Three Mile Island accident Totally Explained

Everything about Three Mile Island Accident totally explained

The Three Mile Island accident was the most significant accident in the history of the American commercial nuclear power generating industry. It resulted in the release of a significant amount of radioactivity, an estimated maximum of 13 million curies of noble gases (480 PBq), but under 20 curies (740 GBq) of the particularly hazardous iodine-131, to the environment. However, there are no immediate deaths or injuries to plant workers or members of the nearby community which can be attributed to the accident. Public reaction to the event was probably influenced by at least three factors: first; the release – a few weeks before the accident – of a popular movie called "The China Syndrome", concerning an accident at a nuclear reactor; secondly, what was felt to be a lack of official information in the initial phases of the accident; and lastly, many of the statements made by political and social activists long opposed to nuclear power. Whatever the sources of the local fear and outrage, public reaction to the event is judged by some epidemiologists to have induced stresses in the local population that could have caused adverse health effects.
   The accident began on Wednesday, March 28, 1979, and ultimately resulted in a partial core meltdown in Unit 2 of the nuclear power plant (a pressurized water reactor manufactured by Babcock & Wilcox) of the Three Mile Island Nuclear Generating Station in Dauphin County, Pennsylvania near Harrisburg. Jack Herbein, Metropolitan Edison's then Vice President for Power Generation initially and erroneously called the accident "a normal aberration." The scope and complexity of this reactor accident became clear over the course of five days, as a number of agencies at the local, state and federal levels tried to solve the problem and decide whether the on-going accident required a full emergency evacuation of the local community, if not the entire area to the west/southwest. In the end, the reactor was brought under control, although full details of the accident were not discovered until much later.
   Although 25,000 people lived within five miles (8 km) of the site at the time of the accident, no identifiable injuries due to radiation occurred, and a government report concluded that "There will either be no case of cancer or the number of cases will be so small that it'll never be possible to detect them. The same conclusion applies to the other possible health effects."
   The accident was followed by essentially a 100% cessation of nuclear construction in the US. The impact of news stories about the accident was no doubt a factor, but other factors were the availability of cheap natural gas, a transition away from manufacturing and toward importation of consumer products, and federal policies that tolerated air pollution in the interest of keeping coal-fired electricity cheap.

Three Mile Island reactor accident

Understanding pressurized water reactors

There are three major water/steam loops in most pressurized water reactors (PWR): the primary loop, the secondary loop, and the condenser feedwater (cooling tower) loop.
   The primary loop runs through the reactor. It consists of purified, demineralized water to which a small, variable amount of boron has been added for reactivity control. It is the primary thermal energy transport loop. The primary loop carries the thermal neutron fission heat energy from the fuel assemblies (the reactor's "core") to an area outside the reactor, where the energy can be more easily harnessed (via the secondary loop). This loop runs at a temperature far higher than the boiling point of water at standard atmospheric pressure, and must remain pressurized or the water will flash to steam, compromising cooling of the core. The water, which always remains in a liquid state, has two functions: ť (a) to moderate or slow neutrons so they can be more easily captured by uranium fuel

   (b) to transfer heat from the reactor.
   In this reactor design, water is used as the primary loop transport medium because it's cheap, has a high thermal transport efficiency, and actually contributes to fission reaction safety. If this primary loop water is lost, neutron moderation will stop and self sustaining fission in the reactor core will be halted. (This is, of course, not desirable because under operating (or recently shutdown) conditions, decay heat alone is sufficient to melt the fuel.)
   The secondary loop resembles the steam cycle in a conventional power plant. The feedwater pump moves cool water into the steam generator, a heat exchanger which uses heat from the primary loop to boil the water in the secondary loop. The resulting steam then spins a turbine that's connected to the electrical generator. Once its energy has been expended, the steam flows through a condenser, which is another type of heat exchanger that changes the steam back to feedwater and transfers the absorbed latent heat to the cooling tower water. The feedwater is then pumped back to the steam generator system and the process repeats.
   The cooling tower loop provides cooling water for the condenser of the secondary loop and other plant operational cooling needs. After being heated by absorbing waste heat from the generation process, the water is cooled by flowing through the cooling tower, which in most cases is a natural draft water-to-air heat exchanger. Water lost to evaporation in the cooling tower is replenished by water from the nearby river.

