Water that could be tainted by radiation has been pouring into a drain on the first floor of reactor No. 3 at the Fukushima No. 1 power plant, Tokyo Electric Power Co. said.

The camera of a rubble-removing robot operating inside the No. 3 building has captured images of a 30-cm-wide water leak, the beleaguered utility said Saturday. It also claimed that none of the water has leaked outside the building so far.

Tepco, as the utility is known, is perpetually pumping water into reactors 1 through 3 to keep their melted cores cool, but leaks have been spotted in parts of No. 3's containment vessel. Tepco is investigating whether the water spotted by the camera is actually the coolant.

The radiation level on the first floor of the No. 3 reactor is a relatively high 30 millisieverts per hour. Tepco said the amount of radioactive material in the just-found leak is unknown because the radiation in the reactor building is already high.