DOE融合ロードマップ: 商業融合電力への道

Since ソビエト科学者によるトカマク炉の発明（1958年）, humanity has technically been able to produce nuclear fusion on Earth, merging lighter atoms into heavier ones in a very energetic reaction.

In theory, this technology could provide humankind with unlimited clean energy, with no carbon emissions, no nuclear waste, and an unlimited supply of fuel as it consumes hydrogen, the most abundant element in the Universe, and turns it into harmless helium.

This atomic reaction is >10x more energetic than even the most powerful nuclear fission reactions.

出典: Nature

However, the practical use of fusion has been elusive ever since, as trigger fusion is a complex process that so far requires more energy than is generated by the nuclear reaction.

(You learn more about the fundamentals of nuclear fusion in our dedicated report “核融合 – 地平線上の究極のクリーンエネルギーソリューション.”)

Still, the potential of nuclear fusion technology has been evolving quickly in the past few years, and many private companies are now claiming to be close to a commercially viable reactor, notably Proxima Fusion, Commonwealth Fusion Systems, and the soon-to-be publicly listed General Fusion (各社とその進捗に関するリンクをご参照ください).

It is in that context of intensifying competition for becoming the first nuclear fusion company with a viable product that the US Department of Energy (DoE) has published a new national report on nuclear fusion outlining how the country could accelerate innovation in the sector, improve technical standards, and ameliorate the transfer of knowledge from academia to the private sector.

The report also emphasizes the importance of improving the technology for “diagnostic” instruments that analyze the quality and stability of the plasma generated by nuclear fusion.

核融合が世界エネルギーにとって重要な理由

So far, humankind is still looking for the ideal energy source. Fossil fuels are polluting, produce climate-damaging carbon emissions, and might run out one day.

But the alternatives to nuclear fission energy produce waste and are complex, while renewables require a lot of land, are intermittent, and need massive energy storage to work as they become larger in the energy mix.

Nuclear fusion could, in theory, be both an ultra-compact energy source with also no pollution and limitless energy.

However, so far, the technology is limited by the complexity of starting and then keeping the energy-producing plasma required to cause fusion. As this plasma is up to 10x hotter than the core of the Sun, this requires extremely complex and ultra-powerful magnetic fields generated by magnets cooled to temperatures close to absolute zero.

出典: DOE

Only minutes- or hour-long stable plasma is going to fuse enough hydrogen to compensate for the initial energy cost of creating the right conditions in the first place, as well as the energy consumption of cooling and keeping active the superconducting magnets.

And only with a massive positive energy generation can such a reactor be commercially viable to pay off for the large investment of creating and operating the nuclear fusion reactor.

DoE 2026年核融合報告書

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DoE融合報告書の背景

This new report by the DoE was the result of a large collaboration of experts on nuclear fusion, sponsored by the DOE’s Office of Science’s Fusion Energy Sciences (FES) program.

It was chaired by Luis Delgado-Aparicio, head of advanced projects at the DOE’s Princeton Plasma Physics Laboratory (PPPL), and co-chaired by Sean Regan, a distinguished scientist and the director of the Experimental Division at the University of Rochester’s Laboratory for Laser Energetics.

The report’s main goal is to provide academic and state support to coordinate and optimize the > $9B of investment made by the private sector on this technology.

It covers all seven identified major research areas in the field of nuclear fusion, which are all theoretical topics, as well as all the main designs of potentially commercially viable nuclear fusion reactors:

• 低温プラズマ。
• 高エネルギー密度プラズマ。
• プラズマ材料相互作用。
• 磁気閉じ込め核融合 — 燃焼プラズマ。
• 慣性閉じ込め核融合 — 燃焼プラズマ。
• 磁気核融合エネルギー — 融合パイロットプラント。
• 慣性核融合エネルギー — 融合パイロットプラント。

DOE融合ロードマップの主要発見

The first finding of the report is that for commercial nuclear fusion to be achieved, 8 distinct infrastructure streams are critical for progress, including plasma science, AI, and testing of reactor components like blankets (providing a continuous fuel stream), fuel cycle, and magnets.

出典: DOE

It also proposes a few initiatives to speed up the pace of progress of research and development of nuclear fusion for energy generation.

The first one is to encourage the use of validation and verification of models by AI and machine learning, as well as the use of digital twins.

It also insists that the most important missing link toward commercial fusion is improvement in the measurement of plasma, a discipline described as plasma “measurement” or “diagnostic”.

