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No Man's Land


JPL engineers face the challenge of building a robot sturdy enough to inspect the damaged, intensely radioactive Chernobyl nuclear reactor.


After sending autonomous machines to explore the surface of Mars, engineers at Jet Propulsion Laboratory and around the country are building a robot to venture into equally inhospitable territory--the interior of Chernobyl's exploded nuclear reactor.

The radiation level inside the reactor that melted down 12 years ago this month is so high that it would take only seconds to absorb more radiation than it is safe to be exposed to over an entire year. That makes it prohibitively dangerous for people to explore the severely damaged reactor, which must be thoroughly surveyed before crews can begin sorely needed repair work.

So instead of humans, officials in Ukraine--home of the Chernobyl power plant--are enlisting the help of Pioneer, a half-ton cross between a tractor and a tank that stands about 4 feet tall. The robot is a joint effort of engineers in the Ukraine and in the U.S. Department of Energy, the National Aeronautics and Space Administration and a handful of American universities and companies. The project is being spearheaded by Pittsburgh-based RedZone Robotics, a spinoff from Carnegie Mellon University.

In the fall, Pioneer will venture inside the nuclear reactor and take hundreds of pictures that will be used to build a lifelike three-dimensional virtual reality model of the damaged building. Construction teams will use the model to plan repairs for the reactor, which was hastily rebuilt after the accident and needs further work. An on-board drill will take samples from the concrete walls that will be examined for clues about the extent of radiation-induced damage.

"This project is important because people are still being sent into Chernobyl in spite of the fact that in 10 seconds a person gets a year's dose of radiation," said Mark Maimone, a member of JPL's technical staff in the machine vision and tracking sensors group who has been working on Pioneer since last fall.

But not even a robot can withstand radiation at the levels found inside Chernobyl, site of the world's worst nuclear accident. Designing Pioneer to withstand a lifetime exposure of 1 million rads--the unit of measurement for radiation exposure--presents a unique engineering challenge. (By comparison, the recommended exposure for humans is no more than five rads a year.)

"We are making it with different materials and electronics, and a different design and operational philosophy," said Mark Rowland, a physicist at the Energy Department's Lawrence Livermore National Laboratory in Northern California, who wrote the project proposal that created Pioneer. "Another difference comes up in reliability--since you can't go in to get it, it better not break."

The electronics that will run Pioneer are particularly vulnerable because radioactive particles will erode silicon chips until they are so "pockmarked that the silicon is no longer useful," said Pioneer team member Geb Thomas, an assistant professor in the department of industrial engineering at the University of Iowa in Iowa City.

Some plastics and polymers that would normally be used to build a robot will become brittle and fail in a high-radiation environment. Radiation also ruins camera lenses by turning glass brown, said Jim "Oz" Osborn, senior project scientist at the Carnegie Mellon University Robotics Institute in Pittsburgh, who has been working on the Pioneer project for about a year.

The most straightforward way to protect a device from radiation is to enclose it in lead or titanium. But that adds weight--protecting a shoe-box-size container requires 150 pounds of metal--and since Pioneer must fit through narrow openings, it must be as small and light as possible.

While much of Pioneer's interior will be encased in lead, most of its electronics will be put on high-end personal computers and Silicon Graphics workstations in a lead-lined room 50 feet from the reactor's core and connected via a cable. But that means there are more opportunities for critical data to be corrupted by noise. Pioneer's reaction time will also be slower than if the electronics were on-board.

"If the drill hits a rebar, for example, you have to be able to stop it fast enough to stop the drilling before the drill bit breaks," said Fred Serricchio, an associate engineer in the Guidance and Control Analysis Group at JPL in Pasadena.

Serricchio and Ali Ghavimi, a senior analyst in the same JPL group, are building the 3-foot, 150-pound drill that will bore into the Chernobyl reactor's concrete walls and retrieve samples for engineers to study.

"What we're expecting to find here is that in some places the strength of the concrete has been reduced, since it was subjected to those explosive forces," Carnegie Mellon's Osborn said. "We expect in other sites that the concrete will have become more brittle because of exposure to radiation."

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