Author Topic: Thorium Fuel Engine  (Read 4482 times)

Thorium Fuel Engine
« on: 04/26/2017 06:19 AM »
I read thorium as a fuel has huge advantage

Is there a thorium fuel engine researched?
why dont rockets, planes, flying cars use thorium as fuel?

is there any disastrous disadvantage in thorium fuel engines?

Offline ChrisWilson68

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Re: Thorium Fuel Engine
« Reply #1 on: 04/26/2017 07:03 AM »
This has been discussed many times in these forums.

The short answer is that Thorium is just another fuel for fission reactors.  It has some benefits and some drawbacks.  For rockets, it's not a good choice.  There are better fuels to use for fission if you want a fission rocket, and there are better choices than fission rockets for what we need today.

There's been a lot of hype recently in some quarters around thorium, but most people who know a lot about nuclear power aren't impressed by the hype.  The hype ignores all the downsides to thorium and exaggerates the upsides.

Re: Thorium Fuel Engine
« Reply #2 on: 04/26/2017 07:17 AM »
ok, im a noob in space tech...
just out of my curiosity

what are the better[cheaper and efficient] fuel than thorium? [for a flying bus or an Iron man suite]
to be able to fly without propellers and less noise/pollution





Offline ChrisWilson68

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Re: Thorium Fuel Engine
« Reply #3 on: 04/26/2017 07:34 AM »
ok, im a noob in space tech...
just out of my curiosity

what are the better[cheaper and efficient] fuel than thorium? [for a flying bus or an Iron man suite]
to be able to fly without propellers and less noise/pollution

Thorium isn't going to power a flying bus or Iron Man suit in the foreseeable future.  Neither is anything else.

Thorium goes in nuclear reactors that are very similar to all the nuclear reactors we currently use in electrical power plants, aircraft carriers, and submarines.

As to what is better/cheaper, the answer is uranium and plutonium.  That's why we use uranium or plutonium in nearly all reactors in use today.

The people who design reactors aren't dumb.  There's a reason we've been using uranium and plutonium for decades.  It's not because people didn't know thorium existed.  It's because they looked at the trade-offs and decided uranium and plutonium were the better choices.

You can start with the Wikipedia article for some advantages and disadvantages of thorium versus uranium and plutonium:

https://en.wikipedia.org/wiki/Thorium_fuel_cycle

Re: Thorium Fuel Engine
« Reply #4 on: 04/26/2017 07:37 AM »
got it

so,
what are the better[cheaper and efficient] fuel for a flying bus or an Iron man suite?
which could be the best fit for this specific purpose?


Offline ChrisWilson68

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Re: Thorium Fuel Engine
« Reply #5 on: 04/26/2017 07:49 AM »
got it

so,
what are the better[cheaper and efficient] fuel for a flying bus or an Iron man suite?
which could be the best fit for this specific purpose?

How do you define "flying bus"?

Depending on your definition, you might say a Bombardier CRJ700 jet is the closest thing we can get to a flying bus with current technology.  It runs on kerosene.  Or, if you define it as something that doesn't need a runway, then maybe the CH-47 Chinook helicopter is the closest thing with can get to a flying bus with current technology.  It runs on kerosene too.

If you want something like what you see in Back to the Future, that looks like a road vehicle but can hover without any wings or rotors, you're going to be disappointed.  We don't have the technology for that, or anything on the horizon that could give us that.

The Iron Man suit is also not anywhere close to being realistic with our current technology or any currently-forseeable technology.

Re: Thorium Fuel Engine
« Reply #6 on: 04/26/2017 08:00 AM »
ive been tracking the future of transport lately

the uber flying cars, human beings on big quad copters, and terrafugia kind of cars etc
out of all i really like this design

a car without disturbing rotors

but it will be hard for this car engine to lift a bus [public transport]...
so, probably it needs a different kind of engine

as the human population is exploding. it would be great if someone could comeup with an idea for
a flying bus, or a flying train or a flying ship which can land/takeoff from the beaches/sea/lakes/rivers etc


imagine a swarm of flying cars overhead  :-[
it would be better if there are few flying objects over my head

Offline sanman

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Re: Thorium Fuel Engine
« Reply #7 on: 04/26/2017 03:46 PM »
Don't forget that fission reactors unavoidably emit radiation that includes neutron radiation. That means you need a lot of heavy shielding, and it's not so good for your health to be sitting too close to the reactor, such as with the small vehicle you posted.

Iron Man's "arc reactor" is just a macguffin - a made-up device to advance a storyplot, which can do something radical/special and not really possible by today's technology.

But take a look at Lawrenceville Plasma Physics (LPP) and their Focus Fusion device. It's not super-huge (about the size of a small bathroom), and their plucky team keeps trying to improve it, bit by bit, in the hopes that it will one day provide gobs of energy.

Offline Stormbringer

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Re: Thorium Fuel Engine
« Reply #8 on: 04/27/2017 05:49 AM »
as far as i know the primary advantages of Thorium are there are gobs and gobs and gobs and gobs of it and until it is ready to use it is basically harmless. so if a freight car of it exploded and fell over the U.S. it would just be a falling object problem and not an environmental catastrophe that needed billions for clean up, medical treatment and relocation monies.

