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BBC MUNDO RADIO
Police are trying to clear residents from the evacuation zone around the Fukushima plant The word "meltdown" goes to the heart of the big nuclear question - is nuclear power safe?
The term is associated in the public mind with the two most notorious accidents in recent memory - Three Mile Island, in the US, in 1979, and Chernobyl, in Ukraine, seven years later.
You can think of the core of a Boiling Water Reactor (BWR), such as the ones at Fukushima Daiichi, as a massive version of the electrical element you may have in your kettle.
It sits there, immersed in water, getting very hot.
The water cools it, and also carries the heat away - usually as steam - so it can be used to turn turbines and generate electricity.
If the water stops flowing, there is a problem. The core overheats and more of the water turns to steam.
The steam generates huge pressures inside the reactor vessel - a big, sealed container - and if the largely metal core gets too hot, it will just melt, with some components perhaps catching fire.
In the worst-case scenario, the core melts through the bottom of the reactor vessel and falls onto the floor of the containment vessel - an outer sealed unit.
This is designed to prevent the molten reactor from penetrating any further. Local damage in this case will be serious, but in principle there should be no leakage of radioactive material into the outside world.
But the term "in principle" is the difficult one.
“Start Quote
End QuoteThe job of keeping dangerous materials sealed in falls to the containment vessel inside.”
Reactors are designed to have "multiply redundant" safety features: if one fails, another should contain the problem.
However, the fact that this does not always work is shown at Fukushima Daiichi.
The earthquake meant the three functioning reactors shut down. But it also removed the power that kept the vital water pumps running, sending cooling water around the hot core.
Diesel generators were installed to provide power in such a situation. They did cut in - but then they cut out again an hour later, for reasons that have not yet been revealed.
In this case, redundancy did not work. And the big fear within the anti-nuclear movement, as used in the film The China Syndrome, is that the multiple containment of a molten core might not work either, allowing highly radioactive and toxic metals to burrow into the ground, with serious and long-lasting environmental impacts - total meltdown.
However, the counter-argument from nuclear proponents is that the partial meltdown at Three Mile Island did not cause any serious effects.
Yes, the core melted, but the containment systems held.
And at Chernobyl - a reactor design regarded in the West as inherently unsafe, and which would not have been sanctioned in any non-Soviet bloc nation - the environmental impacts occurred through explosive release of material into the air, not from a melting reactor core.
To keep things in perspective, no nuclear accident has caused anything approaching the 1,000 fatalities stemming from Friday's earthquake and tsunami.
'Subcritical' reactorsWhether a partial meltdown is under way at Fukushima Daiichi is not yet clear.
The most important factor is summed up in a bulletin from the Tokyo Electric Power Company (Tepco) that owns the facility: "Control rods are fully inserted (reactor is in subcritical status)."
A large explosion was seen at the plant with debris blow out from the building Control rods shut off the nuclear reaction. Heat continues to be produced at that stage through the decay of radioactive nuclei - but that process in turn will begin to tail off.
Intriguingly, Ryohei Shiomi, an official at Japan's Nuclear Safety Commission, is widely quoted as having said a meltdown was possible and that officials were checking.
Meanwhile, a visually dramatic explosion in one of the reactor buildings has at least severely damaged the external walls.
In principle, this should not cause leakage of radioactive material because the building is just an outside shell; the job of keeping dangerous materials sealed in falls to the the metal containment vessel inside.
Chief cabinet secretary Chief Yukio Edano confirmed this was the case, saying: "The concrete building collapsed. We found out that the reactor container inside didn't explode."
He attributed the explosion to a build-up of hydrogen, related in turn to the cooling problem.
Under pressureThe only release of any radioactive material that we know about so far concerns venting of the containment vessel.
When steam pressure builds up in the reactor vessel, it stops some of the emergency cooling systems working, and so some of the steam is released into the containment vessel.
“Start Quote
End Quote Richard BlackThe whole incident so far contains more questions than answers”
However, according to World Nuclear News, an industry newsletter, this caused pressure in the containment vessel to rise to twice the intended operating level, so the decision was taken to vent some of this into the atmosphere.
In principle, this should contain only short-lived radioactive isotopes such as nitrogen-16 produced through the water's exposure to the core. Venting this would be likely to produce short-lived gamma-ray activity - which has, reportedly, been detected.
One factor that has yet to be explained is the apparent detection of radioactive isotopes of caesium.
This is produced during the nuclear reaction, and should be confined within the reactor core.
