SL-1 - AbsoluteAstronomy.com

The SL-1, or Stationary Low-Power Reactor Number One, was a United States Army

United States Army

The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

experimental nuclear power reactor

Nuclear reactor

A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

which underwent a steam explosion

Steam explosion

A steam explosion is a violent boiling or flashing of water into steam, occurring when water is either superheated, rapidly heated by fine hot debris produced within it, or the interaction of molten metals A steam explosion (also called a littoral explosion, or fuel-coolant interaction, FCI) is a...

and meltdown

Nuclear meltdown

Nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. The term is not officially defined by the International Atomic Energy Agency or by the U.S. Nuclear Regulatory Commission...

on January 3, 1961, killing its three operators. The direct cause was the improper withdrawal of the central control rod

Control rod

A control rod is a rod made of chemical elements capable of absorbing many neutrons without fissioning themselves. They are used in nuclear reactors to control the rate of fission of uranium and plutonium...

, responsible for absorbing neutrons in the reactor core. The event is the only known fatal reactor accident in the United States. The accident released about 80 Ci of Iodine-131

Iodine-131

Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical...

, which was not considered significant due to its location in a remote desert of Idaho

Idaho

Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

. About 1100 Ci of fission products were released into the atmosphere.

The facility, located at the National Reactor Testing Station

Idaho National Laboratory

Idaho National Laboratory is an complex located in the high desert of eastern Idaho, between the town of Arco to the west and the cities of Idaho Falls and Blackfoot to the east. It lies within Butte, Bingham, Bonneville and Jefferson counties...

approximately 40 miles (64.4 km) west of Idaho Falls, Idaho

Idaho Falls, Idaho

Idaho Falls is a city in and the county seat of Bonneville County, Idaho, United States, and the largest city in Eastern Idaho. As of the 2010 census, the population of Idaho Falls was 56,813, with a metro population of 130,374....

, was part of the Army Nuclear Power Program

Army Nuclear Power Program

The Army Nuclear Power Program was a program of the United States Army to develop small pressurized water and boiling water nuclear power reactors to generate electrical and space-heating energy primarily at remote, relatively inaccessible sites. The ANPP had several notable accomplishments, but...

and was known as the Argonne

Argonne National Laboratory

Argonne National Laboratory is the first science and engineering research national laboratory in the United States, receiving this designation on July 1, 1946. It is the largest national laboratory by size and scope in the Midwest...

Low Power Reactor (ALPR) during its design and build phase. It was intended to provide electrical power and heat for small, remote military facilities, such as radar sites near the Arctic Circle

Arctic Circle

The Arctic Circle is one of the five major circles of latitude that mark maps of the Earth. For Epoch 2011, it is the parallel of latitude that runs north of the Equator....

, and those in the DEW Line

Distant Early Warning Line

The Distant Early Warning Line, also known as the DEW Line or Early Warning Line, was a system of radar stations in the far northern Arctic region of Canada, with additional stations along the North Coast and Aleutian Islands of Alaska, in addition to the Faroe Islands, Greenland, and Iceland...

. The design power was 3 MW (thermal

Thermal energy

Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

). Operating power was 200 kW electrical and 400 kW thermal for space heating. The core power level reached nearly 20 GW in just four milliseconds, precipitating the reactor accident and steam explosion.

The accident

On December 21, 1960, the reactor was shut down for maintenance, calibration of the instruments, installation of auxiliary instruments, and installation of 44 flux wires to monitor the neutron flux

Neutron flux

The neutron flux is a quantity used in reactor physics corresponding to the total length travelled by all neutrons per unit time and volume . The neutron fluence is defined as the neutron flux integrated over a certain time period....

levels in the reactor core. The wires were made of aluminum, and contained slugs of aluminum–cobalt

Cobalt

Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....

alloy

Alloy

An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

.

