Dirty bomb

From Wikipedia, the free encyclopedia

A dirty bomb or radiological dispersal device (RDD) is a speculative radiological weapon that combines radioactive material with conventional explosives. The purpose of the weapon is to contaminate the area around the dispersal agent/conventional explosion with radioactive material, serving primarily as an area denial device against civilians. It is, however, not to be confused with a nuclear explosion, such as a fission bomb, which by releasing nuclear energy produces blast effects far in excess of what is achievable by the use of conventional explosives. 

Though an RDD would be designed to disperse radioactive material over a large area, a bomb that uses conventional explosives and produces a blast wave would be far more lethal to people than the hazard posed by radioactive material that may be mixed with the explosive. At levels created from probable sources, not enough radiation would be present to cause severe illness or death. A test explosion and subsequent calculations done by the United States Department of Energy found that assuming nothing is done to clean up the affected area and everyone stays in the affected area for one year, the radiation exposure would be "fairly high" but not fatal. Recent analysis of the nuclear fallout from the Chernobyl disaster confirms this, showing that the effect on many people in the surrounding area, although not those in proximity, was almost negligible.

Since a dirty bomb is unlikely to cause many deaths by radiation exposure, many do not consider this to be a weapon of mass destruction. Its purpose would presumably be to create psychological, not physical, harm through ignorance, mass panic, and terror. For this reason dirty bombs are sometimes called "weapons of mass disruption". Additionally, containment and decontamination of thousands of victims, as well as decontamination of the affected area might require considerable time and expense, rendering areas partly unusable and causing economic damage.

Dirty bombs and terrorism

Since the 9/11 attacks the fear of terrorist groups using dirty bombs has increased immensely, which has been frequently reported in the media. The meaning of terrorism used here, is described by the U.S. Department of Defense's definition, which is "the calculated use of unlawful violence or threat of unlawful violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological objectives". There have only ever been two cases of caesium-containing bombs, and neither was detonated. Both involved Chechnya. The first attempt of radiological terror was carried out in November 1995 by a group of Chechen separatists, who buried a caesium-137 source wrapped in explosives at the Izmaylovsky Park in Moscow. A Chechen rebel leader alerted the media, the bomb was never activated, and the incident amounted to a mere publicity stunt.

In December 1998, a second attempt was announced by the Chechen Security Service, who discovered a container filled with radioactive materials attached to an explosive mine. The bomb was hidden near a railway line in the suburban area Argun, ten miles east of the Chechen capital of Grozny. The same Chechen separatist group was suspected to be involved. Despite the increased fear of a dirty bombing attack, it is hard to assess whether the actual risk of such an event has increased significantly. The following discussions on implications, effects and probability of an attack, as well as indications of terror groups planning such, are based mainly on statistics, qualified guessing and a few comparable scenarios.

Effect of a dirty bomb explosion

When dealing with the implications of a dirty bomb attack, there are two main areas to be addressed: (i) the civilian impact, not only dealing with immediate casualties and long term health issues, but also the psychological effect and then (ii) the economic impact. With no prior event of a dirty bomb detonation, it is considered difficult to predict the impact. Several analyses have predicted that RDDs will neither sicken nor kill many people.

Accidents with radioactives

The effects of uncontrolled radioactive contamination have been reported several times.

One example is the radiological accident occurring in Goiânia, Brazil, between September 1987 and March 1988: Two metal scavengers broke into an abandoned radiotherapy clinic and removed a teletherapy source capsule containing powdered caesium-137 with an activity of 50 TBq. They brought it back to the home of one of the men to take it apart and sell as scrap metal. Later that day both men were showing acute signs of radiation illness with vomiting and one of the men had a swollen hand and diarrhea. A few days later one of the men punctured the 1 mm thick window of the capsule, allowing the caesium chloride powder to leak out and when realizing the powder glowed blue in the dark, brought it back home to his family and friends to show it off. After 2 weeks of spread by contact contamination causing an increasing number of adverse health effects, the correct diagnosis of acute radiation sickness was made at a hospital and proper precautions could be put into procedure. By this time 249 people were contaminated, 151 exhibited both external and internal contamination of which 20 people were seriously ill and 5 people died.

The Goiânia incident to some extent predicts the contamination pattern if it is not immediately realized that the explosion spread radioactive material, but also how fatal even very small amounts of ingested radioactive powder can be. This raises worries of terrorists using powdered alpha emitting material, that if ingested can pose a serious health risk, as in the case of deceased former K.G.B. spy Alexander Litvinenko, who either ate, drank or inhaled polonium-210. "Smoky bombs" based on alpha emitters might easily be just as dangerous as beta or gamma emitting dirty bombs.

Public perception of risks

For the majority involved in an RDD incident, the radiation health risks (i.e. increased probability of developing cancer later in life due to radiation exposure) are comparatively small, comparable to the health risk from smoking five packages of cigarettes on a daily basis. The fear of radiation is not always logical. Although the exposure might be minimal, many people find radiation exposure especially frightening because it is something they cannot see or feel, and it therefore becomes an unknown source of danger. Dealing with public fear may prove the greatest challenge in case of an RDD event. Policy, science and media may inform the public about the real danger and thus reduce the possible psychological and economic effects.

Statements from the U.S. government after 9/11 may have contributed unnecessarily to the public fear of a dirty bomb. When United States Attorney General John Ashcroft on June 10, 2002, announced the arrest of José Padilla, allegedly plotting to detonate such a weapon, he said:

[A] radioactive "dirty bomb" (...) spreads radioactive material that is highly toxic to humans and can cause mass death and injury.

— Attorney General John Ashcroft

This public fear of radiation also plays a big role in why the costs of an RDD impact on a major metropolitan area (such as lower Manhattan) might be equal to or even larger than that of the 9/11 attacks. Assuming the radiation levels are not too high and the area does not need to be abandoned such as the town of Pripyat near the Chernobyl reactor, an expensive and time consuming cleanup procedure will begin. This will mainly consist of tearing down highly contaminated buildings, digging up contaminated soil and quickly applying sticky substances to remaining surfaces so that radioactive particles adhere before radioactivity penetrates the building materials. These procedures are the current state of the art for radioactive contamination cleanup, but some experts say that a complete cleanup of external surfaces in an urban area to current decontamination limits may not be technically feasible. Loss of working hours will be vast during cleanup, but even after the radiation levels reduce to an acceptable level, there might be residual public fear of the site including possible unwillingness to conduct business as usual in the area. Tourist traffic is likely never to resume.

There is also a psychological warfare element to radioactive substances. Visceral fear is not widely aroused by the daily emissions from coal burning, for example, even though a National Academy of Sciences study found this causes 10,000 premature deaths a year in the US population of 317,413,000. Medical errors leading to death in U.S. hospitals are estimated to be between 44,000 and 98,000. It is "only nuclear radiation that bears a huge psychological burden — for it carries a unique historical legacy".

