2 years, 7 months ago
What happened during 3 mile Island disaster?
Book: TMI 25 years later
Quote
Alarms went off. An auxiliary feedwater system should have started automatically but it did not. The auxiliary system was to provide emergency source of cooling water to the steam generators, however, critical valves in the system were left closed. Without this critical water supply, the boiling water in the steam generators would boil away completely. A rapid rise in temperature and pressure occurred in the reactor's cooling system.
A pressure-regulating valve opened to reduce pressure in the reactor and associated reactor systems
Steam began flowing from the valve through piping into a collecting tank in the basement of the reactor containment building. The water was contaminated with radioactive material. The flow caused the pressure to decrease.
The pressure regulating valve should have closed but it didn't. The operators had no way of monitoring the valve and therefore did not know it remained open.
What happened on this day that was out of the ordinary? Was this event out of the ordinary is such a way that design had not accounted for the possibility?
Quote
Alarms went off. An auxiliary feedwater system should have started automatically but it did not. The auxiliary system was to provide emergency source of cooling water to the steam generators, however, critical valves in the system were left closed. Without this critical water supply, the boiling water in the steam generators would boil away completely. A rapid rise in temperature and pressure occurred in the reactor's cooling system.
A pressure-regulating valve opened to reduce pressure in the reactor and associated reactor systems
Steam began flowing from the valve through piping into a collecting tank in the basement of the reactor containment building. The water was contaminated with radioactive material. The flow caused the pressure to decrease.
The pressure regulating valve should have closed but it didn't. The operators had no way of monitoring the valve and therefore did not know it remained open.
What happened on this day that was out of the ordinary? Was this event out of the ordinary is such a way that design had not accounted for the possibility?
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M$1 Answer
Meltdown at Three Mile Island. Step by step of the catasthropic event that became the worst nuclear accident in America´s history.
http://www.youtube.com/watch?v=tpiR7mZ6I0k&feature=player_embedded
It all started in the pre-dawn hours of March 28, 1979, in the Three Mile Island nuclear plant near the city of Harrisburg, Pennsylvania. A simple plumbing breakdown occured, then a small valve opened to relieve pressure in the reactor, but unknown to the plant operators it malfunctioned and failed to close. This in turn caused cooling water to drain from the opened valve and the nuclear core began to overheat.
Confronted by contradictory readings the operators shot off the emergency water system that would have cooled the core. If the operators had not intervened shooting down the pumps, the plant would have saved itself. The designers of the plant taught on absolutely everything except the operator’s intervention in anyway.
So the operators taught they were saving the plant by cutting off the emergency water when in fact they were just sealing its fate. Within minutes the control room console went wild with hundreds of lights started flashing accompany by horns and sirens. The operators were so overwhelmed by the situation that they did not addressed on a real time basis, they were trying to catching up, prioritizing and hinting the most important alarms.
By early morning, the exposed part of the core was beginning to cook. Temperatures in the reactor were already reaching 4300 °F.... at 5200 °F Meltdown will start to occur. A scenario called: The China Syndrome.
The core could have turned into a molten white hot mass, it could have gone thru the concrete base of the plant and into the ground water which is immediately below the foundation of the plant, could have fracture the Earth instantly in all directions, and geysers of radioactive steam would have spouted into the air thru the parking lot. A cloud of death would have lofted north over the city of Harrisburg.
"The China Syndrome" is a phrase that comes from the idea that if the core of an atomic reactor melted down, "it would burn its way through to China".
http://www.animatedsoftware.com/hotwords/meltdown/Bpt_Post_19790331_p2.gif
Operators remained convinced that the core was covered and save. No one in the control room could see that Three Mile Island was racing to its meltdown. Most engineers did not believed it could happen. They had this mind set that believed in all the backup safety systems relying one on top of another, this make it difficult for people to realize that a severe damage may occur.
By 6:15 a.m. they got the alarm "Radiation" in the control room. Contaminated water from the open valve had leaked into an adjoining building; it was releasing radioactive gases throughout the plant. With radiation threatening to escape to surrounding communities, the supervisor of the plant declared the first general emergency ever to arise at a nuclear power plant in the US.
The radiation level inside the containment dome was reading 10.000 Rhems per hour, a dose so high, only minutes of exposure will be fatal.
Three Mile Island Nuclear plant.
http://www.ohiocitizen.org/campaigns/electric/2004/ph_three_mile_island500.jpg
http://www.youtube.com/watch?v=tpiR7mZ6I0k&feature=player_embedded
It all started in the pre-dawn hours of March 28, 1979, in the Three Mile Island nuclear plant near the city of Harrisburg, Pennsylvania. A simple plumbing breakdown occured, then a small valve opened to relieve pressure in the reactor, but unknown to the plant operators it malfunctioned and failed to close. This in turn caused cooling water to drain from the opened valve and the nuclear core began to overheat.
