Plutonium-240

Pu240 is a common and somewhat disappointing Plutonium isotope.

Production
It can be bred from Pu239.

Uses
Moderate role in Plutonium Fuel in the form of Reactor Grade Plutonium.

Breeds into nuclear waste.

Can be used in the Custom Nuke. It contributes a 1.05 multiplier to its salted stage.

Trivia

 * It is a high spontaneous fissile rate, which may make it sound good for weapons, it isn't, as it causes premature fission preventing nuclear chain reaction necessary for weapons.
 * Used to breed into lead, but now it breeds into waste.
 * Presumably, due to the next isotope being so unstable it instantly decays into a miscellaneous collection of decay elements.