What is going on at Japan's damaged nuclear reactor?

TOKYO (Reuters) - Japanese engineers are struggling to gain control of the Fukushima Daiichi nuclear power plant, 240 km (150 miles) north of Tokyo, which was seriously damaged by a March 11 earthquake and tsunami.
Two of the six reactors at the plant, operated by Tokyo Electric Power Co (TEPCO), are considered stable but the other four are volatile and once under control will be scrapped.
The chief executive of French nuclear reactor maker Areva has arrived in Japan, broadening out a French delegation that has flown out to help bring the nuclear plant under control.
Following are some questions and answers about efforts to end the world's worst nuclear crisis since the 1986 Chernobyl accident:
WHAT IS HAPPENING?
Workers are struggling to restart the cooling pumps in four reactors damaged by the 9.0 magnitude earthquake and tsunami and have drenched fuel rods with seawater to cool the reactors. The plants have also been flooded by seawater when the tsunami hit.
The challenge is to pump out radioactive seawater flooding the basements in reactors No.1, No.2 and No.3. The water is preventing work to restore electricity to the cooling pumps so that they can operate continuously.
The dilemma is that while it is necessary to pump the water into the reactors to cool them, this increases the amount of radioactive waste water at the plant and there is a danger that the operator will run out of places to store it safely.
Radiation may now be flowing continuously from the plant in seawater. Contamination was now 4,000 times the legal limit in the sea near the plant's drains.
The No.2 reactor has posed especially nasty risks, emitting high levels of radiation at more than 1,000 millisieverts an hour in both the water and air in the basement of the turbine building. That is the highest reading seen in the crisis and compares with a national safety standard of 250 millisieverts over a year. This most likely means that byproducts from a partial meltdown in the reactor core are leaking out into the water.
In the No.1 reactor, workers have been able to start running a circulatory steam condensing system to begin to clear contaminated water. But there is only slight progress.
The same systems in reactors No.2 and No.3 are flooded and so need to be emptied before they can handle the contaminated water. TEPCO has said it may need to think out of the box to clear the dangerous waters, while preventing further flows into the sea and soil.
HOW LONG MIGHT THIS TAKE?
Nobody knows. The most likely scenario is a long, drawn-out fight, with incremental progress interrupted by emergency cooling measures and spikes in radioactivity.
Once the pumps and the residual heat removal systems are running, it would take only a couple days to bring the reactors to a cold shutdown. But engineers are literally working in the dark. Lights have only recently gone on in the control room, but electrically powered monitors and gauges -- workers' eyes and ears inside the reactor -- are still off. Radiation readings outside the reactors are still taken via a moving car, because the monitoring posts are not powered. Temperature and pressure readings from backup systems are all that workers have to "see" what is going on in the reactors.
Workers remain hampered by broken pipes, debris, flooded equipment and a scarcity of replacement pumps and water tanks. Work has also been interrupted by hosing operations to lower rising temperatures in the reactor cores and spent fuel pools, as well as by an occasional fire and radiation injuries.
Because of the high levels of radiation in the water, experts suspect damage to the containment structures around the No.2 reactor core. They said it may take as long as a few months to bring that reactor to a cold shutdown.
WHAT ARE THE RISKS?
The main risk comes from the radiation that will continue to escape each time a pipe leaks or rising pressure forces workers to vent steam containing radiation. Leaking water from within the nuclear pressure vessels could find their way into the soil and the ocean, while spikes in radiation could contaminate crops over a wide area.
The risk that the spent fuel pools could reach recriticality seems remote, as long as there are workers and firefighters willing to douse the reactors with water each time temperatures start to rise.
The same could be said of a small, hypothetical risk of a corium steam explosion, particularly in the No.1 reactor, which is the plant's oldest and which is believed to have a weak spot. If workers are unable to continue hosing operations, and if the nuclear fuel manages to melt through the bottom of the reactor and fall into a water pool below, this would result in a high temperature burst and a sudden release of a huge amount of hydrogen that could, in an unlikely "perfect storm" scenario, breach the containment vessel.
Should either worst-case scenarios happen, it could disperse high levels of radiation up to 20 km (12 miles) around the site, making it impossible to bring the reactors to a cold shutdown without great sacrifice.
WHAT RISK FROM PLUTONIUM?
Plutonium has been found in soil samples at the site, further evidence that fuel rods in at least one reactor may have melted down considerably before they were cooled, and that there is damage to the structures containing the nuclear core.
Only trace amounts of the toxic substance have been detected. The level of up to 0.54 becquerals per kg of soil is not considered harmful. Most people have some plutonium in their bodies from atmospheric and underwater nuclear tests and some pacemakers are powered by plutonium.
But the presence of the radioactive poison outside the reactors compounds worry for the workers there as long as authorities are not sure how the heaviest of primordial elements leaked out.
Plutonium-239, used most in reactors, has a half-life of 24,200 years. It is not readily absorbed by the body but what is absorbed, stays put, irradiates surrounding tissue and is carcinogenic.
WILL THE SITE BECOME A NO-MAN'S LAND?
Most likely, yes.
The plant operator TEPCO officially said the plant will be decommissioned -- something that had been assumed ever since engineers began pumping corrosive seawater into them. But even after a cold shutdown, scrapping the plant would take decades.
There are tonnes of nuclear waste sitting at the site of the nuclear reactors. Enclosing the reactors by injecting lead and encasing them in concrete would make it safe to work and live a few kilometres away from the site, but is not a long-term solution for the disposal of spent fuel, which will decay and emit fission fragments over several thousand years.
The spent nuclear fuel in Fukushima has been damaged by sea water, so recycling it is probably not an option, while transporting it elsewhere is unlikely given the opposition that proposal would bring.

