The Fukushima Daiichi site cleanup will take place overall several years so the systems for remediation are being designed to sustain potential earthquakes, tsunamis, and site blackouts. Electric busses are being wired with redundant taps to the grid, equipment is being situated on higher ground, and structures will need to be capable of withstanding earthquakes. The plan calls for separating the radioactive water based of the level of radioactivity. The mega-float barge will be used for low level storage. High level waste water will be filtered and cooled for recirculation into the reactors.
The plan for cooling the fuel in the reactors is to flood the reactor containment structure with enough water to cover the top of the fuel in the reactor vessel. Below is a simplified diagram showing the reactor containment structure which is the light blue area shaped like a light bulb. The current water level is estimated to be 18 feet which is below the reactor vessel. Concerns about the ability of a flooded reactor containment structure to withstand an earthquake are being addressed. Units 1 will be flooded first. Unit 2 cannot be flooded until the containment leaks are repaired.
Additional information has been provided about the Unit 4 spent fuel pool structure. Photos taken by a drone helicopter showed structural damage to the Unit 4 reactor building which has raised concerns about the integrity of the Unit 4 spent fuel pool. In an effort to reduce the mass of water in the pool, the criteria for adding water has been changed to be temperature based in order to determine an equilibrium point between maintaining cooling and minimizing the amount of water. A plan is being drawn up to install additional supports below the pool.
TEPCO released a radiation survey map of the site which will show progress of cleaning up the site. They have found some highly radioactive concrete chunks which were scattered by the hydrogen explosions. The radioactive debris is being placed in containers which will eventually be shipped to a radioactive waste site.
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