Energy From Thorium Discussion Forum

It is currently Jun 19, 2018 4:30 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 47 posts ]  Go to page 1, 2, 3, 4  Next
Author Message
PostPosted: Mar 06, 2009 9:26 am 
Offline

Joined: Mar 06, 2009 9:11 am
Posts: 6
Hi everyone,

I am interested in the sustainability thorium-derived energy and was wondering how much uranium or other seed is required in thorium-based LWRs and generation IV reactors which utilize thorium. What is the ratio of uranium/thorium in MSR, AHWR, HTGCR and CANDU reactors for example? Is uranium only required initially in these reactors or will it need to be a constant supply? Excluding accelerator-driven systems is it likely that uranium abundance is actually the limiting factor in the sustainability of thorium as an energy supply?

Thanks for your help,

Jack


Top
 Profile  
 
PostPosted: Mar 06, 2009 11:03 am 
Offline

Joined: Jul 28, 2008 5:01 am
Posts: 462
Location: Teesside, UK
thorium87 wrote:
Hi everyone,

I am interested in the sustainability thorium-derived energy and was wondering how much uranium or other seed is required in thorium-based LWRs and generation IV reactors which utilize thorium. What is the ratio of uranium/thorium in MSR, AHWR, HTGCR and CANDU reactors for example? Is uranium only required initially in these reactors or will it need to be a constant supply? Excluding accelerator-driven systems is it likely that uranium abundance is actually the limiting factor in the sustainability of thorium as an energy supply?

Thanks for your help,

Jack


Lots of threads on here you could look through for information, but:-

MSR - the designs usually discussed here need not use any NEW uranium at all, as theycan be started up on the spent fuel already stored at existing reactors, and thereafter be fed only with thorium. Some simplified designs need extra U to keep going, but much less than conventional PWRs

CANDU - in existing plants, a small feed of U would be required. Modified designs and use of isotope-enriched construction materials could in theory remove the need for this, IF it was considered worth the trouble.

AHWR/HTGCR - hopefully someone else will know!

Welcome to the forum.

Luke


Top
 Profile  
 
PostPosted: Mar 06, 2009 12:21 pm 
Offline

Joined: Mar 06, 2009 9:11 am
Posts: 6
Thanks very much but the reason I ask is that i was reading this paper from the US atomic energy commission (below) and it states in section 4.1 that 'the use of the thorium cycle can lead to reductions in the amount of uranium ore that must be mined for the production of electrical energy; nevertheless the amount and cost of uranium ore required still will be more important than the amount and cost of thorium ore'. Do you think this statement is correct? I have read quite a lot of papers on the potential use of thorium as a sustainable energy supply and this is the first that suggests that uranium abundance might actually be the more important consideration.

http://www.energyfromthorium.com/pdf/WASH-1097.pdf


Top
 Profile  
 
PostPosted: Mar 06, 2009 1:51 pm 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2238
Thorium does not have any fissile isotope as the source of neutrons which are the stuff of a nuclear chain reaction. Uranium alone has a fissile isotope 235U from which other fissile isotopes are produced in a nuclear reactor. That is how uranium is essential for use of thorium fuel. However IF accelerators are available to produce particles of sufficient energy to split neutrons from other neuclii or WHEN sufficient 233U which is produced on absorption of neutrons by thorium is available, the mined uranium shall no longer be necessary for using thorium as fuel.


Top
 Profile  
 
PostPosted: Mar 06, 2009 2:02 pm 
Offline
User avatar

Joined: Aug 21, 2008 12:57 pm
Posts: 1058
The other sources of possible U233 breeding are fusion (fusion/fission hybrid), Light Water Reactor (LWR) Waste, and bomb material via the Lftr.

_________________
The old Zenith slogan: The quality goes in before the name goes on.


Top
 Profile  
 
PostPosted: Mar 06, 2009 2:19 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3066
First, lets be clear that there is AMPLE supply of both u238 and th232 - no possibility of a shortage of either of these EVER.

