When the Chernobyl nuclear site in Ukraine was captured by Russian forces last week, the Ukrainian Foreign Ministry warned of the possibility of “another ecological disaster.”

Normal radiation levels in the Chernobyl Exclusion Zone — which includes four closed reactors, one of which melted down in 1986 and spread radioactive waste across Europe — were exceeded according to Ukraine’s state nuclear regulator, reportedly because of military activity in the area.

But, beyond the Chernobyl plant, there are concerns that some of Ukraine’s 15 active nuclear reactors could be caught in the crossfire.