Wednesday, March 28, 2007

March 28:


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

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

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

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