India and Thorium reactors progress

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I understand India has some of the world's largest supply of thorium, and that thorium reactors are the fast breeder type.

How close is India to building a commercial thorium reactor and what other nations would benefit from thorium fission?
 

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  • #2
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that thorium reactors are the fast breeder type.
Actually, they are thermal breeders. This is what is unique about the U-233/Th-232 fuel cycle: unlike plutonium, you can achieve a positive breeding ratio (that is, a net increase in fissile atoms) with thermal (cold) neutrons. In India's nuclear program, they are designing heavy-water reactors (like CANDUs) to run on thorium. This is the "Advanced Heavy Water Reactor" (AHWR) design; I'm not sure how far advanced it is, but they have not built any yet. However, they have tried thorium fuel (partially) in existing HWRs, and they operate a pure-U233 research reactor (KAMINI), so there is substantial progress. According to information from India's nuclear power agency:

http://www.dae.gov.in/publ/3rdstage.pdf [Broken]

You may have been confused because they are separately developing a fast breeder program (the plutonium fuel cycle). This is further advanced; they are already building a commercial-scale, 500 MW sodium reactor.
 
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  • #3
mgb_phys
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Isn't the problem with a thorium reactor that it doesn't produce Pu?
 
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Astronuc
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Isn't the problem with a thorium reactor that it doesn't produce Pu?
The reduction of Pu and transplutonic elements is considered beneficial from a recycling and proliferation issue.

In one significant respect U-233 is better than uranium-235 and plutonium-239, because of its higher neutron yield per neutron absorbed. Given a start with some other fissile material (U-233, U-235 or Pu-239) as a driver, a breeding cycle similar to but more efficient than that with U-238 and plutonium (in normal, slow neutron reactors) can be set up. (The driver fuels provide all the neutrons initially, but are progressively supplemented by U-233 as it forms from the thorium.) However, there are also features of the neutron economy which counter this advantage. In particular the intermediate product protactinium-233 (Pa-233)a is a neutron absorber which diminishes U-233 yield.
Thorium fuel has been demonstrated in the Shippingport reactor.

More at - http://www.world-nuclear.org/info/inf62.html

Thorium fuel cycle — Potential benefits and challenges - http://www-pub.iaea.org/MTCD/publications/PDF/TE_1450_web.pdf
 
  • #5
mgb_phys
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The reduction of Pu and transplutonic elements is considered beneficial from a recycling and proliferation issue.
Unless you have nuclear armed neighbours on both sides of you that you have been more or less at war with for the last 50years
 
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Astronuc
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Unless you have nuclear armed neighbours on both sides of you that you have been more or less at war with for the last 50years
I think India already has a viable nuclear weapons program from their PHWR. One only needs a few production reactors. Each single Pu weapon needs on the order of 10 kg, so 1 MT provides about 100 warheads. These can be in the kT range or enhanced to MT range with the appropriate thermonuclear package.

IIRC, the US and Russia each have about 50 to 60 MTHM of highly enriched (WG) U and Pu. A lot of WGU has been downblended and is being consumed in US reactors. There is a plan to dispose of the WGPu by downblending it and consuming it in LWRs as MOX.

Besides, I seem to remember that one can make a nuclear weapon from U-233, but that Pu-239 is more optimal.
 
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mgb_phys
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Yes I was rather cynically assuming that India's nuclear program was to fuel weapons development rather than to meet it's power needs.
I suppose if it has a lot of thorium but no uranium reserves it might be a good strategic move. They are busy doing a deal with Canada to buy uranium - their earlier dealings having been forgiven.

You should be able to make a device with U233 - so it's possibly more of a proliferation risk than the more optimal but trickier Pu. Don't know if a U233 gun is as simple as a U235 - but everybody attempting a Uranium gun device seems to have got it right first time.
 
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Astronuc
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Yes I was rather cynically assuming that India's nuclear program was to fuel weapons development rather than to meet it's power needs.
I suppose if it has a lot of thorium but no uranium reserves it might be a good strategic move. They are busy doing a deal with Canada to buy uranium - their earlier dealings having been forgiven.
I believe they have a lot more thorium and little uranium or perhaps poor quality U. The thorium fuel cycle requires a fissile driver. In the Shippingport fuel, the thorium was mixed with U-235. The U-235 was necessary to provide the initial fissions. Over time, Th-232 is converted to U-233, and then U-233 becomes the principle fission material.

You should be able to make a device with U233 - so it's possibly more of a proliferation risk than the more optimal but trickier Pu. Don't know if a U233 gun is as simple as a U235 - but everybody attempting a Uranium gun device seems to have got it right first time.
Pu systems are smaller and yields higher (better for multiple (cluster) warhead systems), and they make for better triggers for thermonuclear weapons.
 
