New equipment to better survey seabed cesium

September 11, 2012

New device developed for seabed cesium surveys

http://www.yomiuri.co.jp/dy/national/T120910003618.htm

Jiji Press

A research team said it has developed equipment that will drastically change the way surveys of radioactive cesium deposits on the seabed are carried out.

Undersea cesium surveys have become necessary due to last year's crisis at Tokyo Electric Power Co.'s Fukushima No. 1 nuclear power plant, which experienced three reactor meltdowns.

So far, such surveys have been conducted only at chosen points separated by a few kilometers, the team said Thursday, which includes the University of Tokyo's Institute of Industrial Science and the National Maritime Research Institute.

But the new equipment, which can be towed by boat, will increase the overall area that can be surveyed, according to the team, whose members include University of Tokyo Prof. Tamaki Ura and Thornton Blair, an associate professor.

The equipment consists of radiation-detecting and recording devices packed into a container that can withstand pressure at a maximum depth of 500 meters below the surface.

The container is put in an 8-meter weighted rubber tube that can be towed by a vessel.

The equipment estimates cesium densities on the seabed based on the radiation levels it detects on a second-to-second basis, enabling continuous surveys along the boat's course.

In August, the team carried out experiments in waters off Iwaki, Fukushima Prefecture, the host prefecture of the crippled nuclear plant, and Kita-Ibaraki, Ibaraki Prefecture.

The equipment provided cesium density readings in line with the results of analyses of seabed soil samples collected during the experiments.

The team found that cesium levels gradually declined when the equipment was towed further offshore.

The equipment weighs about 135 kilograms and is easy to tow for a 20-ton fishing boat. The production costs are estimated at several million yen.