On January 3, 1961, the reactor was being prepared for restart after a shutdown of eleven days over the holidays. Maintenance procedures were in progress, which required the main central control rod to be manually withdrawn a few inches to reconnect it to its drive mechanism; at 9:01 p.m. this rod was suddenly withdrawn too far, causing SL-1 to go prompt critical

Prompt critical

In nuclear engineering, an assembly is prompt critical if for each nuclear fission event, one or more of the immediate or prompt neutrons released causes an additional fission event. This causes a rapid, exponential increase in the number of fission events...

instantly. In four milliseconds, the heat generated by the resulting enormous power surge caused water surrounding the core to begin to explosively vaporize. The water vapor caused a pressure wave to strike the top of the reactor vessel, causing water and steam to spray from the top of the vessel. This extreme form of water hammer

Water hammer

Water hammer is a pressure surge or wave resulting when a fluid in motion is forced to stop or change direction suddenly . Water hammer commonly occurs when a valve is closed suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe...

propelled control rods, shield plugs, and the entire reactor vessel upwards. A later investigation concluded that the 26000 pounds (11,793.4 kg) vessel had jumped 9 in 1 in (2.77 m) and the upper control rod drive mechanisms had struck the ceiling of the reactor building. The spray of water and steam knocked two of the men onto the floor, killing one and severely injuring another. One of the shield plugs on top of the reactor vessel impaled the third man through his groin and exited his shoulder, pinning him to the ceiling. The victims were Army Specialists

Specialist (rank)

Specialist is one of the four junior enlisted ranks in the U.S. Army, just above Private First Class and equivalent in pay grade to Corporal. Unlike Corporals, Specialists are not considered junior non-commissioned officers...

John A. Byrnes (age 27) and Richard Leroy McKinley (age 22), and Navy

United States Navy

The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

Electrician's Mate

Electrician's Mate is a United States Navy and United States Coast Guard occupational rating.Electrician's Mates stand watch on generators, switchboards, control equipment and electrical equipment; operate and perform organizational and intermediate maintenance on power and lighting circuits,...

Richard C. Legg (age 26). It was later established that Byrnes had lifted the rod and caused the excursion, Legg was standing on top of the reactor vessel and was impaled and pinned to the ceiling, and McKinley, who stood nearby, was later found alive by rescuers. All three men succumbed to injuries from physical trauma (not the radiation).

Reactor principles and events

Several "kinetic" factors impact the rate at which the power (heat) produced in a nuclear reactor responds to changes in the position of a control rod. Other features of the design govern how rapidly heat is transferred from the reactor fuel to the coolant.

The nuclear chain reaction

Nuclear chain reaction

A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes or the fusion of light isotopes...

has a positive feedback

Positive feedback

Positive feedback is a process in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system that responds to a perturbation in a way that reduces its effect is...

component whenever a critical mass is created; specifically, excess neutrons are produced for every fission. Inside a nuclear reactor, these excess neutrons must be controlled as long as a critical mass exists. The most significant and effective control mechanism is the use of control rods to absorb the excess neutrons. Other controls include the size and shape of the reactor and the presence of neutron reflector

Neutron reflector

A neutron reflector is any material that reflects neutrons. This refers to elastic scattering rather than to a specular reflection. The material may be graphite, beryllium, steel, and tungsten carbide, or other materials...

s in and around a core. Changing the amount of absorption or reflection of neutrons will affect neutron flux, and therefore, the power of the reactor.

One kinetics factor is the tendency of most light-water-moderated reactor

Light water reactor

The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...

(LWR) designs to have negative moderator

Neutron moderator

In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235....

temperature and void coefficients of reactivity. A negative reactivity coefficient means that as the water moderator heats up, molecules move farther apart (water expands and eventually boils) and neutrons are less likely to be slowed by collisions to energies favorable for inducing fission in the fuel. Because of these negative feedback

Negative feedback

Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...

mechanisms, most LWRs will naturally tend to decrease their rate of fissioning in response to additional heat produced within the reactor core. If enough heat is produced that water boils inside the core, fissions in that vicinity will drastically decrease.

