A container of uranium hexafluoride explodes at Oak Ridge. A steam pipe bursts, and the reaction of the UF6 with water produces hydrofluoric acid which kills Peter Bragg and Douglas Meigs and injures 3 others.
The Dragon Assembly at Los Alamos is the first fissile system designed to generate prompt power excursions. First operated on 18 January 1945, the assembly consists of a reconfigurable stack of plastic cubes containing enriched uranium hydride. Another slug of uranium is dropped through a hole in the center to give a burst of activity. In the final experiment, about 6x1015 fissions occur, damaging the core with heat. No one is injured and no active material is lost.
This is a Los Alamos experiment to determine the critical mass of uranium. It uses 35.4kg of 79.2%-enriched uranium metal in the form of half-inch cubes, stacked inside a plastic box. This assembly is placed in a tank which is then filled with water. The box is not watertight; water seeps in, causing a supercritical state. In the 5 to 10 seconds before it boils off, more than 3x1016 fissions occur. Three workers are irradiated.
Working at the Los Alamos Omega Site, Harry Daghlian accidentally drops a tungsten carbide brick onto a plutonium core, making the assembly go critical. He snatches the brick away, but not in time; he is fatally irradiated (estimated fission count: 1016) and dies on 15 September.
While showing some scientists visiting Los Alamos how to measure neutron activity from two half-spheres of plutonium, Canadian physicist Louis Slotin allows the two pieces to fall together. Like Daghlian, he reacts quickly, but not fast enough to avoid a fatal dose estimated at 1,000 rads. Death comes nine days later, on 30 May 1946. Being farther away, the seven observers are not so severely exposed; but all are sickened, and two die a few years later with symptoms of radiation poisoning.
At the Hanford Works, 3 tons of spent uranium fuel are released. The experiment is called "Green Run"; it aims at duplicating the meltdown of a Soviet reactor. Along with the radioactive fuel, 7,800 Curies of I-131 escape into the environment.
This Los Alamos accident occurs in a stainless steel tank holding 13.6 liters of uranyl nitrate. An operator is testing the drop times of new control rods. The solution goes critical when both rods are pulled, but the operator does not notice because monitoring instruments (except for a direct-reading thermometer) are turned off. Based on the thermometer reading, the operator receives a 2.5-rad dose from 4x1016 fissions.
Two physicists are working on top of the ZEEP reactor at Chalk River, Canada. A technician is monitoring the pumping of heavy water into the reactor. He has instructions to stop the pump well before the water gets near criticality level. However, when one of the physicists asks for a tool, the technician jimmies the pump control with a chip of wood so it will keep working. He delivers the tool and then gets involved with the work the physicists are doing. The reactor goes critical and scrams as it's designed to. The three all receive significant doses.
En route from Eielson AFB in Alaska to its home base at Carswell AFB, Texas, B-36 #44-92075 runs into wing icing and develops fires in multiple engines due to carburetor icing in the extreme cold. Twelve crew members bail out after jettisoning the single A-bomb on board (a Mark IV model with its depleted-uranium tamper but lacking the plutonium core.) The high explosives in the bomb detonate on impact with or over the water of Hecate Strait on the British Columbia coast. Years later, the wreckage of the plane is found on the slopes of Mount Kolaget, northeast of Prince Rupert, BC. The fates of the other five crewmen remain unknown, and parts of the story remain controversial.
A B-29 bomber crashes three minutes after taking off from Kirtland Air Force Base in New Mexico. A nuclear bomb with no detonators installed is on board. Its casing is destroyed and the high explosive burns in the fire, but the weapon does not go off.
Taking off from Fairfield-Suisun AFB, a USAF Boeing B-29-NR loses power in its number two engine. In accord with precautionary measures of the time, the nuclear weapon it carries lacks a fissile core. The plane lifts off, but the landing gear cannot be raised, increasing drag. The pilot circles back for an emergency landing, but the heavily laden bomber does not reach the runway.
Twelve occupants are killed in the crash; the other eight receive minor injuries. Twenty minutes after the crash, during firefighting efforts, the 10,000 pounds of high explosive in the bomb detonate. Another 180 people are killed or injured. Although the bomb is destroyed, radiological contamination of the site is negligible.
