Sunday, October 18, 2020

Nuclear fusion is considered the Holy Grail of energy generation, providing limitless power with no CO2 emissions.
Yet it has proven elusive for generations of scientists. A persistent obstacle is that it takes considerably more energy to create the fusion reactions than the amount produced. But this hasn’t stopped multiple nations around the world ploughing in billions of dollars and considerable resources to develop this technology.
The world’s highest profile nuclear fusion project is ITER, near Provence, southern France. ITER is a multi-national, multi-billion dollar development. Thirty-five nations have set aside trade wars and diplomatic disputes to pursue a common goal. The partnership includes China, the EU, India, Japan, Russia, South Korea, and the US.
Those working on ITER estimate that if everything goes according to plan, an input of 50MW will result in an output of 500MW. This would solve the issue of putting in more energy than you get out and help prove the technology’s viability.
“Fusion could be a game-changing technology; a long-term replacement for fossil fuels in the energy market of the future. It would be a much cleaner way to generate electricity, with no greenhouse gas emissions. The fuels are found all over the world and are virtually limitless; just a few litres of fuel could supply one person’s energy needs for decades,” explains professor Ian Chapman, CEO of the UK Atomic Energy Authority. “And fusion is inherently safer than nuclear fission – an accident like Fukushima or Chernobyl is impossible. So it would be a great option alongside renewables, and if we can commercialise fusion, it would really transform the world by giving us abundant low-carbon energy.”
How nuclear fusion works
A simplistic description of man-made nuclear fusion is that it creates a mini-sun in a reactor. Two hydrogen atoms are forced together at extreme velocities to create a helium atom, along with neutrons and the release of substantial energy.
Fusion occurs on a much larger scale in the sun. With a core temperature of 15 million degrees Celsius, its sheer gravitational force crushes protons together to achieve nuclear fusion.
In a man-made reactor lacking such gravitational forces, the most effective fusion method has been found to heat hydrogen isotopes deuterium and tritium to even greater temperatures of 150 million degrees Celsius. Inside a vacuum chamber, the heated hydrogen gas turns into plasma and the conditions are created for two positively charged protons to fuse and heat energy to be released. 
While heating the gas to the necessary temperature is achievable, problems arise when trying to confine the plasma and keep it stable. ITER is being built according to the tokamak reactor design, which will essentially contain the plasma in a doughnut-shaped magnetic field, created by passing a current through heavy-duty metal coils. Vacuum chambers and cooling systems are also required to avoid the intense temperatures causing the reactor to burn up.
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“The tokamak – essentially a ring-shaped magnetic chamber in which we fuse particles to unlock large amounts of energy – is the best design for a fusion reactor that we know of. It is the most advanced concept and one that many researchers around the world are working on,” adds Chapman. “The ITER tokamak in France, which starts up in 2025, will aim to demonstrate fusion power on an industrial level for the first time, which would pave the way for the first power plants.”
 
Machine assembly at ITER
After more than three decades in planning and development, ITER began its machine assembly phase earlier this year. To get an idea of how long ITER has been in development, the project was initially proposed by Soviet Union General Secretary Mikhail Gorbachev to US President Ronald Reagan in 1985.
The scale of ITER is vast and comparable in size to England’s Wembley Stadium, comprising 150,000m3 of concrete and 7,500 tonnes of steel. It will be 80m in both height and width, with a length of 120m. Construction started in 2007.
ITER officials estimate that the project’s overall cost is approximately $22bn. While the US Department of Energy calculated the costs to be three times higher, at $65bn, ITER’s team has rejected this figure and maintains that their estimate is correct.
Manufacturing of ITER’s components is shared between partner nations, which then come together at the site near Provence. Close collaboration and sharing of plans between nations is essential; if specifications are not strictly adhered to, then it could severely delay the entire project.
