ITER wordt grootste R&D project

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22 november 2006 | Meer investeringen dan in het ruimtestation ISS, meer landen die meedoen. Het kernfusieproject ITER is op het Elysée getekend door de EU en zes andere staten: China, India, Rusland, Japan, Zuid-Korea en de USA.”The ambition is huge!” zei president Chirac: “To control nuclear fusion. To control the tremendous amount of energy generated at one hundred million degrees and to design sufficiently resistant materials for the purpose. To produce as much energy from a litre of seawater as a litre of oil or a kilo of coal.”

Er wordt 10 miljard € in geïnvesteerd en in de komende twintig jaar een 20.000 ton zwaar experiment opgezet worden, de International Thermonuclear Experimental Reactor . De samenwerking is voor 35 jaar voorzien en kan nog eens 10 jaar verlengd worden. Doel is te komen tot een energieopwekking via kernfusie. Daarmee zo een ‘oneindige’ energievoorziening mogelijk worden, die geen broeikaseffecten kent: Fusion is the process which powers the sun and the stars. When light atomic nuclei fuse together to form heavier ones, a large amount of energy is released. Fusion research is aimed at developing a prototype fusion power plant that is safe and reliable, environmentally responsible and economically viable, with abundant and widespread fuel resources.

Een overzicht van de opzet, inhoud en belangrijkste wetenschappelijke en maatschappelijke vragen rond ITER leest u hierna.

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How will ITER help fusion power become a reality?

The long-term objective of fusion research is to harness the nuclear energy provided by the fusion of light atoms to help meet mankind´s future energy needs. This research, which is carried out by scientists from all over the word, has made tremendous progress over the last decades. The fusion community is now ready to take the next step, and have together designed the international ITER experiment. The aim of ITER is to show fusion could be used to generate electrical power, and to gain the necessary data to design and operate the first electricity-producing plant.

In ITER, scientists will study plasmas in conditions similar to those expected in a electricity-generating fusion power plant. It will generate 500 MW of fusion power for extended periods of time, ten times more then the energy input needed to keep the plasma at the right temperature. It will therefore be the first fusion experiment to produce net power. It will also test all the key technologies, including the heating, control, diagnostic and remote maintenance that will be needed for a real fusion power station.

ITER is a tokamak, in which strong magnetic fields confine a torus- shaped fusion plasma. The device´s main aim is to demonstrate prolonged fusion power production in a deuterium-tritium plasma. Compared with current conceptual designs for future fusion power plants, ITER will include most of the necessary technology, but will be of slightly smaller dimensions and will operate at about one-sixth of the power output level, and will not generate electricity.

The programmatic goal of ITER is “to demonstrate the scientific and technological feasibility of fusion power for peaceful purposes”. After extensive discussions with the scientific community at large, this general goal is now interpreted into a number of specific technical goals, all concerned with developing a viable fusion power reactor.

First of all, ITER should produce more power than it consumes. This is expressed in the value of Q, which represents the amount of thermal energy that is generated by the fusion reactions, divided by the amount of external heating. A value of Q smaller than 1 means that more power is needed to heat the plasma than is generated by fusion. JET, presently the largest tokamak in the world, has reached Q=0.65, near the point of “break even” (Q=1). ITER has to be able to produce Q=10, or Q larger then 5 when pulses are stretched towards a steady state. This is done so that, in the “burning plasma”, most of the plasma heating comes from the fusion reactions themselves, and so that the plant efficiency can be sufficiently high to have a chance of leading to an economically viable power plant.

Secondly, ITER should implement and test the key technologies and processes needed for future fusion power plants – including superconducting magnets, components able to withstand high heat loads, and remote handling.
Lastly, ITER should test and develop concepts for breeding tritium from lithium-containing materials inside thermally efficient high temperature blankets surrounding the plasma. Tritium self-sufficiency of a fusion power plant is a necessary prerequisite, as tritium is not available in nature.

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What is fusion?

Fusion is the energy source of the sun and the stars. When the nuclei of light atoms come together at very high temperatures, they fuse and this produces enormous amounts of energy. In the core of the sun or a star, the huge gravitational pressure allows this to happen at temperatures of around 10 million degrees Celsius.

At the much lower pressures that we can produce on Earth, temperatures to produce fusion need to be much higher – above 100 million degrees Celsius. To reach these temperatures there must first be powerful heating, and thermal losses must be minimised by keeping the hot fuel particles away from the walls of the container. This is achieved by creating a magnetic “cage” made by strong magnetic fields, which prevent the particles from escaping. The development of the science and technology involved in this process is the basis of the European fusion programme.

What are the attractions of fusion as an energy source?

The key advantages are:

• It could provide a large-scale energy source with basic fuels which are abundant and available everywhere.

• Very low global impact on the environment – no CO2 greenhouse gas emissions

• Day-to-day-operation of a fusion power station would not require the transport of radio-active materials

• Power Stations would be inherently safe, with no possibility of “meltdown” or “runaway reactions”.

• There is no long-lasting radioactive waste to create a burden on future generations.

Is fusion safe?

A fusion reactor is like a gas burner – the fuel which is injected into the system is burnt off. There is very little fuel in the reaction chamber at any given moment (about 1g in a volume of 1000 m3) and if the fuel supply is interrupted, the reactions only continue for a few seconds. Any malfunction of the device would cause the reactor to cool and the reactions would stop.

The basic fuels – deuterium and lithium – and the reaction product – helium – are not radioactive. The intermediate fuel – tritium – is radioactive and decays relatively quickly, producing a very low energy electron (Beta radiation). In air, this electron can only travel a few millimetres and cannot even penetrate a piece of paper. Nevertheless, tritium would be harmful if it entered the body, so the facility will have very thorough safety facilities and procedures for the handling and storage of tritium. As the tritium is produced in the reactor chamber itself, there are no issues regarding the transport of radio-active materials, except at startup and closure.

Extensive safety and environmental studies have led to the conclusion that a fusion reactor could be designed in such a way to ensure that any in-plant incident would not require the evacuation of the local population.

What will be the environmental impact of fusion energy?

The energy generated by the fusion reactions will be used for the same purposes as current sources of energy, such as generation of electricity, heat for industrial use or the production of hydrogen.
The fuel consumption of a fusion power station will be extremely low. A 1 GW fusion plant will need about 100 kg of deuterium and 3 tonnes of natural lithium to operate for a whole year, generating about 7 billion kWh, with no greenhouse gas or other polluting emissions. To generate the same energy, a coal-fired power plan (without carbon sequestration) requires about 1.5 million tonnes of fuel and produces about 4-5 million tonnes of CO2.

The neutrons generated by the fusion reaction cause radio-activity in the materials surrounding the reaction –the walls of the container etc. A careful choice of the materials for these components in future power plants will allow them to be released from regulatory control and possibly recycled about 100 years after the power plant stop operating. Waste from fusion plants will not be a burden for future generations.