Three Mile Island

TMI - Fact Sheet

Three Mile Island, Windscale and Chernobyl have much in common. Near meltdown and global disaster. Cars become more sophisticated as development continues, yet the car is still as lethal today as ten or twenty years ago. Not the technology itself, but the intrinsic dangers associated with that technology. It cannot be made safer. Fire is fire regardless of who, what, when or where it burns. Specious arguments are made in the attempts to mislead and 'talk up' the whole concept of nuclear energy. It's clean and zero carbon dioxide producing, but remains the most dangerous technology on the planet. Uncontrollable, but allegedly controllable though only like a restrained and inherently wild animal. Let a hungry tiger out of its cage and normal animal savagery will be unleashed. Control is an illusion, but only becomes the reality when things go very wrong.

Madness Of Nuclear Power

In 1979 a cooling malfunction caused part of the core to melt in the #2 reactor at Three Mile Island in USA and the reactor was destroyed. Some radioactive gas was released a couple of days after the accident, but not enough to cause any dose above background levels to local residents and there were allegedly no injuries or adverse health effects from the accident.

• The reactor's fuel core became uncovered and more than one third of the fuel melted.
• Inadequate instrumentation and training programs at the time hampered operators' ability to respond to the accident.
• The accident was accompanied by communications problems that led to conflicting information available to the public, contributing to the public's fears
• Radiation was released from the plant. The releases were not serious and were not health hazards. This was confirmed by thousands of environmental and other samples and measurements taken during the accident.
• The containment building worked as designed. Despite melting of about one-third of the fuel core, the reactor vessel itself maintained its integrity and contained the damaged fuel.

A meltdown happened and one third of the fuel 'melted'. The damage to the environment and health of the human population was allegedly minimal or non-existent since containment was effective as designed. Allegedly. However, the meltdown happened. Regardless of improving instrumentation, training or communications, the scenario could recur. The outcome would possibly not be so 'minor'. A virtual non-event. The potential has been seen to manifest in reality and the inherent dangers exposed. The fact that this took place so long ago (1979) does not invite complacency. The containment of one third of the fuel and no hazardous release was the alleged result. Difficult to reconcile given the nature of the accident. However, it has to be accepted that nobody was harmed or lived unaffected.
The Chernobyl disaster was in 1986, only seven years later. The mechanics of the event are irrelevant. The event happened and is the only criterion to consider.
The following not original:
The Three Mile Island power station is near Harrisburg, Pennsylvania in USA and had two pressurized water reactors (PWR), one of which was of 800 MWe (Megawatt electrical) and entered service in 1974 and remains one of the best-performing units in USA. Unit 2 (#2 reactor) was of 900 MWe and almost brand new. The accident to happened at 4 am on 28 March 1979 when the reactor was operating at 97% power. It involved a relatively minor malfunction in the secondary cooling circuit which caused the temperature in the primary coolant to rise. This in turn caused the reactor to shut down automatically. Shut down took about one second. At this point a relief valve failed to close, but instrumentation did not reveal the fact, and so much of the primary coolant drained away that the residual decay in the reactor core heatwas not removed. The core suffered severe damage as a result.

• The operators were unable to diagnose or respond properly to the unplanned automatic shutdown of the reactor. Deficient control room instrumentation and inadequate emergency response training proved to be root causes of the accident.

Within seconds of the shutdown, the pilot-operated relief valve (PORV) on the reactor cooling system opened, as designed, but about 10 seconds later it should have closed, yet did not, leaking vital reactor coolant water to the reactor coolant drain tank. The relief valve was assumed to have shut because instruments showed a "close" signal was sent to the valve, though no instrument feedback mechanism indicated the valve's actual position. High-pressure injection pumps automatically pushed replacement water into the reactor system, but as water and steam escaped through the relief valve, cooling water surged into the pressuriser, raising the water level in it.

• The pressuriser is a tank which is part of the primary reactor cooling system, maintaining proper pressure in the system. The relief valve is located on the pressuriser and in a PWR like TMI-2 (Three Mile Island #2 reactor), water in the primary cooling system around the core is kept under very high pressure to keep it from boiling.