On 7 August, Korea delivered the first of nine vacuum vessel sectors. The steel unit weighs 440 tonnes and took a decade to design, manufacture, and test. Nine of these units will make up the ITER’s doughnut-shaped vacuum chamber. Korea is responsible for producing four, while Europe will provide the remaining five. 
ITER will also feature 18 toroidal field coils – D-shaped superconductive magnets – that are each as tall as a six-storey building and have a combined weight of approximately 6,400 tonnes. These are the most powerful magnets ever constructed and will be used to force extremely hot plasma into a doughnut-shaped containment field. The toroidal field coils will be capable of generating 11.8 Tesla in magnetic fields and storing 41GJ. In order to maintain their superconductivity, cables for the magnets will be encased in metal jackets that will have liquid helium circulated inside at temperatures of -269°C. Japan’s MHI will provide nine toroidal field coils, with Europe delivering ten, to include one spare. 
And in order to withstand such extreme heat, a gargantuan cooling system is vital for keeping temperatures stable. Developed and built in India over eight years by Larsen & Toubro Heavy Engineering Ltd, the cryostat weighs 3,800 tonnes and has a volume of 16,000m3. It will surround the ITER’s superconducting magnets and vacuum vessel inside the tokamak, and achieve temperatures as cold as -193°C. Comprising 54 units, it has been sent to France in four sections for assembly. The cryostat’s 1,250 tonne base was lowered into position at the end of May. In addition, heat shields will provide another crucial layer of protection.
Machine assembly is due to finish before the end of 2024 and ITER’s first plasma is scheduled for 2025. In 2035, it will begin operations using deuterium and tritium. And its team is confident of success.
“ITER is the culmination of 60 years of R&D. Success for ITER means demonstrating the technical and scientific feasibility of fusion by producing a net energy gain,” says an ITER spokesperson. “Despite the huge challenges, not only the teams at work on the project but the governments of the 35 nations that fund ITER, are confident this will be achieved.”
The future for nuclear fusion
ITER only really represents the beginning for nuclear fusion. It has not been designed to act as a power plant; the intention is to provide the proof of principle. Nations around the world are already planning their own nuclear fusion projects, with findings from ITER used to further their advancement.  In the UK, there is a long history of fusion development. The country is working on a programme to make nuclear fusion on a smaller scale and more cost-effective. The British Government is backing this and recently announced an investment of £220m. Next year, the country will provide fuel tests for ITER.
“In the UK, we are fortunate to play host to the world’s biggest fusion experiment, JET, on behalf of the European fusion community, at Culham Science Centre near Oxford. In 1991, JET became the first device to produce fusion power on Earth – it is still running today and playing an important role in preparing for the international ITER project. Next year, JET will run a ‘dress rehearsal’ for ITER with the high-performance fuels that future fusion power plants will use,” says Chapman. 
“Alongside this, the UK has one of the most advanced fusion research programmes of any nation. At the UK Atomic Energy Authority, we are developing designs for compact fusion reactors that could offer a smaller, cheaper route to fusion power. Our latest machine, MAST Upgrade, is about to go into operation, and we’ve recently embarked on a £220m preliminary reactor design programme – STEP – that could see the UK put fusion electricity on the grid by 2040, potentially a world first.”
It should be noted however, that it remains uncertain if the UK will still be part of ITER if the country fails to strike a post-Brexit trade deal with the EU. 
And while Australia is a fairly recent addition to ITER, its HB11 project, by Professor Heinrich Hora’s University of New South Wales team, could open up all sorts of further opportunities for nuclear fusion. Instead of heating up gases to extreme temperatures, two high-powered lasers control the fusion, using hydrogen and boron B-11 as fuel.
It may have taken 100 years since Arthur Eddington announced his theory of releasing huge amounts of energy by smashing together small nuclei, but nuclear fusion power is slowly moving to becoming a reality.
https://www.power-technology.com/features/hotter-than-the-sun-iter-and-the-pursuit-of-nuclear-fusion/