Energy From Thorium Discussion Forum

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PostPosted: Apr 12, 2011 4:28 am 
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From the web, I have established that thorium is about 3½ times more abundant than uranium, and 0.7% of natural uranium is U 235.

If I take a thorium ore, containing 0.5% thorium and consider that the thorium is 100% Th 232, 200 tonnes would need to be mined to produce 1 tonne of fuel (capable of generating about 1 GWyear of electricity).

From these basics, I can see that to obtain 1 tonne of U 235, to feed a PWR, I would need to mine: (200 x 3.5) ÷ 0.007 = 100,000 tonnes of 'equivalent' uranium ore.

I see the 100,000 tonnes as a minimum, but I can't figure out if, because of lower neutron yield, the need for enrichment and the limited 'burn-up', more ore would need to be mined, to get the equivalent (approx. 1 GWyear) of electricity from a typical U 235 fuelled PWR.

I would greatly appreciate anyones help in this calculation.


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PostPosted: Apr 12, 2011 12:06 pm 
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There are four issues that you might consider.
1) LWR's generally operate around 33% thermal efficiency since they are limited in the high temperature by the pressure of the water. So to generate the same amount of electricity you need to burn around 1/3 more fuel. Note that several gen IV designs are high temp comparable to LFTR and would not suffer this disadvantage.

2) When the fuel is spent there is still around 1% 235U left in it so we do not burn up all the fissile. This means we need about 1/3 more 235U than we would if we burned it up completely.

3) In doing enrichment we do not extract all the 235U. Typical numbers would be 0.2 to 0.3% 235U is left in the tails.

4) Even an LWR does some comversion. Neutron captures in 238U creates 239Pu and some of this gets burned as fissile. So an LWR does create some of its own fuel. By the end of a fuel cycle roughly 1/3 of the fissions are in 239Pu saving how much 235U is needed.

These factors might increase your uranium need by 1/3 or so. If you want to do the job right, you should know the specific machine you are comparing against and find out how much fuel it needs of what enrichment and how often to produce how much energy. The wise calculators are useful to do much of this work.


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PostPosted: Apr 12, 2011 12:41 pm 
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I found this calculator

http://www.wise-uranium.org/nfcm.html

It says for 1 ton of refined U being put into the reactor it is 21,291 tons of waste rock. I did not do any background checking on how they calculate this figure or if it ever cited in analytical papers and such. It should give a ballpark figure to start with.

Nick Cooper


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PostPosted: Apr 12, 2011 12:49 pm 
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Lars wrote:
...

4) Even an LWR does some comversion. Neutron captures in 238U creates 239Pu and some of this gets burned as fissile. So an LWR does create some of its own fuel. By the end of a fuel cycle roughly 1/3 of the fissions are in 239Pu saving how much 235U is needed...


Nicely done. So many people ignore this factor. Most seem to forget that a typical LWR fuel load is 95% to 98% U238. Plenty of U238 for breeding there. Plutonium fission power is about 40% of core power at end of core life for a typical fuel load. So 33% is probably plenty accurate enough for this purpose.


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PostPosted: Apr 12, 2011 2:38 pm 
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Thanks Lars.

I think my best bet is to consider the total fission producte is each case and I have a figure from Kim L. Johnson's website of 1116 kgs and 778 kgs. This will give me (100,000 x 1116) ÷ 778 and then all + 1/3 (from below) = 190,000 tonnes.

Lars wrote:
There are four issues that you might consider.
1) LWR's generally operate around 33% thermal efficiency since they are limited in the high temperature by the pressure of the water. So to generate the same amount of electricity you need to burn around 1/3 more fuel. Note that several gen IV designs are high temp comparable to LFTR and would not suffer this disadvantage.

I forgot about this entirely, so I can add this 1/3 and this is probably conservative.

Lars wrote:
4) Even an LWR does some comversion. Neutron captures in 238U creates 239Pu and some of this gets burned as fissile. So an LWR does create some of its own fuel. By the end of a fuel cycle roughly 1/3 of the fissions are in 239Pu saving how much 235U is needed.

I think I can ignore this, after all, the total 235U + 239Pu comes from the enriched fuel 'load'.


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PostPosted: Apr 12, 2011 3:54 pm 
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No I don't think you can ignore it. The Pu239 comes from all that U238. If it wasn't there, the U235 only fuel cycle would be considerably shorter, and hence you would need at least 1/3 more U235 over the long term, probably more.


