Notes:

Compilation of the three images done by me. Sources below:
• @Osinttechnical on Twitter: Chernobyl exclusion zone, Russian trenches and fighting positions
• @DefenceU on Twitter: Ukrainian side making the claims with the same footage
• @Nrg8000 on Twitter: These trenches dug by Russian forces during their invasion of the region were dug in the most irradiated areas of the Chernobyl Radiation Area, see this map of soil Caesium radiation around the disaster area, with the location of the trenches marked. No wonder some got sick.
• GIF version here

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• Article reporting the claims:
+ From The Drive
+ From Australian News.com