NRC Science 101: What is Plutonium? UPDATED

Maureen Conley
Public Affairs Officer

science_101_squeakychalkIn earlier Science 101 posts, we talked about what makes up atoms, chemicals and matter. In this post, we will look at a specific chemical element — plutonium.

Plutonium is a radioactive, metallic element with the atomic number 94. It was discovered in 1940 by scientists studying the process of splitting atoms. Plutonium is created in a nuclear reactor when uranium atoms, specifically uranium-238, absorb neutrons. Nearly all plutonium is man-made.

Plutonium predominantly emits alpha particles—a type of radiation that does not penetrate and has a short range. It also emits neutrons, beta particles and gamma rays. It is considered toxic, in part, because if it were to be inhaled it could deposit in lungs and eventually cause damage to the tissue.

Plutonium has five “common” isotopes, Pu-238, Pu-239, Pu-240, Pu-241, and Pu-242. All of the more common isotopes of plutonium are “fissionable”—which means the atom’s nucleus can easily split apart if it is struck by a neutron.

The various isotopes of plutonium have been used in a number of applications. Plutonium-239 contains the highest quantities of fissile material, and is notably one of the primary fuels used in nuclear weapons. Plutonium-238 has more benign applications and has been used to power batteries for some heart pacemakers, as well as provide a long-lived heat source to power NASA space missions. Like uranium, plutonium can also be used to fuel nuclear power plants, as is done in a few countries. Currently, the U.S. does not use plutonium fuel in its power reactors.

plutoniumNuclear reactors that produce commercial power in the United States today create plutonium through the irradiation of uranium fuel. Some of the plutonium itself fissions—part of the chain reaction of splitting atoms that is the basis of nuclear power. Any plutonium that does not fission stays in the spent fuel. Spent nuclear fuel from U.S. reactors contains about one percent plutonium by weight.

The different isotopes have different “half-lives” – the time it takes for one-half of a radioactive substance to decay. Pu-239 has a half-life of 24,100 years and Pu-241’s half-life is 14.4 years. Substances with shorter half-lives decay more quickly than those with longer half-lives, so they emit more energetic radioactivity.

Like any radioactive isotopes, plutonium isotopes transform when they decay. They might become different plutonium isotopes or different elements, such as uranium or neptunium. Many of the “daughter products” of plutonium isotopes are themselves radioactive.

Many metric tons of plutonium are currently contained in spent nuclear fuel around the world. To be usable, plutonium needs to be separated from the other products in spent fuel through a method called reprocessing. Reprocessing separates plutonium from uranium and fission products through chemical means. Once separated, plutonium oxide can be used as fuel for nuclear power reactors by mixing it with uranium oxide to produce mixed oxide or MOX fuel. The U.S. government has historically discouraged the use of this technology for national security and environmental reasons.

The NRC is currently overseeing construction of a facility in South Carolina to make MOX fuel using plutonium removed from U.S. nuclear weapons declared excess to military needs, as part of a Department of Energy program to convert it into a proliferation-resistant form that would be difficult to convert again for use in nuclear weapons.

Author: Moderator

Public Affairs Officer for the U.S. Nuclear Regulatory Commission

16 thoughts on “NRC Science 101: What is Plutonium? UPDATED”

  1. The NRC is ignoring some construction problems that the NNSA has acknowledged at the MOX plant – incorrect installation of piping and cable trays. There are indications that CB&I AREVA MOX Services employees signed off on this work even though it was improperly done, so the question of fraud hangs in the air. Claiming that the problems are not “safety related,” the NRC is refusing to inspect or investigate. So, just who is properly monitoring constriction of the $12.7 MOX boondoggle? With only one – yes, one – resident NRC inspector at the MOX site don’t count on the NRC to be on top of this debacle of a project.

    Tom Clements, Savannah River Site Watch, Columbia, SC

  2. and, unfortunately we don’t know how to manage it yet. #safetyfirst, #CleanUpAfterYourself, #RealNuclearWasteconfidence before we can continue with uncontainment of the waste we already have.

  3. Quote: “Currently, the U.S. does not use plutonium fuel in its power reactors.” A true statement, tell us why please. Could it be to prevent nuclear weapons proliferation because Plutonium MOX Fuel may be utilized for nuclear weapons?

    After all the postings pointing out the error of your ways – are you now saying that Plutonium MOX fuel can not be utilized for nuclear weapons production? Or, is there a special NRC word definition for “easily?” I guess it depends on your meaning of “is?”

  4. Where is the “revised blog” and the comments that were posted in response to the original blog? They appear to have been taken down. Why?