However, when power output from the nuclear reaction increases rapidly, it may take longer for the water to heat up and boil than it does for the voids to cause the nuclear reactions to decrease. In such an event, reactor power can grow rapidly without any negative feedback from the expansion or boiling of the water, even if it is a mere 1 cm away. Dramatic heating will occur to the nuclear fuel, leading to melting and vaporization of the metals within the core. Rapid expansion, increases in pressure, and failure of core components may lead to the destruction of the nuclear reactor, as was the case with SL-1. As the energy of expansion and heat travel from the nuclear fuel to the water and the vessel, it becomes likely that the nuclear reaction will shut down, either from the lack of sufficient moderator or from the fuel expanding beyond the realm of a critical mass

Critical mass

A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The...

. In the post-accident analysis of SL-1, scientists determined that the two shutdown mechanisms were almost equally matched (see below).

Another relevant kinetics factor is the contribution of what are called delayed neutrons to the chain reaction in the core. Most neutrons (the prompt neutrons) are produced nearly instantaneously via fission. But a few — approximately 0.7 percent in a U-235

Uranium-235

- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...

-fueled reactor operating at steady-state — are produced through the relatively slow radioactive decay of certain fission products. Delayed production of a fraction of the neutrons is what allows reactor power changes to be controllable on a time scale that is amenable to humans and machinery.
In the case of an ejected control assembly, it is possible for the reactor to become critical

Critical mass

on the prompt neutrons alone (i.e. prompt critical

Prompt critical

). When the reactor is prompt critical, the time to double the power is on the order of 10⁻⁵ seconds. The duration necessary for temperature to follow the power level depends on the design of the reactor core. Typically, the coolant temperature lags behind the power by 3 to 5 seconds in a conventional LWR. In the SL-1 design it was about 6 ms before steam formation started.

SL-1 was designed with a main central control rod that was capable of producing a very large excess reactivity if it were completely removed (although this would violate safe operating procedure). In normal operation, control rods are withdrawn only enough to cause sufficient reactivity for a sustained nuclear reaction and power generation. In this accident, however, the reactivity addition was sufficient to take the reactor prompt critical within a time estimated at 3.6 milliseconds. That was too fast for the heat from the fuel to get through the aluminum cladding and boil enough water to fully stop the power growth in all parts of the core via negative moderator temperature and void feedback.

As a result, the final control method (i.e., dissipation of the prompt critical state) occurred by means of catastrophic core disassembly: destructive melting, vaporization, and consequent conventional explosive expansion of the parts of the reactor core where the greatest amount of power was being produced most quickly. It was estimated that this core heating and vaporization process happened in about 7.5 ms, before enough steam had been formed to shut down the reaction, beating the steam shutdown by a few milliseconds.

Events after the power excursion

There were no other people at the reactor site. The ending of the nuclear reaction was caused solely by the design of the reactor and the basic physics of heated water and core elements melting, separating the core elements and removing the moderator.

Heat sensors above the reactor set off an alarm at the central test site security facility at 9:01 p.m., the time of the accident. False alarms had occurred in the morning and afternoon that same day. The first response crew, of six firemen (Ken Dearolon Asst Chief, Mel Hess Lt., Bob Archer, Carl Johnson, Egon Lamprecht, & Vern Conlon), arrived nine minutes later, expecting another false alarm. and initially noticed nothing unusual, with only a little steam rising from the building, normal for the cold 6 °F (-14.4 °C) night. The control building appeared normal. The firefighters entered the reactor building and noticed a radiation warning light. Their radiation detectors jumped sharply to above their maximum range limit as they were climbing the stairs to SL-1's floor level. They were able to peer into the reactor room before withdrawing.

