Energy From Thorium Discussion Forum

It is currently Jun 22, 2018 3:45 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 53 posts ]  Go to page Previous  1, 2, 3, 4  Next
Author Message
PostPosted: Oct 17, 2014 10:26 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1521
I managed to dig an ESBWR total core pressure drop out of some various engineering documents - supposedly around 70kPa.

The pressure drop of the reference uranium/plutonium oxide RBWR-AC core (this is the isobreeder AIUI) is only 120kPa (far lower than the ABWR thanks to it being a pancake core)- while it is greater it is not orders of magnitude greater.

This paper proposes using Nitride fuels that would enable significant increases in heavy metal inventories.
It proposes to either use this to push theoretical max breeding ratio to ~1.15 or to allow for the fuel element pitch to be increased - which I believe would have the effect of reducing core pressure drop, although I don't have figures to absolutely support this.
It seems plausible that such fuel would permit a breakeven core with similar pressure drop to an ESBWR.


Top
 Profile  
 
PostPosted: Oct 18, 2014 2:42 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5053
Checked with the DCD, yes it is around 70 kPa. But not much more is available. They had to go to great lengths (or shortness, in case of the fuel) to get 70 kPa of drive force and get the core pressure drop to be reduced to these low levels. For example the ABWR has around 168 kPa core pressure drop. The ABWR can operate on natural circulation, but only to 40-50% of output whilst staying within the same thermal limits.

120 kPa is asking a lot. Its very unattractive to increase the length of the pressure vessel (it is already 27 meters tall), and we can't gain much more by reducing the pressure drop in steam separators and such.

Nitride fuel would help but this means a different and unproven fuel type. Sort of defeats one of the main pros of this concept, use LWR + uranium dioxide fuel to cut out the critical fuel develpment timeline.


Top
 Profile  
 
PostPosted: Oct 18, 2014 8:18 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1521
While the uranium nitride fuel would require R&D to get the pressure drops down into the same region as the ESBWR (density increases by 40% so it might not be unreasonable to hope that it would be enough) that development does not require a delay in the reactor construction programme.
We can build hundreds of ESBWRs in parallel with the UN fuel development and then switch over when its available and economic to do so.
This is in contrast to something like the SFR where all development tasks must be completed prior to a reactor entering service.

Also UN has some other advantages beyond its ridiculously high density, in terms of having a higher thermal conductivity which should allow for a higher core power with the same fuel centreline temperatures.


Top
 Profile  
 
PostPosted: Oct 18, 2014 8:35 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5053
E Ireland wrote:
While the uranium nitride fuel would require R&D to get the pressure drops down into the same region as the ESBWR (density increases by 40% so it might not be unreasonable to hope that it would be enough) that development does not require a delay in the reactor construction programme.
We can build hundreds of ESBWRs in parallel with the UN fuel development and then switch over when its available and economic to do so.
This is in contrast to something like the SFR where all development tasks must be completed prior to a reactor entering service.

Also UN has some other advantages beyond its ridiculously high density, in terms of having a higher thermal conductivity which should allow for a higher core power with the same fuel centreline temperatures.


Higher power density would mean much higher pressure drop. 2x power density, all things being equal, means 2x the flow which is 4x pressure drop (give or take). This seems to be an issue with all natural circulation designs, not suitable for high power density uprates. This is definately interesting though. If you can prevent higher pressure drop, ESBWR's next limit becomes the cladding (fuel temp isn't a problem, they are overconservative here). They would probably benefit more from advanced cladding such as MIT triplex SiC, than advanced fuel. Or just ODS zircalloy technology like M5 or Zirlo cladding.

I wonder also, are we going to need enrichment for the nitrogen? This could be a supply and possibly cost issue.


Top
 Profile  
 
PostPosted: Oct 18, 2014 11:10 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1521
N enrichment is apparently required, mainly to avoid massive 14C production.

But nitrogen enrichment is not as challenging as say, Lithium. For example I can think of multiple plausible processes off the top of my head. Centrifugation of deuterated ammonia for example.


Top
 Profile  
 
PostPosted: Oct 18, 2014 11:42 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5053
E Ireland wrote:
N enrichment is apparently required, mainly to avoid massive 14C production.

But nitrogen enrichment is not as challenging as say, Lithium. For example I can think of multiple plausible processes off the top of my head. Centrifugation of deuterated ammonia for example.


N2 is nearly 80% of the atmosphere. No need to bother. Just use gas centrifuge. Nitrogen is cheap and you can sell back the nitrogen feedstock. Even better pay the ASU operator for the enrichment step in betwen. I think the cost is reasonable especially since you can recycle the N-15 with this approach - you need reprocessing to get self sustaining cycle. But it does require a bit of supply chain development. Nitrogen enrichment isn't widely used today.


