What to do in the event of an incident involving a significant release of radioactive material?

In recent days, following the start of the Russian-Ukrainian conflict, the Russian invasion of the Chernobyl nuclear power plant site and the attack on the Zaporizhzhya nuclear power plant, many people have asked me what the impact of a nuclear accident in Ukraine could be on Hungary (or on Europe), and what to do in such an event. I will try to summarise this briefly in this paper.

Basics

As I have written several times before, nuclear power plants are designed for a wide range of malfunctions and initial events of various internal and external origin. These so-called "design basis accidents" can be handled by the safety systems of nuclear power plants without resulting in large radioactive releases. However, as we have seen for example in the Fukushima accident, if a nuclear power plant is left without cooling water and without electricity supply (without functioning emergency diesel generators and a functioning electrical grid connection), this can result in a series of events that can damage the reactor fuel and the so-called engineering barriers that are designed to contain the radioactivity. In such a case, higher levels of radioactive material may be released into the environment, the harmful effects of which can only be mitigated by special measures. These are the so called beyond design basis accidents, possibly leading to a major release of radioactivity.

It is important to stress that the type of accident that caused an immediate large release in the Chernobyl accident in 1986, cannot occur in the water-cooled water-moderated reactors now operating in Ukraine. The Chernobyl reactors were graphite-moderated water-cooled reactors in which a very unfavourable reactor physics property, the so-called positive void coefficient, allowed the reactor to runaway (i.e. to increase its power suddenly and enormously), explode, and then the firing of thousands of tonnes of graphite in the reactor for 10 days increased the release of radioactive material into the environment and its dispersion to the higher atmosphere.

The VVER reactors in operation in Ukraine today do not have this unfavourable reactor physics, nor do they have graphite, which could burn for a long time: the moderator of these current reactors is water. Consequently, the accident at the reactors currently operating in Ukraine cannot cause releases close to those experienced in the 1986 Chernobyl accident. It is therefore inconceivable that an accident at these VVER reactors could result in an environmental release many times higher than the release at Chernobyl.

The other important principle is that radioactivity released into the environment is diluted as it spreads through the environment, its concentration decreases and, over time, radioactive isotopes decay, so the longer the release spreads, the less dangerous it is for the environment. Moreover, it is not primarily the geographical distance that is important here, as the air mass containing radioactivity is spreading in the environment depending on the meteorological conditions. Thus, the contamination of a given area will be determined by air currents and precipitation conditions, since the amount of radioactive material that will be released from a radioactive cloud (which is not really a cloud, but just the common name for the radioactive contamination released) to the surface and fall-out will depend on whether precipitation occurs as the polluted air mass passes, which would wash the pollutant out of the air.

As a consequence, releases from even a severe nuclear power plant accident can typically cause high doses to the population within a radius of 10-30 km of the plant that require public protection emergency measures.

Although the lack of official communication after the Chernobyl accident in 1986 caused a great mistrust among the Hungarian and European public, there would have been no reason to take any real public protection measures in Hungary or in other European countries (except in the immediate vicinity of the Chernobyl nuclear power plant). But what these population protection measures might be, more on that a bit later.

How is Hungary prepared to deal with a nuclear accident?

Although the general public fortunately does not really encounter this, Hungary is well prepared, both administratively and in terms of implementation, to deal with the public consequences of a possible nuclear or radiological accident. A nuclear accident is defined as an event involving the potential release of radioactive material from a nuclear facility, nuclear reactor or nuclear fuel, while a radiological accident may occur in the case of other radiation sources (medical, industrial, research, etc.) and may result in additional exposure.

The protection of the population is ensured by the ONER (in Hungarian “Országos Nukleárisbalesetelhárítási Rendszer” – National Nuclear Emergency Preparedness and Response System), with the help of various central, sectoral, regional and local authorities. These authorities typically operate with the assistance of the national emergency management service, may require the setting up of a central or sectoral Operational Task Force, and may have territorial or local civil protection committees in the area concerned. The operational capability of the ONER is tested through regular exercises.

In the event of a nuclear or radiological accident which could release radioactive material into the environment in quantities that could endanger the health of the general public, the authorities involved in ONER may initiate countermeasures to protect the population. Some of these are so-called urgent protective actions, which can be applied in a short time, possibly only a few hours / a few days. Such measures may normally only be necessary in a limited area, for example within a few tens of kilometres of a nuclear power plant.

During the sheltering, the affected population is asked to stay in their homes with closed (possibly sealed) windows, which can significantly reduce the radiation exposure suffered in the early stages of an accident. In some cases it may also be necessary to evacuate the population (i.e. evacuation for a certain period of time).

