At 4 a.m. on March 28, 1979, the worst accident in the history of
the U.S. nuclear power industry begins when a pressure valve in the
Unit-2 reactor at Three Mile Island fails to close. Cooling water,
contaminated with radiation, drained from the open valve into adjoining
buildings, and the core began to dangerously overheat.
The Three Mile Island
nuclear power plant was built in 1974 on a sandbar on
Pennsylvania's
Susquehanna River, just 10 miles downstream from the state capitol in
Harrisburg. In 1978, a second state-of-the-art reactor began operating
on Three Mile Island, which was lauded for generating affordable and
reliable energy in a time of energy crises.
After the cooling water began to drain out of the broken pressure
valve on the morning of March 28, 1979, emergency cooling pumps
automatically went into operation. Left alone, these safety devices
would have prevented the development of a larger crisis. However, human
operators in the control room misread confusing and contradictory
readings and shut off the
emergency water
system. The reactor was also shut down, but residual heat from the
fission process was still being released. By early morning, the core had
heated to over 4,000 degrees, just 1,000 degrees short of meltdown. In
the meltdown scenario, the core melts, and deadly radiation drifts
across the countryside, fatally sickening a potentially great number of
people.
As the plant operators struggled to understand what had happened, the
contaminated water was releasing radioactive gases throughout the
plant. The radiation levels, though not immediately life-threatening,
were dangerous, and the core cooked further as the contaminated water
was contained and precautions were taken to protect the operators.
Shortly after 8 a.m., word of the accident leaked to the outside world.
The plant’s
parent company,
Metropolitan Edison, downplayed the crisis and claimed that no radiation
had been detected off plant grounds, but the same day inspectors
detected slightly increased levels of radiation nearby as a result of
the contaminated
water leak. Pennsylvania Governor Dick Thornburgh considered calling an evacuation.
Finally, at about 8 p.m., plant operators realized 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 was
apparently over.
Two days later, however, on March 30, a bubble of highly flammable
hydrogen gas was discovered within the reactor building. The bubble of
gas was created two days before when exposed core materials reacted with
super-heated steam. On March 28, some of this gas had exploded,
releasing a small amount of radiation into the atmosphere. At that time,
plant operators had not registered the explosion, which sounded like a
ventilation door closing. After the radiation leak was discovered on
March 30, residents were advised to stay indoors. Experts were uncertain
if the hydrogen bubble would create further meltdown or possibly a
giant explosion, and as a precaution Governor Thornburgh advised
“pregnant women and pre-school age children to leave the area within a
five-mile radius of the Three Mile Island facility until further
notice.” This led to the panic the governor had hoped to avoid; within
days, more than 100,000 people had fled surrounding towns.
On April 1, President
Jimmy Carter
arrived at Three Mile Island to inspect the plant. Carter, a trained
nuclear engineer, had helped dismantle a damaged Canadian nuclear
reactor while serving in the U.S. Navy. His visit achieved its aim of
calming local residents and the nation. That afternoon, experts agreed
that the hydrogen bubble was not in danger of exploding. Slowly, the
hydrogen was bled from the system as the reactor cooled.
At the height of the crisis, plant workers were exposed to unhealthy
levels of radiation, but no one outside Three Mile Island had their
health adversely affected by the accident. Nonetheless, the incident
greatly eroded the public’s faith in nuclear power. The unharmed Unit-1
reactor at Three Mile Island, which was shut down during the crisis, did
not resume operation until 1985. Cleanup continued on Unit-2 until
1990, but it was too damaged to be rendered usable again. In the more
than two decades since the accident at Three Mile Island, not a single
new nuclear power plant has been ordered in the
United States.
