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xylophobe
2010-Sep-14, 02:00 AM
I was just reading about thorium (http://en.wikipedia.org/wiki/Thorium) as a fuel for nuclear reactors and was wondering what the drawbacks are to this fuel.

The wikipedia (http://en.wikipedia.org/wiki/Thorium_fuel_cycle) article seems to paint thorium as a panacea for America's energy needs since we have over 1,000 years worth of energy needs represented in U.S. deposits of thorium ore to use.

Thanks.

Jens
2010-Sep-14, 02:18 AM
I was just reading about thorium (http://en.wikipedia.org/wiki/Thorium) as a fuel for nuclear reactors and was wondering what the drawbacks are to this fuel.


In the Wikipedia article you were reading, there is a whole section (http://en.wikipedia.org/wiki/Thorium_fuel_cycle#Disadvantages_as_nuclear_fuel) on the drawbacks. Maybe the easiest thing would be for you to read that section, and then ask questions if there is anything you find difficult to understand. I'm sure that knowledgeable people will be ready to help.

xylophobe
2010-Sep-14, 01:06 PM
In the Wikipedia article you were reading, there is a whole section (http://en.wikipedia.org/wiki/Thorium_fuel_cycle#Disadvantages_as_nuclear_fuel) on the drawbacks. Maybe the easiest thing would be for you to read that section, and then ask questions if there is anything you find difficult to understand. I'm sure that knowledgeable people will be ready to help.

Hey, thanks. It was late at night and I was real tired so I wanted to start the thread before I forgot about it. I was too tired to read on and discover the section that you reference.

Atraveller
2010-Sep-15, 05:48 AM
Maybe not the best source for information about nuclear reactors, but Ambrose Evans-Pritchard (a reasonably respected economist/columnist) in the UK is a big fan of Thorium

http://www.telegraph.co.uk/finance/comment/7970619/Obama-could-kill-fossil-fuels-overnight-with-a-nuclear-dash-for-thorium.html

Ultimately the point he makes is that uranium reactors got the money and focus on research because of the ability for uranium reactors to yeild weapons grade material as a by product (actually for a while the energy was the by product - weapons material was the objective.)

Now Thorium makes better long term sense for energy production, but all that money and research would have to be done again to overcome the technical difficulties.

The end product would be a much safer, simpler, and economical nuclear reactor - other than the money and research, there may be other factors (which we can't talk in this section of this board - need to start a CT thread) which are stopping advancement on these reactors.

Atraveller
2010-Sep-15, 06:44 AM
Another article on current Thorium reactor research:

http://www.wired.com/magazine/2009/12/ff_new_nukes/all/1

The cost difference is what is really exciting:

Uranium reactors make power at a fuel cost of about $50Million /1 GW year or about $0.57 /kw hr (coal is about 1/6 this cost.)

Thorium reactors should make power at about $10,000 /1Gw year or about $0.015 /Kw hr - about 1/10 the cost of coal...

Len Moran
2010-Sep-15, 09:12 AM
There is a very good article on this topic within the July - August 2010 issue of American Scientist magazine (Liquid Flouride Thorium Reactors by Robert Hargraves and Ralph Moir). The content is on line, but you may have to pay for the article download - Iím not sure. There are also a number of useful references listed at the end of the article. There is an online forum probing the practicalities of this fuel involving scientists and engineers at http://energyfromthorium.com

The crux of it is basically as Atraveller says Ė the advantages seem to be quite evident, but we have to start from scratch.

Below are some small extracts from the American Scientist article that serve to give a flavour of the article.



Ö.Of course we canít turn the clock back. Maddeningly to advocates of liquid-fuel thorium power, it is proving just as hard to simply restart the clock. Historical, technological and regulatory reasons conspire to make it hugely difficult to diverge from our current path of solid fuel, uranium-based plants. And yet an alternative future that includes liquid-fuel thorium-based power beckons enticingly...

....A thorium-based fuel cycle brings with it different chemistry, different technology and different problems. It also potentially solves many of the most intractable problems of the uranium fuel cycle that today produces 17 percent of the electric power generated worldwide...

...Liquid fuel thorium reactors offer an array of advantages in design, operation, safety, waste management, cost and proliferation resistance over the traditional configuration of nuclear plants. Individually, the advantages are intriguing. Collectively they are compelling...

xylophobe
2010-Sep-15, 01:55 PM
Another article on current Thorium reactor research:

http://www.wired.com/magazine/2009/12/ff_new_nukes/all/1

The cost difference is what is really exciting:

Uranium reactors make power at a fuel cost of about $50Million /1 GW year or about $0.57 /kw hr (coal is about 1/6 this cost.)

Thorium reactors should make power at about $10,000 /1Gw year or about $0.015 /Kw hr - about 1/10 the cost of coal...

Hey, thanks!

I found this in the article so I googled it: Energy From Thorium (http://energyfromthorium.com/) I have only just started reading on this site so I don't know what it holds. (I see now that Len Moran has this site in Len's post - thanks!)

I was gonna do a college report on energy technologies on the CANDU (http://en.wikipedia.org/wiki/CANDU_reactor) reactor but came across Thorium while reading about CANDU so I am gonna do the report on thorium instead.

