Japanese nuclear experts are struggling to control three reactors damaged by last week’s earthquake and tsunami as fears grow they could go into meltdown tonight.
Cooling water levels dropped suddenly in one, twice leaving the uranium fuel rods completely exposed and increasing the danger. Water levels were restored after the first decrease but the rods remained exposed after the second episode.
Earlier an explosion tore through the building housing a different reactor.
The government has said it expects the death toll from Friday's earthquake and tsunami to top 10,000 but many experts say it could be much higher. The quake and tsunami killed people in more than a dozen of Japan's 47 prefectures and rescue workers are continuing to search the ravaged northeastern coastal cities for survivors.
An earthquake with a preliminary magnitude of 4.1 jolted the Tokyo area tonight, public broadcaster NHK said. There were no immediate reports of injuries or damage and no tsunami warning was issued.
Millions of people are facing a fourth night without water, food or heating in near-freezing temperatures in the devastated northeast.
In a nationally televised speech yesterday, Japanese prime minister Naoto Kan appealed to the country to unite during what he said was the country's worst crisis since the second World War. “Overcoming this crisis depends on each and every one of us Japanese,” he said.
A Japanese police official said 1,000 washed up bodies were found scattered across the coastline of Miyagi prefecture today. Officials in Miyagi said more than 10,000 people are estimated to have died in the province, which has a population of 2.3 million.
The government has sent 100,000 troops to lead the aid effort. It has sent 120,000 blankets, 120,000 bottles of water and 110,000 litres of petrol plus food to the affected areas. However, electricity will take days to restore.
According to public broadcaster NHK, some 430,000 people are living in emergency shelters or with relatives. Another 24,000 people are stranded, it said.
The cascading troubles in the Fukushima Dai-ichi nuclear plant, some 270km north of Tokyo, compounded the immense challenges faced by the government in the wake of the tsunami disaster.
The biggest problem facing engineers was the drop in water levels at the plant’s Unit 2. “Units 1 and 3 are at least somewhat stabilised for the time being,” said a Nuclear and Industrial Agency spokesman “Unit 2 now requires all our effort and attention.”
A Japanese government spokesman said there were signs that the fuel rods were melting in all three reactors, all of which had lost their cooling systems. “Although we cannot directly check it, it’s highly likely happening,” he said.
Some experts would call that a partial meltdown. But others reserve the term for when nuclear fuel melts through a reactor’s innermost chamber but not through the outer containment shell. By contrast, a complete reactor meltdown, where the uranium core melts through the containment shell, would release a wave of radiation and result in major, widespread health problems.
Japan's chief cabinet secretary Yukio Edano said the reactor's inner containment vessel holding the nuclear fuel rods was intact, allaying some fears. Crucially, officials said the thick walls around the radioactive cores of the damaged reactors appeared to be intact.
International scientists say there are serious dangers but little risk of a catastrophe like the 1986 blast in Chernobyl, where the reactor did not have a containment shell.
Earlier the building surrounded Unit 3 exploded in a similar hydrogen blast to the one that destroyed the housing around Unit 1 on Saturday.
The blast actually lessened pressure building inside the reactor, and officials said the all-important containment shell - thick concrete armour around the reactor - had not been damaged.
Radiation levels remained within legal limits, although anyone left within 20km of the scene was ordered to remain indoors. Some 120,000 people have been evacuated from the area.
The explosion injured 11 workers and came as authorities were trying to use sea water to cool the three reactors.
A state of emergency has also been declared at another nuclear plant further north in Onagawa, Miyagi Prefecture.
While four Japanese nuclear complexes were damaged in the wake of Friday’s disaster, the Dai-ichi complex, which sits just off the Pacific coast and was badly hammered by the tsunami, has been the focus of most of the worries.
Operators knew the sea water flooding would cause a pressure buildup in the reactor containment vessels - and potentially lead to an explosion - but felt they had no choice if they wanted to avoid complete meltdowns. Eventually, hydrogen in the released steam mixed with oxygen in the atmosphere and set off the two blasts.
Japan’s meteorological agency did report one good sign. It said the prevailing wind in the area of the plant was heading east into the Pacific, which experts said would help carry away any radiation.
The United Nations atomic watchdog said today there were no signs at the moment, that fuel was melting at Fukushima.
"I think at this time we don't have any indication of fuel ...currently melting," James Lyons, a senior nuclear safety official at the International Atomic Energy Agency (IAEA), told a news conference.
The IAEA said radiation monitored around the Fukushima plant had peaked on Saturday before falling again.
The Japanese government has formally asked the United States for help in cooling the nuclear reactors damaged by a major earthquake last week, the Nuclear Regulatory Commission in Washington said today.
The commission said it is responding to the request and may provide Japan with technical advice. It has already sent two agency officials with expertise in boiling water nuclear reactors to Japan as part of a US International Agency for International Development team.
Along much of the Pacific coast, towns and cities are struggling to recover from Friday’s earthquake, which this weekend was upgraded by Japan's Meteorological Agency to 9.0 on the Richter scale, one of the largest in recorded history. Aftershocks and tsunamis have continued to plague coastal districts.
Across the region, though, many residents expressed fear over the situation.
People in the port town of Soma had rushed to higher ground after a tsunami warning today - a warning that turned out to be false alarm - and then felt the earth shake from the explosion at the Fukushima reactor 40km away.
Authorities there ordered everyone to go indoors to guard against possible radiation contamination.
“It’s like a horror movie,” said 49-year-old Kyoko Nambu as she stood on a hillside overlooking her ruined hometown. “Our house is gone and now they are telling us to stay indoors. We can see the damage to our houses, but radiation? ... We have no idea what is happening. I am so scared.”
Electricity supplies are being badly stretched. Tokyo Electric Power has held off on imposing rolling blackouts planned for today, but called for people to try to limit electricity use. Many regional train lines were suspended or operating on a limited schedule to help reduce the power load.
Preliminary estimates put repair costs from the earthquake and tsunami in the tens of billions of dollars - a huge blow for an already fragile economy.