Physics is always a strange bird that takes us out of our comfort zone. Things which we or rather our brains declare maxims of existence, like that this concrete table is solid, physics rips apart and declares, no, rather, its all mostly empty space. And a collection of forces, the strong and weak forces, the gravitrons, the bends in space time, the quanta, and buzzing things beneath those where position and space dissapear in some space time energy dance.
Now we had fukushima. And if you look at the reactor design from the mindset of the people in the 1950s, it all makes great sense. It just doesn't make any sense in the realm of physics.
All these engineers had just come from projects building nuclear bombs. How do you do that? well simple you build strong compression chambers of thick steel and concrete and then maximize the pressure and a primary fission reaction ignites a secondary fusion reaction and blacmmo a city no longer exists and the clouds shure glow a pretty green.
Well the problem was these same scientists were tasked to design the peacetime nuclear energy reactors. So what did they do? They basically made bombs again. Big massive steel and concrete pressure vessels. And piped in water and made steam and turned turbines.
But Fukushima proved a basic lesson of physics. That four feet of steel and concrete that seems so strong to us humans, well it's nothing to a four thousand degree pool of molten uranium. It would be like making a pan out of WAX and then dropping a red hot BB pellet on it and being astonished that somehow the BB pellet was able to go through the wax. that's exactly how dumb physicists are today.
But it gets worse. They let the material get in contact with WATER! How stupid can you be. Why is this dumb? Well the problem is, we are used to water gently heating and becoming steam. These physicists completely forgot basic physics of what happens when 4,000 degree fissioning material meets water. What happens is that water instantly SHATTERS into pure O2 and Pure H2. The pure oxygen blasts onto fire and the pure Hydrogen EXPLODES. What they were really doing was surrounding the fuel with explosive hydrogen. But nawww no biggie, they have PHDs and I dont. so they MUST know what they are doing right? Dumb ol Giavell... she's just a nobody because she couldnt sit in boring classes with peon brained 120 iq professors who were dumb as stumps for eight years. But the physicists could. No problem. and that makes them.... morons.
Wait it gets even worse. Think of a nuclear reactor as a big backyard grill. And instead of putting a few charcoal brickets in it, you fill it to overflowing with charcoal brickets. Then you get the whole thing red hot even white hot, then cook one small chicken piece with it. And then you are left with forty pounds of blasting hot charcoal brickets burning away for hours and hours. That's exactly what a modern nuclear reactor is. first they make a big hole. then they stuff it full of control tubules which are stuffed with rods and pellets of purified uranium. And the whole thing is straining to light up white hot and burn for 200,000 years and the whole reactor will run for years and year on the huge pile of fuel they put in it which is great EXCEPT when something goes very very wrong. I call this the too much woodon the woodpile problem. The Superphénix reactor in France, for example, was designed hold an initial
core of 5,550 Kg of Plutonium. That's outrageous!
Well dont worry, things wont go wrong because we have control rods. fragile boron indium cadmium rhodium sleeves that slide over the rods. Except... when the rods get hot, they expand, and the sleeves deform, and suddenly YOU GOT HELP ME JESUS a backyard grill with forty foot flames blastin out of it again.
Within seconds the uranium melts, drips onto the floor, blast fragments the water, the hydrogen explodes the pressure vessel, and the molton uranium melts through four feet of steel and concrete which has a melting point of just 3500 degrees in a matter of minutes. And you have Fukushima parts one through four. And the first thing they do? Why they treat it like a REGULAR FIRE like they are FIREMEN and take out long hoses and blast it with what? Why WATER of course! Because in their small tiny pea brains they think this is a form of fire, that concrete is always solid, that steel cant melt, water cant fracture, and loading five hundred tons of uranium into one giant vault is a sensible thing to do.
