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N0KFQ > TODAY 28.03.14 16:02l 95 Lines 4774 Bytes #999 (0) @ WW
BID : 16436_N0KFQ
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Subj: Today in History - Mar 28
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Sent: 140328/1456Z 16436@N0KFQ.#SWMO.MO.USA.NA BPQK1.4.58
Mar 28, 1979:
Nuclear accident at Three Mile Island
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.
73, K.O. n0kfq
N0KFQ @ N0KFQ.#SWMO.MO.USA.NA
E-mail: kohiggs@gmail.com
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