Questions About LFTR - Uranium 233 & Gamma Rays

[QuantumPion]

Actually they went with reactors that bread plutonium because that also produced materials for bombs. Some of the scientists on the Manhattan project such as Eugene Wigner and Alvin Weinberg actually advocated that the thorium fuel cycle be used.

My point was that they could have produced U-233 from thorium for bombs, except that they didn't have a source of HEU or Pu to seed a thorium reactor to start with. So they went with Pu breeding, because that can be done with natural uranium. And once they had worked out how to do Pu breeding, even though they now had fissile material to potentially switch over to U-233 breeding, there was little reason to do so. If Oak Ridge had been able to produce enriched U-235 before they worked out how to breed Pu, they very well may have gone the thorium breeding route instead.

 

[nikkkom]

any reactor design that includes on-site reprocessing will have reduced or even eliminated spent fuel disposal issues.

But added issues with having a small reprocessing plant at *every* reactor. Reprocessing plant is not an easy thing to build and maintain - ask Brits or US.

And you still have to dispose of fission products. They aren't in the fuel anymore (if your reprocessing plant works well), but they still exist.

 

[mheslep]

But added issues with having a small reprocessing plant at *every* reactor. Reprocessing plant is not an easy thing to build and maintain - ask Brits or US.

True, though a major concern with reprocessing spent uranium fuel is that it is unavoidably also a plutonium factory. This is not the case with a thorium cycle reactor, which produces negligible plutonium.

And you still have to dispose of fission products. They aren't in the fuel anymore (if your reprocessing plant works well), but they still exist.

Also true, but again with a thorium reactor the fission products are not mixed in with long half-life uranium actinides made via neutron capture. The radiotoxicity of the fission products alone decays in a ~hundred years to a point requiring ten thousand years for the same level in uranium actinides.

 

[nikkkom]

True, though a major concern with reprocessing spent uranium fuel is that it is unavoidably also a plutonium factory. This is not the case with a thorium cycle reactor, which produces negligible plutonium.

I'm not talking about security or proliferation concerns. The technical challenges of building reprocessing plant are bad enough per se.

British plant has repeated bad leaks.
Japanese plant has problems with vitrification equipment. Years and years behind schedule. Not operational yet.
Not-yet-completed US plant is horribly expensive, took more than a decade to build, and is not even a real, full-cycle reprocessing plant - it can't reprocess real reactor fuel, it will only vitrify existing Hanford waste.

Now imagine this saga repeating at every reactor site.

 

[mheslep]

I'm not talking about security or proliferation concerns. The technical challenges of building reprocessing plant are bad enough per se.

The two issues are not separable in spent uranium processing; that is, one would have hard time pointing to a significant piece of a spent uranium reprocessing plant design and say it is not influenced by the need to account for and secure every mg of plutonium or other uranium actinides in the spent fuel. Such plants also must accommodate the routine transportation of spent and reclaimed fuel, another challenge not required of the closed loop recycling likely to be used in an MSR.

...
Not-yet-completed US plant is horribly expensive, took more than a decade to build, and is not even a real, full-cycle reprocessing plant - it can't reprocess real reactor fuel, it will only vitrify existing Hanford waste.

Now imagine this saga repeating at every reactor site.

I grant processing is a challenging chemical problem, but the cost and schedule problems you cite here are largely driven by the security, proliferation, and long-term waste issues inherent in spent uranium.

 

[nikkkom]

The two issues are not separable in spent uranium processing; that is, one would have hard time pointing to a significant piece of a spent uranium reprocessing plant design and say it is not influenced by the need to account for and secure every mg of plutonium or other uranium actinides in the spent fuel. Such plants also must accommodate the routine transportation of spent and reclaimed fuel, another challenge not required of the closed loop recycling likely to be used in an MSR.

Here is one "small" issue (not related to actinides) you need to deal with in any reprocessing plant:

You need to store and transport fission products. Freshly cast stainless stell containers with vitrified waste at French La Hague reprocessing plant emit 1500000 R/h on contact to the outer canister's surface. Almost all of it coming from fission products, not actinides. That's enough to deliver lethal dose to a nearby human in seconds.

And this waste comes from fuel cooled-down for at least 3-4 years. Waste from operating reactor will be *much worse*.

Do you want to tell me that handling THIS type of material is not a significant challenge?

 

[mheslep]

You need to store and transport fission products. ...