It is my understanding that Thorium reactors must first convert a working amount of harmless Thorium to a highly radioactive relatively short lived isotope of Uranium. So without knowledge of the stuff necessary to do that conversion (probably some sort of reactor in and of itself plus ancillary systems ) it would seem to be simple to only convert the Thorium as needed moment by moment to power the main reactor. But if you had to  have a reactor to convert the Thorium you're back to the original problem anyway;  flying dangerous nuclear material over the Earth's surface with a finite risk of horrible accidents.
« Last Edit: 04/27/2017 05:53 AM by Stormbringer »
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Offline ChrisWilson68

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Re: Thorium Fuel Engine
« Reply #9 on: 04/27/2017 06:18 AM »
as far as i know the primary advantages of Thorium are there are gobs and gobs and gobs and gobs of it and until it is ready to use it is basically harmless. so if a freight car of it exploded and fell over the U.S. it would just be a falling object problem and not an environmental catastrophe that needed billions for clean up, medical treatment and relocation monies.

It is my understanding that Thorium reactors must first convert a working amount of harmless Thorium to a highly radioactive relatively short lived isotope of Uranium. So without knowledge of the stuff necessary to do that conversion (probably some sort of reactor in and of itself plus ancillary systems ) it would seem to be simple to only convert the Thorium as needed moment by moment to power the main reactor. But if you had to  have a reactor to convert the Thorium you're back to the original problem anyway;  flying dangerous nuclear material over the Earth's surface with a finite risk of horrible accidents.

You need to compare apples to apples.  Here you're implicitly comparing thorium to uranium-235 (the radioactive kind of uranium, and the kind used in most nuclear reactors).

But thorium can only be used as a fuel in a breeder reactor.  If you're going to have a breeder reactor, you can use uranium-238.  Uranium-238, like thorium isn't radioactive and can't itself be used as a nuclear reactor fuel.  But it can be hit with neutrons to make a radioactive isotope that can be used as nuclear reactor fuel, just like thorium.

And, while there isn't as much uranium-238 on Earth as there is thorium, there's still an incredibly huge amount of it -- enough to power our civilization for thousands of years.  And if a freight car of uranium-238 exploded and fell over, it would be just as harmless as if a freight car of thorium did the same.

Thorium doesn't have some advantages, but those qualities you listed aren't advantages over uranium-238 used in a breeder reactor.

Offline Stormbringer

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Re: Thorium Fuel Engine
« Reply #10 on: 04/27/2017 06:29 AM »
it is my understanding based on dim memory of years old articles that I read way in the past; that the type of uranium involved is neither the common barely radioactive natural uranium nor the type commonly used in reactors or bombs. but a different even more highly radioactive isotope.

ETA:  Yup uranium 233.

example:  http://wordpress.mrreid.org/2010/07/22/uranium-233-and-the-thorium-future/
« Last Edit: 04/27/2017 06:34 AM by Stormbringer »
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Offline ChrisWilson68

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Re: Thorium Fuel Engine
« Reply #11 on: 04/27/2017 06:39 AM »
it is my understanding based on dim memory of years old articles that I read way in the past; that the type of uranium involved is neither the common barely radioactive natural uranium nor the type commonly used in reactors or bombs. but a different even more highly radioactive isotope.

ETA:  Yup uranium 233.

example:  http://wordpress.mrreid.org/2010/07/22/uranium-233-and-the-thorium-future/

Uranium-233 is the isotope of uranium that thorium is turned into in a breeder reactor.

That's not related to what I was talking about, which is an entirely separate breeder reactor cycle that starts with uranium-238 and produces uranium-235.

You have to compare the thorium/U-233 cycle to the U-238/U-235 cycle.

Offline Stormbringer

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Re: Thorium Fuel Engine
« Reply #12 on: 04/27/2017 06:59 AM »
I think you would be right about that except for the peculiarities of the cycles. the thorium/u233 one can be done on the fly (I think.) I think i recall that the Thorium U233 cycle is safer environmentally and also from a proliferation perspective because you could make U233 at the burn rate for the reactor so there never was much of it at any one time and the uranium was unsuitable for practically sized fission or fusion bombs. Again i don't retain all the details of stuff i read over periods of years and i would be lucky if i got all that right from my poor memory.
« Last Edit: 04/27/2017 07:01 AM by Stormbringer »
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Offline gospacex

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Re: Thorium Fuel Engine
« Reply #13 on: 04/27/2017 07:03 AM »
as far as i know the primary advantages of Thorium are there are gobs and gobs and gobs and gobs of it and until it is ready to use it is basically harmless. so if a freight car of it exploded and fell over the U.S. it would just be a falling object problem and not an environmental catastrophe that needed billions for clean up, medical treatment and relocation monies.

Neither is uranium. If "freight car of U exploded and fell over the U.S", no cleanup would be necessary.

If that's pure U235, authorities would be recovering those chunks of it which are large-ish (since it's a bomb material). If pulverized to tiny particles and distributed over US, it's not recoverable for someone trying to build a bomb, and not hazardous (there are thousands of tons of it in exposed granite rocks anyway).

Offline ChrisWilson68

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Re: Thorium Fuel Engine
« Reply #14 on: 04/27/2017 07:22 AM »
I think you would be right about that except for the peculiarities of the cycles. the thorium/u233 one can be done on the fly (I think.) I think i recall that the Thorium U233 cycle is safer environmentally and also from a proliferation perspective because you could make U233 at the burn rate for the reactor so there never was much of it at any one time and the uranium was unsuitable for practically sized fission or fusion bombs. Again i don't retain all the details of stuff i read over periods of years and i would be lucky if i got all that right from my poor memory.

