SHIZUOKA (Kyodo) A small amount of the radioactive iodine-131 has been detected in the exhaust from one of the five reactors at the Hamaoka nuclear power plant in Omaezaki, Shizuoka Prefecture, Chubu Electric Power Co. said Thursday.
No ill effects have been reported in people, with the density of the radioactivity three times higher than caution levels but lower than legally allowable levels, the utility said.
Chubu Electric said the leak was so small that even if it continued for a year, it would be only 1/20,000th of the amount permitted by safety regulations.
The 1.380 million kw No. 5 reactor was one of two at the plant that came to an automatic halt after a magnitude 6.5 earthquake struck the Tokai region Aug. 11.
The radioactivity was detected Wednesday during the weekly replacement of an exhaust gas filter in the reactor, the company said.
No such amount of radioactivity was detected in the previous filter replacement, conducted Aug. 12, the day after the quake.
Of the plant's five reactors, No. 5 was hardest hit by the quake, which left one woman dead in the city of Shizuoka.
Chubu Electric said it will try to determine if the radioactivity is related to the effects of the quake.
It said there are no clear prospects on when the reactor will be back up and running.