Thinking ahead – fusion energy for the 21st century?
Box 1 | Comparison of amounts of fuel and waste
Comparison of amounts of fuel for fission and fusion reactors
The table below provides a comparison of the fuel requirements for power stations continuously producing one gigawatt of power for one year.
| Power station | Amount of fuel |
| coal-fired | 4.4 million tonnes of black coal* |
| coal-fired | 10.8 million tonnes of brown coal |
| fission reactor | 1.3 tonnes of uranium-235 (from 35 tonnes of uranium oxide or 210 tonnes of uranium ore) |
| fusion reactor | 150 kilograms of deuterium (obtained from two Olympic-sized pools of water) and 500 kilograms of lithium |
*energy density 24 MJ/kg
Control of nuclear reactors
The fission of uranium in a power plant is a self sustaining process, and requires neutron absorbing control rods to prevent uncontrolled meltdown.
In contrast, magnetic fields are used to confine the plasma in a fusion reactor and to keep it hot. Collapse of the magnetic field causes the plasma to cool, so fusion reactions can be stopped with the flick of a switch. There are no chain reactions to control.
Safety concerns
In 1992, the European Safety and Environmental Assessment of Fusion Power concluded that fusion has the potential to be a safe and clean method of generating electricity.
Fusion power plants are said to be intrinsically safe, however there are some safety concerns that need to be addressed:
- Although they produce no 'high level' radioactive waste, one of the most important safety concerns of ITER is to ensure that tritium is not released into the environment. Analysis of the risk of tritium escape in a 'worst case scenario' indicates that if such an event did occur, the public need not be evacuated from the area because the exposure to radioactivity would be below internationally accepted limits.
- A fusion reactor operates by the continual addition of fuel. The amount of fuel in the reactor at any one time is enough for about one minute of operation.
- Most of the radioactive materials produced by a fusion reactor are relatively short lived, with the level of radioactivity decreasing 10,000 fold within 100 years. Radioactive material may be kept on site until it has decayed to a point where it is no longer considered radioactive, it may be stored in a permanent repository or it may be recycled.
- The neutrons released by the fusion reaction can cause the material in the vessel walls to become radioactive, creating an occupational safety risk. The vessel cannot be handled directly, so maintenance of the vessel needs to be done using robots.
- Researchers are designing and selecting new materials for the reactor vessel. Ideally, the vessel materials will have half lives of tens of years, minimising the burden of waste disposal on future generations.
Boxes
Box 2. Fusion science in Australia
Box 3. There's work to be done
Related sites
Safety and environment
(European Commission)
Understanding radiation
(European Commission)
Radioactivity (Georgia State University, USA)
Posted February 2007.