Constructing and obtaining material for a dirty bomb

In order for a terrorist organization to construct and detonate a dirty bomb, it must acquire radioactive material. Possible RDD material could come from the millions of radioactive sources used worldwide in the industry, for medical purposes and in academic applications mainly for research. Of these sources, only nine reactor produced isotopes stand out as being suitable for radiological terror: americium-241, californium-252, caesium-137, cobalt-60, iridium-192, plutonium-238, polonium-210, radium-226 and strontium-90, and even from these it is possible that radium-226 and polonium-210 do not pose a significant threat. Of these sources the U.S. Nuclear Regulatory Commission has estimated that within the U.S., approximately one source is lost, abandoned or stolen every day of the year. Within the European Union the annual estimate is 70. There exist thousands of such "orphan" sources scattered throughout the world, but of those reported lost, no more than an estimated 20 percent can be classified as a potential high security concern if used in a RDD. Especially Russia is believed to house thousands of orphan sources, which were lost following the collapse of the Soviet Union. A large but unknown number of these sources probably belong to the high security risk category. Noteworthy are the beta emitting strontium-90 sources used as radioisotope thermoelectric generators for beacons in lighthouses in remote areas of Russia. In December 2001, three Georgian woodcutters stumbled over such a power generator and dragged it back to their camp site to use it as a heat source. Within hours they suffered from acute radiation sickness and sought hospital treatment. The International Atomic Energy Agency (IAEA) later stated that it contained approximately 40 kilocuries (1.5 PBq) of strontium, equivalent to the amount of radioactivity released immediately after the Chernobyl accident (though the total radioactivity release from Chernobyl was 2500 times greater at around 100 MCi (3,700 PBq)).

Although a terrorist organization might obtain radioactive material through the "black market", and there has been a steady increase in illicit trafficking of radioactive sources from 1996 to 2004, these recorded trafficking incidents mainly refer to rediscovered orphan sources without any sign of criminal activity, and it has been argued that there is no conclusive evidence for such a market. In addition to the hurdles of obtaining usable radioactive material, there are several conflicting requirements regarding the properties of the material the terrorists need to take into consideration: First, the source should be "sufficiently" radioactive to create direct radiological damage at the explosion or at least to perform societal damage or disruption. Second, the source should be transportable with enough shielding to protect the carrier, but not so much that it will be too heavy to maneuver. Third, the source should be sufficiently dispersible to effectively contaminate the area around the explosion.

An example of a worst-case scenario is a terror organization possessing a source of very highly radioactive material, e.g. a strontium-90 thermal generator, with the ability to create an incident comparable to the Chernobyl accident. Although the detonation of a dirty bomb using such a source might seem terrifying, it would be hard to assemble the bomb and transport it without severe radiation damage and possible death of the perpetrators involved. Shielding the source effectively would make it almost impossible to transport and a lot less effective if detonated. 

Due to the three constraints of making a dirty bomb, RDDs might still be defined as "high-tech" weapons and this is probably why they have not been used up to now.

Possibility of terrorist groups using dirty bombs

The present assessment of the possibility of terrorists using a dirty bomb is based on cases involving ISIS. This is because the attempts by this group to acquire a dirty bomb coming to light in all forms of media, in part due to the attention this group received for their involvement in the London bridge attack. 

On 8 May 2002, José Padilla (a.k.a. Abdulla al-Muhajir) was arrested on suspicion that he was an Al-Qaeda terrorist planning to detonate a dirty bomb in the U.S. This suspicion was raised by information obtained from an arrested top Al-Qaeda official in U.S. custody, Abu Zubaydah, who under interrogation revealed that the organization was close to constructing a dirty bomb. Although Padilla had not obtained radioactive material or explosives at the time of arrest, law enforcement authorities uncovered evidence that he was on reconnaissance for usable radioactive material and possible locations for detonation. It has been doubted whether José Padilla was preparing such an attack, and it has been claimed that the arrest was highly politically motivated, given the pre-9/11 security lapses by the CIA and FBI.

Later, these charges against José Padilla were dropped. Although there was no hard evidence for Al-Qaeda possessing a dirty bomb, there is a broad agreement that Al-Qaeda poses a potential dirty bomb attack threat because they need to overcome the alleged image that the U.S. and its allies are winning the war against terror. A further concern is the argument, that "if suicide bombers are prepared to die flying airplanes into building, it is also conceivable that they are prepared to forfeit their lives building dirty bombs". If this would be the case, both the cost and complexity of any protective systems needed to allow the perpetrator to survive long enough to both build the bomb and carry out the attack, would be significantly reduced.

Several other captives were alleged to have played a role in this plot. Guantanamo captive Binyam Mohammed has alleged he was subjected to extraordinary rendition, and that his confession of a role in the plot was coerced through torture. He sought access through the American and United Kingdom legal systems to provide evidence he was tortured. Guantanamo military commission prosecutors continue to maintain the plot was real, and charged Binyam for his alleged role in 2008. However they dropped this charge in October 2008, but maintain they could prove the charge and were only dropping the charge to expedite proceedings. US District Court Judge Emmet G. Sullivan insisted that the administration still had to hand over the evidence that justified the dirty bomb charge, and admonished United States Department of Justice lawyers that dropping the charge "raises serious questions in this court's mind about whether those allegations were ever true."

In 2006, Dhiren Barot from North London pleaded guilty of conspiring to murder innocent people within the United Kingdom and United States using a radioactive dirty bomb. He planned to target underground car parks within the UK and buildings in the U.S. such as the International Monetary Fund, World Bank buildings in Washington D.C., the New York Stock Exchange, Citigroup buildings and the Prudential Financial buildings in Newark, New Jersey. He also faces 12 other charges including, conspiracy to commit public nuisance, seven charges of making a record of information for terrorist purposes and four charges of possessing a record of information for terrorist purposes. Experts say if the plot to use the dirty bomb was carried out "it would have been unlikely to cause deaths, but was designed to affect about 500 people."

In January 2009, a leaked FBI report described the results of a search of the Maine home of James G. Cummings, a white supremacist who had been shot and killed by his wife. Investigators found four one-gallon containers of 35 percent hydrogen peroxide, uranium, thorium, lithium metal, aluminum powder, beryllium, boron, black iron oxide and magnesium as well as literature on how to build dirty bombs and information about cesium-137, strontium-90 and cobalt-60, radioactive materials. Officials confirmed the veracity of the report but stated that the public was never at risk.

In April 2009, the Security Service of Ukraine announced the arrest of a legislator and two businessmen from the Ternopil Oblast. Seized in the undercover sting operation was 3.7 kilograms of what was claimed by the suspects during the sale as plutonium-239, used mostly in nuclear reactors and nuclear weapons, but was determined by experts to be probably americium, a "widely used" radioactive material which is commonly used in amounts of less than 1 milligram in smoke detectors, but can also be used in a dirty bomb. The suspects reportedly wanted US$ 10 million for the material, which the Security Service determined was produced in Russia during the era of the Soviet Union and smuggled into Ukraine through a neighboring country.

In July 2014, ISIS militants seized 88 pounds (40 kg) of uranium compounds from Mosul University. The material was unenriched and so could not be used to build a conventional fission bomb, but a dirty bomb is a theoretical possibility. However, uranium's relatively low radioactivity makes it a poor candidate for use in a dirty bomb.

Little is known about civil preparedness to respond to a dirty bomb attack. The Boston Marathon appeared to many to be a situation with high potential for use of a dirty bomb as a terrorist weapon. However, the bombing attack that occurred on April 15, 2013 did not involve use of dirty bombs. Any radiological testing or inspections that may have occurred following the attack were either conducted sub rosa or not at all. Also, there was no official dirty bomb "all clear" issued by the Obama administration. Massachusetts General Hospital had, apparently under their own disaster plan, issued instructions to their emergency room to be prepared for incoming radiation poisoning cases.

