Nuclear and radiation accidents and incidents


A nuclear and radiation accident is defined by the International Atomic Energy Agency as "an event that has led to significant consequences to people, the environment or the facility". Examples include lethal effects to individuals, radioactive isotope to the environment, or reactor core melt." The prime example of a "major nuclear accident" is one in which a reactor core is damaged and significant amounts of radioactive isotopes are released, such as in the Chernobyl disaster in 1986.
The impact of nuclear accidents has been a topic of debate since the first nuclear reactors were constructed in 1954, and has been a key factor in public concern about nuclear facilities. Technical measures to reduce the risk of accidents or to minimize the amount of radioactivity released to the environment have been adopted, however human error remains, and "there have been many accidents with varying impacts as well near misses and incidents". As of 2014, there have been more than 100 serious nuclear accidents and incidents from the use of nuclear power. Fifty-seven accidents or severe incidents have occurred since the Chernobyl disaster, and about 60% of all nuclear-related accidents/severe incidents have occurred in the USA. Serious nuclear power plant accidents include the Fukushima Daiichi nuclear disaster, the Chernobyl disaster, the Three Mile Island accident, and the SL-1 accident. Nuclear power accidents can involve loss of life and large monetary costs for remediation work.
Nuclear-powered submarine accidents include the K-19, K-11, K-27, K-140, K-429, K-222, and K-431 accidents. Serious radiation incidents/accidents include the Kyshtym disaster, the Windscale fire, the radiotherapy accident in Costa Rica, the radiotherapy accident in Zaragoza, the radiation accident in Morocco, the Goiania accident, the radiation accident in Mexico City, the radiotherapy unit accident in Thailand, and the Mayapuri radiological accident in India.
The IAEA maintains a website reporting recent nuclear accidents.

