The Three Mile Island Incident

The partial meltdown of the second reactor at Three Mile Island was the closest that the United States has come to a nuclear disaster. It created a panic in the surrounding area and tested the response and recovery efforts of agencies that were not totally prepared for an incident of this type. Although it resulted in no injuries or deaths, this incident changed the way the country looked at nuclear power, but it also brought considerable change to the nuclear power industry.
Three Mile Island received its name from the length of the island on which it is located. This island sits in the middle of the Susquehanna River, about ten miles south of Harrisburg, the Pennsylvanian Capitol. Within a five mile radius, there is a population of around 38,000 people, and 636,000 people within 20 miles. The majority of the people who live around Three Mile Island were in support of the reactors. They held a conservative view, both social and political on the world. They welcomed the jobs and tax cuts that the power plant would bring to their area. There were some who were against the power plant, but their anti-nuclear efforts were largely unnoticed by the general public.
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On February 15th, 1974, the plant began its licensing process to open up its second reactor, TMI-2. On February 8th, 1978 the Nuclear Regulatory Commission gave TMI-2 its operating license. This license required the reactor to undergo tests and safety checks before it would be able to operate at full capacity commercially. Meanwhile, opponents argued that airplanes entering and exiting a local airport were a direct threat on the facility; however the plant had been designed to withstand an impact from a large aircraft. While completing the tasks laid out in the operating license, TMI-2 ran into many problems. Before the plant had even started a reaction to create power, a cooling pump had failed. The reactor had experienced many cooling pump, valve and emergency system failures. Some of these failures were serious enough to trip or scram the reactor. This means that the whole reactor was shut down because of a malfunction. This happened at least twenty times, but the scrams were not seen as unusual, because the reactor was only in its testing phase. During TMI-2’s testing phases, it was offline 71% of the time. This was below average, compared to other reactors, but the Nuclear Regulatory Commission saw TMI-2’s progress as satisfactory. In September of 1978 TMI-2 produced power for the electrical grid for the first time, and on December 30th, 1978, it began commercial operation at 80% capacity. Only several months after TMI-2 had begun operation, it would undergo the worst nuclear accident in the United States.
The incident began early on the morning on March 28th, 1979. The reactor was operating at 97% capacity and producing close to its maximum power output of nine hundred megawatts. Operation was normal until 4:00 am when a water pump in the condensate polishing system failed. The condensate polishing system purifies the steam after it condenses back into liquid, after driving the steam turbines. A valve that would have let the water flow around the failed pump failed to open; this created a chain reaction that stopped the turbines, effectively shutting down the plant. The reactor then scrammed, by lowering the control rods into the core. The reaction had now been stopped. The reaction was no longer producing any heat, but residual heat was still a problem. The problem was made worse, when an important valve, called the pilot-operated relief valve was stuck open. This valve allowed coolant from the core to escape. This valve opened after the first water pumps failed, to regulate the pressure in the coolant system, but it had failed to close afterwards. The failure of this valve would be the single cause behind the Three Mile Island incident.
After the first pump failed, the control room lit up with lights and sirens. The control panel lit up with warning lights; however the control panel gave the operators little useful information about what was actually happening to the reactor. The panel told them what was malfunctioning but not the causes behind them. The control panel had no light that indicated that the pilot-operated relief valve was open. There was a light that gave a read out of the pressure of the reactor coolant drain tank; this is where the coolant that was escaping from the pilot-operated relief valve drained to. But this indicator light was on the opposite side of the control panel. The control panel was not well designed to give the operators quick access to vital information that they needed to assess a situation. The control panel gave them no signs of the true problem that was occurring, which was a “loss of coolant accident”. The core was losing coolant and was nearing what was called a core “uncovery” which is where the core loses coolant and is not entirely covered. Another problem with the control panel was that there was no way to actually know how much coolant was in the core. There was no coolant gauge; the amount of coolant was judged by the pressure in the pressurizer. Because the water which was escaping through the pilot-operated relief valve was also flowing through the pressurizer, which was creating pressure, there was no reason for the operators to believe that the core was losing coolant. TMI-2.jpg
Several minutes after the first pump failed the ECCS or emergency core coolant system came online and began flooding the core with coolant. The ECCS was able to replenish the water that was escaping through the pilot-operated escape valve. However, the operators believed that the increase in water would fill the pressurizer with water, which would leave them with little control over the reactor, so they stopped the majority of the flow of water from the ECCS. Then they turned off the four main reactor water pumps. They did still did not realize the true problem, which was the loss of coolant in the reactor. The majority of the coolant now was steam and the core became partially uncovered. The ECCS could not provide enough coolant to offset the loss of coolant through the pilot-operated relief valve and the coolant pumps were not circulating water through the core. The temperature in the core was suspected to have reached over 4000 degrees Fahrenheit, which caused a partial meltdown in the TMI-2 reactor.
