Thinking ahead fusion energy for the 21st century?
Box 3 | There's work to be done
Much of the technology used in ITER has been demonstrated to work using improved computer models of plasma behaviour, but there are a number of technical uncertainties about fusion reactors that can only be answered by doing some experiments. Planned ITER experiments include health, safety and waste management procedures.
Bigger is better
One of the advantages of ITER facility is its size. ITER is twice as big as other tokamaks, with an outer radius of 6.2 meters. Generally, the more room available for plasma to move, the better. A large plasma volume reduces the amount of heat lost to the walls of the reactor and reduces the severity of problems associated with high density neutron fluxes to the walls.
Learning to handle the heat
In the plasma core, the temperature will approach 100 million degrees, which is about 10 times hotter than the core of the sun. Until now, researchers have been able to control the plasma temperature by turning down the heat. But for commercial fusion reactors to become a reality, they need to learn how to hold a lot of energy in a small space and let it out in a controlled way.
Researchers also need to learn how to capture and use the power produced by the reactions. It is likely that liquid coolants will be used to cool the blanket and diverter, and the heated coolant then used to heat water, to drive steam turbines.
Development of advanced materials
A lot of energy generated by fusion reactions is in the form of fast moving neutrons, which will irradiate the beryllium-coated blanket surrounding the plasma. But beryllium may not be well suited to handle the heat and radiation. Japanese researchers are considering building a test facility to develop materials more suited to the task.
If ITER is successful, helium will accumulate in the reactor and will be captured by the diverter at the bottom of the reactor. Researchers need to learn how that will react with the plasma and surrounding materials. The walls may, for example, accumulate radioactive tritium.
Posted February 2007.