Energy From Thorium Discussion Forum

It is currently Dec 14, 2017 3:55 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 15 posts ] 
Author Message
PostPosted: May 05, 2012 7:43 am 
Offline

Joined: Feb 28, 2011 10:10 am
Posts: 347
I have been reading the Rebus-3700 paper, written by Mourogov and Bogov in 2006, which is about a Molten Chloride Fast Reactor concept. The word "awesome" comes to mind when reading about MCFRs. At least on paper, MCFRs seem to be very versatile and the breeding capability is extra-ordinary. But there is much less experience with MCFRs than with the liquid fluoride counterparts.Apparently, what is held against the MCFR is the corrosive effect on the materials caused by sulphur. Mougorov and Bogov have chosen titanium as vessel material, which is a metal that I have not come across often with regard to nuclear vessels and piping. Would titanium really be a good choice as vessel material to mitigate the effects of sulphur ? Or are there better alloys for MCFRs ?

Furthermore, I have been thinking that Alvin Weinberg and ORNL made a historic mistake in the early 1970s with pursuing the MSBR concept. As I understand, funding was cut off to the MSBR project because the liquid metal fast breeder was so much more attractive from a Cold War perspective: breeding plutonium. MCFRs trump LMFBRs in this respect. Should Weinberg and ORNL have proposed the MCFR instead of the MSBR ?


Top
 Profile  
 
PostPosted: May 05, 2012 3:59 pm 
Offline
User avatar

Joined: Nov 30, 2006 9:18 pm
Posts: 1954
Location: Montreal
camiel wrote:
I have been thinking that Alvin Weinberg and ORNL made a historic mistake in the early 1970s with pursuing the MSBR concept. As I understand, funding was cut off to the MSBR project because the liquid metal fast breeder was so much more attractive from a Cold War perspective: breeding plutonium. MCFRs trump LMFBRs in this respect. Should Weinberg and ORNL have proposed the MCFR instead of the MSBR ?

Interesting thought.

I bet that Weinberg & co. were savvy enough to realise that, while MCFR may look great on paper, in terms of fuel evolution, there is little chance for such a reactor to operate in a stable fashion -- except possibly at a very small size, that could not compete against large solid fuel SFRs.

I don't have any information to support this, other than knowing that those ORNL scientists & engineers considered safety as paramount (feel free to flame away...).


Top
 Profile  
 
PostPosted: May 05, 2012 4:20 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3070
camiel wrote:
Furthermore, I have been thinking that Alvin Weinberg and ORNL made a historic mistake in the early 1970s with pursuing the MSBR concept. As I understand, funding was cut off to the MSBR project because the liquid metal fast breeder was so much more attractive from a Cold War perspective: breeding plutonium. MCFRs trump LMFBRs in this respect. Should Weinberg and ORNL have proposed the MCFR instead of the MSBR ?


I believe it is true that Weinberg and ORNL got funding cut off because Milton Shaw was dedicated to getting a LMFBR built and MSBR was a threat to it. I don't think that plutonium production was a significant factor. It is interesting to read "Plentiful Energy" as their reactor funding was also cut off to feed the LMFBR machine.


Top
 Profile  
 
PostPosted: May 06, 2012 7:04 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Hmm. Has anyone ever used fast reactors to breed plutonium for weapons?

I thought it was purely a thermal reactor breeding thing. Mostly dedicated low pressure low temperature graphite moderated fuel channel reactors.

And anyway, if you're going to build a fast reactor for WGPu you must first enrich loads of uranium-235 at a fairly high enrichment. If you're going to do that, why not just use the enrichment capacity to make a much easier U-235 bomb, and just forget about the unproven expensive fast breeder?


Top
 Profile  
 
PostPosted: May 06, 2012 8:28 am 
Offline

Joined: Feb 28, 2011 10:10 am
Posts: 347
Cyril R wrote:
Hmm. Has anyone ever used fast reactors to breed plutonium for weapons?

I thought it was purely a thermal reactor breeding thing. Mostly dedicated low pressure low temperature graphite moderated fuel channel reactors.

