EXPLAINER: Ukraine's nuclear power plant shutdown cuts risks

KYIV, Ukraine (AP) — The forced shutdown of Ukraine’s endangered and crippled Zaporizhzhia nuclear power plant — Europe’s largest — significantly reduces the risk of a radiation disaster that has haunted the world for weeks.

The last of the Russian-occupied Zaporizhzhia plant’s six nuclear reactors was shut down Sunday because Russia’s military actions in Ukraine had repeatedly cut reliable external power supplies. That power is needed to prevent the reactors from overheating to the point of a meltdown that could breach the surrounding concrete and steel containment buildings and spew radiation through Ukraine, Russia and other nearby countries.

Since a Sept. 5 fire caused by shelling knocked the plant off of all external transmission lines, the sixth reactor had had to keep operating — at reduced output — to power reactor cooling and other crucial safety equipment. This “island mode” is unreliable and not designed to be more than a stopgap measure, Ukrainian officials say. On Sunday, one plant connection to Ukraine’s power grid was restored, so the sixth reactor’s power wasn’t needed for the safety systems.

Here is a look at the risks, impact and what could be done if external power is lost again.