Ok now, lets look at some options that dumb phd Physicists haven't been able to figure out. First of all there's the amount of fuel issue. There is absolutely no need for so much fuel. The only reason they stock this massive tank of fuel is because they are so clumsy and it is so difficult for them to get the huge fuel rod assemblies OUT! That's where the spider arm reactor comes in. The spider arm reactor uses sixteen thin rods of fuel each attached to a cantilevered arm. When power fails, the arms move away from each other like a flower blooming until each comes to rest in its own area far from the others. Ahh they never thought of the FUEL ITSELF MOVING apart. And what is the fundamental principle of neutron flux? That it is dependent on ... .say it with me... DiSTANCE! YES distance! Once separated, there is only the neutron flux within each slab of material which is by design NOT self sustaining.
Well this design makes it simple to replace one of the pieces of material, load up a fresh one, and then energize the levers and it lifts back up into the neutron flux of the 16 other wedges. The bays for each individual arm are lined with thick layers of the material they make dopey control rods out of - cadmium boron. No flimsy tube to crumple when the going gets hot.
What about slowing it down when it is in decomissioned state, to make it more easy to handle and store. Why blast it with liquid nitrogen! Being extremely cold, the neutrons will stop moving, and poof the item will have its radioacitivity and fission levels reduced to storable levels quickly. NOT WATER! Nitrogen is inert. period. That's why our atmosphere doesnt catch on fire every time we turn on a gas stove, because our atmosphere is mostly nitrogen. got it?
OK, now these cantilevered arms are designed simply so that if the power goes out, they move apart and each tiny piece of material moves into its own chamber. Since it's easy peachy to replace each piece of material, they don't have to be big or massive. In fact, place it in a lead shielded case about 3' long and 9" wide, and pick it up in one hand and carry it away. It's safe now to store for ten years during which time its radioactive state with subside to closer to zero aka storage level where more pieces can be gathered together and placed in a bigger storage holder where they will sit safely for another hundred years and then recycled. Try doing that with three hundred pound spent fuel rods.
There is no high pressure tank to burst and blow steam into the atmosphere? No we use a heat exchanger plug to transfer the heat energy to another indirect tank which then turns turbines. Just like an air conditioner coil transfers heat out of the house. High pressure see, like a bomb. Because that's all they knew how to build in the 1940s!
Wait, stick with me it gets even better. because the inter distance of each of the sixteen arms is configurable, its very easy to control the neutron flux or the speed of the fission reaction. Want to warm things up? Push them closest together. Slow it down? Move em apart. Easy peachy simple dimple. This is called controlling the K of the reaction, where 1 or balanced is the goal. Less than one is sub critical meaning the reaction will die out, and > 1 and its supercritical or runaway. Now, with a traditional reactor those control rods sliding over the fuel rods are the ONLY THING preventing it from becoming supercritical. If they are damaged, warped or JAM, as they often do, what then? Well with Fukushima, it's time to shit the goose and get the crap out of there and send in the SARCs to clean up. With a spider arm reactor you'd have to have idiots manning the controls to force the system into supercriticality. And even if that did happen, all you have to do is back off the distance and eventually the reaction slows, all with no control rods. Simply by using distance, and non - humungous fuel sources.
Lets go back to the grill analogy. You build a backyard grill forty feet long. You fill it all with charcoal and lighter fluid. then you light it all on fire. But you close the top and your control rod - the oxygen hole opening - controls the reaction. Except that you built the side of the grill out of aluminum foil and at any second the whole side could fall off and the grill erupts into huge twenty foot flames which will burn for eight hours. Yep thats a modern nuclear reactors design in a nutshell with control rods.
And now we get to the best part. What about thorium? Well thorium salt plug reactors follow a few of these principles, no high pressures, automatic recovery with the salt plug melting, but they aren't rate controllable the whole system of moderators like control rods that warp and fall off, is harder with liquid salt designs. And the hardest part is the extraction process and recovery is still theoretical.
