AP: Melted Fukushima fuel is 12 inches from entering ground after eating through concrete, says simulation — Study: Molten core suspected of eroding through concrete foundation — Gov’t Expert: We just can’t be sure until actually seeing inside

EneNews

Associated Press, Nov. 19, 2013: [...] the real challenge: removing melted or partially melted fuel from the three reactors that had meltdowns, and figuring out how to treat and store it so it won’t heat up and start a nuclear reaction again. “This is an unprecedented task that nobody in the world has achieved. We still face challenges that must be overcome,” said Hajimu Yamana, a Kyoto University nuclear engineer who heads a government-affiliated agency that is overseeing technological research and development for the cleanup. [...] Computer simulations show the melted fuel in Unit 1, whose core damage was the most extensive, has breached the bottom of the primary containment vessel and even partially eaten into its concrete foundation, coming within about 30 centimeters (one foot) of leaking into the ground. “We just can’t be sure until we actually see the inside of the reactors,” Yamana said. 

‘Atomic Energy‘ Volume 114 Issue 3, July 2013 (Emphasis Added): [If there's no safety system to cool Fukushima melted fuel from Units 1-3], the accident developed rapidly: the second safety barrier (fuel element cladding) failed 2 hours after the initial event, the third one (reactor vessel) at 13 hours, and the fourth one 7 days after the easing of the dry box of the containment shell melted and through erosion of the concrete foundation occurred. 

These data were transmitted to the operational headquarters of Rosatom and the crisis center at the IBRAE RAN in order to estimate the possibility that the population of our country in the regions bordering with Japan would be exposed to radiation.  [...] According to the computed picture. in all power units of the Fukushima-I NPP flooding with water stopped the downward flow of melt, but because energy continued to be released in the melt it was necessary to feed water into the reactors continually. It is known that the operation of the active safety systems, with whose help the core could be cooled reliably in a closed cycle, could not be restored for another several weeks.

 

See also: ABC Correspondent: Nobody knows where Fukushima's melted cores are now, expert says -- Tepco admitted fuel "is actually eating through the concrete... hopefully it’s not eating through any further" (AUDIO)