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Is there a new nuclear option that Permaculture can endorse?

 
steward
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Someone mentioned earlier in this thread that the MSR would only create a coffee can sized amount of waste.  I didn't see a time unit on that.  Is that annual waste per reactor?
 
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Mike,

The coffee can figure is for a 1 gigawatt reactor for 1 years operation based on the thorium cycle.  The thorium cycle is important and specific to this figure as while operating on the thorium cycle the fuel purification process removes a specific fission product that goes on to be used as a medical isotope.  By that point, the fission decay chain (another post entirely) is down to one decay away from a stable, non-radioactive element.  

The majority of the waste will be in the form of a trans uranic (CORRECTION: this should read as fission products, not TUs.  There are some FPs that suck up neutrons and stop nuclear reactions without the addition of a lot of new, preferably fast, neutrons) build up in the core.  This is many orders of magnitude less than in PWRs because of the liquid fuel.  In solid fuel, uranium gets bombarded by neutrons and some (about 1/3) become plutonium.  The plutonium buildup is significant in solid fuel because there is so much unburned uranium that much will inevitably suck up some stray neutrons.  In the liquid fuel with reprocessing, the removal of the FPs arrests the buildup of plutonium.

This is only a partial answer and I will end it for brevity, but the short answer is that the coffee can volume is for a 1 gigawatt thorium cycle reactor.

Eric
 
Mike Haasl
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Awesome, thanks Eric!  I'm also curious what the waste volume would be when "burning" PWR waste.  
 
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Remember, this guy thinks everything is solved with high tech, while most of us are looking for the lowest tech possible, but it is a very good description of types of "waste " products and some of the salvage value as well as the radiation dangers of the waste and how they disappear over time.
 
bob day
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https://liquidfluoridethoriumreactor.glerner.com/2012-reprocessing-nuclear-waste-from-light-water-reactors/comment-page-1/

This has a real nice flow chart comparing gigawatt reactors, MSR and LWR and the supply chain and waste  stream and amounts. Note the coffee can mentioned earlier does not take into account the many by products that may be salvaged after a short decay period, there is no serious amount of mass lost, it is just radioactively burned so completely that many of the elements created can be removed from the waste stream within the first 10 years  or so, in fact, many can be removed and used in a few months.
 
bob day
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When discussing waste, it's very important to remember that LWR nuclear reactors do not refine and reburn their fuel because as simple as it looks where you see percentages of each element, and then you see the long bar on the graph that is unused fuel, you think that should be an easy solution, just grab that long bar of unspent uranium and repackage it and burn it again.

But the by products are more or less evenly distributed through the spent fuel, and re refining is more difficult than simply extracting the uranium and refining it from the ore.

You see people handling fresh uranium fuel pellets with no shielding, but the reactor turns it into hot stuff, and the hot stuff is much more difficult to work with.

So they seal it up and store it.

In the liquid environment of a thorium reactor, the fuel can be pumped through different "refineries" within the reactor  -- chemical reactions that remove elements, replace refined elements, and return reagents in a closed loop,

 
bob day
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I  know this is a lot of videos this morning, but I found a few of the neat ones,  Kirk Sorensen narrates, with many partial presentations from Carl Sagan, Neil de Grasse Tyson, as well as clips from anti nukes, quick presentations on star nuclear processes, thorium core of the earth, magnetic shield of earth from solar winds, and much more, very fast moving

 
Eric Hanson
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Hi guys,

So I had a long post going into the details of waste coming out of the thorium cycle and of waste coming out of fast fission—and then I lost the post!  But my answer pales in comparison to that of Kirk Sorensen in the video posted above this one.  I will try to get some of the physics explained, but Sorensen is has the best explanation in his video.

Eric
 
Mike Haasl
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FYI, if you have long posts written and then have them lost on you, it might be worth typing them up in Word and then pasting them into permies.  Just in case for long posts.
 
Eric Hanson
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Mike,

That’s a great suggestion—stubbornly I was using my phone!!  Not terribly efficient.  No matter, I will redo it, hopefully better this time around.

Eric
 
Eric Hanson
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OK, I am going to try to attempt to try to explain the waste issue regarding MSRs.  This might have to be a multi-part post because this is a complex issue.

As was stated in an earlier post, the 1 coffee can worth of waste is for 1 year of operation of a 1 Gigawatt reactor running on the Thorium cycle.  I am going to start on the Thorium cycle because it is simpler and instructive for explaining how the reaction takes place and creates waste in the first place.  To start with, the basic fuel, Thorium, comes in only 1 isotope in nature, Th232.  This is important because this gives us only one decay chain to worry about.  Uranium on the other hand comes in two isotopes in nature:  U235 which is a very useful fuel, and U238 which is not a fuel.  In nature, about 0.7 of the Uranium is the U235, the fuel part.  The remainder is the U238 non-fuel.  This is a lousy ratio for making nuclear anything as the U235 and U238 must be at least partially separated through a process commonly known as enrichment.  Isotopic enrichment is a terribly difficult process and leads to many of the headaches associated with PWR nuclear even setting aside the basic issue of radio-toxicity.

