Memories
Justminutesfrom meltdown: Lessons ofnuclearnear-miss
At the time it was the most serious nuclear power plant accident of the atomic age, and was to lead to major safety improvements across the world.
As the first warning alarms went off at the Three Mile Island plant in Pennsylvania, experts were not sure what they were faced with.
The accident began at 4am when a pressure valve in a reactor at the plant, named after the island in Susquehanna River it was built on, failed to close.
Cooling water, contaminated with radiation, drained into adjoining buildings, and the core began to dangerously overheat.
Emergency cooling pumps cut in and, left alone, these safety devices would have prevented the escalation to a larger crisis.
But staff in the control room misread confusing and contradictory readings and shut off the control system.
By early morning, the core had heated to more than 4,000 degrees, just 1,000 short of meltdown.
Had meltdown occurred, radiation would have been released over an area that was home to two million people.
Victor Galinksi, the senior scientist on duty at the Nuclear Regulatory Commission in Washington, said no one appreciated then just how serious the damage already was.
He said: “The fuel was encased in zirconian tubes and there are thousands and thousands of these in a reactor and the water runs past them. People were talking about some possible slight damage to these zirconian tubes. Even that would have been considered very serious.
“In reality, most of them in the reactor had melted down, even before we heard about the accident. But this was not known. Not only was it not known contemporaneously, but it was not known when the reports on the accident were written a year later.
“It wasn’t realised until something like five years later, when the reactor vessel was opened up.”
He said that had this been known at the time “certainly we would have evacuated people from the area, immediately. But I have to say we were desperately worried when he discovered a much lower level of damage a couple of days into the accident.”
At about 8pm plant operators realised they needed to get water moving through the core again and restarted the pumps. The temperature began to drop and pressure in the reactor was reduced.
The reactor had come within less than an hour of a complete meltdown. More than half the core was destroyed or molten, but it had not broken its protective shell, and no radiation was escaping.
The crisis appeared to be over. Two days later it was realised that a bubble of hydrogen gas had exploded on that first day, releasing a small amount of radiation into the atmosphere.
At this point Pennsylvania Governor Dick Thornburgh advised pregnant women and pre-school-age children living within five miles of the plant to leave the area amid fears of a second explosion. This led to the very panic the Governor had hoped to avoid, and within days 100,000 people had fled surrounding towns.
Only when then President Jimmy Carter – a trained nuclear engineer – visited the plant on April 1 was public calm restored.
No one died in the accident, but it set back the expansion of nuclear power in the USA by decades.