Ivan Viehoff
2010-Sep-15, 02:55 PM
Uranium reactors make power at a fuel cost of about $50Million /1 GW year or about $0.57 /kw hr (coal is about 1/6 this cost.
When you calculated that the cost of fuel in a uranium reactor is more expensive than coal, you should have concluded something, ie, that you had an error the calculation. $50m/GW yr = $0.0057/kWh Actually I guess the cost is a little higher than this, because the load factor of a nuclear reactor is perhaps more like 80% than 100%. I suspect that things other than fuel cost will determine which of uranium and thorium reactors would be cheaper in practice.

Glom
2010-Sep-16, 07:10 AM
The drawback is technical in that the thorium cycle is a bit harder to get going. Thorium-232 is not the isotope we want. We want uranium-233. Thorium-232 transmutes to it. So any thorium reactor is a breeder reactor, a more finicky, although ultimately more beneficial technology, than modern light water uranium reactors.

I've forgotten most of what I learned when I started my FFF crusade, but IIRC, thorium reactors have subcriticality issues, which is why accelerator driven systems were being explored by the Indians. ADS's are excellent because they can be used to "incinerate" all sorts of transuranics we have no other use for and would otherwise just sit there as high level waste.

Len Moran
2010-Sep-16, 08:40 AM
The drawback is technical in that the thorium cycle is a bit harder to get going. Thorium-232 is not the isotope we want. We want uranium-233. Thorium-232 transmutes to it. So any thorium reactor is a breeder reactor, a more finicky, although ultimately more beneficial technology, than modern light water uranium reactors.

I've forgotten most of what I learned when I started my FFF crusade, but IIRC, thorium reactors have subcriticality issues, which is why accelerator driven systems were being explored by the Indians. ADS's are excellent because they can be used to "incinerate" all sorts of transuranics we have no other use for and would otherwise just sit there as high level waste.

The article I cited mentioned nothing about subcriticicality as any kind of major issue - that's not to say it isn't of course.

I have to say that the article I referred to in my post presents a compelling (up to date) case for thorium reactors - it was certainly not a media hype type article but I suppose it is possible that they chose only to concentrate on the advantages of Thorium reactors over Uranium in terms of cost, waste, safety and proliferation resistance. Given the importance (and conclusions) of that list, there would have to be very compelling technical reasons for at least not considering a change of direction, but no such technical reasons were especially cited. The major reason cited for a lack of interest concerned the vested interests of the current nuclear power industry, which of course is understandable and to be expected. If there is to be a kickstart for this technology it is going to have to come from goverment so it may well be important for politicians to become familiar with the basic issues between Thorium and Uranium reactors - and those differences seem to me to be pretty important and significant.

Glom
2010-Sep-16, 09:42 AM
Don't get me wrong. Thorium is the future.

A lot of the way nuclear power went was essentially the legacy of the military use of it. It will take time to change direction. First, the old taboo needs to be overcome. Given it's hard enough to build a conventional light water reactor, progressing to newer and better technology is even harder. The nuclear industry needs momentum, but it is hamstrung by the mean people.

whimsyfree
2010-Sep-16, 10:22 AM
The article I cited mentioned nothing about subcriticicality as any kind of major issue - that's not to say it isn't of course.

I have to say that the article I referred to in my post presents a compelling (up to date) case for thorium reactors - it was certainly not a media hype type article but I suppose it is possible that they chose only to concentrate on the advantages of Thorium reactors over Uranium in terms of cost, waste, safety and proliferation resistance. Given the importance (and conclusions) of that list, there would have to be very compelling technical reasons for at least not considering a change of direction, but no such technical reasons were especially cited. The major reason cited for a lack of interest concerned the vested interests of the current nuclear power industry, which of course is understandable and to be expected. If there is to be a kickstart for this technology it is going to have to come from goverment so it may well be important for politicians to become familiar with the basic issues between Thorium and Uranium reactors - and those differences seem to me to be pretty important and significant.

There's no good reason not to use uranium fuel. I've nothing against thorium, but a good part of the interest in it is simply to escape the bad PR that the "mean people" have generated around uranium. A system that relies on "politicians becom[ing] familiar with the basic issues" of advanced technologies for them to be implemented is going to be sluggish at best.

Antice
2010-Sep-16, 10:42 AM
There's no good reason not to use uranium fuel. I've nothing against thorium, but a good part of the interest in it is simply to escape the bad PR that the "mean people" have generated around uranium. A system that relies on "politicians becom[ing] familiar with the basic issues" of advanced technologies for them to be implemented is going to be sluggish at best.

This is not quite true. There are better reasons than to avoid the mean (read anti nuke activist types) people. availability of fuel is a very compelling issue. Thorium is just so abundant that it is generally a waste product that nobody wants. There are litterally garbage dumps full of the stuff. enough to keep the world running for years without even having to mine the stuff.
Uranium is not so easy to obtain anymore. altho there is a goodly amount of "garbage" to burn there too in the form of depleted uranium.

Another reason for a thermal spectrum molten salt reactor is that it can indeed be designed to run on TRU's. The key technology being advocated it not thorium, but molten salt reactors in general.

Here is a blog that has some nice insights into the LFTR advocacy mindset (http://nucleargreen.blogspot.com/2010/09/ansewers-to-douglas-wises-questions.html).