So back to thorium.  Thorium has another advantage,  it starts much lower on the basic decay chain than either U235 or U238 (though not a fuel, it still can be a trouble maker in the waste as we will find out later).  So to simplify a complex issue to a postable level, Thorium in a MSR must be kick-started with a small amount of U235.  The amount does not have to be very large and in fact this will contribute almost nothing to the overall picture of the waste profile, but the issue at hand is that Thorium is just barely radioactive.  It has a 14 billion year half life.  Contrary to popular misconceptions about half-lives and radio toxicity, a long half-life element is plenty safe.  I did a brief explanation of this on an earlier post on this thread, but to reiterate, the longer the half-life, the less radioactive a given element is, and the shorter the half-life, the more radioactive an element is.  Thorium is barely radioactive.  It needs extra neutrons for a very good reason, it can barely produce them by itself.  Thorium needs extra neutrons in order to "breed" the Th232 into U233.  When the Th 232 absorbs the stray neutron and transmutes (eventually, it actually into Protactinium 233 first).  This Pa233 will decay on its own with about a 1 month half-life but it needs to be sequestered because it likes to eat up stray neutrons and stop the reaction in its tracks, but left alone, it will eventually yield us the highly useful U233.  The MSR has a built-in "refinery for chemically separating out the Pa233 and storing it in a sort of holding tank where it slowly gives us the fuel needed for the reaction to be pragmatic.  Now we have a much better nuclear fuel than the thorium ever would be and quite frankly, it is better than the U235 commonly used in reactors.  The reason for using U235 in the first place is that there is no natural source of U233.  U233 simply has too short a half-life to have stuck around (all heavy elements like uranium and thorium and others were created in a supernova that occurred about 5 billion years ago).  There probably was some U233 left over from that supernova, but 5 billion years later it has all decayed away.  This is also the reason there is so much U238 and not much U235.  U238 has a roughly 5 billion year half life where U235 has a 700 million year half-life.  Actually, neither U238, nor U235 are particularly dangerous by themselves (radiologically speaking.  chemically they can be dangerous, sort of like lead or mercury).

Back to the MSR though.  Once the Thorium starts to convert into U233, the U233 will now take over from where the U235 left off.  U233 gives off a good dose of neutrons for each fission event and once enough U233 has been bread, we just don't need the U235 any more.  And in fact, if one wanted to start a second MSR, one could use U233 from the first reactor to get things started.  Anyhow, the U233 will break down into a host of other slightly lighter heavy elements.  Importantly here, the daughter products are all short lived (meaning they are very hot in a radioactivity sense, but are fortunately going away very quickly) and eventually give us Bismuth 209 which is almost stable (half-live is over 10 trillion years).  At this point, the fuel has finished reacting and the remnants are considered to be ash.  There are a few odd reactions that happen hear and there that give us a few mid to longer lived isotopes and those stray reactions is what gives us the coffee can of waste that is left over from the 1 GW reactor running for a year.  

In my opinion, this is a good deal.  This is barely any waste for a huge amount of energy.  This coffee can will be "hot" for about 300 years after which further decay will break the remnants down to background radiation levels.  Also, the thorium cycle is the simple one (so-to-speak) and that's why I started with it.  The decay chain is generally simpler and mostly happens fairly quickly.  Using "natural" uranium gets more dicey.  Finally, if that one coffee can per GW-year is still bothersome, it can be reduced further by placing it into the fast fission reactor which I will try to detail next.

I have tried to point out the technical merits on this post and I am forced to simplify for brevity to fit into a post like this.  I especially have vastly trimmed down the total decay chain of finally getting to the bismuth 209, not to try and disguise or soften a dangerous part of the reactor, but to simplify for this format.

As always, I hope this has helped to inform and if anyone finds any mistake, error or misinterpretation, please let me know and I will either edit or make another post to correct.

Eric
 
Eric Hanson
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So how about actually burning existing waste?  Part 1--the problem with the PWR

This post is in partial response to Mike who previously wanted to know what the waste profile looked like for a MSR reactor running on existing stockpiles of waste.  For fair warning, this answer will be a lot more complicated, I will probably have to terribly grossly simplify some steps, and the post will generally be longer.

