Heroic Japanese workers today plugged a 12-inch crack leaking highly toxic water into sea from a concrete pit at the quake-hit Fukushima nuclear plant, but were confronted with a new problem of gas build-up at one of the six reactors which may cause another hydrogen blast.
The plant's operator, Tokyo Electric Power Company (TEPCO), said the leak of radioactive water from a seaside pit located near the No.2 reactor, which was detected on Saturday last, was stopped at 5.38 am local time after workers injected some 6,000 litres of chemical agents, including "water glass" or sodium silicate.
TEPCO also prepared to 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.
Last month's hydrogen blasts at the No.1 and No.3 reactors following the March 11 mega quake and tsunami destroyed reactor buildings, causing leaks of radioactive steam from the plant.
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According to national broadcaster NHK, TEPCO plans to infuse a total of 6,000 cubic metres of nitrogen gas during a 6-day period and is now checking procedures with the government.
The government's nuclear safety agency said it has ordered TEPCO to keep monitoring the concrete pit, from where the toxic water release was halted, to check whether 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 missing.
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.
Meanwhile, Japan's Crown Prince Naruhito and Crown Princess Masako visited quake survivors and nuclear plant evacuees, who are being sheltered at a stadium in Tokyo.
The couple "encouraged" about 130 evacuees from Iwaki City and other municipalities in Fukushima Prefecture during the visit, NHK said.
The prince and princess talked to families and asked about their health.
One elderly evacuee thanked them for their sympathy, the report said, adding a woman said she appreciates attempts by the Imperial family, including the Emperor and Empress, to curb their power consumption to support quake survivors.
The facility has accepted people from northeastern Japan affected by the twin disaster, particularly from areas near the Fukushima Power Station.
The Japan Coast Guard said the seabed right above the seismic focus of the powerful quake last month moved 24 metres to the east off Miyagi Prefecture in northeastern Japan.
After the quake, the coast guard analysed data on its benchmarks, which had been set on the seabed at a depth of more than 1,000 metres.
They found that one benchmark 120 km east of the Oshika peninsula had moved about 24 metres to the east-southeast and rose 3 metres. Another point 70 km east of the peninsula was found to have moved 15 metres east-southeast and sank 60 cm, NHK said.
The same point moved 10 cm after a magnitude 7.2 earthquake 6 years ago, but such a large shift caused by the latest earthquake is unprecedented.
The Japanese government is also working to improve its system of notifying foreign countries of developments in the ongoing crisis at the crippled Fukushima plant, Kyodo reported.
Anxiety is growing about seawater contamination and safety of seafood, especially after TEPCO started dumping water containing low-levels of radioactive materials into the sea this week.
To make room to store the highly radioactive water that is hampering the plant's restoration work, TEPCO has been pumping 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.
Tokyo's plan to share information on significant developments more quickly with foreign governments comes after the South Korean government expressed displeasure that Japan did not provide sufficient explanations before TEPCO released radioactive water into the Pacific Ocean.
Chief Cabinet Secretary Yukio Edano acknowledged that the government should have informed the public and Japan's neighbouring countries in a more efficient manner in advance about TEPCO pumping out radioactive water into the sea, and expressed his apology.
He instructed the Foreign Ministry and the Economy, Trade and Industry Ministry to take extra care to provide relevant information to neighboring countries, such as South Korea, Russia and China.
Edano also sought a more thorough handling of briefings the Foreign Ministry is giving daily to embassies in Tokyo.
Ministry officials again explained about the contaminated water discharge to the South Korean embassy here.
"One country raised the issue that we were somewhat short on explaining," Foreign Ministry spokesman Satoru Sato said. "We need to consider what proper measures the government should take as a whole based on this experience."
Japan explained the contaminated water discharge plan to other countries about an hour after TEPCO notified the government of its intention.
"It's not easy to speed up information sharing when situations change minute by minute," a ministry source was quoted as saying by Kyodo.
Low radioactive water was dumped into sea to free space to pool highly radioactive water that has flooded basements of the turbine buildings for nuclear reactors at the plant.
A seawater sample taken near the No.2 reactor on Saturday showed a radioactive iodine-131 concentration of 7.5 million times the maximum level permitted under law.
High levels of iodine - about twice the legal limit for vegetables - were found in launce, a small fish, which was caught off Ibaraki prefecture to the south of Fukushima.
The National Federation of Fisheries Cooperatives Associations issued a statement, lodging a strong protest with TEPCO and the government over the release of toxic water.
It said that fishermen are "immeasurably angry" at the "irresponsible" conduct of dumping radioactive water into the sea without any prior consultation with them.
The head of the federation Ikuhiro Hattori held talks with TEPCO Chairman Tsunehisa Katsumata, asking the company to compensate the losses incurred by fishermen due to the crisis.
Meanwhile, pregnant women and small children under three years of age along with their guardians in IItate village in Fukushima, about 40 km from the troubled atomic plant, will be temporarily evacuated if they apply to do so, NHK said.
The decision by local authorities came as concerns mounted over high radiation levels detected in the village, located outside the evacuation zone for the nuclear plant.
The village's radiation level recorded nearly 45 microsievert per hour at its peak on March 15, and has been significantly higher than most other areas more than 30 km away from the plant.
The official death toll from the quake and tsunami in northeastern Japan rose to 12,494, while 15,107 people were still listed as missing. Additional deaths were confirmed across a wide area of eastern Japan, including 7 in Tokyo.
US marines have also finished clearing debris on the remote Oshima Island in Miyagi. The work, started on Friday last, involved 300 marines and heavy construction machinery.
The marines said they cleared about 2,000 tonne of debris in 5 days.
US forces also plan to begin work to survey whether ships and other debris are submerged in the sea surrounding the island.