In the fall of 1950, a number of Mark IV "non-nuclear assemblies" (everything but the plutonium core) are secretly deployed at Goose Bay, Labrador. Canadian Prime Minister Louis St. Laurent grants permission for a six-week stay, but very few people in his government know about this. On 10 November, a B-50A bomber returning one of these bombs to the U.S. has engine trouble and cannot make it home with its cargo. Following standard procedure, the crew sets the bomb to self-destruct at 2,500 feet and jettisons it. The 5,000 pounds of high explosives go off as expected, scattering bits of depleted uranium over the St. Lawrence River near Rivière du Loup, Quebec. The Canadian government is not pleased.
At Los Alamos, an experiment to measure the critical distance between two masses of uranium is under way. The masses are suspended in a tank of water. Three redundant scram mechanisms are employed, one being to raise the masses out of the tank. Unexpected geometry of one source (its center of activity is near its lower end) and the fact that the masses are pulled together by water currents while being raised cause an 0.2-second criticality producing about 1017 fissions. No damage occurs and worker exposures are insignificant.
At the Hanford Works, an experiment to measure the critical mass of plutonium uses a tank holding an aqueous solution of plutonium nitrate with 1.15kg of plutonium. Criticality occurs when a cadmium control rod is withdrawn too rapidly while the tank is filling. The yield is at least 8x1016 fissions. Heat and pressure force some solution onto the floor of the lab, but it is decontaminated a few days later. No significant worker exposures occur.
Two independent calculations regarding an experiment at Los Alamos are both incorrect. Also, contrary to regulations, a graph of the data from previous runs with lower amounts of uranium has not been plotted. These errors lead to the experiment going critical with a yield of 1.5x1016 fissions. The remotely operated mechanism scrams the reaction as intended. No one is irradiated, and the area is not contaminated.
Evaluation of control-rod designs at Argonne National Labs near Chicago uses a light-water-moderated reactor assembly. Contrary to procedure, an attempt is made to remove the central control rod and replace it with a different design. Criticality results in a yield of 1.22x1017 fissions. The thermal power, estimated as 170 Megawatts, ruins the reactor core, but little active material is lost. Four workers receive significant exposures. The lab is "hot" for about a day, but later is easily decontaminated.
In the sixth year of operation of Canada's NRX research reactor in Chalk River, a complicated series of operator errors and safety system malfunctions leads to a massive power excursion which causes partial meltdown of the core. The accident floods the basement with a million gallons of cooling water carrying 10,000 Curies of long-lived radioisotopes. Despite a total estimated yield of 1.2x1020 fissions, worker exposures are apparently low.
A subsequent hydrogen explosion throws the four-ton gas-holder dome to its maximum height, 1.2m. The containment vessel is not breached. But since air is being used to cool some of the fuel rods, thousands of curies of fission products are released into the atmosphere, making this the first major reactor disaster. Lt. Jimmy Carter, then a nuclear engineer in the U.S. Navy, takes part in the cleanup. That involves pumping a million gallons of contaminated water out of the reactor building into shallow trenches near the Ottawa River, removing and burying the core, and installing a replacement. The NRX is back in service in one or two years.
Plutonium is being recovered from spent fuel rods at the Mayak Production Association in the Soviet Union. This operation involves many processing steps on the plutonium nitrate solution. On Sunday, 15 March, operators ignore several established procedures. The most significant violations are using vessels next to each other (which allows neutronic interactions) and exceeding the limit of 500 grams of solution per vessel. The operators transfer the contents of two vessels (#2 & #4) into a third (#18). Another factor is that vessel 18 already holds 5 liters of solution at the beginning of the shift — a transfer for which there is no log entry. Noticing vapor from the solution in vessel 18, and feeling its warmth, the operator there immediately reconnects the transfer hose. Some of the solution is pulled into a vacuum trap, ending the fission reaction.
The two operators, untrained in criticality safety, elect not to report the event. (Also, the facility has no criticality alarm systems.) The accident is not discovered until two days later, when the operator near vessel 18 gets sick.
His dose is estimated as 1,000 rads. He loses both legs, but lives 35 more years.
The criticality measurement table at the Sarov (Arzamas-16) facility in the southern Urals is designated FKBN. Its vertical piston is hydraulically operated and incorporates no fast-acting scram mechanism.