For starters, lets say that we are talking about burning the waste in a thermal spectrum MSR, the same type of MSR I described working in my last post.  At this point we really need to look more closely at what exactly is the waste.  The overwhelmingly vast component of waste are the fuel pellets that are "spent", left over from the remains of a nuclear refueling.  I really consider these pellets to be waste in the truest sense.  And by that I mean that there is just a terrible amount of otherwise perfectly good material that is in these pellets that unless reprocessed, will never be put to practical use and will give us all sorts of nasty ash that has to sit in time-out for thousands of years.  When a fuel pellet is considered "spent", it still has 99% of the original supply of U235 left!  This is appalling.  It would be comparable to your car burning only 1 ounce of gasoline for every gallon you pumped in and the remainder just needing to be stored some place till the end of time.  This inefficiency is just unacceptable.  Why it is accepted as the norm for nuclear (with all the baggage that comes with nuclear) is really beyond me.

But anyways, back to the Uranium.

So a new fuel pellet is generally enriched from the ratio of 0.7%U235 fuel to 99.3% "inert" (we will get to that later) U238 to something like about 20% U235 to 80% U238 via isotopic enrichment, a very difficult task.  The military uses HEU (Highly Enriched Uranium) that consists of about 90% or so U235.  But for the purposes of our discussions we will will stick with civilian enrichment levels.  The U235 gives off its own neutrons spontaneously via decay, but ordinarily these neutrons do not interact with enough other U235 nuclei to create a chain reaction.  But stick in a moderator and concentrate the U235 and then a chain reaction is perfectly possible and that U235 will fission and create its own daughter products.  Owing mostly to the fact that U235 is higher up on the decay chain, U235 will have more daughter products.  That supposedly inert U238 does not just sit there, it get to come to the nuclear party too, but in a roundabout way.  Occasionally, when U238 gets struck by a thermal neutron, the neutron will stick and form Plutonium 238.  Pu238 is actually pretty good nuclear fuel by itself.  It releases quite a few neutrons and releases plenty of heat.  At present, NASA is actually trying to get its hands on PU238 because this is useful for making an extremely simple, bulletproof power supply for spacecraft like mars rovers and probes.  At any rate, the PU238 contributes a good amount of heat to the overall output of a power plant.  But it too has its own decay chain.  By this point, we have 3 decay chains--U235, U238 and Pu238, and the picture only gets more confusing as we look at all of the stuff that the various reactions make.

A nuclear fuel pellet is considered spent, not because it ran out of fuel by a long shot.  Instead, it is spend because the pellet itself becomes both physically unstable and neutronically poisoned.  PWR nuclear fuel is a solid, actually a ceramic made of Uranium Oxide, with a hollow center filled with helium and wrapped with a cladding of zirconium which is fairly strong, neutron transparent (so neutrons can just slip through like it is not there) and has a very high melting point so that the temperatures of the reaction itself don't accidentally melt off the cladding.  Sadly though, the main problems that arrive from a waste perspective is the fact that the fuel is solid.  As the fuel undergoes fission, it creates its own soup of new chemicals that were not there in the first place.  One of the more difficult new materials to handle is Xenon 135.  Xe135 is a gas (obviously) and therefore (again obviously) takes up a LOT more  space per molecule that did the parent Uranium.  Over time, Xe 135 buildup will actually crack the interior of the Uranium pellet which would fall apart were it not for the strength of the cladding.  Xe135 is troublesome in another way in that it is an incredibly strong neutron poison, meaning it likes to suck up neutrons so much that if Xe 135 rises to too high a level, it will actually shut down the reactor.  Oddly, Xe 135 is actually quite radioactive with a 9 hour half-life, meaning that if a reactor operator is not doing his job carefully, a reactor can spontaneously shut down because of neutron poisoning, and then equally spontaneously turn right back on.  This is one of the most difficult aspects of controlling a reactor.  At any rate, over time, the Xenon 135 (a rather common byproduct of fission) and other gasses degrade teh fuel physically to the point where it is dangerous to leave them in the reactor any longer and need to come out.  If that were not enough, other fission products are also neutron sponges as well and act like XE 135, but not quite so strongly. At any rate, the fuel pellet is damaged and poisoned to the point where it can no longer reliably produce fission after less that 1% of the fuel has been consumed, so most of the fuel pellet is actually perfectly good fuel with a few poisons thrown in and cladding that may fail.  I like to think of this as gasoline that has been sitting in a metal gas can (back when you could get a metal gas can), has collected some moisture and oxidized slightly with a rusting container, so that if it were to sit around long enough, the gas would leak and be a fire hazard, but the gas itself is not fit to be burned in an engine and the can would leak anyway if you tried to pour.  Really not a good situation.  And honestly, how many of us have let gasoline sit around to the point where it is no longer any good for an engine, but we don't know what to do with it so we let it sit anyways.  In my opinion, this is what we have done with PWR nuclear.

