「未来のエネ」ドーナツ型核融合装置で実験へ 日欧

【那珂市（日本）ＡＦＰ＝時事】５階建てビル並みの大きさの金属製容器にパイプやポンプが絡まる、１９７０年代のＳＦ映画にでも登場するような装置──。日欧が協力し、量子科学技術研究開発機構（ＱＳＴ）那珂研究所（茨城県那珂市）に１５年の歳月をかけて設置された核融合実験装置「ＪＴ－６０ＳＡ」だ。（写真は量子科学技術研究開発機構（ＱＳＴ）那珂研究所の大型核融合実験装置「ＪＴ－６０ＳＡ」。茨城県那珂市で）
　ドーナツ型の真空容器内に高温プラズマを閉じ込めて核融合を起こす「トカマク式」と呼ばれる装置で、昨年１２月、運転開始記念式典が行われた。装置は高さは１５．５メートルで、幅は１３．７メートル。
　欧州連合（ＥＵ）と６か国がフランスに建設中の国際熱核融合実験炉（ＩＴＥＲ）の弟分に当たる。
　容器内では何百万度という高温で実験が行われる。二酸化炭素（ＣＯ２）を排出せず、無尽蔵の燃料を使う安全な未来のエネルギー源としての核融合発電に資するとされている。
　案内役のＥＵ側のプロジェクトリーダー、サム・デービス氏は「核融合エネルギーは太陽や恒星と同じ反応で生み出され、１９５０、６０年代に地球上で太陽のパワーを再現する方法が模索され始めて以来、数十年にわたってエネルギー分野の研究における大きな目標となってきた」と、ＡＦＰに語った。
　「（核融合によって）温室効果ガスや長寿命放射性廃棄物から解放されるだけでなく、コンパクトで景観を損なうこともなくなる。産業用に有用な量の電力を生み出せるようになる」
　現行の原子力発電所では原子核を分裂させる核分裂が使われているのに対し、核融合は、二つの原子核を合体させることで膨大なエネルギーを生み出す。
　推進派は、こうした反応は安全であり、核兵器用の核分裂性物質や、分解に何千年もかかる有害な放射性廃棄物のような厄介な副産物を発生させないと主張する。
　ＪＴ－６０ＳＡでは、水素同位体の原子核を融合させてヘリウムなどの原子核に変え、エネルギーを発生させるという、太陽をはじめとする恒星の内部で起きているプロセスを模倣しようとしている。
　日本側の鈴木隆博那珂研究所先進プラズマ研究部次長によると、たった１グラムの混合燃料で、石油８トン分に相当するエネルギーが得られる。
　ＩＴＥＲやＪＴ－６０ＳＡが目指すのは、投入したエネルギーよりも多くのエネルギーを大規模に、長期にわたって放出させる技術の開発だ。
　デービス氏はこう語る。「核融合が将来のエネルギーミックスに貢献するのは間違いない。どの程度時間がかかるか正確に言うのは難しいが、最終的にはこの分野にどれだけの投資がなされるか、そして社会がソリューションとしてどれだけ追求したいかにかかってくる」【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2024/03/12-20:24）

With its tangle of pipes and pumps leading to a metal pot the size of a five-storey building, Japan's JT-60SA machine looks to the untrained eye like a contraption from 1970s sci-fi.
But inside it is a doughnut-shaped vessel where experiments done at millions of degrees could help unlock a carbon-free, inexhaustible and safe power source for the future: nuclear fusion.
Fusion energy, the power behind the Sun and the stars, has been a great prize for energy research for decades, ever since it was first attempted in the 1950s and 60s to find some way to reproduce this power of the Sun here on Earth, project leader Sam Davis told AFP on a recent tour.
Not only is (fusion) free from greenhouse gases and free from long-lived nuclear waste, but it's compact, doesn't cover the whole landscape, and can generate industrially useful quantities of power, the British-German engineer said.
Unlike fission, the technique currently used in nuclear power plants, fusion involves combining two atomic nuclei instead of splitting one, generating vast amounts of energy.
The process is safe and there are no nasty by-products like fissile material for a nuclear weapon or hazardous radioactive waste that takes thousands of years to degrade, its proponents say.
- Swirling plasma -
Taking 15 years to build in Naka, northeast of Tokyo, the JT-60SA is 15.5 metres (51 feet) tall and 13.7 metres (45 feet) wide, comprising a so-called tokamak vessel able to contain swirling plasma heated to millions of degrees.
Inside the facility, which was inaugurated in December, the aim is to get nuclei of hydrogen isotopes to fuse into an atom of helium, releasing energy, and mimicking the process that takes place inside the Sun and stars.
With only one gram (0.04 ounces) of a mixed fuel... we can obtain an energy equivalent to eight tonnes of oil, said Takahiro Suzuki, deputy project manager for the Japan side of the joint project with the European Union.
But despite decades of efforts, the technology remains in its infancy and is very expensive.
Currently the largest such facility in operation, the JT-60SA is the little brother and guinea pig of the International Thermonuclear Experimental Reactor (ITER) being built in France.
According to media reports, ITER -- a project run by six countries and the European Union -- is years behind schedule and could end up costing as much as 40 billion euros ($42.3 billion), far more than first projected.
The holy grail of both projects, as well as others around the world, is to develop technology that releases more energy than is needed to fuel it -- and at a large scale and for a sustained period.
The feat of net energy gain was managed in December 2022 at the National Ignition Facility at Lawrence Livermore National Laboratory in the United States, home to the world's largest laser.
- 'Flash in a can' -
But the US facility uses a different method from ITER and the JT-60SA known as inertial confinement fusion, in which high-energy lasers are directed simultaneously into a thimble-sized cylinder containing hydrogen.
Magnetic confinement, and in particular, tokamaks, of the kind that JT-60SA is, are much more applicable to running a steady state power plant, to steady energy production as we would need, Davis said.
This is not just a flash in a can.
But with the world record set by China for heating plasma to the required temperature -- 120 million degrees Celsius (216 million degrees Fahrenheit) -- currently just 101 seconds, there is still a long path ahead.
Nuclear fusion can certainly contribute to a future energy mix. Exactly on what timescale is very hard to say. It will come down ultimately to how much is invested in the field (and) how much society wants to pursue this as a solution, Davis said.