Plutonium fuel cycle

About
The plutonium fuel cycle is a nuclear fuel cycle, or a process by which plutonium is converted to energy by nuclear fission. It is contrasted with the uranium fuel cycle or "once through" fuel cycle in that the fuel is fissile plutonium-239 bred from fertile uranium-238 in a light water reactor or a breeder reactor, rather than uranium-235.

Uranium-238 captures a neutron, and quickly undergoes beta decay to become neptunium-239. Neptunium-239 has a half-life of about 2 days, and beta decays into plutonium-239.

Plutonium-239 has a large neutron capture cross section in thermal spectrum, but fissions only about 75% of the time, compared to 85% for uranium-235 and 92% for uranium-233. In the fast spectrum, the capture cross sections are much smaller, but the probability of fission is higher, particularly for plutonium. If a nuclear reactor can efficiently run on plutonium, then spent fuel from light water reactors can be reprocessed into new fuel for nuclear reactors, theoretically burning natural or even depleted uranium efficiently for large amounts of energy.

The plutonium fuel cycle is the most well-understood nuclear fuel cycle next to uranium-235, and is the basis for the fast reactor.

Reference

 * Wikipedia