Confronted by contradictory readings the operators shot off the emergency water system that would have cooled the core. If the operators had not intervened shooting down the pumps, the plant would have saved itself. The designers of the plant taught on absolutely everything except the operator’s intervention in anyway.
So the operators taught they were saving the plant by cutting off the emergency water when in fact they were just sealing its fate. Within minutes the control room console went wild with hundreds of lights started flashing accompany by horns and sirens. The operators were so overwhelmed by the situation that they did not addressed on a real time basis, they were trying to catching up, prioritizing and hinting the most important alarms.
By early morning, the exposed part of the core was beginning to cook. Temperatures in the reactor were already reaching 4300 °F.... at 5200 °F Meltdown will start to occur. A scenario called: The China Syndrome.
The core could have turned into a molten white hot mass, it could have gone thru the concrete base of the plant and into the ground water which is immediately below the foundation of the plant, could have fracture the Earth instantly in all directions, and geysers of radioactive steam would have spouted into the air thru the parking lot. A cloud of death would have lofted north over the city of Harrisburg.
"The China Syndrome" is a phrase that comes from the idea that if the core of an atomic reactor melted down, "it would burn its way through to China".
Operators remained convinced that the core was covered and save. No one in the control room could see that Three Mile Island was racing to its meltdown. Most engineers did not believed it could happen. They had this mind set that believed in all the backup safety systems relying one on top of another, this make it difficult for people to realize that a severe damage may occur.
By 6:15 a.m. they got the alarm "Radiation" in the control room. Contaminated water from the open valve had leaked into an adjoining building; it was releasing radioactive gases throughout the plant. With radiation threatening to escape to surrounding communities, the supervisor of the plant declared the first general emergency ever to arise at a nuclear power plant in the US.
The radiation level inside the containment dome was reading 10.000 Rhems per hour, a dose so high, only minutes of exposure will be fatal.
Three Mile Island Nuclear plant.
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M$
How can you call it catastrophic when nothing actually happened - it was all "almosts!" No one was killed. There was no explosion. There was no massive leak sickening cities. Nothing newsworthy happened! Every few months people are killed mining coal.Oil refineries and storage areas blow up regularly. Yet here nothing of the sort happened except a shutdown of services and it's a catastrophe? A disaster? If that's the worst that's happened in the history of American nuclear power we need a lot more nuclear power plants!
Reactor #2, is the second cilindrical building in the center of the image. Reactor #1 in the foreground, Reactor #2 behind it.
Some 16 hours after the incident first began; they realized it they should have opened the cooling water system since the beginning, so they proceeded and did it. Saving the reactor and preventing a meltdown.
I believe they closed down TMI reactor #2 after the incident and proceeded to dismantled it in the following years.
I think what they did after the frenetic pace attained during the early atomic years during the 50´s was to jump from prototypes and test reactors, straight to juggernaut nuclear plants. There was nothing in between. This seemed to be the real problem. The US jumped into the big league and left nothing behind to compare or test against.
Therefore, nuclear plants were built with multitude of redundant safety systems... but they took the human factor away of the equation. In the TMI incident that was exactly what happened. Human input altered things in what should have been a zero error-auto-shot down safety system.
---Quote---
As a result of the TMI-2 incident, nuclear reactor operator training has been improved. Before the incident it focused on diagnosing the underlying problem; afterward, it focused on reacting to the emergency by going through a standardized checklist to ensure that the core is receiving enough coolant under sufficient pressure.
---/Quote---
http://en.wikipedia.org/wiki/Three_Mile_Island_accident
Very Dramatic
I'm amazing the hydrogen didn't ignite, at the top of the reactor, produced by the zirconium and water.
How did nuclear plant design change after TMI?
The accident was significant.
Quote from TMI 25 years later
After the alarms started to sound critical valves in the system were left closed. Without the critical water supply, the boiling water in the steam would boil away completely. Both temperature and pressure would rise to dangerous levels. Controls rods dropped into place insulating the neutrons, but the designers did not consider no water in the reactor. Radioactive gases did ventilate to the outside world. Despite the shutdown of the fission process at the beginning of the accident, energy was still being released in the fuel by the decay of the fission products generated during the operation of the reactor. The rods eventual burst and melted, releasing large quanties of radioactivity into the cooling system. Rapid oxidation of the zirconium alloy from which the fuel rods tubes combined with high temperatures produced hydrogen. A pocket of hydrogen formed at the top of the reactor, but did not ignite. Radiation alarms were sounding at various points in the plant. TMI personnel discovered the radioactive water in the auxiliary building and stopped the pumping from the containment building.
While operators were restoring the cooling system, the relief valve continued to release hydrogen into the containment-building atmosphere. The hydrogen combined with the oxygen and this mixture ignited. The building did not breach under the pressure of the igniting hydrogen.
Catastrophic is the right word.