What kind of plutonium is used in reactors

Plutonium belongs to the class of elements called transuranic elements whose atomic number is higher than 92, the atomic number of uranium. Essentially all transuranic materials in existence are manmade. The atomic number of plutonium is Plutonium has 15 isotopes with mass numbers ranging from to Isotopes of the same element have the same number of protons in their nuclei but differ by the number of neutrons.

Since the chemical characteristics of an element are governed by the number of protons in the nucleus, which equals the number of electrons when the atom is electrically neutral the usual elemental form at room temperature , all isotopes have nearly the same chemical characteristics.

This means that in most cases it is very difficult to separate isotopes from each other by chemical techniques. Only two plutonium isotopes have commercial and military applications. Plutonium, which is made in nuclear reactors from neptunium, is used to make compact thermoelectric generators; plutonium is used for nuclear weapons and for energy; plutonium, although fissile, see next paragraph is impractical both as a nuclear fuel and a material for nuclear warheads. Some of the reasons are far higher cost , shorter half-life, and higher radioactivity than plutonium Isotopes of plutonium with mass numbers through are made along with plutonium in nuclear reactors, but they are contaminants with no commercial applications.

In this fact sheet we focus on civilian and military plutonium which are interchangeable in practice—see Table 5 , which consist mainly of plutonium mixed with varying amounts of other isotopes, notably plutonium, , and Plutonium and plutonium are fissile materials. This means that they can be split by both slow ideally zero-energy and fast neutrons into two new nuclei with the concomitant release of energy and more neutrons. Each fission of plutonium resulting from a slow neutron absorption results in the production of a little more than two neutrons on the average.

If at least one of these neutrons, on average, splits another plutonium nucleus, a sustained chain reaction is achieved. The even isotopes, plutonium, , and are not fissile but yet are fissionable—that is, they can only be split by high energy neutrons. Generally, fissionable but non-fissile isotopes cannot sustain chain reactions; plutonium is an exception to that rule.

The minimum amount of material necessary to sustain a chain reaction is called the critical mass. A supercritical mass is bigger than a critical mass, and is capable of achieving a growing chain reaction where the amount of energy released increases with time.

The amount of material necessary to achieve a critical mass depends on the geometry and the density of the material, among other factors.

The critical mass of a bare sphere of plutonium metal is about 10 kilograms. It can be considerably lowered in various ways. The amount of plutonium used in fission weapons is in the 3 to 5 kilograms range. According to a recent Natural Resources Defense Council report 1 , nuclear weapons with a destructive power of 1 kiloton can be built with as little as 1 kilogram of weapon grade plutonium 2.

The smallest theoretical critical mass of plutonium is only a few hundred grams. In contrast to nuclear weapons, nuclear reactors are designed to release energy in a sustained fashion over a long period of time. Over the past few years, the dismantlement of excess nuclear warheads has left the United States and Russia with large stocks of plutonium and highly enriched uranium HEU.

These surpluses have re-ignited the debates around the world about the use of plutonium as an energy source and provided new arguments for continued assistance to on-going plutonium projects.

This article reviews the basic facts regarding plutonium use and provides some cost and technical analysis of the issue. All figures are rounded either to one significant figure or to the nearest 5 metric tons.

The total is not rounded further. Separated commercial plutonium is owned by the only countries that are currently reprocessing: France, Britain, Japan, Russian, India.

In addition, countries that have no current reprocessing have contracts for reprocessing with France and Britain, and also own substantial commercial plutonium stocks. The United States also has a relatively small stock of commercial plutonium from its West Valley reprocessing plant in New York, which was shut down in It takes about 10 kilograms of nearly pure Pu to make a bomb though the Nagasaki bomb in used less.

Producing this requires 30 megawatt-years of reactor operation, with frequent fuel changes and reprocessing of the 'hot' fuel.

Allowing the fuel to stay longer in the reactor increases the concentration of the higher isotopes of plutonium, in particular the Pu isotope, as can be seen in the Table above. For weapons use, Pu is considered a serious contaminant, due to higher neutron emission and higher heat production. It is not feasible to separate Pu from Pu The operational requirements of power reactors and plutonium production reactors are quite different, and so therefore is their design. An explosive device could be made from plutonium extracted from low burn-up reactor fuel i.

