Wednesday, Oct. 19, 2011

By MINORU MATSUTANI

High levels of radiation have been found at a public elementary school in Adachi Ward, Tokyo, near the end of a downspout for rainwater from the roof of a swimming pool's equipment room, a ward official said Tuesday.

The radiation reading — 3.99 microsieverts per hour — was detected 5 cm above the ground near the drainpipe at Higashi Fuchie Elementary School when the ward checked Monday, official Hiroyuki Komatsu said. That compares with the 0.25-microsievert threshold the ward set, above which it would remove soil or take other decontamination action, he said.

The end of the downspout stops dozens of centimeters from the ground, and thus rainwater falls to the soil, not to a sewer, he said.

Adachi Ward is in eastern Tokyo, where radiation levels are higher than other southern Kanto areas apparently due to March rains. High-radiation mini hot spots may also be found in other parts of Kanto, including Kashiwa, Chiba Prefecture.

"There will be hot spots we have yet to identify. We will try to find them and take proper measures," Komatsu said.

The reading of 3.99 microsieverts per hour translates into 21 millisieverts a year, higher than the government limit of 20 millisieverts a year. The ward's standard, 0.25 microsieverts, is equivalent to 1 millisievert a year.

The ward will remove at least 5 cm of soil at the hot spot and bury it on the school premises in a deep hole, Komatsu said.

The ward will also check other areas at Higashi Fuchie Elementary School and take similar action if other hot spots turn up, he said.

The ward received reports Monday from residents that five locations, including the downspout at the school, recorded high radiation levels. All five places are near the end of drainpipes. The ward checked the sites and four other places and found readings of 0.66, 0.95, 0.43 and 0.68 microsieverts per hour 5 cm above the ground.

From June to August, the ward checked radiation levels at 790 locations, the water in 122 outdoor pools and sand of 593 sandboxes. Those sites are mainly at schools and parks.

The per hour to per year sievert conversion is calculated under the assumption that someone stays outside eight hours and indoors 16 hours a day, and the indoor exposure is 0.4 times that of being outdoors.

We welcome your opinions. Click to send a message to the editor.