By Jenny Lee WIRED Korea
There is an old joke that scientists and physicists like to tell about nuclear fusion – that it is the technology that always exists 30 years in the future.
It was in the 1940s when research into nuclear fusion reactors began with a lofty goal of delivering virtually boundless clean energy that generates far less radioactive waste than fission reactors used today. But the decades of effort and billions of dollars spent chasing fusion power have thus far resulted in disappointing results, missed deadlines and cost overruns, leaving many in the scientific community to question fusion’s feasibility.
More sanguine is Yoon Si-Woo, a Korean scientist who works at a national fusion facility located in Daejeon, 160 km south of Seoul. He says fusion power is not a distant dream, but a distinct possibility due to recent scientific advances.
“Stable nuclear fusion in a reactor would be achieved by 2035,” Yoon says. “And commercial fusion power plants may be a reality by the mid-2040s and 2050s.”
Yoon and some 100 researchers at the National Fusion Research Institute (NFRI) are conducting a variety of experiments and tests with a fusion reactor built in the period of time from 1995 to 2007. Many milestones were achieved through a more than decade-long operation of what is called the Korea Superconducting Tokamak Reactor (KSTAR), including superheating clouds of hydrogen plasma to 100 million degrees Celsius – a temperature which is about seven times hotter than the sun’s core.
“Incredibly high temperatures are what it takes to achieve fusion reactions,” says Yoon, director of the KSTAR Research Center. “They are very difficult to initiate and sustain.”
What is Fusion?
The ability to generate such an extreme heat is critical as fusion occurs on the Earth only at temperatures exceeding several hundred million degrees, or when two hydrogen atoms fuse to form helium, as in most stars including the sun.
Both atoms – deuterium and tritium derived from seawater and lithium – are positively charged and have strongly repulsive electrostatic forces which prevent them from getting close enough to collide. When heated to massive temperatures, however, they gain enough kinetic energy to overcome repulsion and fuse together, releasing great torrents of energy.
“With seawater just enough to fill half the bathtub and lithium contained in a laptop battery, you can get as much energy through fusion as 40 tons of coal would generate (which is about 100,000 kilowatt hours),” says Hwang Yong-Seok, a nuclear engineering professor at Seoul National University (SNU). “And its major by-product is helium, which is clean and safe.” To put it into perspective, 100,000 kilowatt hours (kWh) is as much electricity as one person uses in 40 years, or enough energy to power 28 homes for a year.
In that process, the negatively-charged electrons are separated from the positively-charged atomic nuclei, or ions, forming a cloud called plasma. For a useful amount of fusion to occur, this plasma has to be hot, dense and confined long enough.
Many times, a donut-shaped chamber surrounded by magnets made of superconductors is used to contain and control the electrically-conductive plasma. KSTAR is an example of this “tokamak” device, which is deemed the most advanced design for a practical fusion reactor.
“To create a powerful magnetic field, electromagnets are needed such as a metal wire coil in which an electric current flows,” says Yoon, head of the KSTAR project. “Unlike copper coils, superconducting coils (that surround the tokamak device) have zero resistance when cooled at very low temperatures. This implies no current delay, and therefore large, stable magnetic fields can be achieved.”
Slow and Steady Progess
Since the first plasma in 2008, KSTAR scientists have been working toward achieving steady-state operation of the fusion reactor, and it has delivered promising outcomes from experiments carried out every year, says Na Yong-Su, another nuclear engineering professor at SNU.
In late 2016, KSTAR made a progress by sustaining the plasma temperature of 50 million degrees for 70 seconds. The next year, it not only achieved an increase in plasma temperature as well as in operation time, reaching 70 million degrees for about 72 seconds, but also reduced a common plasma instability called edge localized modes (ELMs) for 34 seconds.
Earlier this year, it managed to successfully maintain the plasma temperature of 100 million degrees for about eight seconds, although it was done first by China’s Experimental Advanced Superconducting Tokamak (EAST) in 2018. EAST also has the reputation of being the first facility to sustain conditions necessary for fusion reaction for longer than 100 seconds.
“Our goal is to do it for about 20 seconds this year and for about 300 seconds by 2025,” Yoon says. “Getting to 300 seconds would be a very important milestone because it means there will be no problem running the reactor for 24 hours.”
But there is still plenty of work to be done before nuclear fusion can produce sustainable energy on a commercial scale.
Big Challenges Ahead
First, more heat is needed in KSTAR to boost plasma temperatures well over 150 million degrees. Na says KSTAR’s heating equipment currently functions at half the capacity of those used by other countries.
“KSTAR can maintain plasmas for a long time with high performance, but the heating power is not as high as in other countries yet,” Na says. “Existing devices like those in Europe, the U.S. and Japan can produce plasmas with much higher temperatures.”
But this brings up the issue of government funding, as Na says raising just one megawatt (MW) requires about 10 billion won. Conducting experiments with KSTAR, which cost around 350 billion won during construction, comes at a hefty price tag of about 30 to 40 billion won every year, according to Yoon.
The technology to insulate hot plasmas for long periods of time without heat loss also needs improvement, Hwang says. Heat loss many times is driven by instability.
Another hurdle lies in materials. KSTAR and other test reactors currently run at much lower energies and for much shorter times than a power plant reactor would need to operate, and therefore, it is important to build the interior of these reactors with components that would not erode from a burning plasma that outputs much heat and radiation.
The knowledge and technology obtained through the operation of KSTAR, EAST and other tokamak devices around the world will be the basis of the International Thermonuclear Experimental Reactor (ITER) project, an ambitious energy project that involves Korea and 34 other nations to build a gigantic experimental fusion reactor. Construction of this device is underway in southern France, due for completion in 2025.
The total cost of the ITER project is estimated to be around $22.5 billion (27.6 trillion won), 10 percent of which will be paid by Korea, says Yoon.
“I believe the construction is more than halfway completed,” says Na, who also serves as chairman of ITER Integrated Operation Scenario International Expert Group. “We are expecting a first plasma in 2025 (using the ITER facility). In line with the plan, Korea is drawing up a roadmap, according to which the first nuclear fusion power plant is to be constructed in the 2040s and 2050s.”
저작권자 © WIRED Korea 무단전재 및 재배포 금지
- 최초작성 2020.05.12 09:38
- 수정 2020.05.13 09:49
저작권자 © WIRED Korea 무단전재 및 재배포 금지
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