TOKYO - Japan stopped highly radioactive water leaking into the sea on Wednesday from a crippled nuclear plant while acknowledging it could have given more information to neighbouring countries about contamination to the ocean.
Despite the breakthrough in plugging the leak at the Fukushima Daiichi plant, engineers need to pump 11.5 million litres (11,500 tonnes) of contaminated seawater back into the ocean because they have run out of storage space at the facility. The seawater was used to cool over-heated fuel rods.
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Nuclear experts said the damaged reactors were still far from being under control almost a month after they were hit by a massive earthquake and tsunami on March 11.
Plant operator Tokyo Electric Power (TEPCO) said it had stemmed the leak using liquid glass at one of six reactors that were damaged in the world's worst nuclear disaster since Chernobyl in 1986.
"The leaks were slowed yesterday after we injected a mixture of liquid glass and a hardening agent and it has now stopped," a TEPCO spokesman told Reuters.
Engineers had been frantically struggling to stop leaks from reactor no. 2, even using sawdust and newspapers.
Neighbours South Korea and China are getting concerned over the nuclear crisis and radioactive water being pumped into the sea, local newspapers reported.
"We are instructing the trade and foreign ministries to work better together so that detailed explanations are supplied especially to neighbouring countries," Chief Cabinet Secretary Yukio Edano told a news conference on Wednesday.
"The situation is not under control yet," said Thomas Grieder, Asia analyst at forecasting firm IHS Global Insight.
"TEPCO's decision to displace the contaminated water into the ocean reflected the urgency of clearing the turbine buildings and trenches of radioactive water so as not to damage equipment needed for restoration of cooling systems."
The low-level radioactive water to be pumped into the ocean is equivalent to 5 Olympic size swimming pools.
Workers are struggling to restart cooling pumps -- which recycle the water -- in four damaged reactors.
Until those are fixed, they must pump in water to prevent overheating and meltdowns, but have run out of storage capacity for the seawater when it becomes contaminated.
Radioactive iodine detected in the sea has been recorded at 4,800 times the legal limit, but has since fallen to around 600 times the limit. The water remaining in the reactors has radiation five million times legal limits.
"It's only going to get worse. They are going to be forced to make a tough decision soon. What they are going to have to release is likely to be highly radioactive. The situation could politically be very ugly in a week," said Murray Jennex at San Diego State University, who specialises in nuclear containment.
A floating tanker is being converted to hold contaminated seawater and is due to arrive at the plant site by April 16. TEPCO also plans to build tanks to hold radioactive water.
COOLING REACTORS KEY
Japan is facing its worst crisis since World War Two after the 9.0 magnitude earthquake and tsunami left nearly 28,000 people dead or missing and thousands homeless, and rocked the world's third-largest economy.
It will likely take months to finally cool down the reactors and years to dismantle those reactors that have been damaged. TEPCO has said it will decommission four of the six reactors.
Concerns over a possible buildup of hydrogen gas in reactor No. 1 will see engineers inject nitrogen gas into the reactor on Wednesday night to avoid a hydrogen explosion, TEPCO said.
Hydrogen explosions ripped through reactors 1 and 3 early in the crisis, spreading high levels of radiation into the air.
The key to bringing the reactors under control is the extent of damage to the plant's cooling system, said analysts.
In a sign the cooling systems may be severely damaged, the Sankei newspaper reported on Wednesday the government and TEPCO were considering building new cooling systems for three reactors to operate from outside the reactor buildings.
Kyodo news agency quoted a government source as saying the authorities were also considering covering damaged reactors with special sheets to halt radiation leaks. But they could not be installed until September due to high levels of radiation.
"To put the Fukushima nuclear catastrophe in perspective, Chernobyl involved a single operating reactor core," said Kevin Kamps from Beyond Nuclear, a US radioactive waste watchdog.
"Fukushima Daiichi now involves three reactors in various stages of meltdown and containment breach, and multiple (spent fuel storage) pools at risk of fire," said Kamps.
Kamps said the spent fuel rod pools, which are on the roof of the damaged reactors, alone have more irradiated nuclear fuel than that which exploded and burned at Chernobyl.
MOVES TO AVERT BLACKOUTS
The world's costliest natural disaster has hit Japan's economy, left a
damages bill which may top $300 billion, and forced the heavily-indebted
country to plan an extra budget.
Rolling power blackouts have hit global supply chains, with the world's
largest automaker Toyota Motor Corp idling local plants and saying it
will suspend some US plants also.
Japan is considering ordering TEPCO's big power users to achieve 25
percent cuts in peak summer usage, said a trade ministry official. TEPCO
shares continued to tumble on Wednesday, already having hit a 60-year
low on Tuesday.