Rive said:
The lack (or inadequate amount?) of hydrogen recombiners, the wrong placement of reserve diesels, the lack of filtering on the vent stacks, the old design (IC instead of HPCI), the out of date design basis - that unit were lost in the moment the tsunami arrived.
Unit 1 did have HPCI, it was lacking RCIC. However, there is no evidence of any attempt to start HPCI in unit 1 during the accident.
I'm not at all convinced IC was inherently a worse design than RCIC+HPCI for high pressure cooling. In fact, it is making a comeback in ESBWR. It appears more like there was over reliance on it working due to being a gravity flow system without the need of pumps. The efforts to confirm RCIC operation in unit 2 appear to have been much more aggressive and persistent than the equivalent efforts for unit 1 to confirm proper IC operation. Yet IC was the Plan A for unit 1, with ongoing attempts to replenish water to it from the DDFP.
I think the unanswered key questions are what kind of a flow rate and cooling efficiency the IC did achieve with the partially closed inner isolation valves. The outer valves were not opened for long enough to evaporate more than 20% of the train A shell side inventory.
Also, what would have happened, if
a) after the initial DC power loss to all instrumentation, crews had been sent to manually verify the outer valve positions and finding them closed, directed to open the train A outer valves,
b) another crew was sent outside the reactor building to verify with close and direct observation the steam venting rate from the RB west side steam vents,
c) considering that no operator present had experience operating the IC and that steam observations were difficult to quantify even if done directly (instead of from the other side of the building, looking from the emergency exit of the MCR to observe steam above the building with the vents not visible at all, as was actually done), more aggressive attempt to approach the IC room was done to read local flow rate and temperature gauges,
and
d) upon earlier realisation (as opposed to the actual 18:20 time frame) from the insufficient performance of the IC system, that the inner valves could have closed by the automatic isolation function, crews then sent to verify and manually open all of the internal and external isolation valves of both trains of IC?
TEPCO and NISA had spent quite a lot of effort to investigate whether IC was actually functioning without significant leakage after the earthquake and before the tsunami and their findings indicate that it was not only operable but operating, at the earliest point with both trains. So I fail to see any reason why it could not have been brought back to operation after the tsunami, had its failure been recognised and acted upon. It would not have required any power or compressed air sources. It appears the only resource required would have been people with the correct instructions and perhaps some PPE and tools.
