The Fuel Core uses uranium or plutonium fuel pellets to generate a fission reaction that emits neutrons and generates heat. This is the primary means of making heat in the fission reactor, which is then used to make steam to rotate a turbine and produce shaft power.
When the fuel core has fuel, it has a 5% chance per tick of releasing a neutron along the x or z plane. If a neutron hits a fuel core with fuel, it will have a 25% chance of generating a neutron burst that will release 3 neutrons randomly along the x or z planes and generate heat. The amount of heat produced from the neutron burst depends on the fuel in the bottom slot. A uranium fuel pellet increases the temperature 20 C, where a plutonium fuel pellet increases it by 30 C. The neutron burst also has a 3% chance for uranium and 4% chance for plutonium of depleting the fuel then a 20% chance for uranium or 40% chance for plutonium of producing nuclear waste.
The temperature of the fuel core depends on the biome, the ability of surrounding blocks to absorb heat, and the rate of neutron bursts. The Coolant Cell, Steam Boiler and Sodium Heater blocks can absorb heat from a Fuel Core. Heating the Steam Boiler will produce steam that will rotate a turbine to produce shaft power. The Sodium Heater will heat a Heat Exchanger to heat surrounding steam boilers to produce steam. A Fuel Core will meltdown, causing a large explosion and spreading of radiation, leaving behind a highly radioactive lavalike liquid known as Corium. This happen at temperatures higher than 1800 C, or excessive production of hydrogen, which is produced at temperatures greater than 1400 C. At temperatures higher than 500 C the reactor will fizz and produce smoke.
Items can be piped out from beneath the fuel core and piped into it from above.