Top
 Profile  
 
PostPosted: Oct 18, 2014 2:24 pm 
Offline

Joined: Nov 23, 2010 6:51 pm
Posts: 123
You won't get past 50% 15N by centrifuging N2. Statistically, almost all of the 15N in the atmosphere will be in molecules with one atom of 14N and one atom of 15N. Ordinary NH3 could probably get close to 90% before co-enrichment of deuterium started to complicate matters (15N is ~20 times more abundant than deuterium). Burning the partially enriched ammonia would yield N2 with ~80 % 15N-15N molecules that could be brought to 99+% by centrifuging, along with partially deuterated (~5-10%) water. Alternatively a deuterium-hydrogen exchange with water would allow the ammonia to be brought to 99+% by further centrifuging.


Top
 Profile  
 
PostPosted: Oct 18, 2014 3:00 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5053
Quote:
You won't get past 50% 15N by centrifuging N2. Statistically, almost all of the 15N in the atmosphere will be in molecules with one atom of 14N and one atom of 15N.


Duh. Its the same with H2 enrichment. That doesn't mean you can't get beyond 50%. Just halves the mass difference per molecule over the atomic mass difference, but the mass difference is still huge compared to the mass difference of UF6 in (235/238U).


Top
 Profile  
 
PostPosted: Oct 18, 2014 3:02 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1521
You would need a process.that makes the nitrogen atoms swap, like hydrogen atoms in water do all the time. Otherwise you won't be able to get past 50% enrichment as you can't separate the 15N atoms from the 14N atoms they are all attached to.


Top
 Profile  
 
PostPosted: Oct 18, 2014 3:39 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5053
E Ireland wrote:
You would need a process.that makes the nitrogen atoms swap, like hydrogen atoms in water do all the time. Otherwise you won't be able to get past 50% enrichment as you can't separate the 15N atoms from the 14N atoms they are all attached to.


Good point, I forgot about N2 lack of interchange here.

Doing some search finds that nitrogen monoxide (NO) is currently used for nitrogen enrichment. It isn't necessary to have atoms interchange, since it is monovalent nitrogen.

No mention of price/kg though.


Top
 Profile  
 
PostPosted: Oct 18, 2014 5:12 pm 
Offline

Joined: May 05, 2010 1:14 am
Posts: 129
Doesn't metal fuel have a higher density of heavy metal, and better heat conductivity, than nitride fuel? Plus, of course, no need to separate nitrogen isotopes. I know the melting point is lower, and Fermi one melted a couple of rods, but the results were a lot less problematic than for Three Mile Island. Lightbridge helical cruciform fuel is also supposed to have low pressure drop, since it doesn't need spacers between the rods. I heard that the Russians were planning to move to nitride fuel for their fast reactors, and eventually metal fuel. Are there any major hindrances to going directly to metal?


Top
 Profile  
 
PostPosted: Oct 18, 2014 5:33 pm 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1521
Straight metal fuels swell very badly as burnup increases.
Lightbridge fuels have lower HM content than oxide.


Top
 Profile  
 
PostPosted: Oct 18, 2014 6:57 pm 
Offline

Joined: Nov 23, 2010 6:51 pm
Posts: 123
Cyril R wrote:
Doing some search finds that nitrogen monoxide (NO) is currently used for nitrogen enrichment. It isn't necessary to have atoms interchange, since it is monovalent nitrogen.

No mention of price/kg though.

That seems an odd choice due to co-enrichment of oxygen - 18O is almost as abundant as 15N and the mass difference is larger, and there is a little 17O as well.

Using ammonia, building and operating the centrifuges should be almost the only cost as the 15N-depleted tails will have the same market value as the feedstock.


Top
 Profile  
 
PostPosted: Oct 21, 2014 4:50 am 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2230
Maximum D2O is made in India using an ammonia-hydrogen process. N-15 in nitrogen is a minor complication. Deuterium in hydrogen or O-18 in oxygen is even less and is not a complication.
You need to go to UN only if uranium metal has problems. It may be required for fast reactors but metal/oxide should be OK for water or heavy water cooled reactors including RBWR.


Top
 Profile  
 
PostPosted: Oct 21, 2014 8:23 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1521
Oxide has insufficient density to make these reactors really attractive and metal is useless as it swells up horribly after a tiny amount of burnup.

Nitride is a nice option if you can get the nitrogen enrichment to work.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 53 posts ]  Go to page Previous  1, 2, 3, 4  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