  5. The purpose of blog was to provide a basic discussion of the various isotopes of plutonium and the differences between “reactor grade” and “weapons grade” plutonium. Additionally, the Department of Energy is responsible for plutonium disposition to meet the U.S.-Russia Plutonium Management and Disposition Agreement, which entered into force on July 13, 2011, and committed each country to dispose of at least 34 metric tons of weapon-grade plutonium withdrawn from their respective nuclear weapon programs. The U.S. NRC was granted regulatory and licensing authority over the Mox Fuel Fabrication Facility under the Strom Thurmond National Defense Authorization Act for Fiscal Year 1999. Comments related to plutonium disposition strategies should be addressed to DOE.

    For clarity, the blog has been revised.

    Maureen Conley

  6. The statement you are referring to was inadvertently incorrectly worded. What was meant was when the “weapons grade” plutonium (as MOX fuel) is irradiated in a commercial nuclear reactor, the plutonium is converted into a proliferation-resistant form that can never again be readily used in nuclear weapons. The blog language has been revised.
    Further information regarding the plutonium disposition program can be found at DOE’s website:

    Maureen Conley

  7. The claim in the last sentence that reactor-grade plutonium is not weapons-usable is incorrect and runs counter to the U.S. Government policy on the matter. This incorrect statement is a striking departure from both science and policy and must be corrected.

  8. MOX fuel – the fuel that will cost American Tax Payers billions upon billions of dollars in continued debt while facilitating nuclear proliferation. The fuel that will make the French owned Areva say “merci beaucoup” for your tax dollars.

    Don’t be misled by NRC Trojans bearing gifts and attempting to downplay one of the most extremely dangerous substances known to human kind that has the potential to kill millions..

    Beware of False Claims About Reactor Grade Fuel, Nuclear Control Institute – “”Reactor-Grade” Plutonium Can Be Used to Make Bombs…it’s a dangerous myth that reactor-grade plutonium cannot be used to make workable weapons…The ability to construct a weapon from reactor-grade plutonium was demonstrated decades ago. It is dangerous even to consider it an open question. Hans Blix, director-general of the IAEA, informed our Institute that there is “no debate” on this point in the Safeguards Department of the IAEA, and that the agency considers virtually all isotopes of plutonium, including high burn-up reactor-grade plutonium, to be usable in nuclear weapons.”

  9. There are serious technical errors and omissions in this blog that deserve to be corrected. “Plutonium (Pu) emits alpha particles—a type of radiation that does not penetrate and has a short range.” Pu also emits neutrons, gamma and beta particles, and x-rays. Plutonium and its compounds are toxic and accumulate in bone marrow. The best scientific evidence is that exposure to Pu increases the risk of cancer. Other negative attributes of Pu as a nuclear fuel are the following: Pu oxide forms on the surface of plutonium exposed to air; the oxide is pyrophoric, so greater use of plutonium in the nuclear fuel cycle poses an added fire risk; Pu has a low melting point, and unlike most other substances, increases in density as it melts (+ 2.5%) , making the material more not less reactive in a nuclear accident scenario; Pu is more susceptible than enriched uranium to criticality accidents, as the amount of plutonium required for a critical mass is about one-third that of uranium-235.

    Here is another problem paragraph:
    “A commercial power reactor creates many isotopes of plutonium, including Pu-239, Pu-240, Pu-241, and Pu-242. This is known as “reactor-grade” plutonium. In contrast, “weapons-grade” plutonium is almost pure Pu-239 (more than 90 percent). This form requires a specially designed and operated reactor. Plutonium production reactors operated by the U.S. government during the Cold War have all shut down. The NRC is reviewing an application for a facility in South Carolina that could mix plutonium removed from U.S. nuclear weapons with uranium to create mixed oxide (MOX) fuel. By irradiating the MOX fuel in a commercial power reactor, the weapons-grade plutonium becomes reactor-grade and no longer useful for weapons.”

    In reality, the isotopic mixture of plutonium produced, and its relative attractiveness for use in weapons, is a function of the fuel’s residence time in a reactor, not the type of reactor used. Any “commercial” light water reactor anywhere in the world can be operated on a (deliberately non-economic) cycle to produce “weapons-grade” plutonium, and indeed the Atomic Energy Act (AEA) gives the President emergency standby authority to produce plutonium for the nuclear weapons program in US civil power reactors. Unlike low-enriched uranium either before or after its use in a reactor, almost all isotopic compositions of plutonium will support an explosive growth of the fission chain reaction with prompt neutrons alone. The only isotopic mix of plutonium which cannot realistically be used for nuclear weapons is nearly pure Pu-238, which generates so much heat that the weapon would not be stable. (International rules require equal levels of safeguards for all grades of plutonium except plutonium containing more than 80 percent Pu-238, which need not be safeguarded.)

