Now, I think it's time for me to put in my knowledge. I have done quite a bit of research into Fusion, as it interests me quite a lot.
First off, the difference between cold and hot fusion. Hot Fusion attempts to emulate the chemical process occuring in the sun by heating hydrogen (i'm pretty sure) up to super-hot temperatures, where they shed their electrons and become plasma. These reactors need Deutarium as far as I can remember, and if one of these reactors are breached, the results could be superhot plasma spraying around in the power compartment.
Cold fusion is no myth, it is real and it has already succeeded in passing the break even point in energy creation (produces more energy than it takes to maintain)- something that the Hot Fusion project has not yet managed, despite millions of pounds being spent on it.
Cold fusion takes place at room temperature, and uses metals specially "loaded" with certain elements, and in a electro-chemical reaction produces energy. In fact, it has been suggested that in some variants of cold fusion, the process can be used to dispose of radioactive waste (although what type escapes me).
The greater portion of the scientific community denies cold fusion exists, even though it has been proven to do so. People have different reasons for this, but one of the greatest is probably that they are unhappy that two scientists working on a low budget managed to do something that scientists on a multi-million pound budget had dismissed as impossible.
I personally think the ships in FS2 use Hot Fusion reactors, due to their use of Deuterium.
Interesting facts about fusion:
According to einsteins formulae, E=MC2, a 1 gram raison has more power inherent in it that 20,000 tons of TNT.
Using fusion, a glass full of water can produce the same amount of power as 100 tons of coal, without half the pollution.#
Fusion is the process of two seperate atoms joining to produce energy, fission is basically them splitting apart. Fission is a chain reaction (thus nukes) while Fusion isn't (as far as I know).
And for anyone who disputes these facts, please do research before you argue, do not let your own opinion taint your viewpoint.
IMO, fusion is Humanities best hope for clean energy (but not to say the only one).