Two hours after the beginning of the incident, alarms notified the controllers of radiation in the control room and the containment building, which surrounds the reactor. Increasing radiation levels were also found in the auxiliary building and the coolant water in the primary cooling system. The coolant that had been escaping through the pilot-operated relief valve, which was contaminated, had overflowed its drain tank. The water then spilled on the floor, and was pumped into the auxiliary building by a sump pump. The water then overflowed in the drain tank in the auxiliary building as well. Radiation levels began to rise in both buildings because of the exposed radioactive water. Some of the radiation escaped into the surrounding atmosphere, through a ventilation stack at the top of the auxiliary building. Now the controllers were aware of how serious the situation had become. Until the radiation alarms had gone off, there had been no reason for them to suspect that their problems would become huge emergency. At 6:56am one of the plant supervisors declared a “site emergency”. This evacuated the containment and auxiliary building, prevented anyone from entering the facility and notified the Nuclear Regulatory Committee and the State of Pennsylvania. About fifteen minutes later Gary Miller, the station manager, issued a general emergency, because of new and higher radiation levels. Radiation levels were also taken outside of the plant, but no excess radiation were found across the river, and the levels on the island itself were only slightly higher than normal. The declaration of the site and general emergencies began a chain reaction of response efforts to try to effectively respond to the Three Mile Island meltdown.
The Pennsylvania Emergency Management Agency was notified just after 7:00am that morning. Emergency offices in the surrounding Dauphin, Lancaster, and York counties were then notified. The Bureau of Radiation Protection, which is part of the Department of Environmental Resources, was also contacted. A half hour later the Governor of Pennsylvania, Richard Thornburgh was notified of the accident. Around 7:45am the Nuclear Regulatory Committee was finally notified of the accident. The local Nuclear Regulatory Commission office contacted the control room at TMI-2. Little information about the situation was given to them, but they believed that the situation was dangerous enough to take direct action. The local office contacted the Nuclear Regulatory Commission headquarters and they activated the regional incident response center. The regional incident response center was kept in direct contact with the TMI-2 control room, and a task force of five staff members, were also sent to Three Mile Island. The response to the accident seemed effective, but in reality, the information that was sent through the different levels of response was unclear and the Nuclear Regulatory Commission had no “clearly defined roles and lines of authority”. The Nuclear Regulatory Commission was not prepared or designed to respond to a disaster. They only issued operating licenses and inspected power plants for safety. They did not have the authority to tell the controllers how to operate the plants, or what to do in an emergency. They simply created rules and provided recommendations. No single person was in charge of the response and there was no command structure, just different sub-agencies who collected data about the incident. Even the communication lines between the different levels in the Nuclear Regulatory Commission were weak. They had no dedicated phone lines and many times the phone lines would be busy. As one staff member stated, “The office had no speaker phone for group telephone calls. When a call came in from the plant or the Region I office, the receiver was placed on a chair and staff members gathered around to try to hear what was being reported.” This limited the flow and quality of information that could be transmitted. If the Nuclear Regulatory Commission had their own separate communication system, they would have been better prepared to respond to the incident. Communication is key during a during a disaster and this lack of communication was detrimental to the response effort by the Nuclear Regulatory Commission.
Now the Nuclear Regulatory Commission had to stabilize the core, as this was still the main problem at hand, besides the unreliable communication. In conjunction with the local power company, Metropolitan Edison, the Nuclear Regulatory Commission began devising ways to bring the core back under control. They still were not aware of the true problem and how serious it had become. Some controllers though that there might be a possibility that the core could be uncovered, the truth was that the core had been partially uncovered for several hours and that the uranium rods had already begun to melt. Cooling the core was essential, they knew that the core was overheating, but that turned out to be quite difficult, as most of the coolant in the core had turned to steam. The steam could not cool the core, so the operators tried to repressurize the core to try to condense the steam back to water. They injected water into the core, which covered the core, but it did not affect the super-heated steam. Next, they tried to depressurize the core in the hopes of activating a flood tank that was part of the ECCS (Emergency Core Cooling System). The flood tank released water into the core, but it flashed to steam as soon as it entered, creating more steam and uncovering the core yet again. At around 8:00 pm, it was determined that depressurizing the core was not working and they tried to repressurize it again. They were able start one of the core cooling pumps and heat was being drawn away from the reactor. Three Mile Island was now on its way to being stable after about sixteen hours.