Typical 'reactor-grade' plutonium recovered from reprocessing used power reactor fuel has about one-third non-fissile isotopes mainly Pu d. In the UK, the Magnox reactors were designed for the dual use of generating commercial electricity as well as being able to produce plutonium for the country's defence programme.

A report released by the UK's Ministry of Defence MoD says that both the Calder Hall and the Chapelcross power stations, which started up in and respectively, were operated on this basis 3.

The government confirmed in April that production of plutonium for defence purposes had ceased in the s at these two stations, which are both now permanently shutdown. The other UK Magnox reactors were civil stations subject to full international safeguards. International safeguards arrangements applied to traded uranium extend to the plutonium arising from it, ensuring constant audits even of reactor-grade material. This addresses uncertainty as to the weapons proliferation potential of reactor-grade plutonium.

The 'direct use' definition applies also to plutonium which has been incorporated into commercial MOX fuel, which as such certainly could not be made to explode.

As can be discerned from the attributes of each, it is the first which produces weapons-usable material. Total world generation of reactor-grade plutonium in spent fuel is some 70 tonnes per year. About one-third of the separated Pu has been used in mixed oxide MOX fuel. The UK's plutonium stockpile is tonnes of separated civil plutonium from historic and current operations and foreign swaps. At the end of France had about 75 tonnes of separated civil plutonium stored domestically.

Some Japan at the end of had about 9 tonnes of separated civil plutonium stored domestically, plus The USA had no reactor-grade plutonium separated, but had at the end of about 45 tonnes of weapons-grade material destined for MOX. China at the end of had about 41 tonnes of separated civil plutonium.

Worldwide stocks of civil plutonium are estimated as around tonnes. In June , the USA and Russia agreed to dispose of 34 tonnes each of weapons-grade plutonium by Generation IV reactor designs are under development through an international project. Four of the six designs are fast neutron reactors and will thus utilize plutonium in some way. Despite being toxic both chemically and because of its ionising radiation, plutonium is far from being "the most toxic substance on Earth" or so hazardous that "a speck can kill".

On both counts there are substances in daily use that, per unit of mass, have equal or greater chemical toxicity arsenic, cyanide, caffeine and radiotoxicity smoke detectors. There are three principal routes by which plutonium can get into human beings who might be exposed to it:. Ingestion is not a significant hazard, because plutonium passing through the gastro-intestinal tract is poorly absorbed and is expelled from the body before it can do harm.

Contamination of wounds has rarely occurred although thousands of people have worked with plutonium. Their health has been protected by the use of remote handling, protective clothing and extensive health monitoring procedures.

The main threat to humans comes from inhalation. While it is very difficult to create airborne dispersion of a heavy metal like plutonium, certain forms, including the insoluble plutonium oxide, at a particle size less than 10 microns 0. If inhaled, much of the material is immediately exhaled or is expelled by mucous flow from the bronchial system into the gastro-intestinal tract, as with any particulate matter.

Some however will be trapped and readily transferred, first to the blood or lymph system and later to other parts of the body, notably the liver and bones.

It is here that the deposited plutonium's alpha radiation may eventually cause cancer. However, the hazard from Pu is similar to that from any other alpha-emitting radionuclides which might be inhaled. It is less hazardous than those which are short-lived and hence more radioactive, such as radon daughters, the decay products of radon gas, which albeit in low concentrations are naturally common and widespread in the environment.

In the s some 26 workers at US nuclear weapons facilities became contaminated with plutonium. Intensive health checks of these people have revealed no serious consequence and no fatalities that could be attributed to the exposure. In the s plutonium was injected into and inhaled by some volunteers, without adverse effects.

In the s Queen Elizabeth II was visiting Harwell and was handed a lump of plutonium presumably Pu in a plastic bag and invited to feel how warm it was. Plutonium is one among many toxic materials that have to be handled with great care to minimize the associated but well understood risks.