Advisory Panel for the Decontamination of TMI-2: Group appointed by the governor to oversee the clean up process of Unit 2.

AmerGen Energy LLC: In December 1999, GPU sold TMI Unit-1 to AmerGen Energy LLC.

Alpha particle: A positively charged particle emitted by certain radioactive materials. Alpha particles can be stopped by a sheet of paper.

Atomic Safety and Licensing Board (ASLB): Conducts hearings for the NRC (Nuclear Regulatory Commission) and performs such other regulatory functions as the NRC authorizes.

Babcock & Wilcox : The company that built the Three Mile Island plants.

Background Radiation: Radiation from natural sources (cosmic rays, rocks, and from minerals inside the body). Normal background radiation for Americans is about 100 to 200 millirem per year, with the higher figure occurring at higher altitudes.

Boiling Water Reactor (BWR): boiled in the core; the resulting steam drives a turbine to generate electricity.

Beta particle: A negatively charged particle emitted from an atom during radioactive decay. A beta particle is an electron that has a mass equal to 1/1837 that of a proton. A beta particle can be stopped by an inch of wood or a thin sheet of aluminum.

British Energy of Edinburgh, Scotland: When TMI Unit-1 was sold to AmerGen Energy LLC, AmerGen Energy LLC was British Energy’s joint venture with PECO (now Exelon Corporation).

The “bubble” scare: A false rumor that a hydrogen “bubble” had formed in the reactor that could have potentially exploded.

Carlisle, Pennsylvania: Carlisle is located in the Cumberland Valley of central Pennsylvania, along the Appalachian Mountains, some 20 miles west of the capital city of Harrisburg. Dickinson College is located there.

Jimmy Carter: The (thirty-ninth) president of the United States at the time of the accident. President Carter had been a specialist in nuclear science while in the Navy

Chain Reaction: A self-sustaining series of events that occur when a neutron splits an atom releasing sufficient neutrons to cause many other atoms to split in the same way.

“The China Syndrome:” A Hollywood film depicting a melt-down at a nuclear plant (starring Jane Fonda, Michael Douglas and Jack Lemon); the film was screening in Harrisburg at the time of the emergency.

Chinese atmospheric nuclear weapons test: Beginning with its first test on 16 October 1964, China conducted a total of 45 nuclear weapon tests — 23 atmospheric and 22 underground — ranging in yield from about 1 kiloton to about 4 megatons.

Cladding: The outer covering, usually a zirconium alloy, of a nuclear fuel element. The cladding serves as a barrier by preventing the release of radioactivity into the coolant.

Cold Shut-down: Condition of a reactor when fission process has been halted and temperature in the core coolant has dropped below the boiling point of water.

Combustion Engineering: One of four companies that designed and constructed the reactors.

Condenser: Apparatus where steam which turns the turbines is cooled, and condensed to liquid state for return to steam generator.

Containment: Steel and reinforced concrete structure. that houses a reactor.

Control room: The operation center of a nuclear power plant where the entire plant can be monitored and controlled.

Cooling Tower: The structure where hot water in con- denser tubes is circulated for cooling and then returned to the condenser. Cooling towers are now common to most power plants, whether they use coal, oil or nuclear fuel to make steam. The four cooling towers at TMI are identical. Each is 372 feet high. When the units are operating at full power, 200,000 gallons of water per minute pass through each tower. The evaporative plume or cloud of water vapor varies from 3,000 to 5,000 gallons per minute. The water vapor from the cooling tower is NOT contaminated.

Cooling water: The portion of the plant system that LOOP transfers the heat in the secondary loop to the atmosphere (cooling towers) without the water in the two loops touching.

Core: The core is located in the reactor vessel. It contains the uranium fuel and water.

Walter Cronkite : Anchor of the CBS evening news at the time of the emergency. He was a much loved and trusted anchor whose voice of concern created great anxiety in the public. Many local residents felt that national news coverage was sensationalistic and counter-productive.

Curie: a measure of the rate at which the radioactive material changes, or decays. The official unit is one decay per second which is called a Becquerel (Bq). The older, more traditional unit, is the Curie, which is 37 billion decays per second.

D.C. District Court of Appeals: The United States Court of Appeals for the District of Columbia.

Decay Heat: The heat produced from the decay of radioactive atoms in a reactor. This process continues after the reactor has been shut down.

Decontamination: The removal of radioactive material.

