Ibaraki (ēbäˈräkē) [key], prefecture (1990 pop. 2,845,411), 2,352 sq mi (6,092 sq km), central Honshu, Japan. Mito is the capital. The prefecture yields tobacco, cereals, coal, copper, petrochemicals, and electric machinery. A nuclear fuel plant in Tokaimura, N central Ibaraki, was the site of accident involving an uncontrolled chain reaction in 1999. Parts of the prefecture along the coast suffered damage from the tsunami that followed the 2011 NE Honshu earthquake.