Plutonium is simply a material that is very like uranium, being produced from uranium. It's produced by the absorption of a neutron in uranium, and you get this new metal which has been called plutonium. Its properties are not dissimilar to one of the isotopes of one of the kinds of uranium that exist in the earth's crust. It is fissionable, like the fissionable isotope of uranium. That is to say, you could make a reactor out of it, out of plutonium.