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Degraded Reactor 4 Structure
Shows Signs Of Sinkage

By Yoichi Shimatsu
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A few years ago, I had to make a decision to  either restore an old school building in Hong Kong for an environmental center - or demolish it. The long concrete structure was built atop a garbage dump, and the final decision was demolition due to uneven sinkage. Whenever heavy buildings are not foursquare and level, massive internal stresses build up and rip the structure apart.

In a recent helicopter photo of Reactor 4, seen from the east (ocean side), there are similar signs of building sinkage. Along the middle-to-northeast corner (right side), cross beams have fallen out, and at least two adjoining pillars are of different height. The outer wall panels cracked and fell off as a result.  (Plus one can see clear through from the east to northeast through a gaping hole.) Cross beams snap off due to the displacement of pillars in opposite directions

What the combination indicates is that the footing of the structure has cracked completely, with two-thirds of the building sinking at a slight angle into the broken edge, while the smaller north side, relieved of load, gradually rises with a series of popping noises. This springboard effect is  audible  whenever a column lurches upward, like the two pillars o n the right-hand side lifting the floor above it and breaking out. (The pincher-clawed back-hoe is parked on a pad that spreads the weight over the precarious structure.)

It is very probable that the reactor below is tilting as well. The concrete footing for the structure is too thick to crack under weight alone or even in a major quake, and so the cleavage was probably caused by the corium searing along a line. Once burned, the concrete and rebar lose their strength and can buckle and crack under seismic vibrations and weight from above - especially if the ground is unstable. The March 11 quake probably caused liquefaction that opened an empty pocket below the footing, and water seepage from the tsunami, rainstorms and coolant leakage subsequently eroded the soil.

Since the spent fuel pools are on the south side, the strongest end of the broken structure, one metal tank still appears to be intact, judging from the corner that can be seen.

The twisted, overheated metal leaning out of the holes around the spent fuel pool indicate the framework under the pool is wrecked. If the pools are still level, it would be nothing short of miraculous. Odds are that the pools are tilting, adding massive stress to the   
whatever remains of the supporting frame.

The steel plate over the now-exposed floor/ceiling could be there to prevent people from seeing that the spent fuel pool is tilting and lower than its former position due to the bending of the metal frame below. A tarp would have been melted by the heat released from the jostling of the pool and loss of water in the two series of 2012 quakes that further degraded the structure. Two sheets of steel plate could resist temperature build-ups of up to about 1,000 C or around 2,000 F before bending. Notably, open space is left on either side of the plates to allow heat escape. The presence of the plates point to   
flaring temperatures  on occasion since the spent pool fires of March 14 and 16, 2011.

The demolition work of June 26 had to be done to remove the weight of the upper walls. This is consistent with what must be done when the footing is cracked and lower floors are tilting inward, causing stress buildup throughout the entire fabric of the structure.

That old school building rocked like a boat whenever a bus or truck passed by on the adjoining road. For Fukushima workers, it would be terrifying to be on top of a fractured structure that amplifies seismic waves.

The ongoing self-destruction is inexorable and cannot be repaired or reversed. When I checked the foundation of the old school structure, the concrete was broken clean through in many places along roughly parallel lines. Fixing a broken foundation is impossible, especially when it is on uneven landfill, since the rubble below will firmly not hold up an injection of concrete or jacking. Our team considered the possibility of artificial support for that school building but quickly gave up the idea as unfeasible. The far heavier Reactor 4 structure is following the same pattern of step-by-step degradation, or  phased collapse, in which the stress factors are so complex that there is no way to predict when or what part will be the next to go.

The rate of soil loss under the structure is still the determining factor leading to a final collapse, and this problem of soil sinkage effects the entire Fukushima No.1 plant site, which rests on landfill compromised by  quake-caused liquefaction, erosion by the tsunami, incessant water leakage and melt-through of escaped nuclear fuel. Engineers therefore had to push back the TEPCO plan to remove two fuel rods from Reactor 4 in this month of July. For the same reason of soil instability no attempt has been made to set up a scaffolding or crane along the south wall to lift rods into a casket.

Instead of an apocalyptic moment, as most observers had anticipated, the ongoing degradation of Reactor 4 remains one of nerve-racking suspense, of waiting for the next beam to drop.

Author: Yoichi Shimatsu is an environmental writer and consultant based in Southeast Asia.



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