On the night of June 26, 2026, a wildland fire occurred in the radioactively contaminated area following the fall of fragments of Russian UAVs in the Chernobyl Exclusion Zone (EZ). A description of the dynamics of the formation of fire hotspots, assessments of the intensity of radionuclide emissions – combustion products – and the results of modeling the atmospheric spread of radioactive aerosols during the first three days, from June 26 to 28, 2026, are presented on the website of the Institute for Safety Problems of Nuclear Power Plants of the NAS of Ukraine. This information contains a further description of events from June 29 to July 2, 2026.
Global fire map according to FIRMS operational satellite data. On June 28, forest fires continued on the left bank of the Pripyat River (hotspot No. 1 in Fig. 1), and in two fire hotspots (Nos. 2 and 3 in Fig. 1) in the southern part of the EZ as well. By July 3, active burning in hotspot No. 3 had practically ceased.
On June 29, a new fire hotspot (No. 5 in Fig. 1) appeared in the western part of the Exclusion Zone, with active burning ceasing on July 1..
Fig. 1. Temporal dynamics of the emergence of wildland fire hotspots from June 29 to July 1, 2026 (purple triangles – June 29, red circles – June 30, light blue squares – July 1). Black dots show fire hotspots for the entire period 26.06–04.07.2026
Fig. 2. The same as in Fig. 1, for the period from July 2 to 4, 2026 (green diamond symbols – July 2, yellow diamonds – July 3, purple triangles – July 4)
Radioactive contamination of the wildfire areas.
The main fire hotspot No. 1 on the left bank of the Pripyat River appeared in an area with an average deposition density of 137Cs of 200–300 kBq/m2. During its further burning, wildfire spread northward, covering more contaminated areas where the deposition density of 137Cs reaches 700–800 kBq/m2, while in its southern part the fire moved to less contaminated areas with deposition densities of 50–70 kBq/m2.
The deposition density in hotspots Nos. 2–4 averages 30–70 kBq/m2. Due to the spread of the fire front in hotspot No. 3, vegetation burning on July 3 partially spread to an area with contamination densities of about 300 kBq/m2.
The deposition density of 137Cs in hotspot No. 5 is about 500 kBq/m2.
Assessment of 137Cs emission from the wildfire areas. The intensity of the rise of 137Cs from the fire areas into the atmosphere was estimated using a method proposed by scientists from the Institute for Safety Problems of Nuclear Power Plants of the NAS of Ukraine. The method uses satellite data measuring the fire radiative power (FRP) values in fire hotspots according to FIRMS website information, as well as data on the density of radioactive fallout resulting from the Chernobyl accident in the fire areas, adjusted for 2026. The assessment of the 137Cs emission into the atmosphere for each of the five hotspots is presented in Table 1.
Table 1. Estimates of daily 137Cs emission into the atmosphere during June 26 – July 3, 2026
Small differences in emission values during the first 3 days compared to the previous version of estimates are related to the fact that the new version used FRP data from all five FIRMS satellites, whereas previous estimates were based on measurements from only one satellite, NOAA-21.
The total estimated 137Cs emission into the atmosphere from all five hotspots during the first eight days of the fire – from June 26 to the morning of July 3, 2026 – amounted to 82 GBq.
Model calculations of atmospheric transport of radioactive combustion products.
Fig. 3 shows some results of model calculations of the volumetric concentration fields of 137Cs activity in the near-surface air layer, averaged over 6-hour intervals, caused by the rise of combustion products from individual wildfire hotspots from June 29 to July 2, 2026.
Fig. 3. Concentration of 137Cs activity in the near-surface air layer (μBq/m3), caused by emission of combustion products during the periods 00:00–06:00 June 29 (a), 00:00–06:00 June 30 (b), 12:00–18:00 June 30 (c), 00:00–06:00 July 1 (d), 00:00–06:00 July 2 (e), 12:00–18:00 July 2 (f) 2026
During the first half of June 29, the transport direction remained northeast (Fig. 3a). In the evening of June 29, it began to gradually turn clockwise, so that on June 30 the atmospheric spread of combustion products occurred in the southern and southwestern directions (Fig. 3b). By the end of June 30, the transport direction continued to turn west-northwest (Fig. 3c), and during July 1 – to the north (Fig. 3d). After an almost complete turn of the transport direction, the spread of radionuclides from the Exclusion Zone during July 2 occurred to the north and northeast (Fig. 3e-f).
The results of model calculations of the dynamics of 137Cs activity in near-surface air, averaged over 6-hour intervals, for the entire period considered, from June 26 to July 2, 2026, for four districts of Kyiv, as well as for the city of Slavutych (40 km northeast of the nearest forest fire) and the South Ukraine NPP are obtained. According to the modeling, for other operating NPPs – Rivne and Khmelnytskyi – air contamination due to radionuclide spread from the Exclusion Zone is absent throughout the fire period considered. The highest concentrations of 137Cs in Kyiv could reach 1.5–2.7 mBq/m3 in the evening of June 26, these values are is more than two orders of magnitude lower than the maximum permissible concentration of cesium-137 in atmospheric air for the population, 800 mBq/m3. Subsequently, due to wind direction changes, air contamination in Kyiv caused by the transport of fire products from the EZ significantly decreased on June 27. After the resumption of radioactive aerosol transport towards Kyiv on June 28, modeled 137Cs activity values in near-surface air did not exceed 0.35 mBq/m3, which is a consequence of the overall decrease in radionuclide emission intensity from the wildland fire areas of the EZ at that time.
In the city of Slavutych, according to model estimates, radioactive air contamination could have briefly increased to 0.3–0.5 mBq/m3 on June 29. In the area of the South Ukraine NPP, modeled 137Cs activities in near-surface air could reach 0.6 mBq/m3 on June 26, as well as briefly increase during June 27–28, not exceeding 0.1 mBq/m3.
For the first two days of July 2026, model estimates of additional radioactive air contamination in these regions were obtained only for Slavutych – 32 μBq/m3 on July 2.
Conclusions
During the period from June 28 to July 2, 2026, the intensity of radioactive aerosol emissions from the wildfire areas in the Exclusion Zone significantly decreased. Moreover, the combustion products were predominantly carried north and northeast towards Belarus, which led to a reduction to insignificant levels of additional radioactive contamination of near-surface air practically throughout the territory of Ukraine (except for the Exclusion Zone itself).
Information is provided by the Institute for Safety Problems of Nuclear Power Plants of the NAS of Ukraine