Radioactive fallout
Radioactive precipitation (also from English Fallout called) is produced after a nuclear explosion or from a serious nuclear reactor accident . An explosion with any of these causestransports dust into the atmosphere . This dust spreads in different layers and at different speeds and directions as an aerosol . The resulting precipitation with dust as condensation nuclei is detected and measured on the earth's surface. The radioactivity of the dust particles causes considerable radioactive radiation exposure and possibly poisoning ( radiation sickness ).
Black Rain
A special form of radioactive fallout is black rain , which is mainly associated with the atomic bombs being dropped on Hiroshima and Nagasaki . Among other things, this coined a novel of the same name ; it is also mentioned in many other stories on the subject of nuclear war.
The released when igniting a nuclear weapon energy vaporizes everything near and further inflamed Remote. The resulting ash or smoke , swirled up dust and the water vapor mix with the sublimated radioactive residues of the weapon to form a radioactive cloud that cools down as it rises and finally rains down . This radioactive rain is black due to the high ash content.
Wash out
The washout is another variant of the fallout. During the washout, radioactive particles fall from above onto a cloud cover or they combine with the raindrops in the cloud and fall to the ground. This effect can lead to contaminated particles being deposited at great distances from the source when precipitation occurs. This increases the radiation exposure of the living beings affected, even at close range.
Composition and strength
To consider the strength and composition of radioactive precipitation, the resulting quantities of fission products (the source term), the height of the explosion, the distribution and distribution through the local weather and the individual properties of the individual fission products must be taken into account. The source term is directly proportional to the effectively split uranium or plutonium. Therefore, fusion stages contribute little to the source term. The salted bomb concept provides for the generation of particularly dangerous activation products such as 60 Co in order to contaminate the environment as effectively as possible.
- With a classic nuclear fission bomb based on uranium / plutonium (atomic bomb), fission products are created proportional to the explosive force, which then fall down as radioactive fallout and can contaminate the environment.
- Two-stage nuclear weapons of the Teller-Ulam design produce fewer radioactive fission products in relation to their explosive power , as a large part of the explosive power is provided by the fusion reaction.
- Three-stage nuclear weapons with a casing made of 238 U generate a particularly large number of fission products due to their size.
- In the case of a dirty bomb , which is not a nuclear weapon in the narrower sense, one does not speak of fallout, but of local contamination from the radioactive substances buried in it.
The spatial distribution of the fission products differs significantly when a nuclear weapon is ignited underground, on the ground or at a great height. If an underground explosion does not reach the surface, no radioactive precipitation occurs. In the long term, however, the mobile elements, i.e. H. the noble gases and some other elements that do not bind chemically in the soil reach the surface. In the case of an ignition close to the ground, a large part of the radioactive substances is deposited locally. A significant part also ends up in the atmosphere, from where it is dispersed by winds and rainfall. The following applies: The higher the radioactive cloud rises, the further the radioactive fallout is distributed. Since the amount remains the same, this means a larger area, but locally less intensive radiation exposure. A particularly large amount of radioactive fallout occurs in semi-underground explosions, which are ignited underground, but in which the force of the explosion penetrates the ground to the surface, creates a fountain and leaves an explosion crater .
The composition of the radioactive fallout is diverse. The products that arise from the fission of uranium or plutonium are essential . Well-known fission products are isotopes of the elements cesium , iodine and strontium . The isotopes iodine-131 and cesium-137 are of particular interest. The former, because due to the rather short half-life of 8 days and the simple absorption into the human body via the breath, it can lead to high radiation doses in the thyroid in the first few weeks. The second, because it emits long-term radiation with high intensity due to its half-life of 30 years, so that even relatively small amounts can pose a health risk.
Originally non-radioactive elements, which are converted into unstable isotopes by neutron capture , can contribute to the fallout. A hydrogen bomb explosion releases radioactive tritium .
Distribution of nuclear weapons
The fallout from an atomic bomb can be spread over several thousand square kilometers. Its amount, composition and spatial distribution depends on many factors:
- Weather conditions (wind conditions, humidity, rain at the time of ignition, air temperature or thermal conditions, etc.)
- Ignition height of the atomic bomb (the Hiroshima bomb was detonated 580 meters above ground, the Nagasaki bomb 550 meters above ground)
- Explosive strength of the atomic bomb (two identically constructed atomic bombs can have quite different explosive strengths)
In addition, every aboveground atomic bomb ignition (see also atomic bomb test ) also increases radioactive pollution worldwide, as elements with half-lives of several years are distributed over the earth. The so-called background radiation has increased to this day due to nuclear weapon tests.
In the 1950s and 1960s in particular, the worldwide radioactive fallout from above-ground nuclear weapons tests in the USA and the Soviet Union was considerable, so that above-ground tests were discontinued by a 1963 convention for radiation protection reasons . China conducted its last aboveground atomic bomb test in 1980 .