I will leave this for now, but I will deal with what we actually do with that waste in the next post.  Sorry if it takes so long, but this is complicated to write up.

Eric
 
Eric Hanson
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So what about burning waste? Part 2 the MSR

If we go and take some of the spent pellets from the last post, we can start to do something interesting with them, but first there is a little work.  Mostly, we need to partially reprocess the pellet. This means dissolving the cladding off in acid and reacting the Uranium oxides to get uranium salts.  This is dangerous but perfectly doable work.  Once the uranium is converted to a salt, it can then be added to the flibe mixture in the reactor.  Depending on exactly what you want to do with it, some of the other fission products may also be added to the flibe mixture, but bear in mind that exceeding 99% of the pellet--even if spent--is still uranium.  Only a trace amount is a fission product or plutonium (which works just fine in a MSR).  The picture starts to get a little murky, but U235 will eventually burn down to lead which is stable.  In the process it will make many short-lived and highly radioactive FPs, but being short lived, they will break down quickly.  In my opinion, the most troubling FP is Protactinium 231 which has a half-life of around 32000 years.  This means that it is not exactly a red-hot radioactive material, but neither is it going away quickly.  But expose it to the withering radiation environment of a reactor vessel, and this can be burned off faster, though it is a does not like to capture neutrons like its cousin, Pa233.  At any rate, we have documented evidence of the MSRE running on U235/U238 and the results were favorable.  The reactor could continue burning U235 well past the 1% mark of the PWR, and from calculations, it can apparently continue to burn virtually all of the U235.  Since the MSR has a sort of online chemical refinery, certain, problematic isotopes can be pulled in order to arrest the development of other isotopes.  Unfortunately we never really got to see what the MSR could do because it only ran for 4 years, but while it did it ran very smoothly.  It did not need the kind of refueling like a PWR did (it did need refueling but this could be done on-line, meaning the reactor did not need to shut down) and it did not need to leave behind piles of un-burned fuel like a PWR.  I think it is also worth noting that MSR will not create anything that nuclear waste just sitting on its own won't.  Waste still undergoes fission, just more slowly.  And of course, there is the potential to really generate electricity from the spent fuel in a MSR reactor.  If you take the analogy with which I ended the last post, just imagine if that old can of stale gasoline could now power 100 times better than the old gasoline could.  I think this is an appropriate analogy

In the end, to partially answer Mike's question, about 99% of the waste should eventually be able to be "treated"  Some of this will go on to make some "ash" with a long half-life and that ash is a problem, but it would be a problem anyways just sitting as it does at present.  As my eyeballs are not working from writing 3 of these expansive posts in a row, I need to take a break, but I will work with burning this waste even further in a fast spectrum MSR (FSMR) on the next post.

I hope this helps,

Eric
 
Eric Hanson
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Burning the Waste Part 3--the fast spectrum MSR  or Molten Salt Fast Reactor (MSFR)

If your primary interest in the various forms of MSRs is for the elimination of waste as opposed to the generation of energy, then the MSFR is for you.  Unlike the MSRs we have discussed lately, the MSFR operates in the fast spectrum with unmoderated neutrons.  

What does this mean and why does it matter?

In order for fission to take place, you need a reaction between a neutron and a nucleus.  Typically this means that the neutron will bond onto the neutron but this bonding is unstable and causes the nucleus to break apart almost the instant it is formed.  This is called a prompt fission, releasing prompt neutrons, as opposed to delayed neutrons which we can discuss later.  Protons are held together in a nucleus by something called the strong nuclear force, one of the four fundamental forces, and it is stronger that the other three by an extremely long shot.  Put another way, the strong nuclear force that holds the nucleus together is at least a million times stronger than the electromagnetic force that holds electrons in place.  That is why nuclear energy is so very powerful.  However, the strong nuclear force only acts over incredibly tiny distances, typically acting only a bit further out that the nucleus itself.  In fact, the distance is so tiny that it may place an upper limit on just how big a nucleus can get as any larger and the strong nuclear force cannot contain the whole nucleus.  This is hypothetical, but it gives you an idea of just how tiny the distance we are talking about.  It is much shorter than the distance from the center of the nucleus to the electron cloud.  This is so small that fast neutrons typically just zip past a nucleus and keeps on going without a care in the world.  However, slow that neutron down with a moderator and the neutron stands a better chance of bonding and causing a fission.  This is why most reactors have moderators--they increase greatly the chance of a neutron being able to strike a nucleus and cause a fission.