Ronald Brak
2010-Sep-16, 12:04 PM
Uranium is not so easy to obtain anymore.

We have a lot of uranium in Australia and mining companies that are very eager to sell it. Given the stagnation of the nuclear power sector (http://www.world-nuclear-news.org/newsarticle.aspx?id=27665&terms=another+drop+) there is no real reason to expect uranium prices to increase. However, there are people who think that Australia should form a cartel with other low cost producers and force the price of uranium up. I wonder if thorium reactors are being talked up to discourage producers from trying to raise prices. I wouldn't be surprised if this was the goal of some uranium purchasers.

Glom
2010-Sep-16, 02:13 PM
We have a lot of uranium in Australia and mining companies that are very eager to sell it. Given the stagnation of the nuclear power sector (http://www.world-nuclear-news.org/newsarticle.aspx?id=27665&terms=another+drop+) there is no real reason to expect uranium prices to increase. However, there are people who think that Australia should form a cartel with other low cost producers and force the price of uranium up. I wonder if thorium reactors are being talked up to discourage producers from trying to raise prices. I wouldn't be surprised if this was the goal of some uranium purchasers.

Unfortunately, your mean people are insistent you dig up coal *cough* *cough* *black lung* *cough* rather than uranium.

Ronald Brak
2010-Sep-16, 03:07 PM
Unfortunately, your mean people are insistent you dig up coal *cough* *cough* *black lung* *cough* rather than uranium.
Australian mining companies want to sell coal and uranium overseas. Wether or not people overseas will buy coal and/or uranium depends on a variety of factors. But at least our coal companies aren't total climate change denialists. New coal export terminals are being designed to cope with expected sea level rises.

Len Moran
2010-Sep-16, 03:19 PM
....I wonder if thorium reactors are being talked up to discourage producers from trying to raise prices. I wouldn't be surprised if this was the goal of some uranium purchasers.

Well that may or may not be the case, but I think the case for Thorium seems to stand very well on its own feet. The issues of cost, safety, proliferation resistance, waste disposal are all in its favour (well that's how I understand things anyway) - there is real substance to the intrinsic arguments, and whilst those arguments may gain some ground from real or imagined hidden agendas, it doesn't really need them. What perhaps it does need is some political awareness that a choice is being seriously discussed amongst scientists and engineers that could (if acted upon) have real implications for the supply of safe and widespread nuclear power at a cost that could compare with coal. That doesn't seem to be the case today, plants are so very heavily engineered towards preventing accidents that the capital cost is just under twice as much as coal fired plants per watt (1). Thorium reactors seem to have safety as an inherent part of its design mainly because there is no pressurised water - a disruption to the coolant is a leak rather than an explosion.

(1)- MIT study "The future of Nuclear Power (2009)" gives capital costs of coal power as $2.30 per watt verses $4 per watt for light-water nuclear.

xylophobe
2010-Sep-16, 05:09 PM
There's no good reason not to use uranium fuel. ...

There is an excellent reason to avoid uranium: transuranic waste. Since thorium starts out at an atomic weight of 232 then it takes more neutron absorbtions before it enters the transuranic range.

For thorium reactors: The result is less long-lived, hazardous transuranic waste than in a reactor using the uranium-plutonium fuel cycle. (http://en.wikipedia.org/wiki/Thorium_fuel_cycle)

These wastes from uranium reactors necessitate more stringent waste storage requirements that will last for centuries.

xylophobe
2010-Sep-16, 05:45 PM
Fuels with plutonium and thorium are also an option. In these, the neutrons released in the fission of plutonium are captured by Th-232. After this radiative capture, Th-232 becomes Th-233, which undergoes two beta minus decays resulting in the production of the fissile isotope U-233. The radiative capture cross section for Th-232 is more than three times that of U-238, yielding a higher conversion to fissile fuel that that from U-238. Due to the absence of uranium in the fuel, there is no second generation plutonium produced, and the amount of plutonium burnt will be higher than in MOX fuels. However, U-233, which is fissile, will be present in the SNF*. Weapons-grade and reactor-grade plutonium can be used in plutonium-thorium fuels, with weapons-grade plutonium being the one that shows a bigger reduction in the amount of Pu-239. (http://en.wikipedia.org/wiki/Nuclear_transmutation#Fuel_types)

* - Spent Nuclear Fuel (SNF)

Trakar
2010-Sep-17, 12:55 AM
Australian mining companies want to sell coal and uranium overseas. Wether or not people overseas will buy coal and/or uranium depends on a variety of factors. But at least our coal companies aren't total climate change denialists. New coal export terminals are being designed to cope with expected sea level rises.

LOL, "the Irony-age" may be more appropriate than the Anthropocene.

Antice
2010-Sep-17, 05:32 AM
Fuels with plutonium and thorium are also an option. In these, the neutrons released in the fission of plutonium are captured by Th-232. After this radiative capture, Th-232 becomes Th-233, which undergoes two beta minus decays resulting in the production of the fissile isotope U-233. The radiative capture cross section for Th-232 is more than three times that of U-238, yielding a higher conversion to fissile fuel that that from U-238. Due to the absence of uranium in the fuel, there is no second generation plutonium produced, and the amount of plutonium burnt will be higher than in MOX fuels. However, U-233, which is fissile, will be present in the SNF*. Weapons-grade and reactor-grade plutonium can be used in plutonium-thorium fuels, with weapons-grade plutonium being the one that shows a bigger reduction in the amount of Pu-239.

