If an accident in which radioactive substances are released occurs in a nuclear power plant in Germany, in a neighbouring country, or inside or outside Europe, there can be radiological consequences of varying degrees.

Inventory

The radioactive inventory of nuclear reactors typically contains the non-volatile nuclear fuels

• uranium (uranium-235)
• plutonium (plutonium-239)

as well the fission products resulting from nuclear fission

• noble gases such as krypton (e.g. krypton-85) and xenon (e.g. xenon-133)
• highly volatile radioactive substances such as iodine (e.g. iodine-131, iodine-132), caesium (caesium-134 and -137), ruthenium-106, and tellurium-132
• non-volatile radioactive substances such as strontium (strontium-89 and -90)
  other elements

Which radioactive substances are present in what quantities in the reactor core depends, among other things, on which operating phase a reactor is in (i.e. how far the fuel elements in the reactor have burnt out) as well as (in the event of an accident) how much time has elapsed since the nuclear chain reaction taking place in the reactor was terminated.

Small Modular Reactors (SMR)

There are efforts worldwide to develop and use so-called SMRs (Small Modular Reactors) for energy production in the future. SMRs are small, modular nuclear power plants. Various concepts for such small reactors are currently being developed in various countries.

The BfS is investigating the potential impact of a potential emergency on the surrounding area when it comes to the usage of SMRs. Initial assessments suggest that protective measures outside the actual facility may also be necessary. The BfS's investigations relate to a specific emergency procedure in a specific reactor type. Further specific investigations are necessary to obtain a plant-specific assessment of the hazard potential of SMRs. In general, the impact of emergencies in SMRs would likely be less than when it comes to the large nuclear power plants that are currently in operation.

Together with other national and international institutions, the BfS is monitoring current developments regarding SMRs. Emergency plans in Germany will be adjusted if further assessments indicate that protective measures in Germany may be necessary in the event of possible emergencies related to SMRs abroad (e.g. measures for agricultural products).

Background: For the large nuclear power plants that are currently in operation, the following protective measures could be necessary in the vicinity of the facility in the event of an emergency: evacuation, taking iodine tablets, and staying indoors. Precautions in the agricultural sector are also conceivable. The local civil protection authorities will decide whether and, if so, when these measures need to be taken and will provide information accordingly.

Release

The specific types and quantities of radionuclides that can be released in an accident also depend on the type of reactor and the specific damage to the reactor. It is nearly impossible to make general predictions.

If an accident occurs, the operator of the plant usually makes a statement on the type and quantity of radionuclides released; this is then verified by measurements.

In severe accidents, up to 100% of the radioactive noble gases can be released. Most radioactive noble gases are relatively short-lived and decay immediately after release or after a short dispersion time. To a lesser extent, radionuclides bound to dust particles and gaseous substances can also be released. For example, the gaseous and particle-bound component of iodine-131. If a release occurs via the exhaust stack of the reactor building, the decisive factor is whether the filter in the exhaust stack is fully functional.

• If so, mainly noble gases (e.g. xenon and krypton) as well as also other gaseous radioactive substances (e.g. the gaseous component of iodine-131) escape.
• If not, aerosols (radionuclides bound to airborne dust such as caesium-134, caesium-136, and barium-137 as well as the non-gaseous component of iodine-131) can escape in addition to the noble gases.

Spatial scope of the release

Depending on the type of accident, radioactive substances released can reach different heights in the atmosphere, be transported different distances by the weather (wind and precipitation), and thus spread to varying degrees in the oceans and on the land areas of the Earth.

• If high temperatures are generated in an accident (e.g. because of fires), highly volatile radionuclides released can reach high altitudes with the thermal buoyancy and thus be transported quite far.
• If non-volatile radioactive substances such as strontium and plutonium are released, they are deposited mainly in the immediate vicinity of a nuclear power plant.

Examples include: In the Chornobyl disaster, the radioactive elements released reached high altitudes because of high temperatures and were distributed over large parts of Europe. Because of the lower altitude and the island location of Japan, areas north-west of the reactor plant in particular were highly contaminated in the Fukushima disaster on land. However, only low levels of contamination with radioactive substances from the Fukushima reactors were detected on land masses outside Japan. A large proportion of the radionuclides dispersed across the Pacific as a result of the prevailing winds.

