Weapon-grade and civilian plutonium:
The plutonium used in atomic bombs is much richer in the 239 isotope than the plutonium produced by civilian reactors such as the Pressurized Water Reactors (PWRs). Military plutonium contains 93% of 239, while civilian plutonium has 40% of other isotopes. Civilian plutonium also contains some 20% of plutonium, which would make any bomb produced with it unstable and ineffective.