Tokyo Electric Power Co. has been forced to devise a difficult new step to cool a reactor at the stricken Fukushima No. 1 nuclear plant after its attempt to flood the pressure vessel and containment vessel with water failed.
Tokyo Electric Power Co. has been forced to devise a difficult new step to cool a reactor at the stricken Fukushima No. 1 nuclear plant after its attempt to flood the pressure vessel and containment vessel with water failed.
TEPCO said on May 14 that 3,000 tons of water found in the basement of the No. 1 reactor building had likely leaked from the containment vessel.
The utility had fed more than 10,000 tons of water into the reactor for cooling, hoping to flood the core vessel and outer containment vessel so that damaged fuel rods will be kept submerged, in a process called "water entombment." However, some of the water apparently leaked through pipe joints in the containment vessel.
With the failure of the operation, the utility is now considering recirculating the leaked water to try to cool the fuel rods, most of which are believed to have dropped to the bottom of the pressure vessel in a meltdown.
According to TEPCO, workers discovered about 3,000 tons of water in the basement of the southeastern side of the reactor building on May 13.
The water filled almost half the basement, which stands about 11 meters high.
The utility believes that the water spewed from the joints of pipes connecting the containment vessel and its suppression pool.
Although it has not measured the radiation level of the water, TEPCO said it is very likely highly contaminated.
With the discovery of the massive volume of contaminated water, the company is being forced to consider using the leaked water to cool the reactor core.
"We want to review our plan to circulate water to cool (the reactor)," said Junichi Matsumoto, a senior official with TEPCO.
The utility was initially seeking to pipe water from the containment vessel back into the pressure vessel after cooling the water.
But installing a system to recirculate the contaminated water for cooling will likely prove a big headache for the utility.
The radioactivity level inside the reactor building is very high, with a reading of up to 2,000 millisieverts per hour, an extreme danger to workers. That reading was taken May 13 at a site near a pipe leading to the pressure vessel at the southeastern part of the ground floor of the No. 1 reactor building.
The reading was the highest so far of the checks of radiation in the air conducted after the accident.
TEPCO must look for points where the radiation level is low in the building so that technicians can stay long enough to install pipes.
It also needs to work out a way to deter the flow of the highly contaminated water in the basement into the ocean.
Part of the highly radioactive water that leaked from the No. 2 and No. 3 reactor buildings has already flowed into the sea.
If the volume of contaminated water grows at the No. 1 reactor building, it could flow into the turbine building, then into a trench and finally into the sea. That was the course contaminated water at the No. 2 and No. 3 reactor buildings followed.
To prevent a recurrence, TEPCO must deal with the contaminated water while it is contained in the No. 1 reactor and turbine buildings.
But the volume of contaminated water is expected to increase for some time because the utility must continue to inject water into the reactor core until work to install pipes and the system for recirculating the radioactive water is completed. TEPCO continues pumping 8 tons of water per hour into the No. 1 reactor.
(This article was compiled from reports by Hidenori Tsuboya and Ryoma Komiyama.)