The depth dependence ofCs for the soil changed from 2014 to 2018. The difference between Fields A, B and Fields C, D
became larger. Slightly contaminated rice ears appeared in Fields C and D after the fallowing Fields
137

A and B. The radioactivity concentration was relatively higher in rice ears obtained from the fieldnear irrigation entrance of water. It was thought that the ratio of clay and silt decreased by this water
flow, which became one of the reasons of relatively higher 137Cs concentration in ears. But, thisshould be explored in future studies.
Chapter 6 shows general conclusion.

5○Other theses published in academic research journals

・Title of academic research journals
1) Nguyen Thanh Hai, Masaya Tsujimoto, Sunao Miyashita, Satoru Nakashima, Depth
Distribution of Radioactive Caesium in Soil after Cultivation and the Difference by Year ofthe Uptake of Radioactive Caesium in Rice in Fukushima Prefecture after the 2011 Nuclear
Accident, Radioisotopes, 68(1), 13-18, 2019.
2) Nguyen Thanh Hai, Masaya Tsujimoto, Satoru Nakashima, Study on paddy soil inFukushima using Mössbauer spectroscopy, Hyperfine Interactions, 240, 122 (7 pages), 2019.

・Joint authors
1) Masaya Tsujimoto, Sunao Miyashita, Nguyen Thanh Hai, Satoru Nakashima, A correlation
between the transfer factor of radioactive cesium from soil into rice plants and the grain size
distribution of paddy soil in Fukushima, Radiation Safety Management, 15, 1–8, 2016.

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