So, the one nuclide of possible supply concern would be u235.

The LWR's consume u235 in normal operation. For the past decade (or so) excess military fissile stocks have supplied a major portion of current demand. The military supply is diminishing now and the demand is increasing so one should expect an increase in price. There have been shortages of supply but these were related to inadequate mining (and/or processing) rather than a shortage of minerals. There are estimates of the supply of minerals in the world - the better reports will break out how much is available at what price. Obviously, if you are willing to pay more then it becomes economically attractive to extract uranium out of poorer ore. News reports will often just take the current price supply or perhaps double the current price and conclude there is a looming shortage of uranium.

The fuel cost in a nuclear plant is small enough that it could double, and redouble before significantly impacting the cost of electricity produced. So the whole debate about uranium (u235) supply needs more careful thinking than is normally provided.

If you are using thorium as solid fuel in an LWR then indeed you will still need uranium to run the reactor. The thorium will help extend the supply of uranium but it will not reduce it to zero.


If you are using thorium as is normally discussed in this forum then no uranium is used once the reactor has been started. There likely will be significant u235 used in the initial startup to mix with plutonium from SNF. The amount used here just for startup would be something like 1-8 years worth of operating fuel for an LWR. As the fleet gets built out it will generate its own startup fuel.

Some threads on this site (David Leblanc high converter designs) will need fissile make up fuel to keep operating. They use less than LWR's or even thorium assisted LWRs but they do not achieve break even and will need an external source of fissile material. This could be u235 mined and enriched, or it could be pu239 extracted from spent LWR fuel, or it could be u233 from breeding LFTRs. Most likely u235.


Top
 Profile  
 
PostPosted: Mar 06, 2009 3:08 pm 
Offline

Joined: Dec 05, 2008 8:50 am
Posts: 337
thorium87 wrote:
Hi everyone,

I am interested in the sustainability thorium-derived energy and was wondering how much uranium or other seed is required in thorium-based LWRs and generation IV reactors which utilize thorium. What is the ratio of uranium/thorium in MSR, AHWR, HTGCR and CANDU reactors for example? Is uranium only required initially in these reactors or will it need to be a constant supply? Excluding accelerator-driven systems is it likely that uranium abundance is actually the limiting factor in the sustainability of thorium as an energy supply?

Thanks for your help,

Jack



MSRs don't need any fresh uranium to mine because use as fissile start-up the transuranics "waste" still produced by current LWR fleet (something about hundreds or thousands tonns of fissile per GW electric, depending on the design); because it a breeder, that means it produces more fissile fuel (uranium 233 from thorium in this case) than the fissile it consumes (in our case transuranics waste, before producing enough uranium 233), it needs very low quantity of thorium, something less than (depending on the exact thermal efficiency) only one tonn per GWyear of electricity

It's very difficult if not impossible at all to achieve net breeding even with thorium cycle with the other (solid fuel-slow neutrons) technologies you cite; for comparison LWR and CANDU needs something in the range of 150 and 175 tonn of natural uranium per GWyear of electricity, respectively

Kirk' s slides deal deeply with the topic
http://www.energyfromthorium.com/ppt/


Top
 Profile  
 
PostPosted: Mar 06, 2009 3:13 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3066
Alex P wrote:

MSRs don't need any fresh uranium to mine because use as fissile start-up the transuranics "waste" still produced by current LWR fleet (something about hundreds or thousands tonns of fissile per GW electric, depending on the design);


hundreds or thousands of kilograms (not tonnes).


