Plutonium detected outside N-plant site

10/02/2011 18:56

Yomiuri: Plutonium believed to have been released from the crippled Fukushima No. 1 nuclear power plant after the March 11 earthquake has been detected outside the power plant site for the first time, it has been learned.

One of the spots found contaminated with the hazardous substance is 45 kilometers from the plant.

A map released by the Education, Culture, Sports, Science and Technology Ministry on Friday shows plutonium was found in soil samples taken from a total of six locations in Futabamachi, Namiemachi and Iitatemura, Fukushima Prefecture.

The map is based on a survey conducted by the ministry to determine how much soil around the power plant contains plutonium and strontium, which is also a hazardous radioactive substance.

However, a ministry official said because amounts of both substances were very small, decontamination efforts should focus on radioactive cesium.

The survey was conducted in June and July by sampling soil at 100 locations around the plant. The ministry compared the data obtained from the survey with data obtained in surveys conducted from fiscal 1999 to fiscal 2008 to measure the residual effects of radioactive fallout on Japan from nuclear atmospheric tests conducted during the Cold War.

The six spots where plutonium was detected are all in the no-entry zone, within a 20-kilometer radius of the plant, or in the expanded evacuation zone outside the no-entry zone, which may be exposed to more than 20 millisieverts of radioactive substances within a year from the accident.

Four becquerels per square meter of plutonium-238 was detected at one site in Namiemachi in the latest survey. This is about half of the maximum quantity of 8 becquerels detected in the 1999-2008 surveys.

A preliminary ministry calculation shows that the level of plutonium contamination in Namiemachi will remain at 0.027 millisieverts for about 50 years. The other five spots were contaminated with 0.55 to 2.3 becquerels of plutonium.

The farthest spot from the plant where plutonium was detected was in Iitatemura, about 45 kilometers from the plant.

Meanwhile, strontium-89 and strontium-90, both believed to have been released from the power plant, were detected at 45 spots.

The maximum quantity of strontium-90, whose half-life of about 29 years is much longer than the approximately 50-day half-life of strontium-89, was 5,700 becquerels per square meter detected in Futabamachi. This is six times that of the maximum quantity of 950 becquerels found before the Fukushima plant accident.

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