The flow of replacement water was reduced in the attempt to lower the pressure: training indicated that the only dependable indication of the amount of cooling water in the system was the pressure. Because the pressuriser level was increasing, it was thought that the reactor system was too full of water. The flow was stopped in the attempt to prevent the pressuriser from filling with water. A rupture in the cooling system might otherwise be the result. Steam formed in the reactor primary cooling system and pumping a mixture of steam and water caused the reactor cooling pumps to vibrate. Severe vibrations could damage the pumps and made them unusable, so they were shut down, terminating forced cooling of the reactor core. The system was believed to be nearly full of water since the pressuriser level remained high. However, the reactor coolant water had boiled away and the reactor's fuel core was uncovered to become even hotter. The fuel rods were damaged and released radioactive material into the cooling water. A block valve between the relief valve and the pressuriser was closed at 6.22 am and this action stopped the loss of coolant water through the relief valve. Superheated steam and gases blocked the flow of water through the core cooling system.
More water was forced into the reactor system to condense steam bubbles in the belief that the high-pressure created by the injection of water into the reactor cooling system would collapse the steam bubbles, removing the blockage to allow restoration of the flow of cooling water. Attempts were then made to decrease the pressure in the reactor system allowing a low pressure cooling system to be used and emergency water supplies to be put into the system and by 7:50 pm on 28 March, restarting one reactor coolant pump was made possible to restore forced cooling of the reactor core. The steam had condensed so that the pump could run without severe vibrations. Radioactive gases from the reactor cooling system built up in the makeup tank in the auxiliary building and during March 29 and 30, a system of pipes and compressors was used to move the gas to waste gas decay tanks, but the compressors leaked and some radioactive gas was released into the environment.

When the reactor's core was uncovered (28th March), a high-temperature chemical reaction between water and the zircaloy metal tubes holding the nuclear fuel pellets had created hydrogen gas. A sudden rise in reactor building pressure shown by the control room instruments (28th March) indicated a hydrogen burn had occurred. Hydrogen gas also gathered at the top of the reactor vessel. Between 30th March -> 1st April the hydrogen gas "bubble" was removed by periodically opening the vent valve on the reactor cooling system pressuriser. Regulatory (NRC) officials believed for a while that the hydrogen bubble could explode, though such an explosion was never possible since there was not enough oxygen in the system.

• One month later on 27th April operators had established natural convection circulation of coolant and the reactor core was being cooled by the natural movement of water rather than by mechanical pumping. The plant was in cold shutdown.

When reviewing the TMI-2 accident, it is often in the context of what happened on Friday and Saturday, 30th and 31st March 1979, but only the TMI-2 accident-induced fear, stress and confusion came on those two days. The resultant atmosphere and the reasons for it are described well in the book Crisis Contained, The Department of Energy at Three Mile Island by Philip L Cantelon and Robert C. Williams (1982), an official history of the role of the US Department of Energy during the accident. The Friday appears to have become a turning point in the history of the accident because of two events: the sudden rise in reactor pressure shown by control room instruments on the Wednesday afternoon (the "hydrogen burn") which suggested a hydrogen explosion. On that day it became known to the Nuclear Regulatory Commission and the deliberate venting of radioactive gases from the plant on the following Friday morning produced a reading of 1,200 millirems (12 mSv) directly above the stack of the auxiliary building.
The significance of this was the series of misunderstandings caused, in part, by the problems of communication within various state and federal agencies, but because of confused telephone conversations between people uninformed about the plant's status, officials concluded that the 1,200 millirems (12 mSv) reading was an off-site reading.

• It was believed that another hydrogen explosion was possible and that the Nuclear Regulatory Commission had ordered evacuation: a meltdown was conceivable.

Erroneous information reported by the media generated a debate over evacuation and whether or not there were evacuation plans soon became academic. There was to be a weekend exodus based not on what was actually happening at Three Mile Island but on what government officials and the media imagined might happen. Confused communications (Friday) created the politics of fear. There were no unusually high readings, except for noble gases, and virtually no iodine. Readings were far below health limits.

• Yet a political storm was raging based on confusion and misinformation

The TMI-2 accident caused concerns about the possibility of radiation-induced health effects, principally cancer, in the area surrounding the plant. The Pennsylvania Department of Health, because of those concerns, for 18 years maintained a registry of more than 30,000 people who lived within five miles of Three Mile Island at the time of the accident. The state's registry was discontinued in mid 1997, without any evidence of 'unusual' health trends in the area.

• In a global environment where cancer is commonplace, what would constitute 'unusual' evidence?
  

More than a dozen major, independent health studies of the accident showed no evidence of any abnormal number of cancers around TMI years after the accident and 18 years is a long time to detect trends, though subtle changes are rarely noticed. The only detectable effect was allegedly psychological stress during and shortly after the accident. The studies found that the radiation releases during the accident were minimal, well below any levels that have been associated with health effects from radiation exposure. The average radiation dose to people living within 10 miles of the plant was 0.08 millisieverts, with no more than 1 millisievert to any single individual. The level of 0.08 mSv is about equal to a chest X-ray, and 1 mSv is about a third of the average background level of radiation received by U.S. residents in a year.

• A chest X-ray has exposure times of milliseconds. The 0.08 mSv is a continuous and unremitting exposure over a much longer period: days, weeks, months, years...
  