Top
 Profile  
 
PostPosted: Mar 06, 2009 3:19 pm 
Offline

Joined: Dec 05, 2008 8:50 am
Posts: 337
Lars wrote:
Alex P wrote:

MSRs don't need any fresh uranium to mine because use as fissile start-up the transuranics "waste" still produced by current LWR fleet (something about hundreds or thousands tonns of fissile per GW electric, depending on the design);


hundreds or thousands of kilograms (not tonnes).


right, pardon


Top
 Profile  
 
PostPosted: Mar 07, 2009 11:06 am 
Offline

Joined: Mar 06, 2009 9:11 am
Posts: 6
Thanks for all your advice everyone. I'm trying to write a report on the potential sustainability of thorium reserves for long-term energy production and from what i have gathered it definitely sounds like thorium has a lot of potential. Not knowing a huge amount about nuclear reactor design, i am still unsure as to the extent to which u-235 limits the sustainability of energy from thorium.

As i understand it, excluding fusion and accelerators as a neutron source, mined u-235 is needed for start-up but potentially not once the thorium reactor gets going. Will this always be the case or once reactors based on the thorium fuel cycle become developed will they themselves be capable of producing a startup material for future reactors, so eliminating the need for mined uranium in the future.

I realize that thorium has a huge amount of potential but I'm looking at whether it has the potential to meet the worlds future energy needs in the very long term. On this 100's-1000's year timescale I assume existing U-235 from LWR will not be important. Is u-235 abundance therefore definitely more of an issue that thorium abundance (which i do not necessarily agree is limitless)?


Top
 Profile  
 
PostPosted: Mar 07, 2009 11:42 am 
Offline
User avatar

Joined: Dec 19, 2006 11:01 am
Posts: 395
Location: Knoxville, TN
thorium87 wrote:
As i understand it, excluding fusion and accelerators as a neutron source, mined u-235 is needed for start-up but potentially not once the thorium reactor gets going. Will this always be the case or once reactors based on the thorium fuel cycle become developed will they themselves be capable of producing a startup material for future reactors, so eliminating the need for mined uranium in the future.


Actually you need no U235. You can just flourinate spent PWR fuel to remove out all uranium (to feed it back to LWRs), separate fission products, and use the rest: which is a mix of Pu and other minor actinides, for the startup fissile charge.

All nuclear reactors are breeding some nuclear fuel from fertile isotopes. How much new fuel is bred per one fission depends on design. LFTR is proposed to have 2 versions: net-breeder for "safe" countries, and a unity breeders for the others.


Top
 Profile  
 
PostPosted: Mar 07, 2009 1:02 pm 
Offline

Joined: Feb 03, 2009 3:38 pm
Posts: 48
I hope not to speak out of turn here but I likely have a technical perspective closer to the original poster. Please correct me if I am wrong (I know you guys will).

In short, the "net breeder" design makes it possible to create a thorium energy economy that is completely independent from U-235. To get a global thorium energy economy started requires a finite fissile seed that can come from direct enrichment of mined uranium or from a variety of spent nuclear fuels (SNF). This seed needs to be used only once and thereafter, the startup fissile needs for each thorium reactor can come from U-233 in special reactors that are designed to produce more U-233 (from thorium) than it needs to keep running. The quantity of startup seed material from the more limited mined uranium or SNF is a function of how many thorium reactors you want to start before the breeder designs can produce thorium-sourced startup loads. It could be a single reactor and the thorium fuel (U-233 from thorium) manufacturing could start very slowly, or it could be 500 thorium reactors. That is a function of will and likely to be determined by the economics of SNF disposal/reprocessing and mined uranium/enrichment supply.

In less than 100 years, uranium need not be mined or even recycled from spent nuclear fuel (except from thorium breeders) at all. The thorium reactors could be completely disconnected from external uranium sources. This is what's possible. There are many other considerations, technical and political that come into play that hours of reading here can teach you but from a perspective of needed supply for this fuel, it's limited only by how much thorium you can mine. The uranium need involved is finite and transient.

(I too am quite ill educated in the specifics of these matters and as such, probably understand the question better.)