Nuclear plant accidents

The worst nuclear accident to date was the Chernobyl disaster which occurred in 1986 in Ukraine. The accident killed 31 people directly and damaged approximately $7 billion of property. A study published in 2005 by the World Health Organization estimates that there may eventually be up to 4,000 additional cancer deaths related to the accident among those exposed to significant radiation levels. Radioactive fallout from the accident was concentrated in areas of Belarus, Ukraine and Russia. Other studies have estimated as many as over a million eventual cancer deaths from Chernobyl. Estimates of eventual deaths from cancer are highly contested. Industry, UN and DOE agencies claim low numbers of legally provable cancer deaths will be traceable to the disaster. The UN, DOE and industry agencies all use the limits of the epidemiological resolvable deaths as the cutoff below which they cannot be legally proven to come from the disaster. Independent studies statistically calculate fatal cancers from dose and population, even though the number of additional cancers will be below the epidemiological threshold of measurement of around 1%. These are two very different concepts and lead to the huge variations in estimates. Both are reasonable projections with different meanings. Approximately 350,000 people were forcibly resettled away from these areas soon after the accident. 6,000 people were involved in cleaning Chernobyl and 10,800 square miles were contaminated.
Social scientist and energy policy expert, Benjamin K. Sovacool has reported that worldwide there have been 99 accidents at nuclear power plants from 1952 to 2009, totaling US$20.5 billion in property damages. There have been comparatively few fatalities associated with nuclear power plant accidents. An academic review of many reactor accident and the phenomena of these events was published by Mark Foreman.
DateLocation of accidentDescription of accident or incidentDeadCost
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Mayak, Kyshtym, Soviet UnionThe Kyshtym disaster was a radiation contamination accident at Mayak, a Nuclear fuel reprocessing plant in the Soviet Union.Estimated 200 possible cancer fatalities6
Sellafield aka Windscale fire, Cumberland, United KingdomA fire at the British atomic bomb project damaged the core and released an estimated 740 terabecquerels of iodine-131 into the environment. A rudimentary smoke filter constructed over the main outlet chimney successfully prevented a far worse radiation leak.0 direct, estimated up to 240 possible cancer victims5
Idaho Falls, Idaho, United StatesExplosion at SL-1 prototype at the National Reactor Testing Station. All 3 operators were killed when a control rod was removed too far.3224
Frenchtown Charter Township, Michigan, United StatesMeltdown of some fuel elements in the Fermi 1 Reactor at the Enrico Fermi Nuclear Generating Station. Little radiation leakage into the environment.0132
Lucens reactor, Vaud, SwitzerlandOn January 21, 1969, it suffered a loss-of-coolant accident, leading to meltdown of one fuel element and radioactive contamination of the cavern, which before was sealed.04
Greifswald, East GermanyElectrical error in Greifswald Nuclear Power Plant causes fire in the main trough that destroys control lines and five main coolant pumps04433
Jaslovské Bohunice, CzechoslovakiaMalfunction during fuel replacement. Fuel rod ejected from reactor into the reactor hall by coolant.21,7004
Three Mile Island, Pennsylvania, United StatesLoss of coolant and partial core meltdown due to operator errors and technical flaws. There is a small release of radioactive gases. See also Three Mile Island accident health effects.02,4005
Athens, Alabama, United StatesSafety violations, operator error and design problems force a six-year outage at Browns Ferry Unit 2.0110
Athens, Alabama, United StatesInstrumentation systems malfunction during startup, which led to suspension of operations at all three Browns Ferry Units01,830
Plymouth, Massachusetts, United StatesRecurring equipment problems force emergency shutdown of Boston Edison's Pilgrim Nuclear Power Plant01,001
Chernobyl, Chernobyl Raion, Kiev Oblast, Ukraininan SSR, Soviet UnionA flawed reactor design and inadequately trained personnel led to a failed backup generator test. This test led to a power surge which overheated the fuel rods of reactor no. 4 of the Chernobyl power plant, causing an explosion and meltdown, necessitating the evacuation of 300,000 people and dispersing radioactive material across Europe.
Around 5% of the core was released into the atmosphere and downwind.		28 direct, 19 not entirely related and 15 minors due to thyroid cancer, as of 2008. Estimated up to 4000 possible cancer deaths.6,7007
Hamm-Uentrop, West GermanyExperimental THTR-300 reactor releases small amounts of fission products to surrounding area0267
Surry, Virginia, United StatesFeedwater pipe break at Surry Nuclear Power Plant kills 4 workers4
Delta, Pennsylvania, United StatesPeach Bottom units 2 and 3 shutdown due to cooling malfunctions and unexplained equipment problems0400
Lycoming, New York, United StatesMalfunctions force Niagara Mohawk Power Corporation to shut down Nine Mile Point Unit 10150
Lusby, Maryland, United StatesInspections at Calvert Cliff Units 1 and 2 reveal cracks at pressurized heater sleeves, forcing extended shutdowns0120
Sosnovyi Bor, Leningrad Oblast, RussiaAn accident at the Sosnovy Bor nuclear plant leaked radioactive iodine into the air through a ruptured fuel channel.
Waterford, Connecticut, United StatesLeaking valve forces shutdown Millstone Nuclear Power Plant Units 1 and 2, multiple equipment failures found0254
Crystal River, Florida, United StatesBalance-of-plant equipment malfunction forces shutdown and extensive repairs at Crystal River Unit 30384
Ibaraki Prefecture, JapanTokaimura nuclear accident killed two workers, and exposed one more to radiation levels above permissible limits.2544
Oak Harbor, Ohio, United StatesSevere corrosion of reactor vessel head forces 24-month outage of Davis-Besse reactor01433
Paks, HungaryCollapse of fuel rods at Paks Nuclear Power Plant unit 2 during its corrosion cleaning led to leakage of radioactive gases. It remained inactive for 18 months.03
Fukui Prefecture, JapanSteam explosion at Mihama Nuclear Power Plant kills 4 workers and injures 7 more491
Forsmark, SwedenAn electrical fault at Forsmark Nuclear Power Plant caused multiple failures in safety systems that had the reactor to cool down01002
Fukushima, JapanA tsunami flooded and damaged the plant's 3 active reactors, drowning two workers. Loss of backup electrical power led to overheating, meltdowns, and evacuations. One man died suddenly while carrying equipment during the clean-up. The plant's reactors Nr. 4, 5 and 6 were inactive at the time.1 and 3+ labour accidents; plus a broader number of primarily ill or old people from evacuation stress1,255–2,078 7
Marcoule, FranceOne person was killed and four injured, one seriously, in a blast at the Marcoule Nuclear Site. The explosion took place in a furnace used to melt metallic waste.1