* - Spent Nuclear Fuel (SNF)
The entire SNF issue is easy to solve by going for Molten salts instead of solid fuel bundles. what is being described sounds a lot like a task for the Denatured Molten salt reactor. The main point of these reactors is their ability to turn weapons into start charges for LFTR. As a big bonus they are efficient power producers as well.

Atraveller
2010-Sep-17, 05:43 AM
They shall beat their swords into ploughshares, and their spears into pruning-hooks And their thermonuclear weapons into Liquid Flouride Thorium Reactors.... (don't know how the last bit got missed in the original...:lol:)

whimsyfree
2010-Sep-17, 07:13 AM
availability of fuel is a very compelling issue. Thorium is just so abundant that it is generally a waste product that nobody wants.[/URL].

There is still plenty of Uranium in the world. Australia, for example, mines only a fraction of its known ore bodies. This is because of political reasons. AFAIK there is no crisis of supply in the world Uranium market. Thorium is only about three times as plentiful as Uranium, so it is not wildly abundant as you seem to be suggesting.

I have no idea what you mean by "TRU's".

whimsyfree
2010-Sep-17, 07:22 AM
There is an excellent reason to avoid uranium: transuranic waste. Since thorium starts out at an atomic weight of 232 then it takes more neutron absorbtions before it enters the transuranic range.

For thorium reactors: The result is less long-lived, hazardous transuranic waste than in a reactor using the uranium-plutonium fuel cycle. (http://en.wikipedia.org/wiki/Thorium_fuel_cycle)


What's the big deal about transuranic waste? What makes them so much worse than [sup]231[\sup]Pa? The volume of non-reusuable waste produced by reactor cores is very small. Radioactive elements are very rare and have numerous applications from use as tracers , as reactor fuel, in thermionic/radio-isotope power (eg for deep space probes) etc. If you're that worried about them they can be transmuted in reactors.

Actually transuranics are very rare and valuable, so it is only political restrictions that make them a "waste" problem.

Ronald Brak
2010-Sep-17, 07:39 AM
Actually transuranics are very rare and valuable, so it is only political restrictions that make them a "waste" problem.

Blink. Blink. Processing...

I think what you'll find is a particular element all by itself is often quite valuable. A whole heap of them all mixed up together in a used fuel rod is not so valuable as seperating them out is often quite difficult. And then there is the matter that if Harry Potter were kind enough to grab his magic wand and wave it around and seperate out all used nuclear fuel into its individual elements (in subcritical amounts for the ones that tend to go bang) then this new abundance of pure radioactive materials would drop their price considerrably. For a non-magical example of waste reprocessing you may want to look into France's reprocessing program and see how much it cost them.

Van Rijn
2010-Sep-17, 07:52 AM
Maybe not the best source for information about nuclear reactors, but Ambrose Evans-Pritchard (a reasonably respected economist/columnist) in the UK is a big fan of Thorium

http://www.telegraph.co.uk/finance/comment/7970619/Obama-could-kill-fossil-fuels-overnight-with-a-nuclear-dash-for-thorium.html

Ultimately the point he makes is that uranium reactors got the money and focus on research because of the ability for uranium reactors to yeild weapons grade material as a by product (actually for a while the energy was the by product - weapons material was the objective.)


But he makes some mistakes. For instance:



Thorium is so common that miners treat it as a nuisance, a radioactive by-product if they try to dig up rare earth metals. The US and Australia are full of the stuff. So are the granite rocks of Cornwall. You do not need much: all is potentially usable as fuel, compared to just 0.7pc for uranium.

All the uranium is potentially usable as fuel as well, and U238 already makes an important contribution to the energy production in commercial reactors (it isn't just the .7% of U235 that matters).

And, yes, uranium reactors did get the focus because of weapons research, but commercial reactors are lousy sources for weapons grade plutonium. Countries that want to do that build specialized reactors instead.

I'd like to see more thorium reactor R&D, and think it could be a very important option, but the case isn't as clear-cut as he wants to make it.

Jens
2010-Sep-17, 07:58 AM
And their thermonuclear weapons into Liquid Flouride Thorium Reactors.... (don't know how the last bit got missed in the original...:lol:)

Wow, you're quoting a really old post. What section was that in? :)

Len Moran
2010-Sep-17, 08:43 AM
There is still plenty of Uranium in the world. Australia, for example, mines only a fraction of its known ore bodies. This is because of political reasons. AFAIK there is no crisis of supply in the world Uranium market. Thorium is only about three times as plentiful as Uranium, so it is not wildly abundant as you seem to be suggesting.

I have no idea what you mean by "TRU's".

