
@Ian, the issue under consideration with the hydrogen explosions is HARDENED VENTING. The schema above shows the valves involved. There has been much discussion in late March that at least in Unit 1, the valves that were supposed to stop the backflow into the Standby Gas Treatment System were not closed, letting the gas seep back into the building. The point of note may be that, unlike in US plants, at Fukushima the SGTS is installed BELOW the service floor. I can't find that reference though. This would explain why we see so much damage downstairs. However, in my mind the presence of the gas in Unit 4 remains a mystery. Imagine the enormous draft that such tall stack produces! Makes me think that the flow would be always up and out, unless blocked for some reason. www.beyondnuclear.org

@Ian this wisp?


www3.nhk.or.jp
Water flow falls at No.1 reactor, but restored
The volume of cooling water flowing into the No.1 reactor of the Fukushima Daiichi nuclear plant fell on Monday, forcing workers to inject additional water.
A cooling system is in place at the number 1, 2 and 3 reactors. The system injects 3.7 tons of water every hour into the No.1 reactor.
Tokyo Electric Power Company says the reactor's water flow began to decrease gradually around 9 PM on Sunday night. By 8:13 AM on Monday, only about 3 tons of water was flowing into the No. 1 reactor, setting off an alarm.
Workers immediately began injecting double the usual amount of water. They managed to restore normal water flow in the reactor before 9 AM.
TEPCO says there was no change in temperature or pressure in the No.1 reactor.
The utility says some kind of debris may have clogged the hoses, reducing the water flow, and that it is checking to see how the failure occurred.
Monday, July 04, 2011 17:29 +0900 (JST)
www3.nhk.or.jp