Plutonium-239 & Nuclear Power
- Sylvia Rose
- Apr 5
- 4 min read
Plutonium-239 is an artificial isotope in nuclear energy and technology. It's not usually found in nature, produced primarily in nuclear reactors through neutron capture.
Specifically, when uranium-238, the most common isotope of uranium, absorbs a neutron, it undergoes a series of radioactive decays. It ultimately transforms into Pu-239.
About Plutonium-239
Plutonium-239 (Pu-239) is first synthesized in 1940. With a half-life of 24,100 years, Pu-239 is stable and long-lasting compared to other isotopes.
The nucleus of plutonium-239 has 93 protons and 146 neutrons. This specific structure causes it to undergo fission when it collides with a neutron.
Splitting of the plutonium atom by the neutron releases a huge amount of energy as heat and radiation. This is because the smaller nuclei have less binding energy than the original, heavier nucleus.
Such properties are foundational to its primary roles in nuclear reactors and weapons. For instance, Pu-239 can sustain a chain reaction, valuable in nuclear technology.
Plutonium-239 is not naturally abundant. Trace quantities of plutonium can form through neutron capture by uranium-238. Most plutonium in the environment comes from nuclear power production and weapons testing.
In neutron capture, uranium-238, the most prevalent uranium isotope, snatches a neutron to form uranium-239. It then beta decays into neptunium-239 before ultimately decaying into plutonium-239.
After its production, plutonium-239 is isolated and chemically purified. Extraction involves multiple chemical reactions to separate plutonium from accompanying elements in the nuclear fuel cycle.
A common method is solvent extraction, using organic solvents to isolate plutonium from other isotopes. Several factors make Pu-239 a particularly potent isotope.
Fissile Material: This is the defining characteristic. Pu-239 is a fissile material, meaning it can sustain a nuclear chain reaction. When struck by a neutron, a Pu-239 nucleus is splits (fission), releasing energy and more neutrons. The neutrons then trigger fission in other Pu-239 atoms.
Half-Life: Pu-239 has a half-life of 24,100 years. This means it takes over 24 millennia for half of a sample of Pu-239 to decay into other elements. This long half-life contributes to the long-term radioactivity of nuclear waste.
Radioactive Decay: Pu-239 decays primarily through alpha emission, releasing an alpha particle (two protons and two neutrons) and transforming into uranium-235. Like Pu-239, U-235 is fissile.
Its configuration of protons and neutrons split in a way allowing it to fire off multiple neutrons in the reaction, rather than absorb the neutron to create a larger isotope. Both Pu-239 and U-235 create chain reactions.
Uses of Plutonium-239
1. Nuclear Weapons
Pu-239 is a core component of many nuclear weapons designs. Its ability to sustain a rapid and powerful chain reaction makes it ideal for creating the explosive force of a nuclear bomb.
Modern nuclear weapons use a combination of Pu-239 and other fissile materials like uranium-235. These help achieve optimal yield and efficiency.
Presence of Pu-239 in spent nuclear fuel raises concerns about nuclear proliferation. It can be extracted and used for weapons development.
Plutonium-239 is especially effective in explosive devices due to its ability to maintain a rapid chain reaction. The first atomic bomb using plutonium-239 is detonated in 1945 during the Trinity Test, a landmark moment.
For military use, weapons-grade plutonium-239 must meet strict criteria. Production and handling of plutonium-239 are regulated by international arms control agreements. Military-grade plutonium must have a purity level of over 90%.
2. Nuclear Power Generation
Pu-239 is used as fuel in some types of nuclear reactors like breeder reactors. These reactors are designed to generate electricity and also produce more fissile material (Pu-239) than they consume.
In conventional nuclear reactors, Pu-239 is created as a byproduct of uranium fission. Reactor-grade plutonium can be used as fuel. It has different handling and processing needs than weapons-grade plutonium.
Mixed Oxide (MOX) fuel, a blend of uranium and plutonium oxides, is increasingly used in nuclear reactors. This recycles plutonium from spent nuclear fuel and reduces the amount of high-level radioactive waste.
Dangers & Concerns
Nuclear Proliferation: Accessibility of Pu-239 in spent nuclear fuel is a major concern for international security, especially in preventing proliferation of nuclear weapons.
Radioactive Waste Management: Pu-239 contributes to the long-term radioactivity of nuclear waste. Due to its long half-life, the waste must be stored safely for tens of thousands of years.
Health Hazards: Pu-239 is highly toxic. Inhalation or ingestion can lead to severe health problems, including cancer.
Criticality Accidents: The concentration of Pu-239 above a certain threshold in the presence of a moderator (like water) can lead to an uncontrolled chain reaction. A criticality accident releases a burst of radiation.
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