A nuclear reactor involves heavy elements splitting apart efficiently in the nuclear core using special materials to allow chain reactions. Neutrons are crucial for splitting atoms, with U-235 releasing more than U-238. Critical systems balance neutron births and deaths, while sub-critical systems decline and super-critical systems grow exponentially. Building a core involves seeding neutrons and ensuring they interact optimally with Uranium, with enrichment and moderation methods utilized. Reactor size, materials, and geometries must be carefully considered to achieve criticality. Adjusting control rods can make a system super-critical for sustained nuclear reactions. Startup requires efficient neutron sources like Cf-252 or Pu-238 and Be for safety and efficacy reasons.
https://www.usnc.com/core-build/