Adam Reres

Ms. Cooper
U.S. History II
19 march 2004
Three Mile Island
Three Mile Island is a nuclear power plant located in Harrisburg, PA. It
had two pressurized water reactors. One in which began its service in 1974
and is the best performing reactor in the US. However its other reactor is
almost brand new and suffered a server nuke clear meltdown. March 28th 1979
at approximately 4:00 a.m. a minor malfunction created a rise in
temperature to the primary coolant.

The reactor shut down as a safety result. In no time a pilot-operated
relief valve (PORV) on the reactor’s cooling system opened but did not
close. This caused reactor coolant water to leak out and soon drained the
tank of its coolant (Wikipeia). As a effect of the lost coolant, high
pressure pumps pushed replacement water into the reactor system. Water and
steam then escaped through its relief valve as cooling water surged to the
reactor.

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In this type of situation, the operators were trained to reduce the
flow of the replacement water. Their training told them that the
pressurizer water level was the only dependable indication of the amount of
cooling water in the system. Because the pressuriser level was increasing,
they thought the reactor system was too full of water They were told to do
all they could to keep the pressuriser from filling with water. If it
filled, they could not control pressure in the cooling system and it might
rupture.

Operators responded by reducing the flow of replacement water. Steam then
formed in the reactor cooling system. Pumping a mixture of steam and water
caused the reactor cooling pumps to vibrate. If the severe vibrations could
have damaged the pumps they would made them unusable, so the operators shut
down the pumps. This ended the forced cooling of the reactor.

However, as reactor coolant water boiled away, the reactor’s fuel core was
uncovered and became even hotter. The fuel rods were damaged and released
radioactive material into the cooling water. At 6:22 am operators closed a
block valve between the relief valve and the pressuriser. This action
stopped the loss of coolant water through the relief valve. However,
superheated steam and gases blocked the flow of water through the core
cooling system (Wikipeia). By late afternoon, operators began high-pressure
injection of water into the reactor cooling system to increase pressure and
to collapse steam bubbles. By 7:50 pm, they restored forced cooling of the
reactor when they were able to restart one reactor coolant pump. They had
condensed steam so that the pump could run without severe vibrations. From
March 29 and 30, operators used a system of pipes and compressors to move
the gas to waste gas decay tanks(Wikipeia). The compressors leaked, and
some radioactive gas was released to the environment
After an anxious month, on 27 April operators established natural
convection circulation of coolant. The reactor core was being cooled by the
natural movement of water rather than by mechanical pumping. The plant was
in “cold shutdown”.


The cleanup of the damaged nuclear reactor system at TMI-2 took nearly
12 years and cost approximately $973 million. The Plant surfaces had to be
decontaminated. Any water used and stored during the cleanup had to be
processed. And about 100 tones of damaged uranium fuel had to be removed
from the reactor vessel — all without hazard to cleanup workers or the
public. (Wikipeia)
Opinion
I see Three Mile Island as history repeating itself; It reminded me a
lot of the Titanic. The crew on titanic and in the operators room were
told that an accident was nearly impossible so that when something happened
they didn’t know how to react properly or knew entirely what was going on.

However, they responded with there instincts which only made the problem
worse. Unlike the Titanic though, no one died in Three Mile Island.

The Three Mile Island incident was in a way a good lesion to the US in
working with nuclear generated power. We saw that it is a force of nature
that is very powerful. Its dangers are very real, anything could happen,
and if something did happen when using the nuclear power many could die. We
saw that we should not assume anything in a time of delicate decisions
http://en.wikipeia.com/wiki/Three_Mile_Island, Wikipeia, Joan , last
modified 02:19, 15 Mar 2004
The plant’s main feedwater pumps in the secondary non-nuclear cooling
system failed at about 4:00 a.m. on March 28, 1979. This failure was due to
either a mechanical or electrical failure and prevented the steam
generators from removing heat. First the turbine, then the reactor
automatically shut down. Immediately, the pressure in the primary system
(the nuclear portion of the plant) began to increase. In order to prevent
that pressure from becoming excessive, the pressurizer relief valve (a
valve located at the top of the pressurizer) opened. The valve should have
closed when the pressure decreased by a certain amount, but it did not.

Signals available to the operator failed to show that the valve was still
open. As a result, the stuck-open valve caused the pressure to continue to
decrease in the system.

Meanwhile, another problem appeared elsewhere in the plant. The emergency
feedwater system (backup to main feedwater) was tested 42 hours prior to
the accident. As part of the test, a valve is closed and then reopened at
the end of the test. But this time, through either an administrative or
human error, the valve was not reopened — preventing the emergency
feedwater system from functioning. The valve was discovered closed about
eight minutes into the accident. Once it was reopened, the emergency
feedwater system began to work correctly, allowing cooling water to flow
into the steam generators.

As the system pressure in the primary system continued to decrease, voids
(areas where no water is present) began to form in portions of the system
other than the pressurizer. Because of these voids, the water in the system
was redistributed and the pressurizer became full of water. The level
indicator, which tells the operator the amount of coolant capable of heat
removal, incorrectly indicated the system was full of water. Thus, the
operator stopped adding water. He was unaware that, because of the stuck
valve, the indicator could, and in this instance did, provide false
readings.

After almost eighty minutes of slow temperature rise the primary loop pumps
begin to shudder as steam rather than water began to pass through them. The
pumps were shut down, and it was believed that natural circulation would
continue the water movement. Steam in the system locked the primary loop,
and as the water stopped circulating it was converted to steam in
increasing amounts. After around 130 minutes since the first malfunction,
the top of the reactor core was exposed and the heat and steam drove a
reaction involving hydrogen and other radioactive gases with the zirconium
rod cladding. The quench tank ruptured, and radioactive coolant began to
leak out into the general containment building. At 6 a.m. there was a shift
change in the control room. A new arrival noticed that the temperature in
the holding tanks was excessive and used a backup valve to shut off the
coolant venting. Around 250,000 gallons (950 m) of coolant had already
been lost from the primary loop. It was not until 165 minutes after the
start of the problem that radiation alarms activated as contaminated water
reached detectors, by which time the radiation levels in the primary
coolant water were around 300 times expected levels.