As one of the few options for a large-scale, non-carbon future supply of energy, fusion has the potential to make an important contribution to sustainable energy supplies. Fusion can deliver safe and environmentally benign energy, using abundant and widely available fuel, without the production of greenhouse gases or long-term nuclear waste.
From celestial fusion to terra fusion
Fusion is one of nature's most spectacular achievements. Billions and billions of fusion furnaces, the Sun among them, are flaring in the Universe, creating light and energy. Some seventy years ago scientists understood the physics behind this wonder: the Sun and stars transmute matter, patiently and tirelessly transforming Hydrogen nuclei into Helium atoms and releasing huge amounts of energy in the process.
In the Sun, fusion reactions take place in a context of enormous gravitational pressure at a very high temperature (15 million °C)—conditions which allow the natural electrostatic repulsion that exists between the positive charges of two nuclei to be overcome. The fusion of two light Hydrogen atoms (H-H) produces a heavier element, Helium.
The mass of the resulting Helium atom is not the exact sum of the two initial atoms, however—some mass has been lost and great amounts of energy have been gained. This is what Einstein's formula E=mc² describes: the tiny bit of lost mass (m), multiplied by the square of the speed of light (c²), results in a very large figure (E) which is the amount of energy created by a fusion reaction.
With the understanding of the process of celestial fusion, came the ambition to reproduce, here on Earth, what was happening in the stars. The first fusion experiments in the 1930s were followed by the establishment of fusion physics laboratories in nearly every industrialized nation. By the mid-1950s "fusion machines" of one kind or another were operating in the Soviet Union, the United Kingdom, the United States, France, Germany and Japan. A breakthrough occurred in 1968 in the Soviet Union. There, using a doughnut-shaped magnetic confinement device called a tokamak, researchers were able to achieve temperature levels and plasma confinement times—two of the main criteria to achieving fusion—that had never been attained before. The tokamak became the dominant concept in fusion research, and tokamak devices multiplied across the globe.
From the 1950s’ ‘fusion machines’ onwards, it was clear that mastering fusion would require the marshaling of the creative forces, technological skills, and financial resources of the international community. The Joint European Torus (JET) in Culham, U.K., in operation since 1983, was a first step in this direction. In 1991, the JET Tokamak achieved the world's first controlled release of fusion power. Steady progress has been made since on fusion devices around the world. The Tore Supra Tokamak (France) holds the record for the longest plasma duration time of any tokamak: six minutes and 30 seconds. The Japanese JT-60 achieved the highest value of fusion triple product of any device to date. US fusion installations have reached temperatures of several hundred million degrees Celsius.
Fusion outpaces Moore’s law for transistors
Since the mid-1970s, following “Moore’s Law”’, the number of transistors in a microprocessor has doubled every two years. In the same period, the «Triple product » of density, temperature and confinement time, which measures the performance of fusion plasma, has doubled every 1.8 years. To yield more energy from fusion than has been invested to heat the plasma, the plasma must be held up to this temperature for some minimum length of time. Scaling laws predict that the larger the plasma volume, the better the results. The ITER Tokamak chamber will be twice as large as any previous tokamak, with a plasma volume of 830 cubic meters. It is designed to produce ten times the energy than is required to produce the plasma: 500 MW of fusion power for 50 MW of input power (Q≥10). Although ITER will not convert this power to electricity, it will be the ultimate demonstration of the potential of fusion.
However technically challenging realizing fusion’s potential is, such is the opportunity that the major world powers have decided to work together to take the next step towards producing fusion energy; with the ITER project six nations – China, India, Korea, Japan, Russia, the United States of America plus the European Union have agreed to pool their financial and scientific resources to prove the viability of fusion as an energy source. ITER, therefore, is not only one of the major scientific and technological challenges of the 21st century but is also an unprecedented model for international research collaboration.
More specifically ITER is based on the “tokamak” concept of plasma magnetic confinement, in which the fusion fuel is contained in a doughnut-shaped vessel as previously mentioned. The fuel - a mixture of deuterium and tritium, two isotopes of hydrogen - is heated to temperatures in excess of 100 million degrees, forming hot plasma. The plasma is kept away from the walls by strong magnetic fields produced by superconducting coils surrounding the vessel and an electrical current driven in the plasma.
The role of experimentation
Experimentation permits physicists to identify the most promising combination of elements to reproduce fusion in the laboratory: the reaction between two Hydrogen (H) isotopes Deuterium (D) and Tritium (T). The D-T fusion reaction produces the highest energy gain at the 'lowest' temperatures, requiring nonetheless temperatures of 150 000 000° Celsius—ten times higher than the H-H reaction occurring at the Sun's core. At these extreme temperatures, electrons are separated from nuclei and a gas becomes a plasma—a hot, electrically charged gas. In a star just like in a fusion device, plasmas provide the environment in which light elements can fuse and yield energy. The fusion between Deuterium and Tritium (D-T) produces one Helium nuclei, one neutron, and energy.
