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Status report: Reactor-by-reactor at the Fukushima Daiichi plant

By the CNN Wire Staff

(CNN) -- Since March 11, the six reactors at the Fukushima Daiichi nuclear power plant have been in various states of disrepair after a 9.0-magnitude earthquake and subsequent tsunami struck the area.

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Here is the latest on each reactor and efforts to prevent further releases of radioactive material.

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Reactor No. 1

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The pumping of radioactive water out of the basement of the No. 1 unit's turbine building was halted Tuesday, because the condenser -- which was being to extract the water -- was nearly full, according to Japan's nuclear and industrial safety agency.

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Tsunehisa Katsumata, chairman of Tokyo Electric Power Company which runs the nuclear power plant, said on Wednesday, "Looking at current conditions, ... there are no options other than decommissioning" the No. 1 reactor, as well as Nos. 2, 3 and 4 units. This would mean that the reactor would never be used to produce electricity again.

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The temperature in the reactor's pressure vessel had decreased slightly Wednesday after climbing above 400 degrees Celsius last week, according to the Japan Atomic Industrial Forum trade group. But pressure inside the vessel was gradually increasing.

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This reactor's core has been damaged, but its containment vessel was not, according to the forum. The containment vessel is a concrete and steel structure that keeps radioactive material inside the reactor.

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A hydrogen explosion -- an indicator of core damage -- blew the roof and upper walls off the building housing the reactor on March 12.

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Reactor No. 2

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The injection of water into the No. 2 unit's spent nuclear fuel pool was suspended Wednesday after cracks were found in an injection pump connected to a fire pump truck, the nuclear safety agency said. Authorities switched to the fire pump after the temporary "motor-driven" pump that had been used to inject water malfunctioned.

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Katsumata said Wednesday that, "looking at current conditions," the No. 2 reactor and three others would be decommissioned -- meaning it would never be used to produce electricity again.

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Radioactivity levels that posed an immediate health hazard were detected in a maintenance tunnel leading to the unit's turbine building. That has sparked fresh concerns about the possibility of radiation leaking into the ocean.

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Hidehiko Nishiyama, an official with Japan's nuclear and industrial safety agency, said workers had been using sandbags and concrete panels to keep the water inside the tunnel, which is located about 55 meters (180 feet) from the shore. The agency said there is no evidence of overflow yet.

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Japanese Chief Cabinet Secretary Yukio Edano said Monday that he has received a report that the No. 2 unit's containment vessel "is damaged and water is leaking."

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Workers were pumping freshwater Tuesday into the No. 2 unit's reactor core, which the Japan Atomic Industrial Forum says has been damaged. The building housing the reactor has only been "slightly damaged," according to the forum.

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Reactor No. 3

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Like the Nos. 1, 2 and 4 reactors, the No. 3 reactor is likely to put out of service permanently even after the crisis resolves, Katsumata said Wednesday. Among other issues, the use of seawater in the post-crisis response has corroded the reactor, experts have said.

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The No. 3 reactor had been of particular concern because it is the only one to use mixed-oxide fuel that contains a small percentage of plutonium, which is also a byproduct in other reactors. A small amount of plutonium was detected in soil samples on the plant grounds last week, Tokyo Electric reported Monday. Edano said Tuesday that it was "likely" the plutonium came from this reactor.

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Tokyo Electric, the owner of the stricken plant, said radioactive water was found in the No. 3 unit's turbine building Monday. Efforts are ongoing to clear space to store the contaminated water, but work had not yet started to remove it from the floor, Tokyo Electric said. The process of draining the water could take four or five days to complete, the company said.

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The cooling pool where spent fuel is stored may also have been damaged, the Japan Atomic Industrial Forum reports. Workers used a concrete pump to douse the spent fuel pool with water Tuesday, Nishiyama said.

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Freshwater is being injected into the No. 3 reactor core in order to prevent overheating of nuclear fuel inside.

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The reactor is believed to have suffered core damage, and a hydrogen explosion did extensive damage to the building surrounding the reactor March 14.

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Reactor No. 4

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Freshwater was injected into the No, 4 unit's spent nuclear fuel pool on Wednesday using a concrete pump truck, Japan's nuclear and industrial safety agency said.

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Workers restored power in the reactor's control room Tuesday -- a move that officials say could be a key step in efforts to bring cooling systems back online.

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This reactor was offline in a scheduled outage when the earthquake hit, but a March 15 fire damaged the building that houses the reactor.

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The nuclear fuel rods were in the unit's spent fuel pool, but not in the reactor itself. The reactor's pool of spent nuclear fuel was "possibly damaged," which is why authorities have made repeated efforts to pour water onto the structure. A concrete pump truck has been used to inject seawater into the unit's fuel pool, in order to cool the spent fuel rods.

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Reactors Nos. 5 and 6

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Reactors No. 5 and 6 were not in operation at the time of the earthquake and are in "cold shutdown," Japan's nuclear and industrial safety agency reports.

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The reactors were shut down for a scheduled outage when the quake hit and there are no major issues with the reactors and cores themselves. The cooling systems in the pools of spent nuclear fuel are thought to be functioning, though there are continued concerns about keeping power running to the systems.

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Three holes were punched in each building earlier to relieve pressure and prevent a feared hydrogen explosion.

 
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