Recently there has been a great deal of concern about the stability of the Unit #4 spent fuel pool at Fukushima, and the globally disasterous consequences should it fail.
That is an entirely valid fear. However it's not the worst news from Fukushima. It might even be that focus on the #4 SFP is a deliberate distraction. Because there's something even more terrible off to the side of #4. That is the message of Fukushima Unit Three.
Some people still think it was the reactor pressure vessel of Fukushima Unit #3 that blew up on March 14, 2011. However when one examines aerial shots of the roof wreckage afterwards, it's clear it can't have been the #3 reactor that blew, because the girder framework of the roof is still intact above the reactor well. If the reactor had blown its lid, the pressure dome and the huge floor-plug above it would have punched a hole in the roof girder framework directly above.
Fukushima Unit Three, Mar 30th, 2011.
There is little damage to the girders above the reactor well, and the crane is also present below them. The frame damage in this area seems to be from the impact of rubble from the concrete roof slab, as it fell back down.
Instead we see the girders are entirely destroyed and missing above the #3 Spent Fuel Pool. Mr Gunderson has pointed this out, suggesting there must have been a criticality in the SFP.
I agree. Where I differ from Gunderson, is that I think there were three prompt criticalities in SFP #3, in rapid succession.
There is just one video on the net of the Unit #3 explosion complete with sound. It was recorded live off-air from channel 9 TV in Australia by 'oztvwatcher', before anyone in the MSM networks thought to edit out the sound. It is hard to find the video as it seems to keep being taken down, but here is my saved copy. (679KB) Take and save that now while you can, in case I'm forced to remove it.
It is one of the most significant videos you'll ever see. The crucial point in the video is, there are three very distinct and separate bangs, about equal in intensity, and half a second gap between each.
One bang or three, what's the difference, it blew up, right?
Perhaps it won't seem terribly significant when you first hear them. But once you understand what they signify, and the implications, they carry a terrible message. In this article I will tell you what it is.
The first bang was the hydrogen explosion and immediate first prompt criticality in the SFP, as the hydrogen explosion rearranged fuel pellets that were above the lowered water level and loose because their zirconium tubes had burned away. That burning in steam was what produced the hydrogen for the initial explosion. With possible contribution from exposed rods burning in the reactor core as well, and the gases escaping the pressure vessel.
And then... now pay attention, this is tricky. First you need to understand how the water in SFPs does more than keep the rods cool, and shield the radiation.
If there was no water, decay neutrons leave the vicinity too fast to interact with other rods enough to support a criticality. Not enough neutron-reaction feedback, so no chain reaction criticality. (Never mind that the rods would be overheating and catching fire in air, that's not the point here.)
On the other hand, with water present the neutrons are slowed and absorbed by the water fast enough to prevent them interacting with other rods, so... not enough feedback, and no chain reaction criticality.
Got that? No water, neutrons leave too fast. With water, neutrons slow down too much and get absorbed. Both states mean no nuclear chain reaction, no criticality.
Now for the cold, logical and horribly inevitable truth. It follows from the above that for some degree of neutron slowing/absorption in between the 'water' and 'no-water' states, there is a condition in which neutron-fission positive feedback within the stacked rods is just right, and prompt criticality will occur within milliseconds.
What might this intermediate state between water and no-water be? Why, it's simple. It would be water in the process of flash boiling into steam. At some point, the expanding froth of water/steam will hit the right average density between the fuel rods, and there'll be a nuclear chain reaction.
What would cause a volume of water in a SFP to flash boil? Why... a strong nuclear chain reaction nearby! The huge flux of neutrons from a zone of the rods that went critical, will be absorbed by the water nearby... as in, deeper in the SFP. The neutrons heat the water enormously, and the water suddenly wants to boil. Nothing stopping expansion but its own inertia, and so it begins to expand...
It turns out that SFPs are actually much like strings of firecrackers tied together.
If the tops of the rods are exposed for a while, they burn. In the worst case there's a prompt criticality in the burning section, either spontaneously as pellets fall into clumps, or as a result of shock movement of pellets due to hydrogen explosion.
The criticality causes a huge neutron pulse. Which in turn causes a volume of water lower down in the pool to flash boil.
