http://www.sciencemag.org/news/2021/05/nuclear-reactions-reawaken-chernobyl-reactor

Since 2016, the canopylike New Safe Confinement has sealed off and protected the ruined Chernobyl reactor.

Thirty-five years after the Chernobyl Nuclear Power Plant in Ukraine exploded in the world’s worst nuclear accident, fission reactions are smoldering again in uranium fuel masses buried deep inside a mangled reactor hall. “It’s like the embers in a barbecue pit,” says Neil Hyatt, a nuclear materials chemist at the University of Sheffield. Now, Ukrainian scientists are scrambling to determine whether the reactions will wink out on their own—or require extraordinary interventions to avert another accident.