Accident description

The accident occurred in the TMI-2 reactor. Although the plant had two reactors, TMI-1 was shut down for refueling at the time of the accident. The accident began when the plant's main feedwater pumps in the secondary non-nuclear cooling system failed at exactly 4:00 a.m. EST on March 28, 1979. Coincidentally, this was, to-the-minute, the first anniversary of the unit's startup. The exact cause of the failure was never determined, although it was speculated that water entered a pneumatic air line that controlled the flow through a filter known as a condensate polisher. In fact, the NRC stated that it didn't need to know how the accident started since it could have been prevented at many points along the way. Because water was no longer flowing through the secondary loop, the steam generators no longer removed heat from the reactor. First the turbine, then the nuclear reactor, automatically shut down. Due to the loss of heat removal from the primary loop (the dry steam generators), the primary side pressure began to increase, which is normal and expected during shut down.
   To prevent primary side pressure from becoming excessive, the pilot-operated pressurizer relief valve (PORV), at the top of the pressurizer, opened automatically. The valve should have closed again when the excess pressure had been released, but it didn't do so. The indication to the plant's operators that the signal to close the valve had been sent was, in the absence of any indication to the contrary, taken by them to mean that the valve had closed. (A "positive feedback" lamp in the control room indicating the true position of the valve was eliminated in original construction to save time, but has been retrofitted onto all similar plants after the accident.) As a result of this design error, the PORV remained open, unnoticed by the operators for several hours, and caused the pressure to continue to decrease in the system. Cooling water poured out of the stuck-open valve at the top of the pressurizer and caused the core of the reactor to overheat.
   Meanwhile, another problem appeared elsewhere in the plant with the emergency feedwater system, which is the backup for the main feedwater system. Following the loss of the main feed pumps, three emergency feedwater pumps started automatically, but two valves on the emergency feedwater lines were closed, preventing the feedwater from reaching the steam generators. The emergency feedwater system had been tested 42 hours prior to the accident; and, as part of the test, these valves were closed. They should have been reopened at the end of the test, but on this occasion it appeared that the valves were not reopened, through either an administrative or human error. The President's Commission requested that the FBI investigate whether these valves were closed by an act of sabotage. The valves were discovered closed about eight minutes into the accident. Once they were reopened, emergency feedwater was restored to the steam generators.
   This lack of emergency feed water for eight minutes didn't have a significant effect on the outcome of the accident, but did add to the confusion faced by the operators.
   It was later found that about half the core had melted during the accident;

Health effects and epidemiology

The scientific community is largely agreed on the effects of the Three Mile Island accident. The consensus is that no member of the public was injured by the accident. "The average radiation dose to people living within ten miles of the plant was eight millirem, and no more than 100 millirem to any single individual. Eight millirem is about equal to a chest X-ray, and 100 millirem is about a third of the average background level of radiation received by US residents in a year." While some studies have suggested a link between lung cancer and offsite exposures, no study has found a conclusive link between low level exposure and cancer increases. A recent study has noted that the counties surrounding TMI have the highest radon concentrations in the United States and that this may be the cause of the increased lung cancer noted in the region (External Link

).
The dissenting view cites observations by locals to infer a massive radiation release from the plant . However, "to this day [late2004], Wing's article remains the only one to present original health data supporting a link between Three Mile Island radiation exposure and cancer". This camp also notes that hundreds of out-of-court settlements have been reached with alleged victims. However, a class action lawsuit alleging that the accident caused detrimental health effects was rejected by Harrisburg U.S. District Court Judge Sylvia Rambo. The appeal of the decision in front of U.S. Third Circuit Court of Appeals also failed.
In 1979, as Pennsylvania state secretary of health in the Thornburg administration, Gordon K MacLeod MD managed the health effects of the Three Mile Island nuclear accident. He criticized Pennsylvania's preparedness, in the event of a nuclear accident, at the time for not having potassium iodide in stock, which protects the thyroid gland in the event of radiation exposure, as well as for not having any physicians on Pennsylvania's equivalent to the Nuclear Regulatory Commission.

