Report on “Radiation Disaster Recovery Studies”
Course:Name:Radioactivity Environmental Protection Course
Ooki Kurihara○Regarding “Radiation Disaster Recovery Studies”
Deposition of radioactive materials occurred due to the Fukushima Daiichi Nuclear Power Plant
accident in March 2011. Decontamination has been carried out where the radiation dose rate is higher than
the reference value in order to reduce the air dose rate in the living environment by removing and shielding
radioactive materials. The amounts and the radioactivity concentration of soil and waste generated bydecontamination in Fukushima Prefecture as of January 2016 are estimated; 10 million m3 of soil less than
8,000 Bq/kg, 10 million m3 of soil more than 8,000 Bq/kg and less than 100,000 Bq/kg, 10 thousand m3 ofsoil more than 100,000 Bq/kg, and 1.6 million m3 of incineration ash1). The removed soil by decontaminationin Fukushima Prefecture is stored in flexible containers at temporary storage sites in each municipality, andthen transported to the intermediate storage facility from March 20152). The removed soil contained in theflexible containers transported from the temporary storage sites to the intermediate storage facility is crushed
first and landfilled in the soil storage facility in the intermediate storage facility. Regarding the removed soil,
it is decided by a law to take necessary measures to complete the final disposal within 30 years after the startof interim storage1), and final disposal method will be discussed in 2019-20243). Based on the above, theconstruction of the final disposal facility will be an important social and engineering problem in the nearfuture.
In Japan, disaster waste disposal using a coastal disposal facility that can dispose of huge amounts ofwaste exceeding 10 million m3 at a place has been operated in the recovery from the Great Kanto earthquakeof 1923 and the Great Hanshin Awaji Earthquake of 1995. Unlike in the land disposal facility, most of thewaste in the coastal disposal facility is submerged. In case of constructing a coastal disposal facility,
impervious seawall structure is constructed at the beginning, which makes inner water isolated from theoutside sea. And then, waste is reclaimed into the isolated inner water. After water surface of the coastal
disposal facility disappears and a land appears, the final soil covering is conducted, and the landfill is over.
In my doctoral thesis, I considered a possibility that the coastal disposal facility will be an option of
the final disposal method for the removed soil and developed sealing geomaterial used for the bottom
shielding of the offshore disposal facility intended for the final disposal of the removed soil. The cost of theconstruction of the offshore disposal facility and the disposal of the removed soil was also examined.
In the Phoenix program, I have learned that radiation disaster recovery in a short time is very
important, while enough time is required for security of local residents, which is result of reduction of the air
dose rate due to natural attenuation of radioactivity and decontamination. I had many opportunities to hear
the voice of the residents of the evacuation zone and the construction area of the intermediate storage facility.
Among the people whose residential areas were designated as the site of the intermediate storage facility,
some built new houses in new places and have reconstructed the lives of their families, while others are still
waiting for return of their land by the government 30 years later in order to leave their lands as their livingmarks to the next generation. I got an impressive word from a resident in the evacuation zone, "Five years