Just for the record, from the article I am sourcing from - "Thorium is present in the Earths crust at about four times the amount of uranium and it is more easily extractable". Whether the abundance (or not) of uranium is an issue is not fundamental to the apparent advantages of Thorium reactors - the abundance and easier extraction of Thorium is just one factor that adds weight to the case of Thorium. As far as I can tell, of the major concerns regarding nuclear power generation, all are favourable to Thorium. From the point of view of mass introduction (involving economical capital expenditure compared to coal) of nuclear power in years (maybe many years) to come, Thorium seems (on paper) to be idealy suited. There is (in my opinion) enough of an argument to get politicians interested if they have the will to think long term in the way they are (well they say they are) thinking long term in terms of global warming.

xylophobe
2010-Sep-17, 01:16 PM
The problem with uranium (http://pubs.usgs.gov/bul/b2179-a/B2179-A-508.pdf) as a nuclear fuel is the fact that it must be enriched in order to be used in a nuclear reactor. Uranium is fairly abundant but it is mostly U-238 which is fertile but not fissile. Only 0.7% of all natural uranium is U-235 which is what is needed in a nuclear reactor.

The world's supply of U-235 is only about 80 years worth at present consumption levels. If a large-scale switch to nuclear power occurred then that 80-year figure would plummet since the 80-year figure is based upon fossil fuel supplying most of the world's energy needs.

Current usage is about 68,000 tU/yr. Thus the world's present measured resources of uranium (5.4 Mt) in the cost category slightly above present spot prices and used only in conventional reactors, are enough to last for about 80 years. (http://www.world-nuclear.org/info/inf75.html)

Breeder reactors can make all the U-238 into fissile plutonium, Pu-239, which would turn uranium into an almost inexhaustable source of energy ... but Pu-239 is bomb material that is easily handled. This proliferation issue is a main reason that breeders are not greatly implemented. Plutonium in all forms is great bomb material except for Pu-238, which generates so much heat that the weapon would not be stable.

Thorium, on the other hand, converts into U-233 which is fissile but what makes thorium less of a proliferation issue is the fact that U-232 is also produced which makes the enrichment of U-233 very difficult since U-232 is highly radioactive and can kill quickly in small doses of exposure. This would seem like a safety issue but the U-232, along with U-233, can be chemically separated from the thorium and re-introduced into the reactor to be "burned". A thorium reactor does not generate large amounts of plutonium and a thorium reactor can be used to burn plutonium.

The CANDU (http://en.wikipedia.org/wiki/CANDU_reactor) reactor can burn plutonium and natural uranium, including U-238. If thorium reactors never get built then I would recommend that CANDU reactors be implemented in a large-scale fashion. CANDU reactors can also burn thorium.

Van Rijn
2010-Sep-17, 10:03 PM
The problem with uranium (http://pubs.usgs.gov/bul/b2179-a/B2179-A-508.pdf) as a nuclear fuel is the fact that it must be enriched in order to be used in a nuclear reactor.


Not necessarily, as you noted with the CANDU reactor. Also, in the case of thorium, it must be bred to U233 to be used - enrichment isn't an option. There is no (or almost no) fissile material to be had in thorium in the first place.



Uranium is fairly abundant but it is mostly U-238 which is fertile but not fissile. Only 0.7% of all natural uranium is U-235 which is what is needed in a nuclear reactor.


No, as I noted in my previous post, U238 already makes an important contribution in current commercial reactors. I believe the newer designs get about 50% of their energy from plutonium bred from U238. The trend is for designs that breed more fuel, need less refueling, produce less waste, etc.



The world's supply of U-235 is only about 80 years worth at present consumption levels.


The supply of uranium depends on the price (which is not a large part of the cost of running a reactor, so can increase quite a lot without a major effect on the cost of running the reactor) and the efficiency of use. If price were to increase, uranium that is currently not economical to recover would become available, and there would be more incentive to find new ore. Recovery from seawater is also possible at higher prices. There isn't a significant limit on the amount of uranium available to run reactors, but thorium could be more economical in the long run.



Breeder reactors can make all the U-238 into fissile plutonium, Pu-239, which would turn uranium into an almost inexhaustable source of energy ... but Pu-239 is bomb material that is easily handled.


If it is just Pu-239. If there is a significant amount of Pu-240 or Pu-238, it's much more difficult to build an effective bomb. This is why dedicated reactors make more sense for weapons programs.


This proliferation issue is a main reason that breeders are not greatly implemented.


A bigger issue is that it doesn't make economic sense currently. The countries that want to build plutonium bombs have dedicated reactors for it.



Plutonium in all forms is great bomb material except for Pu-238, which generates so much heat that the weapon would not be stable.


Also Pu-240, which leads to an increased chance of premature detonation. This is why dedicated reactors use a fast fuel cycle that isn't reasonable for commercial reactors (and you want to design for long fuel cycles, both for economics, and to minimize the possibility of inappropriate use).



Thorium, on the other hand, converts into U-233 which is fissile but what makes thorium less of a proliferation issue is the fact that U-232 is also produced which makes the enrichment of U-233 very difficult since U-232 is highly radioactive and can kill quickly in small doses of exposure.


Plutonium isotope separation is also very difficult.

I'm not knocking development of thorium technology. I think there are potential advantages in economics and safety, but it isn't as clear cut as some would like.

xylophobe
2010-Sep-18, 02:32 AM
Not necessarily, as you noted with the CANDU reactor. Also, in the case of thorium, it must be bred to U233 to be used - enrichment isn't an option. There is no (or almost no) fissile material to be had in thorium in the first place. ...

