As workers race to stave off further melting at the Fukushima Daiichi nuclear reactors in Japan, several robots there are waiting on the sidelines for an opportunity to help. Questions remain, however, regarding how these units might assist in an ongoing emergency at a site contaminated with radiation and deluged with tons of corrosive seawater.

Concrete pump trucks sprayed about 130 tons of water into Daiichi's No. 4 reactor on Wednesday, Japan's Nuclear and Industrial Safety Agency (NISA) reported (pdf). Meanwhile, Tokyo Electric Power Company (TEPCo) injected about 35 tons of seawater into the spent fuel pool of the No. 3 reactor to keep the fuel rods there from overheating, according to NISA, which also observed "slightly blackish" smoke generated from the building housing that reactor. Seawater is also being injected into the No. 1 reactor as well as the spent fuel pool of the No. 2 reactor.

TEPCo summoned a small corps of military-grade robots last week from iRobot Corp. in Bedford, Mass. Japan's Mitsui Engineering & Shipbuilding Co. last week sent its Disaster Monitoring Robot, or Moni-Robo, to the Daiichi site as well. Other robotics companies, including Canada's Inuktun Services, are also fielding inquiries about how their technology might be of use. Each of the robots of interest moves on tracks and features a mechanical hand that can be used to lift and manipulate objects.

The roles that robots might play in Japan will depend upon the emergency responders' priorities, whether this includes handling intensely hot or radioactive materials or, later removing sludge from the site or drilling core samples to determine how deeply radiation may have penetrated the facility's walls and floor, says William "Red" Whittaker, a Carnegie Mellon University robotics professor and director of the Field Robotics Center at the school's Robotics Institute in Pittsburgh. Whittaker and several Carnegie Mellon colleagues built robots in the late 1970s and early 1980s to inspect and perform repairs in the basement of Three Mile Island Nuclear Generating Station following the near meltdown there in 1979.

The robots
Mitsui's 600-kilogram Moni-Robo is reportedly on site at Daiichi. The one-armed robot is designed to be operated remotely—from as far as a kilometer away—and includes a camera that can take video as well as 3-D thermographic images. The 150-centimeter-tall Moni-Robo rolls along on tracks and also features sensors for measuring radioactivity and detecting combustible gases.

Inuktun, based in Nanaimo, British Columbia, specializes in making remote-controlled video cameras and "crawler" robots in a variety of sizes, ranging from the Versatrax 100 (which fits in a pipe 10 centimeters in diameter) to the Versatrax 450 TTC (which is 38 centimeters in diameter). These crawler bots are used primarily to inspect confined spaces such as pipes and sewers. "We have not sent any equipment to Japan specifically for the earthquake or Daiichi reactor site, but we do have a representative company in Tokyo that has some of our demonstration equipment," Inuktun president Colin Dobell says. "We believe it is being deployed, but we have not been able to confirm anything."

Four iRobot systems—two Packbots and two Warriors—reached Tokyo Monday night along with six of the company's engineers, who spent Tuesday unpacking the bots, installing batteries and running tests, says Tim Trainer, iRobot's vice president of operations. Given that the Packbot is designed primarily for explosive ordinance disposal and the Warrior is a prototype that will not be commercially available until this summer, iRobot's engineers still need to discuss the robots' capabilities, operation and limitations with TEPCo personnel, he adds.

The 68-kilogram iRobot Warriors were modified so they could carry a 6.4-centimeter fire hose should more water be needed somewhere. Each unit features an arm that can lift up to about 100 kilograms as well as an adjustable track system that allows it to climb stairs and travel up to 12.9 kilometers per hour.

One of the Packbots was fitted with a sensor that can detect radioactivity. Each 10.9-kilogram Packbot is equipped with a three-link arm that can lift up to about 13.6 kilograms, move debris and potentially relocate hazardous materials. In addition to being able to negotiate stairs, the Packbot can travel at up to 9.3 kilometers per hour and climb grades as steep as 60 degrees.

Undefined mission
It is unclear what role, if any, the Packbots and Warriors will play in TEPCo's efforts to restore power to its nuclear reactors and cool its on-site nuclear fuel rods. "We sent the robots without a defined mission in place but to assist where appropriate, whether this means delivering water to the fuel rods, moving equipment within the facility or cleaning up the facility once fuel has become stable," Trainer says.

Ultimately, the goal is to send the robots into the hazardous environment and keep those controlling the robots at a safe distance. "What we don't know is, what are the environments that we're talking about, can the robot sustain operations in those environments and, if they can, what value will they provide to the effort?" Trainer says. "Those things are all being figured out right now as the team is on the ground in Japan over the next several days."

All told, iRobot estimates that it is spending about $500,000 to $1 million worth of robots and spare parts to Japan, as well as several days' access to the company's engineers. Trainer made it clear that those engineers will pass along their knowledge of the robots to TEPCo and will not be going into the nuclear exclusion zones surrounding the reactors.

Radiation woes
Electronics can be made more radiation tolerant in a number of ways, Whittaker says. One is to keep the conductors and insulators on a device's silicon chips farther apart so that heat can more easily dissipate and the chip is more resilient. Another approach to keeping a system functioning in high-radiation environments is to implement redundant systems so it can function even if one of those systems is damaged.

As with most military equipment, the iRobot's units have integrated electromagnetic interference (EMI) shielding to cover the wiring, circuit boards and anywhere else the robot might be susceptible to such interference. The company was concerned that the robots might not be able to operate wirelessly due to radiation interfering with radio signals to and from the robots, so it added fiber-optic tethered spoolers so the Packbots and Warriors could be tele-operated from up to 220 meters and 500 meters, respectively, Trainer says.

With the exception of its charge-coupled device (CCD) cameras and embedded electronics, Inuktun's crawlers are capable of operating in a medium-level radiation field and dosage, says Dobell. For high-radiation situations, the company typically installs radiation-tolerant cameras on its crawler equipment in order to get into the more dangerous areas. The robots themselves are built using stainless steel, which Dobell says allows for easier decontamination.

Water world
It is common in nuclear recovery to operate in shallow water, where a robot might need to be able to withstand being submerged, Whittaker says. This was the case in the basement of the Three Mile Island facility, where several hundred thousand liters of heavily contaminated cooling water had washed through the reactor, he adds. Even if the robot is not completely submerged in water, it will be working in a very wet environment. "In order to interface with humans [again] these robots also have to able to tolerate a high-pressure wash down," he says

Inuktun makes several submersible models. Neither the Packbot nor the Warrior was designed to work in extreme heat or to be submerged in water, though they are able to function in up to meter or so of water, Trainer says. These limitations could pose challenges, especially given TEPCo's ongoing efforts to deliver water to its overheated fuel rods by any means, including fire hoses and airplane drops.