More than a year ago, long before the earthquake and tsunami damaged the Fukushima Daiichi nuclear power plant in Japan and brought reactor safety into the forefront of the news, mechanical engineering professor Harry Asada had already started work on a way to inspect the interior of cooling water pipes in nuclear plants. Asada, director of d’Arbeloff Laboratory for Information Systems and Technology at Massachusetts Institute of Technology, Cambridge, Mass., and a team of graduate students have been developing a self-propelled robot device to travel through the pipes and gather information about their condition.

Because the robot must traverse the reactor’s system of pipes without getting caught on probes, joints, or other obstacles, it was designed in a spherical shape, with a relatively smooth exterior. Current iterations of the device generally are around 12 cm (4.72 in.) in diameter, says graduate research assistant Ian Rust. Progress on the concept to date includes prototypes and testing of various aspects of operation for a spherical, battery-powered, self-propelled, remotely operated vehicle (ROV) equipped with a camera.

Within the robot body, a two-axis gimbal structure moves an eccentric weight inside the robot’s outer shell. This shifts the robot’s center of mass and causes it to rotate in place. The operator tilts the ROV to aim its camera in the desired direction, Rust says.

Graduate research assistant Anirban Mazumdar has been working on the ROV’s propulsion system. Because the robot needs to have a smooth surface, propellers, vanes, or other mechanical devices could not be used for moving or turning the device. Instead, a water-jet system was developed. Pumps located inside the robot’s housing pull in water and send it out through appropriate openings in the robot’s skin to push the robot in the desired direction. A network of passages and Y-shaped fluidic valves lies within the body of the robot. Prototypes were formed by a 3-D printing process, so the passages and valves could be built in. The current test versions have from four to eight jet openings, Mazumdar says.

Since radio communication underwater doesn’t work well, “we’re experimenting with visible light, using blue 470-nm LEDs, overlaying a data signal,” Rust explains, in order to provide two-way communications between the robot and the ground base, which extends into the piping system. Tests show a successful communication range of up to 25 meters, he says. The researchers are also looking into using the reflective interior of the pipes to increase the communications distance.

The robot is operated via a fairly standard PID (proportional-integral-derivative) control system, Rust says. The electrical and other components must operate in a radioactive environment. Nuclear industry contacts have offered guidance about which electrical and other components will be the most robust, given the levels of radiation likely to be encountered. However, the ROV will be essentially “disposable,” Rust says, needing to operate successfully inside the plant’s cooling system only for a specified period of time.