You are bringing up an entirely separate advantage of Thorium, the nuclear weapons proliferation issue.  That doesn't justify your saying "you would be right about that except".

No.  I was right in what I said, with no "except".  I never said there wasn't a weapon proliferation issue.  I even said Thorium had other advantages and disadvantages.  My point was just that the two issues you brought up originally as advantages of thorium aren't really advantages over uranium breeder reactors.

Offline Stormbringer

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Re: Thorium Fuel Engine
« Reply #15 on: 04/27/2017 07:46 AM »
I think you would be right about that except for the peculiarities of the cycles. the thorium/u233 one can be done on the fly (I think.) I think i recall that the Thorium U233 cycle is safer environmentally and also from a proliferation perspective because you could make U233 at the burn rate for the reactor so there never was much of it at any one time and the uranium was unsuitable for practically sized fission or fusion bombs. Again i don't retain all the details of stuff i read over periods of years and i would be lucky if i got all that right from my poor memory.

You are bringing up an entirely separate advantage of Thorium, the nuclear weapons proliferation issue.  That doesn't justify your saying "you would be right about that except".

No.  I was right in what I said, with no "except".  I never said there wasn't a weapon proliferation issue.  I even said Thorium had other advantages and disadvantages.  My point was just that the two issues you brought up originally as advantages of thorium aren't really advantages over uranium breeder reactors.
I did not mean to distract you with proliferation. i just didn't want to multipost so i put that in there.

The meat of it (provided I am correct and not misremembering) is that the Thorium can be converted to U-233 in what amounts to an almost instant manner as needed. I do not think that is the case for normal uranium breeder cycles. if that memory is correct then Thorium could be used in rocket applications with more safety and ease than U238-U235 because the U 235 would need to be made in advance and in the final quantities needed over the between refurbishment lifetime of the craft. The thorium thing would only ever have a hopper full of harmless thorium and a the moment to moment needed amount of U 233 in the reactor.
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Offline gospacex

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Re: Thorium Fuel Engine
« Reply #16 on: 04/27/2017 07:55 AM »
I think you would be right about that except for the peculiarities of the cycles. the thorium/u233 one can be done on the fly (I think.) I think i recall that the Thorium U233 cycle is safer environmentally and also from a proliferation perspective because you could make U233 at the burn rate for the reactor so there never was much of it at any one time and the uranium was unsuitable for practically sized fission or fusion bombs.

That's wrong - there would be more than enough U233 to build a bomb. Reactors have hundreds of tons of fuel in them. 1% burnup of thorium in such a reactor would yield some ~1 ton of U233 - enough for a hundred nukes.

The problem (for bomb makers, that is) is that thorium reactors also generate U232, which has very undesirable radiological properties, contaminating that U233.

Offline gospacex

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Re: Thorium Fuel Engine
« Reply #17 on: 04/27/2017 08:01 AM »
The meat of it (provided I am correct and not misremembering) is that the Thorium can be converted to U-233 in what amounts to an almost instant manner as needed. I do not think that is the case for normal uranium breeder cycles.

I don't think you are remembering it right. IIRC both processes are similar:

Th232+n -> Th233 -> Pa233 -> U233
U238+n -> U239 -> Np239 -> Pu239

Both are beta decay chains with several days half-lives in the second decay.
« Last Edit: 04/27/2017 08:01 AM by gospacex »

Offline Stormbringer

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Re: Thorium Fuel Engine
« Reply #18 on: 04/27/2017 08:18 AM »
The meat of it (provided I am correct and not misremembering) is that the Thorium can be converted to U-233 in what amounts to an almost instant manner as needed. I do not think that is the case for normal uranium breeder cycles.

I don't think you are remembering it right. IIRC both processes are similar:

Th232+n -> Th233 -> Pa233 -> U233
U238+n -> U239 -> Np239 -> Pu239

Both are beta decay chains with several days half-lives in the second decay.
damn. I was nearly certain i had read that part of it. i thought there was an article with the conversion being done in flight. but i guess i was wrong. not that i recall the detail of how rapidly the fuel was used up either.
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Offline sanman

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Re: Thorium Fuel Engine
« Reply #19 on: 04/27/2017 10:36 AM »
I think you would be right about that except for the peculiarities of the cycles. the thorium/u233 one can be done on the fly (I think.) I think i recall that the Thorium U233 cycle is safer environmentally and also from a proliferation perspective because you could make U233 at the burn rate for the reactor so there never was much of it at any one time and the uranium was unsuitable for practically sized fission or fusion bombs.

That's wrong - there would be more than enough U233 to build a bomb. Reactors have hundreds of tons of fuel in them. 1% burnup of thorium in such a reactor would yield some ~1 ton of U233 - enough for a hundred nukes.

The problem (for bomb makers, that is) is that thorium reactors also generate U232, which has very undesirable radiological properties, contaminating that U233.

U233 is a strong gamma-radiator, which makes it too deadly for anyone to isolate into a bomb and carry around.

Likewise, you wouldn't want to be enriching it aboard a spacecraft either, without a lot of shielding and distance for safety.