At 9:17 p.m., a health physicist

Health physics

Health physics is a field of science concerned with radiation physics and radiation biology with the goal of providing technical information and proper techniques regarding the safe use of ionizing radiation...

arrived. He and a fireman, both wearing air tanks and masks with positive pressure in the mask to force out any potential contaminants, approached the reactor building stairs. Their detectors read 25 röntgen

Röntgen

The roentgen is a unit of measurement for exposure to ionizing radiation , and is named after the German physicist Wilhelm Röntgen...

s per hour (R/hr) as they started up the stairs, and they withdrew.

Some minutes later, a health physics response team arrived with radiation meters capable of measuring gamma radiation

Gamma ray

Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...

up to 500 R/hr—and full-body protective clothing. One health physicist and two firefighters ascended the stairs and, from the top, could see damage in the reactor room. With the meter showing maximum scale readings, they withdrew rather than approach the reactor more closely and risk further exposure.

Around 10:30 p.m., the supervisor for the contractor running the site (Combustion Engineering

Combustion Engineering

Combustion Engineering was an American engineering firm and leading firm in the development of power systems in the United States with approximately 30,000 employees in about a dozen states at its peak. Headquartered in Stamford, Connecticut, C-E owned over two dozen other companies including...

) and the chief health physicist arrived. They entered the reactor building and found two mutilated men soaked with water: one clearly dead (Byrnes), the other moving slightly (McKinley) and moaning. With one entry per person and a 1 minute limit, a team of 5 men with stretchers recovered the operator who was still breathing; he did not regain consciousness and died of his head injury at about 11 p.m. Even stripped, his body was so contaminated that it was emitting about 500 R/hr. The third man was discovered at about 10:38 p.m., impaled to the ceiling. With all potential survivors now recovered, safety of rescuers took precedence and work was slowed to protect them.

On the night of January 4, a team of six volunteers used a plan involving teams of two to recover the body of Byrnes. Radioactive gold ¹⁹⁸Au

Isotopes of gold

Gold has one stable isotope, 197Au, and 36 radioisotopes with 195Au being the most stable with a half-life of 186 days.Gold is currently considered the heaviest Monoisotopic element .Gold has been proposed as a material for creating a salted nuclear weapon Gold (Au) has one stable isotope, 197Au,...

from the man's gold watch buckle and copper ⁶⁴Cu

Copper-64

Copper-64 is a radioactive nuclide of copper which has unique decay properties making it useful in nuclear medicine for both imaging and therapy.-Properties:...

from a screw in a cigarette lighter subsequently proved that the reactor had indeed gone prompt critical. Up until the recovery of radioisotopes of uranium, fission products, and the radioactive isotopes from the men's belongings, scientists had doubted that a nuclear excursion had occurred, thinking it inherently safe. These findings ruled out early speculations that a chemical explosion caused the accident.

The third man was discovered last because he was pinned to the ceiling above the reactor by a shield plug and not easily recognizable. On January 9, in relays of two at a time, a team of ten men, allowed no more than 65 seconds exposure each, used sharp hooks on the end of long poles to pull Legg's body free of the shield plug, dropping it onto a 5 feet (1.5 m) by 20 feet (6.1 m) stretcher attached to a crane.

The bodies of all three were buried in lead-lined caskets sealed with concrete and placed in metal vaults with a concrete cover. Some highly radioactive body parts were buried in the Idaho desert as radioactive waste. Army Specialist Richard Leroy McKinley is buried in section 31 of Arlington National Cemetery

Arlington National Cemetery

Arlington National Cemetery in Arlington County, Virginia, is a military cemetery in the United States of America, established during the American Civil War on the grounds of Arlington House, formerly the estate of the family of Confederate general Robert E. Lee's wife Mary Anna Lee, a great...

