Three years ago on March 11, 2011, the largest recorded earthquake in Japan’s history struck off the country’s north-eastern coast, triggering a massive tsunami and the worst nuclear power plant accident since Chernobyl.
Our colleagues at the Science Media Centre of Japan collected comments from Japanese scientists about what progress has been made in cleaning up the Fukushima nuclear site, lessons learned and the work still ahead.
Masatoshi Morita, President of the Society for Remediation of Radioactive Contamination in the Environment, and Visiting Professor at the Faculty of Agriculture, Ehime University comments:
About the current decontamination processes and issues surrounding Fukushima
“When the Fukushima Daiichi Nuclear Power Plant accident happened, radioactive material was released into the environment from reactors 1, 2, and 3. The extent of the radioactive contamination was roughly one fifth of that of the Chernobyl accident. The first radioactive material released into the air was iodine-131, followed later on by highly volatile radioactive cesium-134 and cesium-137. The radioactive material fell to the ground after coming into contact with rain and other tiny particles in the atmosphere.
“Decontamination processes are expected to reach a peak sometime this year. The cesium that has fallen onto the ground, trees, roofs, and roads is being cleaned up by removing the top layer of soil or by high-pressure washing. Due to these efforts as well as the fact that radioactive elements decay naturally over time, radiation levels are thought to have dropped to around half of what they were three years ago when the accident happened.
“New technologies for the adsorptive removal of cesium have been proposed. For example, scientists have found a way to collect and clean up cesium using magnetic adsorbers. Other researchers have used Prussian blue to selectively adsorb cesium. These methods are useful where cesium has dissolved in liquids.
“A current difficulty is how to remove cesium from mineral sheets called mica and clay made up of weathered mica, because the cesium tends to adsorb more firmly. While it is possible to break down the clay and remove the harmful material using concentrated nitric acid, that would be an unrealistic choice to say the least. We need to find an environmentally friendly way to extract the cesium.
“On the other hand, there are a number of other important issues to consider. These include maintaining the support and understanding of the local communities regarding radioactive decontamination, finding a place to store the contaminated soil, addressing the concerns of local residents and consumers, and the economical costs of carrying out decontamination.”
Osamu Sakura is Professor at the Interfaculty Initiative in Information Studies, The University of Tokyo. Prof. Sakura’s research interests include the connection between science & technology and society. He comments:
“In regards to Japan’s policies post-Fukushima, hardly anything could be considered optimistic. It was clear the government needed to abandon its vertically-structured administration of the time and work across departments to deal with the disaster, but this hasn’t happened. Although ministries are capable of breaking down the walls between them, no effective partnerships have been established.
“The Reconstruction Agency is still a branch beneath the Cabinet, the Ministry of the Environment is responsible for radioactive contamination, and the Nuclear Regulation Authority is affiliated with the Ministry of Economy, Trade and Industry. As a result, decontamination is significantly behind schedule.
“One thing worth crediting is last November’s ‘Basic Plan for the Safe Return Home’ development lead by the Nuclear Regulation Authority. This was something the Reconstruction Agency should’ve carried out, but instead the regulation authority members, with some outside help, took action to change the original, conservative return home plan, with something that reflected what people in the disaster zone were experiencing.
“In February this year, the Agency for Natural Resources and Energy finally settled on a basic energy plan, but it regards nuclear energy as an important source. Thus, the possibility for new plants remains open. In this case, what was the point of carrying out a deliberative poll in 2012 where 47 per cent of the country said they wanted Japan nuclear free by 2030?”
Hajime Asama is Professor at the Department of Precision Engineering, University of Tokyo. Prof. Asama is currently chairman of the Robotics Task Force, and a committee member of the Government, TEPCO Decommissioning, and Contaminated Water Response Team. He comments:
“At the nuclear power plant, more than 30 types of robots or devices are being used. Robots have helped with irrigation, clearing rubble, measuring the amount of radiation, taking video footage, taking samples, decontamination, protection, and transporting equipment.
“Very few robots were ready to be used straight after the earthquake and the nuclear accident so, in the beginning, emergency and military robots were brought in from overseas. Later on, Japanese researchers started to develop and send in robots tailored to the needs of people inside the disaster zone. These included robots for measuring things, carrying out light work, flying robots, and aquatic robots. It was proof Japan could produce robots people needed.
