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Nuclear Hydrogen Reactor: Japan’s Next Generation, Earth-friendly Energy

The High Temperature Engineering Test Reactor is not susceptible to core meltdowns. It is the type of small modular reactor that the world is calling for.

Shohei Nagatsuji

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Japan's Next Generation Nuclear Power Production

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In the trend toward decarbonized societies, hydrogen is gaining prominence as a new energy source that does not emit carbon dioxide (CO2).

The only thing released when hydrogen is burned is water. Hydrogen also has a high heat capacity and produces electricity when used in fuel cells. It is a shining star among energy options, but the question is what kind of hydrogen to use. 

If CO2 is emitted in the production of hydrogen, it is rendered meaningless. And even if it is not, energy is wasted when production efficiency is low.

In fact, Japan has developed hydrogen production technology that overcomes these drawbacks. The high-temperature gas-cooled reactor (HTGR) is the next generation of nuclear power generation that can simultaneously produce unlimited amounts of hydrogen along with electricity.

Source of Hydrogen is Important

There are multiple technologies for producing hydrogen. The mainstream method of mass production is “reforming,” which uses natural gas or coal as the raw material. High-temperature steam is used to separate hydrogen from natural gas or other substances, but CO2 is also produced at the same time.

Ammonia, which has attracted attention in recent years as a new fuel option, does not achieve the carbon-free ideal because it uses hydrogen produced by this method.

Hydrogen can be obtained through electrolysis using solar power. CO2 is not emitted, but there is energy loss. For storage of surplus power, pumped-storage power generation has already been put to practical use.

Advanced High Temperature Reactors

Nuclear power also emits no CO2, but has been facing headwinds since the Fukushima accident.

However, the Japan Atomic Energy Agency is developing a new type of reactor, called the “High Temperature Engineering Test Reactor” (HTTR), in the town of Oarai, Ibaraki Prefecture. 

In principle, the HTTR is not susceptible to core meltdowns. Moreover, it is the type of small modular reactor that the world is calling for.

One feature of HTGRs is that they use helium gas to produce a high temperature of 950 degrees, three times higher than that of conventional nuclear power. This high temperature can be used to drive a gas turbine to generate electricity, while producing hydrogen through the thermochemical decomposition of water, in a cyclical process involving iodine and sulfur dioxide.

Commercialization of this reaction, called the IS (iodine-sulfur) process, was considered problematic, but the HTTR research team achieved 150 hours of continuous hydrogen production — the standard for long-time operation — two years ago.

Diagram of an HTTR energy facility showing (1) the HTTR nuclear reactor, (2) in its housing. (3) the helium gas turbine, and (4) hydrogen production using iodine and sulfer dioxide.

A Reactor Free of Serious Accidents

The thermal output of the HTTR is 30,000 kilowatts. Since it is in the first stage of development, it is not equipped with a power generator, but it has all the basic functions of a high temperature gas-cooled reactor. 

The Ibaraki reactor began operation in 1998, but maintained a low profile for years. This all changed after the accident at TEPCO’s Fukushima Daiichi nuclear power plant ten years ago. That is when the new type reactor became a beacon of hope.

The main reason for its recent attention is the reactor’s outstanding level of safety. It is a new type of reactor with a core material and structure completely different from conventional nuclear power plants.

In addition, HTGRs have remained in the shadows for some time because they are structurally unsuitable as larger reactors. But now the global nuclear power market is turning to small modular reactors. This is the second reason for the recent attention. Since this type of reactor does not require water for operation, potential locations are far-reaching, from inland sites to deserts.

The third reason for new interest is the growing demand for hydrogen as an energy source, following the Paris Agreement to stop global warming.

Operation to Resume in Summer

The HTTR is currently undergoing a safety review by the Nuclear Regulatory Commission. Compliance with new regulatory standards was confirmed in June 2020, and approval of the construction plan is underway. If construction work proceeds smoothly, operation is expected to resume in the summer of 2021.

After a full decade of shutdown following the Fukushima accident, a light has finally become visible at the end of the long tunnel.

The Paris Agreement became operational in 2020, and the world is moving rapidly toward a decarbonized society. While the Japanese government has declared its intent to bring CO2 emissions to net zero by 2050 both at home and abroad, it is clear that this goal cannot be achieved merely by making renewable energy such as solar power Japan’s main energy source.

This winter’s cold spells and heavy snowfall have exposed the weaknesses of solar power generation. Moreover, thermal power generation, which had been making up for the shortage of nuclear power, faced delays in procurement of natural gas, resulting in serious power shortages.

Japan’s Trump Card

Unlike Europe, the stable supply of electricity in an island nation like Japan requires diversification of energy sources. Nuclear power, which can operate continuously for over a year once fuel is put into the reactor, plays an important role. But the trauma of Fukushima has made both new construction and the expansion of conventional nuclear power plants (light water reactors) problematic.

This is why the commercialization of serious accident-free HTGRs is urgently needed. Japan currently leads the world in HTGR technology. Both Poland and the United Kingdom have strong expectations for technical cooperation with Japan.

At the climate summit being planned by United States President Joe Biden, Prime Minister Yoshihide Suga should present Japan’s high temperature gas-cooled reactor to world leaders as a pro-hydrogen innovation in decarbonization. It would send a most meaningful message. 

RELATED: Japan Leads Race in Development of High-Temperature Gas Reactors, but China is Catching Up

(Read the report in Japanese at this link.)

Author: Shohei Nagatsuji

Shohei Nagatsuji is a senior staff writer and an editorial writer for the Sankei Shimbun specialized in science and technology.