An iRobot PackBot crawls through the Unit 3 reactor building at the Fukushima Daiichi nuclear plant.

TOKYO--iRobot PackBots are being used to explore the interior of reactor buildings at the Fukushima Daiichi nuclear plant, which was severely damaged in last month's massive tsunami and subsequent hydrogen blasts.

The battle-hardened PackBots, sent to Japan along with iRobot Warriors, have been recording high levels of radiation at the plant, where operator Tokyo Electric Power Company (Tepco) struggles to restore key cooling functions. It's expected to take months to shut down the facility.

The video below shows a remote-controlled PackBot moving through the shadowy first floor of Unit 1. Its caterpillar treads move slowly over debris strewn around the floor. Another video shows the machine carefully opening a door.

Tepco says that robots have been used to measure radiation and do surveys of Units 1, 2, and 3. They apparently measured radiation of up to 57 millisieverts per hour.

In other video related to the plant, a Honeywell T-Hawk micro air vehicle sent to Japan to help with the nuclear crisis has recorded footage of the damaged exterior of the Fukushima plant.

Deployed in Iraq and Afghanistan, the 17-pound T-Hawk measures 14 inches across and flies autonomously or by remote control. It can fly to 10,000 feet, has a top speed of 46 mph, and can operate for about 40 minutes.

In a release, Honeywell said its staff has flown five "successful" missions at Fukushima so far, recording video and images of the plant. The four T-Hawks there are equipped with radiation sensors.

Check out this video, posted by IEEE Spectrum.