And anyway, if you're going to build a fast reactor for WGPu you must first enrich loads of uranium-235 at a fairly high enrichment. If you're going to do that, why not just use the enrichment capacity to make a much easier U-235 bomb, and just forget about the unproven expensive fast breeder?


Yes, these are valid points. That is how it was done in France and the UK, with their dual-purpose (electricity&plutonium) CO2-cooled/graphite-moderated reactors. At the Savannah River Site they used heavy water reactor for this purpose. But I think you must cast your mind back to the 1960s / 1970s. Back then there was the prediction that the world would run out of uranium very soon. Plutonium was seen as extremely valuable by the political and military strategists, especially if you are engaged in a nuclear arms race with the Soviets and need plutonium for your weapon programs. A reactor breeding plutonium was very attractive from that viewpoint. AFAIK, the MSBR was cancelled because the Nixon administration only wanted to fund one type of breeder because of budgetary constraints.

Anyway, would titanium be suitable for reactor vessels ?


Top
 Profile  
 
PostPosted: May 06, 2012 9:55 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
If I understand it correctl, those gas reactors were only initially duel purpose... it was found that Pu production and power production are just too opposite goals for a single reactor, in terms of burnup, reliability/capacity factor, and thermodynamics. You get a reactor that isn't cost effective in making electricity and not the best in making WGPu either. You're much better off with a big, higher burnup, high temp high pressure reactor for electricity, and use a smaller, low temperature, low pressure, low burnup reactor for WGPu.

It's quite silly that they thought uranium would run out. One does not need a lot for bombs, and Deffeyes & MacGregor were already doing work on uranium abundance. Even after their quite decisive work in the 1980s many still believed uranium would run out...

Titanium... pure titanium wouldn't work, if looking at pure thermodynamic considerations. It should be worse than chromium. But ORNL added 0.5-2% titanium to the alloy that seemed to make it more resistant to radiation damage. Though it didn't do much against tellurium attack. For that, 2% niobium was found sufficient under conditions employing effective redox control, and this niobium addition also dealt with the radiation damage issue.

Niobium is a quite nice and undervalued material for a LFTR. Really wonderful material. Not very strong but ductile and doesn't lose strength with temperature. I'm thinking about using it for liners. Incolloy 800H vessel with niobium liner. Or maybe Monel 400, they use that in the enrichment industry, seems inert with fluorides. Does cost an arm and a leg but you only need a 3mm liner.


Top
 Profile  
 
PostPosted: May 07, 2012 12:02 am 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2237
On one hand, the gas cooled reactors are neutron economic. On the other hand, if you did not need power, costly Helium could only be justified for heat extraction. Otherwise, Nitrogen and carbon dioxide are quite satisfactory coolants.
Initial uranium ores in Africa and Canada were tens of percents uranium. Most ores now are hundreds of ppm, three orders of magnitude leaner. You could not consider peak uranium a silly idea. It is just that mining effort is still less than coal for the same power. If MCFR could be developed, thorium would not be necessary. A thorium power production reactor has not been built, even after the light water breeder reactor at Shippingport. A successful breeder MCFR will make a thorium breeder reactor possible but unnecessary.


Top
 Profile  
 
PostPosted: May 07, 2012 8:14 am 
Offline
User avatar

Joined: Oct 06, 2010 9:12 pm
Posts: 136
Location: Cleveland, OH
Re: titanium - I'm usually a fan of titanium alloys, but my understanding is that alloys of mostly titanium were not great at withstanding radiation damage, although paradoxically it seems to be useful as a minor alloy agent. Also, I'd think that any chlorine floating free would corrode the titanium; titanium chloride is an intermediate stage of titanium production. I do not have any hand links to point to, but thats my best recollection. Also, I believe flourine would attack Ti similarly.


Top
 Profile  
 
PostPosted: May 07, 2012 9:17 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
I'm not sure why the REBUS concept assumes titanium as a structural alloy. I suspect this is a major mistake, because they make reference to a different salt, molten nitrates, which should work very well with titanium.