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mgb_phys
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Pu systems are smaller and yields higher (better for muliple (cluster) warhead systems), and they make for better triggers for thermonuclear weapons.
True for an advanced nuclear program like India's.
I was just thinking that Pu is regarded as the proliferation risk while for an 'unofficial' nuclear power U 235 is a lot easier - and I'm guessing that fissile U233 is similair.
 
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I see that Thorium is 3x more plentiful than uranium


are there other fertile element more plentiful than uranium?
 
  • #11
Astronuc
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I see that Thorium is 3x more plentiful than uranium


are there other fertile element more plentiful than uranium?
Thorium and uranium are it. They are the only elements which have very long half-life isotopes Th-232 and U-238, which can produce fissile isotopes with neutron absorption (and subequent beta decays), U-233 and Pu-239, and U-235 which is fissile and has a relatively long half-life. Heavier isotopes are more radioactive, i.e. have shorter half-lives and have decayed away long ago. Elements from Bi up through Ac are radioactive, or do not have fertile isotopes. Bi-209 is considered stable (the only stable isotope of Bi), although there is some experimental evidence that it has a very long half-life >> Th232 or U238.
 
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Thorium and uranium are it. They are the only elements which have very long half-life isotopes Th-232 and U-238, which can produce fissile isotopes with neutron absorption (and subequent beta decays), U-233 and Pu-239, and U-235 which is fissile and has a relatively long half-life. Heavier isotopes are more radioactive, i.e. have shorter half-lives and have decayed away long ago. Elements from Bi up through Ac are radioactive, or do not have fertile isotopes. Bi-209 is considered stable (the only stable isotope of Bi), although there is some experimental evidence that it has a very long half-life >> Th232 or U238.
thanks. So India is nearest to a working Thorium reactor? thanks in advance
 
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Astronuc
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thanks. So India is nearest to a working Thorium reactor? thanks in advance
The US has already done thorium fuel in the Shippingport PWR, and there are academics who have done work in this area. I believe the Russians, and perhaps Chinese, have looked at it.

Indian Point 1 was supposed to use thorium fuel, which it did in the first core. But apparently it didn't work as expected, and the plant was subsequently shutdown in October 31, 1974 because of a number of technical problems (not related to thorium).
http://www.americanscientist.org/issues/feature/thorium-fuel-for-nuclear-energy/1

India is perhaps farthest along in commercial implementation. US, Russia and China have adequate resources to use the more conventional enriched U in LWRs. Canada, of course, has CANDU, heavy water plants that use natual or slightly enriched U in UO2.


This might be of interest - http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/radser.html
 
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mgb_phys
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I also, believe that Am-242m can be added to the list of fissionable materials.
But not really a practical fuel, you have to make it from Pu
 
  • #16
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You're right, it is not a primary energy source. However, it could be potentially used to fuel a reactor, and certainly counts when listing fissile material.
 
  • #17
mheslep
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You should be able to make a device with U233 - so it's possibly more of a proliferation risk than the more optimal but trickier Pu. Don't know if a U233 gun is as simple as a U235 - but everybody attempting a Uranium gun device seems to have got it right first time.
The problem with U233 is that it has a hard gamma emitter somewhere in its decay chain, so anyone attempting to make a weapon out of it is likely going to dangerously expose themselves and certainly give the weapon reliability problems. So while this likely rules out U233 use for a large weapons program by a nation, it might not be hard roadblock for a one bomb terrorist group.

Edit: I see that emitter is Tl 208 - all detailed in the IAEA paper Astronuc linked to:
https://www.physicsforums.com/showpost.php?p=2460821&postcount=4
 
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  • #18
Astronuc
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I know that there are also some academics in Canada working with the thorium cycle, but since we have so much uranium there is no immediate interest in it.

I also, believe that Am-242m can be added to the list of fissionable materials. For example: http://www.iop.org/EJ/article/1742-...quest-id=e14e4fcc-183b-4d8b-87ea-81bfaedcd770
Am-242m is not practical for commercial fuel because of it's radioactivity and that of the other transuranics. The trans-Pu isotopes are problematic for MOX fuel made from recycled/reprocessed commercial fuel.

To use U-233 for a weapon, it would have to be 'cleaned' during the Thorex process.
 
  • #19
mheslep
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To use U-233 for a weapon, it would have to be 'cleaned' during the Thorex process.
As a practical matter, I have no doubt that is true for the reasons stated above. But would it be true for a small group of fanatics who got their hands 10kg?
 
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Astronuc
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As a practical matter, I have no doubt that is true for the reasons stated above. But would it be true for a small group of fanatics who got their hands 10kg?
It would not be practical for a small group of fanatics to steal spent fuel. Any spent fuel whether UO2, ThO2, or MOX would have to reprocess the oxide, separate the fission products and non-fissile fuel, and convert the U-235, Pu-239, or U-233 to metal. That's not a garage or kitchen type of operation.

