For the fusion of two isotopes one needs a lot of energy to overcome the repulsive forces between the isotopes, these are forced close together by high temperatures and pressures. The goal of fusion is to produce a positive net energy, thus the released energy should be greater than the used energy.
There are two fusion methods, with laser beams directed at a pellet the size of a peppercorn to give it lots of energy to fuse together, and the plasma method.
The laser beam fires at the pellet, the sudden surge in pressure and temperature forces the pellet to compress to 100 times the density of lead. When this happens the hydrogen atoms will fuse together creating lots of energy. This energy can then be used to heat water to form steam to feed a turbine.
The plasma is based on the same principle of high temperature and pressure but heats the deuterium and tritium to plasma. This method is able to provide a continuous surge for tens to hundreds of seconds whereas the laser beam can only provide a surge for mere seconds.
There are three mayor problems with this technique at the moment:
- The need for an around the clock operation, to become a reliable source of energy.
- Materials used in the reactor will have to be able to withstand the high temperatures and the beating of the neutrons. There are currently no materials that realize this need.
- Even though the used products and the emissions are zero there is still a possibility that the materials in the reactor become radioactive. The absorption of neutrons by the nucleus can turn any material radioactive.
- The fusion needs deuterium and tritium, deuterium is cheap and abundant but tritium is rare and expensive. It can however be harvested from nuclear reactions, this means that fusion can be self-reliant for tritium. However, the fusion reaction consumes much more than can be provided.
When we look at all these problems it becomes clear that the visions we had about the purity of fusion energy are fading.
Reference: Moyer, Michael. “Fusion’s false dawn”. Scientific American, March 2010