Bur Carlos Rubbia's idea for an Accelerator-Driven Reactor system might be useful for nuclear propulsion one day, if the mass requirements can be kept down. Using fuels like Thorium or U238 which are merely fertile not fissile would at least avoid any danger of runaway chain-reaction meltdown. As soon as the accelerator beam is cut, the nuclear reaction is immediately quenched or shut off.

Re: Thorium Fuel Engine
« Reply #20 on: 04/27/2017 11:28 AM »
Im completely clueless of your technical discussion.
but to my simplistic knowledge and curiosity...

if Petrol, Diesel, Kerosene are the by-products of a Crude oil
is it possible to create Safe-A, Sage-B, Safe-C by-products of fuel from {Whatever the Safest Thorium} is available?


Offline gospacex

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Re: Thorium Fuel Engine
« Reply #21 on: 04/27/2017 12:50 PM »
I think you would be right about that except for the peculiarities of the cycles. the thorium/u233 one can be done on the fly (I think.) I think i recall that the Thorium U233 cycle is safer environmentally and also from a proliferation perspective because you could make U233 at the burn rate for the reactor so there never was much of it at any one time and the uranium was unsuitable for practically sized fission or fusion bombs.

That's wrong - there would be more than enough U233 to build a bomb. Reactors have hundreds of tons of fuel in them. 1% burnup of thorium in such a reactor would yield some ~1 ton of U233 - enough for a hundred nukes.

The problem (for bomb makers, that is) is that thorium reactors also generate U232, which has very undesirable radiological properties, contaminating that U233.

U233 is a strong gamma-radiator, which makes it too deadly for anyone to isolate into a bomb and carry around.

No, U233 is ok.
That's U232. It is a strong gamma-emitter. To be more precise, it has relatively short half-life of 69 years and even though it decays by alpha, all daughters are even more short-lived and you end up having Pb212 and later Tl208, which are beta-active.

Offline gospacex

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Re: Thorium Fuel Engine
« Reply #22 on: 04/27/2017 12:54 PM »
is it possible to create Safe-A, Sage-B, Safe-C by-products of fuel from {Whatever the Safest Thorium} is available?

Thorium has only one long-lived isotope, Th232

Offline sanman

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Re: Thorium Fuel Engine
« Reply #23 on: 04/27/2017 03:12 PM »
No, U233 is ok.
That's U232. It is a strong gamma-emitter. To be more precise, it has relatively short half-life of 69 years and even though it decays by alpha, all daughters are even more short-lived and you end up having Pb212 and later Tl208, which are beta-active.

Apologies, now I remember - U232 is the strong gamma-emitter which isn't easily separable from the U233

Anyway, as has been said, the slowness of that part of the decay chain holds everything up.

Offline as58

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Re: Thorium Fuel Engine
« Reply #24 on: 04/27/2017 03:50 PM »

But thorium can only be used as a fuel in a breeder reactor.  If you're going to have a breeder reactor, you can use uranium-238.  Uranium-238, like thorium isn't radioactive and can't itself be used as a nuclear reactor fuel.  But it can be hit with neutrons to make a radioactive isotope that can be used as nuclear reactor fuel, just like thorium.

I think you mean 'fissile' instead of radioactive; all isotopes of both uranium and thorium are radioactive (though some of them only weakly).

Offline clongton

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Re: Thorium Fuel Engine
« Reply #25 on: 04/27/2017 04:45 PM »
In the early days of the start of the nuclear age there were many types of fuel and reactor designs being considered and tested. Most were flops. In the end it came down to a choice between two fuels; Thorium and Uranium. Both fuels have impressive lists of advantages and disadvantages. Both fuels ran reactors for hundreds of thousands of hours with no problems. In the end it came down to uranium having a single insurmountable advantage over thorium. One needs to consider the context of the times to really understand this but it was a really, really big deal to the United States at the time. The real reason we use uranium over thorium is a result of wartime politics. Cold War-era governments (including ours) backed uranium-based reactors because they produced weapons-grade plutonium —for atomic bombs and icbm warheads. Thorium powered reactors could only produce electricity – no bombs. Every other issue mentioned here is an unimportant aside detail.
« Last Edit: 04/27/2017 04:54 PM by clongton »
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Re: Thorium Fuel Engine
« Reply #26 on: 04/27/2017 06:05 PM »
Would thorium reactors in space be more "politically correct"?  For instance deep space human spacecraft beyond Mars requiring a lot of power that solar cannot give.  Or thorium reactors on Mars for night power production or continuous production in event of dust storms.  Or large NEP spacecraft that would be smaller than a large SEP spacecraft due to the huge amount of solar panels. 

Offline Stormbringer

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Re: Thorium Fuel Engine
« Reply #27 on: 04/28/2017 02:56 AM »

But thorium can only be used as a fuel in a breeder reactor.  If you're going to have a breeder reactor, you can use uranium-238.  Uranium-238, like thorium isn't radioactive and can't itself be used as a nuclear reactor fuel.  But it can be hit with neutrons to make a radioactive isotope that can be used as nuclear reactor fuel, just like thorium.