Actually these facts that you point out are advantages of thorium since thorium does not require expensive and technologically difficult enrichment processes. This makes thorium considerably cheaper than uranium as a fuel.

It is true that thorium needs a fissile material to initiate the nuclear reaction but this can also be seen as a positive since plutonium can be used and will result in the conversion of the plutonium into less hazardous fission products.


... No, as I noted in my previous post, U238 already makes an important contribution in current commercial reactors. I believe the newer designs get about 50% of their energy from plutonium bred from U238. The trend is for designs that breed more fuel, need less refueling, produce less waste, etc. ...

Thank you for noting this because all nuclear reactors do breed fuel, unless they start out with highly enriched fuel which, I believe, is the case with military reactors on submarines and ships. The problem with the current reactors, which are light-water reactors, is that the fuel is in solid form which can degenerate from both the heat and the radiation. This results in large quantities of nuclear waste which could be reprocessed but reprocessing is an expensive and difficult process - which also happens to be illegal in the U.S.A. So large amount of U-238 are included in the reactor fuel but this also results in larger amounts of nuclear waste.

The thorium reactors can be made with liquid cores that eliminate the possibility of fuel pellet degradation. As a liquid the fuel can also be cleansed of fissile products that are re-introduced into the reactor to complete their burn-up. This liquid feature allows almost the entire fuel load to be utilized which greatly improves efficiency and lowers waste handling/storage problems.


...If it is just Pu-239. If there is a significant amount of Pu-240 or Pu-238, it's much more difficult to build an effective bomb. This is why dedicated reactors make more sense for weapons programs.

A bigger issue is that it doesn't make economic sense currently. The countries that want to build plutonium bombs have dedicated reactors for it.

Also Pu-240, which leads to an increased chance of premature detonation. This is why dedicated reactors use a fast fuel cycle that isn't reasonable for commercial reactors (and you want to design for long fuel cycles, both for economics, and to minimize the possibility of inappropriate use).

Plutonium isotope separation is also very difficult. ...

Yes, plutonium isotope separation is very difficult and necessitates centrifuges but it is not highly radioactive like U-232.

With the thorium fuel-cycle the created U-233 is mixed with U-232 and it makes it necessary to perform the separation remotely. For instance, exposure to a mix of U-233 containing 1% U-232 for 0.04 hours will give the same REM exposure as 610 hours of exposure to reactor-grade plutonium. See U-232 and the Proliferation-Resistance of U-233 in Spent Fuel (http://www.torium.se/res/Documents/9_1kang.pdf).

As far as breeder-reactors converting U-238 the following quote is revealing: Breeder reactors in France and other countries have proven not to be economical, and they may not be competitive economically until at least 2030. (http://pubs.usgs.gov/bul/b2179-a/B2179-A-508.pdf)

One last note since this is a space/astronomy website: there is a lot of thorium on the moon/Mars and since a thorium reactor can be much simpler than a uranium reactor then thorium could be used as a power source to colonize the moon or Mars.

whimsyfree
2010-Sep-18, 05:41 AM
Actually these facts that you point out are advantages of thorium since thorium does not require expensive and technologically difficult enrichment processes. This makes thorium considerably cheaper than uranium as a fuel..

That makes no sense at all. He said (a) uranium can be used without enrichment and (b) it can also be bred into a higher grade fuel and (c) thorium *has* to be bred to make a usable fuel. How is that an advantage to thorium?

geonuc
2010-Sep-18, 09:08 AM
... unless they start out with highly enriched fuel which, I believe, is the case with military reactors on submarines and ships.

Yes.

xylophobe
2010-Sep-18, 02:24 PM
That makes no sense at all. He said (a) uranium can be used without enrichment and (b) it can also be bred into a higher grade fuel and (c) thorium *has* to be bred to make a usable fuel. How is that an advantage to thorium?

Your interpretation of his statement (a) is not true because natural unranium can not be used in a reactor unless it also has a fissile initiator, U-235, in a concentration higher than the natural 0.7% value. Uranium must be enriched to 3-4% U-235 before it can be used as a nuclear fuel with the remaining 96-97% being U-238. Then when the enriched uranium is reacted it breeds Pu-239 (your (b)) from the 96-97% U-238 which increases the power output of the reactor since the reactor can now burn both U-235 and Pu-239. Not all 96-97% of the U-238 is burned, though, because the solid fuel pellets do not retain their integrity (http://en.wikipedia.org/wiki/Nuclear_fuel#Oxide_fuel) long enough to allow this to occur plus there is a once-through (http://en.wikipedia.org/wiki/Nuclear_fuel_cycle#Once-through_nuclear_fuel_cycle)use in effect. Solid fuel also does not allow the core of the reactor to be maintained at a high fissile content since the fissile content can not be refined and re-circulated - solid means the reactor is stuck in its initial state of enrichment, for the most part. By the way the solid fuel pellets (http://en.wikipedia.org/wiki/Nuclear_fuel_cycle#Fabrication)are not 100% uranium - these pellets are ceramic-based.

