Missing reactor cores: Since the accident at Fukushima on March 11, 2011, three reactor cores have gone missing. There was an unprecedented three reactor 'melt-down.' These
melted cores, called corium lavas, are thought to have passed through the basements of reactor buildings 1, 2 and 3, and to be somewhere in the ground underneath.
Harvey Wasserman, who has been working on nuclear energy issues for over 40 years,
tells us that during those four decades no one ever talked about the possibility of a multiple meltdown, but that is what occurred at Fukushima.
It is an unprecedented situation to not know where these cores are. TEPCO is pouring water where they think the cores are, but they are not sure. There are occasional
steam eruptions coming from the grounds of the reactors, so the cores are thought to still be hot.
The concern is that the corium lavas will enter or may have already entered the aquifer below the plant. That would contaminate a much larger area with radioactive elements. Some suggest that it would require the area surrounding Tokyo,
40 million people, to be evacuated. Another concern is that if the corium lavas enter the aquifer,
they could create a "super-heated pressurized steam reaction beneath a layer of caprock causing a major 'hydrovolcanic' explosion."
A further concern is that a
large reserve of groundwater which is coming in contact with the corium lavas is migrating towards the ocean at the rate of four meters per month. This
could release greater amounts of radiation than were released in the early days of the disaster.
http://truth-out.org/news/item/19547-fukushima-a-global-threat-that-requires-a-global-response