until returning was very long and it was an enough time for many people to loss the desire to restart thefarming." I thought that, for the affected people, evacuation for a long time would make their reconstruction
more difficult. My research theme is the offshore disposal facility, and the site of the offshore disposal
facility is not individual lands, therefore, it is easier to reach an agreement than land disposal sites which islocated in or near private land. Thus, I believe that my research can contribute to the smooth implementationof the final disposal. While learning radiation disaster recovery, I strongly felt that government decisions
such as policies and criteria, including the decontamination and the disposal of the removed soil, have a great
influence on residents’ lives and cultures over a long period of time. In addition, I also learned the beginningof risk communication, but I could not mention it in my doctoral thesis. However, considering the method offinal disposal of the removed soil, it is important to consider not only technical aspects but also risk
communication with stakeholders.
○Title of Doctoral Thesis
Study on Offshore Disposal Facility for Soils and Wastes Contaminated with Radioactive Cesium○Summary of Doctoral Thesis
Due to the decontamination work carried out after the Fukushima Daiichi Nuclear Power Plant
accident, approximately 22 million m3 of the removed soil and waste are generated, and the disposal of theremoved soil has become an issue of the recovery from the Great East Japan Earthquake. In this study, I
discussed the offshore disposal facility for the final disposal of the removed soil and developed the sealing
geomaterial used for the bottom shielding of the offshore disposal facility. The cost of the construction of theoffshore disposal facility and the disposal of the removed soil was also examined.
In Chapter 1, the background and related research were summarized as an introduction.
In Chapter 2, the structure of the offshore disposal facility and the necessary performance concerning
the permeability and adsorptivity of the sealing geomaterial used for the bottom shielding were describe.
In Chapter 3, the permeability of the sealing geomaterial made with marine clay, bentonite, sand andzeolite was investigated. The consolidation test was carried out on the sealing geomaterial of various
composition to determine the hydraulic conductivity. With addition of sand to marine clay, the hydraulicconductivity for flow in pores kpore was increased due to the reduction of the void ratio compared with thatwithout the addition. By the addition of bentonite and zeolite, kpore decreased due to the addition of bentonite.
With addition of the same amount of bentonite, kpore decreased as the zeolite addition ratio increased. At theend, the hydraulic conductivity was predicted from the change of porosity by adding bentonite, zeolite andsand.
In Chapter 4, the compression and consolidation characteristics of sealing geomaterial made withmarine clay, bentonite, sand and zeolite were examined. Relationships between the change ratio ofcompression index Cc/Cc0 and the addition rate of each material were shown, and Cc/Cc0 of the sample adding
bentonite and sand or zeolite was predicted. The prediction based on the relational expression of the change
rate of consolidation coefficient cv/cv0 and the addition rate of each material was also investigated.
In Chapter 5, the cesium adsorption characteristics of the sealing geomaterial made with marine clay,
bentonite, sand and zeolite was studied. The cesium adsorption characteristics of the sealing geomaterial wasinvestigated by a batch adsorption test and a consolidation and seepage test. The influence of the layer
thickness on the adsorption breakthrough property of cesium was considered, and a target value of Pore
Volume of Flow (PVF) was proposed. It was shown that PVF at the breakthrough point can be predictedfrom the composition of each material. In addition, X-ray diffraction analysis showed that layered silicate
minerals with cesium adsorption effect were present in each material.
In Chapter 6, the method of composition design based on the results of Chapter 3, 4, and 5 wasexplained. The method of adding bentonite and zeolite in consideration of hydraulic conductivity and cesium
adsorption characteristics was shown by using the prediction of hydraulic conductivity examined in Chapter
3 and the prediction of PVF at the breakthrough point examined in Chapter 5. In addition, I showed themethod of adding sand considering compressibility using the prediction of the change rate of compression
index discussed in Chapter 4 and confirmed the time required for consolidation using the prediction of thechange rate of consolidation coefficient.
In Chapter 7, I discussed the permeability and adsorption properties of the clay with the addition of asmall amount of cement (CASC). Vane shear test, consolidation test and hollow cylinder torsional
permeability test were performed on CASC contains about 2-4%of cement. CASC appears to have strengthof several kPa with curing, and it is considered that CASC will be an option of the sealing geomaterial fromthe viewpoint of giving necessary strength for construction. As a result of investigation of the change of thehydraulic conductivity before and after giving the shear deformation, cracks occurred due to shearing
deformation of 20% in the lean-mix cement-treated clay (LCTC) and the hydraulic conductivity of LCTC
was increased, however there was no increase in the hydraulic conductivity of CASC. In addition, studying
the cesium adsorption characteristics showed that PVF at the breakthrough point was not significantly
different from that without the addition.
In Chapter 8, construction method of the offshore disposal facility and disposal method of the removed
soil were shown, and the cost of construction and disposal was examined. When the transportation distanceof the removed soil and dredged soil used for the sealing geomaterial was set to 5 to 200 km, direct
construction costs including the construction cost and transportation cost were 477.6 billion yen to 549.2billion yen, and it was found that the same amount of cost as the intermediate storage facility4) would berequired for final disposal of the removed soil by the offshore disposal facility. In addition, the estimatedconstruction cost per 1 m3 of disposal capacity, including construction cost and transportation cost of dredgedsoil, was 25,600 to 26,500 yen. It was found that when the offshore disposal facility was used for the final
disposal of the removed soil, disposal capacity of 20 million m3 is allocated to a place, and there was apossibility that the construction cost per 1 m3 could be reduced compared with land disposal facilities.
In Chapter 9, the findings obtained in each chapter were summarized as a conclusion, and future tasks
were mentioned.
1) Ministry of the Environment. (2016). Development strategy for volume reduction and recycling technology forintermediate storage removal soil. (in Japanese)
http://josen.env.go.jp/chukanchozou/facility/effort/investigative_commission/pdf/investigative_commission_text.pdf
2) Ministry of the Environment. (2016). On the verification report on pilot transportation. (in Japanese).
http://josen.env.go.jp/chukanchozou/action/investigative_commission/pdf/pilot_transportation_160331_01.pdf

3) Ministry of the Environment. (2016). Strategic process chart of volume reduction and recycling technology
development of intermediate storage removal soil. (in Japanese).
http://josen.env.go.jp/chukanchozou/facility/effort/investigative_commission/pdf/investigative_commission_process.pdf
4) Yasutaka, T., & Naito, W. (2016). Assessing cost and effectiveness of radiation decontamination in Fukushima
Prefecture, Japan. Journal of environmental radioactivity, 151, 512-520.

○Other theses published in academic research journals
1.

Kurihara, O., Tsuchida, T., Takahashi, G., Kang, G. O., & Murakami, H. (2018). Cesium-adsorption
capacity and hydraulic conductivity of sealing geomaterial made with marine clay, bentonite, and zeolite.
Soils and Foundations, 58, 1173-1186. (In Press) (Peer Reviewed)

2.

Kurihara, O., Takaoka, Y., Tsuchida, T., Shiraga, T., Hashimoto, R., & Kumagai, T. (2018). Sealing
geomaterial for coastal disposal facility using marine clay with the addition of a small amount of cement.
International journal of GEOMATE, 15(51), 132-139. (In Press) (Peer Reviewed)

3.

Kurihara, O., Tsuchida, T., Takahashi, G., & Murakami, H. (2018). A study on the permeability ofgeomaterials made with marine clay, bentonite, sand, and zeolite. Journal of Japan Society of Civil
Engineers, Ser. B3 (Ocean Engineering), 74(2), I_874-I_879. (In Japanese) (Peer Reviewed)

4.

Tsuchida, T., Murakami, H., Kurihara, O., Athapaththu, A. M. R. G., Tanaka, Y., & Ueno, K. (2017).
Geotechnical sealing material for coastal disposal facility for soils and wastes contaminated byradioactive cesium. Marine Georesources & Geotechnology, 35(4), 481-495. (Peer Reviewed)