Small amounts of plutonium have been detected inside the Fukushima No. 1 nuclear power plant, its operator, Tokyo Electric Power Co., revealed March 28.
The plutonium was found in soil samples taken near the reactors on March 21 and March 22. TEPCO said tests to determine whether plutonium was present had taken longer than those for other radioactive substances.
The plutonium is believed to have leaked from damaged fuel rods in one of the reactors, but the utility insisted that its “concentration level does not pose a threat to health.”
The industry ministry’s Nuclear and Industrial Safety Agency also said the levels were too small to be dangerous to health.
Plutonium-238, plutonium-239 and plutonium-240 were found in samples taken at two locations about 500 meters from outlets from the No. 1 and No. 2 reactors. TEPCO took soil samples at five locations in the plant.
The largest amount of radioactivity detected was a combined 0.8 becquerels per 1 kilogram of soil.
Experts said it would be difficult to determine which reactor leaked the plutonium. A mixture of uranium and plutonium, known as MOX fuel, has been used at the No. 3 reactor since last year, but plutonium is also produced by reactors using conventional uranium fuel rods.
Plutonium is rare in the natural environment. A tiny amount of plutonium still registers in Japan from nuclear testing by the nuclear powers between the 1950s and 1980s that spread radioactive material worldwide.
The concentration level of plutonium detected inside the nuclear plant is similar to the amount in Japan’s natural environment attributed to those nuclear tests.
Nuclear experts said the detection of plutonium inside the damaged plant was not surprising. Radioactive iodine and cesium are already known to have been released into the atmosphere during the current crisis.
Plutonium can build up in the liver and bones if it is taken into the body, raising the risk of internal exposure and other hazards. It is not easily absorbed by the digestive tract.
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