You cannot get U-233 without it being contaminated with U-232. Their is no method to do it in the world of physics. It is also chemically impossible to separate then two via chemical process which would be the easy way to do it since the 2 atoms are very very identical. Even a centrifuge will have a very hard time separating the two because of their huge inherent similarity. It would also take a lot more time to do that. During that time everyone else would know what you are doing.

If you really want a nuclear weapon you can just stock pile natural uranium into your garage incase it into a carbon fibre brick works and let it sit there for a short while until it turns into U-235. Which is, faster, cheaper, easier, more easily hidden then trying to use U-233 and get the the U-232 out of it. It's the reason we do not make nuclear weapons in this matter. Using thorium to make a nuclear weapon is the worst possible way you can use to make one.

And yes the biggest nuclear device was detonated by the Russians the "Tsar Bomba" and it was huge, U-233 won't make that bomb any much smaller. So it's not something your going see to happening, not to mention as stated many time EVERYONE would know what your doing.

On the off hand we could continue with current nuclear technology have more meltdown and have a continued weapons proliferation since those reactor were made to produce surplus amount of U-235 and plutonium to specifically be used in nuclear weapons. You know all that radioactive waste our current power-plant produce is? it's that the stuff that we use to make weapons with. And with all that waste we have produced more then enough nuclear weapons to nuke the planet 5 times over. In the nuclear war scenarios a lot of the targets that were going to get nuked were going to get nuked 30-40 times over since we have so many damn nukes to use. It was ludicrous overkill.

In a thorium reactor if you take out the U-233 that is generated you essentially shut down your reactor since it needs that U-233 to continue functioning. And Since the Thorium fuel cycle is extremely radioactive working with it to produce a weapon is a deadly proposition for anyone involved in it. But that high radioactivity is also the beauty of it since whiting a week the very deadly elements have decayed away, and in 10 years most of it is going to be stable. The longest time life for the wastes of a thorium reactor is 300 years, which for storing it much easier then the 100000 years of the waste we currently have that we have no clue how we are going to deal with it. But funny thing is with a Thorium reactor we could burn that waste away and get rid of it. All that waste problem we have we could fix it with this tech. our old nuclear weapons we need to start thinking of getting rid ofve because they are nearing the limit of their safety lives could be burned as reactor fuel something that cannot be done with our current reactors.

In addition a thorium reactor would be the only good method to produce some of the isotope we need for medicine and further space exploration, not to mention all the other additional uses we might discoverer because now we can produce more of those isotopes and get more research done on them.

In the end we will run out of fossil fuels it's only a question of time, we will run out of uranium as well since it is very rare too, but we will never run out of thorium since it is just so fucking common. Thorium is literally everywhere, and it has a very nice electromagnetic signature that just waves at us going: "here I am am come and get me!"

Also Thorium reactors are going to happen, China is going full steam towards it and in 10 years if we don't get out asses off the bench they will be selling us reactors, and they will be the dominant energy power in the world. Hell in 10 years time China will be complaining to use about green house emission and pollution. The crazy super polluted smog of Shanghai is something that China is going to make a thing of the pass and this is how they are doing it. India is also working on Thorium by they are trying to use it in a solid fuel format which will do nothing to help waste, their goal is simply to just not to have to rely on uranium imports any-more since they have poor uranium deposits but good thorium ones. They will most likely eventual change course for a liquid fuel as well in the future eventually.

The question remains will be let our selves be left behind or will we forge ahead as well. That is the only question you really have to answer here. because weather of not we do it, a Thorium fuelled world is coming.

Ah...where were we before YouTube?

....oh, that's right....monitoring radioactive fallout from above-ground nuclear testing performed by OTHERS on Australian soil.

Always good to debate 'ideology' whilst real people have lived with the reality....

Oh, goodie....what say you pop over to Maralinga sometime.

It's been over 50 years since....should be squeaky clean and safe as houses....

Only if you let significant amounts of U232 build up.

That sounds too good to be true.

Sure but it's about the level of contamination, which can be kept very low.

Upgrading uranium is very costly because you start with such a small percentage of U235/U238. U233/U232 has a much higher concentration to begin with, and that makes concentrating it a lot easier... in the first case someone has to get rid of 98% of the material, in the second case someone has to get rid of (much) less than 1% of the material. So to get the same result, you can do with 1 centrifuge instead of 100.

There are other ways of knowing whether a country is developing a nuclear bomb. Like, people with a conscience who leak secrets. And what difference does it make if one knows that a country is working on a bomb? By the time you measure the hard gamma radiation from U232, it's already too late, because said country already has the raw materials to make the bomb. You see currently how little difference that knowledge makes: North Korea, Iran just don't care what others think and other countries are reluctant to go to war over such a matter ...

And finally, measuring the hard gamma radiation isn't an easy task, I can imagine several ways to conceal the storage of U233.

For example a thorium reactor like you envision, with fuel that is contaminated by a fair amount of U232, emits a lot of hard radiation. Such a reactor can be used as cover for storing U233/U232.