In June 1996 (17 years after the TMI-2 accident), Harrisburg U.S. District Court Judge Sylvia Rambo dismissed a class action lawsuit alleging that the accident caused health effects. The plaintiffs have appealed Judge Rambo's ruling. The appeal is before the U.S. Third Circuit Court of Appeals. However, in making her decision, Judge Rambo cited:

• Findings that exposure patterns projected by computer models of the releases compared so well with data from the TMI dosimeters (TLDs) available during the accident that the dosimeters probably were adequate to measure the releases.

• That the maximum offsite dose was, possibly, 100 millirem (1 mSv), and that projected fatal cancers were less than one.

• The plaintiffs' failure to prove their assertion that one or more unreported hydrogen "blowouts" in the reactor system caused one or more unreported radiation "spikes", producing a narrow yet highly concentrated plume of radioactive gases.

• Typically, it is the burden of the plaintiff to prove an assertion rather than the defendant to disprove that assertion.
  

Perception Of Conspiracy Theory

Judge Rambo concluded:

• "The parties to the instant action have had nearly two decades to muster evidence in support of their respective cases.... The paucity of proof alleged in support of Plaintiffs' case is manifest. The court has searched the record for any and all evidence which construed in a light most favorable to Plaintiffs creates a genuine issue of material fact warranting submission of their claims to a jury. This effort has been in vain."

More than a dozen major, independent studies have assessed the radiation releases and possible effects on the people and the environment around TMI since the 1979 accident at TMI-2. The most recent was a 13-year study on 32,000 people. None has found any adverse health effects such as cancers which might be linked to the accident.

The comparisons would be of a local environment with a much wider area (global dimensions) and would, of course, show nothing 'unusual'. Cancer is a modern and global phenomenon.

Why?

The cleanup of the damaged nuclear reactor system at TMI-2 took nearly 12 years and cost approximately US$973 million. The cleanup was uniquely challenging technically and radiologically.

Time and cost do not demonstrate effectiveness

Plant surfaces had to be decontaminated. Water used and stored during the cleanup had to be processed. And about 100 tonnes of damaged uranium fuel had to be removed from the reactor vessel: all allegedly without hazard to cleanup workers or the public. Removal of a 'damaged' radioactive fuel simply takes that fuel to another location.

Where?

It remains radioactive.

A cleanup plan was developed and carried out safely and successfully by a team of more than 1000 skilled workers. It began in August 1979, with the first shipments of accident-generated low-level radiological waste to Richland, Washington. In the cleanup's closing phases 12 years later (1991), final measurements were taken of the fuel remaining in inaccessible parts of the reactor vessel. Approximately one percent of the fuel and debris remains in the vessel. Also in 1991, the last remaining water was pumped from the TMI-2 reactor. The cleanup ended in December 1993, when Unit 2 (#2 reactor) received a license from the (NRC) to enter Post Defueling Monitored Storage (PDMS).

• Early in the cleanup, Unit 2 was completely severed from any connection to TMI Unit 1. TMI-2 today is in long-term monitored storage. No further use of the plant is anticipated. Ventilation and rainwater systems are monitored. Equipment necessary to keep the plant in safe long-term storage is maintained.

Defueling the TMI-2 reactor vessel was the heart of the cleanup. The damaged fuel remained underwater throughout the defueling. In October, 1985, after nearly six years of preparations, workers standing on a platform atop the reactor and manipulating long-handled tools began lifting the fuel into canisters that hung beneath the platform. In all, 342 fuel canisters were shipped safely for long-term storage at the Idaho National Laboratory, a program that was completed in April, 1990.
TMI-2 cleanup operations produced over 10.6 megalitres of accident-generated water that was processed, stored and ultimately evaporated safely.

• Evaporation should produce purified water, but is that totally free of any radioactive airborne contaminant? Radioactive water. Water exposed to radiation would in theory become radioactive. Distillation would not necessarily separate closely related isotopes of water.
  

TMI - Fact Sheet
Three Mile Island Unit 1 (TMI-1) has operated at very high levels of safety and reliability since the beginning (1985). Application of the lessons of the TMI-2 accident has been a key factor in the plant's 'outstanding' performance.
At the time of the TMI-2 accident, TMI-1 was shut down for refuelling. It was kept shut down during lengthy proceedings by the Nuclear Regulatory Commission. During the shutdown, the plant was modified and training and operating procedures were revamped in light of the lessons of TMI-2. When TMI-1 restarted in 1985 (October), General Public Utilities pledged that the plant would be operated safely and efficiently and would become a leader in the nuclear power industry. Words only, but those pledges have been kept: ie no further incidents is not proof that a pledge has been kept.

