New admissions featured in an Asahi Shimbun article highlight the extent of the problem discovered on the pedestal inspections of unit 1 at Fukushima Daiichi earlier this year.
They confirm what was fairly obvious from the inspection photos, that a significant portion of the lower concrete pedestal that holds up the reactor vessel has had the concrete melt away. It isn’t currently known how much of the pedestal has sustained this damage, further inspections planned for the spring should confirm the extent.
Asahi Shimbun interviewed the researcher who ran computer simulations to estimate where the pedestal would potentially fail. This estimate found that the pedestal has less than half of its original resistance. The researcher went further to warn that the pedestal could fail in an earthquake as low as the 6-7 range on the Japanese Shindo scale. This is roughly around a magnitude 5 or higher type earthquake.
If the pedestal would fail, the reactor vessel may not have sufficient support to keep it in place. Beyond drastically complicating the fuel debris removal and dismantling of the damaged reactor, what could happen if the reactor vessel dislodged and fell into the remains of the pedestal is not fully understood. While this wouldn’t impact the integrity of the outer building, it would potentially create more openings or leaks through portions of the containment vessel that connect to the reactor vessel.
That kind of catastrophic failure has the potential to send radioactive particles into the air. Unit 1 is already a concern for the release of radioactive dusts to the environment. This has been well documented over the years. The series of tents and covers placed over unit 1 since soon after the initial disaster attempted to contain some of these dusts. The building currently has no cover while a fuel removal shed is built over the building to remove the spent fuel from unit 1’s pool on the refueling floor.
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