The BBC has an excellent article with the latest on the reactor explosion in Japan:

In principle, this should not cause leakage of radioactive material because the building is just an outside shell; the job of keeping dangerous materials sealed in falls to the the metal containment vessel inside.

Chief cabinet secretary Chief Yukio Edano confirmed this was the case, saying: “The concrete building collapsed. We found out that the reactor container inside didn’t explode.”

He attributed the explosion to a build-up of hydrogen, related in turn to the cooling problem.

However, it sounds like, even though the containment vessel itself didn’t explode (good news), it could still be leaking. Because of the venting of cooling water that has turned to steam, the explosion should result in specific radioactive substances in the air:

…this should contain only short-lived radioactive isotopes such as nitrogen-16 produced through the water’s exposure to the core. Venting this would be likely to produce short-lived gamma-ray activity – which has, reportedly, been detected.

Ok, so far, so good, those are not exactly what you want to be breathing, but at least they degrade quickly.

Unfortunately, some of the radioactive particles detected are ones that SHOULD NOT be there, if the problem is limited to the containment shell:  

[More below the jump]

…One factor that has yet to be explained is the apparent detection of radioactive isotopes of caesium.

This is produced during the nuclear reaction, and should be confined within the reactor core.

…

“The amount that you measure would tell you to what degree the fuel rods have been compromised.”

It is an important question – but as yet, unanswered.

So, while the big scary explosion is itself, not as big a deal as one would think (still bad, just not catastrophic), the real area of concern is in what we can’t see: the reactor core’s inner containment vessel may be compromised, as could one or more fuel rods or control rods.

It’s sort of like the reactor is playing the cup game with 3 cups and a rubber ball. While we’re looking “over there” at the impressive smoke, dust, and rubble, the reactor is dropping the ball through a hole in the table.

It seems humanity may be about to lose the bet over whether we can safely build nuclear power plants.

And for the nuclear advocates out there: Yes, this IS a rare event and so highly unlikely that we can’t reasonably expect such disasters all the time. However, nor can we possibly, being fallible, non-omnipotent, and non-omnicient, plan for all and prevent all possibilities.

This is a case of multiple fail-safe mechanisms failing at once due to extraordinary circumstances. The building was earthquake proof (to an extraordinary extent), but the generators were not tsunami proof.

It will be quite some time before the full extent of the failure mechanisms is understood. In the mean time, our planet is studded with power plants designed to withstand everything except whatever was unanticipated when they were built.

I would also like to put in a good word for all the technicians and scientists who are scrambling in the background to prevent this bad situation from becoming a massively horrifying situation. You know that there are people out there struggling to learn exactly what’s going on and stop it before it gets worse. Let’s all keep them in our thoughts as they try to protect the people of Japan and the world.