More than 1,000 people were feared dead after a monster tsunami in Japan

More than 1,000 people were feared dead after a monster tsunami unleashed by a massive quake which wreaked destruction across northeast Japan and triggered an emergency at a nuclear power plant.
Prime Minister Naoto Kan said Saturday 45,000 residents living within 10 kilometres (six miles) of the plant must evacuate amid fears of a slight radiation leak, before stepping onto a helicopter to head for the area.
The atomic emergency came as the country struggled to assess the full extent of the devastation wrought by the massive tsunami triggered by the strongest quake ever recorded in Japan.
The towering wall of water generated by the 8.9-magnitude earthquake -- the seventh biggest in history -- pulverised the northeastern city of Sendai, where police reportedly said 200-300 bodies had been found on the coast. Kyodo News said the final death toll was likely to pass 1,000.
The 10-metre (33-foot) wave of black water sent shipping containers, cars and debris crashing through the streets of Sendai and across open farmland, while a tidal wave of debris-littered mud destroyed everything in its path.
At least 402 people were killed in the earthquake and subsequent tsunamis, police and press reports said.
Scene: Japan tsunami-hit port a frightened ghost town
The National Police Agency said 202 people had been confirmed dead and 673 were missing, with 991 injured, and a spokesman said this did not include the bodies reportedly found on the Sendai coast.
"The damage is so enormous that it will take us much time to gather data," an official at the agency told AFP.
Authorities said more than 3,000 homes were destroyed or swept away.
The tsunami left Rikuzen Takata, a coastal city of some 23,000 people, "almost in shambles," the national Fire and Disaster Management Agency said.
Video footage, taken by a resident from a hill, showed massive waves sweeping away houses, vehicles and other objects as they surged over the city from the sea.
Related article: High radiation in Japan nuclear plant, 'no health hazard'
Before the prime minister told residents around the Fukushima nuclear plant to evacuate, trade minister Banri Kaieda warned there could be a release of radioactive steam in an operation to relieve a pressure build-up after the plant's cooling system was damaged in the quake.
Nuclear plant operator Tokyo Electric Power said Saturday a second of its atomic plants was experiencing reactor cooling problems, Kyodo News reported.
Japan's network of advanced nuclear power plants are designed to shut down as soon as the earth shakes in one of the world's most quake-prone countries.
More than eight million homes lost power, mobile and landline phone systems broke down for many and gas was cut to more than 300,000 homes, meaning many people could not heat their dark homes during a terrifying and cold night.
Japan's military mobilised thousands of troops, 300 planes and 40 ships for the relief effort.
An armada of 20 naval destroyers and other vessels headed for the devastated Pacific coast area of Honshu island, while air force jets flew reconnaissance missions.
Leading international offers of help, President Barack Obama mobilised US military might to provide emergency aid after the disaster which he described as "simply heartbreaking."
The United States, which has nearly 40,000 military personnel in Japan, has ordered a flotilla including two aircraft carriers and support ships to the region to provide aid following the tsunami.
The towering wave set off alerts across the Pacific, sparking evacuations in Hawaii and on the US West Coast, and devastating at least one California port.
Scene: Japan tsunami throws ships into town, houses into sea
Chile said it was evacuating coastal areas and Ecuador's state oil company announced it had suspended crude oil exports due to risks posed by the tsunami.
A Japanese ship with 100 people aboard was reportedly swept away, several trains missing and a dam broke in the northeast prefecture of Fukushima, with homes washed away.
"It was the biggest earthquake I have ever felt. I thought I would die," said Sayaka Umezawa, a 22-year-old college student who was visiting the port of Hakodate, which was hit by a two-metre wave.
The quake, which hit at 2:46 pm (0546 GMT) and lasted about two minutes, rattled buildings in greater Tokyo, the world's largest urban area and home to some 30 million people.
Scene: Millions stuck in Tokyo as quake shuts down subways
Millions who had earlier fled swaying buildings in the capital were left stranded in the evening after the earthquake shut down the city's vast subway system.
The government urged people to stay near their workplaces rather than risk a long walk home as there was major disruption to air travel and bullet train services.
The tsunami also submerged the runway at Sendai airport, while a process known as liquefaction, caused by the intense shaking of the tremor, turned parts of the ground to liquid.
Hours after the quake struck, TV images showed huge orange balls of flame rolling up into the night sky as fires raged around a petrochemical complex in Sendai.
A massive fire also engulfed an oil refinery near Tokyo as the quake brought huge disruption to Japan's key industries.
The Bank of Japan said it would do its "utmost" to ensure the stability of financial markets.
Major manufacturers including Toyota, Nissan and Sony were forced to suspend production at some sites, raising short term concerns for the nation's economic growth.
The first quake struck just under 400 kilometres (250 miles) northeast of Tokyo, the US Geological Survey said. It was followed by more than 70 powerful aftershocks, one as strong as 7.1.
"We were shaken so strongly for a while that we needed to hold on to something in order not to fall," said an official at the local government of the hardest-hit city of Kurihara in Miyagi prefecture.
"We couldn't escape the building immediately because the tremors continued... City officials are now outside, collecting information on damage."
Japan sits on the "Pacific Ring of Fire" and Tokyo is in one of its most dangerous areas, where three continental plates are slowly grinding against each other, building up enormous seismic pressure.
The government has warned of a 70 percent chance that a magnitude-eight quake will strike within the next 30 years in the Kanto plains, home to Tokyo's vast urban sprawl.
The last time a "Big One" hit Tokyo was in 1923, when the Great Kanto Earthquake claimed more than 140,000 lives, many of them in fires.
In 1995 the Kobe earthquake killed more than 6,400 people.
More than 220,000 people were killed when a 9.1-magnitude quake hit off Indonesia in 2004, unleashing a massive tsunami that devastated coastlines in countries around the Indian Ocean.
Small quakes are felt every day somewhere in Japan and people take part in regular drills at schools and workplaces to prepare for a calamity.