On 9 April, during the lunch hour, a single operator is working the apparatus alone in violation of buddy-system rules. He also places steel separators half as thick as called for by the experiment plan (5mm vs. 10 mm) on the lower half of the fissile mass. As the table raises this lower half to the upper, criticality occurs. The resulting heat melts a portion of the plutonium. The excursion sets off an alarm.
About 2 hours later, the operator and a supervisor examine the apparatus closely, receiving low doses of 1-2 rads. The yield of the excursion is about 1016 fissions. The active portion of the apparatus is shipped to the Mayak facility for further analysis and disposition. The remaining parts are clean enough for immediate re-use. However, the FKBN is replaced by a model with better safety features.
High levels of radiation are detected in Troy, NY after a rain. Some puddles measure nearly 3,000 times the current AEC exposure limit. The cause is found to be fallout from the Simon test in Nevada two days before.
Residents of St. George, UT report "an oddly metallic sort of taste in the air". A 1962 AEC report finds that "children living in St. George, Utah, may have received doses to the thyroid of radioiodine as high as 120 to 440 rads". It was fallout from the Nevada test of a 32-kT bomb that became known as "Dirty Harry".
The Lady Godiva reactor at Los Alamos is being set up for a scheduled prompt burst. Apparently too much uranium is inserted by error. The excursion yields 5.6x1016 fissions, about six times the expected value There is no contamination, but several mechanical supports require replacement. Insignificant exposures result since the experiment is operated from a distance of a quarter-mile.
During the early morning, the crew of the Lucky Dragon, a Japanese fishing boat in mid-Pacific, think they see the sun rising to the west of them. It is instead "Castle Bravo" — a 6-MT hydrogen bomb fired at Bikini Atoll, 85 miles away. Four hours later, white ash begins to fall like snow on the boat. Many crew members scoop it off the decks and into bags as souvenirs. By evening, all 23 crew members are sick. They are hospitalized in Japan, where one dies due to radiation-induced kidney failure.
The white flakes also fall on the 86 residents of Rongelap Atoll, closer to the test site, soon piling up half an inch deep. Similar fates befall the residents of progressively more distant atolls named Rongerik, Alininae, and Utirik. By the time they are evacuated 50 to 75 hours later, many are sickened. The first warning of radiation in the fallout is raised seven hours after the blast, when the ash reaches the U.S. personnel at the weather station on Rongerik. They are moved out within 30 hours. These atolls are part of the Marshall Islands, a trust territory for which the U.S. is responsible.
The incident causes a rift between Japan and the U.S., which has not warned other nations about the test. (A mitigating factor is that an overlooked reaction boosted the bomb's yield to about 15 MT and thus expanded the danger area.) The U.S. issued an apology and paid $2 million in compensation. The exclusion was widened for later tests.
A cylinder is being used at Oak Ridge for investigations into the critical properties of aqueous solutions of fissile elements. The cylinder contains a cadmium-clad inner cylinder which acts as a "poisoner": it absorbs neutrons, damping out the fission reaction. On this particular day, the cylinder holds 18.3 liters of highly enriched (93%) uranium fluorate, with more being added slowly. A power excursion of about 1017 fissions happens when the cadmium damper falls from its support, landing in a less effective position. Because of heavy shielding, insignificant exposures result. Contamination is slight; the lab resumes operation in three days.
At the National Reactor Testing Station near Idaho Falls, ID, the BORAX-I has been well-studied and is about to be dismantled. Its operators decide to run one more transient test: an overload which will melt about 4% of its fuel plates.
In the event, the power excursion and subsequent steam explosion completely destroy the core and rupture the tank surrounding it. Pieces of the tank are found 200 feet away. Because of the remote location, nothing else is damaged and no one is exposed to radiation.
Several weeks before sea trials of the USS Nautilus (SSN-571) begin, a small steam pipe bursts in her reactor room. There are no radiation releases and injuries are slight. However, the failure leads to the discovery that the wrong type of piping was used, revealing serious quality control problems.
EBR-1, the experimental breeder reactor at the National Reactor Testing Station, has operated for three years and met its objectives. A final study of "prompt positive power coefficient without coolant flow" is conducted. When power reaches 1 MW, the scram signal is given. Unfortunately the slow motor-driven system is activated by error instead of the fast-acting gravity-driven system. Later examination shows that half the core has melted and vaporized sodium-potassium eutectic has forced some of the highly reactive coolant into the reflector.