I think you mean 'fissile' instead of radioactive; all isotopes of both uranium and thorium are radioactive (though some of them only weakly).
True story:  Bismuth is now (recently) considered to be radioactive...with a halflife somewhat longer than ( a billion times ) the present age of the universe :)

Bismuth used to be considered the last stable element in the periodic table. I dunno if this is a promotion or a demotion.
« Last Edit: 04/28/2017 04:05 AM by Stormbringer »
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Offline Damon Hill

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Re: Thorium Fuel Engine
« Reply #28 on: 04/28/2017 03:31 AM »
Would thorium reactors in space be more "politically correct"?  For instance deep space human spacecraft beyond Mars requiring a lot of power that solar cannot give.  Or thorium reactors on Mars for night power production or continuous production in event of dust storms.  Or large NEP spacecraft that would be smaller than a large SEP spacecraft due to the huge amount of solar panels. 

There's really no such thing as a thorium reactor--thorium is not fissile, though it is fertile.  In an appropriate breeder design, thorium (which is more plentiful than uranium and virtually all of it is the "right" isotope) is converted into a fissile isotope of uranium, which is what generates plentiful energy.  A compact space-based reactor would more likely be fueled with highly enriched uranium or plutonium, so as not to be complicated by the breeder aspect of the thorium fuel cycle.  It may be possible to 'seed' a uranium reactor with thorium which is converted into uranium, but I think that complicates the reactor design and fuel use cycle; it's better to have a reasonably simple design and fuel cycle for space-based nuclear power. 

In terrestrial applications, the thorium fuel cycle must necessarily be tied to a significantly complex recycling process to remove certain isotopes and recover the generated U233.  There are multiple variations of the thorium fuel cycle and reactor design, and I won't (can't) go into details, especially since many of the details have yet to be designed and verified.

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Offline ChrisWilson68

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Re: Thorium Fuel Engine
« Reply #29 on: 04/28/2017 07:34 AM »
In the early days of the start of the nuclear age there were many types of fuel and reactor designs being considered and tested. Most were flops. In the end it came down to a choice between two fuels; Thorium and Uranium. Both fuels have impressive lists of advantages and disadvantages. Both fuels ran reactors for hundreds of thousands of hours with no problems. In the end it came down to uranium having a single insurmountable advantage over thorium. One needs to consider the context of the times to really understand this but it was a really, really big deal to the United States at the time. The real reason we use uranium over thorium is a result of wartime politics. Cold War-era governments (including ours) backed uranium-based reactors because they produced weapons-grade plutonium —for atomic bombs and icbm warheads. Thorium powered reactors could only produce electricity – no bombs. Every other issue mentioned here is an unimportant aside detail.

False.  The plutonium produced in power plants is unsuitable for use in nuclear weapons.  Both the United States and Soviet Union produced all their weapons-grade plutonium in special reactors built just for the purpose of making weapons.  For the United States, it all came from Savannah River or Hanford.  All the plutonium produced by power plants is either buried as waste or reprocessed into more reactor fuel.

The decisions to go with uranium over thorium for power reactors had nothing to do with nuclear weapons.

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Re: Thorium Fuel Engine
« Reply #30 on: 05/03/2017 11:41 PM »
In the early days of the start of the nuclear age there were many types of fuel and reactor designs being considered and tested. Most were flops. In the end it came down to a choice between two fuels; Thorium and Uranium. Both fuels have impressive lists of advantages and disadvantages. Both fuels ran reactors for hundreds of thousands of hours with no problems. In the end it came down to uranium having a single insurmountable advantage over thorium. One needs to consider the context of the times to really understand this but it was a really, really big deal to the United States at the time. The real reason we use uranium over thorium is a result of wartime politics. Cold War-era governments (including ours) backed uranium-based reactors because they produced weapons-grade plutonium —for atomic bombs and icbm warheads. Thorium powered reactors could only produce electricity – no bombs. Every other issue mentioned here is an unimportant aside detail.
False.  The plutonium produced in power plants is unsuitable for use in nuclear weapons.  Both the United States and Soviet Union produced all their weapons-grade plutonium in special reactors built just for the purpose of making weapons.  For the United States, it all came from Savannah River or Hanford.  All the plutonium produced by power plants is either buried as waste or reprocessed into more reactor fuel.

The decisions to go with uranium over thorium for power reactors had nothing to do with nuclear weapons.

Consider: http://www.neis.org/literature/Brochures/weapcon.htm
Quote
The connections linking nuclear power and weapons is more than political or historic. Consider: l FISSIONABLE MATERIALS: It is the same nuclear fuel cycle with its mining of uranium, milling, enrichment and fuel fabrication stages which readies the uranium ore for use in reactors, whether these reactors are used to create plutonium for bombs or generate electricity. In the end, both reactors produce the plutonium. The only difference between them is the concentration of the various isotopes used in the fuel. Each year a typical 1000 mega-watt (MW) commercial power reactor will produce 300 to 500 pounds of plutonium -- enough to build between 25 - 40 Nagasaki-sized atomic bombs.

As Dr. Amory Lovins, director of the Rocky Mountain Institute in Colorado points out, "Every known route to bombs involves either nuclear power or materials and technology which are available, which exist in commerce, as a direct and essential consequence of nuclear power." In order to get plutonium for weapons, one needs a reactor, whether it is a "research" reactor (such as the one which provided India with the fissile material for its first atomic bomb). or a commercial reactor.

And: https://en.wikipedia.org/wiki/Plutonium
Quote
Neutrons from the fission of uranium-235 are captured by uranium-238 nuclei to form uranium-239; a beta decay converts a neutron into a proton to form Np-239 (half-life 2.36 days) and another beta decay forms plutonium-239.


