Is plutonium reusable

Answer 1

Directly, no. Once fissioned the plutonium is gone (it has transformed to other lighter elements).

However indirectly using a breeder reactor, yes. A plutonium fueled breeder reactor with a uranium breeding blanket will produce more plutonium (from uranium-238) than it consumes. This breeder reactor can at the same time be generating electricity like any other power reactor.

Answer 2

This depends on the ratio between the concentration of plutonium isotopes:

r = ([Pu-238] + [Pu-240] + [Pu-242])/([Pu-239] + [Pu-241])
Over a definite ratio plutonium become not usable in a nuclear reactor; for nuclear weapons the condition is more severe.

Answer 3

Yes, plutonium is reusable. The nuclear fuel during burnup produces plutonium. This plutonium in the spent fuel is got out and mixed with uranium in what is called MOX fuel to be used again in the reactor.