Chernobyl wildfires & radiation risk

Contamination by radioactive iodine can cause thyroid cancer, as it was the case after the 1986 Chernobyl nuclear power plant accident.

Health effects of the Chernobyl accident: an overview

If exposure (from radioactive-iodine-contaminated soil/food/water) cannot be avoided, a way to prevent this is to prophylactically ingest potassium iodine before potential exposure, as per WHO's guidelines.

Use of potassium iodide for thyroid protection during nuclear or radiological emergencies

The question I am trying to answer here is do we need to take some in prevention or not.

Please note that I am not a medical doctor and that such decision is usually left to governments. I am not advising anyone to buy and/or consume potassium iodided.

Considering the recent wildfires in the vicinity of the Chernobyl site, I was wondering if there was any risk for my family to be exposed to dangerous levels of radioactive iodine.

As if covid-19 was not enough already.

First question was the altitude that which the potentially radioactive cloud - or "plume" - would reach.

This article below shows that most of the smoke particules are typically distributed between 0 and 5km in the case of European forests.

This is not that high - for reference, most commercial airplanes cruise between 10,000 and 13,000m

A Global Analysis of Wildfire Smoke Injection Heights Derived from Space-Based Multi-Angle Imaging

Second logical question was the winds direction.

Very interestingly - and completely overlooked due to the covid-19 situation - an extraordinarily strong anticyclone has been covering Western Europe (in red on the map). It has been bringing onto us the highest atmospheric pressures ever recorded in the UK, France, and Belgium.

Europe's weather mix: Record high pressure, cold and Storm Gloria

Not to get into advanced meteorology, this means that winds will have a tendency to move away from Western Europe.

Bad news in terms of atmospheric pressure health side effects, but rather good news for Western Europeans from a radioactive contamination point of view.

Now, this is still worth double checking.

If you are familiar with aeronautics, it is reasonably easy to find detailed wind maps.

The one on the side shows winds at the FL100 level, i.e. 10,000ft, or ~3,000m in scientific units.

As one can see, winds are rotating clockwise around the center of the anticyclone described above, as they should in the Northern Hemisphere due to Coriolis forces and anticyclonic rotation.

But most importantly, one can see that winds are blowing towards the South West in the Chernoby region.

If one looks at a satellite picture of the region, this is clearly confirmed as shown by the direction of the smoke clouds.

What it means is that Western Europe, and a fortiori the UK, have very little chance of exposure to any radioactive iodine contamination, but Kiev and Southern populations are to some extent.

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If you are interested in a visual representation of radiation doses - for the sake of interest, not to scare anyone - Randall Munroe's xkcd is a great source of inspiration, as always.


I did not take into account that iodine 131 is only a concern in case of a recent reactor issue as it will have been fully decayed by now.

This does not change the general thinking process (of other radioactive risks, such as caesium 137), but it does make the iodine 131 risk irrelevant, and the potassium iodide useless.

I can't put it better than Charlie Hagedorn, PhD did in his highest upvoted comment (including by myself) via Hacker News:

  • I don't believe that there are any significant I-131 production mechanisms within the decay chains of the fallout.

  • Iodine 131 has an eight-day half life. The accident was 12,409 days ago. There is <2^{-1500} of the iodine remaining.

  • For scale, if the Earth were made entirely, by mass, from I-131 on the day of the accident, there would have been ~10^50 nuclei. All of those nuclei would have decayed into daughters within the first four years.

  • There is certainly plenty of residual radioactivity from Chernobyl, with which one might be concerned regarding forest fires. The specific hazard against which potassium iodide provides protection, however, is no longer present.