Nine of ten nuclear reactors at two locations at Fukushima, Japan, have problems ranging from damaged cooling systems to partial meltdowns, and spent fuel storage facilities at several of these reactors are severely damaged. In some cases, facilities seem to have been shut down safely. In other cases, there is a strong suspicion of serious damage but the degree of damage is uncertain.
Executive summary: The current most likely worst-case scenario is that the spent fuel rods in the storage pool at Reactor Number 4 will undergo a renewed chain reaction. However, two reactors, Number 1 and 3, may be partly melted, and the stored spent fuel rods at Reactor Number 3 contain a somewhat more dangerous fuel, Plutonium, as a percentage of their fissionable material.
A more detailed summary based on information from news sources in Japan:
At Fukushima Daini, Reactor Number 3 was shutdown after the quake and there appears to be no problem there. Reactors number 1, 2 and 4 at this location suffered cooling pump failures, and were shut down. Reported increases in radiation observed at this plant on March 14th were probably due to radiation coming from Fukushima Daiichi. There seems to be little information regarding the nature of the “cooling pump failures” at this plant, and information about the condition of the plant (i.e., what it will take to make it operable again) is not readily available.
At Fukushima Daiichi, Reactor Number 1 was operating at the time of the earthquake. The cooling system has failed and there appears to be a partial melting of the core. The reactor building suffered what appears to be a hydrogen explosion on Saturday, with the roof being blown off. Seawater is being pumped into this reactor to replace the function of the failed cooling system.
Reactor Number 2 was operating at the time of the earthquake. The cooling system here has failed and seawater is being pumped in to take over that function. The fuel rods in the core were fully exposed at one point. The building housing the reactor was damaged by an explosion at Reactor Number 3 on Monday. A second explosion was heard from within the reactor building on Tuesday, and it is believed that this may have involved damage to the reactor containment vessel.
Reactor Number 3 was operating at the time of the earthquake. The cooling system failed and seawater is being pumped in to take over that function. On Monday, a hydrogen explosion damaged the building housing the reactor. It is feared that the reactor has suffered a partial meltdown. High levels of radiation have been measured form this building.
A spent fuel storage pool at this site is compromised. Some of the fuel rods in this facility are said to be “MOX” fuel, which includes Plutonium and is considered to be a bit tricker to manage. A plume of smoke observed on Wednesday is suspected to have come from a fire in this pool, strongly suggesting a lack of water necessary to cool and shield the fuel rods. Various attempts have been made to get seawater into this pool, including dumping it form helicopters and spraying it from high pressure pumps. There is a fear that water poured in an uncontrolled manner into the pool could physically move the fuel rods to an undesirable position.
Reactor Number 4 was not in operation at the time of the earthquake. There is a spent fuel storage pool at this location that appears to be compromised. The temperature of water in this pool has been measured at unsafe levels and a series of fires have occurred. The fires have destroyed most of the building hosing the reactor and pool. Engineers have expressed concern that these fuel rods may restart a nuclear chain reaction.
Reactors 5 and 6 were under maintenance at the time of the earthquake. Both reactors have spent fuel rod pools, and both pools are showing higher than normal temperatures.
There is also a common spent fuel pond at which no problems have been reported.
Any additions or corrections will be appreciated.
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