Aftermath

U.S. President Jimmy Carter ordered a full investigation of the TMI incident. The Pennsylvania House of Representatives conducted its own investigation, which focused on the need to improve evacuation procedures. House investigators also visited the Three Mile Island site, including the control room. Many of the instruments viewed were marked with "error tags," explaining how the instrument was supposed to work and how it actually worked.
   According to the IAEA, the Three Mile Island accident was a significant turning point in the global development of nuclear power . From 1963 to 1979, the number of reactors under construction globally increased every year except 1971 and 1978. However, following the event, the number of reactors under construction declined every year from 1980 to 1998.
   The 1979 TMI accident did not, however, initiate the demise of the U.S. nuclear power industry. As a result of post-oil-shock analysis and conclusions of overcapacity, 40 planned nuclear power plants had already been canceled between 1973 and 1979. No U.S. nuclear power plant had been authorized to begin construction since the year before TMI. Nonetheless, TMI added a significant impact on this demise: At the time of the TMI incident, 129 nuclear power plants had been approved; of those, only 53 (which were not already operating) were completed. Federal requirements became more stringent, local opposition became more strident, and construction times were significantly lengthened.
   The TMI accident also had a psychological effect on the nation. Before the accident, 70 percent of the general public approved of nuclear power. After it, support for nuclear power across the country fell to about 50 percent, where it remained for decades. Recently, public support for nuclear power has been on the rise, and the George W. Bush administration has been particularly supportive of nuclear power, encouraging power companies to begin considering plans for the first new nuclear reactors in the United States in decades.
   The TMI cleanup started in August 1979 and officially ended in December 1993, having cost around US$975 million. From 1985 to 1990 almost 100 tons of radioactive fuel were removed from the site. However, the contaminated cooling water that leaked into the containment building had seeped into the building's concrete, leaving the radioactive residue impossible to remove. TMI-2 had been online only three months, but now had a ruined reactor vessel and a containment building that was unsafe to walk in — it has since been permanently closed. Many similar Babcock and Wilcox reactors on order were canceled — in total, 51 American nuclear reactors were canceled from 1980 to 1984.
   In the end, a few simple water level gauges on the reactor vessel might have prevented the accident. The operators' focus on a single misleading indication, the level in the pressurizer, was a significant contributing factor to the meltdown. Rhetoric based on the movie is still used to debate for and against nuclear power.

Current Status

Today, the TMI-2 reactor is permanently shut down and defueled, with the reactor coolant system drained, the radioactive water decontaminated and evaporated, radioactive waste shipped off-site to an appropriate disposal site, reactor fuel and core debris shipped off-site to a Department of Energy facility, and the remainder of the site being monitored. The owner says it'll keep the facility in long-term, monitored storage until the operating license for the TMI-1 plant expires at which time both plants will be decommissioned. TMI-1's current license expires in 2014. On January 08, 2008, AmerGen Energy Corporation, the operator of TMI-1, submitted a license renewal application to the NRC. If the license is renewed, TMI-1's license will be extended to 2034.

Date	vent
July 1980	Approximately 43,000 curies of krypton were vented from the reactor building.
July 1980	The first manned entry into the reactor building took place.
Nov. 1980	An Advisory Panel for the Decontamination of TMI-2, composed of citizens, scientists, and State and local officials, held its first meeting in Harrisburg, PA.
July 1984	The reactor vessel head (top) was removed.
Oct. 1985	Defueling began.
July 1986	The off-site shipment of reactor core debris began.
Aug. 1988	GPU submitted a request for a proposal to amend the TMI-2 license to a "possession-only" license and to allow the facility to enter long-term monitoring storage.
Jan. 1990	Defueling was completed.
July 1990	GPU submitted its funding plan for placing $229 million in escrow for radiological decommissioning of the plant.
Jan. 1991	The evaporation of accident-generated water began.
April 1991	NRC published a notice of opportunity for a hearing on GPU's request for a license amendment.
Feb. 1992	NRC issued a safety evaluation report and granted the license amendment.
Aug. 1993	The processing of accident-generated water was completed involving 2.23 million gallons.
Sept. 1993	NRC issued a possession-only license.
Sept. 1993	The Advisory Panel for Decontamination of TMI-2 held its last meeting.
Dec. 1993	Post-Defueling Monitoring Storage began.