Cause

One of the required maintenance procedures called for the main control rod to be manually withdrawn approximately four inches in order to attach it to the automated control mechanism from which it had been disconnected. Post-accident calculations estimate that the main control rod was actually withdrawn approximately 26 inches, causing the reactor to go prompt critical

Prompt critical

, which resulted in the steam explosion. The fuel, portions of the fuel plates, and water surrounding the fuel plates vaporized in the extreme heat. The expansion caused by this heating process caused water hammer

Water hammer

as water was accelerated upwards toward the reactor vessel head, producing approximately 10000 pound per square inches (68,947,572.9 Pa) of pressure on the head of the reactor vessel when water struck the head at 160 feet per second (48.8 m/s).

The water hammer not only caused extreme physical damage and distortion of the reactor vessel, it also caused the shield plugs of the vessel to be ejected, one of which impaled Legg. The most surprising and unforeseen evidences of the steam explosion and water hammer were the impressions made on the ceiling above the reactor vessel when it jumped over 9 feet in the air before settling back into its prior location. The post-accident analysis also concluded that the reactor vessel was dry, since most of the water and steam had been either ejected immediately or evaporated due to the heat inside the reactor.

The most common theories proposed for the withdrawal of the rod so far are (1) sabotage or suicide by one of the operators, (2) a suicide-murder involving an affair with the wife of one of the other operators, (3) inadvertent withdrawal of the main control rod, or (4) an intentional attempt to "exercise" the rod (to make it travel more smoothly within its sheath). The maintenance logs do not address what the technicians were attempting to do, and thus the actual cause of the accident is unlikely to ever be known. The investigation took almost two years to complete.

Investigators analyzed the flux wires installed during the maintenance to determine the power output level. They also examined scratches on the central control rod. Using this data, they concluded that the central rod had been withdrawn 26.25 inches. The reactor would have been critical at 23 inches, and it took approximately 100 ms for the rod to travel the final 3.25 inches. Once this was calculated, experiments were conducted with an identically weighted mock control rod to determine whether it was possible or feasible for one or two men to have performed this. Experiments included a simulation of the possibility that the 84 pounds (38.1 kg) rod was stuck and one man freed it himself, reproducing the scenario that investigators considered the best explanation: Byrnes broke the control rod loose and withdrew it accidentally, killing all three men.

Consequences

The remains of the SL-1 reactor are now buried near the original site.

The accident caused this design to be abandoned and future reactors to be designed so that a single control rod removal would not have the ability to produce the very large excess reactivity which was possible with this design. Today this is known as the "one stuck rod" criterion and requires complete shutdown capability even with the most reactive rod stuck in the fully withdrawn position. The reduced excess reactivity limits the possible size and speed of the power surge.

The accident also showed that in a genuine, extreme accident, both the melting of the core and the water to steam conversion would shut down the nuclear reaction. This demonstrates in a real accident one aspect of inherent safety of the water-moderated design against the possibility of a nuclear explosion.

A nuclear explosion requires sufficient force to hold the reacting nuclear components together for a short but necessary time. This is achieved in a nuclear fission weapon by surrounding the core with a carefully engineered tamper (typically U-238

Uranium-238

Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...

), and a shaped explosive charge. This, along with other subsystems of the weapon keep the supercritical mass together long enough for sufficient generations of the fission reaction to produce the desired yield. Lacking these restraints to hold the vaporized core components together, the components of a reactor fly apart, as in this accident. The reaction ends, resulting in a steam explosion and a badly damaged reactor core, but not the type of explosion as would be achieved with a nuclear weapon

Nuclear weapon

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...

.

Even without an engineered containment building

Containment building

A containment building, in its most common usage, is a steel or reinforced concrete structure enclosing a nuclear reactor. It is designed, in any emergency, to contain the escape of radiation to a maximum pressure in the range of 60 to 200 psi...

like those used today, the SL-1 reactor building contained most of the radioactivity, though iodine-131

Iodine-131

Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical...

levels on plants during several days of monitoring reached fifty times background levels downwind.