But it is possible to have a reaction even without a moderator, but to do so, the fuel load needs to be greater and the geometry of the reaction vessel becomes important.  The reason for this is that it becomes necessary for the neutrons to have a second chance (and third, and so on) at fission by having them bounce around enough that they eventually collide with a nucleus.  When they do, the reaction is different than a thermal neutron.  Firstly, a fast fission event almost always causes another fission event instead of occasionally sticking and making a new, larger element (like Plutonium).  Secondly, these collisions tend to produce more neutrons per fission than the thermal neutrons do.  In some of these cases they make a LOT more neutrons.  These two factors have important implications.

Since fast fission 1) almost always causes a fission and 2) releases more neutrons per fission, many, many more elements can be used as nuclear fuel than would normally be the case with thermal neutrons.  In fact, some wastes that would otherwise just sit around and be radioactive waste now becomes a genuine viable fuel.  The fast neutrons also break down numerous unstable (radioactive) by-products that otherwise just won't react and only break down based on their own half-life schedule.  Fast reactors really, truly burn waste.  If you are wondering if fast neutrons are more dangerous somehow than their moderated cousins, the answer is that they are not.  Therefore, there exists a corpus of people who endorse MSFRs as a way to really obliterate large amounts of radioactive waste, and in my mind, this is an extremely laudable goal.

As far as I know, as long as the reaction continues, a MSFR will continue to burn up completely radioactive waste to the point that it is simply not radioactive any more.  The challenge though is that the initial fuel loading is greater, and when the reactor is through, there will still be a vessel filled with radioactive materials.  This might be acceptable though if the radioactive materials were made up from the vast stockpiles of waste we already have.  Another way of looking at it is if we take all of the say 1000 tons of radioactive waste (I assume the actual figure is much higher, I just wanted to start with that as a figure) around the United States and run it through a MSFR and end up with 1 ton when we are finished (again, making up that figure--it might well be smaller), would this not be a better turn of events?  We would still have waste, but we would have so very much less waste than we started.

In the MSFR, the fuel is no longer Flibe.  Flibe contains Florine, Lithium and Beryllium, all of which were included in the product intentionally because they are all neutron moderators, what with high levels of moderation being a necessity for a thermal spectrum reactor.  Instead, we would have simple chloride salts which are both cheap and edible (actually Flibe is kinda chemically toxic, but I was really hoping we are all smart enough to not eat our nuclear fuel).  Chloride salts are well understood chemically and they fully melt at a lower temperature and that gives us a better temperature profile to work with (they still boil at ridiculously high temperatures).  MSFRs need no graphite moderator and this is a big plus.  Graphite has long been used in nuclear reactors as a moderator (a fairly cheap and really, really good moderator), but it has weaknesses.  Under heavy neutron radiation, graphite first shrinks, then swells.  After about 4 years, the graphite has simply had it and needs replacement.  This is not a terribly big deal, but it needs to be done and the graphite will need to be kept safe for around 30 years (much like hospital waste).  For some, graphite makes the MSR a non-starter, but many of those people are open to the MSFR because it needs no moderator.  In fact, the reaction chamber of a MSFR is simply hollow, with the walls being made of a highly neutron reflective material to enhance reactivity.  Geometry also has to be fairly precise, or there will be neutron shadows causing parts of the reactor to not function properly.

Ultimately, there is a lot of potential for the MSFR.  It will produce energy and really consume waste, an ideal combination for a nuclear reactor.  About the only strikes that a MSFR has against it is that as far as I know, there have been no MSFRs produced (but there have been fast spectrum solid fuel reactors) so we don't have actual experience working one, but there should be nothing technical to prevent their use.  Additionally, I think (but don't know and I would like confirmation on this point) that the thermalized MSR actually produces more energy per Kg of fuel thanks to that moderator.  Again, I really want confirmation on this so don't take this as absolute fact.  But in the end, the MSFR is VASTLY better than the PWRs that are in operation today.  One last fact that may already be obvious--MSFRs can operate on just about any nuclear fuel.  They can burn waste, and they can run on the thorium cycle, so they are very flexible.

I have to find a way to finish off this series, so I think I will do so here.  I have tried to give a balanced and nuanced accounting for the potential of both types of MSRs and to at least partially try to answer Mike's question that prompted these last posts.  If anyone finds an error or oversight on my part, please let me know.  I am human and fallible.  I have tried my best, but this had to be vastly simplified.  Overall, I hope it helped your understanding of the potential for either of these approaches to nuclear.

Eric

 
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Tyler Ludens wrote:I would like to see nuclear discussed without comparing it to coal.  Comparing a bad thing to another bad thing is not a great endorsement of the thing, in my opinion.

Except for the express purpose of deactivating existing nuclear waste, I see no benefit in atomic power, at this point in my life.  



