PLUTONIUM – the element created on Earth by humans Until 1940, the chemical element plutonium did not exist on Earth. Plutonium (specifically, plutonium-238) was first produced and isolated in 1940. It was produced by deuteron bombardment in a small cyclotron, in USA. In 1941 they discovered that an isotope of the new element (plutonium-239) could undergo nuclear fission in a way that might be useful in an atomic bomb.
The name Plutonium was an interesting choice. It is named after Pluto – ancient Roman god of death. Romans were afraid to say Pluto’s real name because they were afraid he might notice them and they would die.
Plutonium-239 is the isotope most useful for nuclear weapons. Plutonium-239 and 241 are fissile, meaning the nuclei of their atoms can break apart by being bombarded by slow moving thermal neutrons, releasing energy, gamma radiation and more neutrons. These can therefore sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors. It is also a radioactive poison that accumulates in bone marrow. These and other properties make the handling of plutonium dangerous.
Plutonium was produced in the Manhattan Project during World War II, developing first atomic bombs. The first nuclear test, “Trinity” (July 1945), and the second atomic bomb used to destroy a city (Nagasaki, Japan, in August 1945), “Fat Man”, both had cores of plutonium-239.
Spent nuclear fuel from normal light water reactors contains Plutonium, but it is a mixture of Plutonium-242, 240, 239 and 238. The mixture is not sufficiently enriched for efficient nuclear weapons, but can be used once as MOX fuel. This is nuclear reprocessing. Reprocessing—sometimes incorrectly called “recycling”—is simply the separation process.
The separated plutonium may be used in fresh fuel for reactors, called mixed oxide (MOX) fuel. After the second cycle, the Plutonium can only be consumed by fast neutron (fast breeder) reactors. Nuclear reprocessing is expensive, dangerous, and a weapons proliferation risk.
Plutonium is usually discarded, and forms the longest-lived component of nuclear waste.
Both conventional reactors and fast breeders produce large quantities of high-level nuclear wastes that stay dangerous for at least 100,000 years.
Breeder reactors are more dangerous than conventional reactors, because:
(1) they produce more plutonium-239, with half-life of 24,000 years, which can be used to make nuclear weapons;
(2) they use as a coolant liquid sodium, which is a very dangerous metal: e.g. it explodes when it comes into contact with water.
Large stockpiles of weapons-grade plutonium were built up by both the Soviet Union and the United States during the Cold War. The U.S. reactors at Hanford and the Savannah River Site in South Carolina produced 103 tonnes,and an estimated 170 tonnes of military-grade plutonium was produced in Russia.[
Each year about 20 tonnes of the element is still produced as a by-product of the nuclear power industry.As much as 1000 tonnes of plutonium may be in storage with more than 200 tonnes of that either inside or extracted from nuclear weapons.[IPRI estimated the world plutonium stockpile in 2007 as about 500 tons, divided equally between weapon and civilian stocks.
The alpha radiation plutonium emits does not penetrate the skin but can irradiate internal organs when plutonium is inhaled or ingested. The skeleton, where plutonium is absorbed by the bone surface, and the liver, where it collects and becomes concentrated, are at risk.
Toxicity issues aside, care must be taken to avoid the accumulation of amounts of plutonium which approach critical mass, particularly because plutonium’s critical mass is only a third of that of uranium-235. A critical mass of plutonium emits lethal amounts of neutrons and gamma rays.A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The nuclear chain reaction releases several million times more energy per reaction than any chemical reaction.
Criticality accidents have occurred in the past, some of them with lethal consequences.
During and after the end of World War II, scientists working on the Manhattan Project and other nuclear weapons research projects conducted studies of the effects of plutonium on laboratory animals and human subjects. Animal studies found that a few milligrams of plutonium per kilogram of tissue is a lethal dose.
In the case of human subjects, this involved injecting solutions containing (typically) five micrograms of plutonium into hospital patients thought to be either terminally ill, or to have a life expectancy of less than ten years either due to age or chronic disease condition. This was reduced to one microgram in July 1945 after animal studies found that the way plutonium distributed itself in bones was more dangerous than radium.
Eighteen human test subjects were injected with plutonium without informed consent. The episode is now considered to be a serious breach of medical ethics and of the Hippocratic Oath.
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