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.