(CNN) -- Since March 11, the six reactors at the Fukushima Daiichi nuclear power plant have been in various states of disrepair after being battered by a 9.0-magnitude earthquake and subsequent tsunami.
Here is the latest on the status of each reactor and what is being done to prevent further emissions of radioactive material.
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Reactor No. 1
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Unit 1's core has been damaged, but its containment vessel was not, according to the Japan Atomic Industrial Forum, a trade group. Radioactive water was reported in the unit's turbine plant Monday, the Tokyo Electric Power Company said.
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The temperature has been rising in the reactor's core, Hidehiko Nishiyama of Japan's Nuclear and Industrial Safety Agency said Monday. Emergency crews will compensate by boosting the flow of fresh water into the reactor core, Nishiyama said.
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A hydrogen explosion -- an indicator of core damage -- blew the roof and upper walls off the building housing Reactor No. 1 on March 12.
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The lighting is now working at buildings in and around the No. 1 reactor.
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Reactor No. 2
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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, which houses and protects the reactor, "is damaged and water is leaking." But he added that he hasn't gotten a report about the condition of the unit's pressure vessel, which is inside the larger containment building.
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The reactor's core is thought to be damaged, but the building has only been "slightly damaged," according to the Japan Atomic Industrial Forum.
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Radioactivity levels that posed an immediate health hazard persisted Monday in a tunnel leading to the unit's turbine building.
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Fresh water continued to be pumped Monday in the No. 2 unit's reactor core. Boric acid was needed as a coolant, added Nishiyama. Nishiyama said Monday that the aim is to eventually pump the pooled water out of the turbine building's basement, though he did not give a timetable as to when that might happen.
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Reactor No. 3
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On Monday, Nishiyama said that the "core parameters" -- a reference to temperature and pressure readings -- "have settled down somewhat" at this unit. Fresh water was being injected into the No. 3 reactor core, in order to prevent overheating of nuclear fuel inside.
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Unit 3 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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The No. 3 reactor has 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.
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The cooling pool where spent fuel is stored may also have been damaged, the Japan Atomic Industrial Forum reports.
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Three workers who stepped in highly radioactive water in the unit's turbine building were released from a hospital Monday after four scheduled days of treatment and monitoring. Authorities were still discussing Monday what to do with the highly radioactive water that has pooled in the building's basement.
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Reactor No. 4
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Unit 4 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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On Tuesday, authorities plan to start injecting fresh water instead of seawater into this pool, Nishiyama said. Workers are trying to confirm "the integrity" of the power supply for the No. 4 unit, largely to determine if it can produce electricity to cool the unit.
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Reactors No. 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," the 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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Reactor No. 5
Once again, Nishiyama on Monday reported "no changes" at the No. 5 unit, which he has said previously appears to be in "cold shutdown state." It is once again able to cool the fuel rods in the spent fuel pool, according to the Japan Atomic Industrial Forum.
As with units No. 4 and 6, this reactor was offline in a scheduled outage when the quake hit and there are no major issues with the reactor and core itself. The cooling system in the pool of spent nuclear fuel is thought to be functioning, though there are continued concerns about powering the reactor's cooling system to ensure the fuel rods contained within remain cool.
As with unit No. 6, three holes were punched in the building earlier to relieve pressure and prevent a hydrogen explosion.
Reactor No. 6
As in No. 5, Nishiyama on Monday reported "no changes" at the No. 6 unit, which he has said previously appears to be in "cold shutdown state." It is once again able to cool the fuel rods in the spent fuel pool, according to the Japan Atomic Industrial Forum.
The No. 6 reactor was offline when the tsunami struck, and there are no major concerns about the structure or safety of its core or containment vessel. The cooling system in the pool of spent nuclear fuel is thought to be functioning, though there are continued concerns about powering the reactor's cooling system to ensure the fuel rods contained within remain cool.
As with unit No. 5, three holes were punched in the building earlier to relieve pressure and prevent a hydrogen explosion.