If it has been detected outside the plant, that could imply that the core has begun to disintegrate.
"If any of the fuel rods have been compromised, there would be evidence of a small amount of radioisotopes in the atmosphere [such as] radio-caesium and radio-iodine," says Paddy Regan, professor of nuclear physics at the UK's University of Surrey.
"The amount that you measure would tell you to what degree the fuel rods have been compromised."
It is an important question - but as yet, unanswered.
Cover-ups and questionsIn fact, the whole incident so far contains more questions than answers.
Parallels with Three Mile Island and Chernobyl suggest that while some answers will materialise soon, it may takes months, even years, for the full picture to emerge.
How that happens depends in large part on the approach taken by Tepco and Japan's nuclear authorities.
As with its counterparts in many other countries, Japan's nuclear industry has not exactly been renowned for openness and transparency.
Tepco itself has been implicated in a series of cover-ups down the years.
In 2002, the chairman and four other executives resigned, suspected of having falsified safety records at Tepco power stations.
Further examples of falsification were identified in 2006 and 2007.
In the longer term, Fukushima Daiichi raises several more very big questions, inside and outside Japan.
Given that this is not the first time a Japanese nuclear station has been hit by earthquake damage, is it wise to build such stations along the east coast, given that such a seismically active zone lies just offshore?
And given that Three Mile Island effectively shut down the construction of civilian nuclear reactors in the US for 30 years, what impact is Fukushima Daiichi likely to have in an era when many countries, not least the UK, are looking to re-enter the nuclear industry?
Japanese Earthquake
VIDEO REPORTS
Japan Faces 'Unprecedented Disaster'
Photo: Reuters
Police officers wearing respirators guide people to evacuate away from the Fukushima Daiichi nuclear plant following an evacuation order for residents who live near the plant after an explosion in Tomioka Town in Fukushima Prefecture, March 12, 2011
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Japanese Prime Minister Naoto Kan says his country is trying to cope with what he called "an unprecedented disaster." The magnitude 8.9 earthquake that triggered a deadly tsunami on the country's Pacific coast swept away entire villages and also damaged nuclear powerplants.
Japanese Prime Minister Naoto Kan on Saturday evening addressed Japan expressing hope that as he put it, "this disaster can somehow be survived."
Besides helping the thousands of people injured and made homeless by the quake and tsunami, Kan said his top priority is the emergencies with a pair of damaged nuclear power plants in Fukushima prefecture.
Japanese government officials, including Kan, are stressing that despite a large explosion that injured at least four people at the Fukushima Number One plant, the reactor is undamaged and not single citizen affected by radiation.
A 20 kilometer evacuation zone has been established around that reactor and a 10 kilometer zone around another one.
| Social Media: Disaster in Japan The Crisis Commons volunteer community has mobilized, and part of the effort is being coordinated by Japanese students at U.S. universities. The Red Cross has opened a page on causes.com to raise money for the victims of Friday's disaster in Japan. Many photos are being tweeted of empty market shelves: The State Department tweeted: |
Government officials say a cooling process using sea water and boric acid is underway at the Number One reactor.
Radiation has been detected outside the Number One plant, but the government is saying the intensity of the radiation did not increase after the explosion.
There is little sign of panic here in Fukushima prefecture. Most people are focused on rebuilding damaged homes, seeking clean water and mourning those who have died.
Food supplies are running short. And in the few markets remaining open, rice balls and bottle water are out of stock.
The death toll remains unclear. Troops are finding hundreds of bodies along the beaches where tsunamis swept out to sea entire communities in neighboring Iwate and Miyagi prefectures.
It is expected that 50,000 Japanese troops will get assistance from foreign teams that are beginning to converge on northeaster Japan. More than 50 nations have offered help.
At Fukushima airport, helicopters are constantly landing and taking off with first responders in what is being described as an unprecedented disaster that has overwhelmed Japan.
Radiation leaking from Japan's quake-hit nuclear plant
/www.thehimalayantimes.comAdded At: 2011-03-12 6:01 PM
Last Updated At: 2011-03-12 8:13 PM
AFP
A passenger at a railway station in Seoul watches TV pictures of Japan's Fukushima No. 1 atomic plant spewing smoke
REUTERS
FUKUSHIMA: Radiation leaked from a damaged Japanese nuclear reactor on Saturday after an explosion blew the roof off in the wake of a massive earthquake, but the government insisted that radiation levels were low.
