Fusion technology is advancing in southern France

Energy from atoms

08 January 2010 18:01  [Source: ICB]


Correction: In the article headlined "Fusion technology is advancing in southern France," in the sixth paragraph, please read: "scientists need to heat a mixture of two hydrogen isotopes - deuterium and tritium - to a temperature of 150m˚C (270m˚F)," instead of "scientists need to heat a mixture of two hydrogen isotopes - deuterium and tritium - to a temperature of 150m˚C (302m˚F)." A corrected story follows.

An international consortium is beginning to construct the world's largest fusion reactor in southern France. Huge technical problems need to be overcome, not least in materials selection

 Rex Features/Chris Eyles

WHEN IT comes to sustainable energy, one of the great long-term goals is to use nuclear fusion to generate electricity. Scientists from many countries have been working on the technology since the mid-1950s, but a demonstration project is still several decades away.

However, many researchers are now engaged in a major new project that will move the technology a significant step forward. The culmination of these efforts is taking physical form at Cadarache, in the South of France in the form of the ITER project.

Here an international consortium consisting of China, the EU, India, Japan, South Korea, Russia and the US is providing funding of $10bn (€7bn) over the next 30 years to build and operate a tokamak-type fusion reactor. The tokamak design was developed in Russia and the name derives from the Russian for "toroidal chamber with magnetic coils."

The goal is to produce 500MW of output power for 50MW of input - the first time a fusion facility will have created a net output of energy. If successful, the project will have huge long-term implications for the energy and chemical industries. Entering a new age of unlimited energy would take pressure off oil and natural gas, the two primary feedstocks for the chemical industry.

To create a net output of energy from nuclear fusion, the scientists need to heat a mixture of two hydrogen isotopes - deuterium and tritium - to a temperature of 150m˚C (302m˚F), to create a plasma in which the nuclei of the atoms will collide and react to give off helium, neutrons and energy.

To cope with such extreme temperatures, the plasma is contained in a specially shaped toroidal vacuum chamber using powerful magnetic fields, created by superconducting magnets. These will use magnetic coils formed using niobium-tin or niobium-titanium wires. In the latter case, the wires are coated with nickel and then woven into cables, which are then encased in a steel jacket to make up the final conductor.


Artist's impression of the developed site at Cadarache, France. Source: ITER

Once the fusion reaction is under way, the heat is removed from the reaction vessel through cooling water running behind the reactor inner surfaces. Two independent cooling circuits will be used, with water passing through primary and secondary heat exchangers before cooling and evaporation. The facility is expected to use 1.5m m3/year of water during operation.

The scale of the project is immense. The entire tokamak reactor will weigh 23,000 tonnes, consisting mainly of high-performance steel. The site at Cadarache covers 180ha (445 acres), with a central 42ha area that will house the ITER reactor and buildings. The reactor building will be 57m high.

Material selection has played a big part in the research and design during the run-up to the construction phase. The internal surfaces of the huge vacuum vessel, which forms the heart of the reactor, not only have to withstand the immense temperatures, but also absorb the neutrons produced so they can transfer heat to the cooling fluid and react with lithium in a lining blanket to produce more of the rare tritium isotope.

The huge vacuum vessel at the heart of the fusion reactor weighs 8,000 tonnes. Source: ITER
The blanket wall is modular and consists of 440 individual segments, each weighing 4.6 tonnes. Each segment has a detachable first wall that directly faces the plasma and removes the plasma heat load, and a semipermanent blanket shield dedicated to neutron shielding.

The ITER's blanket is one of the most crucial and technically challenging components. Several materials have been investigated, including carbon fiber-reinforced graphite, reinforced copper and tungsten. But the choice has been made to use beryllium to cover the first wall. The rest of the blanket shield will be made of high-strength copper and stainless steel. At a later stage, some blankets will be adapted to trial the tritium breeding technology.

The ITER site is now prepared and international tendering for components and materials is underway. Contracts for parts of the reactor vessel have already been awarded to South Korea, with others expected to go to the EU shortly. Other members of the consortium have been earmarked to provide many of the main components and in-kind contributions to the overall program. But around 11% of the items will be purchased through a joint fund under the control of the ITER organization.

Construction is expected to take around 10 years, with first plasma generation at around 2020. The operation phase is then expected to last 20 years. If successful, ITER will pave the way to a full demonstration project - DEMO - in the 2030s. Then we might really enter an age of unlimited energy.

More information on the ITER project

By: John Baker
+44 20 8652 3214

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