Why I am not worried about Japan’s nuclear reactors.

1) The 'core catcher' is the bottom of the containment building. This reactor was built by GE.

There is a diagram of the reactor in Google Books: http://books.google.com/books?id=y20F8Yt6UcMC&pg=PA34...

Not sure if that will make it through the HN editor but its worth a look. Would love to get a scan of that diagram online. In 'flask type' reactors the re-inforced concrete pad under the reactor 'catches' the core (if necessary)

2) Its important to understand that since the reactor is shut down, its only source of heat is the decay products from when it was running, minus the heat they pulled off while running on battery power. Further the engineering design target (one assumes they test to that target) is that if you integrate over all the heat you generate from all the byproducts from a reactor that was running at 'full' and now has all of its control rods inserted, is less than the heat you would need to add to melt the containment vessel (the flask) You won't be able to restart it but you won't have the core melt through the vessel either.

His third point, he doesn't understand that long lived radionuclides aren't aerosols. Which is to say they stay in the containment vessel they don't exit with the steam. The impurities in the ocean water need understanding here but we're not talking a significant long term threat.

Number 4 he missed out on what radiation was measured, what the relative value of that radiation was and the how it won't persist. These are gamma rays that can make other things radioactive.

Anyway, if you have the book (I don't) it apparently describes the reactor in question in some detail.