Energy From Thorium Discussion Forum

It is currently Jan 18, 2018 1:02 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 18 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: Jan 12, 2015 3:54 pm 
Offline

Joined: Mar 14, 2014 5:26 pm
Posts: 4
In the case of a 2 fluid breeder reactor, like Flibe is working toward, what material would be used to separate the fuel and blanket layers? Would it still be graphite, as ORNL had planned to do?


Top
 Profile  
 
PostPosted: Jan 12, 2015 4:13 pm 
Offline
User avatar

Joined: Nov 30, 2006 3:30 pm
Posts: 3381
Location: Alabama
Yes, graphite.


Top
 Profile  
 
PostPosted: Jan 12, 2015 4:32 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5057
Graphite is like glass. Its brittle. I've visited chemical plants that still use glass pressure vessel reactors. That sort of thing is being phased out rapidly for ductile, tough steels and alloys. The glass reactor vessels still needed elastomeric materials for sealing and dampening critical areas like flanges, penetrations. Without the flexible seals and metals connectors this glass vessel would not be possible.

You better know what you're doing Kirk.


Top
 Profile  
 
PostPosted: Jan 12, 2015 10:07 pm 
Offline
User avatar

Joined: Nov 30, 2006 3:30 pm
Posts: 3381
Location: Alabama
Not a lot of alternatives. But the pressure differential on either side of the barrier should not be significant.


Top
 Profile  
 
PostPosted: Jan 13, 2015 12:53 am 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3069
Also small leaks in either direction aren't a major issue so a precise seal isn't really needed. This allows the possibility of designing a first wall that can be changed out periodically. Since in the true 2 fluid isobreeding reactor about half the neutrons must go through the wall a graphite wall will see a lot of neutrons and likely will not have a long life.


Top
 Profile  
 
PostPosted: Jan 13, 2015 3:26 am 
Offline
User avatar

Joined: Nov 30, 2006 9:18 pm
Posts: 1954
Location: Montreal
Lars wrote:
This allows the possibility of designing a first wall that can be changed out periodically.

Depends on the design.
In some cases it might mean changing out the entire core......


Attachments:
ORNL_Flibe_two-fluid_core.jpg
ORNL_Flibe_two-fluid_core.jpg [ 747.23 KiB | Viewed 2831 times ]
Top
 Profile  
 
PostPosted: Jan 13, 2015 6:43 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5057
Kirk Sorensen wrote:
Not a lot of alternatives. But the pressure differential on either side of the barrier should not be significant.


Pressure differential between my glass windows is also small. Just some wind forces. Yet it needs flexible seal material for damping (or it will break in a storm) and leak tightness, to mate it to the window framework.

Pressure may be larger than you think. Compact MSRs need considerable pump heads, you'd have to make sure the blanket has a similar pressure, pumped or cover gas/hydrostatic. If the fuel pump trips you get a pressure drop in the primary, that's a pressure spike.

How are you going to provide sealing and damping for the graphite? How will it be connected to the metal reactor piping or vessel, and blanket piping or vessel? Flexible seals don't work in this environment. Epsilon type metal seals might work, but they put a lot of point pressure on your graphite, in a sensitive environment (high rad, high temp, high temp differential, different expansion coefficients...)


Top
 Profile  
 
PostPosted: Jan 14, 2015 3:37 am 
Offline

Joined: May 05, 2010 1:14 am
Posts: 130
Would a flexible, bag-like barrier woven from graphite fibre or nanotubes be possible? If you kept the outside pressure slightly below that of the fuel salt, to balloon it out from the moderator, you'd just have to ring-clamp it at top and bottom. That would give you more design flexibility to change the sleeve more often - just drain both salts, drop the old barrier, free the bottom, pull it out through a port at the top, and slide the new one in. ( I'll leave the details to someone with better 3-D and mechanical intuition :P


Top
 Profile  
 
PostPosted: Jan 14, 2015 3:56 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5057
Bags aren't carriers for liquids, they are sieves.

