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The Windscale fire was caused by a largely unknown
behaviour of materials which have been exposed to
radiation. The graphite channels (which had been
irradiated for some time) stored energy in lattice
dislocations of the carbon atoms. When they were
subsequently heated to release this energy,
they did so
rather more vigorously than was expected, and caught
fire.
The idea is to irradiate graphite (or perhaps something
else) to deliberately create lattice dislocations to store
energy. Then take the graphite (which in itself isn’t
radioactive much), to a place where you need to use
stored energy. Trigger the release by heating it up to the
critical temperature, and hey presto, you get lots of
lovely
heat out without radiation. You can use that to heat your
house, drive a steam turbine or a thermoelectric pile.
Wigner Energy
https://en.wikipedi.../wiki/Wigner_effect
Dislocated atoms in a lattice store neutron energy [Frankx, Sep 26 2019]
Wigner energy batteries
https://www.nature..../s41598-017-01434-8
Academic paper looking at the feasibility. [Frankx, Sep 28 2019]
Beautiful steel
http://m.vam.ac.uk/...-scabbard-masamune/
[Frankx, Sep 30 2019]
[link]
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[link]
With the added advantage of intimate Frenkel
pairs! |
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Hmm. According to Wikipedia, "Accumulation of energy in
irradiated graphite has been recorded as high as 2.7 kJ/g",
which is 5-10 times higher than conventional batteries. On
the other hand, it's about 20x less than hydrocarbon fuels (or
maybe 10x less if you have to supply the oxidiser as well). |
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Of course, if the graphite gets hot enough it will burn, but
then the dislocation energy is only making a minor
contribution to the total energy. |
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// largely unknown behaviour // |
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Wigner energy was a well-known phenomenon; hence the need to repeatedly anneal the moderator. The McMahon Act did severely llimit the flow of information from the much more experienced US reactor engineers, and Britain's previous experience came from GLEEP and BEPO, but the crux of the problem was the use of the GMAC design for a production reactor intended to run at high power. The RBMK is only a bit better and look what happened there ... |
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The problem with the idea is energy density. The energy stored in the lattice dislocations is comparatively small. The problem is localized overheating when the release is triggered. Outside a reactor core, it's not a problem, just inefficient. |
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You'd get better transference by just burning amorphous carbon, rather than lugging lumps of very expensive low-Boron graphite (which has to be made from petroleum coke anyway) from pllace to place ... |
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Costly, woefully ineffficient, wasteful ... go for it [+] |
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//The problem with the idea is energy density.// I wish I'd
said that. |
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//You'd get better transference by just burning amorphous
carbon// and that. |
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Our anno is more comprehensive than yours, though ... |
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I’m still convinced that there’s some practical
application for a lump of carbon which can heat
itself to 3750C without any oxidiser - triggered by
heating it to 250C. |
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Oh, there is, there certainly is ... |
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Just not a very pleasant or peaceable one. |
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They seem to gradually migrate back over time, reducing
the power density. I don't think breaking the graphite would
affect the crystal-scale dislocations. |
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Yes, it does; but the heating effect is so localized that it doesn't propagate. |
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Mechanical shock will only trigger a mass release if the bulk of the graphite is already at or very near the critical temperature; then the additional energy is enough to tip it over the edge into a cascade release. |
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The Wigner effect is very interesting, but it's only really a problem if you run the core too cool. In power reactors, the core's hot enough that the dislocations are continually "baked out" by virtue of the high temperature - analogous to the way that a high neutron flux when the core's diverged keeps it from falling into a Xenon pit (although it's wise to have excess reactivity in the fuel channels to allow throttling to lower powers, as was discovered in the early Oak Ridge piles). |
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GMACs are fine as academic tools; in fact, CP1 and its successors actually had no cooling system whatsoever, because they ran at such low powers (a few watts) that the bulk of the pile didn't get warm, and didn't even need shielding (as long as you didn't stand too close for too long while it was critcal). |
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The killer with WP 1 & 2 is that they were production piles; what was wanted was the neutron flux to cook NUM into plut, and the heat was a waste product. So they tried to run them cool because of the low specific heat of air, hence the Wigner energy buildup (and other, much worse, problems; we could tell you more, but then we'd have to kill you. Just let's say that graphite isn't the only crystalline material that can store Wigner energy ... ) and the requirement for annealing. |
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In the end it made more sense to build power piles that ran hot (like Calder Hall, MAGNOX, the WAGGER, and the subsequent AGR derivatives), sell the "cheap" power, and get the plut for free out the back end when you strip the fuel pins. |
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The Dounreay FBR would have been even better, but outside military applications LM (NAK) cooling hasn't found favour with civilian operators. BiPb is a bit better from a safety point of view, but the need for frequent regeneration is a pain. And the other thing with FBRs is that you're trying to get half a Gigawatt out of a thing the size of a dustbin ... good game, good game. |
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The point is that the UK civil nuclear power programme, up to the 1990's, was never anything more than a puppet operated by the shadowy hand of the MoD. Then they lost interest, and are now staring ruefully at their collection of Nissen huts (we kid you not, actual Nissen huts) stacked end to end with little yellow flasks of plut, all polished up and nowhere to go. |
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But that's another, darker story. |
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True, Dounreay PFR closing was a great shame. Lots of great
research wasted. |
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The really, really frightening thing is that the whole wind
turbine program has absolutely no hidden military agenda and
no useful byproducts except bisected birds. The only point of
all those huge fans is to make electricity. |
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[MB] - //huge fans//
I agree, I’m very enthusiastic about wind power.
