Nuclear fission
Process of radioactive decay in which nucleus of an atom splits into smaller, lighter nuclei. Fission releases very large amounts of energy and causes a nuclear chain reaction in nearby atoms. Fission rocket use fissionable fuel in order to produce thermal power to the reactor.
Fission can be controlled by adjusting proximity of the fuel. There are different approaches to control mechanisms:
- Control rods can be inserted between fuel rods, inhabiting the chain reaction.
- Fuel rods themselves can be moved away slowing down the reaction.
- In liquid core reactors, the fissile fuel itself can be pumped away the reaction chamber.
Current nuclear thermal rockets use either uranium, plutionium or thorium as a fuel source.