In popular media

Aerosmith recorded a song for their 1979 album Night in the Ruts, titled "Three Mile Smile", written about the accident. Bruce Springsteen's song "Roulette" was written about the accident, and the impact of the people affected by it. Bam Margera and "crew" went to a small island near Three Mile Island in the first season of Viva La Bam The song London Calling by The Clash references the accident in its lyrics. Alice Cooper recorded a song titled Nuclear Infected on his 1980 album Flush the Fashion, which mentions Three Mile Island and China syndrome. The titles and subjects on this album were actually headlines from The National Enquirer (External Link

). Midnight Oil recorded a song on their 1984 album Red Sails in the Sunset, entitled 'Harrisburg', an ominous and evocative warning about nuclear power. Electronic Music pioneers Kraftwerk, when rerecording their 1975 song "Radioactivity" ("Radioaktivität") for the 1991 album "The Mix", changed its lyrics to include Harrisburg as one of four nuclear disasters.
   In Isaac Asimov's novel Robots and Empire, Aurorans Kelden Amadiro and Levular Mandamus use a nuclear intensifier to speed up the natural radioactive decay process in the Earth's crust in an attempt to derail the Settler's colonization plans. Amadiro and Mandamus use Three Mile Island as their base, as it's an area on Earth that all Earth's people superstitiously avoid as an ill omened place, due to an ancient disaster that occurred there. The accident is referred to as one which forever turned the people of Earth from the use of fission reactors (the book was written some time before the Chernobyl accident).
   The New Jersey post-punk band Thursday, in their song War all the Time, made a reference to TMI.
   Finnish rock band Eppu Normaali recorded a song called Suomi-ilmiö in 1980. It is a sarcastic account of nuclear power and the first part of the lyrics goes something like this: ť Even though windows have to be closed in Harrisburg

   In Finland you can go without a care ť Harrisburg is on another planet

   That can't happen here ť Under the birch tree and the star

Jimmy Buffett refers to Three Mile Island in his song "Volcano," which he says, "I don't want to land on no Three Mile Island/Don't want to see my skin a-glow"
   Former professional football player Lyle Alzado was given the nickname "Three Mile Lyle" by his teammates because of his short fuse.
   The opening of Saint Seiya's prequel Saint Seiya Episode G by Masami Kurumada is set in Three Mile Island, showing the accident as caused by a renegade saint. The situation is eventually solved by gold saint Aiolia.
   Professional wrestler Bryan Clark portrayed a character by the name of Adam Bomb, who was billed as hailing from Three Mile Island. The character had come in contact with a minor dose of radiation, which caused him to gain great strength and caused his eyes to turn a strangely yellowish-green (or sometimes yellowish-orange) color. Sun Ra recorded "Nuclear War" in 1982. At the time of the accident he was living in the Germantown section of Philadelphia, about 100 miles away from TMI.
   In The Simpsons episode, King-Size Homer, Mr Burns congratulates Homer for turning a potential Chernobyl into a "mere Three Mile Island".
   English novelist Terry Pratchett once accidentally asked for Three Mile Island dressing in a restaurant. He noted "with great presence of mind, they brought Thousand Island Dressing and a bottle of chili sauce."
   The 1979 Saturday Night Live sketch "Pepsi Syndrome" is an allusion to the Three Mile Island accident.
   The cites that the incident was caused by someone attempting to extract energy from the Allspark.
   Folk singer Pat Dailey wrote a song depicting a meltdown at the Davis Bessie Nuclear Reactor near Toledo, Ohio with reference to "TMI".
   The popular restaurant Hooters has a flavor of sauce named Three Mile Island, one notch of intensity above "Hot".

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