Nuclear reactor attacks

The vulnerability of nuclear plants to deliberate attack is of concern in the area of nuclear safety and security. Nuclear power plants, civilian research reactors, certain naval fuel facilities, uranium enrichment plants, fuel fabrication plants, and even potentially uranium mines are vulnerable to attacks which could lead to widespread radioactive contamination. The attack threat is of several general types: commando-like ground-based attacks on equipment which if disabled could lead to a reactor core meltdown or widespread dispersal of radioactivity; and external attacks such as an aircraft crash into a reactor complex, or cyber attacks.
The United States 9/11 Commission found that nuclear power plants were potential targets originally considered for the September 11, 2001 attacks. If terrorist groups could sufficiently damage safety systems to cause a core meltdown at a nuclear power plant, and/or sufficiently damage spent fuel pools, such an attack could lead to widespread radioactive contamination. The Federation of American Scientists have said that if nuclear power use is to expand significantly, nuclear facilities will have to be made extremely safe from attacks that could release radioactivity into the environment. New reactor designs have features of passive nuclear safety, which may help. In the United States, the NRC carries out "Force on Force" exercises at all Nuclear Power Plant sites at least once every three years.
Nuclear reactors become preferred targets during military conflict and, over the past three decades, have been repeatedly attacked during military air strikes, occupations, invasions and campaigns. Various acts of civil disobedience since 1980 by the peace group Plowshares have shown how nuclear weapons facilities can be penetrated, and the group's actions represent extraordinary breaches of security at nuclear weapons plants in the United States. The National Nuclear Security Administration has acknowledged the seriousness of the 2012 Plowshares action. Non-proliferation policy experts have questioned "the use of private contractors to provide security at facilities that manufacture and store the government's most dangerous military material". Nuclear weapons materials on the black market are a global concern,Brian Michael Jenkins. CNN.com, September 11, 2008. and there is concern about the possible detonation of a small, crude nuclear weapon or dirty bomb by a militant group in a major city, causing significant loss of life and property.
The number and sophistication of cyber attacks is on the rise. Stuxnet is a computer worm discovered in June 2010 that is believed to have been created by the United States and Israel to attack Iran's nuclear facilities. It switched off safety devices, causing centrifuges to spin out of control. The computers of South Korea's nuclear plant operator were hacked in December 2014. The cyber attacks involved thousands of phishing emails containing malicious codes, and information was stolen.

Radiation and other accidents and incidents

Serious radiation and other accidents and incidents include:
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Between 16 July 1945 and 23 September 1992, the United States maintained a program of vigorous nuclear testing, with the exception of a moratorium between November 1958 and September 1961. By official count, a total of 1,054 nuclear tests and two nuclear attacks were conducted, with over 100 of them taking place at sites in the Pacific Ocean, over 900 of them at the Nevada Test Site, and ten on miscellaneous sites in the United States. Until November 1962, the vast majority of the U.S. tests were atmospheric ; after the acceptance of the Partial Test Ban Treaty all testing was regulated underground, in order to prevent the dispersion of nuclear fallout.
The U.S. program of atmospheric nuclear testing exposed a number of the population to the hazards of fallout. Estimating exact numbers, and the exact consequences, of people exposed has been medically very difficult, with the exception of the high exposures of Marshall Islanders and Japanese fishers in the case of the Castle Bravo incident in 1954. A number of groups of U.S. citizens — especially farmers and inhabitants of cities downwind of the Nevada Test Site and U.S. military workers at various tests — have sued for compensation and recognition of their exposure, many successfully. The passage of the Radiation Exposure Compensation Act of 1990 allowed for a systematic filing of compensation claims in relation to testing as well as those employed at nuclear weapons facilities. As of June 2009 over $1.4 billion total has been given in compensation, with over $660 million going to "downwinders". shows a mushroom cloud in the background. Scenes such as this were typical during the 1950s. From 1951 to 1962 the government conducted 100 atmospheric tests at the nearby Nevada Test Site.

