Japan Institute for National Fundamentals

　
The Japanese government on September 30 held the first meeting of an expert panel to work out a strategy for the development of a small nuclear fusion reactor that State Minister for Science and Technology Sanae Takaichi has advocated since her run in the ruling Liberal Democratic Party’s presidential election last year. While some commentators call for early investment in the development to win an international competition, I have to point out that practical use of a nuclear fusion reactor for commercial power generation is still nowhere in sight. I would also like to present the current status of the vast International Thermonuclear Experimental Reactor (ITER) under construction in France, hoping that the expert panel would coolly consider the development based on scientific knowledge.

What is a thermonuclear fusion reaction?

Nuclear reactions that generate enormous heat are broadly divided into two: nuclear fusion reaction seen in stars such as the sun and nuclear fission reaction used for nuclear power plants. In the nuclear fusion, the hydrogen isotope deuterium or tritium as ionized gas or plasma must be compressed in a powerful magnetic field to satisfy the Lawson criteria for high temperature and pressure. Representative Lawson criteria include the plasma temperature of 100 million degrees Celsius, the plasma density of 100 trillion per cubic centimeter and the plasma confinement duration of one second. Japan’s JT-60 is among nuclear fusion experimental facilities that have satisfied the Lawson criteria for successful nuclear fusion reaction. The JT-60, operated by the Japan Atomic Energy Research Institute since 1985, heated plasmas with 2 megawatts of electricity and successfully achieved thermonuclear fusion reaction, generating the almost equal thermal energy for 30 seconds. This means that the JT-60 generated 60 (2 x 30) megajoules of energy. The Q-value, which represents the ratio of nuclear fusion energy generated to energy used for heating, is almost 1 for the JT-60. Scientists in Europe and the United States have recently trumpeted successful small nuclear fusion reactors, though with Q-values that do not differ so much from the JT-60 level.

Giant international project ITER

Based on the achievements of the JT-60, a project has been launched to construct the ITER in France. Its completion is said to be around 2025 after a considerable delay. Construction costs have swollen to 2.8 trillion yen (about $20bn). Japan tried to attract the project to Aomori Prefecture, racing with France to host the project. Finally, Cadarache in France has been adopted as the location. Japan is going to provide major ITER components, including superconductive coils for confining plasmas in a powerful magnetic field, a neutral beam heater and a tritium facility. The ITER and relevant facilities are being built on a vast site. The size of a nuclear fusion reactor must be large to achieve commercial power generation. China has also built similar facilities of its own.

The target Q-value for ITER is 10. The reactor is designed to use 50,000 kilowatts of electricity to generate 500,000 kilowatts of nuclear fusion energy for only 400 seconds. A commercial nuclear fusion reactor will have to achieve the Q-value of 40 and continue operating for one year. Humans have not acquired any material for reactor walls that can resist neutron radiation from nuclear fusion for one year. While utilizing the JT-60SA into which the JT-60 has been modified, the Japanese government should concentrate money and human resources on the Japan-led ITER project.

Tadashi Narabayashi is a specially appointed professor at the Tokyo Institute of Technology and a director at the Japan Institute for National Fundamentals.