A pair of remote controlled robots entered a reactor building at the stricken Fukushima Daiichi nuclear power plant on Sunday morning for the first time.
Plant operator Tokyo Electric Power (TECO) is hoping the iRobot Packbots will be able to provide data on the current condition inside the buildings, parts of which contain high levels of radioactivity and are hazardous for workers to enter.
The robots entered the plant's number 3 reactor building and were due to take radiation and temperature readings. They are equipped with video cameras that can provide a live feed to operators.
Photos released by TEPCO showed one of the robots manipulating a handle on the second of a pair of double doors that lead into the reactor building.
On Monday, TEPCO said the robots had measured radiation levels of between 28- and 57 milliSieverts per hour in the reactor building. A later trip into reactor building 1 measured radiation levels of between 10- and 49 milliSieverts per hour.
At the point where the maximum radiation was observed, workers would be able to stay for just under five hours before reaching their maximum-allowed annual dose of 250 milliSieverts per year. In the area of lowest radiation, work would be limited to 25 hours before the annual limit is hit.
The plant owner has been wrestling to bring the Fukushima Daiichi nuclear plant under control for just over a month since a tsunami, estimated at 14 metres high, slammed into the facility and damaging its cooling system. Subsequent explosions have damaged three of the reactor buildings and spread radioactive contamination into the surrounding environment.
Workers initially braved high levels of radiation to prevent an even larger disaster, but their time on-site was strictly limited by the radiation. TEPCO has begun employing remote controlled robots and machinery because they face no such restrictions.
A remote control excavator and transporter are being used to clear debris around the plant and an unmanned helicopter is being employed to shoot video of the outside and upper areas of the reactor buildings. The robots that entered on Sunday will give plant operators their first look at the interior of the reactor building's lower levels.
The iRobot Packbots are designed for use in hazardous environments. More than 3,000 of the robots have been supplied to military and civilian customers, which use them in applications such as bomb defusing.