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Humanity's long-standing engagement with nuclear energy has led to several accidents over the years. And it's hardly surprising, given that incidents like Chernobyl, Three Mile Island, and Fukushima are just a few examples of times when people, power plants, and entire communities have been exposed to radiation.
10. SL-1
Stationary Low-Power Plant No. 1 (SL-1) was a small nuclear reactor located at the Idaho National Laboratory in southeastern Idaho. It began operation in 1958 as part of a prototype military nuclear power plant and was used to train nuclear technicians. SL-1 was housed within a large steel silo.
On December 23, 1960, SL-1 underwent a shutdown for maintenance, with plans to resume operations on January 4. Three men, John Byrnes, Richard McKinley, and Richard Legg, were assigned to prepare the reactor the night before. They arrived around 4:00 PM.
At 9:01 PM, alarms rang at the laboratory's firehouse. Firefighters arrived, equipped with radiation detectors, but initially found nothing unusual. The control room appeared normal, though none of the three men were present. As they neared the stairs leading to the silo, their detectors registered dangerous levels of radiation.
Soon after, men wearing radiation suits and armed with more advanced detectors arrived. Two of them ascended the stairs and took a look at the reactor. The scene inside the silo was catastrophic. Water from SL-1 covered the floor, littered with debris. Byrnes was found dead in it, while McKinley lay nearby, moaning in pain. Legg was still unaccounted for.
Four men rushed in and carried McKinley out on a stretcher. He was placed in an ambulance but passed away shortly after. With no clear solution for handling his radioactive body, they drove it into the desert and covered it with lead blankets temporarily. Legg was discovered later that night, impaled against the silo's ceiling by a control rod. It took six days to recover his body.
It was later concluded that an explosion occurred when Byrnes lifted the central control rod of SL-1 far more than was needed to restart the reactor, causing the reaction to spiral out of control. It was speculated that this may have been accidental, with the rod possibly being stuck and yanked out too far. Others believe that Byrnes intentionally lifted the rod in a suicide attempt, as his marriage was falling apart.
It took months to dismantle SL-1 and thoroughly decontaminate the components. The men's hands were removed and buried as radioactive waste. Byrnes, McKinley, and Legg were all buried in lead coffins.
9. Church Rock Uranium Spill
When it comes to the largest release of radioactive material in U.S. history (excluding nuclear bomb tests), the answer isn't Three Mile Island. That infamous distinction goes to a dam break in Church Rock, New Mexico.
Church Rock, a small town located within the Navajo Nation in northwestern New Mexico, was once a prominent uranium mining site. The area is home to 20 abandoned uranium mines and processing mills, most of which were used to mine uranium for nuclear weapons. For every pound of concentrated uranium produced, thousands of pounds of radioactive tailings were generated and often discarded into tailings ponds.
On the morning of July 16, 1979, a tailings dam at a processing mill run by the United Nuclear Corporation collapsed, releasing 94 million gallons of contaminated wastewater and 1,100 tons of radioactive tailings into the Puerco River. Around 6:30 AM, Church Rock resident Robinson Kelly stepped outside to find the dry arroyo of the Puerco now filled with yellow-tinted water. He later described the smell as the “foulest” odor he had ever encountered.
The water released from the dam had a dangerously low pH of 2 and was laden with radioactive materials like uranium, radium, thorium, polonium, and several other metals that settled into the riverbed. By noon, the water had receded enough for people to wade across the arroyo and recover livestock. However, those who did so suffered blisters and sores on their legs and feet. Shortly after the dam was repaired, the river was found to be 6,000 times more radioactive than the acceptable safety limit.
The Navajo Tribal Council requested that Church Rock be declared a disaster area, but the request was denied. Some of the contaminants in the wastewater emit alpha radiation, which can cause cancer. This radiation doesn’t dissipate quickly, as exemplified by thorium-230, which has a half-life of 80,000 years.
8. NRX
The NRX reactor at Chalk River Laboratories in Chalk River, Ontario, began operating in 1947 and was used for experimental purposes by both the United States and Canada. The reactor was designed to accommodate up to 12 control rods, though seven were sufficient to fully halt any reaction. Four of these rods, known as the safeguard bank, were linked to lower simultaneously. The control rods were controlled by magnets, so if the magnets failed, the rods would fall into the reactor and shut it down. A pneumatic air pressure system was used to raise or quickly push the rods down faster than gravity could alone.