Harold Denton: Sent by the NRC Denton took control of communication and organized federal government and industry communication with the public after the initial event. He was viewed by many as the hero of the emergency.

Department of Energy: The US Department of Energy’s mission is to advance the national economic and energy security; to promote scientific and technological innovation in support of the mission; and to ensure the enviormental clean up of the national nuclear weapons complex.

Dickinson College Archives: The Dickinson Archives and Special Collections carefully preserves and makes available to researchers various materials of a unique and valuable nature which require special care and handling. The department also serves as the primary archival repository for the official records of the college.

Dickinson College Community Studies Center: The Community Center of Dickinson College fosters inter-disciplinary, hands-on learning in the social sciences and humanities. It coordinates ongoing student and faculty research in American Studies, policy studies, education, history, economics, environmental science, psychology and sociology, and serves as a repository for taped interviews, surveys, videotapes and transcripts produced by students and faculty engaged in field work.

Dickinson Electronic Initiative in the Liberal Arts (DEILA): A “home” for existing and developing digital scholarly projects at Dickinson College.

Dose: The amount of radiation that a person has received, measured in millirems.

Dosimeter: A device which can be worn and used to measure the radiation a person receives over a period of time.

Edison Electric Institute (EEI): The EEI is a trade association representing the nation’s privately-owned electric utilities.

Electron: A subatomic particle with a negative electric charge and a mass 1/1837 that of a proton.

Emergency Core Cooling System: A series of backup safety systems designed to dump thousands of gallons of cooling water into the reactor in the event the normal core cooling system fails.

Emergency feed pump: A back-up to the feed pump when that pump fails.

Enriched Fuel: Uranium which has been modified by increasing the concentration of the fissionable isotope, uranium-235. Enriched fuel is more able to sustain a chain reaction and slightly enriched fuel is normally used as the fuel for a nuclear power plant.

EPICOR II: Special equipment for the decontamination of Unit 2.

First Energy of Akron Ohio: TMI Unit-2 (now inoperative) is owned by FirstEnergy but maintained by Exelon, the owner and operator of TMI-1.

Fuel Rods: Long, hollow rods, usually of a zirconium alloy, into which are stacked 200 to 240 pellets of uranium, each of which is approximately .6 inch long. The number of pellets is determined by the design of the reactor.

Fission Products: The atoms formed when uranium is split in a nuclear reactor. Fission products are usually radioactive.

Fission: The splitting or breaking apart of a heavy atom into two new atoms. When a heavy atom, such as uranium, is split, large amounts of energy and one or more neutrons are released.

Fuel Assemblies: Separate bundles of fuel rods. TMI Unit 1 reactor contains 177 fuel assemblies with 36,816 fuel rods. Of the 177 fuel assemblies, 69 contain control rods.

Fuel Pellets: Thimble-sized uranium oxide pellets. A modern reactor core may contain up to 10 million pellets.

Fuel Rods: Long, hollow tubes of zirconium metal that contain stacks of fuel pellets. There are 264 fuel rods in each fuel assembly.

Gamma radiation: The radiation that is most commonly released in radiological emergencies. Exposure to a significant amount over a short time span is what produces radiation sickness.

Gamma Rays: Penetrating electromagnetic radiation emitted in radioactive decay, similar to X-ray radiation.

General Electric: One of four companies that designed and constructed the reactors.

General Public Utilities (GPU): At the time of the Three Mile Island Unit-2 Accident in March of 1979, GPU was an electric utility holding company comprised of the following three operating companies: Jersey Central Power & Light Company (JCP&L), Pennsylvania Electric Company (Penelec), and Metropolitan Edison Company (Met-Ed).

General Public Utilities Nuclear Corporation (GPUN): In January, 1982 operation of Three Mile Island Units 1 and 2 was divested from Met-Ed and vested in GPUN– a newly created subsidiary of GPU – as a means to disassociate the current actions of the company from those at the time of the accident.

Half-life: Term used to describe the time rate at which half of a given quantity of a radioactive material decays into stable element(s).
Harrisburg, Pennsylvania: Capital city of Pennsylvania, north of the Three Mile Island nuclear plants.

Heat Enhancer: A device which transfers heat from one material, such as water or gas, to another substance with no direct contact between the two materials.

Harold W. Hartman Jr.: Former control room operator at TMI.

Dr. Joseph M. Hendrie: Chairman of the Nuclear Regulatory Commission at the time of the accident.