Figure 1: Surface contamination measurements by a Hungarian scientific expedition in the Chernobyl exclusion zone in 2005 (Photo: MNT FINE)

Should I take iodine pills? Where can I get them?

Certain isotopes of iodine in nuclear accident releases contribute a large fraction of the public exposure through the thyroid gland, increasing the risk of developing thyroid cancer. Typically, the use of iodine pills only arises in the event of a nuclear power plant accident and if the accident occurred in an operating reactor. (For example, if there were a significant release from the Chernobyl nuclear power plant today, there would be no release of radioactive iodine-131 because it is only produced in an operating reactor and decays with a half-life of 8 days, so the iodine-131 once found in Chernobyl reactor spent fuel has now been completely decayed.)

An important tool to reduce the radiation exposure of the population living in the vicinity of a radiological event involving the release of radioactive iodine is the distribution and intake of iodine pills containing stable iodine. This is intended to replenish the thyroid's iodine stores with stable, non-radiative iodine before the exposure to radioactive iodine, so that radioactive iodine released into the environment during the accident can no longer be incorporated into the thyroid of exposed people.

It is important to note that iodine pills are only effective in a short time window, a few hours before or immediately after ingestion of radioactive iodine, and are only indicated where the public may be exposed to large amounts of radioactive iodine. In addition, in a small proportion of the population, ingestion of large amounts of iodine may cause allergic reactions or, as a side effect, a small chance of thyroid malfunction. For this reason, high doses of stable iodine should be taken only when and for those who are prescribed it by the authorities! In Hungary and in some other countries in Europe, this is also when the iodine pills stored in central warehouses are distributed to the public.

In summary, iodine pills are not the ultimate and universal "antiradiation drug", but are justified for use in cases where large amounts of radioactive iodine are released and only where the benefits outweigh the risks of their application.

What additional protection measures can be applied in the event of a release of large quantities of radioactive material into the environment?

There are longer-term protection measures that take longer to implement and are sustainable in the longer term. Examples include banning the use of animal feeds contaminated above a certain level or restricting the consumption of food from contaminated areas.

How can you know what to do in such a situation?

It is very important to get information from reliable news sources! In most of the countries, it is worth watching the national TV channels, where, for example, the emergency management authority can provide information on the news within a short time - even minutes. The credible information is then provided by the authorities, who have the access to the necessary measurements and the knowledge to order the necessary measures.

Should I buy a radiation detector?

My personal opinion is that a layman has little need for his own radiation meter. It is not just a question of whether I can measure radiation somewhere, but whether I understand what I have measured and what I can use the data for. From this point of view, it is also much better to follow the data from the highly accurate radiation measurement system operated by the authorities and to listen to the instructions of the authorities and the experts.

Here you can access online data from the Hungarian radiation monitoring network:

• https://www.katasztrofavedelem.hu/modules/hattersugarzas/aktualis_adatsor
• https://www.met.hu/levegokornyezet/gammadozis_teljesitmeny/magyar/
• EURDEP is an EU operated visualisation system where data from several countries are available online, including some Ukrainian measurements: https://remap.jrc.ec.europa.eu/Advanced.aspx

Of course, if someone is reassured that they have their own radiation detector, I would not discourage them from doing so, but would encourage them to learn how to take the measurements and interpret the results.

It is also important to know that background radiation varies over a wide range in space and time. In Hungary and also in other European countries, the typical background radiation in nature is about 100 nSv/h (100 nano-sieverts per hour), but in some places it is as low as 60 nSv/h for long periods, while in other places it can be as high as 150-200 nSv/h. This is perfectly normal and 200 nSv/h is no more harmful to health than 100 nSv/h.

It should also be noted that this value is affected by a number of circumstances, such as precipitation: when rain washes significant amounts of dust out of the air, radon and its decay products and other natural radioactive substances bound to the dust are washed out of the air and appear on the detector placed in the open air, so that in some cases, when rain arrives, there could be a temporary increase of 20-50% in the data of the instruments measuring the open air radiation dose rate. I emphasise that these so-called rain spikes are completely natural and pose no danger to humans (this is how nature has worked for thousands of years, even if we as average humans do not monitor it on a daily basis.)

Figure 2: Example of peak rainfall

The figure above shows data from three background radiation measurement stations in and around Budapest. The data show perfectly the effect of the overnight precipitation (3-5 mm of rain) on 22 February, 2022. Note also that the baseline value of the station in the city (SOTE, 9^th district of Budapest, Hungary) is inherently 15-20% higher than the other two. Source of data: EURDEP, https://remap.jrc.ec.europa.eu/Advanced.aspx.