Editor's Note: John Boyd is an IEEE Spectrum contributor reporting from Kawasaki, Japan. This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency. For more details on how Fukushima Dai-1's nuclear reactors work and what has gone wrong so far, see our explainer and our timeline.
During the past few days, workers at the damaged nuclear power plant in Fukushima Japan contended with high radiation levels, unexpected pools of water contaminated with radioactive material, and narrowing options for what to do with that water as they continued to try to bring the plant completely under control.
Tokyo Electric Power Co. (TEPO) raised already heightened concerns when over the weekend it reported a huge spike in radiation levels at the damaged Fukushima Dai-1 Nuclear Power Plant Saturday. But the company later had to apologize for giving incorrect figures.
TEPCO initially reported it had detected 2.9 billion becquerels of iodine-134 per cubic centimeter in water pooled on the floor of the No. 2 reactor turbine building on Saturday night. The news was relayed by the Nuclear and Industrial Safety Agency (NISA) on Sunday morning when it said that the radioactivity level was “10 million times higher” than water found in a typical reactor.
But only hours later TEPCO said it had been mistaken and revised its figures downward to 100 000 times higher than normal—still very high. The radiation level at the surface of the pooled water was measured at more than 1000 millisieverts per hour on Monday.
TEPCO’s announcement followed the discovery that three workers had stepped in radioactive water in the turbine basement building of the No. 3 reactor last Thursday and had been exposed to between 173 to 180 millisieverts of radiation. TEPCO has raised the maximum level of radiation a worker may be exposed to in one year from a relatively low 50 millisieverts to 250 millisieverts so as to be able to cope with the emergency.
One of the doctors in the hospital where the three workers had been taken for examination said Monday that the workers had left the hospital at noon, having been found to be in good health. He said they would be examined again in several days, but any symptoms that might later develop were not expected to be serious.
Finding a place to put the contaminated water is proving to be a problem. Hidehiko Nishiyama, deputy director general of NISA, told reporters Monday morning that TEPCO planned to pump radioactive water in the No. 2 turbine room into the condenser tank located in the same building. The condenser tank is used to take steam from the reactor used to turn the turbines, and turn it back into water to complete the cycle. But the procedure had been delayed when TEPCO found the tank itself was already almost full of water. The company then decided to transfer the condenser water to nearby outside storage tanks, only to discover that these too were full. Nishiyama says TEPCO must now empty these outside tanks before it can begin draining the No. 2 turbine room.
A similar situation exists for the No. 3 turbine room, condenser tank, and outside storage tanks, says Nishiyama.
Yukio Edano, the Chief Cabinet Secretary, said in a press conference at 11:30 Monday morning that based on preliminary analysis it seemed the contaminated water in the No. 3 turbine basement had come into contact with “possibly melted fuel elements, and had leaked out” of the reactor. He added that it was essential the water should not be allowed to seep into the ground or the sea.
But that dangerous scenario looked likely to happen when TEPCO later told reporters that radiated water had been found in an area called “the trench” outside the No. 2 turbine building the day before. NISA’s Nishiyama later described the trench to reporters as a deep concrete tunnel used to carry electric cables and pipes for the turbine room. Originally he said the cables and pipes had been laid on the ground, but to prevent accidents they were housed inside this tunnel. At one end of the trench there is 16-meter shaft with an inspection manhole and when the manhole was removed, water was found to have leaked into the trench and risen “to a height of 14.9 meters and is increasing,” Nishiyama said. Radiation readings were taken and found to be more than 1000 millisieverts per hour on the surface—similar to the radiation found pooling in the turbine room, from where it has presumably leaked.
Nishiyama said the trenches of the No. 1 and No. 3 turbine buildings were also inspected and similar amounts of water were found in these tunnels too. However, the radiation level for the water filling the trench outside the No. 1 turbine building measured only 0.4 millisieverts per hour. Debris surrounding the manhole for the No. 3 turbine room prevented workers from taking a reading there.
Nishiyama added that the trenches were roughly 55 to 60 meters from the ocean and it was thought the contaminated water had not entered the sea. Nishiyama said TEPCO was making every effort to prevent this from happening.