The report identifies four topics where public-private partnerships (PPP), national teams, and multi-lab coordination can anchor national investment in fusion research:

• 放射線耐性診断装置および関連センサー。
• AI、機械学習、リアルタイムデータ分析。
• トリチウム生成と熱負荷管理。

出典: DOE

Lastly, it is recommended to provide seed funding for a more reliable and diverse supply chain for fusion equipment. This is because fusion power plants will require robust, radiation-tolerant internal components that can be manufactured at scale way beyond the current one-of-a-kind lab experiments.

“高温耐火金属ベースの部品の製造には、堅牢な先進製造方法（例：レーザーベッド3Dプリンティング）と、インフラ（例：小規模テストスタンド、中規模デモプラットフォーム、大規模施設）の組み合わせによる試験が必要となります。”

プラズマ診断に焦点を当てる

Diagnostic is the most important missing link for commercial fusion, as it determines how the plasma can be analyzed in real-time and modified,  so it can be stabilized and made more productive.

To make plasma diagnostic progress quicker, the report proposes a much greater level of national coordination, relying on forming national teams, a national network potentially to be called Calibration NetUS.

It also encourages the establishment of a standardized approach to diagnostic calibration that can help compare different designs and prototypes.

On the human and management side, the report pushes for investing in workforce development, help for measurement innovation to be performed remotely, and improving knowledge transfer to the private sector.

The report also looks at alternative paths to fusion that are promising, but have been less explored so far, despite potentially being more efficient, reliable, or cheaper than previously established paths to fusion. This covers:

• ステラレータ（トカマクに似ていますが、はるかに複雑な磁場発生装置を持つ）
• 液体金属PFC（「プラズマ接触部品」の略で、従来の固体PFCに対抗）
• 磁気ミラー構成のHTS磁石
• シアードフロー安定化Zピンチ核融合。

核融合開発を遅らせる重要技術ギャップ

The report also points to the missing technical elements that could make fusion energy generation a reality sooner, with many maybe less complex than the production of the fusion itself, but likely to impact a future commercial plant’s costs, and therefore the competitiveness of fusion technology against renewables and already existing nuclear fission.

One is the lack of validated data on damage caused by neutrons emitted by the fusion process on adjacent materials, with potential embrittlement, creep-fatigue, swelling, etc. As commercial plants will need to operate efficiently and safely for decades, a deeper understanding of such damages will be important. This could affect many components of a fusion reactor, like welds, structural walls, coolant, etc.

Manufacturing practice will also need to be tested and optimized. The production of “nuclear grade” heat will require especially reliable and consistent welds, joints, and other structural elements.

Coolant compatibility, supply chain for the tritium-generating blanket, insulation from electrical and magnetohydrodynamics (MHD) effects, and tolerance to magnetic fields will all need to be evaluated as well.

適切な政策

While the report is mostly addressing technical considerations, regulations are also discussed so that the right policy framework can support the technical & research efforts.

Nuclear fusion relies on hydrogen, lithium, boron, and other common elements that are not fissile or usable for the production of nuclear weapons. Even the in-situ production of tritium in the fusion reactors, a radioactive isotope of hydrogen, would not be a serious proliferation risk.

So the report insists on keeping fusion energy out of the context of nuclear fission frameworks for regulatory and non-proliferation policy, in order not to hinder research and investment in the field with unwarranted roadblocks designed for more dangerous materials like uranium or plutonium.

Design rules and a list of materials acceptable in a commercial fusion power plant will also need to be established and commonly accepted, while staying flexible enough to evolve as the industry’s best practices improve or new technologies are adopted.

While not consuming radioactive material, fusion plants do emit neutrons, which can slightly radioactive the surrounding materials, especially any parts directly inside the reactor. So, regulations regarding the safe disposal and storage of these materials will also be required.

核融合への投資

General Fusion / Spring Valley Acquisition Corp. III

General Fusionは、核融合を公的資金による物理プロジェクトではなく、民間セクターのベンチャーにする先導的スタートアップの一つです。

The company was started as long ago as 2002, with a goal to develop Magnetized Target Fusion (MTF) technology. MTF is expected by the company to be a shorter path to energy-positive fusion and to be a lot less costly.

General Fusion was the first in the world to build and commission a compact toroid plasma injector at a power plant scale in 2010 and has reached many more milestones since.

This approach differs from tokamak-style systems and laser-based inertial confinement because it is designed around rapid pulse compression rather than relying solely on large superconducting magnets or high-powered lasers.

The company has raised roughly $440M since its launch, and Fusion announced in 2026年1月 that it would soon become publicly listed through a deal with the SPAC Spring Valley Acquisition Corp. III, valuing General Fusion at a $1B market capitalization. They declared that the new corporate entity would be called General Fusion and would be listed on the Nasdaq under the GFUZ ticker.

The soon-to-be-joined companies are aiming to make MTF fusion technology commercially available around the mid-2030s.

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