Fukushima update 2

WNN is reporting a somewhat improved outlook at Fukushima...

Fukushima Daiichi has six reactor plants; THREE, not two, were online and providing power to the grid when the quake hit and were shut down in an emergency shutdown procedure. The other three plants at that site were not operating.

Apparently the EDG's did start and run but for reasons not yet known they only ran an hour. While diesel generators have arrived at the site with more on the way, it appears (and this is where the WNN report omits details, so I'll suppose) that Unit 1 at this site in all probability had the most serious decay heat, and probably lifted relief valves because containment pressure and temperature are above limits. It is the containment, apparently, that the operators plan to vent.

It appears the plants were cooled by feed and bleed, perhaps accompanied by relief valve lifts during the time ECCS were not operable when the EDG's shut down and before portable EDG's arrived. It is this situation that led to the provision of coolant by the US to the plant. This might indicate that the plants had "checked down" the list of primary injection water inventories as they were expended.

All this is highly speculative and naturally conditions at each of the three plants can be expected to differ.

While eleven plants shut down in emergency, the situation at Fukushima Daiichi is the most serious due to the combination of scram from load and loss of EDG's / LOOP.

Nearby Fukushima Daini, with four plants, apparently DID use feed and bleed and did not lose AC power totally - either the site's EDG's all continue to run or offsite power remained available; most probably it is the former.

More to follow.