The blast raised fears of a meltdown at the facility north of Tokyo as officials scrambled to contain what could be the worst nuclear disaster since the Chernobyl explosion in 1986 that shocked the world.
The plant was damaged by Friday's 8.9-magnitude earthquake, which sent a 10-meter (33-foot) tsunami ripping through towns and cities across the northeast coast. Japanese media estimate that at least 1,300 people were killed.
Chief Cabinet Secretary Yukio Edano said there had been no major change in the level of radiation after the explosion because it did not occur inside the reactor container.
"The nuclear reaction facility is surrounded by a steel storage machine, which is then surrounded by a concrete building. This concrete building collapsed. We learnt that the storage machine inside did not explode," he told a news conference.
Edano initially said an evacuation radius of 10 km (6 miles) from the stricken 40-year-old Daiichi 1 reactor plant in Fukushima prefecture was adequate, but then an hour later the boundary was extended to 20 km (13 miles). TV footage showed vapor rising from the plant, 240 km (150 miles) north of Tokyo.
Along the northeast coast, rescue workers searched through the rubble of destroyed buildings, cars and boats, looking for survivors in hardest-hit areas such as the city of Sendai, 300 km (180 miles) northeast of Tokyo.
Dazed residents hoarded water and huddled in makeshift shelters in near-freezing temperatures. Aerial footage showed buildings and trains strewn over mudflats like children's toys.
"All the shops are closed, this is one of the few still open. I came to buy and stock up on diapers, drinking water and food," Kunio Iwatsuki, 68, told Reuters in Mito city, where residents queued outside a damaged supermarket for supplies.
Across the coastline, survivors clambered over nearly impassable roads. In Iwanuma, not far from Sendai, people spelled S.O.S. out on the roof of a hospital surrounded by water, one of many desperate scenes.
The earthquake and tsunami, and now the radiation leak, present Japan's government with its biggest challenge in a generation.
The explosion at Chernobyl's nuclear plant's fourth reactor in 1986 sent thousands of tonnes of toxic nuclear dust billowing across the Ukraine, Russia and Belarus. It was the worst civil nuclear disaster.
The blast at the Japanese nuclear facility came as plant operator Tokyo Electric Power Co (TEPCO) was working desperately to reduce pressures in the core of the reactor.
The company has had a rocky past in an industry plagued by scandal. In 2002, the president of the country's largest power utility was forced to resign along with four other senior executives, taking responsibility for suspected falsification of nuclear plant safety records.
Earlier the operator released what it said was a tiny amount of radioactive steam to reduce the pressure and the danger was minimal because tens of thousands of people had already been evacuated from the vicinity.
Reuters journalists were in Fukushima prefecture, about 70 km (40 miles) from the plant. Other media have reported police roadblocks in the area to prevent people getting closer.
INTERNATIONAL RELIEF EFFORT
Friday's tremor was so huge that thousands fled their homes from coastlines around the Pacific Rim, as far away as North and South America, fearful of a tsunami.
Most appeared to have been spared anything more serious than some high waves, unlike Japan's northeast coastline which was hammered by the huge tsunami that turned houses and ships into floating debris as it surged into cities and villages, sweeping aside everything in its path.
"I thought I was going to die," said Wataru Fujimura, a 38-year-old sales representative in Koriyama, Fukushima, north of Tokyo and close to the area worst hit by the quake.
"Our furniture and shelves had all fallen over and there were cracks in the apartment building, so we spent the whole night in the car ... Now we're back home trying to clean."
In one of the worst-hit residential areas, people buried under rubble could be heard calling out for rescue, Kyodo news agency reported earlier.
The international community started to send disaster relief teams on Saturday to help Japan, with the United Nations sending a group to help coordinate work.
The disaster struck as the world's third-largest economy had been showing signs of reviving from an economic contraction in the final quarter of last year. It raised the prospect of major disruptions for many key businesses and a massive repair bill running into tens of billions of dollars.
Toyota Motor Corp, the world's largest carmaker, said it would suspend operations at all of its 12 factories in Japan on Monday to confirm the safety of its employees.
Italy's National Institute of Geophysics and Volcanology said the earth's axis shifted 25 cm as a result of the earthquake, and the U.S. Geological Survey said the main island of Japan had shifted 2.4 meters.
The earthquake was the fifth most powerful to hit the world in the past century. It surpassed the Great Kant quake of September 1, 1923, which had a magnitude of 7.9 and killed more than 140,000 people in the Tokyo area.
The 1995 Kobe quake caused $100 billion in damage and was the most expensive natural disaster in history.
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