reply to post by Human0815
This Building is immense and massive!
The "cover" on the blasted and leaning structure that used to be called Reactor Building Number Four is in no way as massive as the original
structure. The walls in the original building were reinforced concrete three feet thick and they didn't hold. Basically the new "building" is a
hood with ventilation and filtering capability should there be a whoopsie. That they built the cover is indicative of the expectation they could
encounter problems removing fuel rods.
If that occurs, the filters and ventilation apparatus will allow venting to the atmosphere preventing the earlier resulting explosion from the build
up of hydrogen gasses. The gasses will be vented… to the atmosphere… to prevent an explosion.
The first rods to be removed will be the 200 or so that were ready to be loaded in the empty reactor well at the time of the quake. These are as yet
unexposed in a core and a lot less dangerous than the other "spent" fuel rods in the pool. The danger still exists that they may snag or even drop
one of these unused fuel rod bundles as they begin to lift it clear of the storage racks.
Supposedly they have cameras and sensors on the hoist to quickly detect if they are loading the motor with too much strain during lifting. Any strain
detected during slow creep for each fuel assembly and they will halt and try to clear any snagged debris or misshapen rods.
If they can't clear the debris they may re-lower the assembly into its rack and try to raise a larger portion of the racks itself containing many
fuel rod assemblies.
Problems that might occur with this process are:
Snagging during lifting
Fuel rod assembly stuck half way in and out of its rack. That could teeter and may collapse on its own or fall, breaking apart either during removal
or reinsertion (cross your fingers to prevent quake after shocks).
The rod bundle may also snag on an obstruction during lifting, breaking open the ceramic cladding that contains the fuel pellets. If these pellets
fall to the bottom of the tank in a pile touching each other, this could start another uncontrolled fission chain reaction that could
other fuel rods. Like throwing a lit match into a box of matches.
That is a worst case scenario and odds of that occurring are low… … …
Other problems are transport of the fuel rods to their respective cask inside the new "building" and the transport of those casks to the on site
common fuel storage facility. This process involves hoists and moveable overhead cranes that lift and lower these items hopefully without dropping
any of them
As long as all goes according to plan they will have successfully removed all the fuel rods from number four spent fuel pool and transferred them to
another storage facility on site.
They will still be on site. There are three other fuel pools. None of this takes into consideration the other melted down cores of reactors one
So yah, first careful decommissioning baby steps to remove radioactive materials at Fukushima, Daichi. Hopefully they have the time to carry it
through before other issues at the plant prevent them from working there.