On February 24, 2022, the first day of Russia’s all-out attack on Ukraine, armored vehicles approached the Chernobyl nuclear power plant in Northern Ukraine. Russian occupation of the plant, which would last thirty-five days, had begun. Only the dedication and resolve of Ukrainian personnel, who were held hostage and worked shifts for weeks instead of days, spared the world a new Chernobyl accident. Meanwhile, a much more dangerous situation developed at the Zaporizhia nuclear power plant in Southern Ukraine, the largest such facility in Europe. Following an attack there in March 2022, the Russian military remains in control. In this lecture Serhii Plokhii discusses the challenges that the Russian takeover of the nuclear sites presents to the world. We must face up to a new reality:there has already been warfare at two nuclear sites, and others are vulnerable. The lecture is based on Plokhii’s most recent book, Chernobyl Roulette (2024).