Trafficking and thefts

The International Atomic Energy Agency says there is "a persistent problem with the illicit trafficking in nuclear and other radioactive materials, thefts, losses and other unauthorized activities". The IAEA Illicit Nuclear Trafficking Database notes 1,266 incidents reported by 99 countries over the last 12 years, including 18 incidents involving HEU or plutonium trafficking:

Nuclear meltdown

A nuclear meltdown is a severe nuclear reactor accident that results in reactor core damage from overheating. It has been defined as the accidental melting of the core of a nuclear reactor, and refers to the core's either complete or partial collapse. A core melt accident occurs when the heat generated by a nuclear reactor exceeds the heat removed by the cooling systems to the point where at least one nuclear fuel element exceeds its melting point. This differs from a fuel element failure, which is not caused by high temperatures. A meltdown may be caused by a loss of coolant, loss of coolant pressure, or low coolant flow rate or be the result of a criticality excursion in which the reactor is operated at a power level that exceeds its design limits. Alternately, in a reactor plant such as the RBMK-1000, an external fire may endanger the core, leading to a meltdown.
Large-scale nuclear meltdowns at civilian nuclear power plants include:
Other core meltdowns have occurred at:
A criticality accident occurs when a nuclear chain reaction is accidentally allowed to occur in fissile material, such as enriched uranium or plutonium. The Chernobyl accident is not universally regarded an example of a criticality accident, because it occurred in an operating reactor at a power plant. The reactor was supposed to be in a controlled critical state, but control of the chain reaction was lost. The accident destroyed the reactor and left a large geographic area uninhabitable. In a smaller scale accident at Sarov a technician working with highly enriched uranium was irradiated while preparing an experiment involving a sphere of fissile material. The Sarov accident is interesting because the system remained critical for many days before it could be stopped, though safely located in a shielded experimental hall. This is an example of a limited scope accident where only a few people can be harmed, while no release of radioactivity into the environment occurred. A criticality accident with limited off site release of both radiation and a very small release of radioactivity occurred at Tokaimura in 1999 during the production of enriched uranium fuel. Two workers died, a third was permanently injured, and 350 citizens were exposed to radiation. In 2016, a criticality accident was reported at the Afrikantov OKBM Critical Test Facility in Russia.

Decay heat

accidents are where the heat generated by the radioactive decay causes harm. In a large nuclear reactor, a loss of coolant accident can damage the core: for example, at Three Mile Island a recently shutdown PWR reactor was left for a length of time without cooling water. As a result, the nuclear fuel was damaged, and the core partially melted. The removal of the decay heat is a significant reactor safety concern, especially shortly after shutdown. Failure to remove decay heat may cause the reactor core temperature to rise to dangerous levels and has caused nuclear accidents. The heat removal is usually achieved through several redundant and diverse systems, and the heat is often dissipated to an 'ultimate heat sink' which has a large capacity and requires no active power, though this method is typically used after decay heat has reduced to a very small value. The main cause of release of radioactivity in the Three Mile Island accident was a pilot-operated relief valve on the primary loop which stuck in the open position. This caused the overflow tank into which it drained to rupture and release large amounts of radioactive cooling water into the containment building.
For the most part, nuclear facilities receive their power from offsite electrical systems. They also have a grid of emergency back-up generators to provide power in the event of an outage. An event that could prevent both offsite power, as well as emergency power is known as a "station blackout". In 2011, an earthquake and tsunami caused a loss of electric power at the Fukushima Daiichi nuclear power plant in Japan. The decay heat could not be removed, and the reactor cores of units 1, 2 and 3 overheated, the nuclear fuel melted, and the containments were breached. Radioactive materials were released from the plant to the atmosphere and to the ocean.

