The level of radioactive iodine detected in seawater near the Fukushima No. 1 nuclear power plant was 1,250 times above the maximum level allowable, the Nuclear and Industrial Safety Agency said Saturday, suggesting contamination from the reactors is spreading.
Meanwhile, plant operator Tokyo Electric Power Co. turned on the lights in the control room of the No. 2 reactor the same day, and was analyzing and trying to remove pools of water containing radioactive materials in the turbine buildings of reactors 1 to 3.
The iodine-131 in the seawater was detected at 8:30 a.m. Friday, about 330 meters south of the plant’s drain outlets. Previously, the highest amount recorded was about 100 times above the permitted level.
If a person drank 500 ml of water containing the newly detected level of contamination, it would be the equivalent of 1 millisievert of radiation, or the average dosage one is exposed to annually, the NISA said.
“It is a substantial amount,” NISA spokesman Hidehiko Nishiyama told a news conference.
But he also stressed there is “no immediate risk to public health,” as the changing tides will dilute the iodine-131, and its half-life, or the amount of time it takes for it to lose half its radioactivity, is only eight days.
Nishiyama said the high concentration was perhaps caused by airborne radiation that contaminated the seawater, or contaminated water from the plant that flowed out to sea.
Tepco said early Saturday that it had detected a radiation reading of 200 millisieverts per hour in a pool of water in the No. 1 reactor’s turbine building on March 18 and failed to notify workers, but later denied that a radiation level that high was found.
“If we had warned them, we may have been able to avoid having workers (at the No. 3 reactor) exposed to radiation,” a Tepco official said.