During the worldwide aboveground nuclear weapons tests from 1954 to 1966 a fallout of 2500 becquerel per square meter 90 strontium and 4000 becquerel per square meter 137 cesium was measured on the soil of the old federal states . Much of the debris is still there today.
Distribution in case of nuclear power accidents
Chernobyl
The 1986 Chernobyl disaster also produced fallout that fell in Central Europe and is measurable to this day. In Neuherberg near Munich, the Society for Radiation Research measured 19,000 Becquerel per square meter for 137 cesium on April 26, 1986 - almost five times as much as through the nuclear weapon tests. In addition, 210 Becquerel 90 Sr were deposited per square meter . 90 Sr is a beta emitter with a decay energy of 0.546 MeV and decays to 90 Y with a half-life of 28.78 years , which in turn decays to the stable 90 Zr with beta decay. 90 Sr is a frequently occurring fission product in the nuclear fission of uranium , for example of 235 U in nuclear power plants .
The cause of the large-scale shipment was the violent graphite fire in the Chernobyl reactor, which carried the radioactive particles high up into the atmosphere. A very large, but relatively small proportion of the fallout fell on the surrounding regions of Ukraine , Belarus and Russia. The population in the immediate vicinity of the nuclear power plant was lucky in that the wind hit mostly thinly populated areas before the evacuation of cities like Pripyat.
In Chernobyl there was a very high release that spread widely across the globe. With the light water reactors common in the west, a lower release is usually to be expected due to the existing containment . However, due to the lack of fire thermals, this remains relatively close to the ground (invisible cloud) and can therefore lead to higher radiation doses in the vicinity than in Chernobyl.
Fukushima
The Radiation effects from the Fukushima Daiichi nuclear disaster is an essential part of this nuclear disaster .
Distribution of radioactive particles through fire
During the forest and peat fires in Russia in 2010 , the disaster control ministry in Moscow warned that the fires would spread to the Bryansk region , especially in the south in the Novosybkow district , which was severely contaminated by the Chernobyl disaster in April 1986. In the worst case, radioactive substances would be released again. Minister Sergei Shoigu warned that if a fire breaks out there, radioactive particles will rise with the smoke and further areas could be contaminated with fallout.
During the first British nuclear test, Operation Hurricane , in 1952, glowing scraps of metal ignited Spinifex grass growing on the island. The atomic cloud formed in the explosion reached a height of 4500 meters.
Distribution of radioactive particles by wind
Radioactive dust can contaminate large areas through air movements alone, even without moisture. Such a catastrophe occurred, for example, between 1967 and 1968 around the dried up Karachay Lake , which had previously been used for years as a storage facility for radioactive waste from the Mayak nuclear facility . After a drought, the wind carried radioactive dust away from the dry area that was previously covered by the lake and polluted half a million people and an area of around 1,800 km² with an activity of 600 Curie (22 Tera -Becquerel).
Effects
At very high doses, radioactive fallout can lead to acute and usually fatal radiation sickness , or, in the longer term, to leukemia and cancer ( tumors ) at smaller but adequate doses .
The BIU published a detailed report on the possible effects of core meltdown accidents or their radioactive fallout on humans, animals and plants. The report outlines and comments on the results of the “German Risk Study on Nuclear Power Plants” - both those of “Phase A” and those of “Phase B”. The latter was presented to the German public on June 30, 1989 by the Federal Minister of Research and the Society for Plant and Nuclear Safety .
Monitoring and information
The Federal Office for Radiation Protection (BfS) in Salzgitter provides up-to-date measured values for information about the radiation level in precipitation in Germany. This is done by the nationwide ODL measuring network , which detects the local dose rate with around 1700 probes. The current measured values can be viewed on the Internet on the website of the Federal Office for Radiation Protection.
Web links
- Nuclear weapons A – Z (radioactive fallout)
- Medical ABC manual - extensive information on the formation, distribution and health effects of radioactive fallout
- List of Radiation Radioactive Nuclear Fallout Monitoring Websites , ppalme.wordpress.com, March 14, 2011
Individual evidence
- ↑ Forest fire disaster: Minister fears the release of radioactive substances at Chernobyl , Spiegel Online from August 5, 2010.
- ^ Olaf M. Johannessen et al .: Radioactivity and Pollution in the Nordic Seas and Arctic. Springer 2010, ISBN 978-3-540-24232-1 , limited preview in the Google book search
- ^ Production Association Mayak - Chelyabinsk-65 / Ozersk , GlobalSecurity.org, accessed March 16, 2011.
- ↑ a b Core meltdown accidents in German nuclear power plants and their effects on people and the environment , biu-hannover.de
- ↑ Radioactivity measuring network of the Federal Office for Radiation Protection , ODL Germany - Federal Office for Radiation Protection