The core of a nuclear reactor is often referred to as "no-man's land," because it's just too hot for anyone to venture near it. So how do you inspect it, to make sure it's still safe and in good repair? A researcher at the University of Missouri-Rolla has come up with a solution based entirely on off-the-shelf parts.

Akira Tokuhiro, assistant professor of nuclear engineering and director of the university's nuclear reactor, is working on a water-submersible craft outfitted with a radiation-resistant camera. A prototype has been in the university's swimming pool, and the aim is to build a small craft that can travel down through 30 feet of water to the research reactor's core, to take pictures. The goal of the project is to help maintain and secure the nation's nuclear reactor facilities, Tokuhiro said.

"Because the radiation level near the core is lethal, we can't just put on a wetsuit and swim down into the pool to check the reactor," he said. "The submersible with the camera can withstand the radiation, and acts as an in-service inspection device."

The university's reactor was built in 1961, and some of its components have been under water for 40 years, according to Tokuhiro. The reactor has been photographed by cameras outside the pool, but those cameras generate images that are distorted by the water. He said that the grade of aluminum used for the reactor components has been used in other research reactors, and has held up well, but the university would like to be able to visually confirm the working condition of its reactor.

This submersible craft carries a radiation-resistant camera that will photograph the core of a nuclear reactor.

Tokuhiro's submersible, which weighs about five pounds, was built entirely from pieces purchased from a hardware megastore. The device is roughly the size of a 20-inch computer monitor, and somewhat resembles the Starship Enterprise, Tokuhiro said. It's made of PVC, uses an air pump and bleed valves to make it lower and rise up, and uses lead slugs for ballast on its right and left sides. A central tube area, complete with window, will house the radiation-resistant camera.

The prototype device operates as a tethered submersible, with an airline and a powerline connecting it to the surface. Two propeller drives move the small sub through the water. According to Tokuhiro, it can move about as fast as a human can swim.

At this point, the sub doesn't have very precise movements, but that isn't an issue. All it has to do is sink to the bottom of the reactor pool and make slight angle corrections, Tokuhiro said. The biggest issue is providing a leakproof enclosure for the camera.

Like the rest of the parts, the camera was an off-the-shelf purchase, a solid-state imaging camera from Cidtec of Liverpool, N.Y. The camera uses proprietary charge-injection-device architecture, originally developed by General Electric for aerospace applications. According to Cidtec, the camera can operate at total radiation doses more than 100 times greater than conventional charge-coupled devices.

But, while the camera can withstand the radiation from the reactor core, it's not meant to withstand the effects of the water that the core sits in. That's where the sub comes into play.

Tokuhiro brainstormed the idea for the camera-equipped submersible and came up with its design, but a team of about a half-dozen students from various disciplines has been involved in building the first version.

"These kinds of projects really bring together all the students," Tokuhiro said. "It's not just engineering students, but also computer engineering, electrical engineering, mechanical engineering, and so on. It's become a multidisciplinary team."

In all, the craft has been under development for about one year, with roughly three months of actual work time devoted to the project, which has been running on a shoestring, with no funding.

The prototype submersible has been tested successfully in the university's swimming pool. Tokuhiro said he doesn't have high expectations for the prototype, since it's just the first generation of the device. Leakage, in particular, continues to be a problem. But, improvements are in the works.

"Within the next year, we hope the submersible will be fully operational, and it will go down into the reactor core and take some images of the components," he said.

Ultimately, he expects to create an untethered, radio-controlled version of the camera-toting submersible. Electrical and computer engineering students are currently working on microcontrollers to make that happen.

For now, Tokuhiro is focusing on demonstrating the principles behind the device. Once it's functional and well-tested, he intends to seek funding from government agencies and the corporate arena.

home | features | weekly news | marketplace | departments | about ME | back issues | ASME | site search

© 2004 by The American Society of Mechanical Engineers