Published on January 30, 2020. Citing a Sankei Shimbun column by Nagatsuji Shohei, this article introduces the High Temperature Engineering Test Reactor (HTTR) developed by the Japan Atomic Energy Agency, as well as the safety, hydrogen-production capability, fuel technology, and research cooperation with Poland related to high-temperature gas-cooled reactors. It discusses this next-generation nuclear reactor, free from core meltdown and hydrogen explosions, as a key to a decarbonized society and to the future of Japan’s nuclear technology.

January 30, 2020
People who only subscribe to the Asahi Shimbun and similar newspapers, or who only watch programs such as NHK’s Close-up Gendai, know only truly worthless people.
The following is from a serialized column by Nagatsuji Shohei published in yesterday’s Sankei Shimbun.
I learned his name for the first time through this article, but there are many genuine scholars like him in Japan.
People who only subscribe to the Asahi Shimbun and similar newspapers, or who only watch programs such as NHK’s Close-up Gendai, know only truly worthless people.
When I learned that he was a graduate of Kyoto University’s Faculty of Agriculture, I thought that was only natural, and at the same time I felt pleased.
Next-Generation Nuclear Power in Poland
The Long-Awaited High-Temperature Gas-Cooled Reactor
There exists in Japan an innovative reactor with extremely high safety: a high-temperature gas-cooled reactor, which is free from both core meltdown and hydrogen explosions.
It is the High Temperature Engineering Test Reactor, or HTTR, carefully nurtured by the Japan Atomic Energy Agency.
Located in Oarai Town, Ibaraki Prefecture, the HTTR, although still in the first stage of development, is the world’s highest-performance high-temperature gas-cooled reactor.
Its name may sound as if it could be mistaken for thermal power generation, but a high-temperature gas-cooled reactor emits no carbon dioxide and has the ability to produce both electricity and hydrogen.
This next-generation nuclear reactor, which holds the key to realizing the decarbonized society the world is aiming for, has taken three major steps toward practical application.
Safety Is Its Trump Card
Ordinary nuclear power plants are of the light-water reactor type, which extracts heat from the reactor using water.
By contrast, a high-temperature gas-cooled reactor extracts heat from the reactor using helium gas.
In pressurized-water and boiling-water light-water reactors, the steam that turns the turbine is at a temperature of 300 degrees Celsius, but in the case of a high-temperature gas-cooled reactor, a gas turbine is turned by helium gas at 950 degrees Celsius.
That is why it is called a high-temperature gas-cooled reactor.
Because it does not use water, it can even be located in a desert.
The fuel is uranium, but its form, the structure of the reactor core, and the materials used are completely different from those of light-water reactors.
As a result, it possesses inherent safety, and even if piping ruptures and the helium gas coolant is lost, the nuclear fission reaction stops naturally.
After shutdown, the reactor core cools without any operation.
There is no need to worry even if a total loss of power occurs.
That is what a high-temperature gas-cooled reactor is.
Contributing to a Hydrogen Society
The “hop” toward practical use is the leap forward in hydrogen production.
Hydrogen is expected to serve as a clean fuel, but if it is produced from natural gas and similar raw materials, carbon dioxide is generated as a byproduct.
If it is produced by electrolysis of water, energy loss and cost become problems.
Hydrogen and oxygen can also be obtained through thermal decomposition of water, but that requires an ultra-high temperature of 4,000 degrees Celsius.
By contrast, with a chemical reaction that cyclically uses iodine and sulfur dioxide, known as the IS process, hydrogen can be produced from water at 900 degrees Celsius, and that is where the high-temperature gas-cooled reactor comes into play.
The IS process had been difficult to use because of factors such as the strong corrosiveness of the reaction liquid, but in January of last year, the high-temperature gas-cooled reactor research team at the Japan Atomic Energy Agency succeeded in producing 30 liters of hydrogen per hour.
Using equipment with ordinary piping for plant use, it achieved the world’s longest continuous operation of 150 hours.
With this breakthrough, the entrance to a true hydrogen society has come into view.
Improving the Performance of Fuel
The second step, the “step,” is improving the performance of the uranium fuel used in high-temperature gas-cooled reactors.
Through joint research by the Japan Atomic Energy Agency and the manufacturer Nuclear Fuel Industries, the energy of the fuel was raised to the level required for commercial high-temperature gas-cooled reactors, and its mass-production technology was also established.
This was reported at the Atomic Energy Society of Japan meeting last September.
In the core of a high-temperature gas-cooled reactor, which is composed of graphite blocks, many cylindrical fuels called compacts, 25 millimeters in diameter and 40 millimeters high, are loaded in an orderly arrangement, and each compact contains about 13,000 spherical fuel particles one millimeter in diameter.
A compact is made by uniformly mixing these particles with graphite powder and firing them into a tube-like shape.
The spherical fuel has a robust precision structure in which the uranium dioxide at the center is surrounded by four layers of ceramics.
Here lies the essence of the technology.
These tiny spherical fuel particles can withstand the generation load of combustion energy three times greater than before.
A Path Appears Overseas
The leap corresponding to the “jump” is the “Implementing Arrangement for Cooperation in Research and Development on High-Temperature Gas-Cooled Reactors,” concluded in late September of last year between the Japan Atomic Energy Agency and Poland’s National Centre for Nuclear Research.
Because Poland uses large amounts of coal as fuel for factories and other facilities, it has struggled to reduce carbon dioxide emissions.
Against this background, Polish officials, including a deputy minister of the Ministry of Energy, visited the HTTR in 2016, and the country has shown strong interest in high-temperature gas-cooled reactors.
At present, plans have begun in Poland to construct both a research reactor and a commercial reactor using high-temperature gas-cooled reactor technology.
Japanese technology will be provided there in the form of joint research.
Japan’s HTTR is the first stage of high-temperature gas-cooled reactor development.
It has a thermal output of 30,000 kilowatts and is not equipped with a generator.
Japan would like to proceed to the next stage, but since the Fukushima accident, new domestic plans are difficult for the time being.
Against this background, the government has set forth the promotion of high-temperature gas-cooled reactor development through international cooperation in the current Strategic Energy Plan.
Therefore, cooperation in the development of high-temperature gas-cooled reactors in Poland is also a timely and welcome opportunity for Japan.
High-temperature gas-cooled reactors also possess the characteristics of small modular reactors suited to distributed power sources.
Since the Fukushima accident, they have attracted a high level of attention around the world.