Also: http://nuclearweaponarchive.org/Library/Plutonium/
Quote
All plutonium originates in nuclear reactors and is produced by the capture of extra neutrons by uranium-238 to form U-239, which then undergoes a series of decays to form Pu-239: U-238 + n -> U-239 -> Np-239 -> Pu-239. Some of this plutonium gets consumed by fission before it is removed from the reactor, and some of it gets transmuted to heavier isotopes of plutonium by capturing more neutrons:     Pu-239 + n -> Pu-240

Plutonium does not exist naturally to be mined. It is only available as a byproduct of a nuclear fuel cycle that uses uranium as the fuel. There is no nuclear fuel cycle of any kind with thorium that can produce plutonium and THAT is why uranium was chosen as the fuel for nuclear reactors.
« Last Edit: 05/03/2017 11:57 PM by clongton »
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Offline gospacex

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Re: Thorium Fuel Engine
« Reply #31 on: 05/04/2017 12:00 AM »
In the early days of the start of the nuclear age there were many types of fuel and reactor designs being considered and tested. Most were flops. In the end it came down to a choice between two fuels; Thorium and Uranium. Both fuels have impressive lists of advantages and disadvantages. Both fuels ran reactors for hundreds of thousands of hours with no problems. In the end it came down to uranium having a single insurmountable advantage over thorium. One needs to consider the context of the times to really understand this but it was a really, really big deal to the United States at the time. The real reason we use uranium over thorium is a result of wartime politics. Cold War-era governments (including ours) backed uranium-based reactors because they produced weapons-grade plutonium —for atomic bombs and icbm warheads. Thorium powered reactors could only produce electricity – no bombs. Every other issue mentioned here is an unimportant aside detail.

False.  The plutonium produced in power plants is unsuitable for use in nuclear weapons.

Well... if you operate them "normally", yes, the resulting plutonium will be no good for bombs (contaminated by Pu240,241,242). However, if you run power reactor for a short time (a month or even less) and then unload and process the fuel, then you get weapon-grade Pu.

Ironically, that's what effectively happened at Three Mile Island. The accident happened early in the very first fuel campaign of Unit 2, and therefore fuel debris from the TMI accident contained weapon-grade plutonium. After reactor vessel cleanup, It was decided to hand it over for storage to the military.

Offline ChrisWilson68

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Re: Thorium Fuel Engine
« Reply #32 on: 05/04/2017 12:22 AM »
In the early days of the start of the nuclear age there were many types of fuel and reactor designs being considered and tested. Most were flops. In the end it came down to a choice between two fuels; Thorium and Uranium. Both fuels have impressive lists of advantages and disadvantages. Both fuels ran reactors for hundreds of thousands of hours with no problems. In the end it came down to uranium having a single insurmountable advantage over thorium. One needs to consider the context of the times to really understand this but it was a really, really big deal to the United States at the time. The real reason we use uranium over thorium is a result of wartime politics. Cold War-era governments (including ours) backed uranium-based reactors because they produced weapons-grade plutonium —for atomic bombs and icbm warheads. Thorium powered reactors could only produce electricity – no bombs. Every other issue mentioned here is an unimportant aside detail.

False.  The plutonium produced in power plants is unsuitable for use in nuclear weapons.

Well... if you operate them "normally", yes, the resulting plutonium will be no good for bombs (contaminated by Pu240,241,242). However, if you run power reactor for a short time (a month or even less) and then unload and process the fuel, then you get weapon-grade Pu.

Ironically, that's what effectively happened at Three Mile Island. The accident happened early in the very first fuel campaign of Unit 2, and therefore fuel debris from the TMI accident contained weapon-grade plutonium. After reactor vessel cleanup, It was decided to hand it over for storage to the military.

In both the West and the Soviet block, all plutonium ever used in nuclear weapons came from special reactors designed and built explicitly to produce weapons-grade plutonium.  None of it ever came from a power reactor -- not even the power reactors designed and owned by the military, such as those in aircraft carriers and submarines.

So the claim that uranium was chosen over thorium for power reactors because it generated plutonium for nuclear weapons is false.

Maybe Iran or North Korean built dual-use reactors that were intended to produce power as a front and secretly to get plutonium too.  Maybe even Israel did that.  But not the United States.  Not Russia.  Not China.  They had their own, better ways to get plutonium for weapons.  They never used or needed to use power reactors to give them plutonium for weapons.

There were many factors going into the decisions to use uranium instead of thorium for power reactors, but for the vast majority of power reactors in the world, those decisions were not made because someone wanted to produce plutonium for nuclear weapons.

Offline ChrisWilson68

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Re: Thorium Fuel Engine
« Reply #33 on: 05/04/2017 12:26 AM »
Plutonium does not exist naturally to be mined. It is only available as a byproduct of a nuclear fuel cycle that uses uranium as the fuel. There is no nuclear fuel cycle of any kind with thorium that can produce plutonium and THAT is why uranium was chosen as the fuel for nuclear reactors.

I already refuted that in the post you replied to, but you offered nothing that addressed the refutation.

Offline clongton

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Re: Thorium Fuel Engine
« Reply #34 on: 05/04/2017 12:37 AM »
Plutonium does not exist naturally to be mined. It is only available as a byproduct of a nuclear fuel cycle that uses uranium as the fuel. There is no nuclear fuel cycle of any kind with thorium that can produce plutonium and THAT is why uranium was chosen as the fuel for nuclear reactors.