Terrorist organizations may also capitalize on the fear of radiation to create weapons of mass disruption rather than weapons of mass destruction. A fearful public response may in itself accomplish the goals of a terrorist organization to gain publicity or destabilize society. Even simply stealing radioactive materials may trigger a panic reaction from the general public. Similarly, a small-scale release of radioactive materials or a threat of such a release may be considered sufficient for a terror attack. Particular concern is directed towards the medical sector and healthcare sites which are "intrinsically more vulnerable than conventional licensed nuclear sites". Opportunistic attacks may range to even kidnapping patients whose treatment involve radioactive materials. Of note is the public reaction to the Goiânia accident, in which over 100,000 people admitted themselves to monitoring, while only 49 were admitted to hospitals. Other benefits to a terrorist organization of a dirty bomb include economic disruption in the area affected, abandonment of affected assets (such a buildings, subways) due to public concern, and international publicity useful for recruitment.

Dirty bomb tests

Israel carried out a four-year series of tests on nuclear explosives to measure the effects were “hostile forces” ever to use them against Israel, Israel’s Haaretz daily newspaper reported June 8, 2015.

Detection and prevention

Dirty bombs may be prevented by detecting illicit radioactive materials in shipping with tools such as a Radiation Portal Monitor. Similarly, unshielded radioactive materials may be detected at checkpoints by Geiger Counters, gamma-ray detectors, and even Customs and Border Patrol (CBS) pager-sized radiation detectors. Hidden materials may also be detected by x-ray inspection and heat emitted may be picked up by infrared detectors. Such devices, however, may be circumvented by simply transporting materials across unguarded stretches of coastline or other barren border areas.

One proposed method for detecting shielded Dirty Bombs is Nanosecond Neutron Analysis (NNA). Designed originally for the detection of explosives and hazardous chemicals, NNA is also applicable to fissile materials. NNA determines what chemicals are present in an investigated device by analyzing emitted γ-emission neutrons and α-particles created from a reaction in the neutron generator. The system records the temporal and spatial displacement of the neutrons and α-particles within separate 3D regions. A prototype dirty-bomb detection device created with NNA is demonstrated to be able to detect uranium from behind a 5 cm-thick lead wall. Other radioactive material detectors include Radiation Assessment and Identification (RAID) and Sensor for Measurement and Analysis of Radiation Transients, both developed by Sandia National Laboratories.

The International Atomic Energy Agency (IAEA) recommends certain devices be used in tandem at country borders to prevent transfer of radioactive materials, and thus the building of dirty bombs. They define the four main goals of radiation detection instruments as detection, verification, assessment and localization, and identification as a means to escalate a potential radiological situation. The IAEA also defines the following types of instruments:

• Pocket-Type Instruments: these instruments provide a low-power, mobile option to detection that allows for security officers to passively scan an area for radioactive materials. These devices should be easily worn, should have an alarm threshold of three times normal radiation levels, and should have a long battery life - over 800 hours.
• Handheld Instruments: these instruments may be used to detect all types of radiation (including neutron) and may be used to search specific targets flexibly. These instruments should aim for ease of use and speed, ideally weighing less than 2 kg and being able to make measurements in less than a second.
• Fixed, installed instruments: these instruments provide a continuous, automatic detection system that can monitor pedestrians and vehicles that pass through. To work effectively pedestrians and vehicles should be led close to the detectors, as performance is directly related to range.

Legislative and regulatory actions can also be used to prevent access to materials needed to create a dirty bomb. Examples include the 2006 U.S. Dirty Bomb Bill, the Yucca Flats proposal, and the Nunn-Lungar act. Similarly, close monitoring and restrictions of radioactive materials may provide security for materials in vulnerable private-sector applications, most notably in the medical sector where such materials are used for treatments. Suggestions for increased security include isolation of materials in remote locations and strict limitation of access.

One way to mitigate a major effect of a radiological weapons may also be to educate the public on the nature of radioactive materials. As one of the major concerns of a dirty bomb is the public panic proper education may prove a viable counter-measure. Education on radiation is considered by some to be "the most neglected issue related to radiological terrorism".

Personal safety

The Dirty Bomb Fact Sheet from FEMA states that the main danger of a dirty bomb comes from the initial blast rather than the radioactive materials. To mitigate the risk of radiation exposure, however, FEMA suggests the following guidelines:

• Covering the mouth/nose with cloth to reduce risk of breathing in radioactive materials.
• Avoiding touching materials touched by the explosion.
• Quickly relocating inside to shield from radiation.
• Remove and pack up clothes. Keep clothes until instructed by authorities how to dispose of them.
• Keep radioactive dust outside.
• Remove all dust possible by showering with soap and water.
• Avoid taking potassium iodide, as it only prevents effects from radioactive iodine and may instead cause a dangerous reaction.

Other uses of the term

The term has also been used historically to refer to certain types of nuclear weapons. Due to the inefficiency of early nuclear weapons, only a small amount of the nuclear material would be consumed during the explosion. Little Boy had an efficiency of only 1.4%. Fat Man, which used a different design and a different fissile material, had an efficiency of 14%. Thus, they tended to disperse large amounts of unused fissile material, and the fission products, which are on average much more dangerous, in the form of nuclear fallout. During the 1950s, there was considerable debate over whether "clean" bombs could be produced and these were often contrasted with "dirty" bombs. "Clean" bombs were often a stated goal and scientists and administrators said that high-efficiency nuclear weapon design could create explosions which generated almost all of their energy in the form of nuclear fusion, which does not create harmful fission products. 

But the Castle Bravo accident of 1954, in which a thermonuclear weapon produced a large amount of fallout which was dispersed among human populations, suggested that this was not what was actually being used in modern thermonuclear weapons, which derive around half of their yield from a final fission stage of the fast fissioning of the uranium tamper of the secondary. While some proposed producing "clean" weapons, other theorists noted that one could make a nuclear weapon intentionally "dirty" by "salting" it with a material, which would generate large amounts of long-lasting fallout when irradiated by the weapon core. These are known as salted bombs; a specific subtype often noted is a cobalt bomb.

In popular culture

• In the 1964 British movie Goldfinger, both Auric Goldfinger and James Bond refer to the nuclear device being smuggled into Fort Knox as "dirty."
• The crime drama television series Numb3rs has an episode that revolves around a dirty bomb (season 1, episode 10).
• In a two-part 2011 episode of Castle, former US soldiers plot to detonate a dirty bomb in New York City and frame a Syrian immigrant for the crime.
• In the 2012 series finale of Flashpoint, an officer is poisoned by caesium from a dirty bomb and is administered Prussian blue to assist in recovery.
• In the 2013 Indian movie Vishwaroopam, the plot revolves around a dirty bomb developed by scraping caesium from oncological equipment to trigger a blast in New York City.
• In the 2014 movie, Batman: Assault on Arkham, the Joker has a dirty bomb which he plans on detonating in Gotham.
• In the January 14, 2016 Republican presidential debates, Ben Carson referenced dirty bombs twice when speaking on US foreign policy.
• In the June 1, 2015 game by Splash Damage, Dirty Bomb, the game is played in a dirty bomb fallout area in London.
• In the Madam Secretary episode "Right of the Boom", a dirty bomb is detonated at a women's education conference in Washington, D.C.
• The American political drama web television series House of Cards has an episode that revolves around a dirty bomb (season 5, episode 7).
• In the 2006 movie Right At Your Door multiple dirty bombs are detonated in Los Angeles.
• In the 2018 video game Detroit: Become Human one of the endings has a character setting off a dirty bomb in southern Detroit.
• In the 2019 video game Metro Exodus one of Russia's major cities, Novosibirsk, has been struck by a dirty bomb during the end of World War III.

