8:00 PM Eastern US Time.
Here is the latest reliable information available on the status of the reactors at Fukushima Daiichi:
Reactor 1: The oldest reactor at the plant, reactor one has generated the most concern. It lacks some of the redundancy and cooling systems of the other reactors. An explosion in the reactor support area severely damaged portions of Unit-1 which are not directly related to the operation of the reactor.
Because of the extreme damage to systems on reactor 1, operators decided to use seawater injection for direct cooling. Last reports are that the reactor pressure and temperature is stable. Containment systems are not in danger of failure.
The reactor is probably a write-off. It is possible that a partial meltdown has occurred of some of the fuel. In any case, the core appears to have sustained some severe damage which will preclude it from being put back into operation.
Reactor 2: Auxiliary cooling for reactor two is functioning normally. There does not appear to be any significant damage to the reactor itself, although severe damage to the turbines, electrical equipment and steam systems is likely to have occurred.
Reactor 3: Numerous systems were severely damaged by the tsunami. For a period of time, auxiliary systems on unit 3 continued to provide adequate cooling, but due to the damage incurred, sufficient cooling could not be assured by March 13. Cooling has resumed. TEPCO initially stated that the possibility of hydrogen buildup could not be dismissed, but it appears that any hydrogen has been successfully ventilated.
The status of the core is unknown. The reactor appears to have been stabilized, but it is likely that the core has suffered some level of deformation or, at the very least, cladding degradation. There is no indication of any leak in the reactor containment systems.
Reports now indicate that they are cooling the reactor with seawater. This is unfortunate as it signals that officials have basically decided that the reactor cannot be saved for a return to service. Seawater is obviously not the best choice of coolants as it will contaminate the reactor with salt and other materials. It seems that there is simply no freshwater to cool the reactors because of the destruction of the local water system.
Reactor 4: Unit four was shut down for refueling and routine maintenance. There is sufficient coolant in the system to assure system safety and stability. There are no indications of any leak in the reactor systems.
Reactor 5: Unit five was shut down for refueling and routine maintenance. There is sufficient coolant in the system to assure system safety and stability. There are no indications of any leak in the reactor systems.
Reactor 6: Unit six was shut down for refueling and routine maintenance. There is sufficient coolant in the system to assure system safety and stability. There are no indications of any leak in the reactor systems.
Radiation levels: There have been sporadic and inconsistent reports on the level of radiation measured at the plant. A number of reports have indicated an increase in ambient radiation measurements. This is to be expected due to the venting of steam containing minute amounts of radioactive nucleotides. Increases in background radiation may also occur due to smokey fires in the area, dust kicked up by collapsing structures and other sources of natural radiation. Because of this it is difficult to ascertain exactly how much can be directly attributed to the plant.
A number of reports claimed levels at the plant had risen to anywhere from 70 microserviets per hour to as high as 882 microserviets per hour. There is very little context for these reports – it’s not clear whether this is the level on the plant grounds in general or at the point of the vapor release. It is also not clear whether this is a sustained reading or represents only a momentary high level.
At this point all that can be said for sure is that there is no significant increase in ambient radiation beyond the plant boundary.
There have also been reports of individuals who were “exposed to radiation.” There have been vague reports of three workers who may have received a high enough dose to necessitate medical attention. At this point there’s no solid information on what the doses may have been or the nature of the exposure (whether it was proximity exposure or contamination by radioactive material etc).
At this point we simply do not have any context to the reports of individuals being “exposed to radiation.” However, there remains no evidence of the general public being exposed to radiation, despite some very dramatic photographs of school children being swept with Geiger counters.
UPDATE (11:30 PM EST Mar 13): A second explosion has apparently occurred at the Fukushima Daiichi plant, possibly associated with reactor number 3. The explosion did not cause any significant damage to the reactor itself or to the containment structure. The explosion may also have been caused by hydrogen gas. Officials had warned of the possibility of further explosions because of the difficulties in venting hydrogen gas from the coolant.
It is important to note that while the reactors and containment structures remain sound, the plant and surrounding area have been decimated by the quake and tsunami. Turbines, electrical distribution equipment, administrative buildings and support infrastructure have been damaged or destroyed. The entire area is experiencing continuing fires, explosions and other effects of the damage to industry.
Update 2 (11:00 PM EST Mar 14): Reactor 2, which had been relatively stable with auxiliary systems functioning normally has experienced a series of system failures. An explosion was reported at the unit, although the cause and severity remain unclear.
Update 3 (12:15 PM EST Mar 15): Reported fire in spent fuel pool of reactor 4. It is likely that the fire was the result of reduced levels of water covering spent fuel. Fresh spent fuel requires cooling or heat can build up resulting in cladding catching fire. Fire was reportedly contained and extinguished rapidly. Some radioactive material possibly released but extent unknown.
The importance of keeping water in the pool and the need to refill evaporating water depends heavily on how recently the reactor was refueled. Fuel bundles that have been in the pool for a year or more should be okay with just air convection cooling. Newer fuel bundles are much hotter. Any information on the age of the most recent bundles would be appreciated.