Americium-241

Americium-241 is a rare radioisotope produced only by the decay of Plutonium-241 in RBMK nuclear reactors.

Production
Am-241 makes up 25% of Pu-241-based Short-Lived Nuclear Waste from RBMKs. It requires the SILEX to extract.

Uses
Low and Medium enriched Americium RBMK fuels, as well with its own highly enriched fuel that runs on fast neutrons.

High strength RTG pellet. They provide 20 power per tick. If RTG decay is enabled, each will have a lifespan of 3,384,000,000 ticks, computing to ~53.5 IRL years, with a stated in-game lifespan of 705 years (assuming a 100 day year). They decay to Neptunium-237 pellets. This also means it will make 676,800,000,000 power in total over that time.

Trivia

 * Am-241 is also fissile, but only to fast neutrons.
 * Am-241 is used in ionization type smoke detectors, in microscopic quantities of course.