The main benefit, if one wanted to call it that, is the relativity equation: Energy = mass x the square of the speed of light. Multiplying anything by the square of the speed of light gives you an enormous output for even a tiny input. The idea of nuclear power, therefore, is that only a small amount of fuel is needed to generate a huge amount of energy. Think of the difference between a rocket stove and a plain ol' fireplace, in terms of how much wood you need to get through the winter. By analogy, think of the nuclear plant as a rocket stove, and some other kind of power plant as a fireplace.

Of course the analogy breaks down when we look at the waste products.
 
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Eric Hanson wrote: As I stated earlier, I grew up not far from a PWR and regularly went canoeing on the lake and streams that provided coolant to the reactor.  This was a most welcome bit of natural "wilderness" in the middle of the Central Illinois prairie now turned into corn forests.  Wilderness basically does not exist in Central Illinois except for a pocket here and there.  The waterways around the local nuclear plant were one of these few, precious patches of "wilderness" and were not contaminated or radioactive.  I thoroughly enjoyed them and have wonderful childhood memories of canoeing up a creek that looked like pristine nature (though of course it was surrounded by corn fields--I am sure that the pesticides on those corn fields did more damage than any of the fuel at the power plant).



Yes! I once worked for the Forest Service at the Savannah River Site. What an amazing sight, those huge lakes (Par Pond and L Lake), with completely undeveloped shorelines. You just don't see undeveloped lakes in South Carolina -- anywhere other than Savannah River Site, lakes that size would be hemmed in with waterfront homes, maybe marinas, too. If you're lucky, there might even be a public park where you can actually get to the lake without being a property owner...
 
bob day
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Don't let the title fool you, this is about much more than desalinating oceans.

An interesting conversation about energy and standard of living. Kirk Sorensen and friends visit recycling plants, discuss the economics of recycling, with references to the immense amount of environmental repair possible with cheap energy.
 
Eric Hanson
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Bob,

I watched this too, and just to add my 2 cents, I think even more important than the energy being cheap is the fact that the energy is environmentally benign.

A good video though to be sure.

Eric
 
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Chris Kott wrote:And sorry, Bob. I should have specified what I meant by post-steam.

I would like to know if there's a fuel cell analogue in the future for nuclear, wherein a fission-specific material absorbs the radiation directly and produces electricity, like solar energy hitting a solar panel. I want to know if it will be possible to eliminate the heat cycle. Does fission require the release of heat, or is that a detectible and easily-used byproduct? Consequently, could fission generate electricity without heat, and wouldn't that be more efficient and safer, requiring reactions on a much smaller scale?

Largely just spitballing, but I would genuinely like to know.

-CK



The answer is so far as I know the only way to capture the alpha and beta particle energy is in the form of heat.  Now the gama part of it some of the energy can be captured the by equivalent of a solar cell and converted directly into electricity but depending on its frequency which is dependent on the fission process, the efficiency can be fractions of one percent up to about 25% conversion.  So in most cases it is not practical.

Now there is one other one that might be more to your liking that is nuclear thermal.  They put a fairly hot nuclear source in a box designed to produce X watts of heat at say 400 degrees.  They then pass this heat thru a thermoionic module to a colder side to produce electricity.  As long as the cold side exists they are reliable and small fairly light weight sources of power.  Because the amount of nuclear material is limited they can't melt down.  And so they are solid state with no moving parts and they can be fairly light weight.  The problems are 2 told.  They are terribly inefficient is one and they have to have a fairly hot fuel source which makes them high risk for terrorism etc.  So their use is mostly limited to satellites and a few military applications.
 
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Very good thread with a good discussion of the issues.

Some things to add.

Probably the most important thing I see missing from this discussion is the destruction of low level nuclear wastes like old piping,gloves, concrete etc.  Currently the US is simply storing it.  But for 30 plus years France has been destroying theirs.  They have 3 reactors that all the power goes to destroying the low level waste materials.  Basically the process goes like this.  They take the waste and tear it down to its raw elements and seperate out the isotopes.  This is a hugely energy intensive process.  The isotopes are then place in a reactor with the right moderator materials around it.  A tiny fraction actually comes out hotter than when it went in.  Most is unchanged.  But another fraction is has now been rendered safe.  Remove it from the reactor.  Separate out the safe material and put the rest in back in the reactor.  Eventually they burn away all the isotopes.  The repeated runs thru a huge host of physical, chemical and electrical separation processes is hugely expensive in both cost and energy.  But when it is done there is nothing radioactive left to threaten future generations.  Surely the US can learn to do it since France has been doing it so long.

Not only do we need to discuss the politics and economics of the answers we look at.  We also need to include human nature.  While it would be nice if everyone went back to nature and reduced energy usage to nearly zero how many will if it isn't forced on them?  Not many.  Humans are both creatures of habit and comfort.  So we need to factor that into our thinking.  We will have the best result if we can maintain current comfort levels while at the same time meeting needs.  But that also means we are not going to drive electric use down towards zero.  We like out AC, refrigeration, washers and driers.  We like to drive.

