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Liquid Fluoride Thorium Reactor

by gcarlin
Tags: fluoride, liquid, reactor, thorium
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mheslep
#145
Jun19-12, 01:09 PM
PF Gold
P: 3,098
Yes the patent link was posted up thread, but it does not help me with the accepted scientific theory behind accelerated decay, especially given this admission in the patent:

Generally speaking, the scientific community believes that the decay rate of a radioactive nucleus is immutable. However, it is possible to ...
Which was also my understanding.
seeyouaunty
#146
Jun25-12, 04:31 AM
P: 13
Quote Quote by mheslep View Post
Anyone know the scientific basis for asserting that a high E field can change the decay rate of a nucleus? If that was (is?) possible, seems like it throw a large kink in all the historical dating done from isotope ratios, at least in the cosmos where high E fields can occur naturally.
There is some observational evidence that radioactive decay rates are not constant like assumed. It has been suggested the sun is somehow influencing the rate of decay.
long-term observation of the decay rate of silicon-32 and radium-226 seemed to show a small seasonal variation. The decay rate was ever so slightly faster in winter than in summer
http://phys.org/news201795438.html
Stanley514
#147
Nov14-12, 10:45 AM
P: 300
Stanley, the gamma radioactivity from U232 decay chain is only an issue if someone wants to isolate the uranium bred in the reactor and run away with it - then there is additional protection in the Th/U cycle which is not necessarily present in U235 or U238/Pu239 based fuels.

As long as the uranium stays in the reactor (as it should), this activity is insignificant compared to all the "regular" gammas associated with the fission process and FP decays. Therefore there are no additional measures or costs due to U232 activity.
Are you completely sure in it?According to some info some countries refused from U235-Th cycle exacly because very high gamma radioactivity which would require some specific kind of protection that doesn`t exist in any kind of known reactor type.
wizwom
#148
Nov15-12, 06:28 AM
P: 71
Since 232U is just the alpha decay product of 236Pu, which is found in all spent fuel from Uranium powered reactors, and concentrated in MOX. There is no additional shielding needed.
Google books has Neeb's Radiochemistry of Nuclear Power Plants With Light Water Reactors, and on pg 78-79 he gives activity measurements for spent fuel isotopes from enriched uranium after differeent burnups.

You can compare that yourself to the activity from fission products, which he gives earlier.

The ~2MeV γ is not unusual for reactors, the prompt γ average is 1MeV.

So, really, the 232U "hard gamma" claim is somewhat of a red herring: its a feature of ALL spent fuel - and all Plutonium, all recycled Uranium and all recycled Thorium. Since 228Th has a half life of 1.9 yrs vs. 232U's half life of 68.9 yrs, the concentration of 228Th is determined by 232U, and Thorium recycling shouldn't add any worries.
mesa
#149
Nov25-12, 01:30 PM
P: 553
So is the general opinion that working on development of LFTR good or bad?
Seems like from what I have read in this thread it is leaning strongly towards good...
wizwom
#150
Nov25-12, 05:42 PM
P: 71
LFTR has a complex radiological path, and all of it is running at molten fluoride temperatures. Molten fluorides are NOT fun things to work with, they are very active. There are significant engineering hurdles for making a 700 C Material that can handle fluence for a reactor. Since there is no fuel loading - additional reactivity is inserted as needed from 233U-F4 salts in storage as needed, and fission products are removed in a chemical treatment of the main coolanant/fuiel salt, you're going to need materials which can handle 10^15 n/cm^2/s at 700 C for decades, not just a few years.
mesa
#151
Nov25-12, 06:15 PM
P: 553
Quote Quote by wizwom View Post
LFTR has a complex radiological path, and all of it is running at molten fluoride temperatures. Molten fluorides are NOT fun things to work with, they are very active. There are significant engineering hurdles for making a 700 C Material that can handle fluence for a reactor. Since there is no fuel loading - additional reactivity is inserted as needed from 233U-F4 salts in storage as needed, and fission products are removed in a chemical treatment of the main coolanant/fuiel salt, you're going to need materials which can handle 10^15 n/cm^2/s at 700 C for decades, not just a few years.
I can understand that but some of the Oak Ridge scientists who have worked with this type of reactor seem to think it really wouldn't be that big of a deal to figure out, here is a link:
http://www.youtube.com/watch?v=_yO0Qk-_Gms

Also, don't we have better suited materials today than these guys had 47 years ago?
Are the materials the biggest concern for building this type of reactor?
mesa
#152
Nov25-12, 06:43 PM
P: 553
Quote Quote by mesa View Post
I can understand that but some of the Oak Ridge scientists who have worked with this type of reactor seem to think it really wouldn't be that big of a deal to figure out, here is a link:
http://www.youtube.com/watch?v=_yO0Qk-_Gms
I just realized that interview is kind of lengthy, Dick Engel gives his thoughts about these materials at timeframe 23:10 (although I found the interview as a whole really quite insightful).
zapperzero
#153
Nov26-12, 04:47 AM
P: 1,044
Quote Quote by mesa View Post
I just realized that interview is kind of lengthy, Dick Engel gives his thoughts about these materials at timeframe 23:10 (although I found the interview as a whole really quite insightful).
TL;DL: "we kinda sorta thought we might be able to solve the corrosion problems at some unspecified point in the future because we did a few lab tests"