Despite these numerous safety features, they proved inadequate. On December 12, 1952, an operator in the basement beneath the reactor accidentally opened the valves connected to the control rods’ pneumatic system, lowering the air pressure above the rods. As a result, several rods began to rise out of the reactor. The supervisor hurried to the basement to close the valves, which should have forced the rods back down, but for reasons not entirely understood, the rods did not fall all the way back into the reactor.
The supervisor contacted the control room and instructed an operator on which numbered buttons to press to make the pneumatic system force the rods down. Unfortunately, he mistakenly gave the number for the button that would withdraw the safeguard bank. The supervisor quickly realized his mistake, but the technician had already hung up the phone and pressed the buttons.
The reactor’s power output began escalating rapidly. The technicians eventually managed to reduce it, but not before one or more explosions inside the reactor caused ruptures, leaking 1 million gallons of radioactive water and releasing radioactive gas into the air.
The contaminated water had to be pumped out and discarded in shallow trenches near the Ottawa River. The NRX reactor was ultimately buried as radioactive waste, with a new reactor constructed in its place. Future U.S. president Jimmy Carter was involved in the cleanup efforts.
Chalk River Laboratories experienced another incident in 1958 with a different reactor. A fuel rod caught fire, dispersing fission products throughout the building. Additionally, the ventilation system became stuck open, releasing gas downwind. Technicians had to repeatedly rush past the fire to throw wet sand on it to extinguish the flames.
7. Baneberry
Baneberry was a 10-kiloton nuclear explosion set off 270 meters (890 ft) beneath the surface at Yucca Flat, part of the Nevada Test Site, on December 18, 1970. Since 1963, underground nuclear testing had been the standard due to the Partial Test Ban Treaty, and these tests were considered less dangerous than the dramatic mushroom clouds of the 1950s. However, in the days leading up to Christmas in 1970, geology unexpectedly threw a wrench into the works.
Baneberry was detonated at 7:30 AM, and everything appeared to be proceeding as planned. But just three minutes later, at 7:33, a fissure opened roughly 90 meters (300 ft) from the detonation site, releasing radioactive dust and gas into the air. The fallout continued even after the ground above the explosion collapsed—something typical of underground detonations. The gas kept venting for another 24 hours.
The cloud from the detonation was visible from Las Vegas, a rare occurrence in recent years. The radioactive dust rose to an altitude of 3,000 meters (9,800 ft) and drifted across multiple neighboring states. Fallout from the unexpected release affected 86 workers at the test site, two of whom later died from leukemia four years afterward.
The Nevada Test Site halted testing for six months while experts examined the Baneberry incident. It was determined that the ground where the device was placed contained unusually high water content, which caused the fissure to open up.
6. Acerinox Plant
Acerinox is a Spanish company known for producing stainless steel. In May 1998, a cesium-137 source ended up at one of their scrap metal recycling plants in Los Barrios, Cadiz. Although the plant was equipped with monitoring systems to detect such dangers, the source bypassed detection and was melted in one of the furnaces.
A radioactive cloud was quickly released into the atmosphere. The plant's chimney detectors failed to detect the release, but neighboring countries including France, Germany, Austria, Switzerland, and Italy did. The radioactivity was about 1,000 times higher than normal, and the ashes produced at the plant were hazardous enough to pose a risk.
Six workers at the plant experienced minor contamination from cesium-137. In addition to the plant, two other facilities that received its contaminated waste also underwent decontamination. The incident resulted in 40 cubic meters (1,400 ft) of contaminated water, 2,000 metric tons of radioactive ash, and 150 metric tons of contaminated equipment. The total cleanup and lost productivity amounted to $26 million. In the grand scheme of radiation-related incidents, this one ended relatively well.
5. Chuetsu Earthquake
The Kashiwazaki-Kariwa Nuclear Power Plant (KKNPP) located in Japan's Niigata Prefecture has the capacity to generate more power than any other power plant in the world—when it is operating. Since becoming fully operational in 1997, the plant has faced a series of scandals that have forced it to shut down some or all of its seven reactors. Notable issues include covering up evidence of stress fractures and hiding the fact that the plant was built near fault lines.
