(转)Three Mile Island 29 Years Later

Three Mile Island 29 Years Later: Nuclear Safety Problems Still Unresolved
Adding New Plants to Aging Fleet Will Increase Risk Without Safety Reform, Science Group Says

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Nuclear Reactor Security

WASHINGTON (March 27, 2008) — The partial meltdown at the Three Mile Island nuclear power plant began on March 28, 1979. Since the accident, not a single new nuclear power plant has been ordered in the United States. Indeed, 74 plants under construction at the time of the accident were cancelled. But in just the past year, the nuclear industry has stepped up its efforts to secure government funding for a new fleet of nuclear power plants. Unfortunately, over the last three decades, neither plant owners nor the Nuclear Regulatory Commission (NRC) have adequately addressed the basic flaws in U.S. nuclear safety that led to the Three Mile Island accident, according to the Union of Concerned Scientists (UCS).

"Three Mile Island was almost 30 years ago so perhaps the industry and the NRC have forgotten about it," said Dave Lochbaum, the director of UCS's Nuclear Safety Project. "But you can bet that even the people who welcome new plants in their communities will want to know if what happened at Three Mile Island could happen to them. As of right now, the industry and the NRC haven't done enough to ensure them it won't."

The Three Mile Island accident was triggered by a loss of reactor cooling water. Before the accident, the plant's cooling system valves had broken down 10 times over the preceding year. Instead of replacing the faulty valves, workers opened them manually to keep the plant operating. When other equipment problems occurred during the eleventh valve failure in March 1979, control room operators were overwhelmed and the plant suffered a partial meltdown.

Since then, the NRC and plant owners have focused more on keeping nuclear plants running over the short-term than ensuring their safety, Lochbaum said. That strategy has allowed a number of safety problems at plants to build up over time. When the accumulated problems cause enough interruptions to harm a plant's profitability, owners shut them down for extensive safety overhauls. Since Three Mile Island, utilities have had to shut down 41 plants for a year or more, a total of 51 times.

Nuclear accidents are most likely to occur at the beginning or end of a plant's operating lifetime, Lochbaum pointed out. When a plant first goes on line, workers have to acclimate to new equipment that has not been tested in real-world situations. Meanwhile, at the end of a plant's life, workers have to compensate for increasingly degraded hardware. Three Mile Island and other major nuclear accidents, including ones at Chernobyl, Browns Ferry in Alabama and Fermi near Detroit, occurred shortly after the plants started operating. Now most of the 104 currently operating U.S. nuclear power plants are entering the high-risk period at the end of their originally intended 40-year lifespans.

If the nuclear industry constructs a new fleet of power plants, Lochbaum said, there will be at a higher risk for a nuclear accident because nearly all of the plants in the United States will be either very new or very old.

"If the industry wants to build a new generation of nuclear plants, it first should prove that it can safely operate the ones currently in operation," he said. "And before the NRC approves any new plants, the agency should make sure the industry isn't as careless with its new plants as it was with its old ones."