Yeah. Well.
zapperzero
#154
Nov26-12, 05:07 AM
P: 1,044
Quote Quote by mesa View Post
Are the materials the biggest concern for building this type of reactor?
One of the. There is also a big concern with designing adequate valves and things of that nature.
nikkkom
#155
Nov26-12, 05:30 AM
P: 617
Building a small reprocessing plant near every reactor also doesn't sound inspiring. Those things are complex, expensive, and deal with very nasty stuff.
Rive
#156
Nov26-12, 10:27 AM
P: 357
Quote Quote by nikkkom View Post
Building a small reprocessing plant near every reactor also doesn't sound inspiring. Those things are complex, expensive, and deal with very nasty stuff.
As I get it the reprocessing would be part of the reactor (or at least the block), not a separated plant.
mesa
#157
Nov26-12, 11:25 AM
P: 553
Quote Quote by zapperzero View Post
TL;DL: "we kinda sorta thought we might be able to solve the corrosion problems at some unspecified point in the future because we did a few lab tests"

Yeah. Well.
If you are going to quote someone it must be accurate:

Dick Engel during his interview by Kirk Sorenson was asked, “Did the people on the program, in particular the chemists and material scientists feel that corrosion was an insurmountable problem?”

Engel replied, “Uhh, no, I think the people that I dealt with, or spoke with, said ‘okay this is an issue, specifically the tellurium issue but we can get around that’. And some of the subsequent work, subsequent to the initial shutdown they did some experimental work that bode very favorably for an ability to solve that issue.”

Coming from an engineer that has actual experience with this type of reactor it would seem reasonable to assume the materials are not as big an issue as you have thought.
mesa
#158
Nov26-12, 11:32 AM
P: 553
Quote Quote by nikkkom View Post
Building a small reprocessing plant near every reactor also doesn't sound inspiring. Those things are complex, expensive, and deal with very nasty stuff.
I thought for LFTR's this was part of the reactor and not some 'separate' re-processing plant. I understand that the liquid salts are dangerous to work with but are these systems by any means as complex (or dangerous for that matter) as the way our current nuclear reactors are run?
mheslep
#159
Nov26-12, 03:35 PM
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P: 3,098
Quote Quote by wizwom View Post
LFTR has a complex radiological path, and all of it is running at molten fluoride temperatures. Molten fluorides are NOT fun things to work with, they are very active. There are significant engineering hurdles for making a 700 C Material that can handle fluence for a reactor. Since there is no fuel loading - additional reactivity is inserted as needed from 233U-F4 salts in storage as needed, and fission products are removed in a chemical treatment of the main coolanant/fuiel salt, you're going to need materials which can handle 10^15 n/cm^2/s at 700 C for decades, not just a few years.
I'm not sure why it must be so that material lasts the life of the reactor, when the design specifies the fluoride salt can be drained away from the fission core / moderator area at any time, allowing replacement of the core material (graphite?) at whatever schedule desired.

Yes there will need to be thorough certification process for material in contact with the salt (Hastelloy-N?), but then again that effort should be seen in the context of the conditions which the LFTR would replace: a PWR with 153 atm water at 300C and fuel reaching 600C in zircalloy, also w/ 10^15 n/cm^2/s.
mheslep
#160
Nov26-12, 05:05 PM
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Quote Quote by mesa View Post
I thought for LFTR's this was part of the reactor and not some 'separate' re-processing plant. I understand that the liquid salts are dangerous to work with but are these systems by any means as complex (or dangerous for that matter) as the way our current nuclear reactors are run?
I think the point was, built-in or loosely coupled, the reprocessing step is required for LFTR which adds significant complexity that existing PWR/BWRs don't require.

On the other hand, the advantage of LFTR over PWR/BWR is that i) the fuel enrichment / production step is greatly simplified or goes away entirely, ii) waste is greatly reduced and the waste that is produced has a much shorter half life, iii) no 150 atm water/steam to contain.
mesa
#161
Nov26-12, 06:19 PM
P: 553
Quote Quote by mheslep View Post
I think the point was, built-in or loosely coupled, the reprocessing step is required for LFTR which adds significant complexity that existing PWR/BWRs don't require.

On the other hand, the advantage of LFTR over PWR/BWR is that i) the fuel enrichment / production step is greatly simplified or goes away entirely, ii) waste is greatly reduced and the waste that is produced has a much shorter half life, iii) no 150 atm water/steam to contain.
I would imagine given a choice of chemical seperation vs. isotopic, chemical will always be the easier path so long as rates of reaction are good. The idea that we shouldn't develop LFTR 'cause we haven't done it yet' seems absurd.

If the advocates are correct and the LFTR is capable of doing what they say I am on board, but getting the rest of the public and the political will in Washington will likely become the biggest challenge.
mheslep
#162
Nov26-12, 07:23 PM
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P: 3,098
Quote Quote by mesa View Post
I would imagine given a choice of chemical seperation vs. isotopic, chemical will always be the easier path so long as rates of reaction are good. ...
Different problems. Unlike enrichment of uranium, the chemicals in a LFTR will have strong gamma and beta emitters, and the process will necessarily be in close proximity to an operational reactor.


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