Three Mile Island - A Look Back
Mike Williams
March 23, 2006
By now, I?m sure most folks are familiar with the infamous ?Three-Mile-Island? nuclear disaster. A nuclear power plant located near Harrisburg Pennsylvania ,in which, the unthinkable happened on March 28, 1979. The incident was also considered a catalyst for the creation of yet another federal agency. What happened at 4:00 a.m. that morning? Here?s a detailed account of what happened and beyond.
At 4:00 a.m., workers at TMI were attempting to clear a blocked secondary water circulation system. It?s a system of water piping that is responsible for cooling the nuclear reactor. When the workers tried to clear the system, they started a chain of events in motion that eventually lead to the disaster. In trying to clear the piping, the workers instead blocked the flow of precious cooling water. The water that is already present in the system is no longer flowing or moving and begins to heat up and build pressure. The pilot-operated-relief-valve (PORV) opens automatically releasing steam. The temperature in the reactor continues to rise. Automatically, the control rods are thrust down into the reactor effectively stopping the nuclear fission reaction.
The PORV valve should now automatically close. Inside the control room, all indicators show that it has closed. The reality was that the valve is stuck open. A good comparison would be the ?thermostat? inside your automobile. It controls the water flowing throughout your car?s cooling system. On many occasions, I have had this valve stick closed or open. If it sticks in the closed position, your car will overheat and most likely, blow a hose or two. If it sticks open (especially in Winter), your car will not generate much heat and it will look as though your heater doesn?t work.
With the PORV valve stuck in the ?open? position, the steam lowers and water inside the cooling tank begins to boil violently. Water begins to seep out through the broken valve. The drop in pressure signals a ?leak? to the control system which then activates emergency water pumps to put more water into the cooling system. Still unaware that the PORV valve is stuck open, the operators see no need to add more water to the system and shut the emergency pumps down. This will prove to be a costly error. In the past, the emergency pumps had kicked on for no apparent reason. The operators didn?t see this as any different from any of the previous incidents.
From around 4:05 a.m. to about 6:00 a.m., the water inside the reactors cooling system is boiling away. Latent radiation in the water from the previous months of continuous operation continues to keep the heat levels up. The nuclear core is becoming exposed as more water boils away. There is no direct level indicator for the operators who still have no idea that they are loosing valuable cooling water. In effect, they have no idea what?s happening.
Just after 6:00 a.m., the operators realize that the PORV valve ?might? be stuck open. The use a secondary valve to close the system. It takes them a full hour after closing the valve to also realize that the system may now be low on cooling water. By now, the control rods have melted due to open exposure. The operators do not know this and begin to inject cool water into the reactor. Because of the melted rods, the water has no immediate effect. Heat continues to rise.
The super-heated mass of water and nuclear materials begins to spill into the bottom cavity of the reactor. At the bottom, a five-inch thick steel plating is the only thing protecting the bottom of the reactor. Given enough time, the nuclear mass will eat its way through it.
The small miracle comes when the newly injected water begins to cool everything down. The nuclear mass never gets any further then the steel plating. The radiation levels around the reactor have risen to levels that require a declaration of a ?state of emergency.? A general declaration is slow in coming. By the evening hours of March 28th, radiation levels begin to fall. The people involved are still slow in realizing that a core meltdown has occurred.
By the evening of the next day, reality sets in and TMI begins to wonder whether or not radioactive steam has been released into the atmosphere. On Friday, fearing that radiation may have been leaked into the atmosphere, Governor Richard Thornburgh urges pregnant woman and young children to leave the area.Later that evening, the FDA begins to wake up the drug companies in a frantic search for potassium iodide tablets in case they?re needed. These tablets help prevent damage to the thyroid gland.
The real concern now switches to an alleged build-up of hydrogen gas which operators fear might cause the reactor to explode. With a melted core and the continuing separation of oxygen and hydrogen from the cooling water, the engineers believe that an explosion may be imminent. Leaks to the press suggest that an evacuation of 10 to 20 miles around TMI may be necessary.
On Sunday April 1st, President Jimmy Carter and his wife visit TMI in an effort to show the public that the nuclear danger has passed. The ?experts? now conclude that a hydrogen explosion is no longer possible. Crisis over.
I imagine an engineer in the wee morning hours clenching his fists and jumping up and down in the middle of the control room screaming, ?This is not supposed to be happening!? The reports we saw after this tragedy suggest that the control room operators were overworked, fatigued, and in some reports maybe even drunk. I?m not so sure about the drunk part but, it seems that logic and reason didn?t take over until later in the morning when fresh faces began to appear inside the control room.