This revelation came to light after the Chuetsu earthquake struck on July 16, 2007. The earthquake, registering a magnitude of 6.8, had its epicenter only 24 kilometers (15 miles) offshore from the plant. The intensity of the shaking exceeded what the plant was designed to handle, as it was built before Japan revised its earthquake standards in 2006.
The Chuetsu earthquake served as an ominous preview for the Fukushima Daiichi disaster, as it caused significant damage to KKNPP and its reactors. The Tokyo Electric Power Company confirmed that 1,200 liters of mildly radioactive water leaked into the sea, and that many barrels of low-level nuclear waste had ruptured during the quake. Additionally, an exhaust pipe was found to be leaking radioactive iodine.
A report from the Nuclear Information and Resource Service (NIRS), published on July 19, stated that the release of radioactive material was far more severe than initially reported. According to NIRS, the water that leaked into the sea originated from one of the reactors' irradiated fuel pools. Moreover, another reactor had been releasing radioactive steam since the earthquake. The Associated Press also reported widespread damage to the plant’s infrastructure, with cracks and leaks present everywhere. Liquefaction (where solid ground turns to mud) was observed under certain parts of KKNPP.
4. K-431
On August 10, 1985, the K-431, an Echo-II nuclear submarine, was docked at the Chazhma Bay naval base near Vladivostok, which had been a secret location during the Cold War. The submarine's upper lid seal on one of its two reactors was being repaired, and both reactors had been refueled the day before.
As a boat passed by in the bay, its wake caused the ship servicing K-431 to rock. The ship’s crane arm tore loose all of the reactor's control rods. This triggered a massive steam explosion, which sent the 12-metric-ton upper lid and all the fuel assemblies flying out of the reactor compartment, destroying the pressure hull. The explosion instantly claimed the lives of 10 people.
A radioactive plume shot up 50 meters (160 feet) into the air and drifted towards the nearby Dunai Peninsula, leaving behind a -kilometer-long (2.2 miles) trail of radioactive fallout. The bay floor and adjacent shorelines were contaminated with cobalt-60, causing radiation levels to soar to 16,000 times above normal. A fire ignited and took four hours to extinguish, while radioactive material continued to leak from K-431 for seven hours.
Of the 2,000 personnel who responded to the accident and carried out the decontamination of the submarine, 290 received significant radiation doses, and 10 developed acute radiation sickness. The damaged K-431 was eventually docked at a nearby submarine base (though not dry-docked). The incident remained classified until 1993.
Later that same year, sediments from Chazhma Bay were still contaminated with radiation at levels 2,000 times higher than normal. Certain areas of the bay emitted radioactivity equivalent to 3,000 chest X-rays per hour in the 1990s. By the 2000s, radiation levels on the Dunai Peninsula were still in the range of 30–400 chest X-rays per hour. The bay remains further polluted from its use as a scuttling site for old nuclear submarines. Around 30,000 people live nearby.
K-431 was finally dismantled for scrap in 2010, with the process carefully monitored for any spikes in radiation.
3. Santa Susana Field Laboratory
The Santa Susana Field Laboratory (SSFL), located near Los Angeles, covers 2,850 acres and was used by private companies to conduct rocket engine tests for NASA. The site is heavily contaminated with both toxic chemicals and radiation. Cleaning up this mess is extremely challenging due to the vast extent of pollution, compounded by the deteriorating condition of many of the site's structures. The worst-hit area is Area Four, which housed 10 nuclear reactors. The largest of these, known as the Sodium Reactor Experiment, experienced a partial meltdown on July 13, 1959.
According to a former worker, radiation levels in the building where the meltdown took place were “off the charts.” In order to avoid an explosion that could have rivaled Chernobyl, radioactive gas had to be released into the atmosphere. Unfortunately, attempts to repair the reactor only generated more gas. For weeks afterward, radioactive gas continued to be vented from the building, mostly at night. Residents in nearby areas such as Simi Valley, Chatsworth, and Canoga Park were “bombarded” with radiation.