For example dig a very deep hole, build a lab 100 meters under the ground, and store the U233/U232 there after it's been delivered in small lead-protected packets. Good luck detecting hard radiation behind 100 meters of rock.

At straws? Pretty strong ones like this:

http://www.princeton.edu/sgs/publications/sgs/pdf/9_1kang.pdf

"the proliferation resistance of thorium fuel cycles depends very much upon how they are implemented."

You're staring blindly at one "perfect" situation where everything goes as you planned, but others might not share your vision, they will find ways...

Perhaps you're right that low-pressure salt thorium nuclear plants contain too much U-232. That's also their own doom then, because the plants become highly radioactive, have to be abandoned after a while and people face very high cost to dispose of them.

And then there's countries who think further, make some modifications on the existing designs and make them suitable for generating material for nuclear weapons.

I don't think countries are interested at first in a "perfect" weapon. A low-grade, high-radiative bomb will be just as good a deterrant as a "perfect" bomb.

And having a centrifuge to refine enough material for the 1st bomb is also perfectly possible. No matter if it becomes radiaoctive after a while... as long as you have enough materials to make a few bombs, then an investment of a few tens of millions for a disposable centrifuge is worth it!

Once a deterrant is in place, the rest of the world will just have to live with it, and a country can go on on a more elaborate nuclear weapons program.

Check the chapter on "Two-stage thermonuclear weapons" here:

http://en.wikipedia.org/wiki/Nuclear_weapon_design

"Even six-inch (152 mm) diameter nuclear artillery shells can be two-stage thermonuclears"

I.e., portable hydrogen bombs.

Ok then, looks like you know a lot more about this than I do

What about the possibility to refine the U233 by a centrifuge? You cannot really prevent this, can you?

According to this

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

a breeder-type reactor which doesn't extract Pactinium to let it decay peacefully into U-233, doesn't only produce U-232 but also U-235.

I'm sorry but I don't really understand why people even bother with such a dirty fuel.

Why can't they invest all that research money into the pursuit of nuclear fusion, or cheaper solar cells, or whatever?

Solar and wind power are no wear near capable of providing the amount of energy that we need. They require that wast amounts of land be dedicated and they are location dependent and only produce power part of the time. At best solar and wind power can best be described as life support but nothing more. Solar and wind power are the most costly to build, use the most land per Mw/h then any other forms of power. Don't get me wrong they are cool but they are totally incapable of meeting our energy needs.

Hydro and geothermal are the only reliable that could come close to meeting the energy needs. But they are booth very sensitive to location. For Hydro to generate good amounts of power you need a lot of water which you cannot find anywhere. A lot of countries in the would only be able to produce at best 10% of their power from hydro and others still much less. Geothermal seems like a magic bullet but it is also location dependent. You can only reliably produce geothermal in volcanic active regions were the mental is thin enough. If not you need to drill for miles and miles into the earth some would need to be deeper then the deepest oil wells we have ever drilled then you have the added challenge then you need to drill a return well that will intersect your first well at just the right point. And after that try to circulate water into the long pipe will be difficult because of the resistance that builds up over time from friction plus the hot water at the button that wants to turn to steam and is pushing on booth sides. When all that is done you need to start drilling again a because over time that water will create mineral deposits on the walls of the wells slowly clogging them up.

Not on the other hand a LFTR uses only Thorium as an intake fuel source. You can also feed it other radioactive substances or waste that emits neutron to get the reactor started or continuously feed it those substances in order to burn them up. So all that radioactive waste that we have from our current nuclear power plants that we do not know what to with because it will continue to be deadly for hundreds of thousands of years we can burn it up and make it go away by using it as an added fuel source. But back to Thorium, it is recognized as a radioactive substance, but it has a half life of 14.2 billion years. That is more of less as old as the universe is. That also makes it one the least radioactive substance they we know of, it certainly the least radio active substance that I know of for me personally. I'll go out on a limb here but Thorium is so inactive that you probably get more radiation daily from household appliances and driving your car then you would standing next to a fully loaded dump truck full of the stuff. Storing and handling Thorium requires no more safety measure necessary then the ones you use for storing rocks that you intend to use in your driveway or your garden. It doesn't dissolve in water and it can not be metabolize by the human body and animal or plant life.

And to finish with to produce equivalents amounts of energy a standard reactor today will consume 250 tons of materiel and will have 90% very often all the way up to 99% of that material come back out as waste. That is a lot of nuclear waste. But a Thorium fuel cycle will need on 1T of Thorium and only 1% of it will come out at the end. Not then mention that the Thorium fuel cycle waste will become inert in 300 years vs hundreds of thousand of year for the current fuel cycles we are using.

Thorium fuel cycle: 1Kg of waste for 300 years
Current fuel cycles: at best 225T of waste for 100000 years +

Take your pick!