“With decommissioning expected to take another 30 to 40 years, it’s not an exaggeration to say its success and failure depends on robotic technology development. Robots have made a large contribution in dealing with the accident at first, and will continue to have a role in the decommissioning of the reactors.
“Scientists will continue to invent and test their robots on site, and are expected to make mistakes. But it’s learning from our failures that enable us to build up our understanding and ultimately reach success. It’s already clear scientists still have to invent robots capable of detecting, measuring, and cleaning up the contaminated water, and robots able to withstand extreme conditions such as high pressure or high radioactivity. I expect our scientists to work with others overseas in order to overcome obstacles, and test their devices in more realistic settings to ensure the robots are dependable.
“It’s also important to prepare for the next big disaster. To do this, we will need to have remote controlled devices and robots on standby at all times – and even, perhaps, establish an emergency response robot centre.”
Hiroshi Nishizawa is a chief researcher at the Mitsubishi Electric Corporation Advanced Technology R&D Center. Mr Nishizawa is involved with research and development into radiation monitoring for nuclear power plants and for environmental radiation monitoring. He comments:
What have been the biggest advances in technology in the past three years?
“I think the biggest advances have been in developing systems capable of detecting tiny amounts of radioactive material in a short amount of time, and inventing gamma cameras capable of taking images of radioactive contamination. In both cases, a clear motivator has been that people in the devastated areas needed this technology as soon as possible because it had significant effects on food safety and living environment quality.
“There were a number of challenges though. The fact that Japan has extremely strict conditions concerning the amount of radiation in food compared to overseas, about one tenth of what is accepted in the United States or the EU, meant scientists needed to develop a device capable of detecting tiny amounts of radioactive material. Also, the device had to be able to measure a large number of samples, so scientists needed to make sure the device carried out measurements quickly. Despite these issues, many devices have been successfully developed over the past three years.
What has been accomplished over the past three years and what can be expected in the future?
“Over the past three years, scientists have made huge leaps in taking already known principles and technologies, and turning them into real things that people need.
“So there were no groundbreaking discoveries, but you do need to remember that no matter how great a discovery, a number of walls stand between it and making it something you can hold. You need to think about how to make it the right size and weight, how to minimize the amount of time and labour to make it, how to create a design easier for production, and how to minimize the cost. It might seem a bit boring, but a lot of effort has gone into breaking down those walls, and it has lead to the development of these devices.”
Hiroyuki Takahashi is Professor at the Department of Nuclear Engineering and Management, Department of Bioengineering, University of Tokyo. Prof. Takahashi specializes in research and education into radiation measurements. He comments:
Looking back on how technology for measuring radiation has changed over the past three years
“There have been significant advancements in fundamental research for scintillators, particularly in inorganic scintillators which detect gamma rays from radioactive cesium. The new GAGG scintillator has a larger density, picks up less body radiation, and has a larger amount of luminescence, all of which are improvements on the quality of conventional NaI(Tl) scintillators. Furukawa Co. has already begun putting these into mass production.
“In terms of applied systems, I think advances in the following technologies should be acknowledged: aircraft monitoring that enables quick check ups of contamination over a large area of land; in-car radiation monitoring systems such as KURUMA; pinhole type gamma cameras helping decontamination activities on site at the nuclear power plant; Compton cameras that take measurements over a wide area; unmanned helicopters that are designed to monitor contamination; towable gamma ray monitoring systems that allow speedy calculations of the amount of sea contamination; GAGG detector systems that carry out non-destructive analysis on fish; whole body counters for young children; electronic radiation dose calculators such as the D-shuttle; and, finally, AMS (Accelerator Mass Spectrometry) methods to analyze iodine-129 to iodine-131.”
What has been accomplished in the past three years, and what can we expect in the future?
“Whether you’re talking about fundamental research or applied systems, people have become more aware of it, and more people are using it. There have been particular advances in gamma ray monitoring technology. In terms of fundamental development of scintillators and compound semiconductors, more industries and scientists are working on improving it, and I think we can expect to see more improvements in this area in the future.”
Concluding remarks
“People have become exclusively concerned about the effects of radioactive cesium on their health, but no one has considered the effects of natural radiation like radon or thoron in the overall picture. In other words, if people start worrying about the effects of radon and thoron too, we need to look into science fields largely ignored up until now.”