On average, the radioactive substances produced by a nuclear weapon explosion are more short-lived than the radioactive substances released into the environment in a nuclear power plant accident. For example, if the radiation situation caused by a nuclear detonation is a thousand times the radiation situation caused by a serious nuclear power plant accident one hour after the explosion, the difference in the severity of the radiation situations has levelled out within a few days.

After one year, the fallout of radioactive substances caused by the nuclear explosion will be approximately three per cent of the fallout caused by a nuclear power plant accident. On the other hand, the shorter half-life of the radioactive substances produced in a nuclear explosion also means that, after a nuclear weapon explosion, the dose rates will rise much higher in the initial phase than after a nuclear power plant accident.

The differences between a nuclear detonation and a nuclear power plant accident must also be taken into account in the planning of sheltering. Protecting against a nuclear detonation requires seeking quick protection in civil defence shelters, but in the event of a nuclear power plant accident, seeking protection indoors (in an apartment or public building) is the most important protective measure.

At its worst, nuclear fallout can extend to the territories of several countries hundreds, even thousands of kilometres away. This is influenced by the properties of the explosive, explosion height, the quality of ground surface and weather conditions. Explosion height in particular has a significant impact on whether or not local fallout occurs and, if so, how far it spreads.

Nuclear material (Fin:ydinaineet) refers to specific fissionable substances and source materials suitable for producing nuclear energy. Specific fissionable substances include plutonium-239 (Pu-239) and uranium enriched with isotopes uranium-235 (U-235) or uranium-233 (U-233). The source materials are natural uranium, depleted uranium and thorium.

Nuclear use items (Fin:ydinmateriaali) refers to nuclear substances and other substances used in nuclear weapons or in their design and manufacture (e.g. deuterium and graphite), devices (e.g. fuel processing devices), equipment (e.g. enrichment and waste treatment plants), data materials and agreements.

When a nuclear bomb explodes, a huge amount of thermal radiation is released, causing all the residues of the bomb parts to heat up to several tens of millions of degrees and vaporise. As all gases are created in the original volume of the bomb, evaporation creates enormous pressure that is about one million times that of the normal atmosphere. The thermal radiation of hot gases mainly consists of X-rays, which are absorbed into the surrounding air within a radius of a few metres in an air explosion. The fireball is created as a result of air and the chemical processes of the materials of the weapon's vaporised residues.

The Radiation and Nuclear Safety Authority (STUK) monitors the use of nuclear material in Finland and is a national data centre in matters related to nuclear test monitoring. STUK also cooperates with international operators, such as the IAEA and CTBTO. STUK collects information and maintains situational awareness. STUK also has a standby task if a weapon explodes in a place that may threaten the population. 

Spent nuclear fuel is not the primary material for nuclear weapon construction. The plutonium isotope ratio of the spent fuel is unfavourable for the construction of a bomb, which makes the construction of an effective nuclear weapon more challenging than if actual weapons-grade plutonium were used. Separating plutonium from spent fuel also requires complicated chemical waste treatment. In addition, this would have major political and economic consequences, as such activity would violate the strict conditions of use of nuclear material safeguards and fuel purchase agreements.

The greatest hazards of nuclear weapons arise from their actual use as a bomb, but there is also a minor risk of a nuclear weapon accident associated with manufacturing, storage and transport.  

Nuclear bombs have been destroyed in accidents involving aircraft carrying them in Thule (1968) and Palomares (1966), for example. The accidents contaminated the environment. In 2012, the submarine Yekaterinburg  with nuclear warheads caught fire during maintenance in Kola, Russia. If the warheads had also ignited, plutonium could have spread into the environment. 

Two nuclear bombs have been used in war. During the Second World War, the United States detonated nuclear bombs in Hiroshima and Nagasaki in 1945. In addition, more than 1,000 nuclear bombs have been detonated in nuclear tests, most of them much more powerful than the bombs used in Hiroshima and Nagasaki.

No, it cannot. The Zaporizhzhya nuclear power plant can be cooled even if the water in the Kakhovka reservoir disappears beyond reach. The cooling water needed by the plant is normally taken directly from the reservoir, but the plant is prepared for the possibility that it will not be available. The cooling water required is then taken from a large pool built next to the nuclear power plant. The last of the plant's six reactors stopped generating electricity in autumn 2022, meaning that all reactors have been shut down. This means that considerably less water is needed for cooling than would be required if the reactors were normally generating electricity. The water in the water pool is sufficient.