But it might be possible to have a composite, with woven carbon fibers of sorts for tensile strengths, then some kind of hermetic carbon layer on the inside. We are talking major RD&D here for your critical development path.


Top
 Profile  
 
PostPosted: Jan 14, 2015 7:53 pm 
Offline

Joined: Jun 05, 2011 6:59 pm
Posts: 1326
Location: NoOPWA
I am told that one problem with graphite is that it shrinks then grows. Can I take it that with the ability to fine tune the chemistry, this is not a reactivity issue?

_________________
DRJ : Engineer - NAVSEA : (Retired)


Top
 Profile  
 
PostPosted: Jan 14, 2015 9:36 pm 
Offline

Joined: Apr 28, 2011 10:44 am
Posts: 247
The reactivity changes are slow and can be handled by adjusting the fuel.
The problem is structural. The contraction and then expansion depends on
the neutron flux, and the flux is different in different parts of the core.
So we have differential expansion and contraction. The design
has to accommodate this. Hard enough in a one salt design.


Top
 Profile  
 
PostPosted: Jan 20, 2015 12:39 am 
Offline

Joined: Feb 25, 2011 1:55 am
Posts: 90
Why not have both, in a ways? Say a sandwich composite of woven carbon fiber, some sort of carbon foam/aerogel, and a CVD'd hermetic carbon layer? Pretty soon the techniques for unifying graphene platelets into fairly uniform sheets might enable making sealed carbon bag tanks.

Basalt fiber as woven fabric might also be interesting, and there is the rockwool equivalent (similar to glass fiber insulation).


Top
 Profile  
 
PostPosted: Jun 23, 2015 6:47 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1493
How about cold worked DepMo derived TZM/straight Molybdenum?

Whilst normally Moly is far too good at capturing neutrons there are currently ADS target proposals that are using Molybdenum depleted in 95Mo as matrices.
URENCO has apparently quoted $11/g in quantities of a few tonnes a year.
That sounds like a lot, but if you put $50/kW on a gigawatt scale reactor that gets you fifty million dollars, which is 4500kg of it.
When its not under any kind of pressure that is going to go a long way. And its almost certainly going to be easier to work with than Graphite.

Typical isotopic makeup of DepMo is:
56% 92Mo
6% 94Mo
0.6% 95Mo
0.14% 96Mo
0.7% 97Mo
13% 98Mo
23% 100Mo

Interestingly because of the absolutely huge cross section of 95Mo it will still account for a significant fraction of captures, alongside 97Mo - the only two isotopes with significant thermal cross sections.
Which seems to mean that material recovered from reactors would potentially have a lower capture cross section than the material that is fresh, as the two highly captured isotopes will 'burn out'.

There is only one long lived molybdenum radioisotope likely to cause a problem - that being 93Mo. Which decays with a half life of 4000 years to Niobium by positron emission.
It would be interesting to see just what the equilibrium value of its concentration with the 92Mo is, as the capture cross section of that isotope is miniscule.

Either way, reuse of the material does not seem out of the question although it would probably require suitable precautions it is unlikely to be highly active.


Top
 Profile  
 
PostPosted: Jun 24, 2015 11:19 am 
Offline

Joined: Jan 14, 2012 5:49 am
Posts: 57
The tubes could be made of Magnesium fluoride and have a thin coating of TZM(depleted mo). Magnesium fluoride should remain a solid at normal operating temperatures and not absorb too many neutrons. The TZM would just prevent the magnesium fluoride from going into solution with the flibe. I don't have any idea what happens to magnesium fluoride in a neutron flux. (swells, shrinks, stays the same?)


Top
 Profile  
 
PostPosted: Jun 24, 2015 11:22 am 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2230
If you have to change the boundary material, why not metallic thorium. It will act two in one, the boundary material and the blanket. It can be easily reprocessed by electrolysis. MP is also quite high!


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 18 posts ]  Go to page 1, 2  Next

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