The operator of the crippled Fukushima Daiichi nuclear plant has suspended a preliminary survey inside a containment vessel due to failure of the robot's camera.
Tokyo Electric Power Company suspects that high radiation inside the vessel likely affected the camera.
Engineers sent a remote-controlled robot into the vessel of the No.2 reactor on Thursday. It moved forward on a metal rail, clearing debris with water from a pressure hose.
As it advanced toward the center for about a meter, images sent from one of its 3 cameras began turning dark. The engineers suspended the survey and retrieved the robot.
Analysis of the images suggests that extremely high radiation of up to 650 sieverts an hour inside the containment vessel caused the failure.
Images in another survey last month by a remote-controlled camera pointed to an estimated level of up to 530 sieverts an hour.
The utility plans a full survey using a scorpion-shaped robot to directly measure radiation levels and temperatures.
But it is being forced to review the method of the survey as the strong radiation inside the vessel might make it difficult to conduct a survey, which is crucial as a preparatory step.