Radiation exposure limits prior to the accident were 100 röntgen

Röntgen

The roentgen is a unit of measurement for exposure to ionizing radiation , and is named after the German physicist Wilhelm Röntgen...

s to save a life and 25 to save valuable property. During the response to the accident, 22 people received doses of 3 to 27 Röntgens full-body exposure. Removal of radioactive waste and disposal of the three bodies eventually exposed 790 people to harmful levels of radiation. In March 1962, the Atomic Energy Commission

United States Atomic Energy Commission

The United States Atomic Energy Commission was an agency of the United States government established after World War II by Congress to foster and control the peace time development of atomic science and technology. President Harry S...

awarded certificates of heroism to 32 participants in the response.

The documentation and procedures required for operating nuclear reactors expanded substantially, becoming far more formal as procedures which had previously taken two pages expanded to hundreds. Radiation meters were changed to allow higher ranges for emergency response activities.

After a pause for evaluation of procedures, the Army continued its use of reactors, operating the Mobile Low-Power Reactor (ML-1

ML-1

ML-1 was an experimental reactor built as part of the US Army Nuclear Power Program. Unlike the other seven reactors of this program, it did not use a steam turbine, but instead used a nitrogen coolant under several atmospheres of pressure to drive a closed cycle gas turbine.Though the concept of a...

), which started full power operation on February 28, 1963, becoming the smallest nuclear power plant on record to do so. This design was eventually abandoned after corrosion

Corrosion

Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

problems. While the tests had shown that nuclear power was likely to have lower total costs, the financial pressures of the Vietnam War

Vietnam War

The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...

caused the Army to favor lower initial costs and it stopped the development of its reactor program in 1965, although the existing reactors continued operating (MH-1A

MH-1A

thumb|right|300pxMH-1A was a pressurized water reactor and the first floating nuclear power station. One of a series of reactors in the US Army Nuclear Power Program, its designation stood for mobile, high power.-History:...

until 1977).

Movies and books

The U.S. Government produced a video about the accident for internal use in the 1960s. The video was subsequently released and can be viewed at The Internet Archive and YouTube

YouTube

YouTube is a video-sharing website, created by three former PayPal employees in February 2005, on which users can upload, view and share videos....

. SL-1 is the title of a 1983 movie, written and directed by Diane Orr and C. Larry Roberts, about the nuclear reactor explosion. Interviews with scientists, archival film, and contemporary footage, as well as slow-motion sequences, are used in the film. The events of the accident are also the subject of two books, one published in 2003, Idaho Falls: The untold story of America's first nuclear accident.

Another author, Todd Tucker, studied the accident and published a book detailing the historical aspects of nuclear reactor programs of the U.S. military branches. Tucker used the Freedom of Information Act

Freedom of Information Act (United States)

The Freedom of Information Act is a federal freedom of information law that allows for the full or partial disclosure of previously unreleased information and documents controlled by the United States government. The Act defines agency records subject to disclosure, outlines mandatory disclosure...

to obtain reports, including autopsies of the victims, writing in detail how each person died and how parts of their bodies were severed, analyzed, and buried as radioactive waste

Radioactive waste

Radioactive wastes are wastes that contain radioactive material. Radioactive wastes are usually by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine...

. The autopsies were performed by the same pathologist known for his work following the Cecil Kelley criticality accident

Cecil Kelley criticality accident

The Cecil Kelley criticality accident was a nuclear accident that took place on December 30, 1958, at the Los Alamos National Laboratory in Los Alamos, New Mexico, in the United States...

. Tucker explains the reasoning behind the autopsies and the severing of victims' body parts, one of which gave off 1,500 R/hour on contact. Because the SL-1 accident killed all three of the military operators on site, Tucker calls it "the deadliest nuclear reactor incident in U.S. history."

