Regarding the Possible Impact of Forest Fires on the Radioactive Pollution of Groundwater in the Chornobyl Exclusion Zone

Wood in the Chornobyl Exclusion Zone (CEZ) is contaminated with ¹³⁷ Cs and ⁹⁰ Sr. The ⁹⁰ Sr activity concentration in the wood reaches tens of kBq/kg. According to laboratory experiments, complete combustion of 1 kg of dry pinewood generates about 2.8 g of ash, resulting in a ⁹⁰ Sr concentration in the ash that is approximately 360 times higher. The specific activity of ⁹⁰ Sr in the ash from six wood samples ranged from 0.16 to 3.4 kBq/g. In filtrate samples, the specific activity of ⁹⁰ Sr, under consistent experimental conditions, reached 0.5 to 0.72 kBq/l. The fraction of ⁹⁰ Sr washed out during the experiment was 12–33% for wood ash and 10.8–13.2% for forest litter ash. The high concentrations of potassium, sodium, calcium, and phosphate ions in the wood ash are readily leached, which increases groundwater mineralization and its ionic strength. This, in turn, contributes to a decrease in the sorption capacity of soils and an increase in the migration capacity of ⁹⁰ Sr in the aquifer. The largest fires in the CEZ occurred in 2020 at the Temporary Radioactive Waste Location Point (PTLRW) “Red Forest” site, where the ⁹⁰ Sr activity in wood peaked. The concentration of ⁹⁰ Sr activity in groundwater samples from observation wells in this section of the CEZ shows an increase of 2 to 60 times, climbing from approximately 2 to about 180 Bq/l, beginning at the end of 2022. Radioactivity concentrated in ash on the soil surface in the burned area is vulnerable to rapid leaching by atmospheric precipitation; as a result, it can become a significant local source of radioactive contamination of surface and groundwater, necessitating updates to the regulations for monitoring radioactivity in the relevant CEZ observation wells.