Russian forces fired missiles at a physics institute in Kharkiv, according to Ukraine’s Security Service, marking the second attack on a Ukrainian nuclear facility in under a week.

Ukraine’s Security Service stated in a Facebook post on Sunday that the Russians were firing at the Kharkiv Institute of Physics and Technology from Grad launchers. Inside the institute is nuclear material and a reactor, which the service said could lead to a “large-scale ecological disaster” if hit, according to the Daily Mail.