Critically damaged reactors at the Fukushima nuclear plant are still leaking radioactive pollution into the air, and probably into the soil and sea, say experts.Radioactivity levels at the Fukushima plant are very high due to gaseous discharges and leakage from inside the some of the reactor vessels.Tests have shown "a very high concentration -- equivalent to a dose of 1,000 millisieverts (mSv) per hour -- in reactor 2, and 750 mSv in reactor 3," France's Nuclear Safety Authority (ASN) said.
"Someone who stands next to such water will, within 15 minutes, absorb the maximum dose a nuclear facility worker in Japan is allowed to take in during an entire year," or 250 mSv, said Thierry Charles, head of France's Institute for Radiological Protection and Nuclear Safety (IRSN).
Even the 250 mSv limit -- set at the outset of the Fukushimia crisis -- is two-and-a-half times more than what had been the long-standing ceiling.
The plant's operator, Tokyo Electric Power Co. (TEPCO), acknowledged Monday for the first time that highly radioactive water has leaked from the buildings housing both of these reactors, and has already reached the Pacific Ocean.
Concentrations of iodine 1,000 to 2,000 times above normal -- but still below the danger threshold, according to experts -- has been detected in adjacent coastal waters.
Iodine 131 is relatively short-lived, decreasing in radioactivity by half every eight days.
By contrast, cesium 137 -- with a so-called "half-life" of 30 years rather than eight-days -- is more likely to concentrate in sediment below shallow waters.
Both elements have spread through the air "well beyond" the 30-kilometre exclusion zone around Japan's Fukushima nuclear plant, though not in concentrations likely to be directly hazardous to human health, the ASN said Monday.
Slightly radioactive plumes carried by winds across the Pacific and to Europe are without health consequences, experts say.
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