People with suspected radiation contamination are being evacuated Technicians are battling to stabilise a third reactor at a quake-stricken Japanese nuclear plant, which has been rocked by a second blast in three days.
The Fukushima Daiichi plant's operators have resumed pumping seawater into reactor 2 after a cooling system broke.They warned of a possible meltdown when the fuel rods became exposed after the pump stopped as its fuel ran out.
A cooling system breakdown preceded explosions at the plant's reactor 3 on Monday and reactor 1 on Saturday.
The latest hydrogen blast injured 11 people, one of them seriously. It was felt 40km (25 miles) away and sent a huge column of smoke into the air.
The outer building around the reactor was largely destroyed.
But as with the first explosion, Tokyo Electric Power Company (Tepco) said the thick containment walls shielding the reactor cores remained intact. It also said radiation levels outside were still within legal limits.
Mass evacuation Shortly after the blast, Tepco warned that it had lost the ability to cool Fukushima Daiichi's reactor 2.
Continue reading the main story 
The fuel rod exposure at Fukushima Daiichi number 2 reactor is potentially the most serious event so far at the plant.
A local government official confirmed the fuel rods were at one point largely, if not totally exposed; but we do not know for how long.
Without coolant around the rods, temperatures can rise to hundreds of degrees Celsius, almost certainly resulting in some melting.
This opens the possibility of a serious meltdown - where molten, highly radioactive reactor core falls through the floor of the containment vessel and into the ground underneath.
However, engineers appear to have restored some water flow into the reactor vessel and if they are successful, temperatures will begin to fall again rapidly.
Analysis
A local government official confirmed the fuel rods were at one point largely, if not totally exposed; but we do not know for how long.
Without coolant around the rods, temperatures can rise to hundreds of degrees Celsius, almost certainly resulting in some melting.
This opens the possibility of a serious meltdown - where molten, highly radioactive reactor core falls through the floor of the containment vessel and into the ground underneath.
However, engineers appear to have restored some water flow into the reactor vessel and if they are successful, temperatures will begin to fall again rapidly.
Hours later, the company revealed that the fuel rods inside had been exposed fully at one point, reportedly for about two-and-a-half hours. It said a fire pump being used to pump seawater into the reactor had run out of fuel.
The company is now trying to inject sea water into the reactor to cover the fuel rods, cool them down and prevent another explosion. Initially, water levels continued to fall despite the efforts, as only one of the five fire pumps was working, officials said. The other four were believed to have been damaged by the blast at reactor 3.
By Monday evening, however, the water level inside the reactor had risen to 2m (7ft), the Kyodo news agency reported.
Exposure for too long a period of time can damage the fuel rods and raise the risk of overheating and possible meltdown.
Japan's Nuclear and Industrial Safety Agency said workers were also battling rising pressure within the reactor. They have opened vents in the containment vessel, which could release small amounts of radiation.
Chief Cabinet Secretary Yukio Edano earlier said the emergency effort to cool reactor 2 would hopefully stabilise the situation, and that radiation around the plant remained at tolerable levels despite the various crises.
Click to play
Chief Cabinet Secretary Yukio Edano said the core container at the reactor was still intact
The US said it had moved one of its aircraft carriers from the area after detecting low-level radiation 160km (100 miles) offshore.
Experts say a disaster on the scale of Chernobyl in the 1980s is highly unlikely because the reactors are built to a higher standard and have much more rigorous safety measures.
Earlier, Tepco said it had restored the cooling systems at two of the three reactors experiencing problems at the nearby Fukushima Daini power plant, 11.5km (7.1 miles) to the south.
Complete devastation Meanwhile, the relief operation is continuing after Friday's magnitude 9.0 earthquake, which triggered a tsunami that devastated swathes of the north-eastern coast of the country.
About 2,000 bodies had been found washed ashore on beaches in the north-eastern prefecture of Miyagi, police said.
A thousand were found on the Ojika peninsula and another thousand in the town of Minamisanriku, which was flattened by the tsunami.
Click to play
The BBC's Alastair Leithead is near the town of Minamisanriku which has been virtually flattened
Everything in the tsunami's path was flattened, with only the town's hospital and a government building remaining, our correspondent says. Apart from that, she adds, there are just a few rooftops here and there.
The total number of people killed by the disaster remains unclear. The official death toll stands at 2,800, but officials in Miyagi have estimated that 10,000 people died in the prefecture alone.
Tens of thousands are still unaccounted for, while many remote towns and villages remain cut off and have had no help since Friday's earthquake.
Kyodo reported that more than 500,000 people had been displaced by the earthquake, tsunami and nuclear emergency.
Millions of others have spent three nights without water, food or heat in near-freezing winter weather.
The government has deployed 100,000 troops to lead the aid effort. They have been given 120,000 blankets, 120,000 bottles of water, tonnes of food, and 111,000 litres (29,000 gallons) of petrol to distribute.
More than 500,000 people are believed to have been displaced from their homes "People are surviving on little food and water. Things are simply not coming," he told the Associated Press.
Communications networks are also down in many areas.
The government asked people not to go to work or school on Monday because the transport network would not be able to cope with demand.
The capital, Tokyo, is still experiencing regular aftershocks, amid warnings that another powerful earthquake is likely to strike very soon.
A 6.2-magnitude tremor on Monday triggered a new tsunami scare on the Pacific coast, with the authorities telling people to flee to higher ground.
The Foreign Office has updated its travel advice to warn against all non-essential travel to Tokyo and north-eastern Japan. British nationals and friends and relatives of those in Japan can contact the Foreign Office on +44(0) 20 7008 0000.
http://www.bbc.co.uk/news/world-asia-pacific-12733393
Comments