Tokyo Electric Power Co. said Saturday it has detected radiation of up to 4,000 millisieverts per hour in the building housing the No. 1 reactor at the Fukushima No. 1 nuclear plant.
The radiation reading, which was taken when Tepco sent a robot into the No. 1 reactor building on Friday, is believed to be the highest detected in the air at the plant so far.
On Friday, Tepco found steam spewing from the basement into the building’s first floor. Nationally televised news Saturday showed blurry video of a steady stream of smoky gas curling up from an opening where a pipe rises through the floor.
The radiation is so high now that any worker exposed to it would absorb the maximum permissible dose of 250 millisieverts in only about four minutes. Tepco said there is no plan to place workers in that area of the plant and said it will carefully monitor any developments.
The utility said it took the reading near the floor at the southeast corner of the building. The steam appears to be entering from a leaking rubber gasket that is supposed to seal the area where the pipe comes up through the first floor. No damage to the pipe was found, Tepco said.
The reactor’s suppression chamber is under the building, and highly radioactive water generated from cooling the reactor is believed to have accumulated there, Tepco said, adding that the steam is probably coming from there.
Meanwhile, tanks for storing radioactive water were on their way Saturday to the plant.
Tepco has said radioactive water could start overflowing from temporary storage areas on June 20, or possibly sooner if there is heavy rainfall.
Two of the 370 tanks were due to arrive Saturday from a manufacturer in nearby Tochigi Prefecture, Tepco said. Two hundred of them can store 100 tons, and 170 can store 120 tons.
The tanks will continue arriving through August and will store a total of 40,000 tons of radioactive water, according to Tepco.
Workers have been fighting to get the plant under control since the March 11 tsunami knocked out power, destroyed backup generators and halted the crucial cooling systems for the reactors, causing the world’s worst nuclear disaster since Chernobyl in 1986. Several explosions have scattered radioactive debris around the plant, and reactors are spewing radiation into the air and leaking it into the sea.
On Friday, nine workers who entered the building to attach a pressure gauge to the pressure vessel of reactor No. 1 were exposed to around 4 millisieverts of radiation, according to Tepco.
The fuel rods are believed to have melted almost completely and sunk to the bottom of the containment vessels of reactors 1, 2 and 3.
A complete meltdown would have seen the fuel melt entirely through the containment vessels and into the reactor floor.