Early heart pacemakers used Pu as the power source, and after 30 years some were still running well. 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. The United States wants to dismantle older warheads so that it can substitute some of them with newer, more lethal weapons. Russia, too, is building new, dangerous weapons. The United States has a vast amount of deadly plutonium, which terrorists would love to get their hands on. Under another agreement, Washington and Moscow each are required to render unusable for weapons 34 metric tons of plutonium.
The purpose is twofold: keep the material out of the hands of bad guys, and eliminate the possibility of the two countries themselves using it again for weapons. An Energy Department website says the two countries combined have 68 metric tons designated for destruction - enough to make 17, nuclear weapons. But the United States has no permanent plan for what to do with its share. Plutonium must be made permanently inaccessible because it has a radioactive half-life of 24, years.
Graphic: Burying the problem - tmsnrt. Edwin Lyman, a physicist at the Union of Concerned Scientists, a science advocacy group based in Washington, says solving the problem of plutonium storage is urgent. In an increasingly unstable world, with terrorism, heightened international tensions and non-nuclear countries coveting the bomb, he says, the risk is that this metal of mass annihilation will be used again.
Washington has not even begun to take the steps needed to acquire additional space for burying plutonium more than 2, feet below ground - the depth considered safe. Savannah River used to house a reactor. Local opponents of the storage, such as Tom Clements, director of SRS Watch, contend the facility was never built for holding plutonium and say there is a risk of leakage and accidents in which large amounts of radioactivity are released.
The Energy Department has a small experimental storage site underground in New Mexico. Environmental groups there have strongly opposed expansion. Under an agreement with Russia, the United States was to convert 34 metric tons of plutonium into fuel for civilian reactors that generate electricity.
But the U. The alternative method is known as dilute-and-dispose. It involves blending plutonium with an inert material and storing it in casks. The casks, however, are projected to last only 50 years before beginning to leak, and so would need to be buried permanently deep underground. President Donald Trump has sided with the Energy Department in wanting to kill the MOX project because of the extreme cost overruns and delays. The Energy Department, beginning in the Obama administration, favored closing down the MOX project for the same reason, but Congress overruled it.
The federal budget adopted in February, however, specifies a means for ending the project, if a study shows that dilute-and-dispose would be at least 50 percent cheaper than making MOX. The later development of fusion boosted weapons in the mid s eliminated it entirely since the fusion boosting effect ensures efficient weapons, even with low initial fission yields.
Plutonium can be obtained from special purpose plutonium production reactors, or as a by-product of commercial power or research reactors. At left is the loading face of the world's first plutonium production reactor, the B-Reactor located at Hanford Washington.
Uranium fuel rods were inserted in the holes for irradiation. Essentially all of the plutonium currently in weapons throughout the world was produced in special purpose plutonium production reactors. Initially each of the five declared nuclear powers began producing plutonium for weapons on a large scale many years before they developed significant numbers of commercial power reactors. Special purpose reactors were required for weapons production because there was no other sources of plutonium available.
These special purpose reactors produce "weapon grade" plutonium, as opposed to grades with higher Pu concentrations, for two reasons: Economics: the only reason the reactor exists is to produce plutonium. Burning plutonium up in fission, or transmuting it to less fissile Pu reduces output and increases cost up to a point, this must be balanced against the cost of processing fuel with low plutonium concentrations.
Handling problems: although neutron emissions do not create serious problems in weapon design, it can produce problems with weapons manufacture and handling. Neutron emissions create occupational exposures to plutonium for those assembling weapons, or handling weapons already assembled. In fact weapons that are kept in close proximity to people like the W may even require special "supergrade" low neutron emission plutonium for this reason.
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