The worker’s death was probably unrelated to the nuclear disaster, but it can’t help moral much at the crippled site. Fission and cooling still remain issues at the Fukushima plant. Although fission is not happening to any large degree, or possibly at all, there has been fission more recently than many expected, and there is still concern that the reaction could restart. Various attempts at introducing long term cooling solutions at the site have been less than successful. It is clear that at least two of the reactors will have to be covered by a protective overarching structure.
The reactor in unit one, which is now known to have experienced a meltdown several hourse after the earthquake, has shown no recent evidence of criticality and the engineers and regulatory authorities are fairly satisfied that the reaction in this unit is under control. However, stable and reliable has not been achieved at this reactor. Although nitrogen is still being injected at a precaution, H2 buildup is not happening and the pressure of the reactor vessel is being maintained at a safe level. The reactor vessel, however, is leaking radioactive material presumably through breaches in the container via the pump system’s connectors, and possibly from small holes that formed at the base of the vessel during the meltdown (there is concern, though this has not been verified, that some of the radioactive material from this vessel actually breached the foundation structure of the reactor building). Further leakage of radioactive material is expected and engineers and authorities are concerned about this.
Fission reactions are not occurring in Reactor 2, and overall the situation is more serious than that of Reactor 1, though cooling is more of a concern here. It is thought that the March 14 hydrogen explosion, thought at the time to have been a harmless and expected event, damaged the containment vessel, resulting in leaking. Containment of radioactive material at Reactor 2 has not been achieved. It appears at this point that the only way to achieve containment here is to cover the reactor area with a superstructure.
Fission reactions appear to be continuing at a low level in Reactor 3. Cooling in this reactor is not achieved, and pressure varies unpredictably. There is a crack in the primary containment of this unit. Aside from this crack the reactor pressure vessel appears to be leaking via broken seals at pipes. Radioactive material continues to be released from this reactor, and as with REactor 2, it appears that the only way to stop this is to build a super structure over the reactor.
It is not entirely clear that fission reaction are totally stopped or limited in Reactor 4. The fuel rods are thought to be intact and in position but there is some conflicting data suggesting otherwise. While the fuel assembly seem to be covered by water and cooling achieved make-shift, there is also a lack of data from this reactor via TEPCO.
Quite a bit more information is to be found in Ana’s Feed (below).
Regarding exposure to radiation in the vicinity, the International Atomic Energy Agency has this statement:
Continue reading Japan Nuclear Disaster Update 24: Reactor 1 did melt down, fission and cooling remain issues, worker dies, sarcophagi in Fukushima’s future.