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PostPosted: Apr 12, 2011 5:33 pm 
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At current enrichment level and for rough calculations you can figure that the plutonium generated and fissioned just about compensates for the 235U still left in the spent fuel.


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PostPosted: Apr 13, 2011 10:57 am 
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lftrsuk wrote:
From the web, I have established that thorium is about 3½ times more abundant than uranium, and 0.7% of natural uranium is U 235.


I think this statement is quite misleading, the actual number should be there is in the planet 3 or 4 times more thorium than uranium at a certain cost usually considered, say, less than 130 $/kg of raw material mined

Quote:

If I take a thorium ore, containing 0.5% thorium and consider that the thorium is 100% Th 232, 200 tonnes would need to be mined to produce 1 tonne of fuel (capable of generating about 1 GWyear of electricity).

From these basics, I can see that to obtain 1 tonne of U 235, to feed a PWR, I would need to mine: (200 x 3.5) ÷ 0.007 = 100,000 tonnes of 'equivalent' uranium ore.

I see the 100,000 tonnes as a minimum, but I can't figure out if, because of lower neutron yield, the need for enrichment and the limited 'burn-up', more ore would need to be mined, to get the equivalent (approx. 1 GWyear) of electricity from a typical U 235 fuelled PWR.

I would greatly appreciate anyones help in this calculation.


A typical LWR or HWR is not fuelled by uranium 235 only but a mixture of 235-238, i.e. low enriched uranium or natural uranium (in HWR/Candu), about 30 to 50% of nuclear heat actually comes from U-238 not U-235 (the higher figure in Candus)

Rougly, you can consider it takes ~ 200 ton of natural uranium to fuel a typical GWe of LWR or Candu, and one tonn of natural thorium (or natural uranium) to fuel a thorium MSR breeder (or a fast breeder reactor), I do note you can have a breeding cycle with thorium without fast spectrum neutrons, unlike uranium - the fission of one gram of nuclear fuel in every case produces about one MWday of heat. I don't know if this can help


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PostPosted: Apr 13, 2011 11:34 am 
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lftrsuk wrote:
From the web, I have established that thorium is about 3½ times more abundant than uranium, and 0.7% of natural uranium is U 235.

If I take a thorium ore, containing 0.5% thorium and consider that the thorium is 100% Th 232, 200 tonnes would need to be mined to produce 1 tonne of fuel (capable of generating about 1 GWyear of electricity).

From these basics, I can see that to obtain 1 tonne of U 235, to feed a PWR, I would need to mine: (200 x 3.5) ÷ 0.007 = 100,000 tonnes of 'equivalent' uranium ore.

I see the 100,000 tonnes as a minimum, but I can't figure out if, because of lower neutron yield, the need for enrichment and the limited 'burn-up', more ore would need to be mined, to get the equivalent (approx. 1 GWyear) of electricity from a typical U 235 fuelled PWR.

I would greatly appreciate anyones help in this calculation.

There is no similarity between fissile U235 and fertile Th232. The Th232 is a different fertile from U238. It requires more fissile than U238 to create a reactor fuel. Then it also creates more U233 than Pu239. U233 is in some ways a better fissile than Pu239. U238, on the other hand, is also fissionable with fast neutrons.
Thorium fuel is a good follow up to uranium if you have managed your fissile material well.


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PostPosted: Apr 14, 2011 7:26 am 
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Alex P wrote:
Rougly, you can consider it takes ~ 200 ton of natural uranium to fuel a typical GWe of LWR


I am only considering LFTRs Vs LWRs, so if the 200 tonnes supplies 1 GW of electricity for 1 year, then all of the 'internal goings-on' and systems efficiencies are irrelevant and the calculation becomes: 200 x 200 x 3½
= 140,000 tonnes.

Am I understanding you correctly?


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PostPosted: Apr 14, 2011 10:31 am 
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http://www.wise-uranium.org/nfcmf.html

Using the defaults it says 168,000 tonnes of ore mined to generate 200 tonnes of uranium.


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PostPosted: Apr 15, 2011 3:25 pm 
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lftrsuk wrote:
Alex P wrote:
Rougly, you can consider it takes ~ 200 ton of natural uranium to fuel a typical GWe of LWR


I am only considering LFTRs Vs LWRs, so if the 200 tonnes supplies 1 GW of electricity for 1 year, then all of the 'internal goings-on' and systems efficiencies are irrelevant and the calculation becomes: 200 x 200 x 3½
= 140,000 tonnes.