Nuclear fallout

From Wikipedia, the free encyclopedia

Nuclear fallout, or fallout, is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes. The amount and spread of fallout is a product of the size of the weapon and the altitude at which it is detonated. Fallout may get entrained with the products of a pyrocumulus cloud and fall as black rain (rain darkened by soot and other particulates, which fell within 30–40 minutes of the Atomic bombings of Hiroshima and Nagasaki). This radioactive dust, usually consisting of fission products mixed with bystanding atoms that are neutron activated by exposure, is a kind of radioactive contamination.

Types of fallout

Atmospheric nuclear weapon tests almost doubled the concentration of radioactive ¹⁴C in the Southern Hemisphere, before levels slowly declined following the Partial Test Ban Treaty.

 

Fallout comes in two varieties. The first is a small amount of carcinogenic material with a long half-life. The second, depending on the height of detonation, is a huge quantity of radioactive dust and sand with a short half-life. 

All nuclear explosions produce fission products, un-fissioned nuclear material, and weapon residues vaporized by the heat of the fireball. These materials are limited to the original mass of the device, but include radioisotopes with long lives. When the nuclear fireball does not reach the ground, this is the only fallout produced. Its amount can be estimated from the fission-fusion design and weight of the weapon. A modern W89 warhead weighs 324 pounds (147 kg). The fission bomb dropped on Hiroshima (Little Boy) weighed 9,700 pounds (4,400 kg).

Global fallout

After the detonation of a weapon at or above the fallout-free altitude (an air burst), fission products, un-fissioned nuclear material, and weapon residues vaporized by the heat of the fireball condense into a suspension of particles 10 nm to 20 µm in diameter. This size of particulate matter, lifted to the stratosphere, may take months or years to settle, and may do so anywhere in the world. Its radioactive characteristics increase the statistical cancer risk. Elevated atmospheric radioactivity remains measurable after the widespread nuclear testing of the 1950s.

Radioactive fallout has occurred around the world, for example people have been exposed to "Iodine-131" from atmospheric nuclear testing. Fallout accumulates on vegetation, including fruits and vegetables. Starting from 1951 people may have gotten exposure, depending on, whether they were outside, the weather forecast, and whether they drank contaminated milk, vegetables or fruit. Exposure can be on an intermediate time scale or long term. The intermediate time scale results from fallout that has been put into the troposphere and ejected by precipitation during the first month. Long term fallout can sometimes occur from deposition of tiny particles carried in the stratosphere. By the time that stratospheric fallout has begun to reach the earth, the radioactivity is very much decreased. Also, after a year it is estimated that a sizable quantity of fission products move from the northern to the southern stratosphere. The intermediate time scale is between 1–30 days, with long term fallout occurring after that. 

Examples of both intermediate and long term fallout occurred after the Chernobyl accident. Chernobyl was a nuclear power facility in Soviet Russia, and in 1986 it accidentally contaminated over about 5 million acres in Ukraine. The main fuel of the reactor was Uranium, and surrounding this was graphite, both of which were vaporized by the hydrogen explosion that destroyed the reactor and breached its containment. An estimated 31 people died within a few weeks after this happened, including two plant workers killed at the scene. Although residents were evacuated within 36 hours, people started to complain of vomiting, migraines and other major signs of radiation sickness. The officials of Ukraine had to close off an 18-mile area. Long term effects included at least 6000 cases of thyroid cancer, mainly among children. Fallout spread throughout Western Europe, with Northern Scandinavia receiving a heavy dose, contaminating reindeer herds in Lapland, and salad greens becoming almost unavailable in France.

Local fallout

During detonations of devices at ground level (surface burst), below the fallout-free altitude, or in shallow water, heat vaporizes large amounts of earth or water, which is drawn up into the radioactive cloud. This material becomes radioactive when it combines with fission products or other radiocontaminants, or when it is neutron-activated. 

The table below summarizes the abilities of common isotopes to form fallout. Some radiation taints large amounts of land and drinking water causing formal mutations throughout animal and human life. 

The 450 km (280 mi) fallout plume from 15 Mt shot Castle Bravo, 1954

 

Per capita thyroid doses in the continental United States resulting from all exposure routes from all atmospheric nuclear tests conducted at the Nevada Test Site from 1951–1962

 

A surface burst generates large amounts of particulate matter, composed of particles from less than 100 nm to several millimeters in diameter—in addition to very fine particles that contribute to worldwide fallout. The larger particles spill out of the stem and cascade down the outside of the fireball in a downdraft even as the cloud rises, so fallout begins to arrive near ground zero within an hour. More than half the total bomb debris lands on the ground within about 24 hours as local fallout. Chemical properties of the elements in the fallout control the rate at which they are deposited on the ground. Less volatile elements deposit first.

Severe local fallout contamination can extend far beyond the blast and thermal effects, particularly in the case of high yield surface detonations. The ground track of fallout from an explosion depends on the weather from the time of detonation onwards. In stronger winds, fallout travels faster but takes the same time to descend, so although it covers a larger path, it is more spread out or diluted. Thus, the width of the fallout pattern for any given dose rate is reduced where the downwind distance is increased by higher winds. The total amount of activity deposited up to any given time is the same irrespective of the wind pattern, so overall casualty figures from fallout are generally independent of winds. But thunderstorms can bring down activity as rain allows fallout to drop more rapidly, particularly if the mushroom cloud is low enough to be below ("washout"), or mixed with ("rainout"), the thunderstorm.

Whenever individuals remain in a radiologically contaminated area, such contamination leads to an immediate external radiation exposure as well as a possible later internal hazard from inhalation and ingestion of radiocontaminants, such as the rather short-lived iodine-131, which is accumulated in the thyroid.

Factors affecting fallout

Location

There are two main considerations for the location of an explosion: height and surface composition. A nuclear weapon detonated in the air, called an air burst, produces less fallout than a comparable explosion near the ground. A nuclear explosion in which the fireball touches the ground pulls soil and other materials into the cloud and neutron activates it before it falls back to the ground. An air burst produces a relatively small amount of the highly radioactive heavy metal components of the device itself. 

In case of water surface bursts, the particles tend to be rather lighter and smaller, producing less local fallout but extending over a greater area. The particles contain mostly sea salts with some water; these can have a cloud seeding effect causing local rainout and areas of high local fallout. Fallout from a seawater burst is difficult to remove once it has soaked into porous surfaces because the fission products are present as metallic ions that chemically bond to many surfaces. Water and detergent washing effectively removes less than 50% of this chemically bonded activity from concrete or steel. Complete decontamination requires aggressive treatment like sandblasting, or acidic treatment. After the Crossroads underwater test, it was found that wet fallout must be immediately removed from ships by continuous water washdown (such as from the fire sprinkler system on the decks). 

Parts of the sea bottom may become fallout. After the Castle Bravo test, white dust—contaminated calcium oxide particles originating from pulverized and calcined corals—fell for several hours, causing beta burns and radiation exposure to the inhabitants of the nearby atolls and the crew of the Daigo Fukuryū Maru fishing boat. The scientists called the fallout Bikini snow. 

For subsurface bursts, there is an additional phenomenon present called "base surge". The base surge is a cloud that rolls outward from the bottom of the subsiding column, which is caused by an excessive density of dust or water droplets in the air. For underwater bursts, the visible surge is, in effect, a cloud of liquid (usually water) droplets with the property of flowing almost as if it were a homogeneous fluid. After the water evaporates, an invisible base surge of small radioactive particles may persist. 

