International Atomic Energy Agency chief Rafael Grossi says that the U.N. nuclear watchdog’s long-awaited expert mission to the Zaporizhzhia power plant in Ukraine is now “on its way.” The site is Ukraine’s and Europe’s biggest nuclear facility. Russian forces have controlled it since soon after the war began. Grossi tweeted Monday that “the day has come.” Russia and Ukraine have traded claims of strikes at or near the plant in recent days. Fears are intensifying that the fighting could cause a massive radiation leak.