Am I understanding you correctly?


I don't really understand your math, particurally why you multiply x 3,5...anyway to produce a GWyear of electricity in a LWR (or Candu) it takes 200 tons of natural uranium or one ton of thorium in a LFTR thorium breeder (or one tonn of uranium, even depleted uranium, in a fast breeder). Assuming an ore grade of 0,5% as you guess, but today there are uranium mines down to even 350 ppm, in the first case (enriched uranium in a LWR or natural uranium in a Candu) you have to mine about 40,000 tons of mine rocks or 200 tons of rocks in the case of thorium LFTR (or fast breeders for the uranium counterpart)


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PostPosted: Apr 16, 2011 5:44 am 
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Please see previous discussion for further calculations and information:

viewtopic.php?f=39&t=2757

40,000 tons of rock for low grade ore in light water reactor is much better than 4,000,000 tons of coal+rock (decent 50% coal seam versus rock grade). 100x less mining. Coal plant also makes 200,000 tons of heavy metal contaminated ash that has to be guarded forever, versus 40 tons of spent fuel for the light water reactor that is valuable as startup for LFTR fissile and fission products are also valuable. All you have to do is wait a couple of centuries. Contrast to coal waste which stays toxic forever and is not economical to mine for valuables ever. (heavy metals not very valuable, volume is huge). We're not even talking about the thousands of tonnes of ash that end up going out of the chimney WITH the most advanced electrostatic precipitators. Not to mention the fact that the tiniest most carinogenic particles mostly go right through those filters. Or the 8 million tons of CO2 produced every year. This is 250 kg of CO2 going to our good Lord every SECOND. Imagine throwing a large car into the atmosphere every 8 seconds. Engineers are talking about moving that 250 kg/second stream under the ground. Unfortunately wiping 250 kg of CO2 per second under the carpet turns out to be really hard, you need a really big carpet, and even then it is likely very risky. Imagine a trillion pounds of CO2 sitting below ground under extreme pressure. A trillion. 1,000,000,000,000 pounds.


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PostPosted: Apr 22, 2011 4:01 am 
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India has more than 300,000tons of thorium in Monazite sands containing 4-10% thorium. It also has the world's only research reactor (KAMINI) currently functioning on Th-U233 cycle. It also has an AHWR design using thorium fuel awaiting construction. It could still be beaten in deployment of thorium fueled power reactors by someone with better access to fissile material, like China.
Thorium ore is only one of the factors in production of energy from thorium.


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PostPosted: Apr 22, 2011 9:40 am 
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lftrsuk wrote:
From the web, I have established that thorium is about 3½ times more abundant than uranium, and 0.7% of natural uranium is U 235.

If I take a thorium ore, containing 0.5% thorium and consider that the thorium is 100% Th 232, 200 tonnes would need to be mined to produce 1 tonne of fuel (capable of generating about 1 GWyear of electricity).

From these basics, I can see that to obtain 1 tonne of U 235, to feed a PWR, I would need to mine: (200 x 3.5) ÷ 0.007 = 100,000 tonnes of 'equivalent' uranium ore.

I see the 100,000 tonnes as a minimum, but I can't figure out if, because of lower neutron yield, the need for enrichment and the limited 'burn-up', more ore would need to be mined, to get the equivalent (approx. 1 GWyear) of electricity from a typical U 235 fuelled PWR.

I would greatly appreciate anyones help in this calculation.



Note that the assumption of the 1 tonne of thorum per GW is the theoretical minimum. It's not clear that all of the thorium can be recycled without losses or eventually the need to discard the thorium because of the buildup of isotopes that are just too hard to separate from thorium. The ORNL MSBR design just assumed that the salt/thorium would be replaced on a 5 year cycle. My calculation on the thorium feed rate for the MSBR single fluid design was 6 tonnes per GWe-year. Still much better than once-through LWRs which use approximately 200 tonnes of uranium per year.

The once-through system might be superior in this regard in that the difficult to separate isotopes (primarily the lanthanides) may not have as much of an impact. I've looked at ORNL-4528, but didnt see the blanket salt discard rates. As some point they will compete with the thorium and will reduce the Th-232 capture rate and hence the U-233 production.

Economics will likely drive the amount of thorium used per GWe. At some point it may be too costly to clean up the salt versus discarding it. A up-to-date design study is needed, particularly taking into account that we will likely not need to optimize the system for breeding.


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