Even the CANDU reactor (http://en.wikipedia.org/wiki/CANDU)must be started with an enriched fissile material. If reprocessing is allowed and used then the fissile enriching substance can be plutonium such as in MOX (http://en.wikipedia.org/wiki/MOX_fuel).

Your point (c) is an advantage because the atomic mass of Th-232 is lower than U-235 and U-238 which means that a thorium reactor does not create as many dangerous transuranic elements. This advantage also stems from the fact that thorium is basically a pure isotope (http://en.wikipedia.org/wiki/Isotopes_of_thorium)in nature which means it does not need to be enriched and this fact avoids a very expensive process. Plus the fact that a liquid core reactor can be continually recycled means that the uranium by-products can be chemically separated** and re-introduced into the reactor to complete their burn up.

** Chemical separation is much, much easier than isotopic separation. Isotopes (http://en.wikipedia.org/wiki/Isotope) can not be chemically separated since isotopes have the same chemical reactivity with other substances.

whimsyfree
2010-Sep-19, 09:38 AM
Your interpretation of his statement (a) is not true because natural unranium can not be used in a reactor unless it also has a fissile initiator, U-235, in a concentration higher than the natural 0.7% value.


I've never heard of an "unranium" reactor, but CANDU reactors have run on unenriched uranium.


Uranium must be enriched to 3-4% U-235 before it can be used as a nuclear fuel with the remaining 96-97% being U-238.


Wrong. See above.


Then when the enriched uranium is reacted it breeds Pu-239 (your (b)) from the 96-97% U-238 which increases the power output of the reactor since the reactor can now burn both U-235 and Pu-239. Not all 96-97% of the U-238 is burned, though, because the solid fuel pellets do not retain their integrity (http://en.wikipedia.org/wiki/Nuclear_fuel#Oxide_fuel) long enough to allow this to occur plus there is a once-through (http://en.wikipedia.org/wiki/Nuclear_fuel_cycle#Once-through_nuclear_fuel_cycle)use in effect. Solid fuel also does not allow the core of the reactor to be maintained at a high fissile content since the fissile content can not be refined and re-circulated - solid means the reactor is stuck in its initial state of enrichment, for the most part. By the way the solid fuel pellets (http://en.wikipedia.org/wiki/Nuclear_fuel_cycle#Fabrication)are not 100% uranium - these pellets are ceramic-based.

Even the CANDU reactor (http://en.wikipedia.org/wiki/CANDU)must be started with an enriched fissile material.


Where does it say that?


If reprocessing is allowed and used then the fissile enriching substance can be plutonium such as in MOX (http://en.wikipedia.org/wiki/MOX_fuel).

Your point (c) is an advantage because the atomic mass of Th-232 is lower than U-235 and U-238 which means that a thorium reactor does not create as many dangerous transuranic elements. This advantage also stems from the fact that thorium is basically a pure isotope (http://en.wikipedia.org/wiki/Isotopes_of_thorium)in nature which means it does not need to be enriched and this fact avoids a very expensive process.


No, that means it cannot be enriched. It means it must be transmuted. You are being disengenuous. Your argument is like saying being born without legs is an advantage because it avoids the expense of buying $1000 shoes.


Plus the fact that a liquid core reactor can be continually recycled means that the uranium by-products can be chemically separated** and re-introduced into the reactor to complete their burn up.

** Chemical separation is much, much easier than isotopic separation. Isotopes (http://en.wikipedia.org/wiki/Isotope) can not be chemically separated since isotopes have the same chemical reactivity with other substances.

You've posted a lot but none of it supports the claims I challenged.

xylophobe
2010-Sep-20, 03:30 AM
I've never heard of an "unranium" reactor, but CANDU reactors have run on unenriched uranium.

Wrong. See above.

Where does it say that? ...

Yes, you are correct that CANDU reactors can and do run on natural, un-enriched uranium and the CANDU does not require an enriched core - this was my mistake relying on memory only.

Which is why I recommended the CANDU (see post #29 (http://www.bautforum.com/showthread.php/107673-Thorium-Reactors?p=1791976#post1791976)of this thread) if thorium reactors were not implemented.


... No, that means it cannot be enriched. It means it must be transmuted. You are being disengenuous. Your argument is like saying being born without legs is an advantage because it avoids the expense of buying $1000 shoes. ...

I guess we can parse words but the facts that thorium neither can be enriched nor needs to be enriched both point to the same conclusion: that the expensive step of uranium enrichment for fuel processing for LWRs is avoided for thorium reactors.

btw: you spelled "disingenuous" wrong.


...You've posted a lot but none of it supports the claims I challenged.

That makes no sense at all. He said (a) uranium can be used without enrichment and (b) it can also be bred into a higher grade fuel and (c) thorium *has* to be bred to make a usable fuel. How is that an advantage to thorium?

(a) You were correct in pointing out that uranium can be used without enrichment but for commercial reactors natural uranium can only be used in CANDU reactors which total only 56 (http://en.wikipedia.org/wiki/CANDU#Active_CANDU_reactors) out of 438 reactors worldwide.

