Saturday, March 28, 2015

Today in American History: Three Mile Island Disaster 03/28/1979

Today in American History, The nuclear power plant located at Three Mile Island in Dauphin County, Pennsylvania suffered a partial nuclear meltdown, it was March 28, 1979.

When the first alarms began to sound at the Three Mile Island nuclear power plant at 4:11am on March 28th, 1979, the plant operators were still unaware of what was happening, and why it was happening.  Eleven hours earlier the plant operators had attempted to fix a blockage in one of the eight condensate polishers.  The condensate polishers are filters that clean the secondary loop water.  These filters exist to stop minerals and impurities in the water from accumulating in the steam generators that would increase corrosion in the system.  Generally speaking, these blockages are common and easily fixed, and were surely routine for the operators at this time.  But on March 27, 1979 when the operators forced the stuck resin out with compressed air, it failed.  So the operators tries to blow out the compressed air into the water in an attempt to clean the resin with clean water.  Unfortunately, a small amount of clean water got past the check valve that was stuck open and it found its way into an instrument air line.  This would eventually cause the feedwater pumps, condensate booster pimps and condensate pumps to stop functioning around 4:00am on March 19th, 1979.  This event would cause a turbine to trip in the cooling system.

Because the steam generators were no longer getting any feedwater, the heat and pressure builds up in the reactor cooling system.  This, in turn, caused the reactor to perform an emergency shutdown (called SCRAM).  Within eight seconds the control rods were inserted into the control reactor to stop the nuclear chain reaction.  At this point the reactor continues to generate heat from the decay process and because the steam is not being used by the turbine and is not being vented from the primary water loop.

But events of the day were playing against the operators at the nuclear plant at Three Mile Island.  Normally, if this were to occur the three auxiliary pumps would automatically kick in.  But, at 4:00am on March 29th, 1979 the TMI-1 reactor along with the auxiliary pumps were shut down for maintenance -- and thusly unavailable.  It is worth noting that in 1979 this was in violation of the National Regulatory Committee's rules that said a reactor must be shut down if all auxiliary feed pumps are offline for maintenance.  The NRC later singled this out as one of the key failures that caused the meltdown.

Nuclear Reactor Design at Three Mile Island
Because of the heat build up and inability for the system to release the pressure, the pilot-operated relief valve (PORV) at the top of the pressurizer opened automatically.  Once the excess pressure had been vented, the valve should have closed on its own and the power to the electric solenoid cut.  But on this day, the valve's mechanicals failed and it became stuck open.  With the valve stuck open, radioactive coolant water would flow freely out of the plant and ultimately be the mechanical cause of the partial meltdown that would follow.

But all of these events begs the question, why didn't the operators act on these events as they happened?  As is usually the case, a combination of human factors and mechanical/design flaws ultimately contributed to the disaster.  In the early morning hours of March 29, 1979, when the valve was open the light indicated as such.  Unfortunately, when the valve was supposed to close the system saw the events that would have closed it and turned off the indicator.  And the with the design being fundamentally flawed, the operators saw the light that indicated the valve had closed.  They had no idea that the valve was stuck open for hours.  But when things started to go wrong, the unlit PORV lamp caused the operators a great deal of confusion -- how could this be happening with the PORV closed?  What they were seeing wasn't consistent with the pressure being vented, and the valve being closed.  This was precious time that was lost in their attempt to rectify the situation by following false information.  In the end, the disaster was already occurring -- but the time lost made the end-result much worse.  It was not until the new shift of plant operators came in at 6:00AM that they were able to get past the assumptions being made by the operators on duty and begin to see things with a fresh set of eyes.  Almost immediately the stuck valve was identified -- but severe damage had already been done.  Looking back, the NRC cited that the operators lacked sufficient training to diagnose the issue -- they didn't know exactly how the PORV indicator worked, so the didn't understand why it might be giving them inaccurate information.  In addition, the temperature indicator in the PORV valve would have told them there was a problem (the new crew noticed it) however, it was not included as a "safety grade indicator" in their training and was located on the back of the desk -- out of the site-line of the operators.

With the PORV still open, the pressurizer relief tank that would normally collect the overflow from the PORV overfilled.  This is what caused the containment building sump pump to sound an alarm at 4:11am.  This, in addition to the higher than normal temperature in the PORV discharge line, plus unusually high containment temperatures and pressures were a clear indication that there was a loss-of-coolant event occurring.  As stated above, these indicators were not noticed, and the ones that were noticed were ignored because the PORV valve indicator said it was closed.  At 4:15am, the relief diaphragm in the pressurized relief tank ruptured and radioactive coolant began to leak into the containment building.  This caused that radioactive coolant to be pumped from the containment building sump to an auxiliary building -- which was outside the main containment unit -- until 4:39am when the sump pumps stopped.

The temperature continued to rise for almost 80 minutes causing the primary loop's four main reactor coolant pumps to begin to cavitate as the steam bubble and water mixture passed through them.  Only clean water is supposed to go through the coolant pumps.  The pumps were shut down, but it is believed that the steam bubble/water mixture caused the inability for natural water movement to occur.  But as the steam increased, less and less water was able to circulate.  A little over two hours after the initial malfunction and mishandling of the situation, the top of the reactor core was exposed to the heat and it caused a reaction to occur between the steam in the reactor core and the nuclear fuel rod cladding.  The combination of the exposed fuel rods and the damaged fuel pellets, which began releasing radioactive isotopes into the reactor coolant, produced hydrogen gas -- this is believed to have caused the small explosion that occurred in the containment building later in the afternoon.  However, by the time action was
End State of Reactor 2 at Three Mile Island
Showing Significant Damage
taken well after 6:00am, the radiation levels were 300 times safe levels in the reactor chamber.

