Idaho Blowdown

It is a nightmare that has nagged scientists since the dawn of nuclear power. A cooling-system pipe ruptures. The temperature of the nuclear reactor's core fuel shoots up, melting its zircaloy shielding. Finally the heat becomes so intense that the entire domed building disintegrates, leaking out a cloud of radioactive fallout that kills tens of thousands of people.

That gloomy scenario is, happily, still no more than hypothetical. But could such a blowdown, as scientists call it, really occur? Most officials say the risk is infinitesimally small. Even if a loss of coolant did occur, the reactor's back-up emergency core cooling system would presumably swing into action. Critics remain unpersuaded. They point out that there has never been a real test of a core cooling system in the 27 years of atomic power.

Last week, near snow-swept Mud Lake, Idaho, the Nuclear Regulatory Commission undertook to allay fears. It staged a nuclear accident in miniature, deliberately sabotaging a small test reactor's primary cooling system to see if the back-up system would avert a blowdown.

The $10 million exercise was officially dubbed a Loss of Fluid test (LOFT). It was held in the Department of Energy's Idaho National Engineering Laboratory. As some 200 scientists and technicians paced anxiously, the countdown began. On signal, two blowdown pipe valves snapped open, simulating a rupture. In a flash, reactor cooling fluid escaped. As the core's temperature soared, the secondary cooling system also failed, again according to plan. Then after only 17 seconds, the third system's coolant began pouring hundreds of gallons of water on the hot core. Its temperature, which had jumped to 516DEG C (960DEG F), still far short of zir-caloy's melting point, soon settled back to 149DEG C (300DEG F). Exclaimed the Nuclear Regulatory Commission's Thomas Morley: "I pronounce this experiment a success!" Then off he went for a victory party of pizza and beer.

Antinuke forces thought such celebrating was premature. Physicist Henry Kendall of the Union of Concerned Scientists called the test meaningless because the LOFT reactor has less than 2% of the output of a typical atomic plant. Said his colleague Robert Pollard: "It's like using a kite to prove a moon rocket will work." But LOFT scientists rejected that argument. Said one: "It isn't necessary to crash 747s against buildings to test their safety." One thing was indisputable: the emergency core cooling system did work. Just to make sure that it does the job under different conditions, the Commission will stage about 20 more LOFT tests through the 1980s.

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