Safety and environment
Climatically harmful emission does not occur in a fusion power plant. Safety precautions are necessary because of the radioactive tritium and high-energy neutrons, which activate the walls of the plasma vessel.
A fusion power plant has an important property ordained by nature: It can be designed in such a way that it does not contain any energy sources that – should they get out of control – could destroy a safety shield from the inside.
Nor can a fusion power plant "run wild": In the combustion chamber there is always just as much fuel burning as is actually needed – about one gram of deuterium and tritium distributed in a volume of about 1000 cubic metres. The extremely thin fuel, despite the high temperature, therefore has a low power density, comparable to that of an ordinary light bulb.
The radioactive fuel constituent, tritium, must be safely confined. What is released from the power plant in normal operation to the most highly exposed person is equivalent to about one per cent of the natural radioactive dose. Even after a major accident the limit values for introducing evacuation procedures are far from reached.
On termination of operation the walls of the plasma vessel remain as radioactive waste and have to be put in intermediate storage. Its activity decreases fast: after about hundred years to a ten-thousandth of the initial value. After a decay time of one hundred to five hundred years the radiotoxic content of the waste is comparable to the hazard potential of the entire ash from a coal-fired power plant, which always contains natural radioactive substances.
If special materials with low activation potential can be developed, there would no longer be any waste to dispose of after a decay time of about hundred years. Some of the material would then be re-used in new power plants, the rest be given clearance. No permanent storage would be needed.