The Cooper Heavy Industries Mark IV Uranium Hexafluoride Reactor Stardrive has been a mainstay in medium-range space vehicle construction for twenty years. While the exact details of its energy-producing process are still a corporate secret, physicists have been able to deduce the following:
Primary Catalysts: Oxygen, Nitrogen, Radon, Uranium Hexafluoride
The energy production process usually begins with readily-available oxygen or nitrogen in liquid form. The gas is allowed to vent into a cloud chamber, where high energy protons from a particular source (which varies with end-user design, including cosmic rays) create 10-beryllium as a fission product. 10-Be has a half-life of 1.36 million years, making it useful as a secondary power source (since electrons are its decay product), but is primarily combined with Alpha particles from Radon to form 12-Carbon and a slow neutron.
Neutrons liberated by this process are used to bombard gaseous Uranium Hexaflouride, which bypasses expensive refinement procedures to produce 235-Uranium, which is captured via micro-loop cyclotron and stored within Stage One of the reactor. Slow thermal neutrons from the same Be/a process as before induce a highly-controllable fission reaction, allowing for a precise level of reactor energy output as well as an end-user selectable fission product menu. This process also makes a runaway reaction impossible, since an undesired level of fission would simply require the operator (or an automated system) to cease primary neutron bombardment. Some third-party companies offer neutron moderator customization (such as in the form of graphite rods), but there is no evidence that use of these moderators has ever been necessary.
This does not mean that the Cooper Mk IV cannot fail catastrophically by another method. Uranium Hexaflouride is highly corrosive, and if containment systems fail, any number of critical systems could be damaged. While aluminum alloys are the only storage and transfer conduit construction materials authorized, careless doping of those alloys can result in substandard material susceptible to failure. Furthermore, the popular secondary energy modification of 197-198-Gold/neutron flux/gamma generation can be fatal to organic life if not properly shielded, but of course Cooper Heavy Industries warns against this sort of modification in their standard EULA.