Tohoku late Thursday suffered its largest aftershock since the March 11 killer temblor, but no abnormalities were found in radiation levels around nuclear reactors along the region's Pacific coast, including the crippled Fukushima No. 1 power plant, government officials said Friday.
At the Onagawa nuclear plant at Ishinomaki, Miyagi Prefecture, and the Higashidori plant in Higashidori, Aomori Prefecture, cooling systems for spent fuel pools stopped for 20 to 80 minutes Thursday night after the quake.
However, the cooling systems were all restored after that, with little change in water temperatures of the pools during that time, according to the Nuclear and Industrial Safety Agency.