Severity and duration of environmental contamination and its consequences

The extent to which the environment is affected by a nuclear power plant accident depends on

• the type and amount of radioactive substances released
• how far they are transported as a result of the weather
• how much they are diluted by air or water during transport
• where and to what extent they are deposited on the ground

How long the environment is affected by the consequences of a nuclear power plant accident depends primarily on the half-life of the radioactive substances released. For example, radioactive iodine-131 is almost completely decayed after only three months because of its relatively short half-life of around eight days. On the other hand, radioactive caesium-137, which has a half-life of around 30 years, and plutonium isotopes, which have half-lives of many thousands of years, can lead to long-term environmental contamination.

Decontamination measures such as the cleaning of surfaces with high-pressure cleaners, the removal and disposal of topsoil, and the mowing and disposal of contaminated land can help reduce the impact of environmental contamination.

Importance for Germany

If a serious accident occurs at a nuclear power plant in a neighbouring country, Germany could – depending on the wind direction at the time of the accident – be affected by the radioactive cloud to the same extent as a serious nuclear power plant accident within Germany.

In the case of serious nuclear power plant accidents in other European countries further away from the border or in other parts of the world, the level of contamination in Germany depends on the type and quantity of release during the accident, the current weather conditions, and the distance from Germany. The concentration of particles in the air decreases the greater the distance from Germany. In the case of accidents outside Europe, only tiny traces of radioactivity can be measured in Germany with highly sensitive measuring instruments.

Nuclear facilities that are not nuclear power plants include final and interim storage facilities for radioactive waste, facilities for nuclear fuel supply and disposal, and research reactors.

Inventory

The radioactive inventory of these facilities is usually much smaller than in nuclear power plants. For example, research reactors are operated with only a few kilograms of uranium-235, whereas nuclear power plants require upwards of several tonnes of uranium-235 per year.

Nuclear installations other than nuclear power plants may contain various radioactive substances, including:

• highly volatile radioactive substances such as iodine (iodine-131), caesium (caesium-134 and -137), ruthenium-106, and tellurium-132
• non-volatile radioactive substances such as plutonium- 238/239/240/241 and strontium (strontium-89/90)
• other elements

Release

The types and quantities of radioactive substances that can be released in the event of an accident depend, among other things, on the type of nuclear facility and the quantities of radioactive substances that are present there. Only long-lived radioactive substances are still present in the inventory of final and interim storage facilities (i.e. no short-lived radioactive substances such as radioactive iodine, ruthenium-106, or tellurium-132).

If an accident occurs, the operator of the plant usually makes a statement on the type and quantity of radionuclides released; this is then verified by measurements.

Spatial scope of the release

Depending on the type of accident and the type of nuclear facility involved, released radioactive substances can spread over different distances. Whilst non-volatile radioactive substances such as plutonium or strontium are usually deposited in the immediate vicinity of the accident site, highly volatile radioactive substances can be dispersed and deposited with wind and weather.
Soil and water in the immediate vicinity of the nuclear facility involved in the accident can also be contaminated.

Severity and duration of environmental contamination and its consequences

The extent to which the environment is affected by an accident at a nuclear facility depends on

• how much of a radioactive substance was released in an accident
• how far it can spread
• how much it is diluted in the process
• where and to what extent it is actually deposited

How long the environment is affected by the consequences of an accident in a nuclear facility depends primarily on the half-life of the radioactive substances released. For example, because of its relatively short half-life of about eight days, radioactive iodine-131 decays almost completely after about three months. On the other hand, radioactive caesium-137, which has a half-life of about 30 years, can lead to long-term environmental contamination.

Decontamination measures such as the cleaning of surfaces (e.g. roads, houses, and roofs) with high-pressure cleaners, the removal and disposal of topsoil, the mowing and disposal of contaminated vegetation, and the cleaning of gutters can help reduce the impact of environmental contamination.

Importance for Germany

If a serious accident were to occur in a nuclear facility (not a nuclear power plant) in Germany or in a neighbouring country, Germany would be affected to a much lesser extent than in the case of a serious accident in a nuclear power plant.

In the case of severe accidents in nuclear facilities (not nuclear power plants) in other European countries far from the border or in other parts of the world, contamination in Germany depends on the type and quantity of release at the time of the accident, the current weather conditions, and the distance from Germany. Because of the considerably smaller inventory compared with nuclear power plants, the extent of damage is also much smaller than in the case of a severe accident in a nuclear power plant.

The concentration of the particles in the air or water becomes lower the further they are transported. In the case of accidents outside Europe, only tiny traces of radioactivity – if any – can be measured in Germany using highly sensitive measuring instruments.

In terrorist or otherwise motivated attacks, radioactive substances can also play a role and be misused.

