Scram reduces it to 3% almost instantly, ~1% after about a minute, and it continues to rapidly decrease from there as the short lived radionuclides rapidly decay out. I noticed this when I was researching the data on three mile since I had also always heard the fabled 7% number and wondered why the decay heat post scram didn't line up with 7% since the reactor was functioning at 97% power when they suffered loss of heat sink.
But I otherwise agree with your post.
Still should be at least some sub nucleate boiling but not enough to support steam production, collapse of the steam voids produces a vacuum effect and pulls from the discharge leg. That said he did raise two interesting points if true. Namely:
There are a couple of phenomena that seem to correspond to what Kimura believes happened. One is that a pump designed to draw up water from the bottom of the containment vessel seems to have been activated frequently, indicating that damage to piping caused coolant to leak and accumulate at the bottom of the vessel.
The other is that radioactive contamination was taking place at a much faster rate than was estimated by Tepco....
So it sounds like they had their sump pump cycling on and off repeatedly. This could have been due to a high sump water level that they were planning on pumping down during a later plant evolution. Then the earthquake could have caused water slosh causing the sensor to repeatedly trip and cycle the pump. Or they could have seen their PORV's (Pilot Operated Relief Valve) open up and vent down to the sump, tripping the pump to cycle on. Or there could have been a broken piece of piping, the severity of which is difficult to establish after the loss of instrumentation. Or it could have been an electrical failure due to the earthquake causing a faulty sensor reading, or possibly damaging the sump pump control circuit.
The later claim is difficult to address, since it does not specify where this contamination occurred. According to the article a worker was unable to enter the reactor building due to high radiation. But this high radiation could have occurred from any number of sources, including an open PORV and subsequent degassing of radioactive Argon-41 into the containment vessel and reactor building.
I suppose the real problem with an event like this is that we typically can't stabilize the site for a lengthy period of time, and thus will likely need to wait until 2021 for a more definitive survey of what the actual timeline was.
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