I already refuted that in the post you replied to, but you offered nothing that addressed the refutation.

Please explain how to obtain plutonium without a uranium fuel cycle.
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Offline gospacex

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Re: Thorium Fuel Engine
« Reply #35 on: 05/04/2017 12:59 AM »
In the early days of the start of the nuclear age there were many types of fuel and reactor designs being considered and tested. Most were flops. In the end it came down to a choice between two fuels; Thorium and Uranium. Both fuels have impressive lists of advantages and disadvantages. Both fuels ran reactors for hundreds of thousands of hours with no problems. In the end it came down to uranium having a single insurmountable advantage over thorium. One needs to consider the context of the times to really understand this but it was a really, really big deal to the United States at the time. The real reason we use uranium over thorium is a result of wartime politics. Cold War-era governments (including ours) backed uranium-based reactors because they produced weapons-grade plutonium —for atomic bombs and icbm warheads. Thorium powered reactors could only produce electricity – no bombs. Every other issue mentioned here is an unimportant aside detail.

False.  The plutonium produced in power plants is unsuitable for use in nuclear weapons.

Well... if you operate them "normally", yes, the resulting plutonium will be no good for bombs (contaminated by Pu240,241,242). However, if you run power reactor for a short time (a month or even less) and then unload and process the fuel, then you get weapon-grade Pu.

Ironically, that's what effectively happened at Three Mile Island. The accident happened early in the very first fuel campaign of Unit 2, and therefore fuel debris from the TMI accident contained weapon-grade plutonium. After reactor vessel cleanup, It was decided to hand it over for storage to the military.

In both the West and the Soviet block, all plutonium ever used in nuclear weapons came from special reactors designed and built explicitly to produce weapons-grade plutonium.  None of it ever came from a power reactor -- not even the power reactors designed and owned by the military, such as those in aircraft carriers and submarines.

So the claim that uranium was chosen over thorium for power reactors because it generated plutonium for nuclear weapons is false.

Your conclusion does not follow from the premise - the decision to go with uranium could be influenced by the _possibility_ to quickly make a lot of weapon-grade Pu-239, if necessary - even if the need to actually do that with power reactors never materialized in history.

Moreover, there is testimony from people involved in the nuclear programs of both US and USSR who claim that the decision WAS influenced by these considerations.

RBMK's on-load refueling feature is especially conductive to producing weapon-grade Pu _without disturbing power generation_.

Offline randomly

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Re: Thorium Fuel Engine
« Reply #36 on: 05/05/2017 03:49 PM »
Thorium reactors do produce material (U233) that can be used for bombs, it has a critical mass about 50% larger than plutonium 239. It wasn't that thorium doesn't produce fissile material in a reactor, but that plutonium cores could be produced more rapidly than Uranium 233 that made it the preferred core material. It was all limited by the neutron economy (spare neutrons you could generate in the reactor to make new material).

There are three primary isotopes that can be used as fissile materials (materials than can support a nuclear chain reaction). Uranium 233, Uranium 235, and Plutonium 239. You can make bombs or reactors out of any fissile material. Uranium 235 is the only one that occurs naturally because it's the only one with a long enough half life for some of it to still be around since the earth formed. U233 and Pu239 can be made in a reactor by neutron absorption and subsequent beta decay from the fertile materials Thorium 232 and Uranium 238 respectively. Thorium 232 absorbs a neutron and the Thorium 233 double beta decays to U233 with a half life of 27 days. Uranium 238 absorbs a neutron and double beta decays to Pu239 with a half life of 2.4 days, so the process is much quicker. This speed of processing advantage and the smaller critical mass of Pu239 means you can make bombs faster going the Pu239 route.

All the early development of nuclear power came out of defense applications, and that knowledge and experience base had a lot of momentum. The other thing weighing against early thorium power was the necessity of running two different fuel streams instead of one, since you still need to power the reactor with an enriched uranium feed until you can develop the technology to have the breeding ratio high enough for the Pu233 to satisfy the reactor needs. Uranium also is a much simpler fuel stream as it's just once and done, you don't need any complicated processing on highly radioactive material. Until you have a reactor design like a molten salt reactor to simplify handling, even then breeding fuel is more expensive than just digging up more uranium.

For space use breeder reactors of any kind including thorium are not a viable approach. Breeder reactors are an order of magnitude larger in mass, and that just kills the idea right there. For planetary use the trade space changes and it might be a viable option, but not for use in space where minimal mass is so important.

It is true that Thorium is about 3 times more common in the earths crust than Uranium, but a mitigating factor is that Uranium is much more water soluble. This has the effect that it's geologically concentrated and high concentration ores can be found. Thorium on the other hand does not concentrate as easily, but it is extracted as a secondary output from rare earth and other ore streams.
« Last Edit: 05/05/2017 04:00 PM by randomly »

Offline DLK

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Re: Thorium Fuel Engine
« Reply #37 on: 05/06/2017 01:24 AM »
For breeder cycles, an advantage of Th232->U233 over U238->Pu239 is that you can do it with thermal-spectrum neutrons. This makes it possible to build a much more compact reactor, as your fissile inventory can be much smaller and lighter. This advantage becomes practical with continuous fuel reprocessing, which is a factor in the current interest in molten salt reactors.