Cleanup

The site was cleaned in 1961 to 1962, removing the bulk of the contaminated debris and burying it. The massive cleanup operation included the dismantling and disposal of the reactor and building. A burial ground was constructed approximately 1,600 feet (488 m) northeast of the original site of the reactor. This was done to minimize radiation exposure to the public and site workers that would have resulted from transport of contaminated debris from SL-1 to the Radioactive-Waste Management Complex over 16 miles (26 km) of public highway. Original cleanup of the site took about 18 months. The entire reactor building, contaminated materials from nearby buildings, and soil and gravel contaminated during cleanup operations were disposed of in the burial ground. The majority of buried materials consist of soils and gravel.

Recovered portions of the reactor core, including the fuel and all other parts of the reactor that were important to the accident investigation, were taken to the INEL's Test Area North for study. After the accident investigation was complete, the reactor fuel was sent to the Idaho Chemical Processing Plant for
reprocessing. The reactor core minus the fuel, along with the other components sent to Test Area North for study, was eventually disposed of at the Radioactive Waste Management Complex.

The SL-1 burial ground consists of three excavations, in which a total volume of 99,000 cubic feet (2,800 cu. m) of contaminated material was deposited. The excavations were dug as close to basalt as the equipment used would allow and ranges from 8 to 14 feet (2.4 to 4.3 m) in depth. At least 2 feet (0.6 m) of clean backfill was placed over each excavation. Shallow mounds of soil over the excavations were added at the completion of cleanup activities in September 1962. The site and burial mound are collectively known as United States Environmental Protection Agency

United States Environmental Protection Agency

The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

Superfund

Superfund is the common name for the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 , a United States federal law designed to clean up sites contaminated with hazardous substances...

Operable Unit 5-05.

Numerous radiation surveys and cleanup of the surface of the burial ground and surrounding area have been performed in the years since the SL-1 accident. Aerial surveys were performed by EG&G Las Vegas in 1974, 1982, 1990, and 1993. The Radiological and Environmental Sciences Laboratory conducted gamma radiation
surveys every 3 to 4 years between 1973 and 1987 and every year between 1987 and 1994. Particle-picking at the site was performed in 1985 and 1993. Results from the surveys indicated that cesium-137 and its progeny (decay product) are the primary surface-soil contaminants. During a survey of surface soil in June 1994, "hot spots," areas of higher radioactivity, were found within the burial ground with activities ranging from 0.1 to 50 milliroentgen (mR)/hour. On November 17, 1994, the highest radiation reading measured at 2.5 feet (0.75 m) above the surface at the SL-1 burial ground was 0.5 mR/hour; local background radiation was 0.2 mR/hour. A 1995 assessment by the EPA recommended that a cap be placed over the burial mounds. The primary remedy for SL-1 was to be:
This remedial action was completed in 2000 and first reviewed by the EPA in 2003.

External links

INEEL Publication "Proving the Principle"
- Chapter 15 "The SL-1 Reactor" 9.5 MB PDF
- Chapter 16 "The Aftermath" 4.3 MB PDF
US Department of Energy Idaho Freedom of Information Act request archives, including eight documents on the SL-1 accident.
"SL-1 Reactor Accident on January 3, 1961, Interim Report", May 1961. From the above page. 15.5 MB PDF.
SL-1 Accident
Atomic Energy Insights - July 1996
ALPR summary page for this design.
Dr. George Voelz, M.D., one of two doctors at the site, oral history of the events.
KPVI, a television station in eastern Idaho, has posted a two-part story about the SL-1 accident. Some of the original video footage is included in the story and can be viewed online at KPVI.com
Runaway Reactor
SL-1 The Accident: Phases I and II U.S. Atomic Energy Commission Idaho Operations Office video (Youtube 1) (Youtube 2)
SL-1, 50 Years Later A document about the SL-1 facility today, 50 years after the accident.
Context IV: Nuclear Reactor Testing

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

The accident

Reactor principles and events

Events after the power excursion

Cause

Consequences

Movies and books

Cleanup

See also

External links