Jack Herbein: The public relations specialist who was handling communication with the public prior to the arrival of Harold Denton. He was seen as an untrustworthy informant by many.

Iodine-131: Iodine-129 and iodine-131 are produced by the fission of uranium atoms during operation of nuclear reactors and by plutonium (or uranium) in the detonation of nuclear weapons.

Isotope: Different forms of the same chemical element which are distinguished by having different numbers of neutrons in the nucleus. A single element may have many isotopes. For example, the three isotopes of hydrogen are protium, deuterium, and tritium.

Jersey Central Power & Light Company (JCP&L): JCP&L operated wholly in New Jersey during the time of the accident.

Kemeny and Rogovin: John Kemeny on behalf of the President of the United States and Mitchell Rogovin of the Nuclear Regulatory Commission conducted separate investigations of the TMI accident. Their research found that although the accident was initiated by equipment malfunctions, safety equipment operated properly to protect the public. The accident was made worse by human error and ineffective preparation.

Kilowatt: A unit of electric energy equal to 1,000 watts.

Kilowatt-Hour: A unit of energy consumption that equals 1,000 watts used for one hour. For example, ten 100-watt light bulbs burned for one hour use one kilowatt-hour of electricity.

Krypton gas: One of the products of uranium fission. About three times heavier than air, krypton is a noble gas that is colorless, odorless, and tasteless.

Lancaster, Pennsylvania: One of the largest cities threatened by the emergency, located south of Harrisburg near the Susquehanna River.

Roger Mattson: Was the director of the Division of Systems Safety within the Office of Nuclear Reactor Regulation (NRR) at the time of the accident.

Marinelli Beaker: a relatively large plastic beaker with an annular bottom slid over NaI crystal.


Megawatt: A unit of energy equal to 1,000 kilowatts (1 million watts).

Meltdown: A condition in which the fuel of a nuclear plant becomes so overheated that it melts and falls to the floor of the reactor vessel.

Metropolitan Edison Company (Met-Ed): Was the direct operator of both Unit one and Unit two plants during the time of the accident.

Middletown, Pennsylvania: Town directly east of Three Mile Island; technically the plant is within the boundaries of the Borough of Middletown.

Millirem: A measure of radiation. A millirem is one-thousandth of a rem (Roentgen), the basic measure of radiation. The annual average radiation exposure for U.S. residents is 228 millirem.

NaI Crystal: NaI is a kind of scintillation crystal. It is widely used in nuclear medicine, well logging, environmental monitoring, high energy physics and in many other applications.

Neutron: An uncharged particle with a mass nearly equal to the mass of a proton. Neutrons are the particles which sustain a chain reaction in a nuclear reactor.

Noble gasses: The chemical elements in group 18 (old-style Group 0) of the periodic table. This chemical series contains helium, neon, argon, krypton, xenon and radon.

Nuclear Reactor: The device in which a fission chain reaction can be initiated, maintained and controlled. Heat from the fission process is used to make steam to turn generators for producing electricity.

Nuclear Regulatory Commission (NRC): The U.S. Nuclear Regulatory Commission (NRC) is an independent agency established by the Energy Reorganization Act of 1974 to regulate civilian use of nuclear materials. NRC is headed by a five-member Commission.

Nucleus: Core or center of an atom containing protons and/or neutrons. Although the nucleus is only about 1 /10,000 of the diameter of an atom, it contains nearly all the mass of an atom.

Oyster Creek: Oyster Creek is a 636-megawatt nuclear station in Lacey township, a community of about 26,000 people in Ocean County, New Jersey. The plant is owned and operated by AmerGen Energy Co., a wholly owned Exelon company. Oyster Creek opened in 1969 and has the distinction of being America’s oldest commercial nuclear power plant.

The Patriot: Newspaper covering all of Pennsylvania.

PECO (now Exelon)/ Exelon Corporation: Exelon Corporation became the full owners of AmerGen in December 2003.

Pennsylvania Electric Company (Penelec): Penelec operated in Pennsylvania at the time of the accident, though did not directly operate the plant on TMI.

Pilot-operated relief valve (PORV): The purpose of the PORV is to relieve the reactor coolant system pressure increases.

Presidential Commission (Kemeny Commission): A Presidential Commission is a special task force ordained by the President to complete some special research or investigation. In 1979, President Carter appointed John Kemeny to chair the Presidential Commission (hence, why reffered to as the Kemeny Commission) to investigate the Three Mile Island accident.