The use of a "dirty bomb" (i.e. a conventional bomb containing radioactive material as an incidental load that is dispersed in an explosion) and comparable scenarios are considered a possible case of the deliberate misuse of radioactive material. Other scenarios such as the use of an improvised nuclear weapon are considered to be much less likely.

Radioactive substances that may be released

A potential perpetrator will presumably use radioactive substances that are often used in technology or medicine to make a "dirty bomb".

It is nearly impossible to predict which radioactive substances may be released and in what quantities during an attack.

Spatial scope of the release

Depending on the amount of explosive used and other parameters such as weather conditions, radioactive substances released can spread over different distances.

It is expected that the release will affect mainly the immediate vicinity of the explosion (a few hundred metres to a maximum of a few kilometres away). Buildings and soil in the immediate vicinity can also become contaminated.

Severity and duration of environmental contamination and its consequences

How severely and for how long the environment is affected by the consequences of a terrorist or otherwise motivated attack with radioactive substances depends on

• which and how much of a radioactive substance is introduced and released
• how far it can spread
• how much it is diluted in the process
• where and to what extent it is actually deposited

Decontamination measures such as the cleaning of surfaces with high-pressure cleaners, the removal and disposal of topsoil, and the mowing and disposal of contaminated plants can help reduce the impact of environmental contamination.

Radiological importance

The radiological dangers of a "dirty bomb" are generally overestimated. This explicitly refers to the radiological hazards; this assessment does not apply to the assessment of other hazard aspects (e.g. explosion effects or psychological effects).

On the operational side, the German security authorities – including the BfS – are well prepared to defend the country against an attack situation using a "dirty bomb". Prevention against the illegal acquisition and misuse of such sources is highly important. The measures already taken in the Federal Republic of Germany in the areas relevant here justify a high standard by European comparison.

Radioactive substances are used in many areas of social life such as medicine, technology, research, and energy production. The transport of these by road and rail to their place of use must comply with strict safety regulations.

Recommendations of the International Atomic Energy Agency (IAEA) are implemented worldwide in the legal regulations for the transport of radioactive substances. In accordance with the concept of the “safe package”, safety in the transport of radioactive substance should be largely ensured by the package itself – irrespective of the mode of transport.

Radioactive substances that may be released

The transport of radioactive substances ranges from material needed for medical purposes to Castor transports of spent fuel elements. In terms of numbers, radioactive substances for measurement, research, and medical purposes account for the largest proportion of transports of radioactive substances. These can be the highly volatile and non-volatile radioactive substances

• iodine-131 (thyroid) for medical purposes
• phosphorus-32 for medical purposes (radiotherapy)
• carbon-14 for research purposes (age determination)

other elements .

It is nearly impossible to predict which radioactive substances may be released in the event of a transport accident.

If radioactive substances with higher activities (e.g. spent fuel elements) are transported, the transport containers must be designed in such a way that they remain leak-tight even in the event of the most severe accidents so that any leakage of radioactivity is virtually impossible.

Spatial scope of the release

If an accident occurs during the transport of radioactive substances, usually only a relatively small area (in the range of a few metres) around the accident site is affected because of the safety requirements for transport containers.

Severity and duration of environmental contamination and its consequences

If a release occurs because of an accident during the transport of radioactive substances, it is likely to be rapid and of relatively short duration.

How long the environment is affected by the consequences of such an accident depends primarily on the half-life of the radioactive substances released. For example, because of its relatively short half-life of about eight days, radioactive iodine-131 decays almost completely after three months. On the other hand, radioactive caesium-137, which has a half-life of about 30 years, can lead to long-term environmental contamination.

Decontamination measures such as the cleaning of affected surfaces with high-pressure cleaners and the removal and disposal of topsoil can help reduce the impact of environmental contamination.

Despite state control in the handling of radioactive substances, the loss of a radiator or the discovery of an orphan source cannot be completely ruled out. Accidents during the handling of radioactive substances or the accidental melting down of radioactive sources are also conceivable.

Orphan sources, which are usually disposed of as a result of ignorance, are often found in scrap or rubbish containers because most of the companies active in this field in Germany have appropriate radiation measuring equipment.

Activity of radioactive substances that may be released

In most cases, the activity of the found or lost radiation sources is low (e.g. in the case of unknowingly disposed ionisation smoke detectors). As a result, no high hazard is to be expected in the case of misuse.

Spatial scope of the release

If orphan sources are found, the consequences are usually only small-scale; neither disaster control measures nor precautionary radiation protection measures are required.

