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 meters 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 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.