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MHI, Hitachi reviving Japan’s nuclear power industry

Hitachi also targeting small modular reactors in the UK together with GE

After Japanese Prime Minister Fumio Kishida, in late August, ordered the development and construction of new nuclear power plants, Japan’s nuclear power plant builders are quickly following up with new and safer reactors.

Mitsubishi Heavy Industries (MHI) on September 29 announced the conceptual design of a new light-water nuclear reactor with additional safety features. The very next day, September 30, it was reported that Hitachi-GE Nuclear Energy is also designing its own new reactor with enhanced safety features.

Mitsubishi Heavy

Developed in collaboration with four Japanese utilities – Hokkaido Electric Power, Kansai Electric Power, Shikoku Electric Power and Kyushu Electric Power – the MHI reactor is touted as meeting the regulatory requirements for “resistance to natural disaster and security against terrorism and unforeseen event.”

Incorporating “lessons learned from the Fukushima Daiichi accident,” the SRZ-1200 is a 1200MWe-class advanced light-water reactor. The lessons learned manifest themselves as safety mechanisms that “include, but are not limited to, an advanced accumulator design, and systems which effectively reduce the probability of radioactivity release in the event of a postulated accident.” SRZ stands for safe, resilient and ultimate (the Z in A-to-Z).

A light-water reactor is cooled with ordinary water. There are three types: pressurized, boiling and super-critical. MWe stands for Megawatts electric, the electrical output of a power plant. An average nuclear power plant generates 1000MWe or 1GWe (gigawatt).

MHI is Japan’s pressurized water reactor (PWR) specialist. It has been involved in the construction and maintenance of all 24 of the PWRs built in Japan and it designed, manufactured and constructed all but the first few.

According to the World Nuclear Association, there are at present 33 nuclear reactors in Japan classed as operable. Of these, 16 are PWRs and 17 are boiling water reactors (BWRs). Japan’s other two nuclear power plant builders, Hitachi and Toshiba, use BWR technology.

The accumulator is a passive injection device that replenishes the reactor coolant in the event of a loss-of-coolant accident – the kind of accident that caused the Fukushima disaster in 2011.

“Furthermore,” continues the press release, “the SRZ-1200 design is intended to enhance operational flexibility which will effectively allow for improved electrical power delivery alongside variable electric power sources such as renewables. The ability to adapt the SRZ-1200 for hydrogen production will also be studied to ensure that all potential uses of energy generated from this plant are efficiently and proactively applied for all societal needs.”

MHI will now move to the basic design stage, aiming to create a safe, stable and zero-carbon supply of energy for Japan. As things stand now, commercialization is expected in the mid-2030s. If the SRZ-1200 proves to be a success, that may enable the revitalization of MHI’s overseas nuclear power business.


The Hitachi-GE entry will be an advanced BWR featuring a passive cooling system (no electric power required) and a ventilation system that filters out radioactivity.

This addresses two major causes of the Fukushima nuclear disaster. As noted on the Tokyo Electric Power Co. (TEPCO) website:

Flooding caused by the tsunami rendered emergency power equipment inoperable, thereby rendering cooling equipment useless. As a result, the water inside the pressure vessels of Units 1~3 evaporated causing water levels to drop.

In conjunction with the drop in water level, fuel rods (rods filled with nuclear fuel such as uranium) [became] exposed from the water surface, and hydrogen was generated by the chemical reaction between the fuel rods and water vapor. This hydrogen that accumulated inside the reactor buildings and caused hydrogen explosions at Units 1 and 3 that blew off the ceiling and walls of the reactor buildings.

At Unit 4, hydrogen flowed into the reactor building through joint ventilation pipes used to expel air from inside the Unit 3 containment vessel and accumulated in the reactor building where we assume an explosion occurred.

Commercialization of Hitachi-GE’s new reactor is also expected in the mid-2030s. In the meantime, the Japanese government is reactivating more of the reactors shut down after Fukushima. It is also considering an extension of the current 60-year limit on nuclear power plant operation.

GEH and small modular reactors

Hitachi has two joint ventures with General Electric, Hitachi-GE Nuclear Energy in Japan and GE Hitachi Nuclear Energy (GEH) overseas. In early September, GEH and Sheffield Forgemasters announced an agreement to collaborate on the possible deployment of BWRX-300 small modular reactors (SMRs) in the UK.

The BWRX-300 is a 300MW boiling-water reactor, equipped with passive safety features, that is designed to provide flexible baseload electric power at prices competitive with those of natural gas combined-cycle plants. On a per-MW basis, it is cheaper to build than conventional nuclear power plants.

Sheffield Forgemasters designs and manufactures forgings and castings for use in the nuclear, thermal and renewable power, steel, marine and defense industries. In December 2021, it signed a contract to manufacture forgings for Rolls-Royce SMRs.

CEO David Bond told the press:

SMRs have the potential to become a standard for civil nuclear power generation and as an emerging technology, our long track record of supplying nuclear grade components brings a wealth of technical forging experience to the market. Sheffield Forgemasters is undergoing a transformation to Industry 4.0 manufacturing technologies, the centerpiece of which is our investment of up to £400m over ten years, to replace the company’s defense-critical assets. We look forward to working with GEH to explore the possibilities of becoming a UK supply chain partner in the delivery of complex nuclear grade forgings into the commercial BWRX-300 SMR build program.

Last March, UK Prime Minister Boris Johnson stated that his government wanted nuclear power to provide 25% of the nation’s energy, aiming to reverse a downward trend that has taken that figure to 16% and could take it lower.

It would also be a reversal for Hitachi, which withdrew from the Wylfa Newydd nuclear power plant project in Wales in 2020.

GE Hitachi Nuclear Energy is also working on SMR projects in Saskatchewan, Poland and Estonia. The first commercial BWRX-300 could be put into operation by the end of this decade.

Source: Asia Times