Energy from fusion is an area that has hardly been tapped. the united states has not built a new reactor since somewhere in the 70's because of an environmental act. The radioactive decay of various materials gives rise to the rate at which the atoms will chaotically breakdown in a fission reaction. when this occurs a neutrons are released which collide with other unstable atoms to create a 'chain reaction'. If one atom breaks down and releases 2 or 3 neutrons to break another 2 or 3 atoms the exponential rate will eventually consume all the mass of the reactants. Most of the reactants are not actually used though, only around 2 or 3 % of the fuel in a nuclear bomb is actually converted to energy.
The idea of harnessing this energy was simple, heat water to drive a steam engine. There are a few safety steps involved though, i think its cobalt that is used to suck up the neutrons to stop a meltdown in a nuclear core. they will absorb the neutron and prevent another uranium or plutonium atom from splitting. there is also a 'barns theory' which is what it was called when i was introduced which stated that when you slow the neutrons down they have a greater chance of hitting another atom. i think carbon or some other additive can be used to create a critical mass below the 14 kg for plutonium and 25 or 26 for uranium.
Rods are an extremely inefficient means of going critical though they present a better surface for low rate reactions. With many rods piled together in a tightly controlled matrix, heat can be generated in a very uniform manner. This is how the nuclear reaction is controlled. many rods are sealed in a matrix of cobalt and are pulled out to react with each other but can be dropped back in to prevent a melt down. Water is the heating medium to cool the rods though i think there has been research into various oils and composites with higher heat capacities, the problem is the radiation.
When a water molecule absorbs a neutron, normally the hydrogen, we get deuterium and tritium. these are the fuels for fusion. deuterium is a hydrogen atom with a neutron. when we fuse two together we get a helium atom and massive amounts of energy are released. this was the idea for a fusion bomb, pack deuterium around the core of a fission bomb and the deuterium will fuse causing a hydrogen bomb.
Well there is another use for this deuterium, there is another element called palladium which has a specific crystal lattice which packs hydrogen atoms very close together. when deuterium is used you have the ingredients for fusion tightly packed needing only the energy to push them close enough to fuse. This is the idea of cold fusion, when you can fuse only a few atoms at a time you have a much safer energy generator. the idea is the same as nuclear reactor with a steam engine. Cold fusion was pioneered by fleischman and ponds (i'm not sure of spelling).
They were not able to reproduce their results though. they were using an exploding wire technique with direct electricity to steam to electricity. they used a calorimeter to measure the energy outcome and found helium in the environment which was a clear indication of fusion. their means was far too unstable and was never reproduced which cause cold fusion to be brushed under the rug for a few years and discredited by many.
The next step in cold fusion is here and it is more than probable to be producible on a mass scale. The idea of cold fusion has been proven using lasers to dump a massive amount of energy onto a marble of palladium to create enough radiation energy to expand the palladium to collapse the hydrogen into helium. The problem is that the lasers take too much energy and it is not a positive return as of yet. I work in the field of electroceramics and I have been looking into sonofusion by means of cavitation. Basically an ultrasound device focuses compression wave energy into space to maximize the received echo power. When the energy is focused properly it can cause a phenomenon called cavitation where bubbles form and collapse in water almost instantaneously. It happens because enough energy was focused to create compression wavefronts together to rip the water apart, not on an atomic scale but the surface viscocity is broken because of the compression fluctuations. Anywho these bubbles can be very highly focused and deliver massive amounts of energy as needed to fuse the deuterium.
The doe and many scientists are now picking this up as a feasible possibility for fusion. And with enough engineering it might be possible to miniaturize for ships and eventually airplanes and then maybe cars.