The source concludes its report with this optimistic note: "During this accident no one received more than trivial radiation from airborne fission products, and direct exposure was essentially zero." Public Citizen quotes a report that says: "The public is not made aware of this meltdown until Lewis Strauss, head of the Atomic Energy Commission, is confronted by the Wall Street Journal and has to admit his ignorance of the accident."
During investigation of reactor parameters at Oak Ridge, an unexpected prompt criticality occurs in a tank containing 27.7kg of U-235 in solution. The yield is 1.6x1017 fissions, and a quantity of solution is forced out of the cylinder. Scram systems activate, but it appears the reaction persists for several seconds longer. Analysis shows that a depth increment of 1mm can tip the balance in this configuration. This suggests that waves raised by the cadmium plate falling into the solution are the cause. The room requires extensive decontamination, and the apparatus is slightly damaged. 0.6 rem is the largest dose received.
En route to an overseas deployment, a B-47 from MacDill Air Force Base near Tampa, Florida fails to rendezvous with a KC-135 tanker over the Mediterranean Sea for its second refueling. The bomber, carrying two "nuclear capsules", is never seen again. Its last known position is over the mid-Atlantic; the exact location of the crash is unknown.
While docked at the shipyard for repair of damage due to snaring a fishing net on 22 April, the USS Nautilus (SSN-571) suffers a fire caused by a welder's torch. The Navy reports that the fire, the third to break out on the submarine, causes little damage.
Two explosions destroy a portion of Sylvania Electric Products' Metallurgy Atomic Research Center in Bayside, Queens, NY. Nine workers are injured.
A CDC document indicates that this facility was engaged in research on uranium and thorium powder metallurgy, and also investigated the health effects of beryllium and uranium powders in its main building until the AEC Medical Division required it to construct a separate laboratory for health studies. According to the CDC document, referenced below, the facility operated from 1947 through 1962 or 1965, the State of New York declared the site decontaminated of radioactivity in 1985, and condominiums were subsequently built on the site.
This accident occurs at Los Alamos in a machine having little inherent negative reactivity feedback. Uranium foils enriched to 93% were arranged in a honeycomb of aluminum tubes on a motorized cart. The total mas of U-235 was 58kg. As the cart slowly approached an identical stationary honeycomb, prompt criticality produced a burst yield of 3.2x1016 fissions.There was no damage and no contamination. Since the operators were a quarter-mile away, no one was exposed to radiation.
A U.S. B-47 practising landings at Lakenheath Air Base in Suffolk, England, skids into a bunker holding three Mark VI bombs. A secret cable to SAC commander Gen. Curtis LeMay from Gen. James Walsh, commander of U.S. 7th Airborne Division, reports that "The B-47 tore apart the igloo and knocked about three Mark Sixes. Aircraft then exploded, showering burning fuel over all. Crew perished. ... Preliminary exam by bomb disposal officer says a miracle that one Mark Six with exposed detonators sheared didn't go." Gen. Walsh refers to the risk of the bombs' high-explosive charges being set off by the fire, spreading radioactivity over the area.
A Defense Department description of the accident says "no capsules of nuclear materials were in the weapons or ... the building."
The experimental sodium-cooled reactor aboard USS Seawolf (SSN-575) suffers a failure during a full-power test while the new vessel is docked at Groton. Two cracks occur in its steam piping, as well as a leak in a superheater. Makeshift repairs allow the Seawolf to complete its sea trials by February 1957, but the Navy subsequently decides to discard the troublesome sodium-cooled reactor and thereafter uses only conventional reactor designs.
Soviet Quebec class M-256 sinks in the Baltic Sea after a fire starts in the closed-cycle diesel compartment and rages through the ship, destroying her structural integrity. Sources report that the captain and 35 to 40 crewmen are lost in the incident.
Soviet Quebec class M-200 Komsomolets collides with a Soviet destroyer, near Talinn, Estonia. A fire breaks out, fed by liquid oxygen. The submarine explodes and sinks, killing 28 crewmen. Only seven are saved. M-200 took part in the attempt to rescue the crew of M-256 two months earlier. Soviet seamen refer to Quebec-class boats as "cigarette lighters" because of the ease with which they catch fire.