I suspect that the complexities of reprocessing would offset advantages in a space-borne reactor, but a terrestrial MSR unit (terrestrial on Mars, whatever that's called) for colony power production and industrial process heat may be a good choice.

For propulsion, whatever realizable system that weighs the least and can drive a sufficient amount of your reaction mass out at the highest velocity is what you'd want.

(is Kirk Sorensen on this list?)

Offline randomly

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Re: Thorium Fuel Engine
« Reply #38 on: 05/07/2017 03:17 AM »
Yes the neutron economy is more favorable with U233 in the thermal range than U235 or Pu239, but even with that advantage a reactor designed to breed it's own fuel will be many times more massive than a burner design, and that's just the reactor core and doesn't include all the inline reprocessing equipment needed to remove the fission products and extract the protactinium 233 produced etc. Fortunately the energy density of nuclear fuel is so high, you can just put sufficient fuel into the core to handle most space based needs without the need to breed fuel.

Kirk is occasionally around, I think he's rather busy these days though.

Offline gospacex

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Re: Thorium Fuel Engine
« Reply #39 on: 05/08/2017 03:14 PM »
There are three primary isotopes that can be used as fissile materials (materials than can support a nuclear chain reaction).

There is also neptunium. Somewhat surprisingly, both long lived isotopes, Np236 and Np237 are fissile. (Not that it has much to do with the thread).

Offline randomly

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Re: Thorium Fuel Engine
« Reply #40 on: 05/08/2017 06:58 PM »
yes there are other fissile isotopes like Neptunium and Californium, but they can't be made nearly as efficiently or cost effectively as U233, U235, or Pu239. Neptunium is produced in reactors about 20 times slower than Plutonium.

Offline gospacex

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Re: Thorium Fuel Engine
« Reply #41 on: 05/08/2017 08:57 PM »
yes there are other fissile isotopes like Neptunium and Californium, but they can't be made nearly as efficiently or cost effectively as U233, U235, or Pu239. Neptunium is produced in reactors about 20 times slower than Plutonium.

But all neptunium in spent fuel from *power reactors* is still weapons-grade, unlike plutonium. US alone has 75000 tons of spent fuel. It contains, very roughly, 50 tons of Np.
« Last Edit: 05/08/2017 08:58 PM by gospacex »

Offline Arch Admiral

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Re: Thorium Fuel Engine
« Reply #42 on: 05/09/2017 07:32 AM »
There is a lot of misinformation in this thread.

-- many reactors during the Cold War produced both weapons-grade Pu and electric power for the commercial grid. In the 50s and 60s, the UK Central Electricity Generation Board produced more Pu than the modest British nuclear weapons program could use, so the surplus was bartered to the USA in return for tritium from Savannah River. The Soviet RBMK reactors were similar to the British ones and had the same dual purpose. They also had similar accidents (Windscale and Chernobyl). In the US some of the Hanford Pu production reactors also fed the grid, but this was on a much smaller scale.

-- It's not clear that the distinction between "reactor-grade" and "weapons-grade" Pu has any meaning anymore. The US apparently produced warhead designs using reactor-grade Pu around 1960, but the last time I checked they didn't admit having tested them. In the 1980s there was a short-lived program to produce "super-grade" Pu with very low Pu-240 content that could be mixed with reactor-grade Pu to produce a weapons-grade product. Most proliferation experts think that Japan's huge stockpile of "reactor-grade" Pu is intended as a weapons reserve -- they have never built the fleet of breeder reactors it is supposedly for.

-- there were two periods of interest in the Th-232/U-233 breeder cycle. In the 1950s there was hope in the USA that U-233 would be a useful material for weapons, but when its nuclear properties were measured it turned out to be pretty useless. India did some work on it in the 1970s because they have much larger domestic reserves of thorium than uranium (in some areas the natural background radiation from thorium actually exceeds that allowed in US nuclear plants). But nothing came of this program either.

Today's modest interest in thorium breeding seems mostly because it is different, and it is easy to mistake "different" for "better". You see this all the time on the other threads on this site, where old bad ideas about spaceflight are dug up and proclaimed as the best thing since sliced bread.


Offline Radical_Ignorant

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Re: Thorium Fuel Engine
« Reply #43 on: 05/25/2017 10:27 AM »
I think OP mixed two things. Molten salt reactors and Thorium reactors - those are often connected but are separate things. If that's a case - molten salt reactors are supposed to be much smaller and use coolant which doesn't have to be in super bulky extremely high pressures loop and under super heavy contamination dome. That's huge advantage - that's why original research on MSR was done by money from USAF - they hoped to put those reactors on planes.

As for space... I  have no idea how standard nuclear reactors could be used. There is no river around to provide heat sink and classical solution - change heat to electric energy via steam turbine - seems to be in realm of fantasy. As for space as Mars, Moon... that could be a thing. I hope it will be.

Offline gospacex

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Re: Thorium Fuel Engine
« Reply #44 on: 05/25/2017 11:43 AM »
As for space... I  have no idea how standard nuclear reactors could be used. There is no river around to provide heat sink and classical solution - change heat to electric energy via steam turbine - seems to be in realm of fantasy.

Wrong, it is possible.
This one was even built and tested (on Earth):
https://en.wikipedia.org/wiki/Safe_Affordable_Fission_Engine

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