Updates:Atleast 29 people were reported killed after a huge earthquake and tsunamis

The biggest earthquake to hit Japan in 140 years struck the northeast coast on Friday, triggering a 10-metre tsunami that swept away everything in its path, including houses, cars and farm buildings on fire.

At least 29 people were reported killed after a huge earthquake and tsunamis up to 10 meters (33 feet) high slammed into the Pacific coast Friday.

The 8.9 magnitude quake caused many injuries, public broadcaster NHK said, sparked fires and the wall of water, prompting warnings to people to move to higher ground in coastal areas.

The Philippines, Taiwan and Indonesia all issued tsunami alerts, reviving memories of the giant tsunami which struck Asia in 2004. The Pacific Tsunami Warning Centre issued alerts for countries to the west and across the Pacific as far away as Colombia and Peru.

There were several strong aftershocks. In Tokyo, buildings shook violently. An oil refinery near the city was on fire, with dozens of storage tanks under threat.

GREAT KANTO QUAKE

"I was terrified and I'm still frightened," said Hidekatsu Hata, 36, manager of a Chinese noodle restaurant in Tokyo's Akasaka area. "I've never experienced such a big quake before."

Stunning TV footage showed the tsunami carrying the debris and fires across a large swathe of coastal farmland near the city of Sendai, which has a population of one million. The pictures suggested the death toll was going to rise.

Sendai is 300 km (180 miles) northeast of Tokyo and the epicentre at sea was not far away.

NHK showed flames and black smoke billowing from a building in Odaiba, a Tokyo suburb, and bullet trains to the north of the country were halted.

Thick smoke was also pouring out of an industrial area in Yokohama's Isogo area. TV footage showed boats, cars and trucks floating in water after a small tsunami hit the town of Kamaichi in northern Japan. An overpass, location unknown, appeared to have collapsed into the water.

Kyodo news agency said there were reports of fires in Sendai where waves carried cars across the runway at the airport.

The western prefecture of Wakayama ordered 20,000 people to evacuate after further tsunami warnings.

"The building shook for what seemed a long time and many people in the newsroom grabbed their helmets and some got under

their desks," Reuters correspondent Linda Sieg said in Tokyo.

"It was probably the worst I have felt since I came to Japan more than 20 years ago."


GREAT KANTO QUAKE

The quake was the biggest since 1872, according to the Japan Meteorological Agency. It surpasses the Great Kanto quake of September 1, 1923, which had a magnitude of 7.9, killed more than 140,000 people in the Tokyo area. Seismologists had said another such quake could strike the city any time. The 1995 Kobe quake caused $100 billion in damage and was the most expensive natural disaster in history. Economic damage from the 2004 Indian Ocean tsunami was estimated at about $10 billion.