In the second excursion involving the Lady Godiva reactor at Los Alamos, the criticality is thought to result from the proximity of a large mass of graphite and polyethylene that is moved close to the reactor to be irradiated by neutrons. The burst yield of 1.2x1017 fissions is equivalent to the energy in 1.7 lb of high explosive. But since most of the fission energy manifests as heat, damage to the apparatus matches that of just 0.024lb of HE. The operators are at safe remove; insignificant exposures result.
Using remote-control handling equipment in an isolation box, H. E. Northway, manager of the Houston plant of M. W. Kellogg Co., opens a can containing ten pellets of Iridium-192. He and another employee are in the room. They discover that two of the pellets are "powderized" but apparently do not report this fact to the AEC. Some of the dust escapes the box and at least one of the two employees becomes contaminated. Although the company is licensed by the AEC to encapsulate sources for radiographic cameras, the agency does not learn of the problem for five weeks.
The event is reported in the 13 May 1956 issue of Time (and reportedly by Look Magazine in 1961.) By then, at least eight private homes and seven automobiles have been contaminated. Only the two employees suffer radiation injuries, but press coverage leads to ostracism of plant workers in their community and widespread public fears of radioactivity.
During precipitation of uranyl oxalyte trihydrate at the Mayak Production Association in the Soviet Union, the automatically collected filtrate builds up to critical mass in a collecting vessel. Incorrect procedures, inadequate instrumentation, and lack of operator training contribute to this accident. When the operator notices gas building up in the vessel, and filtrate being ejected to the floor of the glovebox, he merely picks up the substance with his hands, returns it to the vessel, and goes on working. The reaction continues for ten minutes before sufficient solution is pushed from the vessel to stop it. Only when the operator sickens and a radiation control person is summoned is it discovered that a criticality accident had occurred. The operator receives an estimated 3,000-rad dose and dies 12 days later. As a result of the accident, procedures are improved and radiation monitoring gear is installed.
A bomber accidentally drops a 10-MT hydrogen bomb near Albuquerque, NM. The trigger explosives detonate, blasting a 12-foot-deep crater on uninhabited land owned by the University of New Mexico. Some radiation is detected.
A C-124 Globemaster leaves Dover Air Force Base with three nuclear weapons and a nuclear capsule. The cargo plane loses power in two of its four engines. In order to stay in the air, the crew jettisons two of the weapons over the Atlantic somewhere between Rehobeth, Delaware and Cape May or Wildwood, New Jersey. One of them is later located beneath about 18 feet of sand in shallow water, but recovery is deemed too hazardous. The other weapon reportedly is never found.
A capsule of radium salt, used by the Keleket Company to calibrate the radiation measuring instruments it manufactures, bursts at its Covington, KY facility. The spill requires a cleanup lasting five months and costing $250,000.
At the Rocky Flats weapons facility 27 km from Denver, CO, finely-divided plutonium powder in a glove box begins to spontaneously combust about 10 PM. The fire is not immediately noticed, and soon the plastic glove box ignites. The ventilation system pulls burning fragments through the building's air ducts to the paper stack filters that keep contamination inside. The filters are damaged, allowing plutonium and other contaminants to escape the plant. Firefighting efforts begin at the glove box at 10:38. The filter fire is detected later and put out by 2 AM on 12 September.
Research done in 1999 finds that approximately 63 kilograms (kg) of plutonium were in the room where the fire occurred and that 13-21 kg were actually involved in the fire. This leads to an estimate that between 40 and 500 grams of plutonium were carried off the site by wind currents. (Another source reports the amount of plutonium lost as 25,618 micrograms, but this seems suspiciously precise.)
Cooling system failure causes an explosion in a waste storage tank at the Mayak nuclear fuel complex near Chelyabinsk, Russia. The force of the explosion is estimated to equal that of 75 tons of TNT. It releases approximately 20 MCi (700 PBq) of waste, exposing (by various estimates) 124,000 to 270,000 people to dangerous levels of radiation.
This event, known as the "Kyshtym Disaster", is merely the best known of a series of releases that both precede and follow it. More than 500,000 inhabitants of the region are affected, both by direct exposure and through contaminated water supplies. It is known to the U.S. government but withheld from the public until 1977, when a Freedom of Information Act (FOIA) request breaks it free. Russia does not admit it until 1992, when Glasnost (openness) takes hold.
