The T-Hawk drone, which can transmit both infrared and optical images, hovered over the damaged housings of the No. 1, 3 and 4 reactors and the pools of spent fuel, utility spokesman Junichi Matsumoto told CNN.
Tokyo Electric also is employing remote-controlled heavy machinery to clear debris.
Some 60,000 tons of radioactive water were being piped into holding areas Sunday.
The March 11 earthquake and tsunami damaged four of the nuclear plant's six reactors and the cores have been under continual dousing to prevent a meltdown. The runoff has been going into the Pacific Ocean, but Tokyo Electric said holding areas had been set up to contain the radioactive water, the Kyodo news agency said.
Some water not considered highly radioactive will still be allowed into the ocean, officials said.
Meanwhile, federal officials in Tokyo Sunday announced enforcement of the 15-mile evacuation zone around the plant would be stepped up.
Residents have been allowed to make brief visits to their homes to pick up belongings since the disaster, but plans are under way to declare the area off-limits to anyone not involved in disaster relief, Kyodo said.
Government officials also said radiation readings have fallen in northeastern and eastern Japan.
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