Credit goes to "We almost lost Detroit"

[link to www.wsrl.org]

This is the meat of the story...

How the accident happened...

Fascinating story...

""
Just before the start of the experiment, an assistant operator in the basement below the reactor opened, by mistake, four valves that kept air pressure form raising the control rods after the initial start-up. If the rods were to rise, the fuel in the reactor would immediately begin splitting atoms at a faster unplanned rate, leading to one of the most feared circumstances of all, a nuclear runaway. From that point on it would be impossible to predict what would happen.

At the control panel, the supervisor of the operation was horrified when he saw red warning lights suddenly flash on the panel board. He grabbed the phone and yelled to the operator in the basement to stop what he was doing, then rushed down to the basement, leaving his assistant in charge of the panel.

In the basement, he was relieved to find that not all the valves were open. He closed the valves immediately, and was sure the control rods had returned to their proper position.

He checked the air pressure, and it was good. Up in the control room the red warning lights went off, indicating that the control rods were where they should be.

What hd did not know, nor did anyone else at the time, was thatin some inexplicable way the rods had jammed, and had dropped down just far enough to turn off the warning lights, but not far enough to choke off the reactivity which was rising rapidly.

When the supervisor realized what was happening, he grabbed the basement phone to call the control room, intending to order his assistant to push buttons numbered 4 and number 3 to stop the reactivity. Instead, he said: "Push number 4 and number 1".

Up at the control panel, in order to reach the two buttons, the assistant had to put the phone down. The moment he did so, the supervisor in the basement realized he had called out the wrong numbers. He yelled into the phone, but no one heard him. The reactor began to run out of control - "above critical" in the parlance of the nuclear engineer.

It took only twenty seconds to realize this. Meanwhile, the power of the NRX reactor was doubling every two seconds. By that time, the reactor was on its way to a fuel meltdown. Four banks of control rods had been raised when the assistant had pushed button number 1. He immediately took the prescribe safety measure: He scrammed the reactor, tripping it so that all the control rods would slide safely back into place.

But, because of a lack of air pressure the control rods were not forced back into place. The galvanometer, which measures the electric current, indicated that the power level was still climbing on its way to disaster. The assistant at the controls screamed over the phone for the supervisor to do something about the air pressure, so that the control rods would drop and stop the reaction. There was no way to do this. The combination of errors had snowballed into an uncorrectable situation.

Exactly forty-four seconds after the accidental pushing of button number 1, a plant physicist realized that the only thing left to do was to dump the heavy water from the reactor, and thus cut off the fission process. There were thousands of barrels of heavy water in the reactor-each barrel worth more than a Cadillac. But it was the only option. The physicist reached over and slammed the dump switch.

It took several second to see what would happen. The power seemed to drop, but almost immediately another hazard loomed up: The whole sealed reactor vessel might collapse form the vacuum formed by the dumping. The operation was halted, then cautiously resumed. A sigh of relief went up when the instruments went back to normal, about thirty seconds after the dumping had begun.

But the disaster was far from over. Someone looked through an open basement door, and saw tons of water rushing out of the reactor, flooding the basement area. The supervisor and his assistant rushed with a bucket, carefully handled at a distance, to take a sample. A quick test showed it to be ordinary light water, but highly radioactive.

Then, four minutes after button number 1 had been accidentally pushed, a dull rumble was heard. The huge Four-Ton lid on the reactor vessel, called a gasholder, rose in the air. A spurt of water gushed out through the top of the reactor, spilling over the building floor. Radiation alarms went off, and the sensor near the steam fan showed lethal doses of radiation escaping.
""