During an operation to release Wigner Energy from the graphite portions of Windscale Pile No.1 at Sellafield, north of Liverpool, England, technicians mistakenly overheat the reactor pile because poorly placed temperature sensors indicate it is cooling rather than heating. The resulting fire burns four days in the air-cooled pile, consuming a significant portion of it. A deluge of water finally cools the pile and quenches the blaze.
Radiation levels in the area are comparable to those from the 1979 meltdown at Three Mile Island in the U.S. Milk distribution is banned in the 200 square miles surrounding the plant, located in west Cumbria. Contamination is also detected in southeast England. The full report of the inquiry is not made public until 1988. At that time, it is disclosed that a canister of polonium 210 also burned in the fire. Both Pile No. 1 and No. 2 are later shut down and decommissioned in an effort that lasts until 1999.
A B-47 carrying a nuclear weapon, with its fissile core in a separate container for safety, crashes just after takeoff into an inhabited area 3,800 feet from the end of the runway at Homestead AFB, Florida. Enveloping the weapon and its core, the fire burns and smolders for four hours.
Afterward the fissile core is recovered intact in its shipping container. Just half the nuclear weapon remains, but all its major components are recovered in damaged condition. Nothing is reported about radiation levels in the area.
On the first shift after the New Year's holiday, a dedicated and experienced team at the Mayak Production Association works to ascertain critical parameters of high concentration, highly enriched uranyl nitrate solutions. After conducting an experiment in a large stainless steel vessel, the four-member team begins, per procedure, to drain the solution through a tube into a series of small bottles for storage. But they apparently decide the experiment vessel holds a subcritical mass, so they unbolt the vessel and three of them lift it to the floor, preparing to pour the remaining solution directly into the bottles. Unfortunately, in doing this they move the vessel near their bodies and the floor of the room, reflecting neutrons back into the vessel. It does go critical and the three holding it receive doses extimated at 6,000 rads. They die within 6 days. The fourth worker is 2.5 meters from the vessel; she receives a 600-rad dose and survives, but develops cataracts years later. The critical-parameters experiment program is discontinued.
An eastbound freight train of the Nickel Plate Road derails near Hamburg, NY. Five rail cars carrying classified AEC material overturn. According to reports, there is no damage to these materials and none of the AEC personnel accompanying them is injured.
A B-47 with a fully armed nuclear weapon aboard crashes during takeoff on alert training at an American air base in north Africa. This is probably Sidi Silmane, 90 miles northeast of Rabat, Morocco. (Another report suggests it may be near Tripoli, Libya.) Many aircraft and ground vehicles are contaminated. The Air Force evacuates everyone within 1 mile of the base. However, Moroccan officials are not notified.
Near Savannah, Georgia, a B-47 collides with an F-86 fighter during simulated combat. The damaged bomber attempts three landings at Hunter Air Force Base, but cannot land safely with its cargo: a nuclear weapon with no plutonium core. The crew jettisons the bomb from 7,200 feet over water near Tybee Island; it is never recovered.
Note: Lutins puts the date of this accident at 25 May 1958.
A fragmentary account says an unidentified aircraft crashed "on base" while carrying an MK-7 training weapon. Apparently the weapon was demolished and parts scattered over a wide area. The account probably comes from the 1958 annual report of nuclear weapons incidents issued by Headquarters Ogden Air Materiel Area, Hill AFB, Utah.
Shortly after taking off from the U.S. air base at Greenham Common, England, a B-47E of the 310th Bomb Wing develops problems and jettisons its two external 1,700-gallon fuel tanks. Both tanks miss their designated safe impact area. One hits a hangar; the other strikes the ground 65 feet behind another B-47E parked on the tarmac. The parked B-47E, carrying a B28 1.1-MT hydrogen bomb and with a pilot aboard, is engulfed by burning jet fuel. The fire ignites parts of the parked aircraft's magnesium fuselage and sets off the B28's high explosive charges. Two men are killed and eight injured. Convection currents distribute plutonium and uranium oxides over a wide area. Sixteen hours and a million gallons of water are needed to put out the fire.
The American and British governments throw a blanket of secrecy over the event. As late as 1985, the U.K. claims that a taxiing aircraft struck a parked one, and that no fire was involved. However two scientists with the Atomic Weapons Research Establishment at Aldermaston, F. H. Cripps and A. Stimson, working independently, discover high levels of radioactivity around the base in 1960. Their report on the accident remains under wraps until 1996.