Titanium is used however in condenser tubing due to its resistance to seawater and low pressure steam. However this is all at low temperature, aqeous, oxidising environment, very different from a molten chloride environment.


Top
 Profile  
 
PostPosted: May 08, 2012 3:57 am 
Offline

Joined: Feb 28, 2011 10:10 am
Posts: 347
Titanium was chosen for the REBUS-3700 concept because of the opinion of a materials expert, Dr Michel Albert (see page 2764 in the paper, which is attached). They do mention the possible radiation damage, which can be mitigated by using a shield-reflector in a final design, according to Mourogov and Bokov. Hastelloy-F and TZM alloy (which is mostly molybdenum) are mentioned as other candidates for the reactor vessel.


Attachments:
Rebus 3700.pdf [235.63 KiB]
Downloaded 165 times
Top
 Profile  
 
PostPosted: May 08, 2012 4:16 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
camiel wrote:
Titanium was chosen for the REBUS-3700 concept because of the opinion of a materials expert, Dr Michel Albert (see page 2764 in the paper, which is attached). They do mention the possible radiation damage, which can be mitigated by using a shield-reflector in a final design, according to Mourogov and Bokov. Hastelloy-F and TZM alloy (which is mostly molybdenum) are mentioned as other candidates for the reactor vessel.



Thanks Camiel. I'm not sure why a materials expert would suggest titanium. It's difficult to work with and there are very few suppliers that can weld large vessels out of titanium. Basically you don't use titanium unless you really have to. In the case of seawater condenser tubing, it's one of the best materials possible. We ordered a large number of tubes two years ago for a large thermal installation. They still haven't arrived. Supplier says it will take another year at least.

ORNL did work on titanium behaviour in the MSBR system. Results were not encouraging; titanium is almost certainly worse than chromium. Ok if you have 2% titanium in the alloy. Not okay if you have pure titanium. Titanium also suffers from tellurium integrannular attack.

I see no reason to believe it will be much better for a chlorides system.

http://moltensalt.org/references/static ... M-3763.pdf


Top
 Profile  
 
PostPosted: May 17, 2012 4:52 am 
Offline
User avatar

Joined: May 24, 2009 4:42 am
Posts: 826
Location: Calgary, Alberta
Back to a well published MCFR challenge, radiosulphur which comes from irradiating natural chlorine. In the form of a question, would it be sufficient to take a side-stream of fuel salt and bubble hydrogen through it, presumably forming H2S?


Top
 Profile  
 
PostPosted: May 17, 2012 6:26 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Lindsay wrote:
Back to a well published MCFR challenge, radiosulphur which comes from irradiating natural chlorine. In the form of a question, would it be sufficient to take a side-stream of fuel salt and bubble hydrogen through it, presumably forming H2S?


This is what some of the early chloride reactor papers (eg from Ottewitte, Taube) suggested. If I recall the specifics, they use a certain combination of H2 and HCl that allows removal of sulphur mutants as H2S ("hydrochlorination") without disturbing the fuel redox chemistry. If you check the document repository for these papers there will be more talk about it.


Top
 Profile  
 
PostPosted: May 18, 2012 1:10 pm 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2237
TiCl4 is a volatile compound.
http://www.webelements.com/compounds/ti ... loride.htm
In a chloride environment, the corrosion would be heavy. A silica enamel may be required.
Cl37, which is nearly one-fourth of natural chlorine, is probably less reactive to neutron. The absorption x-section difference is very large. Enrichment may be necessary.


Top
 Profile  
 
PostPosted: May 20, 2012 11:09 pm 
Offline
User avatar

Joined: May 24, 2009 4:42 am
Posts: 826
Location: Calgary, Alberta
For pure salts, chlorides are less corrosive than fluoride salts apparently, what I can't tell you is how that changes when fission products are part of the mix.

O Benes in JRC-ITU-TN-2008/40 wrote:
In general the chlorides have higher vapor pressures and lower thermodynamic stability at high temperatures compared to fluorides, but on the other hand, they are less aggressive against the structural materials and their melting points are lower.

Corrosion studies at University of Wisconsin also show less corrosion in the chloride salts tested there.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 15 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group