Plutonium facts for kids

A button of plutonium above a calcium chloride salt cake.

Plutonium is a chemical element with the symbol Pu and atomic number 94. It is a very radioactive metal. Plutonium is famous for being used in most nuclear weapons.

Plutonium has different forms called isotopes. The most important one is plutonium-239 (²³⁹Pu). It takes 24,110 years for half of a sample of plutonium-239 to break down. This time is called its half-life. This isotope can be made from natural uranium and can be split apart (it's fissile).

Another isotope, plutonium-244 (²⁴⁴Pu), has an even longer half-life, about 80 million years. Because it lasts so long, tiny amounts of plutonium-244 can be found naturally. Plutonium-238 is used in special power sources called Radioisotope Thermoelectric Generators.

Like other transuranium elements, plutonium can react with many things. These include water, oxygen, and carbon. When it's in moist air, it can form new substances called oxides and hydrides. This makes the plutonium expand a lot, up to 70%! Pieces can then flake off and even catch fire at room temperature. Plutonium is also toxic, meaning it can be harmful. Because it reacts easily and is toxic, handling plutonium is difficult.

Uses of Plutonium

For Explosives

The atomic bomb dropped on Nagasaki, Japan in 1945 had a plutonium core.

Plutonium-239 is a key part of nuclear weapons. It's easy to split and readily available. To make a bomb work, a certain amount of plutonium is needed. This is called the critical mass. If the plutonium core is surrounded by a dense material, it helps reflect tiny particles called neutrons back into the plutonium. This means less plutonium is needed for the bomb to work. For example, the amount needed can drop from 16 kg to about 10 kg. This is a sphere about 10 cm across. This is much less than the amount needed for uranium-235.

The "Fat Man" atomic bomb, dropped on Nagasaki in 1945, used plutonium. It used explosives to squeeze the plutonium, making it much denser. This, along with a special neutron source, made the bomb more efficient. Only 6.2 kg of plutonium was needed to create an explosion as powerful as 20,000 tons of TNT. With very advanced designs, even less plutonium, maybe as little as 4 kg, could be used for an atomic bomb.

Mixed Oxide Fuel

Spent nuclear fuel from nuclear power plants still contains plutonium. This plutonium is a mix of different isotopes, like plutonium-242, 240, 239, and 238. This mix isn't good for making efficient nuclear weapons. However, it can be used once as a special fuel called MOX fuel.

MOX fuel helps use up plutonium and other transuranic elements. This also helps reduce the danger of nuclear waste that lasts a very long time. This is why nuclear engineers often want to build special reactors called fast neutron reactors.

The most common way to get plutonium and uranium from used nuclear fuel is a process called PUREX. These recovered materials can then be made into MOX fuel. Even plutonium used in weapons can be added to this fuel mix. MOX fuel is used in many nuclear reactors, especially in Europe.

In 2000, the United States and Russia agreed to get rid of 34 tons of weapons-grade plutonium each. The U.S. planned to turn its plutonium into MOX fuel to be used in power plants. This helps turn dangerous weapons material into useful energy.

MOX fuel helps burn up more of the fuel in a reactor. After about three years, used fuel rods are reprocessed to remove waste. Any new uranium or plutonium made during that time stays, and the rod can be used again. Plutonium from used reactor fuel is not easy to use for weapons. This is because it has too much of the non-fissile plutonium-240 and plutonium-242. It's very hard to separate these isotopes.

The IAEA considers all plutonium as "direct-use" material. This means it could be used to make parts for nuclear explosives without needing to be changed much.

Power and Heat Source

A glowing cylinder of ²³⁸PuO₂

The ²³⁸PuO₂ radioisotope thermoelectric generator of the Curiosity rover

Plutonium-238 has a half-life of about 87.74 years. It gives off a lot of heat energy but very little harmful radiation that can pass through things. Because it mostly gives off alpha particles, which don't travel far, it needs very little shielding. Even a sheet of paper can block the alpha particles from plutonium-238. One kilogram of this isotope can create about 570 watts of heat.

These features make plutonium-238 perfect for powering devices that need to work for a very long time without being fixed. It is used in radioisotope thermoelectric generators (RTGs) and radioisotope heater units. These are found in space probes like Cassini, Voyager, Galileo, and New Horizons. It also powers the Curiosity on Mars.

The two Voyager spacecraft, launched in 1977, each had a 500-watt plutonium power source. More than 30 years later, these sources still produce about 300 watts. This allows the spacecraft to keep working. Earlier versions of this technology powered equipment left on the Moon by the Apollo missions, starting with Apollo 12 in 1969.

Plutonium-238 has also been used to power artificial pacemakers for the heart. This helped reduce the need for repeated surgeries. Today, most pacemakers use lithium batteries. However, as of 2003, there were still some plutonium-powered pacemakers working inside patients. By 2007, that number had dropped to just nine. Plutonium-238 mixed with beryllium is also used to create neutrons for scientific research.

Images for kids

• 

  A ring of very pure plutonium, enough for one bomb core. It weighs 5.3 kg and is about 11 cm wide. Its shape helps keep it safe from accidental nuclear reactions.

• 

  Different colors of plutonium depending on its chemical state in a liquid.

• 

  Plutonium can glow like a hot coal under certain conditions because it can catch fire easily.

• 

  A tiny amount (twenty micrograms) of pure plutonium hydroxide.

• 

  A sample of plutonium metal on display at the Questacon museum.

• 

  Glenn T. Seaborg and his team were the first to make plutonium in a lab.

• 

  The dwarf planet Pluto, which the element plutonium is named after.

• 

  The Hanford B Reactor being built. This was the first reactor made to produce plutonium.

• 

  A sphere of plutonium surrounded by blocks that reflect neutrons. This shows an experiment from 1945.

See also

In Spanish: Plutonio para niños