Liquid Fluoride Thorium Reactor

zapperzero

One of the. There is also a big concern with designing adequate valves and things of that nature.

nikkkom

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

As I get it the reprocessing would be part of the reactor (or at least the block), not a separated plant.

mesa

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

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

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

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

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

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.

mesa

Okay, is it that the gamma and beta radiation will interfere with the chemical reactions? or are there problems with shielding for personel? both? or something else I am completely missing?

wizwom

I suppose one could do a tubesleeve system, although swelling issues are significant, and then replace the tubes when they seem to have lost cohesion. The lack of significant pressure will also alleviate the material concerns; you can be more brittle when your hoop stresses are lower.

Since ZrF4 was used as fluoride salt component in various MSRs, I'd expect Zircaloy is right out as a tubing material; The temperature range puts us into SiC or ZrC ranges; but they are non-ductile. I expect ODS alloys will be the likely tubing.

Of course, this is assuming we can't separate the corrosion resistance and ductility under radiation problems; if we can work out a reasonable method for SiC coating parts that stands up to radiation and thermal changes then almost all corrosion difficulties can be ignored, and the structural material can be chosen on retention of ductility alone.

mesa

Are there issues with using Hastelloy N that were not adressed during the running of the research reactor at ORNL or are these simply better choices (cost, durability, etc.) by comparison due to material advancement in the last half century?

mheslep

We may be talking about two different things.

In the case of a liquid molten salt reactor, it seems to me there are two primary materials to select. The first is the moderator, which will suffer the neutron flux, but has little structural support responsibility. The ONR experiment used a graphite block w/ channels through which the salt was pumped. I assume that's still the first choice for a moderator. The second material is for structural containment. It receives relatively small neutron flux, high radiation, and must structurally contain the ~700C salt. ONR used Hasteloy N.

mheslep

Yes there's a problem that was recognized but not yet addressed (AFAIK) in an operation. It is mentioned in the video interview link you provided and on the MSR experiment wiki page. They found that Tellurium, a fission product, causes cracking presence of radioactivity in the alloy ONR used. This would not be trivial thing to test.

mesa

Agreed, but certainly possible.

Here is another interview with Dick Engel where he discusses this exact problem, it rings deeper than just the Tellurium (which it seems the material scientists had a solution for)

http://www.youtube.com/watch?v=ENH-j...layer_embedded

The question is raised at 17:25 and goes to 20:56, although (once again) I really found the discussion as a whole very interesting.

I like Dick Engals take on how to test materials for future reactors, same link but starting at time frame 19:41.

mheslep

Yes I'd seen it previously. I just watched it again and Engel raised an obvious point that I missed before. He points out that if the Te corrosion problem is solved, the overall corrosion problem may not be solved because another element might cause trouble. The larger point being that fission of course means a large chunk of the periodic table would be present, everything from gallium to hafnium, including the very reactive alkali and halogen groups. Does this mean a chemical analysis the interaction of most of the elements in the periodic table against Hasteloy N must be done under LFTR conditions?

One of the advantages of LFTR is supposed to be that high burnup and low waste is possible in part because fission poisons, esp. xenon, can be chemically removed from a liquid fueled reactor, unlike a solid fueled reactor which must have the fuel replaced every couple years. But while targeting the removal of some elements is surely feasible, I doubt it is so easy to remove most of the periodic table.

It may be that in the case of long term corrosion the issue turns in favor short turn fuel supplies, as while fission also generates products in the solid fuel Zirc alloy rods, they're pulled out of service while LFTR is intended to keep going for 30 years or so.

mheslep

I've just read some of the critical final report on the Molten Salt Reactor Experiment written by the AEC in 70's after the shutdown. I knew of its existence but had avoided it given the politics of the time heavily favoring light water reactors and liquid metal breeders, and I thought it biased.

The structural material discussion starts on page 30. The argument seems valid, if overly absolute ("not suitable").

http://www.energyfromthorium.com/pdf/WASH-1222.pdf