So with that in mind it is my own personal belief that in the short to mid term term permaculture needs to endorse some nuclear option and the reasons are 4 fold.  1.  None of the existing renewable technologies will meet our needs without drastically cutting energy usage.  Simply put we need some sort of power plant power for the foreseeable future.  I think eventually we will develop technology to do it with purely renewables.  But that is probably 30 to 100 years out and we need solutions NOW.  2.  If we want to implement current electric car and battery technology we need a number of rare earths.  If we don't want China to have us over a barrel on these we need to be able to mine them in the US.  For that to happen we need a solution to thorium.  Best answer is to mine it and use it for fuel.  Make a dangerous waste product into a fuel source with economic value. 3.  If we are not going to leave massive problems for our children and grandchildren in the form of already existing nuclear waste we need to find a way to burn it up.  4.  Finally we have a whole world to raise to our energy use level.  It will happen.  There again that is human nature.  So unless we want uncontrolled fossil fuels pollution we need another large scale answers we can share with the rest of the world.

So while I don't like to say it, we need nuclear now for the rest of the world and for ourselves too.  In the short term while we learn to do the others I am afraid that means light water reactors.  We need the safest design we can produce set up as a cookie cutter design to keep it cheap that can be implemented as safely as possible anywhere in the world.  If we really only do have 10 years to fix global warming problems then we need to be able to make changes quickly and most of the stuff on molten salt or traveling wave reactors is looking at least 10 years out to have them in commercial use.  And we are probably 20 to 30 years out to have any real number of them deployed.  So much as I hate to say it that likely means some form of light water reactor.  Pebble bed designs with passive damper flooding look like the best option to me.  So to me this is step one.

Step 2 is we need nuclear waste processing to deal with low level nuclear waste.  This one will have to be government funded.  Lets learn from France and begin protecting our children today.

Step 3. We need to get some sort of MSR running using thorium.  This is the only practical way to mine the rare earths we need for other changes we need to make.  This also has the advantage of allowing for smaller reactors better suited to throttling up an down in the background to match renewables' failings like being unreliable.

Step 4.  We need to get something that will burn up high level wastes researched and running.  These will likely be the longer term reactors simple because of the volume of already existing fuel we have to deal with.  Traveling wave reactors look like the best bet to me.  But fast spectrum molten salt would work too.  These are going to take research.  Even the most optimistic proposals for these are basically a decade out to even have an experimental reactor running.  And it will probably take at least another decade to have a commercial reactor running.

Are these in keeping with permaculture principles?  The answer is no.  Then why would permaculture support it you ask?  Which leads to the question we should maybe be asking intead:  But the real question is are they in keeping with the end goals of permaculture principles.  Did we leave a better planet for out children and grandchildren.   And in that if we do this carefully I think we can leave a much better place for them.  And isn't that the real deciding factor in all of those?
 
Eric Hanson
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C.,

Thanks for the thoughtful, balanced and well-reasoned response.  When this thread started it was a great thread with lots of technical details and passionate yet reasoned opinions.  Unfortunately some people were just put off by nuclear altogether and the exchanges turned ugly before the moderators stepped in.  It is nice to see that months later this thread still provokes thoughtful discourse.

All that being said, I have to ask about your interest in the TWR.  As I understand the reactor, fuel rods are constantly being shuffled around to ensure burnup, but this is a difficult way to achieve this goal.  Worse, the reactor (again, as I have seen it) is cooled by a pool of liquid sodium which also serves as a burial cask.  I would think that sodium burial would be practically asking for some massive future uncontrollable chemical reaction.  Lastly, (and again, maybe I am wrong), but aren’t TWR’s still just theoretical reactors?  Molten salt reactors have actually run.  I am wondering why TWR’s would be of any use given that MSR’s are a proven technology.

Again, I commend you for adding insightful commentary to this thread, I just have a couple of questions regarding the TWR.

Thanks,

Eric
 
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Eric

 The reason I think traveling wave looks like a better end bet is that if I understand correctly you end up with a more complete burn than any other process.  With about 20% left instead of 40% and up left and with fewer by products in intermediate stages.  As for molten salt is is of concern.  But the risks I see look much the same between MSR and traveling wave.  As for entombment for a burial cask that was in the early discussions of design when they were basically talking about burying this huge reactor full of fuel and running it till it quit and then burying it away.  Surely we are not that stupid.  It will need to be unloaded and reprocessed and the radioactive parts used for fuel again.  One of the more recent discussions is sort of like a giant doughnut with the generator at the middle.  Burn the reactor on one side and load and unload on the other and just keep walking both around the circle.  As for moving rods how is that much different than an other reactor?  The fact that they are moving in and out of a molten salt mixture and have to be sealed from air is the only real difference.  And rather than completely removing the rods what if we simply did a 2 or 3 layer design  With the outer rod being neutron reflector material.  Inside that a rod of moderator material.  Then none of them would ever be completely pulled from the reactor.

