About half of the monitoring posts around an active nuclear power plant in Kagoshima Prefecture are unable to detect the high radiation levels that would spark an immediate evacuation of residents.

Of 48 monitoring posts installed within 5 to 30 kilometers of Kyushu Electric Power Co.'s Sendai plant, 22 can only detect radiation levels of up to 80 microsieverts per hour — far lower than the 500 microsieverts per hour that would spark an immediate evacuation. The plant was restarted last year.

The government's guidelines say residents within a 5-km radius of nuclear plants must evacuate immediately in the event of a severe accident, but that those living between 5 and 30 km of the site should take shelter first and then evacuate if a radiation dose of 500 microsieverts per hour is detected.