For subsurface land bursts, the surge is made up of small solid particles, but it still behaves like a fluid. A soil earth medium favors base surge formation in an underground burst. Although the base surge typically contains only about 10% of the total bomb debris in a subsurface burst, it can create larger radiation doses than fallout near the detonation, because it arrives sooner than fallout, before much radioactive decay has occurred.

Meteorological

Comparison of fallout gamma dose and dose rate contours for a 1 Mt fission land surface burst, based on DELFIC calculations. Because of radioactive decay, the dose rate contours contract after fallout has arrived, but dose contours continue to grow.

 

Meteorological conditions greatly influence fallout, particularly local fallout. Atmospheric winds are able to bring fallout over large areas. For example, as a result of a Castle Bravo surface burst of a 15 Mt thermonuclear device at Bikini Atoll on March 1, 1954, a roughly cigar-shaped area of the Pacific extending over 500 km downwind and varying in width to a maximum of 100 km was severely contaminated. There are three very different versions of the fallout pattern from this test, because the fallout was only measured on a small number of widely spaced Pacific Atolls. The two alternative versions both ascribe the high radiation levels at north Rongelap to a downwind hotspot caused by the large amount of radioactivity carried on fallout particles of about 50–100 micrometres size.

After Bravo, it was discovered that fallout landing on the ocean disperses in the top water layer (above the thermocline at 100 m depth), and the land equivalent dose rate can be calculated by multiplying the ocean dose rate at two days after burst by a factor of about 530. In other 1954 tests, including Yankee and Nectar, hotspots were mapped out by ships with submersible probes, and similar hotspots occurred in 1956 tests such as Zuni and Tewa. However, the major U.S. "DELFIC" (Defence Land Fallout Interpretive Code) computer calculations use the natural size distributions of particles in soil instead of the afterwind sweep-up spectrum, and this results in more straightforward fallout patterns lacking the downwind hotspot.

Snow and rain, especially if they come from considerable heights, accelerate local fallout. Under special meteorological conditions, such as a local rain shower that originates above the radioactive cloud, limited areas of heavy contamination just downwind of a nuclear blast may be formed.

Effects

A wide range of biological changes may follow the irradiation of animals. These vary from rapid death following high doses of penetrating whole-body radiation, to essentially normal lives for a variable period of time until the development of delayed radiation effects, in a portion of the exposed population, following low dose exposures.

The unit of actual exposure is the röntgen, defined in ionisations per unit volume of air. All ionisation based instruments (including geiger counters and ionisation chambers) measure exposure. However, effects depend on the energy per unit mass, not the exposure measured in air. A deposit of 1 joule per kilogram has the unit of 1 gray (Gy). For 1 MeV energy gamma rays, an exposure of 1 röntgen in air produces a dose of about 0.01 gray (1 centigray, cGy) in water or surface tissue. Because of shielding by the tissue surrounding the bones, the bone marrow only receives about 0.67 cGy when the air exposure is 1 röntgen and the surface skin dose is 1 cGy. Some lower values reported for the amount of radiation that would kill 50% of personnel (the LD₅₀) refer to bone marrow dose, which is only 67% of the air dose.

Short term

Fallout shelter sign on a building in New York City

 

The dose that would be lethal to 50% of a population is a common parameter used to compare the effects of various fallout types or circumstances. Usually, the term is defined for a specific time, and limited to studies of acute lethality. The common time periods used are 30 days or less for most small laboratory animals and to 60 days for large animals and humans. The LD₅₀ figure assumes that the individuals did not receive other injuries or medical treatment.

In the 1950s, the LD₅₀ for gamma rays was set at 3.5 Gy, while under more dire conditions of war (a bad diet, little medical care, poor nursing) the LD₅₀ was 2.5 Gy (250 rad). There have been few documented cases of survival beyond 6 Gy. One person at Chernobyl survived a dose of more than 10 Gy, but many of the persons exposed there were not uniformly exposed over their entire body. If a person is exposed in a non-homogeneous manner then a given dose (averaged over the entire body) is less likely to be lethal. For instance, if a person gets a hand/low arm dose of 100 Gy, which gives them an overall dose of 4 Gy, they are more likely to survive than a person who gets a 4 Gy dose over their entire body. A hand dose of 10 Gy or more would likely result in loss of the hand. A British industrial radiographer who was estimated to have received a hand dose of 100 Gy over the course of his lifetime lost his hand because of radiation dermatitis. Most people become ill after an exposure to 1 Gy or more. The fetuses of pregnant women are often more vulnerable to radiation and may miscarry, especially in the first trimester.

One hour after a surface burst, the radiation from fallout in the crater region is 30 grays per hour (Gy/h). Civilian dose rates in peacetime range from 30 to 100 µGy per year.

Fallout radiation decays relatively quickly with time. Most areas become fairly safe for travel and decontamination after three to five weeks.

For yields of up to 10 kt, prompt radiation is the dominant producer of casualties on the battlefield. Humans receiving an acute incapacitating dose (30 Gy) have their performance degraded almost immediately and become ineffective within several hours. However, they do not die until five to six days after exposure, assuming they do not receive any other injuries. Individuals receiving less than a total of 1.5 Gy are not incapacitated. People receiving doses greater than 1.5 Gy become disabled, and some eventually die.

A dose of 5.3 Gy to 8.3 Gy is considered lethal but not immediately incapacitating. Personnel exposed to this amount of radiation have their cognitive performance degraded in two to three hours,^[12][13] depending on how physically demanding the tasks they must perform are, and remain in this disabled state at least two days. However, at that point they experience a recovery period and can perform non-demanding tasks for about six days, after which they relapse for about four weeks. At this time they begin exhibiting symptoms of radiation poisoning of sufficient severity to render them totally ineffective. Death follows at approximately six weeks after exposure, although outcomes may vary.

Long term

Comparison of predicted fallout "hotline" with test results in the 3.53 Mt 15% fission Zuni test at Bikini in 1956. The predictions were made under simulated tactical nuclear war conditions aboard ship by Edward A. Schuert.

 

Following the detonation of the first atomic bomb, pre-war steel and post-war steel which is manufactured without atmospheric air, became a valuable commodity for scientists wishing to make extremely precise instruments that detect radioactive emissions, since these two types of steel are the only steels that do not contain trace amounts of fallout.

 

Late or delayed effects of radiation occur following a wide range of doses and dose rates. Delayed effects may appear months to years after irradiation and include a wide variety of effects involving almost all tissues or organs. Some of the possible delayed consequences of radiation injury, with the rates above the background prevalence, depending on the absorbed dose, include carcinogenesis, cataract formation, chronic radiodermatitis, decreased fertility, and genetic mutations.

Presently, the only teratological effect observed in humans following nuclear attacks on highly populated areas is microcephaly which is the only proven malformation, or congenital abnormality, found in the in utero developing human fetuses present during the Hiroshima and Nagasaki bombings. Of all the pregnant women who were close enough to be exposed to the prompt burst of intense neutron and gamma doses in the two cities, the total number of children born with microcephaly was below 50. No statistically demonstrable increase of congenital malformations was found among the later conceived children born to survivors of the nuclear detonations at Hiroshima and Nagasaki. The surviving women of Hiroshima and Nagasaki who could conceive and were exposed to substantial amounts of radiation went on and had children with no higher incidence of abnormalities than the Japanese average.

