(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 was being done to prevent further emissions of radioactive material:
Reactor No. 1
An official with the Tokyo Electric Power Co., which runs the embattled nuclear plant, said it knew March 18 about pooled water in the No. 1 reactor's turbine building, but that a sample of the water wasn't taken for analysis until March 24.
Saturday, Tokyo Electric said the radiation level in the turbine building's water was about 200 millisieverts per hour -- high, but still about half that as in reactor No. 3's turbine building.
Fresh water was injected into the unit's reactor core Saturday. This is in place of the saltwater that had been used for the same purpose, to cool nuclear fuel rods in the reactor and spent fuel pools. Besides its cooling purposes, experts hope the fresh water will help flush out salt to allow better operation of the cooling system.
Friday, Hidehiko Nishiyama of Japan's nuclear and industrial safety agency told reporters the situation appeared "rather stable" at the reactor, despite previously fluctuating pressure and temperature readings.
According to the Japan Atomic Industrial Forum, a nuclear trade group that has been keeping tabs on government and utility company accounts of the nuclear crisis efforts, the lighting is now working at buildings in and around the No. 1 reactor.
The same group has said the No. 1 unit's reactor core has been damaged, but its containment vessel was not. Saturday, the reactor's cooling systems were still not operational.
Still, the building was "severely damaged" by an earlier hydrogen explosion.
Reactor No. 2
Like with No. 1, there had been evidence of high radiation levels in spots in and around the No. 2 reactor -- though not as high as that of the No. 3 unit. Specifically, Tokyo Electric said Saturday that water inside the No. 2 unit's turbine building had between 200-300 millisieverts of radiation.
Such radiation readings -- and the fact that authorities haven't been able to pinpoint the source -- prompted a suspension of some work Saturday in and around the reactor.
Also Saturday, authorities started injecting fresh water -- rather than the current seawater -- into the reactor's core and spent nuclear fuel pool. The water is being pumped in to help cool down nuclear fuel rods and prevent the further emission of radioactive material. The fresh water also aims to flush out salt.
Damage is "suspected" in this unit's containment vessel, according to the Japan Atomic Industrial Forum. The reactor's core is also thought to be damaged, but the building itself has only been "slightly damaged," the group reports.
Even though the temperature and pressure levels are "unknown," the containment vessel pressure is considered "stable," the nuclear industry trade group reports.
Reactor No. 3
The water that three men stepped in while laying cable in the basement of the No. 3 unit's turbine building had 10,000 times the amount of radiation typical for that locale, Nishiyama said. The workers -- each of whom tested positive for 173 or more millisieverts of radiation, including two with direct exposure on the skin -- were admitted Friday for four days of observation at Japan's National Institute for Radiological Sciences, a research hospital in Chiba.
Friday, Nishiyama noted that the contamination likely came from the reactor's core, adding there is a possibility of leakage. That potentially could come from a crack in the reactor core, though Nishiyama cautioned there is no definitive answer yet on how the radioactivity got into the basement.
Despite the suspected damage to the reactor core -- something that isn't presumed at any of the other five reactors -- the nuclear safety official said there is evidence that pressure is somehow being maintained in the vessel, making it less likely there is a big gash.
Fresh water was being being pumped Saturday into the No. 3 reactor. This replaces the seawater that had been used previously. The aim of using fresh water is simultaneously to cool down nuclear fuel and flush out accumulating salt that might hinder the reactors' existing cooling systems.
The No. 3 reactor has been of particular concern, experts have said, because it is the only one to use a combination of uranium and plutonium fuel, called MOX, considered more dangerous than the pure uranium fuel used in other reactors.
The Japan Atomic Industrial Forum, an industry trade group that is tracking official accounts of the cleanup efforts at the Fukushima Daiichi plant, said the pressure of the No. 3 reactor's containment vessel has been upgraded to "stable."
Whereas the group had stated Friday that damage was suspected in the reactor, on Saturday its assessment changed to "unknown" -- a further acknowledgment of uncertainty as to whether the contaminated water was the result of a leak in the nuclear reactor core or had some other cause.
The building of the No. 3 reactor was "severely damaged" after an explosion caused by the buildup of hydrogen gas, the Japan Atomic Industrial Forum reported. Its core reactor is also damaged and its fuel rods are either partly or fully exposed. As to its pool of spent nuclear fuel, reports are that the pool was "possibly damaged" and the water level has been low -- a reason for the repeated spraying.
Reactor No. 4
A concrete pump truck was used once again Saturday to inject seawater into the unit's fuel pool. Seawater was also being pumped in using a "fuel pool cooling line," according to the International Atomic Energy Agency.
Along with the No. 5 and 6 reactors, the No. 4 was offline in a scheduled outage when the earthquake hit, and as a result the reactor's water level and pressure are safe.
The reactor's pool of spent nuclear fuel, however, was "possibly damaged," which is why authorities have said its water levels are low and why they've made repeated efforts to fill it up with water.
Reactor No. 5
The No. 5 unit appears safe, Nishiyama has said. Its capability to cool the fuel rods in the spent fuel pool is working again, 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 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 in order to relieve pressure and prevent a hydrogen explosion.
Reactor No. 6
The No. 6 unit appears safe for now, Nishiyama said. Its capability to cool the fuel rods in the spent fuel pool is working again, 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 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 in order to relieve pressure and prevent a hydrogen explosion.