This will be a brief post, following the issued raised in this article in the NYT tonight. My summary of the findings discussed is simple: there is a direct underground connection between at least one of the damaged reactors and the Pacific Ocean.
The questions that occur to me are also simple: How would things look if at least one of the reactor cores, perhaps the core from Unit 2, had melted through all the containment, through the floor of the building, and down through the soil? What would we be observing if the core were resting on bedrock well below the reactor building?
The answers seem to be that the temperature gauges would not be registering high temperatures, because the hot core would not be close to them. Groundwater throughout the site, including in the basements of reactors five and six, could contain numerous radioactive isotopes, including short-lived isotopes that would have decayed to tiny levels if containment were still good. Radiation levels in the ocean near the stricken plant might not be low. With containment, they would by now be quite low, as the currents on the east coast of Japan are quite strong. Physical dispersion and radioactive decay would together have brought the levels way down, and only long-lived decay products would be observed.
These observations have all been made since early in the crisis. Some made sense — continuous cooling could have explained temperature gauges reporting reasonable temperatures (instead of temperature gauges reporting reasonable temperatures because they were far from the heat source(s)). We FDLers were puzzled at the radiation levels reported in the basements of Units 5 and 6 in particular. What was that all about? It has never been explained, as far as I know. As the article lays out, there is strong evidence that there is no containment for at least one of the cores.
Personally, I see no data suggesting that any of the core remains in the reactor building for Unit 2. If there is evidence that there is any containment whatsoever at this point, beyond deep self-burial (self-deportation?), surely it would be in the public record. I can find no reference to such evidence.
I do not know what the implications could be if the core has in fact already melted through the floor and out of the building for one or more units. Probably it simply means that cleanup is going to be even harder than anyone has yet articulated. I.e., there are probably no urgent, unappreciated risks associated with a core that is deep in the ground instead of in a wrecked reactor building — but I could be wrong. I do not have a good grasp of what the differential risks are for a situation like this. Before worrying about that, it would be interesting for someone with access to TEPCO to ask them why they believe the Unit 2 core is anywhere within the Unit 2 reactor building.