Why is that unique to anything? Clearly, storage of fission products in spent fuel is not unique to reprocessing, but is necessary for every once-through power reactor in existence, either via storage pools or caskets or both. And I don't know that any long distance *transportation* of fission products would ever be required a thorium fueled reactor.

For instance: Connecticut Yankee waste storage

Such a facility would be completely inadequate for storing separated plutonium.

 

[mheslep]

And this waste comes from fuel cooled-down for at least 3-4 years. Waste from operating reactor will be *much worse*.

As is the waste when its first removed from the core and placed in a pool, in *any* reactor. Yet current reactors handle a very hot gamma emitter, N-16 (page 7-7), in all of the primary cooling plumbing.

 

[Astronuc]

As is the waste when its first removed from the core and placed in a pool, in *any* reactor. Yet current reactors handle a very hot gamma emitter, N-16 (page 7-7), in all of the primary cooling plumbing.

That's among the reasons why no one goes in containment when the reactor is at power. The control room is outside of containment. Other than the pumps, some valves (which usually sit open or closed), control systems and movable instruments (control elements are usually parked out of reactor for PWRs, or infrequently (or rather periodically) moved in-core for BWRs), the reactor has no moving parts. A waste treatment plant is actually a bit more complicated.

N-16 is a more significant issue for BWRs, since it can be transported to the steam turbine, and that can restrict access to the balance of plant if the activity is too high.

A waste treatment plant is actually more complicated than a nuclear reactor, and part of that is the necessary remote handling, particularly for maintenance and repair, and troubleshooting.

 

[Astronuc]

Why is that unique to anything? Clearly, storage of fission products in spent fuel is not unique to reprocessing, but is necessary for every once-through power reactor in existence, either via storage pools or caskets or both. And I don't know that any long distance *transportation* of fission products would ever be required a thorium fueled reactor.

Ultimate storage of spent fuel or high level waste (fission products) is the more or less the same issue. Away-from-reactor storage in a centralized geologic repository is the goal - either way.

 

[mheslep]

Ultimate storage of spent fuel or high level waste (fission products) is the more or less the same issue. Away-from-reactor storage in a centralized geologic repository is the goal - either way.

Same issue? The waste from the U-235 reactors produces radioisotopes with 10,000 year half-lives or more. In a thorium reactor such as the LFTR (thread topic), theoretically the half-lives are a ~hundred years (see chart post #33) , which would not require geologic time scale storage, nor security for the storage designed around proliferation concerns.

 

[Astronuc]

Same issue? The waste from the U-235 reactors produces radioisotopes with 10,000 year half-lives or more. In a thorium reactor such as the LFTR (thread topic), theoretically the half-lives are a ~hundred years (see chart post #33) , which would not require geologic time scale storage, nor security for the storage designed around proliferation concerns.

I'm looking at the radiotoxicity of the fission products. I do believe the policy is to place the f.p. in a geologic repository in a remote and geologically stable location, rather than leave them parked on the surface for millennia.

 

[nikkkom]

Why is that unique to anything? Clearly, storage of fission products in spent fuel is not unique to reprocessing, but is necessary for every once-through power reactor in existence

Not the same thing. In today's reactors, fuel is not disassembled, it is merely moved from reactor to storage pool and then to dry storage. Almost all radioactivity is still behind two physical barriers: insoluble ceramic fuel, and cladding.

During reprocessing, these barriers do not exist, and several streams of much more volatile (liquid and gaseous) material appear.

 

[nikkkom]

As is the waste when its first removed from the core and placed in a pool, in *any* reactor.

In LFTR, you can't place anything "in a pool". The fuel is not in a suitable form for that - it is not an insoluble ceramic inside hermetically sealed metal tubes.

 

[nikkkom]

Same issue? The waste from the U-235 reactors produces radioisotopes with 10,000 year half-lives or more. In a thorium reactor such as the LFTR (thread topic), theoretically the half-lives are a ~hundred years (see chart post #33) , which would not require geologic time scale storage, nor security for the storage designed around proliferation concerns.

Are you claiming that U-233 fissions do NOT produce Tc-99? Cs-135? I-129? That's quite a claim.

 

[mheslep]

Are you claiming that U-233 fissions do NOT produce Tc-99? Cs-135? I-129? That's quite a claim.