    The fact that the even-numbered isotopes Pu-240 and Pu-242 fission only at higher neutron energies, well above the thermal neutron spectrum used in most civil power reactors, is likely the origin of a mistaken notion, prevalent among supporters of “closing” the civil nuclear fuel cycle, that Pu-240—a supposedly useless “non-fissile” isotope that builds up steadily with fuel exposure in a thermal reactor—can serve to “denature” the explosive properties of the plutonium produced in spent fuel, often referred to as “reactor-grade” plutonium. In reality, for neutron energies above about 0.7 million electron volts (MeV), the fission “cross-section” of Pu-240 is smaller than that of Pu-239, the preferred plutonium isotope for making nuclear explosives, but larger than Uranium-235, the other preferred nuclear weapons material.

    As a consequence, i.e. the “bare critical mass” of Pu-240 – i.e. the minimum amount needed as metal at normal density to support a self-sustaining chain reaction with fast neutrons, before the addition of neutron reflectors and compression by high explosives – is 23 percent less than needed for a bare critical mass of weapon-grade uranium. Hence for all fuel burnup levels and at any time following discharge from a reactor, the critical mass of “reactor-grade plutonium” metal will be intermediate between Pu-239 and Pu-240, with the latter being more reactive than weapons-grade uranium. While nuclear explosives made of reactor-grade plutonium will not provide the same predictability of yield and long-shelf life of weapons fabricated from phase-stabilized “weapon-grade” plutonium metal, these attributes may not matter to terrorists or sub-national organizations bent on quick assembly of a nuclear explosive device.

    Finally, what makes plutonium in irradiated MOX fuel relatively unusable in weapons is not the isotopic “grade” of the plutonium but rather the fact that it is encased as a mixed oxide within sealed zircaloy fuel tubes containing a matrix of uranium, other actinides, and high-emitting fission products that makes the fuel bundles “self-protecting” for a considerable period, thus requiring remote shearing of the fuel elements and aqueous- or electro-chemical separation to extract the plutonium, a complex and costly endeavor. Ironically, however, the MOX fuel facility the NRC contemplates licensing itself relies upon a feedstock stream of 100% plutonium oxide that will support an explosive fast-neutron chain reaction if certain assembly parameters are met. The blog’s implication that licensing this MOX facility would reduce the risk of proliferation is misplaced.

    Christopher Paine, Senior Nuclear Policy Analyst, Natural Resources Defense Council (NRDC)

  10. Well considering that 350 micrograms into the lung is a pretty certain death sentence, then 5 mg per M3 would be massive, further considering the average human breathes 80 M3 per day.

    That would be a massive concentration and extremely dangerous.

    You heard of the Beagle testing in which 255 out of 255 Beagles were killed by inhaled plutonium, usually the lung cancers killed them before the liver cancers did, although the liver cancers were also present, and bone tumors.

    Is this called being “over afraid”?

  11. Its pretty clear that MOX with it’s much higher nuetron density, is more prone to the Borax test type of Moderated Prompt Criticality, a form of runaway nuetrons and thus a form of atomic explosion. The MPC takes near perfect conditions to occur with standard fuel, but will occur a lot more easily with MOX fuel.

    Plus if you have a reactor or equipment pool accident and you are using MOX, then the accident scenario just got 100 times worse because now Plutonium is being released.

    So NO GO on the MOX, Dry Cask and forget the reprocessing, which is 10 times more expensive than dry cask anyway.

  12. West, and more specially USA, is over afraid of Plutonium in every aspects. This is far excessive for simple reasons like these:
    1- A Pu atom-bomb is larger far more difficult to detonate than the “simple” U235 bomb, it requires advanced pyrothechnics a terrorist group cannot develop.
    2- Iran knows it, this is why they strive so much to enrich natural U to 93% with centrifugation, not taking the easy Pu.
    3- Pu is extremely easy to manufacture with only 8000 liters of heavy water and 2tons of natural uranium. Even Saddam Hussein had enough resources to extract such a small amount of uranium, enough oil to distillate water (very expensive, but feasible for a State) then produce 3 bombs per annum with this simple device…
    Concerning its supposed “toxic” aspects and “infinite” radiological life, one shall just consider that it is 180,000 times more radioactive than natural Uranium available eveywhere (some shale rocks in Sweden have 3 pounds of it per cubic meter). Take 3 pounds and devide it by 180,000 and you get the same radioactive flux as 7.5mg of hevillish Plutonium.
    Imaging media reaction if someone detects 5mg of Plutonium per cubic meter in a large field..!! So much that 277 billion of Becquerels.
    A mediatic storm would be immediately triggered.
    This shows how stupid is our mediatic system !

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