Plutonium is necessary for manufacturing the teleports and krakaton, it is also assential for terran's reactors and is used in terran's armed forces. Plutonium is mined in plutonium mines, devastators, devastatols and collectors.

Please don't confuse plutonium as an element with chemical symbol Pu and plutonium in F&E with abbreviation Pl. Plutonium (Pl) isn't an element, but it's noble mixture for high-powered reactors.
Between Pu and Pl is the difference just like between iron and steel!