What I assert is what has been measured and illustrated in the chart above, that the total radiotoxicity of all fission products and actinides for a thorium reactor becomes 10⁴ less than that of a U-235 reactor within hundreds of years, dropping below that of natural uranium. This includes weak beta emitters like Tc-99 because they are weak, or trace products in the case of Cs-135 because they are trace, on the order of 10³ less prevalent than Cs-137.

 

[mheslep]

I'm looking at the radiotoxicity of the fission products. I do believe the policy is to place the f.p. in a geologic repository in a remote and geologically stable location, rather than leave them parked on the surface for millennia.

The only geologic storage policy in existence is that for U-235 products and actinides. Nuclear medical waste is not destined for the like of Yucca mountain. In this thread we're discussing thorium reactors, i.e. U-233 waste. The radiotoxicity falls below that of natural uranium on the order of hundreds of years, obviating any need for geologic storage.

 

[mheslep]

In LFTR, you can't place anything "in a pool". The fuel is not in a suitable form for that - it is not an insoluble ceramic inside hermetically sealed metal tubes.

This discussion has been about the difficulty of the required *reprocessing* for any molten salt reactor, in which i) fission products are necessarily removed from the the molten salt to avoid poisoning, and ii) breeding to protactinium to U-233 can occur for a thorium reactor. The removed fission products are necessarily stored, I would guess vitrification would be the likely endgame for radioisotopes with no other practical use, and so constrained certainly a pool is a reasonable, though not necessary, short term storage mechanism capable of handling the decay heat.

 

[mheslep]

Not the same thing. In today's reactors, fuel is not disassembled, it is merely moved from reactor to storage pool and then to dry storage. Almost all radioactivity is still behind two physical barriers: insoluble ceramic fuel, and cladding.

During reprocessing, these barriers do not exist, and several streams of much more volatile (liquid and gaseous) material appear.

As I mentioned before, the primary loop water in a PWR contains the hottest gamma emitter (N-16) in the reactor. And in reprocessing, the number of barriers is design parameter, not doomed to never exist as you assert.

 

[Morbius]

My point was that they could have produced U-233 from thorium for bombs, except that they didn't have a source of HEU or Pu to seed a thorium reactor to start with.

QuantumPion,

You do NOT need HEU to seed your thorium reactor. You just need a core that can go critical on LEU, and then you add a thorium blanket to that.

 

[Morbius]

Same issue? The waste from the U-235 reactors produces radioisotopes with 10,000 year half-lives or more. In a thorium reactor such as the LFTR (thread topic), theoretically the half-lives are a ~hundred years (see chart post #33) , which would not require geologic time scale storage, nor security for the storage designed around proliferation concerns.

An "advantage" that is made totally MOOT if one reprocesses / recycles. If the fuel cycle is closed via reprocessing / recycling, which everyone BUT the USA does; then one only has to deal with fission products; the longest lived of which is Cesium-137 with a half-life of 30 years.

 

[Morbius]

What I assert is what has been measured and illustrated in the chart above, that the total radiotoxicity of all fission products and actinides for a thorium reactor becomes 10⁴ less than that of a U-235 reactor within hundreds of years, dropping below that of natural uranium. This includes weak beta emitters like Tc-99 because they are weak, or trace products in the case of Cs-135 because they are trace, on the order of 10³ less prevalent than Cs-137.

That's really an apples and oranges comparison. If one reprocesses / recycles your uranium-fueled PWR spent fuel; then you don't have the plutonium isotopes in the waste stream; you only have fission products. In that case, your spent fuel storage requirements for thorium-cycle vs uranium-cycle are essentially the same.

 

[QuantumPion]

QuantumPion,

You do NOT need HEU to seed your thorium reactor. You just need a core that can go critical on LEU, and then you add a thorium blanket to that.

Yes you could do this, but the context of my post was on the production of weapons grade material early on in the Manhattan project before any enriched uranium was available. So yes you could make a natural uranium reactor with a thorium blanket to produce U-233, but you would be producing Pu-239 from the uranium anyway, so why bother with a thorium blanket.

 

[Morbius]

Yes you could do this, but the context of my post was on the production of weapons grade material early on in the Manhattan project before any enriched uranium was available. So yes you could make a natural uranium reactor with a thorium blanket to produce U-233, but you would be producing Pu-239 from the uranium anyway, so why bother with a thorium blanket.

As far as using U-233 as a weapon fuel; that was pretty much off the table. The unavoidable presence of U-232 makes U-233 a less than desireable weapons fuel.