As that water changes state into steam (which takes a little while, say, oh, half a second) a moment will come when a new area of the fuel rods in the volume of expanding water/steam froth suddenly reaches criticality. Causing another huge pulse of neutrons.
These in turn heat another shell of water, still deeper in the SFP. And the cycle repeats until it runs out of fuel rod length, or water, or some other limit is reached. In the case of Fukushima #3 SFP, the cycling stopped after the third criticality pulse.
Why not two pulses, or five? It doesn't matter. The point is it kept going after the first.
Note that each prompt criticality will only be brief, since it will stop as soon as the flash boiling water expands further and becomes sufficiently like 'no water'. It's likely that the rods going briefly critical would still be sitting there afterwards, rather than actually blowing up. They just produced a brief, huge thermal and neutron power pulse.
Then afterwards, exposed to air, they'll suffer a zirconium fire and burn. But that's much later compared to the fast process of the 'SFP firecracker string' effect. The newly exposed rod casings burning may be why unit #3 had so much white smoke in the day or so after the main explosion.
The fuel pellets thrown for kilometers around SFP #3 would be from the initially burnt top sections of the rods, before the nuclear-flash boiled water below turned the SFP into a giant steam-powered shotgun. That fired three times. Three bangs.
Note that this effect may have involved quite a small proportion of the total fuel load in the SFP. Other sections of the rod racks may be mostly undamaged. The initial zirconium fires may have been only among areas of recently added rods, with their higher heat output. The first criticality may have been in a relatively small volume of the collapsed burnt rods. Only some rod groups will be sufficiently active enough to support criticality at all.
Also the brief criticalities themselves may not have done much physical damage to the racks. A steam flash boil explosion down in the pool would direct its force up, between the vertical fuel rods. But the three-shot series of steam bangs from the gun-barrel-like SFP, mixed with rubble and uranium dust went straight up.
The original hydrogen explosion produced a powerful distributed overpressure pulse, that blew out the concrete side wall panels and set the concrete roof slab moving rapidly upwards. The steel girder structure below the roof slab would have been relatively unaffected by the hydrogen explosion overpressure due to the low surface area of the beams, and their strength and ductility. But the high velocity jet of material ejected upwards from the SFP by the steam explosions then completely obliterated the roof structural girders above the SFP. Basically, the jet cut them to pieces.
In the video we see an incredible dense vertical shaft of upwards-directed material, that just seems to go on and on. In a classic nuclear mushroom cloud the 'column' is fairly static - it's just a smoke trail rising slower than the fireball. But with Fuku #3 that column looks like it's all going UP, fast, the whole time. The reason the explosion jet looks so continuous, is that the base was being resupplied with newly ejected material, blasted out of the concrete 'shotgun barrel' of the SFP by three successive criticalities. The jetting material probably was virtually continuous, with only invisible pressure waves coming in the distinct pulses that we heard as three bangs.
There are some other details in the photo above. Over to the right the roof girders are also severely damaged. The rubble in this area seems to consist of many large concrete fragments, and the way a major roof strut is twisted to the side suggests the damage was due to that heavy concrete rubble falling back down after the explosions. In contrast, at the left around the SFP, the concrete rubble appears much more finely powdered, and there are a large number of the light colored 'twisty straw' objects. These are lengths of corrugated galvanised iron, that was originally formwork on the underside of the poured concrete roof slab. As the slab was pulverized, these metal strips were torn loose then settled back with the rest of the ejecta. They are common in all the aerial shots of the three destroyed reactor buildings.
If there's any one detail of this whole tragic saga that should prove finally and forever that humans are not capable of 'safe design' of fission power stations and their fuel chains, it is this. No one seems to have ever predicted that 'spent fuel pools' are capable of firecracker-string rapid fire sequential prompt criticalities.
But they are. In that video we hear and see it happening.
Bang... Bang... Bang... Nuclear fission power is dead.
Every single spent fuel pool, in every nuclear plant and storage facility on Earth, has this incredibly stupid and dangerous design flaw. Lose the water cooling system, and this can happen. Fukushima Unit Three demonstrates it.
Some generations of nuclear plants may have insane features like fuel pools up on top of tall buildings, in earthquake zones. Emergency generators in basements, that get flooded. Backup diesel fuel tanks on seaside docks, that get washed away. There are endless such stupidities, but they don't tend to be universal to all designs. Fukushima #3 demonstrates there can be unseen fatal traps across all nuclear plants. Deep conceptual flaws, unaccounted for in designs. Spent fuel pools are suddenly and unexpectedly shown to be fundamentally unsafe.
