Title: Fissile Material Basics - Institute for Energy and Environmental Research
Headings: Fissile Material Basics
Fissile Material Basics
What are fissile materials?
What is plutonium-239?
How is plutonium made?
What is plutonium used for?
Where is plutonium produced?
What is highly enriched uranium?
How is highly enriched uranium made?
What is HEU used for?
Where is HEU produced?

Content: First, in a nuclear reactor, uranium-238 absorbs a neutron. This leads to nuclear reactions which convert it to plutonium. The plutonium ends up in the spent nuclear fuel along with unused uranium and highly radioactive fission products. Essentially all nuclear reactors in the world produce plutonium in this way, but plutonium in spent fuel is not usable for nuclear energy or nuclear weapons. To get plutonium into a usable form, a second key facility, a reprocessing plant, is needed to chemically separate out the plutonium from the other materials in spent fuel. Reprocessing is generally regarded as one of the key links between civilian nuclear power capability and nuclear weapons production capability (the other is uranium enrichment — see below). What is plutonium used for? Once plutonium is separated, it can be processed and fashioned into the fission core of a nuclear weapon, called a “pit”. Nuclear weapons typically require three to five kilograms of plutonium. Plutonium can also be converted into an oxide and mixed with uranium dioxide to form mixed-oxide (MOX) fuel for nuclear reactors.