(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.
.
Reactor No. 1
.
The temperature has been rising in the reactor's core, Hidehiko Nishiyama of Japan's nuclear and industrial safety agency said Monday.
.
To address this issue, the flow rate of fresh water into the reactor core will be further adjusted, the nuclear safety official said. That water is being directed in via a fire truck and temporary electricity-driven pump.
.
On Tuesday, the plan is to switch over to more a permanent power generator for the unit's cooling system, Nishayama said. The No. 1 unit's power supply will be distinct than those for other reactors to "avoid risks" trickling down elsewhere if there is a breakdown, according to the official.
.
Cable was being laid Monday to supply power to permanent monitoring outposts around the No. 1 unit complex, Nishayama said. Since the March 11 quake, radiation has been monitored from mobile systems.
.
The plan is to start pumping fresh water -- rather than seawater, as has been done -- into this reactor's spent nuclear fuel pool on Tuesday. These pools contain fuel rods that, as in the reactor, could lead to the release of radioactive material if they overheat.
.
On Sunday, workers went from using one to three pumps to get out the puddled water, which tests showed had higher-than-normal radiation readings -- although not as high as that in the Nos. 2 and 3 unit's turbine building basements.
.
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.
.
The building was "severely damaged" by an earlier hydrogen explosion.
.
Reactor No. 2
.
The No. 2 unit was "the priority" for the switch-over in the cooling system's power supply, said Nishiyama. An electrical pump and a diesel generator became operational Sunday, replacing a more temporary pumping system, to power the system used to cool the nuclear fuel inside the reactor.
.
Fresh water continued to be pumped Monday in the No. 2 unit's reactor core. The official said that boric acid was needed as a coolant, added Nishiyama.
.
The plan is to start injecting fresh water, rather than seawater, into the unit's spent nuclear fuel pool on Tuesday.
.
Radiation levels in pooled water tested in the No. 2 nuclear reactor's turbine building are 100,000 times normal, utility company and government officials said Sunday, correcting an earlier finding of 10 million times normal. The reading applies to radioactive iodine-131, which has a half-life of eight days.
.
Iodine-134, which loses half its radioactive atoms every 53 minutes, was at less than a detectable amount, officials said, correcting an earlier figure of 2.9 billion becquerels per cubic centimeter.
.
High levels of radioactive substances may have come from "melted fuel," Japanese Chief Cabinet Secretary Yukio Edano said Monday. This could suggest a full or partial meltdown in the No. 2 reactor, which occurs when nuclear fuel rods get so hot that they melt the steel and concrete structure containing them, spilling out in a worse-case scenario into the air and water with potentially deadly results.
.
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.
.
The plan is to pump out the tainted water using what the nuclear safety official called a condenser. But that apparatus is "almost full," as are several storage tanks nearby. Some of those tanks will have to be emptied before the process can occur.
.
While work has been halted in the turbine building's basement, an official with the Tokyo Electric Power Company (which runs the plant) said Sunday that people continued to work in other buildings -- including a control room, which got power and light for the first time in weeks the previous afternoon -- in the No. 2 reactor's complex.
.
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 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 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.
.
On Monday, Nishiyama said that the "core parameters" -- likely 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.
.
On Monday, the plan was to switch over from the fire truck and temporary electricity used to power the cooling system to a more permanent power supply, similar to (but distinct from) that installed already at the No. 2 unit.
.
The seawater now being used to keep the No. 3 unit's spent nuclear fuel pool cool will be replaced Tuesday by fresh water, said Nishiyama.
.
Authorities were still discussing Monday what to do with the highly radiaoctive water that has pooled in the No. 3 unit's turbine building. The plan, eventually, is to pump the water out of the basement.
.
This had 10,000 times the amount of radiation typical for that locale, Nishiyama had said. Three workers who stepped in it Thursday tested positive for 173 or more millisieverts of radiation, including two with direct exposure on the skin. They were set to be released Monday after four days of observation at Japan's National Institute for Radiological Sciences, a research hospital in Chiba, according to Chief Cabinet Secretary Yukio Edano.
.
The Japan Atomic Industrial Forum, an industry trade group that is tracking official accounts of the cleanup efforts at the plant, said Sunday that 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 for 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
.
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 nuclear fuel rods were in the unit's spent fuel pool, but not the reactor itself.
.
The reactor's pool of spent nuclear fuel 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.
.
A concrete pump truck has been used to inject seawater into the unit's fuel pool, in order to cool its nuclear fuel rods.
.
On Tuesday, authorities plan to start injecting fresh water instead of seawater into this pool, Nishiyama said.
.
The nuclear safety official also said that workers are trying to confirm "the integrity" of the power supply for the No. 4 unit, largely to determine if it can process electricity to cool the unit.
.
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 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 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.
الرئيسية 
موضوع: Status report: Reactor-by-reactor at the Fukushima Daiichi plant 
الإثنين مارس 28, 2011 1:43 am