Deliberately making Pu-239 or U-233 optimally for weapons use requires another deliberate approach.
 
  • #21
mheslep
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It would not be practical for a small group of fanatics to steal spent fuel. Any spent fuel whether UO2, ThO2, or MOX would have to reprocess the oxide, separate the fission products and non-fissile fuel, and convert the U-235, Pu-239, or U-233 to metal. That's not a garage or kitchen type of operation.

Deliberately making Pu-239 or U-233 optimally for weapons use requires another deliberate approach.
I am not sure I follow that argument on spent fuel, as I don't know that 'spent' addresses all of the scenarios. These proposed reactor designs based on fertile fuels, whether Th or U-238, require, by their nature, a fissionable charge (U-233/235) at least at start-up if not continuously. So it seems at least at start-up, and perhaps for sometime thereafter, concentrated fission material could be obtained given uninterrupted access to the reactor. Now, for the reactor the fuel could be (would be?) in the form of an oxide. Is it the case that weapons can only be made from metals, i.e. oxygen somehow impedes the fast spectrum chain reaction? I'm still exploring my earlier premise that, even if someone got their hands on the U-233 charge, they probably could not make a weapon from it.
 
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Astronuc
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I am not sure I follow that argument on spent fuel, as I don't know that 'spent' addresses all of the scenarios. These proposed reactor designs based on fertile fuels, whether Th or U-238, require, by their nature, a fissionable charge (U-233/235) at least at start-up if not continuously. So it seems at least at start-up, and perhaps for sometime thereafter, concentrated fission material could be obtained given uninterrupted access to the reactor. Now, for the reactor the fuel could be (would be?) in the form of an oxide. Is it the case that weapons can only be made from metals, i.e. oxygen somehow impedes the fast spectrum chain reaction? I'm still exploring my earlier premise that, even if someone got their hands on the U-233 charge, they probably could not make a weapon from it.
The O would absorb neutrons and reduce the density of the fissile material, thus one would need a much greater mass for criticality.

In a commercial reactor (LWR), the fuel has a specific composition and geometry. In a Th cycle, U233 or U235 would be diluted in Th232, so even fresh fuel would have to processed to increase enrichment. I would expect enrichment would be on the order of 5% or so, much like conventional LWR fuel.
 
  • #23
mheslep
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The O would absorb neutrons and reduce the density of the fissile material, thus one would need a much greater mass for criticality.
I see, thanks.

In a commercial reactor (LWR), the fuel has a specific composition and geometry. In a Th cycle, U233 or U235 would be diluted in Th232, so even fresh fuel would have to processed to increase enrichment. I would expect enrichment would be on the order of 5% or so, much like conventional LWR fuel.[/QUOTE]In at least two of the concepts I know of, the U-233 or 235 is kept concentrated and separated from the fertile fuel.

See for instance the travelling wave reactor concept here:
http://intellectualventureslab.com/?p=21 at 25s.
The orange ball is a fission ready charge to start the reactor. The intent is that it is small amount and is depleted rapidly. The remaining fuel in green is either unrefined Th or U which is bred into Pu and immediately fissioned.

The liquid thorium fluoride reactor concept also maintains U-233 separate from the Th.
 
  • #24
Astronuc
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See for instance the travelling wave reactor concept here:
http://intellectualventureslab.com/?p=21 at 25s.
The orange ball is a fission ready charge to start the reactor. The intent is that it is small amount and is depleted rapidly. The remaining fuel in green is either unrefined Th or U which is bred into Pu and immediately fissioned.

The liquid thorium fluoride reactor concept also maintains U-233 separate from the Th.
I've been meaning to write more about TWR, particularly the physics involved. Frankly, I don't see it being a commerical concept.

In a ThF reactor, I don't see a commerical type system being established where in the fissile match is separate from the fertile material.
 
  • #25
Astronuc
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It doesn't appear to me that the intellectualventureslab's simulation addresses the real physics of irradiated fuel. The problem is that fission productions represent most of the natural elements with their various properties, e.g., fission gases Xe, Kr, which would migrate upwards, volatiles like Cs, I, Rb and others which would similarly migrate upward, and the various metals. The redistribution of radionuclides changes the spatial nuclear characteristics - as well as thermophysical properties.

Furthermore, the fission process doubles the volume, so depending on how efficient the process is, the internal volume must increase. I'd like to the calcs on the TWR for say increasing the internal volume by 5 or 10%. If they get a huge amount of fissions, maybe they need to consider 20-30% increase in volume of the spent fuel. In a sealed system, this would produce significant stress on the core containment/pressure vessel.

From that simulation, I don't see how they transfer heat from the core, and keep the fuel temperatures within current limits, which do not allow fuel melting under abnormal events.
 

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