But with a spider arm reactor design, thorium is no problem used solid in purified form. And here is the better issue. To initiate a reaction all you have to do is use a hot plug from a currently active reactor to get the whole thing going. Or even better, each reactor can use a protron synchrotron to initiate the reaction and no uranium is ever used. All very possible and made much easier because you have infinite control of the neutron flux distances.
finally, lets say that somehow magically the spider arms fail to move apart when power is killed and there is a runaway reaction? Well the floor first of all, we'll make out of TANTALUM CARBIDE or the highest melting point stuff on earth. Not out of steel and concrete. They use it on jet engine nozzles which routinely hit temperatures above 4,000 degrees. They should be enough to prevent melt through but if that doesnt stop it the emergency blast from the liquid nitrogen tanks will.
What about CANDU and Pebble Bed reactors, those are safe aren't they? Pebble bed reactors don't suffer from LOCA (loss of coolent accident) unless they run out of their gas coolent like Helium. But the pebbles themselves break or often jam when they are supposed to exit - "The reactor also suffered from the unplanned high destruction rate of
pebbles during normal operation, and the resulting higher contamination
of the containment structure, and problems with compact pebble
allocations, which caused deformations in the control rods and of the
side reflector arrangement." CANDU reactors still use fuel rods so they still have issues.
There are some technical issues with the design. Criticality with enriched Uranium for examply, typically requires a massive amount of some 50 tonnes. In a spider arm design, with 25 arms, that means each arm needs to be engineered to hold 2 tonnes. It's not easy but it's certainly doable. Think of the weight of a midsize car on each arm. This, however, might simply be the amount required for dinosaur designs and certainly for designs which did not use linear accelerators for instantiation of the reaction. With this more modern design, a reactor could possibly achieve sustainability with only ten tons of material. Or it might require a periodic burst from a linear accelerator, like your hand hitting a wheel to keep it spinning. This very new technique, could extract the energy from a much tinier "pile" even perhaps as small as one ton. We also know that these huge numbers cannot be correct. We have nuclear submarines do we not? Certainly they don't have 150 tons sitting on one end. Most likely this early research number was never updated as technology advanced and became classified. With this "hand slap by accelerator" technique, we get one more advantage - because we have designed the reaction NOT to be sustainable it must naturally decrease without runaway fission. An optimal design would have the reaction grow and produce heat for say 24 hours, then naturally begin to lessen.
In between the arms wedge shape as a moderator would be 100 tons of purified graphite. Although costlier, for the reasons mentioned with H2O direct explosion at high temperature, graphite is the moderator of choice. A moderator is a material which takes the 50 million kelvin super speedy neutron and having particles of roughly the same weight, results in multiple elastic collisions, extending that heat via thermolyzation into the moderator and allowing the neutron to then impact additional material at the correct energy level to yield more fission. The use of graphite brings into question issues of Wigner energy and one reactor in England burst into flames in the 50s because of the accumulation of this energy. But Wigner energy only accumulates when collisions occur below the Wigner annealing temperature. Since the spider arm reactor is a high intensity reactor, this Wigner buildup will not occur. Now we get the ninth advantage of the Spider Arm Reactor (SAR) design. By the arms moving the nuclear material away from the moderator, again the neutrons will be traveling with too much energy to split other atoms. The use of water as a neutron shield still makes sense, but as a ring around the entire facility, a neutron moat if you will. Finally, the graphite moderator can also be designed on cantilevered arms, for the occasional need to replace or repair. The alternating wedges of moderator and fissile material forming a pie, akin to the piece on the board game trivial pursuit.
Another issue with graphite was the corrosion of ducting used to carry away heat. This was solved in pebble bed designs by the natural space around the spheres. While the solution is unclear, a natural solution of the graphite blocks with a 3d design to allow airflow is envisioned. This will obviate the need for metal ducting.
The spider arm reactor is not a new technology, it is simply the best minds understanding of how to bring technical solutions to a reaction we understand well. In the 1950s there was not a good understanding of these failure issues. Now that we have learned from each of the disasters, it's time to take that knowledge and put it into better reactor designs like the spider arm reactor. By doing so, it will be possible to remove and rid our Nation and Japan both of the dangerous reactors designed in the 1950s and 1960s.