• A potentially dangerous dog even if kept under strict control can never be regarded as 'safe'
  

The plant's capability factor for 1987, including almost three months of a five-month refueling and maintenance outage, was 74.1 percent, compared to an industry average of 62 percent. (Capability factor refers to the amount of electricity generated compared to the plant's maximum capacity.)

• The accident to happened at 4 am on 28 March 1979 when the reactor was operating at 97% power.

• For 1989, the TMI-1 capability factor was 100.03 percent and the best of 357 nuclear power plants worldwide, according to Nucleonics Week.

• In 1990-91, TMI-1 operated 479 consecutive days, the longest operating run at that point in the history of US commercial nuclear power. It was named by the NRC as one of the four safest plants in the country during this period.

• By the end of 1994, TMI-1 was one of the first two plants in the history of US commercial nuclear power to achieve a three-year average capability factor of over 90% (TMI-1 had 94.3%).

• In 1998 (October), TMI workers completed two full years without a lost workday injury.

• Since its restart, TMI-1 has earned consistently high ratings in the NRC's program, Systematic Assessment of Licensee Performance (SALP).

• In 1999, TMI-1 was purchased by AmerGen, a new joint venture between British Energy and PECO Energy.

Training reforms are among the most significant outcomes of the TMI-2 accident. Training became centred on protecting a plant's cooling capacity, whatever the triggering problem might be. At TMI-2, the operators turned to a book of procedures to pick those that seemed to fit the event. Now operators are taken through a set of "yes-no" questions to ensure that, firstly, the reactor's fuel core remains covered. Secondly, the specific malfunction is determined: the "symptom-based" approach for responding to plant events.

• A style of training that gives operators a foundation for understanding both theoretical and practical aspects of plant operations underpins the approach.

The TMI-2 accident also led to the establishment of the Atlanta-based Institute of Nuclear Power Operations (INPO) and the National Academy for Nuclear Training. These two industry organisations have been effective in promoting excellence in the operation of nuclear plants and accrediting their training programs.

• INPO was formed in 1979 and the National Academy for Nuclear Training was established under its auspices in 1985. TMI's operator training program has passed three of its accreditation reviews since then.

• Training has gone well beyond button-pushing and communications and teamwork, emphasising effective interaction among crew members, are now part of TMI's training curriculum.

• Close to half of the operators' training is in a full-scale $18 million electronic simulator of the TMI control room and permits operators to learn (and be tested) on all kinds of accident scenarios.

Disciplines in training, operations and event reporting that grew from the lessons of the TMI-2 accident have made the nuclear power industry demonstrably safer and more reliable. Those trends have been both promoted and tracked by the INPO and to remain in good standing, a nuclear plant must meet the high INPO standards as well as the strict regulation of the US Nuclear Regulatory Commission. A key indicator is the graph of significant plant events, based on data compiled by the Nuclear Regulatory Commission (NRC). The number of significant events decreased from 2.38 per reactor unit (1985) to 0.10 (1997). In terms of reliability, the median capability factor for nuclear plants (percentage of maximum energy that a plant is capable of generating) increased from 62.7 percent (1980) to almost 90 percent (2000). The goal was 87 percent for the year 2000.

Other indicators for US plants tracked by INPO and its world counterpart, the World Association of Nuclear Operators (WANO) are the unplanned capability loss factor, unplanned automatic scrams, safety system performance, thermal performance, fuel reliability, chemistry performance, collective radiation exposure, volume of solid radioactive waste and industrial safety accident rate. All have been reduced (substantially improved) from 1980.

• The reactor's fuel core became uncovered and more than one third of the fuel melted.

• Inadequate instrumentation and training programs at the time hampered operators' ability to respond to the accident.

• The accident was accompanied by communications problems that led to conflicting information available to the public, contributing to the public's fears

• Radiation was released from the plant. The releases were not serious and were not health hazards. This was confirmed by thousands of environmental and other samples and measurements taken during the accident.

• The containment building worked as designed. Despite melting of about one-third of the fuel core, the reactor vessel itself maintained its integrity and contained the damaged fuel.

However,

• There was no China Syndrome.

• There were no injuries or detectable health impacts from the accident, beyond the initial stress.

But,

• Applying the accident's lessons produced important, continuing improvement in the performance of all nuclear power plants.

• The accident fostered better understanding of fuel melting, including improbability of a China Syndrome meltdown breaching the reactor vessel or the containment building.

• Public confidence in nuclear energy, particularly in USA, declined sharply following the TMI accident. It was a major cause of the decline in nuclear construction through the 1980s and 1990s.

Related Links: Safety of nuclear power reactors

Sources:

GPU Nuclear Corporation, 10 briefing papers (1999).
NEI, Nuclear Energy Overview (8/5/00).