The media response to the Three Mile Island incident was quite well carried out. They did not over exaggerate the situation. Walter Cronkite, who was the news reporter at the time, stated that the Three Mile Accident was “the first step in a nuclear nightmare, but as far as we know at this hour, no worse than that.” The Nuclear Regulatory Commission also had to deal with the spreading of rumors. There were many rumors, to stories of full county evacuations, and that leaked radiation had been measured as a far away as sixteen miles. The next morning many press conferences were held, where officials gave the information that they had to the public. The information that they had was not the most accurate, and it was later stated that the media gave the impression that the situation was not a serious as it turned out to be.
Later on an issue derived on whether or not there should be any evacuations. Rumors had been spreading, and people were becoming anxious. Many developed distrust with the authorities, and believed that they were hiding information about the radiation from them. Radio Stations began reporting rumors, that pregnant women and children should leave the area. The final authority regarding evacuations was left to Governor Thornburgh. He knew the risks of calling an evacuation as stated by him, “I had to weigh the potential risks of Three Mile Island against the proven hazards of moving people under panic conditions.” He was concerned for the people who would be vulnerable during an evacuation such as the elderly, hospitalized patients and other immobile persons. The risks to healthy people were also apparent as they could be injured in traffic accidents. Thornburgh thought deeply about this decision, because an evacuation had never been executed during a radiological disaster. The fear and misunderstanding of radiation would undermine any attempts by local officials to carry out a calm and peaceful evacuation. Thornburgh also looked at the long term effects, at the effect of small business, jobs and the local economy. The risks of an evacuation outweighed the threat posed from Three Mile Island, and Thornburgh decided not to order an evacuation. However, later after some discussion with the Chairman of the Nuclear Regulatory Committee he advised pregnant women and young children within five miles of Three Mile Island to leave the immediate area; he also closed several schools within the five mile area of the plant. By only having the most vulnerable evacuate, he mitigated the risk of a mass evacuation accompanied by mass panic.
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The Response effort by both the State and the Nuclear Regulatory Commission were not particularly successful. They were both not prepared to deal with a disaster of this type. The result of the Three Mile Island incident created many changes in the Nuclear Regulatory Commission and in the ways that it operated. Current nuclear plants were upgraded to new building standards, which included fire proofing, redundant cooling systems, new designs for critical individual components, such as pressure relief valves and electronic systems. The Nuclear Regulatory Commission also increased and improved its operator training, and redesigning the control panels to give operators useful data that can be used to identify and solve problems. Emergency management became a priority as well. Emergency drills became a required part of the nuclear licensing process, and state and local agencies now participate in drills with the Federal Emergency Management Agency (FEMA) and the Nuclear Regulatory Commission. It is also now required that inspectors live within close proximity to the plant that they work at so they can immediately respond to an emergency. These inspectors are now also trained in risk assessment, so that they can mitigate and prevent the risk from turning into a hazard. A totally new agency, the Institute of Nuclear Power Operations, was formed. They are responsible for evaluating the plants and training the operators. More radiation detecting equipment, both inside and outside of nuclear power plants was now required. Three Mile Island revolutionized not only the way the Nuclear Regulatory Commission responds and handles an incident, but how they prepare and mitigate against them.
Today the reactor at TMI-2 is permanently inactive and has been stripped of all its uranium fuel rods. The coolant system which held contaminated water has been cleaned up. The radioactive waste was sent off to be disposed and the building is being closely monitored. TMI-1 is still operational but will be decommissioned after its operating license expires in 2014. The cleanup took fourteen years to complete at an estimated cost of one billion dollars, which involved shipping tons or radioactive waste and decontamination of the entire building. The clean up was successful and the area is completely void of any radiation.
The incident at Three Mile Island was the worst nuclear accident that had occurred in the United States. However, luckily it was not a catastrophe, but a mere wake up call to the dangers of Nuclear Power. This incident changed America’s views on nuclear power, as anti-nuclear protests became larger and more common. However, the Three Mile Island incident did not affect the building of new nuclear reactors. Plants that were being built at the time of the incident were finished on schedule, and new plants were built to stricter building and safety codes. It could be said that radiation leak at TMI-2 saved the US nuclear industry. If Three Mile Island had resulted in a huge release of radiation that affected thousands across the country, the opposition to nuclear power could have possibly killed nuclear power in the country. However, the nature of this incident, allowed the Nuclear Regulatory Commission to adapt and mitigate against future risks of Nuclear Power, making it safer and more reliable.

Works Cited


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