The leak of radioactive water from a seaside pit located near the No 2 reactor, which was detected on Saturday, Apr 2 stopped at 5:38 am local time after the plant operator, Tokyo Electric Power Company (TEPCO), injected some 6,000 liters of chemical agents, including "water glass" or sodium silicate.
The government's nuclear safety agency said it has ordered TEPCO to keep monitoring the pit to check whether the water leakage into the Pacific Ocean has completely stopped, nearly four weeks after the magnitude-9 quake and tsunami struck Japan's northeast leaving nearly 30,000 people dead or unaccounted for.
There is a possibility that the water, which has lost an outlet, may show up from other areas in the plant''s premises, it said. The highly radioactive water is believed to have come from the No 2 reactor's core, where fuel rods have partially melted, and ended up in the pit.
The pit is connected to the No 2 reactor's turbine building and an underground trench connected to the building, both of which were found to be filled with high levels of contaminated water.
TEPCO also said that it may inject nitrogen into the No 1 reactor's containment vessel where hydrogen gas was building up. Hidehiko Nishiyama, a spokesman for the Nuclear and Industrial Safety Agency, said the move is being considered in a bid to stop a possible hydrogen explosion "in advance" and that it does not mean there is an "immediate danger," Kyodo news agency reported.
The nitrogen injection process is expected to take several days, and may lead to the release of radioactive substances in the air. Blasts caused by a build-up of hydrogen gas took place earlier in three reactors in the aftermath of the earthquake.
To make room to store the highly radioactive water that is hampering the plant's restoration work, TEPCO is also dumping into the sea massive amounts of low-level contaminated water from a nuclear waste disposal facility at the site, as well as from the No 5-6 unit buildings, a move which has triggered concerns among neighbouring countries.
The move would be followed by some repair work to make sure the facility can keep highly radioactive water safely without fear of the stored liquid leaking outside.