I fully agree this is a purely experimental technology.  I do think that MSR reactors are not a huge amount ahead of this.  We have done very little with them over the long haul.  So personally I am going to say the footing is closer to even than you imply. MSRs are not a mature technology.  The learning curve with both is huge.  I am perfectly will to see a Beta vs VHS battle here to see which wins even though it is wasteful in resources.  The reason is that we will learn more in the process and the eventual outcome should be safer for it.  Cost wise it might be better to pick one and go with it.  But what if we pick wrong? or what if something we learn from one might save an accident with the other one?  Higher risks and higher potential rewards?

But the most important thing here is finding some process to eliminate the danger to future generations while powering us now during the transition to a pure renewable base.
 
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A fun exercise for sure......... but, we have a perfectly perfected reactor design already, with the very best sheilding and safety record in existance.

Economical to operate, as in absolutely free for billions of years past and into the future, safe as it gets for such titanic energy flow and guilt free...... we didnt put it on line or cause its failure in any way and so are quite removed from the responsibility for it, just as it should be. (Read as ' squirrels plant trees so what the heck are we doing exactly?')

The only tech required to hook into it it to bask in it and plant seeds in its rays, and scoop up the water distributed by it and cool ourselves in the winds provided by it and sometimes put rocks (photovoltaics) or refined metal ore out exposed to it if air conditioning, communications, transport and lights or most any other work are desired.... although that may not give you every bit and more on demand "dammit here and i said right now!", as you "deserve". Ok nothings perfect.

The sun is a perfect nuclear reactor, is 90 some million miles away and costs us absolutely nothing to make use of.

Problems start from a point of " sure theres running water in that river over there, but i really just have this unstoppable ambition to get it to run right here instead"

Devolvements cascade into cascades of failure and it is what we see before us currently and at an exponetial rate.

Stop hitting your selves in the head with hammers or paying others to, and your head will surely stop hurting.
 
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frank li wrote:A fun exercise for sure......... but, we have a perfectly perfected reactor design already, with the very best sheilding and safety record in existance.

Economical to operate, as in absolutely free for billions of years past and into the future, safe as it gets for such titanic energy flow and guilt free...... we didnt put it on line or cause its failure in any way and so are quite removed from the responsibility for it, just as it should be. (Read as ' squirrels plant trees so what the heck are we doing exactly?')

The only tech required to hook into it it to bask in it and plant seeds in its rays, and scoop up the water distributed by it and cool ourselves in the winds provided by it and sometimes put rocks (photovoltaics) or refined metal ore out exposed to it if air conditioning, communications, transport and lights or most any other work are desired.... although that may not give you every bit and more on demand "dammit here and i said right now!", as you "deserve". Ok nothings perfect.

The sun is a perfect nuclear reactor, is 90 some million miles away and costs us absolutely nothing to make use of.

Problems start from a point of " sure theres running water in that river over there, but i really just have this unstoppable ambition to get it to run right here instead"

Devolvements cascade into cascades of failure and it is what we see before us currently and at an exponetial rate.

Stop hitting your selves in the head with hammers or paying others to, and your head will surely stop hurting.



And how, exactly, does that help us get rid of the levels of nuclear waste we already have to figure out solutions for? Surely you don't propose we put it in rockets and shoot it up into the sun?

Where are these solar panels that cost nothing, along with requisite electrical infrastructure, also free? And tell me, have they licked the solar panel recycling problem yet?

Oh, and where within the ten to twelve-year window would this solution put us, then?

-CK
 
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Frank, the waste stream from solar has been the reason I’ve been less inclined to get into it. Can you give some links to the batter path you refer to? I’ve been in places where the old panels (and of course circuit boards and lcds) are “ recycled “ in the majority world and I try to participate as little as possible in further production.

If there is a way of production that’s not further dragging us into a disposable culture I’m far more inclined. This is an honest request I literally have just shelved my plans to increase the solar because of the production and waste streams from the cheap stuff largely going in.
 
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Took less than a minute to get industry report.......

https://www.solarpowerworldonline.com/2018/04/its-time-to-plan-for-solar-panel-recycling-in-the-united-states/

"EPRI found that most panel recycling in Europe through the Waste Electrical and Electronic Equipment(WEEE) Directive—which established rules for solar panel recycling in 2012—happens at glass recyclers. Panels are crushed or shredded and then glass and metals are separated. Other chemical and thermal processes may be used to recover high-value material like silver or copper."
 
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