Out just in time for holiday shopping, a new family board game modeled on such perennial favorites as 'Clue' and 'Balderdash' has made its debut. The game is modeled on the ongoing nuclear disaster in Fukushima, Japan, and steers players through a delightful series of ever-worsening 'expert' analyses for the purpose of guessing where the corium from each of the three melted reactors might be…
Yeah, that's snarky satire, making light of not just one or two, but three different 'model' results of official studies released on the last day of November, 2011.
First up is the simulation released by TEPCO purporting to establish that none of the corium flows at Fukushima Daiichi's three melted reactors has yet managed to melt through the concrete and steel linings of the primary containment vessels. Though it does report that unit-1's corium - comprising 85-90% (or, according to a TEPCO spokesperson, all 100%) of the reactor's fuel load - has come to within a foot of the last barrier.
But Tepco's simulation also underlined the severity of the accident at Fukushima No. 1 plant, as the results indicated that the nuclear fuel in reactor 1 likely penetrated through as much as 65 cm of the containment vessel's concrete floor, reaching as close as 37 cm to the vessel's outer steel shell, the last line of defense. Reactor 1 suffered the worst damage from the March 11 earthquake and tsunami.
The findings also suggest that the nuclear fuel in reactor 2 melted through 12 cm of the vessel's concrete floor, while fuel from reactor 3 burned through 20 cm.
The simulation and its rosy analysis was released November 30th during a Nuclear and Industrial Safety Agency [NISA] meeting of 'experts' from around the world assessing the current state of affairs at Daiichi. TEPCO used a simulator modeling program developed by a subsidiary of Westinghouse Electric based on gas sampling results.
The New York Times painted a not-so rosy picture of what the new simulation reveals, and cites "some nuclear experts" who dispute TEPCO's insistence that the corium masses melting their way through the containment vessels are being adequately 'cooled' by pouring water into the essentially empty steel reactor vessels.
TEPCO's Matsumoto was unable to convey too much optimism in the NISA presentation…
Because the simulation suggests that heat released as a result of radioactive decay "far overwhelmed" the effect of the cooling water, he said, and because temperatures in the inner pressure vessel that originally housed the fuel are thought to have dropped quickly, Tepco now assumes that "100 percent of the fuel at Unit 1 has slumped" into the outer primary containment vessel.
In addition, the simulation suggests that the fuel bored more than two feet into the concrete, Mr. Matsumoto said.
The simulation did not follow the corium past the first days of the disaster to tell us where it might be now, eight and a half months later.
Study shows deeper meltdown offers some explanation of the actual simulations from TEPCO and JNES…
Wednesday's simulations depict what happened early in the crisis and do not mean a recent deterioration of the No. 1 reactor. Oyama said, however, the results are based only on available data and may not match the actual conditions inside the reactors, which cannot be opened for years.
Ignore all the distraction of TEPCO's insistence that it can somehow achieve "cold shutdown of the reactors" by next month. They can't, there's no functional core in any of those reactors to achieve "cold shutdown." There might be a little bit of fuel stuck on some fixture or other still in the bottomless vessel of one or two of 'em, but the rest of it is in an entirely NON-geometrical molted blob melting its way through concrete and/or dirt and rock. It's still occasionally fissioning (exponential re-heating), only its exposed upper surface is available to flash incoming water to steam and gases, the rest is well shielded (until and unless it hits groundwater).
There is no such thing as "cold shutdown" for massive tonnage of molten corium. There is the hope that it will eventually incorporate enough non-fuel material to dilute the tons and tons of fuel so it cools enough not to be actively melting whatever it touches.
An even less rosy scenario was presented at the same meeting by the Institute of Applied Energy pointed out that it is possible that corium melting through the containment vessel has caused the vessel to 'tilt' - as in, fall over. This could only happen if the corium melted past the juncture of the containment vessel's concrete coat and steel liner to dis-attach it from the underlying facility pad (also concrete). Which fits in with the presentation by JNES, which stated…
…the erosion of the concrete could be deeper and the possibility of structural damage to the reactor's foundation needs to be studied.
Of course, meltdown to corium, corium-steel and corium-concrete interactions don't take eight long months to occur, but mere minutes, hours and/or days. That's what the quote above…
"Wednesday's simulations depict what happened early in the crisis and do not mean a recent deterioration of the No. 1 reactor…"
Means. Thus what we are once again being treated to by Japanese 'officials', the utility responsible for Daiichi, various nuclear 'experts' and such is a tale of what happened during the first days of the disaster, not things as they stand eight and a half months later. All involved agree that somewhere between 70 and 100+ tons of reactor core material that used to be inside the reactor vessels of units 1, 2 and 3 was released as corium and is melting into (and possibly through) the concrete and steel of the containments.* At least one of the containment vessels is probably 'tilted', and so far no one appears to have considered the possibility that the concrete pedestals on which these containments stand may also be as (or more) cracked by seismic activity as the actual ground on which the Daiichi facility sits.
* Unit 1 was a 460 MW reactor with 400 fuel assemblies in its core representing ~70 tons of uranium oxide fuel. Units 2 and 3 were 784 MW reactors with 548 fuel assemblies in their cores representing that much more tonnage of fuel. So when TEPCO reports that units 2 and 3 might not have 'spilt' as much of their core's worth of corium, we could still be talking equivalent masses for each of those flows.
By way of contrast, the famous Chernobyl "elephant's foot" corium formation - melted an estimated 9 feet into the concrete pad beneath the plant - represents a mere 2 metric tons of corium lava. Perhaps half that mass consisting of melted uranium/plutonium fuel. It stopped actively melting into the pad because it had incorporated enough concrete components and other metals to dilute the volume of fuel generating heat. There is, if the model is accurate [100% unit 1 core], 70 times as much concentrated fuel in the corium mass beneath Daiichi-1. It is unlikely to be diluted to standstill yet by concrete and incidental metals, and it is unlikely to be effectively cooled by showering water onto its presented surface (which occasionally causes flash fission).
The deeper the mass melts into the substrate, the less surface area it's presenting to the water shower from above. At the same time, the more concrete components it's absorbing and mixing into its mass. This information is more than 8 months old per the timeline described by the models. No one has ever melted this much fuel to know anything much about how far it'll get before becoming too dilute to keep melting everything it touches. No telling where the corium flows are now, as Hiroaki Kiode pointed out in the NYT article linked above…
"I have always argued that the containment is broken, and that there is the danger of a wider radiation leak," Mr. Kiode said. "In reality, it's impossible to look insidethe reactor, and most measurement instruments have been knocked out. So nobody really knows how bad it is."
Horace Boothroyd III has a diary to this subject up - Only 37 Centimeters of Concrete - that makes some excellent points. This diary is to flesh out the extended dishonesty ongoing in the material publicly released, because I'm betting that 37 centimeters of concrete was left behind months ago. It would be slower going through the bedrock, but again the extensive fissuring could spread out the corium flows widely. Some considerable tonnage could be very close to the cliff right now, much more than was in the "elephant's foot" formation that got 9 feet into the rock at Chernobyl, not mere centimeters.
IOW, they're still admitting all these months later that the first days' events were far, far worse than anything they admitted to previously. They have not come close to admitting the true situation as it stands at this point in time. I wanted to make that point as clearly as possible, because the nuclear disaster at Fukushima Daiichi is nowhere near "under control" and won't be under control in any of our lifetimes. We need to understand this before we the people of planet earth put another dime into 'new' nuclear development, anywhere in the world.