The Baby Tooth Survey founded by the husband and wife team of physicians Eric Reiss and Louise Reiss, was a research effort focused on detecting the presence of strontium-90, a cancer-causing radioactive isotope created by the more than 400 atomic tests conducted above ground that is absorbed from water and dairy products into the bones and teeth given its chemical similarity to calcium. The team sent collection forms to schools in the St. Louis, Missouri area, hoping to gather 50,000 teeth each year. Ultimately, the project collected over 300,000 teeth from children of various ages before the project was ended in 1970.

Preliminary results of the Baby Tooth Survey were published in the November 24, 1961, edition of the journal Science, and showed that levels of strontium 90 had risen steadily in children born in the 1950s, with those born later showing the most pronounced increases. The results of a more comprehensive study of the elements found in the teeth collected showed that children born after 1963 had levels of strontium 90 in their baby teeth that was 50 times higher than that found in children born before large-scale atomic testing began. The findings helped convince U.S. President John F. Kennedy to sign the Partial Nuclear Test Ban Treaty with the United Kingdom and Soviet Union, which ended the above-ground nuclear weapons testing that created the greatest amounts of atmospheric nuclear fallout.

The baby tooth survey was a "campaign [that] effectively employed a variety of media advocacy strategies" to alarm the public and "galvanized" support against atmospheric nuclear testing, with putting an end to such testing being commonly viewed as a positive outcome for a myriad of other reasons. The survey could not show then at the time, nor in the decades that have elapsed, that the levels of global strontium-90 or fallout in general, were in any way life-threatening, primarily because "50 times the strontium-90 from before nuclear testing" is a minuscule number, and multiplication of minuscule numbers results in only a slightly larger minuscule number. Moreover, the Radiation and Public Health Project which currently retains the teeth has had their stance and publications heavily criticized: A 2003 article in The New York Times states that the group's work has been controversial and has little credibility with the scientific establishment. Similarly, in an April 2014 article in Popular Science, Sarah Fecht explains that the group's work, specifically the widely discussed case of cherry-picking data to suggest that fallout from the 2011 Fukushima accident caused infant deaths in America, is "junk science", as despite their papers being peer-reviewed, all independent attempts to corroborate their results return findings that are not in agreement with what the organization suggests. The organization had earlier also tried to suggest the same thing occurred after the 1979 Three Mile Island accident but this was likewise exposed to be without merit. The tooth survey, and the expansion of the organization into attempting the same test-ban approach with US nuclear electric power stations as the new target, is likewise detailed and critically labelled as the "Tooth Fairy issue" by the Nuclear Regulatory Commission.

Effects on the environment

In the event of a large-scale nuclear exchange, the effects would be drastic on the environment as well as directly to the human population. Within direct blast zones everything would be vaporized and destroyed. Cities damaged but not completely destroyed would lose their water system due to the loss of power and supply lines rupturing. Within the local nuclear fallout pattern suburban areas' water supplies would become extremely contaminated. At this point stored water would be the only safe water to use. All surface water within the fallout would be contaminated by falling fission products.

Within the first few months of the nuclear exchange the nuclear fallout will continue to develop and detriment the environment. Dust, smoke, and radioactive particles will fall hundreds of kilometers downwind of the explosion point and pollute surface water supplies. Iodine-131 would be the dominant fission product within the first few months, and in the months following the dominant fission product would be strontium-90. These fission products would remain in the fallout dust, resulting rivers, lakes, sediments, and soils being contaminated with the fallout.

Rural areas' water supplies would be slightly less polluted by fission particles in intermediate and long-term fallout than cities and suburban areas. Without additional contamination, the lakes, reservoirs, rivers, and runoff would be gradually less contaminated as water continued to flow through its system.

Groundwater supplies such as aquifers would however remain unpolluted initially in the event of a nuclear fallout. Over time the groundwater could become contaminated with fallout particles, and would remain contaminated for over 10 years after a nuclear engagement. It would take hundreds or thousands of years for an aquifer to become completely pure. Groundwater would still be safer than surface water supplies and would need to be consumed in smaller doses. Long term, cesium-137 and strontium-90 would be the major radionuclides affecting the fresh water supplies.

The dangers of nuclear fallout do not stop at increased risks of cancer and radiation sickness, but also include the presence of radionucleides in human organs from food. A fallout event would leave fission particles in the soil for animals to consume, followed by humans. Radioactively contaminated milk, meat, fish, vegetables, grains and other food would all be dangerous because of fallout.

From 1945 to 1967 the U.S. conducted hundred of nuclear weapon tests. Atmospheric testing took place over the US mainland during this time and as a consequence scientists have been able to study the effect of nuclear fallout on the environment. Detonations conducted near the surface of the earth irradiated thousands of tons of soil. Of the material drawn into the atmosphere, portions of radioactive material will be carried by low altitude winds and deposited in surrounding areas as radioactive dust. The material intercepted by high altitude winds will continue to travel. When a radiation cloud at high altitude is exposed to rainfall, the radioactive fallout will contaminate the downwind area below.

Agricultural fields and plants will absorb the contaminated material and animals will consume the radioactive material. As a result, the nuclear fallout may cause livestock to become ill or die, and if consumed the radioactive material will be passed on to humans.

The damage to other living organism as a result to nuclear fallout depends on the species. Mammals particularly are extremely sensitive to nuclear radiation, followed by birds, plants, fish, reptiles, crustaceans, insects, moss, lichen, algae, bacteria, mollusks, and viruses.

Climatologist Alan Robock and atmospheric and oceanic sciences professor Brian Toon created a model of a hypothetical small-scale nuclear war that would have approximately 100 weapons used. In this scenario, the fires would create enough soot into the atmosphere to block sunlight, lowering global temperatures by more than one degree Celsius. The result would have the potential of creating widespread food insecurity (nuclear famine). Precipitation across the globe would be disrupted as a result. If enough soot was introduced in the upper atmosphere the planet's ozone layer could potentially be depleted, affecting plant growth and human health.

Radiation from the fallout would linger in soil, plants, and food chains for years. Marine food chains are more vulnerable to the nuclear fallout and the effects of soot in the atmosphere.

Fallout radionuclides' detriment in the human food chain is apparent in the lichen-caribou-eskimo studies in Alaska. The primary effect on humans observed was thyroid dysfunction. The result of a nuclear fallout is detrimental to human survival and the biosphere. Fallout alters the quality of our atmosphere, soil, and water and causes species to go extinct.

Fallout protection

During the Cold War, the governments of the U.S., the USSR, Great Britain, and China attempted to educate their citizens about surviving a nuclear attack by providing procedures on minimizing short-term exposure to fallout. This effort commonly became known as Civil Defense.

Fallout protection is almost exclusively concerned with protection from radiation. Radiation from a fallout is encountered in the forms of alpha, beta, and gamma radiation, and as ordinary clothing affords protection from alpha and beta radiation, most fallout protection measures deal with reducing exposure to gamma radiation. For the purposes of radiation shielding, many materials have a characteristic halving thickness: the thickness of a layer of a material sufficient to reduce gamma radiation exposure by 50%. Halving thicknesses of common materials include: 1 cm (0.4 inch) of lead, 6 cm (2.4 inches) of concrete, 9 cm (3.6 inches) of packed earth or 150 m (500 ft) of air. When multiple thicknesses are built, the shielding is additive. A practical fallout shield is ten halving-thicknesses of a given material, such as 90 cm (36 inches) of packed earth, which reduces gamma ray exposure by approximately 1024 times (2¹⁰). A shelter built with these materials for the purposes of fallout protection is known as a fallout shelter.

