Hi
I want to show you an idea I had, when running some fusion reactors with the rocket science mod on my server. Maybe this has already been mentioned, but I still want to show it to you.
First thing is, that the way it functions is a bit to simple (imo), how about setting the reactor up like the nuclear reactor in IC2, but with a bigger energy output and different components and setups? This option would also require the cooling of the reactor of course, but would also make it more variable in the way you can run it
Running the reactor could look like this:
The neibour tritium and deuterium cell are considered "connected" and performing the fusion reaction producing energy. The right setup with the 4 deuterium-cells will produce much more energy (and heat!) but the central tritium cell will also deplete 4 times faster then the surrounding cells (fusion works at a 1:1 ratio ) The surrounding lithium cells are bred into He3-tritium cells, which can be put in the isotope separator to get a new tritium cell Tritium of course breeds a lithium cell faster then deuterium does.
You can also use deuterium cells only, but this will be much less efficient... on the other side, a tritium-tritium-fusion wont work.
Every used (and depleted) deuterium cell also has a small chance (lets say 1/4) to change into a half-tritium cell which can be crafted in a full one. (<-- an extra type of cell is needed since the reactor should stop working, when a cycle is done)
Some things should still be thought of, like the heat management (since fusion reactions need a LOT of heat). The same cooling elements like in the nuclear reactors could be used for the heat-management, but the reactor would still need a basic heat to produce energy... or the reactor could get a heat-limit which must be reached to get the maximum energy output of the cells, by placing heating elements inside the reactor instead of cooling ones (which would also require to make the reactor invincible to heat damage). Since fusion reactions in normal conditions require around 150 million degrees, the second way would be the best i think (like placing heating rods and heating distributors inside to reach a very high temperatures). This would force players to find the best way between puting energy-producing cells or heat-producing elements inside the reactor for a maximum output
The lifetime of the cells must be increased of course (maybe like an hour or two) and they also shouldn't be stackable anymore since they would need a lifebar like uranium cells.
Since the code for running a reactor is already inside of IC2, it should be possible to add something like this 
What do you think of this idea?
Greetings P.
P.S. Sorry for my bad english
lol