To achieve net fusion power in a D-T reactor such as a tokamak, three conditions must be fulfilled: very high temperature (greater than 100 million° Celsius); plasma particle density of at least 10²² particles per cubic meter; and an energy confinement time for the reactor on the order of 1 second. Energy confinement time is the time the plasma is maintained at a temperature above the critical ignition temperature. This is the fusion triple product. ITER will, for the first time, be able to produce burning deuterium-tritium plasma in which the majority of the heating needed to sustain the fusion reaction is produced by fusion generated alpha-particles. The production and control of such self-heated plasma has been the long-standing goal of magnetic fusion research for more than 50 years. Therefore ITER will allow full exploration of the science relevant to fusion power, as well as testing key technologies for future power plants.
The device is designed to generate 500 megawatts of fusion power for periods of 300 to 500 seconds with a fusion power multiplication factor, Q, of at least 10 (Q ≥10). The device is also intended to demonstrate non-inductive steady-state operation with a fusion power multiplication factor of 5 and, ultimately, pulse lengths of up to several thousand seconds. In addition, the design does not exclude the possibility that controlled ignition can be achieved.
ITER incorporates many of the technologies necessary for a fusion reactor and will demonstrate the integrated operation of these technologies. It will also test a range of materials and components required for a reactor and, in particular, will test tritium breeding module concepts that would allow tritium self-sufficiency, the extraction of high grade heat and electricity production in a future fusion reactor.
East-Meets West: Reagan and Gorbachev Agree to Pursue Fusion Research, Geneva 1985
The ITER project was the fruition of a 1985 summit in Geneva between Soviet Secretary General Gorbachev and U.S. President Ronald Reagan, during which the leaders agreed to cooperate on the develop fusion as a “source of energy…for the benefit of all mankind.” The design for a large, international fusion facility was collaboratively developed by the Soviet Union, the US, the European Union and Japan from 1988 to 2001; this design provided the basis for the ITER project that is taking shape today.
With the completion of negotiations at the end of 2005, a provisional agreement on how to share the ITER hardware procurements among the future ITER Members was reached. This envisages that 89% of the items will be provided "in kind”. Each of the seven ITER Members thus contributes components to the machine, and shares in the management aspects of the project including scientific collaboration, financing, staffing, and auditing. Europe contributes 45.45 percent to the construction of ITER, and China, Japan, Korea, Russian Federation and the USA will contribute 9.09 percent each.
Today, the ITER Organization with its Headquarters in Southern France is staffed by approximately 500 people from the Member communities and nearly as many contractors. Domestic Agencies located in each ITER Member organize procurement activities and conclude contracts with industry. The ITER combined operational and cost budget the first couple years after the start of integrated commissioning in April 2019 will be approximately 313 million Euros. This however does not include the in-kind contributions in materials and equipment from ITER Member State contributors.
Tokamak Construction Site March 2013
Construction of the ITER scientific buildings began in 2010. In total, 39 buildings and technical areas will be needed to house the plant systems necessary for the operation of the ITER tokamak. In 2013, construction is set to begin on the 360,000 ton tokamak complex, the heart of the ITER structure. In December 2012, a consortium of Vinci, Razel Bec and Ferrovial Agroman was awarded a EUR230 million civil engineering contract for this work. The last year has also seen the contract awards for the ITER cryostat - the largest in history, the award for the welding the vacuum vessel, and the selection of a logistics service provider to coordinate shipping of components from the four corners of the world to France starting in 2014.
In November 2012, the 30-month-long licensing process came to an end when Jean-Marc Ayrault, prime minister of ITER’s host country, France, signed a decree authorizing the creation of a basic nuclear installation, and clearing the way for ITER construction. This was the first time in world history that a nuclear fusion device has undergone scrutiny by a nuclear regulator to obtain licensing.
Fusion’s advantages in a post-Fukushima world
Nuclear fusion reactors produce no high activity/long life radioactive waste. The "burnt" fuel is helium, a non-radioactive gas. Radioactive substances in the system are the fuel (tritium) and materials activated while the machine is running. During the operational lifetime of ITER, remote handling will be used to refurbish parts of the vacuum vessel. All waste materials will be treated, packaged, and stored on site. The half-life of most radioisotopes contained in this waste is lower than ten years
Maintenance waste during ITER operation will amount to about 1,200 tons over 20 years. Upon the dismantling of the ITER installation, the waste that will be removed and processed will be composed 90% of very low level or low and intermediate level short-lived waste. After 100 years of natural decay, ITER will be left with about 6,000 tons of waste (packaged, that is equivalent to a cube with edges measuring 10 meters).
These figures, together with the fact that run-away reactions simply cannot occur in a fusion machine and that the fusion fuels – hydrogen isotopes – are abundant and freely accessible, are perhaps the most outstanding pro fusion arguments.
ITER is not an end in itself: it is only the bridge toward a first plant that will demonstrate the large-scale production of electrical power and tritium fuel self-sufficiency. This is the next step after ITER: the Demonstration Power Plant, or DEMO for short. If all goes well, DEMO will lead fusion into its industrial era, beginning operations in the early 2030s, and begin putting fusion power into the grid as early as 2040. Our world will then enter the Age of Fusion—an age when mankind covers a significant part of its energy needs with an inexhaustible, environmentally benign, and universally available resource.
Contributor Sabina Griffith is a Communication Officer, Department of Communications and External Relations, with the ITER Project. Sabrina can be contacted at Sabina.Griffith@iter.org for further information.