Personal protective equipment

As the nuclear energy sector continues to grow, the international rhetoric surrounding nuclear warfare intensifies, and the ever-present threat of radioactive materials falling into the hands of dangerous people persists, many scientists are working hard to find the best way to protect human organs from the harmful effects of high energy radiation. Acute Radiation Syndrome (ARS) is the most immediate risk to humans when exposed to ionizing radiation in dosages greater than around 0.1 Gy/hr. Radiation in the low energy spectrum (alpha and beta radiation) with minimal penetrating power is unlikely to cause significant damage to internal organs. The high penetrating power of gamma and neutron radiation, however, easily penetrates the skin and many thin shielding mechanisms to cause cellular degeneration in the stem cells found in bone marrow. While full body shielding in a secure fallout shelter as described above is the most optimal form of radiation protection, it requires being locked in a very thick bunker for a significant amount of time. In the event of a nuclear catastrophe of any kind, it is imperative to have mobile protection equipment for medical and security personnel to perform necessary containment, evacuation, and any number of other important public safety objectives. The mass of the shielding material required to properly protect the entire body from high energy radiation would make functional movement essentially impossible. This has led scientists to begin researching the idea of partial body protection: a strategy inspired by hematopoietic stem cell transplantation (HSCT). The idea is to use enough shielding material to sufficiently protect the high concentration of bone marrow in the pelvic region, which contains enough regenerative stem cells to repopulate the body with unaffected bone marrow. More information on bone marrow shielding can be found in the Health Physics Radiation Safety Journal article Selective Shielding of Bone Marrow: An Approach to Protecting Humans from External Gamma Radiation, or in the Organisation for Economic Co-operation and Development (OECD) and the Nuclear Energy Agency (NEA)'s 2015 report: Occupational Radiation Protection in Severe Accident Management.

The Seven Ten Rule

The danger of radiation from fallout also decreases rapidly with time due in large part to the exponential decay of the individual radionuclides. A book by Cresson H. Kearny presents data showing that for the first few days after the explosion, the radiation dose rate is reduced by a factor of ten for every seven-fold increase in the number of hours since the explosion. He presents data showing that "it takes about seven times as long for the dose rate to decay from 1000 roentgens per hour (1000 R/hr) to 10 R/hr (48 hours) as to decay from 1000 R/hr to 100 R/hr (7 hours)." This is a fairly rough rule of thumb based on observed data, not a precise relation.

Government Guides to Fallout Protection in the 1960s

The United States government, often the Office of Civil Defense in the Department of Defense, provided guides to fallout protection in the 1960s, frequently in the form of booklets. These booklets provided information on how to best survive nuclear fallout. They also included instructions for various fallout shelters, whether for a family, a hospital, or a school shelter were provided. There were also instructions for how to create an improvised fallout shelter, and what to do to best increase a person’s chances for survival if they were unprepared.

The central idea in these guides is that materials like concrete, dirt, and sand are necessary to shield a person from fallout particles and radiation. A significant amount of materials of this type are necessary to protect a person from fallout radiation, so safety clothing cannot protect a person from fallout radiation. However, protective clothing can keep fallout particles off a person’s body, but the radiation from these particles will still permeate through the clothing. For safety clothing to be able to block the fallout radiation, it would have to be so thick and heavy that a person could not function.

These guides indicated that fallout shelters should contain enough resources to keep its occupants alive for up to two weeks. Community shelters were preferred over single-family shelters. The more people in a shelter, the greater quantity and variety of resources that shelter would be equipped with. These communities’ shelters would also help facilitate efforts to recuperate the community in the future. Single family shelters should be built below ground if possible. Many different types of fallout shelters could be made for a relatively small amount of money. A common format for fallout shelters was to build the shelter underground, with solid concrete blocks to act as the roof. If a shelter could only be partially underground, it was recommended to mound over that shelter with as much dirt as possible. If a house had a basement, it is best for a fallout shelter to be constructed in a corner of the basement. The center of a basement is where the most radiation will be because the easiest way for radiation to enter a basement is from the floor above. The two of the walls of the shelter in a basement corner will be the basement walls that are surrounded by dirt outside. Cinder blocks filled with sand or dirt were highly recommended for the other two walls. Concrete blocks, or some other dense material, should be used as a roof for a basement fallout shelter because the floor of a house is not an adequate roof for a fallout shelter. These shelters should contain water, food, tools, and a method for dealing with human waste.

If a person did not have a shelter previously built, these guides recommended trying to get underground. If a person had a basement but no shelter, they should put food, water, and a waste container in the corner of the basement. Then items such as furniture should be piled up to create walls around the person in the corner. The more things a person can surround themselves with the better. If the underground cannot be reached, a tall apartment building at least ten miles from the blast was recommended as a good fallout shelter. People in these buildings should get as close to the center of the building as possible and avoid the top and ground floors. Once again, people should surround themselves with whatever they can find and acquire whatever resources they can to create a barrier between themselves and fallout particles and radiation. 

During this time, schools were a favorable place to act as a fallout shelter according to the Office of Civil Defense. For starters, schools, not including universities, contained one-quarter of the population of the United States when they were in session at that time. Schools distribution across the nation reflected the density of the population and were often a best building in a community to act as a fallout shelter. Also, schools also already had organization with leaders set in place. The Office of Civil Defense recommended altering current schools and the construction of future schools to include thicker walls and roofs, better protected electrical systems, a purifying ventilation system, and a protected water pump. The Office of Civil Defense determined 10 square feet of net area per person were necessary in schools that were to function as a fallout shelter. A normal classroom could provide 180 people with area to sleep. If an attack were to happen, all the unnecessary furniture was to be moved out of the classrooms to make more room for people. It was recommended to keep one or two tables in the room if possible to use as a food serving station.

The Office of Civil Defense conducted four case studies to find the cost of turning four standing schools into fallout shelters and what their capacity would be. The cost of the schools per occupant in the 1960's were $66.00, $127.00, $50.00, and $180.00. The capacity of people these schools could house as shelters were 735 ,511, 484, and 460 respectively.

Nuclear reactor accident

Fallout can also refer to nuclear accidents, although a nuclear reactor does not explode like a nuclear weapon. The isotopic signature of bomb fallout is very different from the fallout from a serious power reactor accident (such as Chernobyl or Fukushima). 

The key differences are in volatility and half-life.

Volatility

The boiling point of an element (or its compounds) is able to control the percentage of that element a power reactor accident releases. The ability of an element to form a solid controls the rate it is deposited on the ground after having been injected into the atmosphere by a nuclear detonation or accident.

Half-life

A half life is the time it takes half of the radiation of a specific substance to decay. A large amount of short-lived isotopes such as ⁹⁷Zr are present in bomb fallout. This isotope and other short-lived isotopes are constantly generated in a power reactor, but because the criticality occurs over a long length of time, the majority of these short lived isotopes decay before they can be released.

