Tepco has announced that the damaged Fukushima Daiichi unit 1 reactor building is flooded; in one stairwell the water pools 4m deep. The company estimates that the total amount of water is about 6000 cubic metres.

In a progress report published a month after the original roadmap to site stabilisation, it admits that leaks in the unit 1 primary containment vessel are so extensive that it will no longer try to flood the unit 1 core, (as reported on 17 May) but but instead is shifting its focus to establishing a closed-loop cooling system there.

Starting in June, Tepco plans to treat and recirculate low and intermediate-level wastewater back into the reactor by constructing a treatment plant, and installing a desalination plant to treat the water.

Tepco has also announced plans to start to pump water out of the unit 3 turbine building basement. The wastewater will be pumped through pipes laid alongside those pumping out the unit 2 trench and turbine building. Almost 6000 tons of water had been pumped out of the trench by 16 May.

The water will be pumped to the centralised waste treatment facility process main building, which was waterproofed after the tsunami, and the miscellaneous solid waste volume reduction treatment building, where the waterproofing has just been completed.

Tepco has also issued a provisional explanation of the unit 4 hydrogen explosion, previously thought to have occurred in the spent fuel pond. It suggests that hydrogen gas vented by unit 3 toward the ventilation stack was sucked into the reactor building by unit 4’s standby gas treatment system, which runs close to the unit 3 exhaust pipe. If the hydrogen gas were sucked up by the SGTS, it would have been pumped through exhaust ducts on the fourth and fifth floors of the building; these were the areas most heavily damaged in the subsequent explosion.

Other hydrogen explosions occurred in unit 1 and unit 3.

Reactor-by-reactor Fukushima Daiichi summary, 18 May from JAIF. This can be downloaded via: www.tinyurl.com/3t6gdt6

Fukushima Daiichi parameters as of 16 May by JANTI. The latest plant parameters can be downloaded via this link: www.tinyurl.com/6f47lhx

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