Emergency declared at Fukushima No.1 nuclear plant
Work to vent air from the containers of the reactors at the plant was carried out on Saturday afternoon and Sunday morning. The measure was taken to release pressure in the containers after the reactors' cooling system failed. The power company says the procedure may have led to higher radiation levels and is investigating.
The company says radiation levels near the front gate of the plant gradually went down after rising to 1,015 microsieverts per hour on Saturday afternoon. But levels rose again to 882 microsieverts on Sunday morning. Radiation levels above 500 microsieverts must be reported to the government by law.