Questions About LFTR - Uranium 233 & Gamma Rays

[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.

 

[nikkkom]

Long term fission products (half lives of a thousand years or more), by themselves, are either trace or weak.

Tc-99 yield per one fission is 6%, its decay energy is 300 KeV.
This is neither trace, nor particularly weak.
Cs -135 yield is 7%, decay is 270 KeV. Again, not a trace amount - in fact, it's almost the same yield as notorious Cs-137.

 

[mheslep]

...

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

Chernobyl had no reprocessing, the cost of which is the point of this discussion. Anyway, why reference a graphite fire? Or theoretical accidents at 300 atm water loops for that matter? The material here is a liquid salt at low pressure.

 

[mheslep]

Tc-99 yield per one fission is 6%, its decay energy is 300 KeV.
This is neither trace, nor particularly weak.

Weak enough to be inserted in the body for a couple days, and then dumped in the waste water system.

 

[mheslep]

Cs -135 yield is 7%, decay is 270 KeV. Again, not a trace amount - in fact, it's almost the same yield as notorious Cs-137.

That yield is high by 3 orders of magnitude for 135 for U233 fission.
https://www-nds.iaea.org/wimsd/fpyield.htm

 

[Astronuc]

That yield is high by 3 orders of magnitude for 135 for U233 fission.
https://www-nds.iaea.org/wimsd/fpyield.htm

Those yields seem to be individual yields, but cumulative yields are important for the cumulative fission/decay product quantity, e.g., Se -> Te -> I -> Xe -> Cs

 

[mheslep]

Those yields seem to be individual yields, but cumulative yields are important for the cumulative fission/decay product quantity, e.g., Se -> Te -> I -> Xe -> Cs

Yes for cumulative yield over short half lives (decades or less). Tc 99 has half life on order 10^5 yrs, really the only non trace fission product around that long. The point has been in determining what type of storage is required for pure fission products free from any actinides after some decades: geologic or a radioisotope box in the back room? I don't see any point in geologic storage for that which is already dumped in waste water for nuclear medicine usage.

 

[nikkkom]

That yield is high by 3 orders of magnitude for 135 for U233 fission.
https://www-nds.iaea.org/wimsd/fpyield.htm

Look at yields of I-135 and Xe-135 in that table. Then think what they decay to, and with what lifetime.

 

[nikkkom]

Weak enough to be inserted in the body for a couple days, and then dumped in the waste water system.

Medical uses of Tc-99m employ incomparably tiny amounts.

Tc-99m medical imaging uses Tc-99m doses up to 1GBq.

Even if all of that Tc-99m remains in the body and decays to Tc-99 (which takes ~two days to be more than 99% complete), then the resulting Tc-99 has miniscule activity of 3.2 Bq.

But in reprocessing, you have to deal with many kilogram quantities of Tc-99. Every *gram* of Tc-99 is 629MBq.

 

[nikkkom]

Chernobyl had no reprocessing, the cost of which is the point of this discussion.

Chernobyl, though, is a good example what you can do with a large volume of escaped fission products: nothing. You have to live with the consequences.

(Before you start talking that Chernobyl had other contaminants too, find the maps of Cs-137, Sr-90 and plutonium fallout in Chernobyl, and see for yourself which one is by orders of magnitude the largest)

 

[Morbius]

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

WRONG! France, UK, Russia and Japan have the facilities to do reprocessing.

However, the all the other countries that have nuclear power plants, but don't have the reprocessing facilities; Sweden, for example; have one of the countries with reprocessing facilities reprocess their spent fuel. Sweden has its spent fuel reprocessed by France.

The number of countries that have a policy of a "once through" fuel cycle with geologic disposal and no reprocessing is precise one; the USA.

 

[mheslep]

Look at yields of I-135 and Xe-135 in that table. Then think what they decay to, and with what lifetime.

To what end? Do you accept the cumulative radio-toxicity levels of fission products as shown in the APS chart, or not? Is the cumulative radiotoxicity of *all* fission products below that of natural uranium within hundreds of years or not? Does natural uranium ore require "geologic storage"?

 

[Morbius]

To what end? Look, do you accept the cumulative radio-toxicity levels of fission products as shown in the APS chart, or not? Is the cumulative radiotoxicity of *all* fission products below that of natural uranium within hundreds of year,s or not? Does natural uranium require "geologic storage"?

EXACTLY! Unfortunately, that's the problem; people can't put the risk in perspective.

We have so many like Helen Caldicott preaching that any amount of radiation is deadly no matter how small; and in particular; no matter that natural exposure swamps the amount she is complaining about.

People would be well served to think of germs as an analogy. Does it make any sense to attempt to sterilize items like Howard Hughes used to do when practically everything has some level of germ contamination to no ill effect. In fact, people like Howard Hughes have a mental disorder - OCD for Obsessive Compulsion Disorder.

 

[nikkkom]

>> Look at yields of I-135 and Xe-135 in that table. Then think what they decay to, and with what lifetime.

To what end?

To this end: you are obviously wrong about long-lived fission products being "only trace". I merely pointing it out to you in this particular post: even though Cs-135 is rare as a *direct* fission product, it is a daughter of two other more common short-lived fission products, and therefore cumulatively its production adds up to ~7%.