The Tokyo stock market extended losses after the quake. The central bank said it would do everything to ensure financial stability.

Passengers on a subway line in Tokyo screamed and grabbed other passengers' hands during the quake. The shaking was so bad it was hard to stand, said Reuters reporter Mariko Katsumura.

Hundreds of office workers and shoppers spilt into Hitotsugi street, a shopping street in Akasaka in downtown Tokyo.

Household goods ranging from toilet paper to clingfilm were flung into the street from outdoor shelves in front of a drugstore.

Crowds gathered in front of televisions in a shop next to the drugstore for details. After the shaking from the first quake subsided, crowds were watching and pointing to construction cranes on an office building up the street with voices saying, "They're still shaking!," "Are they going to fall?"

Asagi Machida, 27, a web designer in Tokyo, sprinted from a coffee shop when the quake hit.

"The images from the New Zealand earthquake are still fresh in my mind so I was really scared. I couldn't believe such a big earthquake was happening in Tokyo."

The U.S. Geological Survey earlier verified a magnitude of 7.9 at a depth of 15.1 miles and located the quake 81 miles east of Sendai, on the main island of Honshu. It later upgraded it to 8.9.

A police car drove down Hitotsugi Street, lights flashing, announcing through a bullhorn that there was still a danger of shaking.

Japan's northeast Pacific coast, called Sanriku, has suffered from quakes and tsunamis in the past and a 7.2 quake struck on Wednesday. In 1933, a magnitude 8.1 quake in the area killed more than 3,000 people.

Last year fishing facilities were damaged after by a tsunami caused by a strong tremor in Chile.

Earthquakes are common in Japan, one of the world's most seismically active areas. The country accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater.

A Huge Earthquake and Tsunami Has Hit Japan.

A massive 8.8-magnitude earthquake shook Japan on Friday, unleashing a powerful tsunami that sent ships crashing into the shore and carried cars through the streets of coastal towns.

Multiple injuries, but no immediate deaths, were reported from the Pacific coastal area of Miyagi on the main Honshu island, police said according to media, and TV footage showed widespread flooding in the area.
The quake hit in the early afternoon, also strongly shaking buildings in greater Tokyo, the world's largest urban area with 30 million people.
At least six fires were reported in Tokyo, where the subway system stopped, sirens wailed and people streamed out of buildings.

The first quake struck about 382 kilometres (237 miles) northeast of Tokyo, the US Geological Survey said, revising the magnitude from an earlier 7.9.
Japan, is located on the "Pacific Ring of Fire" and dotted with volcanoes, and Tokyo is situated in one of its most dangerous areas.
A tsunami warning was issued for Japan, Taiwan, Russia and the Mariana Islands, the Pacific Tsunami Warning Center said.

"An earthquake of this size has the potential to generate a destructive tsunami that can strike coastlines near the epicentre within minutes and more distant coastlines within hours," the centre said in a statement.

It also put the territories of Guam, the Philippines, the Marshall Islands, Indonesia, Papua New Guinea, Nauru, Micronesia and Hawaii under a lower tsunami watch.

The yen fell to 83.30 against the dollar from 82.81 before the quake struck.
The mega-city of Tokyo sits on the intersection of three continental plates -- the Eurasian, Pacific and Philippine Sea plates -- which are slowly grinding against each other, building up enormous seismic pressure.
The government's Earthquake Research Committee warns of a 70 percent chance that a great, magnitude-eight quake will strike within the next 30 years in the Kanto plains, home to Tokyo's vast urban sprawl.
The last time a "Big One" hit Tokyo was in 1923, when the Great Kanto Earthquake claimed more than 140,000 lives, many of them in fires. In 1855, the Ansei Edo quake also devastated the city.

More recently, the 1995 Kobe earthquake killed more then 6,400 people.
More than 220,000 people were killed when a 9.1-magnitude quake hit off Indonesia in 2004, unleashing a massive tsunami that devastated coastlines in countries around the Indian Ocean as far away as Africa.
Small quakes are felt every day somewhere in Japan and people take part in regular drills at schools and workplaces to prepare for a calamity.
Nuclear power plants and bullet trains are designed to automatically shut down when the earth rumbles and many buildings have been quake-proofed with steel and ferro-concrete at great cost in recent decades.

Japan issued a tsunami warning

Japan issued a tsunami warning Wednesday after a major 7.2-magnitude quake struck 160 kilometres (100 miles) east off the main Honshu island at 0245 GMT, swaying buildings in the capital Tokyo.
The tremor struck 10 kilometres below the sea floor, said the Japan Meteorological Agency, which issued a tsunami warning for Honshu's Pacific coast, warning of waves 50 centimetres (20 inches) high.