Transport

Transport accidents can cause a release of radioactivity resulting in contamination or shielding to be damaged resulting in direct irradiation. In Cochabamba a defective gamma radiography set was transported in a passenger bus as cargo. The gamma source was outside the shielding, and it irradiated some bus passengers.
In the United Kingdom, it was revealed in a court case that in March 2002 a radiotherapy source was transported from Leeds to Sellafield with defective shielding. The shielding had a gap on the underside. It is thought that no human has been seriously harmed by the escaping radiation.
On 17 January 1966, a fatal collision occurred between a B-52G and a KC-135 Stratotanker over Palomares, Spain. The accident was designated a "Broken Arrow", meaning an accident involving a nuclear weapon that does not present a risk of war.

Equipment failure

Equipment failure is one possible type of accident. In Białystok, Poland, in 2001 the electronics associated with a particle accelerator used for the treatment of cancer suffered a malfunction. This then led to the overexposure of at least one patient. While the initial failure was the simple failure of a semiconductor diode, it set in motion a series of events which led to a radiation injury.
A related cause of accidents is failure of control software, as in the cases involving the Therac-25 medical radiotherapy equipment: the elimination of a hardware safety interlock in a new design model exposed a previously undetected bug in the control software, which could have led to patients receiving massive overdoses under a specific set of conditions.

Human error

Many of the major nuclear accidents have been directly attributable to operator or human error. This was obviously the case in the analysis of both the Chernobyl and TMI-2 accidents. At Chernobyl, a test procedure was being conducted prior to the accident. The leaders of the test permitted operators to disable and ignore key protection circuits and warnings that would have normally shut the reactor down. At TMI-2, operators permitted thousands of gallons of water to escape from the reactor plant before observing that the coolant pumps were behaving abnormally. The coolant pumps were thus turned off to protect the pumps, which in turn led to the destruction of the reactor itself as cooling was completely lost within the core.
A detailed investigation into SL-1 determined that one operator manually pulled the central control rod out about 26 inches rather than the maintenance procedure's intention of about 4 inches.
An assessment conducted by the Commissariat à l’Énergie Atomique in France concluded that no amount of technical innovation can eliminate the risk of human-induced errors associated with the operation of nuclear power plants. Two types of mistakes were deemed most serious: errors committed during field operations, such as maintenance and testing, that can cause an accident; and human errors made during small accidents that cascade to complete failure.
In 1946 Canadian Manhattan Project physicist Louis Slotin performed a risky experiment known as "tickling the dragon's tail" which involved two hemispheres of neutron-reflective beryllium being brought together around a plutonium core to bring it to criticality. Against operating procedures, the hemispheres were separated only by a screwdriver. The screwdriver slipped and set off a chain reaction criticality accident filling the room with harmful radiation and a flash of blue light. Slotin reflexively separated the hemispheres in reaction to the heat flash and blue light, preventing further irradiation of several co-workers present in the room. However, Slotin absorbed a lethal dose of the radiation and died nine days later. The infamous plutonium mass used in the experiment was referred to as the demon core.

Lost source

Lost source accidents, also referred to as orphan sources, are incidents in which a radioactive source is lost, stolen or abandoned. The source then might cause harm to humans. One case occurred at Yanango where a radiography source was lost, also at Samut Prakarn a phosphorus teletherapy source was lost and at Gilan in Iran a radiography source harmed a welder. The best known example of this type of event is the Goiânia accident in Brazil.
The International Atomic Energy Agency has provided guides for scrap metal collectors on what a sealed source might look like. The scrap metal industry is the one where lost sources are most likely to be found.
Experts believe that up to 50 nuclear weapons were lost during the Cold War.