Because it's a liquid fuel you can leave the fuel inside the reactor until it has been completely spent. A solid fuel reactor produces that much waste and is so inefficient because it doesn't allow for the fuel to be homogeneously mixed together. Yes the neutron absorber need to be chemically filtered out for for the 27 days period till they turn into U-233 at which point they re re-injected into the reactor to keep the reaction going. The chemical extraction method is provided by the thermal heat the reactor it's self generates. Also part of the waste products are not waste by it's self.  actinium-225 and bismuth-213 are products we can produce in a LFTR that would be highly desirables for medical treatments for cancer. Because they are alpha emitters.

Bismuth-213 can currently only be produced inside a particle accelerator currently because it has a half life of only 45 ish minutes. Because it's half life is so short it is impossible to extract the isotope from solid fuel. How ever the liquid fuel reactor could chemically separate it to transfer it to cancer treatment centre which would likely be built next tot he reactor plant in order to ensure it gets tot he patient on time.

Same story pretty much with Actinium, but it has a half life of 10 days. Does allow use to extract it from solid fuel, but requires that you dedicate this reactor to producing that since you need to open the reactor up often to remove the isotopes you want. With the closing of the Chalk River reactor in Canada that produce the majority in some cases of the world medical radio isotopes we are heading toward a shortage since no one else seems interested or capable of reliably providing those isotopes.

A LFTR can provide those isotopes and keep running because you do not need to shut-down the reactor to remove the isotopes you want or need. 

A breeder reactor is a reactor that is design to produce more fissile material then it needs to continue to operate. Breeder reactor rimes with proliferation, far the most part. The thing is it's a liquid fuel so your U-235 would also be contaminated by the U-232. And you will only get U-235 is you use U-238 to start your reactor and you keep feeding in U-238. It's doable but more complicated then just using standard reactor of even just using the bunker method of enriching uranium which is dirt cheap and so simple you could do it in your garage. Essentially you pile it up then enclose it in a carbon casing and let it do it's thing for a while, you end up with enriched and depleted uranium. We don't really use that method no more, it was use in the early days of the Manhattan project. Today method are more sophisticated, but getting it from LFTR would be more complicated than any of the methods we currently use. http://en.wikipedia.org/wiki/Enriched_uranium

I think you are also mistaken in your understanding between irradiation and contamination. Irradiation is the alpha, beta and gamma ray that a radioactive source emits, if you get exposed to them in large amount they can be deadly, but their do not linger into the environment. The rays fly out away from their source of emission and hits other matter and once it get absorbed which for alphas is very short, beta longer and gammas being the most penetrating of the 3 it over. It stop there end of story for that ray. We use irradiation to sterilise food and medical equipment and so on, X-ray are irradiation.

Contamination on the other hand lingers in the environment, it provide a source for irradiation to continue to occur from. Contamination is what happen when you detonate a bomb because the isotope are not al burned up in the explosion. Those isotopes fall to the ground and into the water and their remain there continuing to give of radiation. That is why the nuclear test sites are radioactively hot and why they are exclusion zones around Chernobyl and Fukushima.

That is also the beauty of the LFTR because the reactor room is irradiated to high lvls while in operation it burns up and destroyed any contaminating isotopes that might have escaped outside. already in India when their walk into their solid fuel reactors burning up thorium the Radiation levels are barely noticeable. 

Have a look at India's "JUNK" thorium reactor.

Yeah, as safe as houses with their rooves caving in, exposed electical wiring, nearby faulty plumbing and the floorboards giving way.

BTW, Paul, did you know we had so many experts gracing these 'ere Stardock forums?  We got nuclear experts; we got scientific experts; we got weather experts; we got political experts... and we got climactic change experts.

On the internet, everyone is an expert on everything!

Just say you know a little bit about a lot of stuff instead of a lot a bit about a little stuff. I do. Works for me. 

Here is a link to the article about the salt using nuclear reactors I mentioned earlier.  http://www.triplepundit.com/2012/04/liquid-fluoride-thorium-power-pros-cons/  This article is part of a series that attempts to give the pros and cons of each type of energy 'solution' that's on the radar.  The author admits his bias (unlike many other pundits) and seems to cover all the bases.  Hope the experts find it helpful in perfecting their pudnit-ness.

BTW e....  Solar and wind power may not be capable of fulfilling all energy needs, as you say.  Quite true.  But some need fulfilled in a healthier manner is better than no need fulfilled in a healthier manner.  Nevertheless, considering your points: their cost, which you suggest, requires too much land, and is too expensive contains two errors.  First, cost is, in part, determined by economies of scale.  If society were to embrace such technologies, costs would decrease.  More importantly, you seem to think of solar as only large areas dedicated to the electrical solar panel mode of gathering power from sunlight.  In contrast, harnessing energy from sunlight has many modes.  Merely the design of our buildings and homes may increase the capture of energy in a passive manner.  Also, there are solar heating towers, where a mirror array is used to focus sunlight to heat water which then runs a turbine which transforms much of the energy into electrical energy.  There are many, many more methods of harnessing solar that are not predicated on the currently expensive electron-plate modalities.   And yes, geography does play a role in where these technologies are best placed.  Oil, coal and gas are also not uniformly distributed across the globe, and we clever humans have embraced those sources.  Could not the same be done with "other' energy sources?