No need to get angry just because you are proven wrong.

Do you accept the cumulative radio-toxicity levels of fission products as shown in the APS chart, or not?

The y-axis units are not specified on your chart. Hmmm.

Okay, this needs some verifying. I found another chart - see attached.

It claims that after about 900 years, fission products' decay rate is dominated by Tc-99, and it stands somewhere near 1GBq/kg. Google tells me that uranium ore is about 25 MBq/kg.

So, no, I don't accept your claim.

 

[mheslep]

The y-axis units are not specified on your chart.

The radiotoxicity chart is from APS, as you known, it's not 'mine'; yes all the relevant units are there implicitly via the natural uranium ore reference line.

...Tc-99 ... stands somewhere near 1GBq/kg...uranium ore is about 25 MBq/kg

Which is specific activity, not total radioactivity nor, more importantly, total radiotoxicity. For instance, with the some 40x10^12 tonnes of uranium estimated throughout the Earth's crust and oceans, that implies something like 10^24 Bq total activity from uranium. Oh no, run away, run away.

So, no, I don't accept your claim.

APS claim about total radiotoxicity, which for some dogmatic reason you don't care to understand.

 

[kiskrof]

There to be or not to be U232...

No, U-232 is generated by neutron absorption in the reactor. If you chemically separate the proactinium outside of the reactor and wait for it to decay to U-233 there will be no U-232 contamination.

There is an apparent contradiction, to my eyes at least, between some of the posts on this thread. U233 is said to be difficult to process because of U232, and then Mr QuantumPion tells us the above: no U232. If you get U233 inside the reactor with no U232, isn't that exactily what you would need for a bomb?

 

[QuantumPion]

There is an apparent contradiction, to my eyes at least, between some of the posts on this thread. U233 is said to be difficult to process because of U232, and then Mr QuantumPion tells us the above: no U232. If you get U233 inside the reactor with no U232, isn't that exactily what you would need for a bomb?

Which posts are you referring to? U-233 inside the reactor would be contaminated with U-232. But it is physically possible to reprocess protactinium in a thorium cycle to produce clean U-233.

 

[kiskrof]

I am reffering to posts on the first or second page of this thread, from where I took your quote (by the way thank you for all your interventions QuantumPion). I was not aware that my post would appear at the very end of the thread. The problem is:
1. U232 is often quoted as the solution to nuclear proliferation. i have read several times: "it is very difficult to make a bomb from a LFTR because the U233 is mixed with U232.
2. U232 comes from the reaction: Pa233 + n --> U232 + n + n + beta To avoid this, you take the Pa233 from away from the reactor for a while, till it beta-decays to U233.
Both ideas are very nice, but I think that unfortunately, you cannot have your cake and eat it. If you want to avoid the building of U232 in your power plant (which probably makes many things easier), than U232 won't help you stop proliferation.
I am not a physicist, tell me where I am wrong. Apparently, wikipedia agrees with me: http://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reactor#Removal_of_fission_products (long article, see "disadvantages", and "Proliferation risk from Protactinium separation")

 

[QuantumPion]

I am reffering to posts on the first or second page of this thread, from where I took your quote (by the way thank you for all your interventions QuantumPion). I was not aware that my post would appear at the very end of the thread. The problem is:
1. U232 is often quoted as the solution to nuclear proliferation. i have read several times: "it is very difficult to make a bomb from a LFTR because the U233 is mixed with U232.
2. U232 comes from the reaction: Pa233 + n --> U232 + n + n + beta To avoid this, you take the Pa233 from away from the reactor for a while, till it beta-decays to U233.
Both ideas are very nice, but I think that unfortunately, you cannot have your cake and eat it. If you want to avoid the building of U232 in your power plant (which probably makes many things easier), than U232 won't help you stop proliferation.
I am not a physicist, tell me where I am wrong. Apparently, wikipedia agrees with me: http://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reactor#Removal_of_fission_products (long article, see "disadvantages", and "Proliferation risk from Protactinium separation")

Your thinking is correct. Fuel from a regular commercial LFTR reactor producing dirty U-233 could not be stolen to use in a bomb because it would be too radioactive to handle. This aspect may be what people are referring to in regards to proliferation resistance. However, if you owned the LFTR plant, you could feasibly configure it to produce clean U-233.

 

[Kelson Adams]

I've seen an interesting film lately on a guy who believes that the Liquid Fluoride Thorium Reactor is the best nuclear reactor to be created -- http://topdocumentaryfilms.com/thorium-energy-solution/

I'm curious to know both the advantages/disadvantages of LFTRs and the technology that still needs to be developed to make LFTRs a reality. Your thoughts?

 

[nikkkom]

I've seen an interesting film lately on a guy who believes that the Liquid Fluoride Thorium Reactor is the best nuclear reactor to be created -- http://topdocumentaryfilms.com/thorium-energy-solution/

I'm curious to know both the advantages/disadvantages of LFTRs and the technology that still needs to be developed to make LFTRs a reality. Your thoughts?

Please read this thread from the start. A number of people already gave their (varying) opinions on LFTR.