A B-47 from Hunter Air Force Base in Georgia, en route to an overseas base, drops an unarmed nuclear weapon into the yard of Walter Gregg in Mars Bluff near Florence, SC. The bomb's trigger explosives go off, destroying Gregg's house and injuring six members of his family. Five other houses and a church are also damaged. Local residents looking for souvenirs carry away radioactive pieces of the bomb, which have to be recovered by an Air Force cleanup crew. Five months later, the Air Force pays Mr. Gregg $54,000 of his estimated $300,000 loss.
After passing through the Panama Canal, the USS Nautilus (SSN-571) is running submerged in the Pacific en route to the North Pole when a fire breaks out in insulation around one of its turbines. The insulation has become soaked with oil during the vessel's three years of operation. The fire is put out with only minor injuries, but the Nautilus has to surface to ventilate.
Several metallic uranium fuel rods in the NRU reactor overheat and rupture inside the reactor core. One of the damaged rods catches fire and is torn in two while being removed from the core by a robotic crane. As the remote-controlled crane carries the larger portion of the damaged rod, a three-foot length of fiercely burning uranium fuel breaks off and falls into a shallow maintenance pit. The ventilation system is jammed in the "open" position, admitting contamination to the rest of the building as well as a sizable area downwind from the reactor site. A relay team of scientists and technicians eventually extinguishes the fire by running past the maintenance pit at top speed wearing full protective gear, dumping buckets of wet sand on the burning uranium fuel.
Over a thousand men were involved in the cleanup operations following the NRX and NRU accidents. More than 600 men were required for the NRU cleanup alone. Official AECL reports stress that very few of these men were over-exposed to radiation. The reports also imply that no adverse health effects were caused by the exposures received. However, no medical follow-up has ever been done.
The NRU reactor produces 70% of the world supply of molybdenum-99, a precursor of Technicium-99m used in medical diagnosis. It is due to be phased out in 2005, after 42 years of operation. Two modern Maple-10 reactors, on-line since 2000, will take over the task of Mo-99 production.
During a transfer of material thought to be safe, a prompt criticality accident occurs in the C-1 wing of building 9212 in the Y-12 complex at Oak Ridge, TN. Due to a leaky valve, a solution of highly enriched uranyl nitrate collects in a 55-gallon stainless steel drum. It reaches critical mass. Afterwards, the dosimeters of all employees in the complex are checked to evaluate their neutron and gamma exposure. 31 employees are found to have received significant doses; they are routed through the medical facility.
In the reactor at the Boris Kidrich Institute in Vilna, Yugoslavia, a subcritical foil counting experiment is in progress. The operators desire the maximum foil activation, so the reactor is run as close to critical as possible. After about 5 minutes, one of the operators smells ozone and realizes that the reactor has gone critical. Of the three neutron flux sensors, two are indicating steady power level. The third is disconnected after behaving erratically. It is later found that the two working sensors have reached saturation, while the power level is ramping up.
The reactor reportedly withstands the burst energy of about 2.6x1018 fissions (80 MJ), but the six operators present are strongly irradiated, receiving estimated doses of 200 to 433 rem. One dies; the other five recover after severe bouts of radiation sickness.
Power output of the High Temperature Reactor Experiment (HTRE-3) at the National Reactor Testing Station is being raised to 120KW under control of a servo-system. After reaching 80% of this level, the indicated power begins to fall off. The servo pulls the control rods out farther, but the indicated power continues to drop. The reactor scrams automatically 20 seconds later. (It is thought that this is triggered by thermocouple wires melting open.)
The cause turns out to be control instrumentation failure. A newly added noise filter in the high voltage line to the ion chamber is sensitive to high neutron flux, dropping the chamber's voltage as the flux increases and thus mis-leading the servosystem. In the excursion, of about 2.5x1019 fissions, all core fuel elements experience some melting. Some fission products escape the building, but operator personnel exposures apparently are negligible.
A critical mass of plutonium solution is accidentally assembled during chemical purification at Los Alamos. The crane operator dies of acute radiation sickness. The March 1961 Journal of Occupational Medicine prints a special supplement medically analyzing this incident. Subsequently, federal facilities forbid hand-manipulation of critical assemblies.
An F-100 interceptor parked or taxiing at an unspecified air base in the Pacific burns when its external fuel tanks are inadvertantly jettisoned during an alert. The fire is put out after about seven minutes. No contamination results from the nuclear weapon the plane carries.