Top
 Profile  
 
PostPosted: Mar 07, 2009 1:52 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3066
thorium87 wrote:
Is u-235 abundance therefore definitely more of an issue that thorium abundance (which i do not necessarily agree is limitless)?


u235 is not a limit for LFTR. It is convenient to help us get going in the early stages. After that, it isn't likely that it will even be used. IMHO one of the advantages of LFTR is that it will eliminate any non-military justification for uranium enrichment and that this far outweighs any proliferation risk one can dream up for a LFTR.

Current thorium reserves estimates are 4e6 tonnes (wikipedia). So we could run 8,000 GWe for 500 years based on what we are already fairly confident of. But one must remember that thus far thorium is in so little demand that it is difficult to justify spending any money looking for it. Second, since we only need 1 tonne to generate 1GWe-year we can afford to pay a fair amount for that 1 tonne. I doubt electricity consumption will decrease significantly if you had to pay 2 cents US per kWhr for the thorium. This translates to US$175 million per tonne (0.02*24*365*1e9/1e3) or US$5000 per ounce. At that price we will find much much more thorium.

But lets dream really BIG, say 30,000 GWe for 1,000 years and we actually run out of economically recoverable thorium (I really, really doubt this). The same reactors can run on u238. We know a bit more about the reserves of uranium simply because u235 has economic value. We mined 40 thousand tonnes in 2007 (http://www.world-nuclear.org/info/inf23.html) which is more than sufficient to supply all 30,000 reactors at todays prices. At $130/kg on 2007 data there are 5.5 million tonnes of uranium (wikipedia). Thorium is generally recognized to be three time more abundant than uranium so a reasonable estimate for low priced thorium (ore costing 0.0015 cents / kWhr) would be around 16.5 million tonnes.

Beyond this, uranium is known to be accessible in seawater if someone were willing to pay $300,000 per tonne. The ocean has 1.3 billion km^3 and contains 3.3mg/m^3 or 3.3 tonnes/km^3 so if we assumed we could recover 1/2 of this we would have 650 million tonnes or 20x the supply of the most extreme deployment I could think of.

In summary, we don't absolutely need u235 and we won't run out of thorium. Our limits will be elsewhere.


Top
 Profile  
 
PostPosted: Mar 07, 2009 6:36 pm 
Offline

Joined: Mar 06, 2009 9:11 am
Posts: 6
Thanks, these last two posts in particular have really helped clear things up, but going back to the original paper which led to my query (section 4.1 in http://www.energyfromthorium.com/pdf/WASH-1097.pdf) do you think that the author is incorrect to suggest it is u-235 which limits the thorium economy's sustainability? If so, is this likely to be due to improvements in technology since 1969 which have removed this dependence?


Top
 Profile  
 
PostPosted: Mar 07, 2009 7:30 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3066
"The use of the thorium cycle can lead to reductions in the amount of uranium ore that must be mined for the production of electrical energy; nevertheless the amount and cost of the uranium ore required still will be more important than the amount and cost of thorium ore. For example, a thorium fueled reactor might require on the order of 0.1 kg ThO2/kWe to provide its initial fertile material requirement compared to about 5-10 times as much uranium ore to provide for its initial fissile fuel requirement."

This statement from section 4.1 is easy to misunderstand. You do need a startup charge of fissile material (true for every reactor). The startup fissile material will cost more than the startup fertile material. This says nothing though about long term operation or about the startup of a large number of reactors. Later in the report section 5.3.3 talks about a breeding ratio of 1.05 to 1.07. In other words, once started the reactor will create more fissile (u233 in this case) than it consumes. Over time, this excess fissile can be used to start up another power plant.

Also, yes this report was written while MSBR was still evolving. From the introduction:
"The design data upon which the review was based are limited, particularly those for the molten salt breeder reactor (MSBR) and for the thorium-fueled light-water cooled reactors. In the case of the MSBR, the system is in a very early experimental stage and detailed design information still must be developed. Thus, the review was based upon a very preliminary design which has been hanging as a result of continuing technical reassessments and developments."


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 47 posts ]  Go to page 1, 2, 3, 4  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group