Nuclear power wasn?t new to us at the time of this accident. The engineers had a few opportunities to control the situation but refused to believe that the real world and science don?t always agree. They made assumptions that later proved to be false.
Pennsylvania dodged the bullet back in 1978.
I, for one, am glad that my daughter does not have two heads.
At 4:00 a.m., workers at TMI were attempting to clear a blocked secondary water circulation system. It?s a system of water piping that is responsible for cooling the nuclear reactor. When the workers tried to clear the system, they started a chain of events in motion that eventually lead to the disaster. In trying to clear the piping, the workers instead blocked the flow of precious cooling water. The water that is already present in the system is no longer flowing or moving and begins to heat up and build pressure. The pilot-operated-relief-valve (PORV) opens automatically releasing steam. The temperature in the reactor continues to rise. Automatically, the control rods are thrust down into the reactor effectively stopping the nuclear fission reaction.
The PORV valve should now automatically close. Inside the control room, all indicators show that it has closed. The reality was that the valve is stuck open. A good comparison would be the ?thermostat? inside your automobile. It controls the water flowing throughout your car?s cooling system. On many occasions, I have had this valve stick closed or open. If it sticks in the closed position, your car will overheat and most likely, blow a hose or two. If it sticks open (especially in Winter), your car will not generate much heat and it will look as though your heater doesn?t work.
With the PORV valve stuck in the ?open? position, the steam lowers and water inside the cooling tank begins to boil violently. Water begins to seep out through the broken valve. The drop in pressure signals a ?leak? to the control system which then activates emergency water pumps to put more water into the cooling system. Still unaware that the PORV valve is stuck open, the operators see no need to add more water to the system and shut the emergency pumps down. This will prove to be a costly error. In the past, the emergency pumps had kicked on for no apparent reason. The operators didn?t see this as any different from any of the previous incidents.
From around 4:05 a.m. to about 6:00 a.m., the water inside the reactors cooling system is boiling away. Latent radiation in the water from the previous months of continuous operation continues to keep the heat levels up. The nuclear core is becoming exposed as more water boils away. There is no direct level indicator for the operators who still have no idea that they are loosing valuable cooling water. In effect, they have no idea what?s happening.
Just after 6:00 a.m., the operators realize that the PORV valve ?might? be stuck open. The use a secondary valve to close the system. It takes them a full hour after closing the valve to also realize that the system may now be low on cooling water. By now, the control rods have melted due to open exposure. The operators do not know this and begin to inject cool water into the reactor. Because of the melted rods, the water has no immediate effect. Heat continues to rise.
The super-heated mass of water and nuclear materials begins to spill into the bottom cavity of the reactor. At the bottom, a five-inch thick steel plating is the only thing protecting the bottom of the reactor. Given enough time, the nuclear mass will eat its way through it.
The small miracle comes when the newly injected water begins to cool everything down. The nuclear mass never gets any further then the steel plating. The radiation levels around the reactor have risen to levels that require a declaration of a ?state of emergency.? A general declaration is slow in coming. By the evening hours of March 28th, radiation levels begin to fall. The people involved are still slow in realizing that a core meltdown has occurred.
By the evening of the next day, reality sets in and TMI begins to wonder whether or not radioactive steam has been released into the atmosphere. On Friday, fearing that radiation may have been leaked into the atmosphere, Governor Richard Thornburgh urges pregnant woman and young children to leave the area.Later that evening, the FDA begins to wake up the drug companies in a frantic search for potassium iodide tablets in case they?re needed. These tablets help prevent damage to the thyroid gland.
The real concern now switches to an alleged build-up of hydrogen gas which operators fear might cause the reactor to explode. With a melted core and the continuing separation of oxygen and hydrogen from the cooling water, the engineers believe that an explosion may be imminent. Leaks to the press suggest that an evacuation of 10 to 20 miles around TMI may be necessary.
On Sunday April 1st, President Jimmy Carter and his wife visit TMI in an effort to show the public that the nuclear danger has passed. The ?experts? now conclude that a hydrogen explosion is no longer possible. Crisis over.
I imagine an engineer in the wee morning hours clenching his fists and jumping up and down in the middle of the control room screaming, ?This is not supposed to be happening!? The reports we saw after this tragedy suggest that the control room operators were overworked, fatigued, and in some reports maybe even drunk. I?m not so sure about the drunk part but, it seems that logic and reason didn?t take over until later in the morning when fresh faces began to appear inside the control room.
Nuclear power wasn?t new to us at the time of this accident. The engineers had a few opportunities to control the situation but refused to believe that the real world and science don?t always agree. They made assumptions that later proved to be false.
Pennsylvania dodged the bullet back in 1978.
I, for one, am glad that my daughter does not have two heads.
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