|
MIDDLETOWN, PA. -- The last layer of debris still rests on the bottom of the steel reactor vessel at Three Mile Island Unit 2. An underwater camera panning slowly through the murk at the vessel floor shows shattered fuel rods and odd bits of metal.
The images flicker across television monitors like old nightmares. Here a broken fuel tube, its ceramic-coated uranium pellets spilled into the dark sludge below; there a blob of some undefinable substance, contorted by temperatures that soared over 5,000 degrees Fahrenheit.
A decade after an accident turned the heart of a $700 million nuclear reactor into 150 tons of radioactive rubble, cleanup operations are continuing at TMI-2. Bit by painstaking bit, round-the-clock crews here have removed more than two-thirds of the debris, packed it into shielded canisters and loaded it into special casks for shipment to the federal nuclear reservation at Idaho Falls.
Shortly after the accident, some nuclear experts estimated that the cleanup would cost around $40 million and that the plant ultimately would be repaired and put back in service.
Any illusions about future operations at TMI-2 were dashed when technicians got their first look at internal damage several years after the accident. Where officials expected to find the damaged core, there was a void. The part of the core left uncovered by cooling water had simply melted, resolidifying several feet down like a pool of candle wax. By some estimates, the core was 30 minutes away from melting through the eight-inch-thick steel reactor vessel when cooling water was finally restored.
The cleanup, nearly two years from completion, so far has cost about $1 billion.
The cost reflects the intricacy of the operation. Workers standing atop the reactor vessel maneuver specially designed tools at the end of 40-foot poles through the cloudy water covering the core. Despite their heavy protective clothing, workers cannot peer directly into the vessel or linger long at the edge of the narrow openings that admit their tools.
The task also has required exotic technology, such as the plasma arc torch now being used to cut apart five two-inch-thick stainless steel grids in the lower part of the vessel. Workers must remove the grids to get at core material that slumped to the bottom of the reactor.
The costs associated with the TMI accident don't stop there. Like dozens of other nuclear installations, TMI-1 has been forced to upgrade its operations, equipment and training programs to reduce the likelihood of a similar catastrophe.
2Before the accident, there were 350 workers involved in operating both reactor units on the island. Today, 800 employees are involved in operating TMI-1 alone. General Public Utilities-Nuclear spokeswoman Carol Clawson said control-room operators spend one-fourth of their time in training, much of it in simulated control rooms grappling with a variety of potential malfunctions.
The control room has been changed as well, down to the detail of painting instrument panels a different color to enhance the visibility of warning lights.
Across the back wall of the control room is a solid panel of lights attached to systems that monitor crucial pumps, valves and other equipment. The panel allows operators to check the status of the entire reactor at a glance.
During the TMI accident, at least one crucial gauge was not visible to operators. About 20 steps away from the main operator's seat, facing away from the control room, was a gauge that would have warned operators that a pressure relief valve had stuck open and was draining water from the core.
Clawson, standing in the control room where the drama started a decade ago, pointed out the gauge. "If they'd looked at it," she said, "they would have known right away what the problem was."