Preventative measures

Nuclear fallout can occur due to a number of different sources. One of the most common potential sources of nuclear fallout is that of nuclear reactors. Because of this, steps must be taken to ensure the risk of nuclear fallout at nuclear reactors is controlled. In the 1950's and 60's, the United States Atomic Energy Commission (AEC) began developing safety regulations against nuclear fallout for civilian nuclear reactors. Because the effects of nuclear fallout are more widespread and longer lasting than other forms of energy production accidents, the AEC desired a more proactive response towards potential accidents than ever before. One step to prevent nuclear reactor accidents was the Price-Anderson Act. Passed by Congress in 1957, the Price-Anderson Act insured government assistance above the $60 million covered by private insurance companies in the case of a nuclear reactor accident. The main goal of the Price-Anderson Act was to protect the multibillion-dollar companies overseeing the production of nuclear reactors. Without this protection, the nuclear reactor industry could potentially come to a halt, and the protective measures against nuclear fallout would be reduced. However, because of the limited experience in nuclear reactor technology, engineers had a difficult time calculating the potential risk of released radiation. Engineers were forced to imagine every unlikely accident, and the potential fallout associated with each accident. The AEC's regulations against potential nuclear reactor fallout were centered on the ability of the power plant to the Maximum Credible Accident, or MCA. The MCA involved a "large release of radioactive isotopes after a substantial meltdown of the reactor fuel when the reactor coolant system failed through a Loss-of-Coolant Accident". The prevention of the MCA enabled a number of new nuclear fallout preventative measures. Static safety systems, or systems without power sources or user input, were enabled to prevent potential human error. Containment buildings, for example, were reliably effective at containing a release of radiation and did not need to be powered or turned on to operate. Active protective systems, although far less dependable, can do many things that static systems cannot. For example, a system to replace the escaping steam of a cooling system with cooling water could prevent reactor fuel from melting. However, this system would need a sensor to detect the presence of releasing steam. Sensors can fail, and the results of a lack of preventative measures would result in a local nuclear fallout. The AEC had to choose, then, between active and static systems to protect the public from nuclear fallout. With a lack of set standards and probabilistic calculations, the AEC and the industry became divided on the best safety precautions to use. This division gave rise to the Nuclear Regulatory Commission, or NRC. The NRC was committed to 'regulations through research', which gave the regulatory committee a knowledge bank of research on which to draw their regulations. Much of the research done by the NRC sought to move safety systems from a deterministic viewpoint into a new probabilistic approach. The deterministic approach sought to foresee all problems before they arose. The probabilistic approach uses a more mathematical approach to weigh the risks of potential radiation leaks. Much of the probabilistic safety approach can be drawn from the radiative transfer theory in Physics, which describes how radiation travels in free space and through barriers. Today, the NRC is still the leading regulatory committee on nuclear reactor power plants.

Determining extent of nuclear fallout

The International Nuclear and Radiological Event Scale (INES) is the primary form of categorizing the potential health and environmental effects of a nuclear or radiological event and communicating it to the public. The scale, which was developed in 1990 by the International Atomic Energy Agency and the Nuclear Energy Agency of the Organization for Economic Co-operation and Development, classifies these nuclear accidents based off the potential impact of the fallout:

• Defence-in-Depth: This is the lowest form of nuclear accidents and refers to events that have no direct impact on people or the environment but must be taken note of to improve future safety measures.
• Radiological Barriers and Control: This category refers to events that have no direct impact on people or the environment and only refer to the damage caused within major facilities.
• People and the Environment: This section of the scale comprises of more serious nuclear accidents. Events in this category could potentially cause radiation to spread to people close to the location of the accident. This also includes an unplanned, widespread release of the radioactive material.

The INES scale is composed of seven steps that categorize the nuclear events, ranging from anomalies that must be recorded to improve upon safety measures to serious accidents that require immediate action.

Chernobyl

The 1986 nuclear reactor explosion at Chernobyl was categorized as a Level 7 accident, which is the highest possible ranking on the INES scale, due to widespread environmental and health effects and “external release of a significant fraction of reactor core inventory”. The nuclear accident still stands as the only accident in commercial nuclear power that led to radiation-related deaths. The steam explosion and fires released approximately 5200 PBq, or at least 5 percent of the reactor core, into the atmosphere. The explosion itself resulted in the deaths of two plant workers, while 28 people died over the weeks that followed of severe radiation poisoning. Furthermore, young children and adolescents in the areas most contaminated by the radiation exposure showed an increase in the risk for thyroid cancer, although the United Nations Scientific Committee on the Effects of Atomic Radiation stated that "there is no evidence of a major public health impact" apart from that. The nuclear accident also took a heavy toll on the environment, including contamination in urban environments caused by the deposition of radionuclides and the contamination of “different crop types, in particular, green leafy vegetables … depending on the deposition levels, and time of the growing season”.

Three Mile Island

 

The nuclear meltdown at Three Mile Island in 1979 was categorized as a Level 5 accident on the INES scale because of the “severe damage to the reactor core” and the radiation leak caused by the incident. The explosion was the most serious accident in the history of American commercial nuclear power plants, yet the effects were different than that of the Chernobyl accident. A study done by the Nuclear Regulatory Commission following the incident reveals that the nearly 2 million people surrounding the Three Mile Island plant “are estimated to have received an average radiation dose of only 1 millirem above the usual background dose”. Furthermore, unlike those affected by radiation in the Chernobyl accident, the development of thyroid cancer in the people around Three Mile Island was “less aggressive and less advanced”.

Fukushima

Like the Three Mile Island incident, the incident at Fukushima was initially categorized as a Level 5 accident on the INES scale after a tsunami disabled the power supply and cooling of three reactors, which then suffered significant melting in the days that followed. However, after combining the accidents on the three reactors rather than assessing them as individual events, the explosion was upgraded to a Level 7 accident. The radiation exposure from the incident caused a recommended evacuation for inhabitants up to 30 km away from the plant. However, it was also hard to track such exposure because 23 out of the 24 radioactive monitoring stations were also disabled by the tsunami. Removing contaminated water, both in the plant itself and run-off water that spread into the sea and nearby areas, became a huge challenge for the Japanese government and plant workers. During the containment period following the accident, thousands of cubic meters of slightly contaminated water were released in the sea to free up storage for more contaminated water in the reactor and turbine buildings. However, the fallout from the Fukushima accident had a minimal impact on the surrounding population. According to the Institut de Radioprotection et de Surêté Nucléaire, over 62 percent of assessed residents within the Fukushima prefecture received external doses of less than 1 mSv in the four months following the accident. In addition, comparing screening campaigns for children inside the Fukushima prefecture and in the rest of the country revealed no significant difference in the risk of thyroid cancer.

International nuclear safety standards

Founded in 1974, the International Atomic Energy Agency (IAEA) was created to set forth international standards for nuclear reactor safety. However, without a proper policing force, the guidelines set forth by the IAEA were often treated lightly or ignored completely. In 1986, the disaster at Chernobyl was evidence that international nuclear reactor safety was not to be taken lightly. Even in the midst of the Cold War, the Nuclear Regulatory Commission sought to improve the safety of Soviet nuclear reactors. As noted by IAEA Director General Hans Blix, "A radiation cloud doesn't know international boundaries." The NRC showed the Soviets the safety guidelines used in the US: capable regulation, safety-minded operations, and effective plant designs. The soviets, however, had their own priority: keeping the plant running at all costs. In the end, the same shift between deterministic safety designs to probabilistic safety designs prevailed. In 1989, the World Association of Nuclear Operators (WANO) was formed to cooperate with the IAEA to ensure the same three pillars of reactor safety across international borders. In 1991, WANO concluded (using a probabilistic safety approach) that all former communist-controlled nuclear reactors could not be trusted, and should be closed. Compared to a "Nuclear Marshall Plan", efforts were taken throughout the 1990s and 2000s to ensure international standards of safety for all nuclear reactors.