Products sold as food supplements do not protect the thyroid gland in a radiation hazard situation. The strength of the iodine preparation Jodix sold in Finland differs a thousandfold from the iodine sold as a food supplement.

Side effects of potassium iodide are very rare. However, if you have thyroid disease, you should exercise caution. If necessary, talk to your treating physician before taking iodine tablet.

Potassium iodide is not recommended for those who have had their thyroid gland removed. If you have hyperthyroidism, dermatitis herpetiformis or vasculitis with reduced complement levels (hypocomplementemic vasculitis), you should not take iodine tablets containing potassium iodide. Do not take an iodine tablet if you have previously had a serious allergic reaction to iodine.

Iodine allergy associated with the use of contrast agents does not prevent the use of iodine tablets.

The protective role of potassium iodide on the thyroid gland is limited in patients with hypothyroidism receiving thyroxine or other thyroid hormones.

Iodine tablets are classified as a medicine and their shelf life is stated in the package leaflet. Do not use any medicine after the use-by date stated in the package. Do not discard expired or unused medicines among household waste or pour them down the drain. Return any unused medicines to the pharmacy for disposal.

​​​​​​There is currently no risk related to radiation in Finland and there is no need to take iodine tablets. However, the situation in Ukraine has raised the need for citizen’s preparedness and demand for iodine tablets has increased. The availability problems related to the tablets in pharmacies are temporary. The Finnish pharmaceutical manufacturer responds to the high demand for iodine tablets as much as possible and regulates the production of medicines.

In the event of radiation hazard situations resulting from nuclear power plant accidents, sheltering indoors is the primary protective measure and is effective in reducing radiation exposure. Taking iodine tablets is a secondary protective measure in radiation hazard situations, complementing sheltering indoors.

Additional information: 72hours.fi - Sheltering indoors

A single iodine dose provides protection for one day and some protection on the second day after taking it. The iodine dose should be taken 1–6 hours before exposure to radioactive iodine in order to provide full protection. The later the iodine dose is taken, the greater the reduction in the protective effect. The iodine dose is of no use if the radioactive substances were inhaled more than 12 hours before taking the dose. To ensure correct timing, the iodine tablet should only be taken as instructed by the authorities.

No link has been found between exposure to radioactive iodine and thyroid cancer in adults. This is why the World Health Organisation (WHO) does not recommend iodine tablets for people over 40 years of age in emergency situations. Exceptions are pregnant women and workers at risk. The most vulnerable group in a radiological emergency are young children and foetuses. The risk of adverse effects from an extra dose of iodine also increases with age, as does the incidence of thyroid disease.

The public health care distributes iodine products to newborns that can be accurately dosed for children under 3 years of age or under one month of age. Some pharmacies also offer 65 mg iodine tablets, which can be divided into doses small enough for children under 3 years of age. The iodine tablet is a medicine. Medicines must be administered in doses specified by the manufacturer in the package leaflet. 

The most commonly available iodine tablets in pharmacies, with a strength of 130 mg (Jodix), cannot be reliably divided into doses small enough for children under 3 years of age. The instructions in the iodine preparation package leaflet do not contain any information about giving the iodine tablet to a child under the age of 3.

It is especially important that children and pregnant women take iodine tablets as instructed by the authorities in a radiation hazard situation. The thyroid glands of children and the foetuses are more sensitive to radiation than those of adults. It is also recommended that pregnant women with a thyroid condition take the iodine tablet to protect the foetus. If necessary, talk to your treating physician about taking iodine tablets.

The iodine tablet taken at the right time saturates the thyroid gland with normal non-radioactive iodine and thus prevents the accumulation of radioactive iodine in the thyroid gland. Radioactive iodine will be quickly eliminated from the body by the kidneys. The protective effect of the tablet is reduced if the tablet is taken too early or too late.

A serious nuclear power plant accident may release radioactive iodine into the atmosphere, and this typically builds up in the thyroid gland after entering the body by inhalation, for example. The primary protective measure is sheltering indoors. The build-up of radioactive iodine in the thyroid gland can be reduced by taking an iodine tablet. The efficiency of this measure depends on correct timing. The tablets must therefore only be taken when instructed by the authorities. Instructions for using the iodine tablet are provided via radio and television. Guidance can also be found by following the authorities' communications on their websites and social media channels.