Because of that, there was never any serious consideration of using U-233 as a fuel; and the programs for producing U-235 at Oak Ridge and Pu-239 at Hanford proceeded apace.

 

[nikkkom]

What I assert is what has been measured and illustrated in the chart above, that the total radiotoxicity of all fission products and actinides for a thorium reactor becomes 10⁴ less than that of a U-235 reactor within hundreds of years, dropping below that of natural uranium. This includes weak beta emitters like Tc-99 because they are weak, or trace products in the case of Cs-135 because they are trace, on the order of 10³ less prevalent than Cs-137.

If you look more carefully at that chart, you'll notice that "fission products" line is not attributed to PWR or LFTR. That's because it's almost the same for both.

And among fission products, there *are* long term ones. They are much less radiactive, yes, but it's not like you can smelt technetium-99 bullions and hold them in your hands without dying. You still need to store Tc-99,Cs-135, I-129 safely.

 

[nikkkom]

As I mentioned before, the primary loop water in a PWR contains the hottest gamma emitter (N-16) in the reactor. And in reprocessing, the number of barriers is design parameter, not doomed to never exist as you assert.

Its half-life is 7 seconds - completely different regime. It is not an issue in fuel storage or reprocessing - it is an operational issue for BWRs because you need to shield the turbine and condenser now.

 

[nikkkom]

An "advantage" that is made totally MOOT if one reprocesses / recycles. If the fuel cycle is closed via reprocessing / recycling, which everyone BUT the USA does

"Everyone" here stands for only three countries: France, UK, Russia. And none of them remove minor actinides from final waste, IIRC.

 

[mheslep]

If you look more carefully at that chart, you'll notice that "fission products" line is not attributed to PWR or LFTR. That's because it's almost the same for both.

Yes indeed. The distribution of thermal fission products of U-235 and U-233 are similar (slight differences) and therefore so too the radiotoxicity levels over time.

And among fission products, there *are* long term ones. They are much less radiactive, yes, but it's not like you can smelt technetium-99 bullions and hold them in your hands without dying. You still need to store Tc-99,Cs-135, I-129 safely.

We've been there already. Long term fission products (half lives of a thousand years or more), by themselves, are either trace or weak. Thus Tc-99m (half life 6 hours, decays to Tc-99) is suitable as a medical isotope though the Tc-99 compound with its weak beta stays in the body for days, finally excreted into the water supply.

It is the total radiotoxicity of fission products after some hundred years that matter, and that is below that of natural uranium ore, as the chart shows.

Uranium

 

[mheslep]

Its half-life is 7 seconds - completely different regime. It is not an issue in fuel storage or reprocessing - it is an operational issue for BWRs because you need to shield the turbine and condenser now.

This is not the point.

If I understand your general argument, earlier you stated that reprocessing plants are "horribly expensive", long to build, (post 34) etc. Perhaps so. Further, you point out that since a LFTR essentially must have a built-in reprocessing plant it must suffer the same difficulties. I pointed out that one of cost drivers in reprocessing U-235 waste must be proliferation concerns because of the plutonium buildup, as well as the other long half life actinides which accumulate in significant volume and have a radiotoxicity several orders or magnitude higher than fission products over time, so that geologic storage must come into play.

You argued instead that reprocessing was so expensive was because of the difficulty of pushing very hot fission products through the system. I responded that handling highly radioactive isotopes in the plumbing is *not* unique to reprocessing plants but is dealt with in every reactor design. My example was N-16, a 6 MeV gamma emitter that is *always* present in the primary loop of an operating water cooled reactor as it is continually generated.

 

[nikkkom]

You argued instead that reprocessing was so expensive was because of the difficulty of pushing very hot fission products through the system.

Correct.

I responded that handling highly radioactive isotopes in the plumbing is *not* unique to reprocessing plants but is dealt with in every reactor design. My example was N-16, a 6 MeV gamma emitter that is *always* present in the primary loop of an operating water cooled reactor as it is continually generated.

And my argument is that N-16 issue is very, very different from issue of containing fission products.

Leaks of primary loop which release N-16 to the athmosphere are not a *long-term* problem, because N-16 concentration falls by about one billion time after 200 seconds. You simply need to wait a very short time for it to be gone, then you can go and repair the leak.

But if there is a spill of a liquid or vapor containing fission products, you can't wait them out. Ask Chernobyl.