While docked at New London, CT, the USS Triton (SSN-586) suffers a galley fire caused by testing of a deep-fat fryer. According to the Navy, the fire spreads into the ventilation lines of the crew's mess, but quick action by crew members prevents further damage and possible loss of life.
A C-124 Globemaster crashes at takeoff from Barksdale AFB, Bossier City, LA. The cargo plane is completely destroyed, and so is the nuclear weapon (sans fissile core) that it carries. Some contamination is found beneath the wreckage, but not enough to hamper firefighting or rescue efforts.
At the Santa Susana Field Laboratory 30 miles northwest of Los Angeles, Rocketdyne operates the 20-MW Sodium Reactor Experiment (SRE) for the AEC. SRE is a prototype of a high-temperature liquid-metal-cooled reactor for civilian applications. A cooling channel becomes blocked. This causes 30% of the fuel elements in the core to melt. Most radionuclides are contained in the reactor building; only some krypton and other noble gases are released, after being held for a time to allow their activity to diminish. Of the nine radiological incidents at SSFL, this is the only one from which detectable radioactivity is observed off-site.
The Santa Susana Field Laboratory opened in 1948 and operated to circa 1989. Rocketdyne Corporation used it primarily to test rocket motors; but ten research reactors (all but SRE under 1 MW output) and seven criticality test setups were operated in Area IV. Over the years, the site became contaminated not only with radionuclides but with trichloroethylene, mercury and hydrazine. Workers were also irradiated at the site, and studies done in the 1990s document a statistical correlation between cumulative doses and cancer rates among these workers. It should be noted that weather and topographic factors limit the spread of contaminants into surrounding populated areas.
A helicopter engine explodes aboard the aircraft carrier USS Wasp (CVS-18). The resulting fire threatens to engulf the forward ammunition stores and the separate compartment holding nuclear weapons. The crew floods the ammunition stores and prepares to flood the nuclear weapons, but the fire is brought under control before that latter command is given.
One is killed and three others seriously burned in the explosion and fire of a prototype nuclear reactor at the U.S. Navy training center in West Milton, NY. The reactor is intended for the USS Triton (SSRN/SSN-586). The official Navy statement claims the accident is "completely unrelated to the reactor or any of its principal auxiliary systems." But sources familiar with the operation disagree.
A B-52 carrying two nuclear weapons collides at 32,000 feet with a KC-135 tanker. Both planes are from Columbus AFB in Mississippi. The bomber crashes near Hardinsburg, KY, killing all 8 crewmen. Although one of the weapons is partially burned, both are recoverd intact and no contamination results.
"Apparently intentional" damage to electrical cables of the USS Nautilus (SSN-571) is discovered when the vessel is overhauled at the naval shipyard in Portsmouth, NH. This Navy disclosure follows a story about a series of incidents involving "sabotage-type" damage including fires and broken pipes.
At the Idaho Chemical Processing Plant, a facility that reprocesses spent fuel rods from various reactors, 34kg of enriched uranium in the form of uranyl nitrate are stored in a series of "pencil tubes" — vessels shaped to avoid the possibility of criticality. Transfer hoses join these vessels and also connect them to a large waste tank. The hoses are positioned to prevent gravity-draining of solutions into the tank. However, during a sparging operation, a defective pressure gauge fools the operators into thinking there is no pressure in part of the plumbing system. So they apply more, inadvertently siphoning some of the solution into the waste tank. An initial spike of possibly 1017 fissions is followed by multiple criticality events in the tank over a 15-20 minute period. Thanks to thick shielding, none of the operators received significant prompt irradiation; but during evacuation several were exposed to airborne fission products, with one exposure of 50 rads. Subsequent investigation revealed a number of deficiencies.
A chemical explosion occurs during decontamination of processing equipment at the radiochemical processing plant at Oak Ridge. The cause is thought to be hot nitric acid mixing with phenol left in an evaporator which, contrary to procedures, has not been flushed with water. No injuries result, but the building is extensively contaminated, and radiation escapes it to wind up on surrounding streets and the exteriors of nearby buildings. An estimated 15g quantity of plutonium-239 is lost.
Areas that cannot be decontaminated are covered with concrete or bright warning paint. Subsequently, all radiochemical processing apparatus is fitted with secondary containment.