Following is a factfile on plutonium, which Japan says has been found at very low levels at five locations at the stricken Fukushima nuclear plant:
WHAT IS IT?
Plutonium is a highly radioactive silvery metal that is used in nuclear bombs and nuclear power. It is a heavy and essentially man-made element, derived from the transformation of uranium through fission. Traces of two of its atomic variants, or isotopes, exist naturally.
Advertisement: Story continues below
HISTORY
Plutonium was found by US scientists in 1940. The new element was named after Pluto, the god of the Roman underworld, and assigned the abbreviation of Pu in the periodic table. It is one of the most complex elements, for it is a metal yet does not conduct heat or electricity well. Only a slight rise in temperature makes it switch from solid state similar to cast iron to plastic malleability.
FISSILE MATERIAL
Plutonium's military potential was swiftly recognised. It provided the material for the first nuclear device, detonated at Los Alamos in July 1945, and for the second nuclear bomb, "Fat Man," which was dropped on Nagasaki the following month. The first nuclear bomb, dropped on Hiroshima, used uranium. Not until after World War II were the discoverers of plutonium allowed to publish their findings. Plutonium's very high energy density also brought it into use in civilian nuclear power, especially after the 1970s oil shocks.
ISOTOPES
Plutonium has 15 isotopes. The longest-lived is plutonium 244, which takes 80.8 million years to decay to half its level of radioactivity. The most commonly-used isotopes -- and those found at Fukushima -- are plutonium 238, with a half life of 88 years; plutonium 239, with a half life of 24,000 years; and plutonium 240, with a half life of 6,500 years.
AIRBORNE HAZARD
Plutonium 238, 239 and 240 are highly radioactive but their radiation is in alpha particles, which only travels very short distances and cannot penetrate human skin. Where they are highly dangerous is if they are inhaled. Their radiation causes DNA damage in tissue, which then boosts the risk of cancer. The bone marrow and liver, where plutonium is transported through a blood protein called transferring, are especially vulnerable. Just a dozen milligrams of plutonium are lethal for a human, according to tests on lab animals cited by France's Institute for Radiological Protection and Nuclear Safety (IRSN).
INGESTION PERIL
Other dangers, but for which there is less data, come from exposure to plutonium through ingestion or through an open wound. Plutonium is only eliminated from the body very slowly, though excretion. It takes around 50 years for plutonium to be biologically removed from the skeleton and about 20 years for it be eliminated from the liver, says the IRSN.
PLUTONIUM LEVELS AT FUKUSHIMA
According to plant operator Tokyo Electric Power Company (TEPCO), soil at five sites at the Fukushima plant was found to have plutonium. At least two of these sites had isotopes where there was a "high possibility" of a connection to the accident. But no sample was of a level of contamination that was hazardous for health, it said. France's Nuclear Safety Authority (ASN) described the data as being in the same category as "background levels" that are a legacy of atmospheric nuclear bomb tests. Around four tonnes of plutonium were released into the global environment before atmospheric testing ended.
SOURCE OF FUKUSHIMA PLUTONIUM
This is unclear. Experts at France's Nuclear Safety Authority (ASN) say it could have come from the No. 3 reactor, which uses mixed oxide, or MOX, which comprises plutonium and uranium that has been extracted from spent nuclear fuel and reprocessed. Alternatively, it could have come as a fissile byproduct from burning uranium in the No. 1 and 2 reactors.
No comments:
Post a Comment