Nuclear fusion is the holy grail of energy generation. Elaborate state-sponsored efforts since 1957 to develop this technology have been unsuccessful, but the private sector is now making impressive progress. The story is summarised by Lev Grossman in Time magazine of November 2nd.
There are two ways to extract energy from the atomic nucleus: nuclear fission and nuclear fusion. In nuclear fission the heaviest atoms, uranium, split in two (fission) and in the process a small amount of matter is converted to enormous energy, according to Einstein's equation E = MC2 . Nuclear fusion works in the opposite direction. Here the lightest atoms, hydrogen, fuse together, releasing enormous energy.
Nuclear fusion is a far superior method of generating energy than either nuclear fission or burning fossil fuels. Firstly, nuclear fusion releases much more energy per unit input of energy. Secondly, fusion is pretty much nonpolluting, whereas both fission and the burning of fossil fuels produce dangerous wastes. Thirdly, nuclear fusion releases no carbon-dioxide, solving the global carbon emission problem, whereas burning fossil fuels releases copious amounts of carbon-dioxide, contributing strongly to global warming. Fourthly, the raw materials (hydrogen from seawater and lithium) required for fusion are plentifully available in the long term, whereas uranium and fossil fuels are finite resources that will run out before too long. Fifthly, fusion is safe – there’s no chain reaction to run out of control – whereas serious nuclear fission accidents can happen and the fossil-fuel cycle claims many lives every year.
Nuclear fusion reactors are very common in the natural world. You can see them by looking at the sun or stars. The sun fuses hydrogen atoms into helium in its incredibly hot (17,000,000 degrees) and dense core, producing the light and heat that sustain life on Earth.
Positive atoms
In order to build a fusion reactor, we must ignite a star on Earth. Because this star will be tiny compared with the sun, initiation of fusion requires a higher temperature of 100,000,000 degrees. At millions of degrees, electrons are stripped from atoms, and matter exists as a sea of free-moving positive atoms and electrons called a plasma. Plasma is so incredibly corrosive that it cannot be contained in any material container. Luckily it is affected by electromagnetic fields, and can be contained by these nonmaterial forces.
The traditional way to contain plasma in prototype fusion reactors is in the tokamak, a hollow metal doughnut wrapped in powerful electromagnetic coils that create a magnetic field to contain and compress the plasma inside the doughnut. When you heat and compress the plasma enough, some of the atoms bump into each other so forcefully that they fuse.
Government-funded demonstration fusion reactors, mostly tokamaks, are under construction worldwide. The biggest tokamak to date, the International Thermonuclear Experimental Reactor, is under construction in France, with a projected completion date of 2027. It will be 30m tall, weigh 23,000 tons and hold 840 cubic metres of plasma. The tremendous $20 billion cost of the project is borne by a consortium that includes the US, Russia, the EU, China, Japan, South Korea and India.
The goal of demonstration reactors is to pass break-even point, where the reactor produces more energy than it takes to ignite fusion. The next step will be to build a working full power reactor and finally to build commercial reactors.
Progress in fusion development has been painfully slow and bedevilled by delays and cost overruns. The inside joke is that fusion is 30 years away and always will be.
Numerous start-up fusion companies have arisen in recent years, funded by private investors. The attitude is that fusion research has been too slow, too cautious, lavished money on too few possible solutions and is too academically oriented, with the primary goal to produce academic papers, not energy.
The private sector treats fusion as an application of science, not primarily a science-driven development. Some of these companies are making impressive progress with novel prototype fusion reactors, and they bullishly predict that they will make nuclear fusion technically and commercially viable within 20 years. Perhaps we are nearly there at last.
- William Reville is an emeritus professor of biochemistry at UCC. http://understandingscience.ucc.ie