Researchers seek method to clean nuclear waste
TAKASHI KUROKAWA, Nikkei staff writer
TOKYO -- Experts in Japan hope nuclear transmutation -- a technology which can be used to turn radioactive nuclear waste to safer substances -- can help decommission the still-leaking Fukushima Daiichi nuclear power plant operated by Tokyo Electric Power But there is a catch, the scientific method requires a large-scale system.
To remove the obstacle of size, a team of researchers from Tohoku University and Mitsubishi Heavy Industries are seeking to develop a more simple system for the transmutation of nuclear waste based on past studies of cold fusion.
In April, a collaborative research lab, Condensed Matter Nuclear Reaction Division, opened at Tohoku University's Research Center for Electron Photon Science. The unit is a joint research center and a base for advancing the science of nuclear physics. The division was established by Tohoku University and Tokyo-based research company Clean Planet.
A group of scientists, led by Tohoku University professor Jirota Kasagi, a specialist in nuclear physics, are working to develop cold fusion technology using a small-scale system. Their research is aimed at extracting and utilizing thermal energy generated by turning radiation-free hydrogen into helium or changing radioactive substances that emit radiation for hundreds of thousands of years into radiation-free stable matter through nuclear transmutation.
A matter of atoms
All matter on earth is made up of atoms, which consist of an atomic nucleus surrounded by electrons. The nucleus -- formed by protons and neutrons -- determines the kind of element it is, such as hydrogen or uranium. The atomic bonds holding these elements together are so strong that incredibly high levels of energy are needed to transform them. That said, an atom's nucleus can be split in two or more using methods such as hitting it with high-speed neutrons.
An example of such splitting is the nuclear fission created in nuclear reactors. When an atom's nucleus is split into more than two kinds of matter, heat is generated. It is this energy that nuclear power plants use to generate power.
In contrast, nuclear fusion occurs when more than two atomic nuclei are merged to form different matter. Nuclear transmutation uses both fission and fusion.
For years, Kasagi and his fellow researchers have been trying to achieve nuclear fusion that generates helium, together with heat, by merging two units of radiation-free deuterium. On the other hand, France is currently building an ITER thermonuclear experimental reactor that will use deuterium and tritium for triggering nuclear fusion. Tritium is slightly radioactive. Kasagi's research does not use tritium.
To combine units of deuterium, they use nanometer-level metal microparticles. By inserting these particles into high-pressure deuterium gas, they expect deuterium to fuse either on the particles' surface, or inside the particles, to generate stable helium and heat.
What's more, Yasuhiro Iwamura, a former Mitsubishi Heavy Industries nuclear expert, now a specially-appointed professor at Tohoku University, joined the project in April. The research team has embarked on the following nuclear transmutations: turning radioactive palladium, which emits beta rays for hundreds of thousands of years, into radiation-free and stable tin; transforming radioactive selenium into stable strontium; changing radioactive zirconium into ruthenium; and turning radioactive cesium into praseodymium, which has a half-life of only 13.6 days.
Experts say that the radioactive materials listed above are the most challenging to process among nuclear power plant byproducts. The government has selected the research team's method, aimed at turning nuclear waste into radiation-free material, as one of the project candidates for its Impulsing Paradigm Change through Disruptive Technologies (ImPACT), a program of government-sponsored research launched in 2014.
More than 10 institutions, including Tohoku University and Mitsubishi Heavy, are taking part in the nuclear transmutation research project, partially funded by ImPACT. The research focuses on hitting radioactive material with neutrons to change the number of neutrons inside atomic nuclei so that the material will not emit radiation. However, until now, only large-scale facilities have been able to generate and accelerate the neutrons used in the transmutation process.
Thus, Kasagi and other researchers have decided to conduct research triggering nuclear transmutation through reactions between radioactive materials and deuterium gas or hydrogen gas, a far simpler method.
Research in the area of nuclear transmutation became popular more than two decades ago. In 1989, scientists in the U.S. and U.K. demonstrated the possibility of nuclear transmutation with their test results. They pointed to the possibility of low-temperature fusion of hydrogen atoms. This is why the process was known as cold fusion at that time.
Originally, nuclear fusion was referred to as "a sun on the earth" because experts believed that it could only occur at Celsius temperatures in the millions. The discovery of cold fusion was a worldwide sensation. Nevertheless, the original presenters were not nuclear experts and the data from their experiments was found to contain errors. As a result, their findings were discredited and many scientists ended their research in the area.
"Researchers around the world were vying to replicate this with their own experiments and some of them produced new findings," said Kasagi. "But some papers were not based on thorough arguments and paper assessments were not always rigorously done." He added that the scientific community ceased accepting papers on the topic.
Yet, Kasagi stressed the importance of his continued research. "Since we have data that defies nuclear science's conventional knowledge, I think I need to try and understand the mechanism," he said.
People engaged in the business of nuclear power didn't believe in the possibility of cold fusion back then, said Iwamoto. "But we need the technology for transforming radioactive waste into safe matter."