Robots essential in decommissioning

April 14, 2015

Stalled robot still useful in moving Fukushima decommissioning forward, TEPCO says

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201504140034

By HIROMI KUMAI/ Staff Writer

All was not lost when a robotic probe broke down inside a highly radioactive containment vessel at the crippled Fukushima No. 1 nuclear power plant, the plant operator says.

Tokyo Electric Power Co. said the mission showed that robotics has a vital role to play in the decommissioning process.

“It shows that monitoring devices (attached to the robot) can function amid high levels of radiation for two to three days,” said a TEPCO official, referring to the tubular-shaped robot that stopped dead in its tracks just hours after entering the first floor of the No. 1 reactor's containment vessel on April 10.

Images taken by the robot, released on April 13 by the plant operator, reveal fist-sized stone-like objects and other debris scattered on the floor. The images also appeared to show a latch and other wreckage, but TEPCO officials said they had no idea where those objects were originally located.

The robot measured radiation levels at six points inside the containment vessel. They ranged from 7.0 to 9.7 sieverts per hour, while temperatures fluctuated between 17.8 and 20.2 degrees.

The sleek, shape-changing robot entered the containment vessel through piping on April 10. But after covering 10 or so meters--about two-thirds of its planned route--the device came to a standstill.

The operation marked the first time to introduce a robotic probe to shoot images in the containment vessels for the No. 1 through No. 3 reactors, where meltdowns occurred after the March 2011 earthquake and tsunami disaster.

The mission was viewed as essential in paving the way for a full-blown investigation scheduled for the end of this fiscal year. It is part of preparatory work required to eventually retrieve melted nuclear fuel, the toughest part of the decommissioning process.

While the robot failed to complete its intended mission, the images it took showed there is enough space and no obstacles in an area connecting the first floor and the basement--the planned next probe site--and that pipes on the survey route are more or less intact.

TEPCO gave up trying to retrieve the robot and cut the cable connecting the device to an outside power source on April 13. The plant operator speculated that the robot broke down after it collided with a step or other obstacles.