(Updates with water treatment)
By Mayumi Negishi
(TOKYO, April 27, Reuters) - Japanese engineers were struggling to take control of the Fukushima Daiichi nuclear power, 240 km (150 miles) North of Tokyo, which was severely damaged by the earthquake on March 11 and the tsunami.
Two of six reactors at the plant, operated by the Tokyo electric power (TEPCO) Co, are considered to be stable, but the other four are volatile.
Here are a few questions and answers about efforts to end the nuclear crisis the worst of the world since the 1986 Chernobyl accident:
What is going on?
Workers are trying to fill the reactors with enough water to bring the nuclear fuel rods in a "cold case", in which the water cooling is less than 100 degrees Celsius and reactors are considered stable.
TEPCO has been pouring water in vessels of reactor containing sticks since the disaster to cool the as an emergency measure. [ID: nL3E7FI0C7]
In a further step towards a cold closed, TEPCO fills the containment vessel - a steel shell and concrete that houses the reactor vessel - with water in a water called procedure to the Tomb. He began by increasing the amount of water being poured into the reactor n ° 1.
System, which works like a radiator in a car cooling at the same time that it will work to restore reactors. TEPCO said mounting a separate external cooling system is also a possibility.
For reactors as No.2, who is suspected of having a damaged containment vessel, TEPCO said he hoped seal articles damaged with cement to prevent water pumped into leaking.
WHAT IS HINDERING THE OPERATION?
The large amounts of runoff from the TEPCO a pumping water in to prevent overheating of fuel rods and nuclear fusion. The operator estimates the amount of water in the Daiichi plant contaminated tonnes approximately 87,500.
TEPCO plans to begin a system to treat contaminated water of operation in June. The system, developed by Toshiba, of Kurion, Areva (CEPFi.PA), and Hitachi-GE nuclear energy closes U.S., would adsorb and isolate radioactive elements, and then the treated water may be reused to cool the reactors.
Radioactive materials isolated would remain in the nuclear power plant for the moment.
For the moment, TEPCO was transfer of radioactive water that has accumulated in the building of the reactor in the reservoirs and storage at the plant, but the process was progressing very slowly.
Storage on the site of many tanks were damaged by the tsunami and earlier authorities in April, made a decision to pump water contaminated with lower levels of radiation in the ocean to secure storage space. Which has since ceased, but could resume if they run out of storage again.
In the meantime, the radiation continues to infiltrate the TEPCO nuclear complex in the sea and in the air, but at much lower levels than at the height of the crisis in mid-March.
To contain the contamination, workers have tried pouring glass liquid to stop a leak and spraying the ground with the sticky resin to radiated capture dust. They are also nitrogen injection in
to prevent new explosions of hydrogen would be spread highly radioactive in the air.
THIS COULD BE HOW LONG?
On 17 April TEPCO announced a timetable for its operations. In the first three months it intends to cool the reactors and spent fuel stored in some of them at a stable level and reduce radiation leaks. [ID: nL3E7FH03J]
TEPCO hope then make reactors to a cold case in another period of three to six months.
But some experts said that the process could take more time. TEPCO himself said constants replicas, power outages, high levels of radiation and the threat of explosions of hydrogen are the factors that could impede his work.
Weather conditions, as the rainy season approaching and typhoons and lightning during the summer, could also pose problems.
WHAT ARE THE RISKS?
The risk is the radiation continues to infiltrate, or burst, each time a pipe or pressure leaks forces workers to vent steam. Water leaking in nuclear pressure receptacles could find its place in soil and ocean, while the tips of radiation could contaminate crops on a large area.
The risk that the spent fuel pools could enter in a chain reaction is low, as long as the temperature indicators are accurate. But some more contaminated runoff may have to be disposed in the sea, if the workers run out of space to store water.
There is also a low risk of an explosion of steam corium, particularly in the reactor n ° 1, which is the oldest of the plant and who believes having a weak point.
If workers are unable to continue a jet of water operations, and nuclear fuel manages to melt through the bottom of the reactor and fall into a swimming pool with water below, this would result in a burst of high temperature and a sudden release of a huge amount of explosion of hydrogen which could violate the containment vessel.
Should any worst case produce, high levels of radiation up to 20 km (12 miles) around the site could be dispersed, making it impossible to bring the cold without great sacrifice shutdown reactors.
THE SITE WILL BECOME A NO-MAN LAND?
Very probably, Yes. Even after a cold there is tonnes of nuclear waste sitting on the site of nuclear reactors.
Burying concrete reactors make safe 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 radiation over thousands of years.
Nuclear fuel irradiated at Fukushima was damaged by sea water, kind of recycling, it is probably not an option, while transport elsewhere it is little likely due to the opposition proposal bring.
Experts say that cleaning will take decades. (Other reports by Shinichi Saoshiro and Yoko Kubota;) (Editing by Alex Richardson)
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