What is the Goal of Your Research?

We are facing two critical problems caused by the heavy consumption of fossil fuel; enormous CO₂ emissions after the industrial revolution resulting in the global warming, and the exhaustion of energy resources. Nuclear power, which can provide a large amount of energy without emitting CO₂, is an important energy resource that can solve these critical problems. Today, more than four hundred nuclear power plants are operating in the world. Operation of the plants generates radioactive waste which needs to be disposed of, and we must establish a safe disposal method. In addition, a method to select a suitable strategy for decommissioning nuclear facilities, which is a combination of technology assessment, cost evaluation and stakeholder agreement, must be developed as the plants approach the end of their service life. The other important and challenging task in Japan is to solve the problems caused by the nuclear accident at Fukushima Daiichi Nuclear Power Plant. Environmental remediation is taking place in the wide area contaminated with radiocesium based on the fundamental science and engineering of the migration behavior of cesium in the environment. At the same time, technologies to safely decommission the damaged reactors and properly manage the radioactive waste need be studied. The goal of our laboratory is to establish engineering solutions for these problems.

 

What is Interesting about the Research in Nuclear Waste Disposal?

Figure 1  Concept of Geological disposal of high-level radioactive waste

Radioactive waste generated from nuclear power plants will be disposed of underground. For example, high-level radioactive waste will be buried deep underground in a stable geological formation as shown in Figure 1. In this disposal system, vitrified waste having low solubility in groundwater packed in a metal canister called an overpack, will be embedded in a host rock together with clay buffer materials. For the safety assessment of this disposal system, we must evaluate the long-term performance of each barrier, such as the corrosion rate of the overpack, the glass dissolution rate, and the migration rate of radionuclides in the clay buffer and the host rock.

Figure 2  Concept of prediction for safe geological disposal of high-level radioactive waste

However, the means have not been available to predict the durability and the performance of these environmental barrier materials for long terms extending hundreds to tens of thousands of years. What we are now trying is to establish a new method to predict the future of the geological disposal systems. This type of prediction requires a detailed study on properties of materials used in the disposal system and a deep understanding of mechanisms for the various reactions related to the disposal. Careful consideration is also required to determine whether the extrapolation of our knowledge in the distant future is appropriate or not. One of the attractive points in this field of research is that it is based on new ideas and new experimental data obtained using the most advanced analytical instruments. Research in our laboratory includes migration experiments using radiotracers, observation of internal microstructures of environmental materials using quantum beams and computer simulations of mass transport at a nanometer scale.

 

Research and Human Resource Development for Remediation of Fukushima

Figure 3  Example of migration behavior of cesium at the edge of a clay mineral simulated by molecular dynamics calculations

Radiocesium released into the environment from the accident at Fukushima Daiichi Nuclear Power Plant is mostly fixed in soil. However, the degree of fixation may be affected by not only the mineral composition of the soil but also the change of organic matter caused by microbial activities and other factors. For this reason, it is important to understand the behavior of cesium in soil in relation to physical, chemical and biological properties of the soil in order to conduct environmental remediation and for safe storage and disposal of the decontamination waste. Our approach in this area of research involves experiments using the soil collected in Fukushima as well as reference materials, and computer simulation (Figure 3).

In addition to the decontamination of waste from the surrounding area, it is expected that a large amount of heterogeneous radioactive waste such as concrete and metal will be generated from the decommissioning of the Fukushima Daiichi Nuclear Power Plant. Therefore adequate radioactive waste management including pre-treatment, conditioning and final disposal should be considered based on the chemical and physical state and the distribution of radionuclides in the waste. We are studying the migration behavior of radionuclides in cement materials.

Figure 4  A field work of environmental remediation in Fukushima Prefecture

It will take a long time period of thirty to forty years to decommission the Fukushima Daiichi Nuclear Power Plant. There are difficult technological challenges to overcome to safely decommission the damaged plant, and continuing research and development by distinguished researchers and engineers will be indispensable. We have been developing a capacity building program under a project funded by the Ministry of Education, Culture, Sports, Science and Technology, Japan since 2011, on the environmental radioactivity, the disposal of radioactive waste, and the decommissioning. The program includes field work in Fukushima Prefecture, in which students work on the environmental remediation (Figure 4). We are also making open educational resources, and several lectures have been opened for free on the web site of the OpenCourseWare of Hokkaido University
(http://ocw.hokudai.ac.jp/OpenLecture/Seminar/2013/EnvRadBeginner/).

 

References

(1) Michio Ishikawa, Tamotsu Kozaki, et al., Decommissioning of Nuclear Reactor (genshiro kaitai), Kodansha.

(2) Tamotsu Kozaki, Disposal of radioactive wastes (hosyasei haikibutsu no syobun), Atomic Energy Society of Japan, Reprocessing and Recycle Technology Division "Nuclear Fuel Cycle", http://www.aesj.or.jp/~recycle/nfctxt/nfctxt_7-4.pdf