The operator of the damaged Fukushima Daiichi nuclear power plant has begun its delayed robot probe of the inside of the facility's No.1 reactor.

Tokyo Electric Power Company, or TEPCO, had planned to start the survey of the reactor's containment vessel on January 12, but postponed it due to mechanical trouble.

Engineers noticed during preparations that data from radiation-measuring equipment installed in a robot was not shown correctly.

The engineers later found out that electromagnetic waves emitted from the robot's device for extending and winding up cables had affected its radiometers. They solved the problem, and confirmed that the data was then shown accurately.

TEPCO started the survey on Tuesday morning. Officials of the utility say they initially planned to end the probe by August, but that the schedule will be moved back due to the delay.

The probe is part of efforts to remove molten fuel debris from inside the reactor.