In the case of sealed radioactive sources, possible release is locally confined to the site of the source. On the other hand, contamination from radioactive sources, the enclosure of which has been unintentionally or wantonly damaged or opened can be carried away by humans and vehicles or dispersed by fire or wind with the air.

Severity and duration of environmental contamination and its consequences

The duration of the impairment of the environment depends on the level of contamination and the half-lives of the nuclides involved.

Without decontamination measures, this would be about three months for contamination by iodine-131 and about 300 years for contamination by caesium-137. Decontamination measures such as rinsing the surfaces of objects or replacing soil can shorten the period of impairment.

If satellites have a higher energy requirement, they sometimes use radionuclide batteries with nuclear or radiologically relevant material or a miniature nuclear reactor to supply power.

At the end of their life, such satellites are launched into a higher earth orbit so that the activity present in them can subside. So far, there have been two crashes of a satellite with a miniature reactor on board: once over the South Atlantic (1983) and once over Canada (1978).

Radioactive substances that may be released

The radioactive inventory of a satellite equipped with a miniature nuclear reactor is similar to that of a small nuclear reactor. It consists mainly of uranium-235 and its fission products.

Various radioactive substances can be used in radionuclide batteries. Plutonium-238 is predominantly used; however polonium-210, strontium-90 and others are also conceivable.

Compared with nuclear power plants, which have a capacity of around 3,000 megawatts, the power of the batteries or miniature reactors used in satellites is considerably lower – usually between 0.01 and 1 kilowatt (radionuclide batteries) and 10 to 100 kilowatts (miniature reactors). Their inventory of radioactive substances is correspondingly smaller.

Spatial scope of the release

If the satellite and its radionuclide battery burn up as it enters the upper atmosphere, the radioactive substances contained in the satellite may be distributed over a large area (possibly even worldwide). These remain in the upper atmosphere for years and decades and cannot be detected on the ground.

If the satellite and its radionuclide battery do not burn up completely when it enters the atmosphere, fragments of the satellite that have not burned up can reach the Earth’s surface. When the satellite crashes, these fragments can spread over a length of several hundred kilometres and a width of several tens of kilometres along the original direction of flight. Around the fragments of the radionuclide battery or reactor, high dose rates can occur in close proximity (i.e. up to a few tens of metres away).

Severity and duration of environmental contamination and its consequences

The extent to which the environment is affected by the crash of a satellite equipped with nuclear or radiologically relevant material depends on

• how large the radioactive inventory of the satellite was
• whether and to what extent the satellite burnt up on entering the Earth’s atmosphere
• where and how widely distributed the satellite fragments reach the Earth’s surface

How long the environment is affected by the consequences of such a crash depends primarily on the half-life of the radioactive substances released. For example, plutonium-238, which is most commonly used in radionuclide batteries and has a half-life of just under 88 years, can lead to long-term environmental contamination.

Radioactive particles deposited on the ground are difficult to dissolve because they were exposed to high temperatures in the atmosphere. Transfer into food or into plants is thus virtually impossible. Milk, meat, root vegetables, and peeled plants are not contaminated. Only plant foods such as surface-grown fresh vegetables and fruits exposed to direct fallout may be contaminated.

Decontamination measures focus primarily on finding, collecting (by removing the top layer of soil), and transporting away radioactive fragments.

Importance for Germany

A satellite crash over Germany is highly unlikely. Modern satellites are usually targeted for crashing over the Pacific Ocean in areas with little shipping traffic.

An unclear situation exists when reports or rumours indicate a release (e.g. because of an accident in a nuclear facility) but the information has not been confirmed. An example of such a situation is the Measurement of ruthenium-106 at numerous measuring stations in Europe at the beginning of October 2017.

It is difficult to predict which radionuclides will be released, how severe the release will be, how far it will extend spatially, and how long it will last.

When a nuclear bomb explodes, nuclear fission and/or fusion processes result in the dispersion of radioactive substances in the environment. In general, radioactive substances of different types and quantities are released very quickly and over a relatively short period of time (explosively). Depending on the physical distance from the explosion site, the consequences for Germany may vary widely.

Radioactive substances that might be released

Most of the radioactive substances contained in a nuclear weapon or formed in the blast also appear in the radioactive inventory of nuclear power plants. However, whereas an accident at a nuclear power plant primarily releases radioactive substances that are volatile or, at any rate, gaseous, a nuclear blast releases all of the radioactive substances contained in the weapon and produced in the blast into the environment, regardless of their individual volatility.

This is because the blast produces such enormously high temperatures within the first few minutes that all radioactive substances from the explosion process are initially present in gaseous form – unlike in an accident at a nuclear power plant – and are therefore released. As they cool, these substances become liquid or solid and adhere to stirred-up dust, for example.