But I think nuclear power also has an important
part to play. |
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[8th] //not the only crystalline material// |
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Intriguing- can you tell us more? |
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There’s been some research into applications of
Wigner energy as a power source [link] including
some “feasible” implementations. As [MB] says,
energy densities of up to 2.7MJ/kg, better than
many batteries and/or supercapacitors, but not
close to fuels. So an application where rapid
discharge of heat energy with no oxidiser...
submarines, torpedos, space applications...
perhaps an alternative to RTGs... |
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Also noted that other covalently bonded crystal
structures show the same property... Silicon, Boron
perhaps? Carbides, nitrides, transition metal
oxides? |
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"As is "War and Peace", Would have spit coffee if I was
drinking any. Funny to start the day. + |
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// other covalently bonded crystal structures show the same property // |
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They certainly do, and the consequences are extremely interesting. |
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By the way, when we said "No" we were not attempting to be offensive (for once). It is simply that the information is highly restricted and cannot be publicly disclosed. |
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Ok, appreciated!
Thanks [8th] |
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//Would have spit coffee// If I can cause just one person to
soil themselves in any way, my day has not been wasted. |
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Actually, hang on a moment. |
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Wigner energy comes from atoms being dislocated from a
crystalline matrix. Neutrons are an inconvenient way of doing
this. There should be a way to achieve the same result
chemically. Maybe some sort of crystal which intercalates a
solvent, followed by removal of the solvent to leave the
crystal matrix in an uncomfortable state. |
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What about mechanically? If the lattice dislocations could be designed and constructed artificially, a piston could be used to load energy. A heat spring. |
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You're going to be busy with your piston (if you'll pardon the
expression). On the order of 10^20 atoms to dislocate. |
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Isn't a dislocation then going to be stronger than the next location ready to dislocate? |
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It depends if you exceed the material's elastic limit and either induce a fracture or drive it into plastic flow. |
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//hence the need to repeatedly anneal the moderator// |
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Quench hardening of steel is a perhaps similar
property: many atoms are dislocated from the
regular crystal lattice - in steel’s case forming
martensite. So tempering is analogous to Wigner
annealing, and should be exothermic (if only very
slightly) |
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Work-hardening is the mechanical analogue-
repeated strains cause accumulation of
dislocations in the crystal lattice which pin the slip
planes - and again, annealing allows them to find
their lowest-energy arrangement. |
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It might be worth looking at semiconductors for
interesting analogies too. Dislocations in a crystal
lattice are a bit like vacancies in doped silicon. Is
there some electro-thermal cascade poperty? |
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How about a Wigner motor for a
torpedo/submarine? Water is ducted into a
graphite core, heated to steam, and ejected as a
high speed jet (or driving a turbine/propeller) |
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// Quench hardening of steel is a perhaps similar property […] in
steel’s case forming martensite // |
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So can you make martensite by irradiating steel? |
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// How about a Wigner motor for a torpedo/submarine? Water is
ducted into a graphite core, heated to steam, and ejected as a
high speed jet (or driving a turbine/propeller) // |
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Or for an aircraft. This could be the long-sought solution to
getting airliners off of hydrocarbons. All a jet engine needs is a
source of heat; the fact that all current practical ones use
combustion of fuel to do that doesn't mean another heat source
wouldn't work. |
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// the long-sought solution to getting airliners off of hydrocarbons. // |
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<Points at [MB]'s anno about energy density at top of thread/> |
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<Brings board duster to launch readiness/> |
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*looks at mentioned anno* |
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// 5-10 times higher than conventional batteries // |
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So 5–10 times more likely to be the solution than
conventional batteries are. Right? |
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... but 10 - 20 times less than hydrocarbon fuels. |
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Electrochemical batteries aren't practical; a Wigner battery is better, but still nowhere near as good. |
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To be a " replacement", the solution needs to be at least as good as the existing one. |
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In terms of inducing defects, the linked paper has: |
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"defects [can be generated by] neutron, ion or electron bombardment, or through laser irradiation" |
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Also I'd note that 2.7MJ/kg is the extreme for graphite - a first-generation practical device would probably be far lower. |
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That said, this property was an undesired side-effect in graphite; it wouldn't be surprising to find a material with higher energy densities/more practical properties following research and development. Compare, for instance, the first electrochemical batteries with current (oops, sorry) ones. |
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...or has some other advantage that outweighs
some of the downsides of the existing technology. |
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[notexactly] //martensite by irradiating steel// |
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Lots of metals suffer embrittlement in reactors,
mostly (probably) from neutrons knocking atoms
out of their crystal lattice. Martensite is a specific
thing with carbon steels when they’re quenched
(very distorted crystal structure, and carbon-iron
regions in various ratios) |
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Probably, with neutron embrittlement you get
some of the properties (hardness, strength,
brittleness) but I wouldn’t think you’d actually get
martensite. |
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//for aircraft//
Perhaps, but I would imagine that the high cost of
production limits use to esoteric applications
where (comparatively) high energy density and no
oxidiser/oxygen are constraints |
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// I wouldn’t think you’d actually get martensite. // |
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... and you wold be correct not to do so; not only embrittlement, but swelling and distortion. |
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//swelling and distortion// |
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...which, in the hands of Masumane, make one of
the most beautiful artefacts ever created by
mankind [link] |
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