As reported by Cybersecurity 202 at the Washington Post.
Ukraine has a couple dozen operating atomic reactors, including a number not far from the Ukraine-Russia border, where the two countries, or their proxies, have already been warring for 8 years.
Ukraine also has closed reactors, such as the four units at Chernobyl. But even there, highly radioactive wastes in storage must be managed safely and securely at all times, less a catastrophe unfold.
Direct cyber attacks on nuclear power plant sites could certainly increase safety, health, and environmental risks significantly, perhaps even catastrophically. But so could indirect cyber attacks, such as on the electricity grid, which is the primary source of electricity for cooling and safety at atomic reactors, irradiated nuclear fuel storage pools, etc.
Russia did cyber attack Ukraine's electricity grid in 2015, the largest such cyber attack in history. Also, armed separatists allied with Russia closely approached a Ukrainian nuclear power plant during the early fighting in the war that began in 2014.
On a related note, the Ukrainian military is reportedly bolstering defenses in its radioactively contaminated Chernobyl region, for fear Russian troops will invade the country across its border with Belarus, whose dictator, Lukashenko, is allied with Russia's Putin.