Comparisons

Comparing the historical safety record of civilian nuclear energy with other forms of electrical generation, Ball, Roberts, and Simpson, the IAEA, and the Paul Scherrer Institute found in separate studies that during the period from 1970 to 1992, there were just 39 on-the-job deaths of nuclear power plant workers worldwide, while during the same time period, there were 6,400 on-the-job deaths of coal power plant workers, 1,200 on-the-job deaths of natural gas power plant workers and members of the general public caused by natural gas power plants, and 4,000 deaths of members of the general public caused by hydroelectric power plants with failure of Banqiao dam in 1975 resulting in 170'000-230'000 fatalities alone.
As other common sources of energy, coal power plants are estimated to kill 24,000 Americans per year due to lung disease as well as causing 40,000 heart attacks per year in the United States. According to Scientific American, the average coal power plant emits 100 times more radiation per year than a comparatively sized nuclear power plant in the form of toxic coal waste known as fly ash.
In terms of energy accidents, hydroelectric plants were responsible for the most fatalities, but nuclear power plant accidents rank first in terms of their economic cost, accounting for 41 percent of all property damage. Oil and hydroelectric follow at around 25 percent each, followed by natural gas at 9 percent and coal at 2 percent. Excluding Chernobyl and the Shimantan Dam, the three other most expensive accidents involved the Exxon Valdez oil spill, the Prestige oil spill, and the Three Mile Island nuclear accident.

Nuclear safety

Nuclear safety covers the actions taken to prevent nuclear and radiation accidents or to limit their consequences. This covers nuclear power plants as well as all other nuclear facilities, the transportation of nuclear materials, and the use and storage of nuclear materials for medical, power, industry, and military uses.
The nuclear power industry has improved the safety and performance of reactors, and has proposed new safer reactor designs but there is no guarantee that the reactors will be designed, built and operated correctly. Mistakes do occur and the designers of reactors at Fukushima in Japan did not anticipate that a tsunami generated by an earthquake would disable the backup systems that were supposed to stabilize the reactor after the earthquake. According to UBS AG, the Fukushima I nuclear accidents have cast doubt on whether even an advanced economy like Japan can master nuclear safety. Catastrophic scenarios involving terrorist attacks are also conceivable.
In his book Normal Accidents, Charles Perrow says that unexpected failures are built into society's complex and tightly-coupled nuclear reactor systems. Nuclear power plants cannot be operated without some major accidents. Such accidents are unavoidable and cannot be designed around. An interdisciplinary team from MIT have estimated that given the expected growth of nuclear power from 2005 – 2055, at least four serious nuclear accidents would be expected in that period. To date, there have been five serious accidents in the world since 1970, corresponding to the beginning of the operation of generation II reactors. This leads to on average one serious accident happening every eight years worldwide.

Ecological impacts

Impact on land

Isotopes released during a meltdown or related event are typically dispersed into the atmosphere and then settle to the surface through natural occurrences and deposition. Isotopes settling in the top soil layer can remain there for many years as a result of the half-life of said particles involved in nuclear events. Due to the long term detrimental affects on agriculture, farming and livestock, it carries further potential to affect human health and safety long after the actual event. After the Fukushima Daiichi accident in 2011, surrounding agricultural areas has been contaminated with more than 100,000 MBq km−2 in cesium concentrations. As a result, eastern Fukushima food production saw massive limitations. Due to the topographical nature of Japan, as well as the weather pattern for the prefecture, cesium deposits as well as other isotopes reside in top layer of soils all over eastern and northeastern Japan. Luckily, mountain ranges have shielded western Japan. The Chernobyl disaster in 1986 caused approximately 125,000 mi2 of land across the Ukraine, Belarus and Russia to be exposed to radiation. The amount of focused radiation caused severe damage to plant reproduction - resulting in most plants being unable to reproduce for a minimum of three years. Many of these occurrences on land can be a result of the distribution of isotopes through water systems.