In April 2001, there were 438 nuclear power plants in the world ... (http://pubs.usgs.gov/bul/b2179-a/B2179-A-508.pdf)

(b) I never stated that U-238 could not be bred into fissile material but I did point out that Breeder reactors in France and other countries have proven not to be economical, and they may not be competitive economically until at least 2030. (http://pubs.usgs.gov/bul/b2179-a/B2179-A-508.pdf)

(c) I have never proposed that thorium does not have to be bred to be fissile - I have tried to explain the process and the need for thorium reactors to have a fissile core in order to initiate the thorium reactor. I also explained the difference between thorium in regards to starting out with an atomic weight of 232 as opposed to uranium which starts out with an atomic weight of 235 & 238 in regard to nuclear wastes. If you need additional information on this difference and why it is advantageous for thorium then feel free to ask.

We can either sit around and wait until 2030 when commercially viable uranium breeder reactors will be available

or

we can go with thorium reactors that have a much smaller facility size, simpler architecture, and inherently safer mode of operation

or

we can build a whole lot of CANDU reactors.

or

we can continue to use fossil fuels and hope they don't run out in our lifetimes.

Antice
2010-Sep-20, 04:23 AM
we can go with thorium reactors that have a much smaller facility size, simpler architecture, and inherently safer mode of operation


This option is hereby seconded. Any objections or should we put it to the vote?

xylophobe
2010-Sep-20, 01:44 PM
So, light water reactors require fuel with an enhanced amount of 235U in the uranium, that is, enriched uranium which generally contains between 3% and 5% 235U by weight (http://en.wikipedia.org/wiki/CANDU#Purpose_of_using_heavy_water)

Because the CANDU reactor was designed to work with natural uranium, CANDU fuel can be manufactured from the used (depleted) uranium found in light water reactor (LWR) spent fuel. Typically this "recovered uranium" (RU) has a U-235 enrichment of around 0.9%, which makes it unusable to an LWR, but a rich source of fuel to a CANDU (natural uranium has a U-235 abundance of roughly 0.7%). (http://en.wikipedia.org/wiki/CANDU#Fuel_cycles)

It is estimated that up to half of the power produced by a standard "non-breeder" reactor is produced by the fission of plutonium-239 produced in place, over the total life-cycle of a fuel load. (http://en.wikipedia.org/wiki/Nuclear_fission#Chain_reactions)

The above three quotes are very revealing about the efficiency of current nuclear reactors at using their total fuel load.

If the LWR reactor starts out with 5% U-235 and at the end of the fuel cycle there is only 0.9% U-235 then that means that 82% of the U-235 fuel is consumed, or 4.1% of the total fuel load. Considering the fact that 3 neutrons are released during the fission of one U-235 atom then it can be realized that an additional 4.1% of the total load represented by U-238 undergoes transmutation (http://en.wikipedia.org/wiki/Nuclear_transmutation) into Pu-239 and is burnt in the reactor. This means that only 8.2% of the total nuclear fuel load is consumed by LWRs - the other 91.8% is relegated to the waste dump.

It is true that a CANDU reactor can use the spent fuel from LWRs but since the number of LWRs greatly exceeds the number of CANDU reactors then this means that the majority is considered waste. This waste can be re-processed into MOX but this is a difficult process and is illegal in the U.S.A.

The thorium reactor as represented by the LFTR (http://en.wikipedia.org/wiki/LFTR) converts almost the entire thorium load into U-233 which is reacted to created energy.

Comparison to ordinary light water reactors (http://en.wikipedia.org/wiki/LFTR#Comparison_to_ordinary_light_water_reactors)

whimsyfree
2010-Sep-23, 09:50 PM
btw: you spelled "disingenuous" wrong.


I'm glad there's something you can get right.



(b) I never stated that U-238 could not be bred into fissile material but I did point out that Breeder reactors in France and other countries have proven not to be economical, and they may not be competitive economically until at least 2030. (http://pubs.usgs.gov/bul/b2179-a/B2179-A-508.pdf)


Where are the economically competitive thorium breeders? What is the evidence that thorium breeding would be economically competitive? At the moment prices for nuclear fuels are depressed by the supply of ex-weapons U-235 and Pu-239. U-233 would be competing in the same market space.

I wish the thorium industry the best but your posts seem like the sort of one-eyed advocacy I see on nutty single-issue websites.

Antice
2010-Sep-24, 06:34 AM
I'm glad there's something you can get right.



Where are the economically competitive thorium breeders? What is the evidence that thorium breeding would be economically competitive? At the moment prices for nuclear fuels are depressed by the supply of ex-weapons U-235 and Pu-239. U-233 would be competing in the same market space.

I wish the thorium industry the best but your posts seem like the sort of one-eyed advocacy I see on nutty single-issue websites.

MSR reactors are cheaper breeders because they use liquid fuels. separating out the breed fissionables from an already liquid state is much easier than when having to reprocess the fuel from a solid fuel bundle. With the market depressed the way it is now with the excess plutonium still affecting the market we can expect breeders to remain uneconomical until the fuel costs at least reach a level that is double the current level. It's not breeding itself that is uneconomical. it is actually the reprocessing that is uneconomical. Any system that makes that step either go away (DMSR) or become as easy as just deflourination and separation is going to win out economically. (LFTR does this btw. IFR the competing technology uses solid fuel and has to pay the full cost of reprocessing in order to achieve a 100% burnup of the fuel)