The released radioactive substances can be divided into groups based on the processes by which they were formed:

• Fission products
  Some radioactive isotopes are formed during nuclear fission of the weapon material . This group of "fission products" includes hundreds of different radionuclides, of which the vast majority are very short-lived. In terms of radiation protection, the following nuclides from this group are particularly relevant: barium-140, lanthanum-140 and -142, tellurium-132 and -134, iodine-132, -133, -134 and -135, zirconium-95 and -97, niobium-95 and -97, strontium-91 and -92, yttrium-92, caesium-137 and -138, cerium-143 and -144, molybdenum-99, and ruthenium-103 and -106.
• Activation products
  Due to contact with neutrons formed during nuclear fission of the actual (radioactive) weapon material , it is also possible for originally non-radioactive materials that are incorporated into the nuclear weapon or present in its surroundings (air, soil) to be converted into radioactive substances. For example, this group of "radioactive activation products" includes manganese-54 and -56 as well as cobalt-58 and -60.
• Nuclear material
  Remaining nuclear material, typically uranium-235 and -238 as well as plutonium-239, is also released.

A large proportion of the radioactive substances produced in a nuclear blast are short-lived – in other words, they decay very quickly. Accordingly, the quantity of radioactive substances (and therefore the radiation dose or, more precisely, the dose rate) following such an explosion decreases much faster in affected areas than it does following an accident at a nuclear power plant, for example. Specifically, it decreases by a factor of approximately 100 within 48 hours. This means that, after 48 hours, only some 1% of the radioactive substances originally released in a nuclear blast are still present in the environment.

Spatial scope of release

When a nuclear weapon explodes, it produces initial and residual radiation:

• Initial radiation is produced by nuclear reactions taking place during the explosion and spreads out in all directions at light speed. Its source dies out again within a few seconds. For people who are present within a radius of a few kilometres of the explosion site without protection, the initial radiation is generally fatal. A significant part of the initial radiation comes from fission and activation products that are produced in the nuclear blast and decay again in fractions of a second.
• Residual radiation originates from the slightly longer-lived radioactive substances formed in the blast. Here, "slightly longer-lived" means that, unlike the fission and activation products that are primarily responsible for the initial radiation, these radionuclides exist for longer than around 60 seconds before decaying. They are dispersed over different distances depending on the design of the nuclear weapon and on other parameters such as the weather conditions and are gradually deposited on the ground (fallout).

Fallout from the residual radiation can affect much larger areas than the initial radiation, although the duration of dispersal and deposition of the radioactive substances is limited: 48 hours after a nuclear blast, only some 1% of the radioactive substances originally released are still present in the environment.

Key factors affecting the atmospheric dispersion of the radioactive substances responsible for the residual radiation include the blast yield of the nuclear weapon and, above all, the height of the detonation above the ground:

• In the case of an explosion close to the ground, the radioactive fallout is dispersed over areas at a short distance from the explosion site. These areas are affected significantly more by radiation than in the event of explosions at a height.
• Explosions at a great height have the effect of maximising the radius of the shock wave (a typical military application) and dispersing the released radioactive substances over a much larger area. However, the longer transport path through the air and the larger dispersal area result in a lower concentration of radioactive fallout than in an explosion near the ground.

Severity and duration of environmental contamination and its consequences

How severely and for how long the environment is affected by the radiological consequences of a nuclear blast depend on, among other things:

• which radioactive substances and how much of them are released
• how far they can be dispersed
• how much they are diluted in the process
• where and to what extent they are actually deposited.

Decontamination measures such as cleaning surfaces with high-pressure cleaners, removing and disposing of topsoil, and mowing and disposing of contaminated plants can help to reduce the impact of environmental contamination.

Radiological significance for Germany

In the event of a nuclear blast inside or outside Europe:

• the initial radiation is generally fatal for people who are present within a radius of a few kilometres of the explosion site without protection.
• the residual radiation could affect parts of Germany in the form of radioactive fallout, depending on the distance and on the weather conditions – including in the event of nuclear blasts abroad, although the concentration of radioactive particles in the air becomes more diluted the longer the distance to Germany.

In the case of nuclear blasts outside Europe, only tiny traces of radioactivity can be measured in Germany using highly sensitive measuring instruments. For example, tiny traces of the radioactive substances released in overground nuclear weapons tests in the 1940s to the early 1980s can still be detected in the environment. These levels are decreasing due to radioactive decay of the released radionuclides.