Yet no one foresaw this! All the so called expertise of the nuclear industry, so called safety analysis, so called redundant fail-safe designs, and no one saw that a simple arrangement of used fuel rods in a pool of water can act like a nuclear firecracker string.
So what is the message of Fukushima Unit Three?
This. Humans are inherently fallible and blind. No matter how hard we try, no matter how certain we feel, we can still screw up horrifically. And given this sorry but inescapable fact, we cannot, MUST NOT, ever, ever build things that can destroy the planet if they go wrong. Or even whole nations. Or cities... Or anything bigger than a quite small area, really.
It's a nightmare tour of the horrors of Chernobyl, over 25 years later. Understand that Fukushima is already worse - far worse. There just hasn't been time for the reality to become visible as endless death and disfigurement. Not only is the scale of the disaster worse, but it is amplified by Japanese cultural and political weaknesses, that seem to prevent the decisive and honest steps necessary to realistically deal with the crisis. Wait another 25 years, and see the horror that Fukushima will have brought the world.
Now here's a thing few people understand. The science of Epigenetics. In a general sense, it means the way the information in our genes is transmitted from generation to generation, over long time-frames. Overall, the genetic integrity and health of all species is a balance between information loss due to errors occurring in the DNA, and the weeding out of such errors and unfitness in the DNA due to evolutionary competition. So in the long term it's a balance — accumulating errors vs reproductive competition.
This can only work for complex species with long reproductive cycles, if the accumulating error rate is quite low. Which fundamentally means, only if the background environment radiation level is very low. As it has been on Earth for billions of years. Till now. Till Chernobyl, Fukushima, and the several next such events.
In the Russian video about Chernobyl, there's concern that in future there will be no more people in Belarus. They are right; after some generations of spreading and accumulating radioactive genetic tragedy, there may not be.
But it's worse than that. Complex systems interact. There are hundreds of nuclear power stations in the world. As regions like Belarus, Japan, and surrounding badly affected areas lose social cohesion due to declining genetic fitness, there will be more such nuclear accidents. Like the chain of explosions in a spent fuel pool, unexpected dependencies will bite, and the nuclear contamination problem will snowball. Slowly at first, but I do not believe that we humans as a species currently have the political intellectual grasp and strength of will it would take to avert this cascade of spreading genetic chaos and death.
It will continue.
The long term containment of the ruin at Chernobyl is still unresolved, even with the new shield building. It will require continuous maintenance for centuries, perhaps thousands of years, and has rendered a large portion of the Ukrainian nation uninhabitable for generations.
Fukushima will be even more intractible, especially as it is on the sea shore with almost no possibility of preventing radioactive runoff to the Pacific Ocean. The ongoing airborne emission of radioactive isotopes including Caesium-134, 137, Iodine-131 from continuing criticalities in the melted-down cores appears likely to make most or all of Japan uninhabitable within a few years. Areas of the west coast of the USA have already registered dangerous levels of contamination.
This just from two nuclear accident sites! There are hundreds of such potential sources of disaster in the world. All it would take to convert them all to Fukshimas, would be a loss of human capacity to maintain the scientific and industrial infrastructure required to keep these sites running safely, and the nuclear materials isolated from the environment. But that failure could easily occur, globally even, with just one or two further unexpected events. A couple more earthquakes near reactors, or a medium-sized asteroid strike, or a solar flare taking out large areas of the electrical distribution grid. Or something slower but equally dangerous - supposing Japan really does become uninhabitable, or is still inhabited but experiences a social breakdown as the genetic tragedy unfolds. What will happen to the nuclear reactors in Japan, and their spent fuel pools?
We're walking very close to the edge here.
I recall first seeing the images of Unit #3 exploding that day; the second plant to explode at Fukushima, and saying to myself as the cloud still rose "That is the end of nuclear power, right there."
But I was mistaken. It was actually the end of the human race, and possibly all advanced life on Earth. It's just going to take a few more generations before the dead world walking finally falls, and lies silent.
To illustrate the scale: Fukushima and the Pyramids [Larger image]