Pressurized Water Reactor: The most common type of commercial pressurizer vessel designed to control pressure in the reactor vessel and main coolant system.

Primary Loop: The loop through which the reactor coolant circulates. Coolant is heated in the reactor and then pumped under pressure to the steam generator, or heat exchanger. There, the water in the secondary loop is flashed into steam, which turns the turbine.

Proton: A subatomic particle with a positive electric charge, and a mass 1,837 times that of an electron.

Radiation: Energy radiated or transmitted as rays, waves, in the form of particles.

Radioactive venting: Radioactivity released off-site through reactors from venting and evaporation of contaminated gases.

Radioactive xenon gas: Produced by uranium fission in nuclear reactors.

Radon progeny: Radon progeny is one of products in the radioactive decay series which originates with uranium. Radon is a gas which can diffuse out of the ground to mix with the air. As radon decays its progeny, which are not gases, can attach themselves to particulates in the air, and these particulates may be trapped in the lungs of people breathing the air. The result is a lung dose from alpha and beta radiation emitted by the radon progeny.

Reactions to the Reactor project: This was the informal title of the field work project that is represented in this web site.

Reactor vessel: The structure that contains the nuclear fuel that produces the heat that makes the plant operative.

Relief Valve: A valve designed to lift or open at a designated pressure to reduce excess pressure in the system.

Rems: Measure of radioactive emission.

Roentgen (R): The röntgen or roentgen (symbol R) is a unit of exposure to ionizing radiation (X or gamma rays), and is named after the physicist Wilhelm Röntgen.

Salvage archaeology: Rescue archaeology was a movement of the early 1970s, particularly in Britain which sought to lobby to help stop the loss of archaeological evidence, where it was threatened by building development work in the historic cities, and by agriculture. It is called Salvage archaeology in the United States.

Lieutenant Governor William Scranton Jr.: Served as the Republican lieutenant governor of the state of Pennsylvania from 1979 to 1987 in the administration of Governor Richard Thornburgh.

Secondary Loop: The loop through which steam circulates from steam generators to turbines, then through condenser and back in the form of water to the steam generator.

The Sentinel: Newspaper coverning Cumberland county.

Steam Generator: A piece of equipment within which heat is transferred from the primary loop to the secondary loop without the water of the two systems actually touching.

Victor Stello: Harold Denton’s second-in-command at TMI.

Susquehanna River: Three Mile Island is located in the Susquehanna river. The river flows south from Otsego Lake near Cooperstown, New York, through the northern and central ranges of the Appalachian Mountains in Pennsylvania. The island is just south of Harrisburg.

Edward Teller: Nuclear physicist, strong advocate of nuclear power, “father of the hydrogen bomb” and long-time government science advisor.

Three Mile Island: The island on which the nuclear plants (Three Mile Island Units 1 and 2) are located. Unit 2 has been inoperative since the accident.

Governor Richard Thornburgh: Former Pennsylvania Governor. He was in his first year of office in March 1979 when the nuclear accident at Three Mile Island occurred.

“Thornburgh plan” (July 1981): A comprehensive TMI cleanup cost- sharing plan that calls for a 50/50 split of the uninsured cleanup costs between national and local sources. This includes the GPU, the electric utility industry, remaining insurance proceeds, the
federal government and the state governments of Pennsylvania and New Jersey.

TMI: Acronym for Three Mile Island and a term used by local residents as a quick reference to the entire emergencyas in “I survived TMI . . . . I think.”

TMI Unit 1/Unit 2: Pressurized water reactors of TMI.

Turbie: The device which converts the heat energy in steam into electrical energy.

U-235: Uranium-235 is an isotope of uranium that differs from the element’s other common isotope, uranium-238, by its ability to cause a rapidly expanding fission chain reaction.

U-238: Uranium-238 is used as fuel for nuclear reactors.

Westinghouse Corp: One of four companies that designed and constructed the reactors.

Xenon: A colorless, very heavy, odorless, rare noble gas, xenon occurs in the earth’s atmosphere in trace amounts.

Zirconium: A lustrous gray-white, strong transition metal that resembles titanium, zirconium is obtained chiefly from zircon and is very corrosion resistant. Zirconium is primarily used in nuclear reactors for a neutron absorber and to make corrosion-resistant alloys.