Impact on water

Fukushima Daiichi accident

In 2013, contaminated groundwater was found in-between some of the affected turbine buildings in the Fukushima Daiichi facility, including locations at bordering seaports that led into the Pacific Ocean. In both locations, the facility typically expulses clean water to feed into further groundwater systems. The Tokyo Electric Power Company, the entity that manages and operates the facility, further investigated the contamination in areas that would deem safe to conduct operations. They found that a significant amount of the contamination originated from underground cable trenches that connected to circulation pumps within the facility. Both the International Atomic Energy Agency and TEPCO confirmed that this contamination was a result of the 2011 earthquake. Due to damages like these, the Fukushima plant released nuclear material into the pacific ocean and has continued to do so. After 5 years of leaking, the contaminates reached all corners of the pacific ocean from North America, to Australia, to Patagonia. Along the same coastline, Woods Hole Oceanographic Institute found trace amounts of Fukushima contaminates 100 miles off of the coast of Eureka, California in November 2014. Despite the relative dramatic increases in radiation, the contamination levels still fall below the World Health Organization's standard for clean drinking water.
In 2019, the Japanese government announced that it was considering the possibility to dump contaminated water from the Fukushima reactor into the Pacific Ocean. Japanese Environmental Minister Yoshiaki Harada reported that TEPCO had collected over a million tons of contaminated water, and by 2022 they would be out of space to safely store the radioactive water.
Multiple private agencies as well as various North American governments monitor the spread of radiation throughout the pacific to track the potential hazards it can introduce to food systems, groundwater supplies, and ecosystems. In 2014, the United States Food and Drug Administration released a report stating that radionuclides, traced from the Fukushima facility, were present in the United States food supply, but not to levels deemed to be a threat to public health – as well as any food and agricultural products imported from Japanese sources. It is commonly believed that, with the rate of the current radionuclide leakage, the dispersal into the water would prove beneficial as most of the isotopes would dilute into the water as well as become less effective over time, thanks to radioactive decay. Cesium is the primary isotope released from the Fukushima Daiichi facility. Cs-137 has a long half-life, meaning it could potentially have long-term harmful effects, but as of now, its levels from 200 km outside of Fukushima show close to pre-accident levels with little spread to North American coasts.

Chernobyl accident

Evidence can be seen from the 1986 Chernobyl event. Due to the violent nature of accident in Chernobyl, a sizable portion of radioactive contamination resulted from the atmosphere were particles what where dispersed during the explosion. Many of these contaminates settled in groundwater systems in immediate surrounding areas, but also Russia and Belarus. Due to the resulting radiation in groundwater, the ecological effects of the disaster can be seen in various aspects down the environmental process line. Radionuclides carried by groundwater systems in and around the areas of Chernobyl have resulted in the uptake to plants in the region and up the food chains into animals, and eventually, humans – as one of the largest exposure points of radiation was through agriculture contaminated by radioactive groundwater. Again, one of the largest concerns to the local populaces within the 30 km exclusion zone is the intake of Cs-137 through the consumption of agricultural products contaminated with groundwater. Comparatively, thanks to the environmental and soil conditions outside the exclusion zone, the recorded levels are below those that require remediation based on a survey in 1996. During this event, the groundwater transportation of radioactive material carried over borders in to neighboring countries. Belarus, lying to Chernobyl's northern border, was subject to approximately 250,000 hectares of previously usable farmland being held by state officials until deemed safe.
Off-site radiological risk may be found in the form of flooding. Many citizens in the surrounding areas have been deemed at risk of exposure to radiation due to the Chernobyl Reactor's proximity to floodplains. A study conducted in 1996 was conducted to see how far the radioactive effects were felt across eastern Europe. Lake Kojanovskoe in Russia, 250 km from the Chernobyl accident site, was found to be one of the most impacted lakes traced from the disaster area. Fish collected from the lake were found to be 60 times more radioactive than the European Union Standard. Further investigation found that the water source feeding the lake provided drinking water for approximately 9 million Ukrainians, as well as provided agricultural irrigation and food for 23 million more.
A cover was constructed around the damage reactor of the Chernobyl nuclear plant. This helps in the remediation of leaking radioactive material from the site of the accident, but does little to help aid the local area with isotopes that were dispersed in its soils and water ways more than 30 years ago. Partially due to the already abandoned urban areas, as well as international relations currently affecting the country, remediation efforts have minimized compared to the initial clean up actions and more recent accidents such as the Fukushima incident. On site laboratories, monitoring wells, and meteorological stations can be found in a monitoring role on key locations affected by the accident.

Effects of acute radiation exposure