It was not until 6:56am that a State of Emergency was declared at Three Mile Island -- and 7:27am that the plant manager declared a General State of Emergency in the area surrounding Three Mile Island.  Over three hours after the initial event.  Because of the confusion and lack of consistent information from within the plant, the White House wasn't notified until almost 10:00am when the NRC became involved -- however, the NRC had the same issues getting the correct information and using it to take action.

When the first line of containment is breached in a nuclear plant, it is possible that the fission reactions may escape into the environment.  This has happened in more than one case throughout the world.  And this happened at Three Mile Island.  What is different in this case is that it was discovered later that the operators allowed the radioactive material to not only be vented in the atmosphere, but also the water to be released into the Susquehanna River  --  increasing the impact by an unknown amount because it would now impact those who lived down-river from the plant.  This caused the areas radiation alarms to sound, and the EPA to become involved.  In the days and months following, there were conflicting evidence of radiation in the surrounding environment.  Some claimed there was minimal evidence of raised radioactive material -- and some as high as five times safe levels.

Twenty-eight houses after the incident, William Scranton (Lieutenant Governor of Pennsylvania) gave a press conference assuring the public that Metropolitan Edison (owner of Three Mile Island) had said the situation was under control.  However, later that same day, he gave another press conference and said the situation was "more complex than the company first led us to believe."  At that time, schools were closed, residents were urged to stay indoors and farmers were told to keep their animals under cover.  Shortly after this announcement, Governor Dick Thornburgh, based on the advice of the NRC, urged pregnant women and pre-school aged children within a five-mile radius of Three Mile Island to evacuate immediately.  Late in the afternoon on Friday, March 30th, this recommendation was expanded to a twenty mile radius.  Within three days of the 30th of March, only 140,000 people are estimated to have left the area.  Over 500,000 people within a twenty mile radius remained, and based on a survey conducted in late April over 98% of the population had returned to their homes within three weeks.  Ten years later, a survey conducted said that over 50% of the public was satisfied with the way the incident and later evacuations were handled by the local, state and federal government.  And in the same survey, Metropolitan Edison was almost universally panned for its handling of the disaster.

There were a number of investigations into the disaster, and President Jimmy Carter toured the plant on April 1st, 1979.  The investigations strongly criticized everyone involved in the plant, but essentially cleared the operators and management on-duty of any wrong doing.  They cited lapses in general quality assurance, lack of effective communication of important safety information from the top, inadequate operator training, poor upper management and complacency in standard operating procedure.  The heaviest criticism stated that "fundamental changes were necessary in the organization, procedures, practices and above all attitudes in the Nuclear Regulatory Commission."  The investigators went on to say that the operators were inappropriate but consistent with "operating procedures that they were required to follow, and our review and study of those indicates that the procedures were inadequate."  They also stated that the control room as "greatly inadequate for managing the incident."  But it fell short of making any statements regarding the safety and future of the nuclear industry as a whole.

TMI-Unit 2 was too badly damaged and contaminated to repair, and was closed.  It had only been online for 13 months at the time of the disaster.  Initially, the efforts focused on clean up and decontamination of the site.  The clean up began in 1985 and 91 tons of radioactive fuel was removed from the site.  This first clean up phase completed in 1990.  The material was shipped to the Department of Energy's National Engineering Lab for storage in Idaho.  However, the containment cooling water that leaked during the disaster had seeped into the concrete of the building, leaving radioactive residue that was impossible to clean up.  In 1988, the NRC announced that, although it was possible to further clean up the site, it was impractical and that they felt the contamination was "contained" enough for safe occupation of the site.  Further clean up was deferred until until the material further decayed.  The clean up effort cost over $2.4 billion dollars.

In ensuing years, John Gofman used independent studies to predict 333 excess cancer/leukemia deaths in the area related to the Three Mile Island incident.  A peer-reviews research article by Dr. Steven Wing has found that a "significant number" of cancer cases have occurred between 1979 and 1985 in the area that could be attributed to Three Mile Island.  In 2009, Dr. Wing stated that the local radiation levels increased by what is probably "thousands of times greater" than the NRC's initial estimates.  A study of Pennsylvania's Cancer Registry shows that the incidence of thyroid cancer in the counties down river of Three Mile Island were markedly increased, but the PCR did not draw an official link between these and Three Mile Island.

It is worth noting that this incident occurred only twelve days after the release of the movie, "The China Syndrome".  In the movie Kimberly Wells (played by Jane Fonda) and her cameraman Richard Adams (Michael Douglas) were taping a television series on nuclear power plants, and ended up filming a nuclear disaster in the process.  Art imitating life?  Or life imitating art?

Bruce has worked in educational technology for over 18 years and has implemented several 1:1/BYOD programs.  He also has served as a classroom teacher in Computer Science, History and English classes.  Bruce is the author of five books: Sands of TimeTowering Pines Volume One:Room 509The Star of ChristmasPhiladelphia Story: A Lance Carter Detective Novel and The Insider's Story: A Lance Carter Detective Novel.  Follow Bruce's Novel releases by subscribing to his FREE newsletter!

Be sure to check out Bruce's Allentown Education Examiner Page, his Twitter and his Facebook!

No comments:

Post a Comment