Last week, U.S.-based iRobot sent four robots to help with recovery efforts at the Fukushima nuclear power plant, damaged as the result of a 9 magnitude earthquake and tsunami on March 11.

Workers' efforts to bring the plant's reactors under control have been hampered by high radiation levels, and it is hoped the robots could help inspect and even repair parts of the reactors by working in areas too dangerous for humans.

iRobot sent four robots to Japan: two lightweight, portable robots called PackBots (costing around $100,000 each), and two large, heavy-duty robots called Warriors, expected to be on sale this summer. The PackBots, which weigh about 60 pounds, use caterpillar tracks to get around and a long extendable arm with a camera and a gripper on the end; they are already used by the U.S. military for bomb disposal. The Warrior weighs 350 pounds and has a large robotic gripper at the end of a two-meter-long arm capable of lifting up to 200 pounds. It is many times stronger than the PackBot, says Tim Trainer, vice president of operations at iRobot.

"We don't know whether these will be used for search and rescue purposes or for efforts at the nuclear plant—that is for the Japanese to determine," says Trainer. The robots rely on a human controller. All four have been equipped with fiber-optic tethers for communication, in case radio signals don't work in the plant's highly radioactive environment. An iRobot team is currently in Japan and has trained operators to use the robots. The robots can act as "eyes and ears in a hazardous environment, to keep a human operator safe," says Trainer.

Most commercial robots are not designed to be used in this kind of environment.

Max Lungarella, a roboticist at the Artificial Intelligence Lab at the University of Zurich in Switzerland, and chief technology officer at Dynamic Devices, says mobile rescue robots—the kinds typically used in the field for surveillance or rescue—have sensors that are not well protected from radiation. He says it would be trickier to operate them without radio communications, which often are noisy during a disaster.

Lungarella adds that constructing robots designed to withstand high levels of radiation would be difficult. "For radiated environments, one needs robots that are particularly rugged," he says. "Such robots typically are rather large, slow, have only a few CPUs and sensors."

Some experts also question how helpful robots would be after a nuclear plant disaster. Something as simple as a locked door could prevent a robot from doing its job.