Everyone involved in the incident was sworn to secrecy. Six weeks later, the Atomic Energy Commission released a statement claiming that a minor incident had occurred and that no radiation had been released. The full truth came to light only in 1979. Other accidents involving the release of radioactive gas took place in Area Four during the 1960s.
Radiation from the laboratory is suspected to be linked to higher cancer rates in nearby communities. One local resident remembers that every house on her street had at least one person diagnosed with cancer. In 2007, the CDC reported a 60 percent higher incidence of certain cancers among those living within 3 kilometers (2 mi) of the SSFL.
2. Tomsk-7
Tomsk-7, now known as Seversk, is a city located in Siberia, approximately 3,000 kilometers (2,000 mi) east of Moscow. During the Cold War, it was designated as a 'secret city,' housing 107,000 people who worked at the Siberian Chemical Combine (SCC), a facility responsible for producing uranium and plutonium for the Soviet Union's nuclear weapons program. The families of the workers also resided in Tomsk-7, which should not be confused with the nearby city of Tomsk.
The SCC experienced several nuclear incidents throughout its operation. The most infamous took place on April 6, 1993. On that day, a nitric acid solution was being added to a storage tank known as Object 15 to separate plutonium from spent nuclear fuel. Object 15 contained about 8,700 kilograms (19,200 lb) of uranium and 450 grams of plutonium. Compressed air was needed to properly mix the nitric acid with the spent fuel.
Insufficient compressed air was likely pumped into the tank, possibly due to human error. As a result, the solutions settled into layers within the tank instead of blending. Chemical reactions in the nitric acid layer caused both the temperature and pressure inside the tank to rise. Object 15 was designed to handle up to 12 atmospheres of pressure, but it exploded at 18 atmospheres, tearing down the walls on two floors of its building and igniting the roof.
The explosion released a radioactive plume that contaminated an area of 120 square kilometers (50 mi) surrounding the SCC. Over the following days, radioactive snowfall increased radiation levels by 100 times in some regions. The soil in these areas showed elevated levels of cesium-137 and plutonium for years after the incident.
The situation was worsened by the likelihood that the SCC area was already heavily contaminated. The facility stored massive amounts of nuclear waste and had experienced approximately 30 major accidents during its operation. The people of Seversk have faced continuous exposure to radioactivity.
1. Rocky Flats
The Rocky Flats Plant was situated 26 kilometers (16 miles) northwest of Denver's city center. It was involved in producing plutonium triggers for nuclear weapons. Plutonium is an inherently hazardous material; it can even ignite spontaneously without any external source of fire.
On September 11, 1957, a fire broke out in Building 71, which was used for plutonium processing. Despite being designed as a fireproof facility, the building was soon engulfed in flames. The entire structure was at risk of being destroyed.
The firefighters were fully aware that using water on a plutonium fire could lead to a criticality event. A blue flash from such a chain reaction would have been the signal of a lethal dose of neutrons for everyone present. However, in a desperate move, the men decided to use water in an attempt to control the fire.
Fortunately, no blue flash occurred. Instead, a thunderous explosion sent the heavy lead lid of the 46-meter (152-foot) smokestack flying into the air, and flames shot 60 meters (200 feet) above its top. The fire continued raging for another 13 hours before being extinguished... with more water.
Radioactive smoke blanketed the Denver area throughout the incident. It's impossible to determine how much plutonium was released, as most of the measuring equipment that could have detected it was destroyed. The fire also caused damage to 620 filters, which had not been replaced in four years, and these filters were packed with plutonium and other dangerous byproducts. A school 19 kilometers (12 miles) away from Rocky Flats showed heavy plutonium contamination in its soil. Plutonium was detected up to 50 kilometers (30 miles) from the site, with the plume likely extending even further.
The local residents were neither alerted nor evacuated, and the incident was kept out of the media. It wasn't until a similar fire on Mother's Day in 1969 that the Department of Energy finally admitted the full extent of the disaster. After that fire, it was revealed that areas surrounding Rocky Flats had plutonium concentrations exceeding those found in Nagasaki. Furthermore, it was disclosed that 5,000 barrels had been left out in the open for 11 years, leaking radioactive waste into the groundwater and soil.
The site of Rocky Flats is now a wildlife refuge. The isotope plutonium-239, the most common form of plutonium, has a half-life of 24,000 years.
