Energy From Thorium Discussion Forum

It is currently Sep 24, 2018 10:01 am

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 226 posts ]  Go to page Previous  1 ... 8, 9, 10, 11, 12, 13, 14 ... 16  Next
Author Message
PostPosted: Dec 12, 2011 8:23 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5045
USPWR_SRO wrote:
Cyril R wrote:
...Apparently this is almost mandatory for ultra high burnup fuel rods: without venting, the pressure from fission gas generation would build up and rupture the cladding...


FYI, current PWR fuel pins are pressurized with 400psia at ambient temperature of helium at manufacture. After about 30,000MWD/MTU of burnup the internal pressure rises to ~1200-1400psia at ambient temperature due to fission product gases.

The initial pressure is to improve heat transfer fromt the fuel pellets and to prevent collapse of the pin in the high pressure primary system when new.


Well, if your primary coolant pressure is 2200 psia then that is nice to have similar pin pressure.

With sodium cooled reactors in a pool type design, the pressure is essentially atmospheric plus hydrostatic head from the pool.

And with a metal fuel the fission gas release is bigger.

30,000 MWd/tU is quite low burnup. The TWR would require burnups more like >100,000 MWd/tU, perhaps 200,000 MWd/tU


That gives some scary amount of volatile fission products. Vented fuel starts to look really good for such a configuration.


Top
 Profile  
 
PostPosted: Dec 12, 2011 9:41 am 
Offline
User avatar

Joined: Nov 30, 2006 9:18 pm
Posts: 1946
Location: Montreal
Cyril R wrote:
Anyone know the burnup in GWd/ton they are aiming for?

In the video, they say that a burnup greater than 30% is required "to sustain a wave in uranium" -- which corresponds to 550 DPA - Displacements Per Atom in the fuel rods and cladding.
Its also at least 2 or 3 times higher than anything that's been demonstrated so far in solid fuel (fast reactors like EBR & Phenix - which IIRC went up to about 150,000 MWd/tU).

PS. I don't see the need for a camera for refuelling: the fuel assemblies are installed in rigid grid restraints (egg-crate style), which are accessed by the combined offset rotating plugs & fuelling machine, at predictable locations - a fairly simple automated operation that relies on a set of 2-D core "map" coordinates.
Its not like trying to dock with the International Space Station :lol:

However, I think its disingenuous to claim that, by putting a steel dome over the reactor deck, the TP reactors are proliferation proof, because irradiated fuel is kept inside the core and can't get out: The dome obviously has several access hatches (visible in the 3-D CAD model), just like the French Phenix & Superphenix reactors, for removing/repairing/replacing defective components in the instrument column, fuelling machine, and control rod drives.
Plant operators in some foreign country could conceivably remove irradiated fuel assemblies by positioning a shielded transfer flask over one of these access hatches, and then rig up some way of hoisting the fuel from the core to the flask: tricky, but probably not impossible (for example, one could remove the fuelling machine with fuel in it).


Top
 Profile  
 
PostPosted: Dec 12, 2011 10:17 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5045
550 dpa! That's crazy. There is no cladding that can take this and keep pressure integrity.

But, if the reactor is started with reactor grade plutonium, that plutonium is intrinsically weapons-useless, due to extreme spontaneous fissions rate. One would want some of that useless plutonium in the fertile periphery elements. Of course, if the foreign country has control over its fuel rods supply it can just decide to not add the useless plutonium to the periphery elements, and use these to make a bomb. That would be a credible proliferation hazard (but only for a government with a lot of resources, that should have no trouble appropriating bomb material otherwise)


Top
 Profile  
 
PostPosted: Dec 12, 2011 1:54 pm 
Offline

Joined: Mar 01, 2010 11:33 pm
Posts: 61
Location: Berkeley, CA
@Cyril In the paper they say the neutronics support up to 40% burnup (400 GWd/tHM) without reprocessing.

@Jaro Where did you get the 3-D model? Are you sure you're not looking at the demo plant, which has fast flux test ports and other access for maintenance?

By the way, by some accounts the thermal U-Th reactor at Ft St Vrain achieved 170 GWd/t burnup. Actually it's by WNA's account, but when I asked them they couldn't produce a reference. Wikipedia says 90 GWd/t.

Edit: I wonder if anyone has ever tried making an amorphous metal out of DU. Zr is a common alloying element in amorphous metals. At least, displacements per atom may not be so structurally damaging to them.

-Carl


Top
 Profile  
 
PostPosted: Dec 12, 2011 2:31 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5045
Fort St. Vrain used TRISO type fuel which is known to facilitate high burnup without venting. This is done by leaving a lot of space full of porous carbon where the fission gas can go into and by having a very strong ceramic coating.

Travelling wave reactor uses a different fuel, metal fuel with metal cladding. This fuel is cheaper to make and easier to reprocess, but can it take 550 dpa? In particular can the cladding take it? It's okay if the fuel gets smashed into goo since it only has to sit there, lots of space for swelling by the metal bonding technology which is awesome. The cladding however must perform a containment function for most of the fission products, even if it is vented fuel. Embrittlement point creeps up to higher and higher temperatures with more lattice displacement, when the reactor operating temperature has been reached it gets ugly. Recently I read about a lead cooled fast reactor fuel design, they were counting on 4-8 dpa and then they had to swap out the fuel because the cladding couldn't take any more.

How many dpa do the state of the art ODS zirconium claddings achieve?


Top
 Profile  
 
PostPosted: Dec 12, 2011 3:08 pm 
Offline

Joined: Mar 01, 2010 11:33 pm
Posts: 61
Location: Berkeley, CA
Ft St Vrain had prismatic graphite fuel embedded with both fissile and fertile (thorium) TRISO particles. In fact it contained over 20 times more thorium than uranium. The fuel is said to be much cheaper to produce than normal fuel rods. Another spec sheet says it was rated to 100 GWd/t (6 years in the core). The reactor containment was prestressed concrete and the plant achieved 40% thermal efficiency. To my eye, simply iterating on this design would be a better engineering target to what TerraPower are undertaking. General Atomics is currently pushing a design called EM^2, but it is a fast reactor.

-Carl


Top
 Profile  
 
PostPosted: Dec 12, 2011 4:43 pm 
Offline
User avatar

Joined: Nov 30, 2006 9:18 pm
Posts: 1946
Location: Montreal
clumma wrote:
@Jaro Where did you get the 3-D model? Are you sure you're not looking at the demo plant, which has fast flux test ports and other access for maintenance?

Its a still frame from the presentation video.

Yes, it is the demo plant -- as you can see in the photo, "TP-1" ( 1200 MWth).

Yes, there is some extra instrumentation compared to the 3000 MWth commercial model ("TPRP").
But the large access ports in the top of the dome will always be needed - just as they were needed in Phenix & Superphenix - for removing damaged equipment like the fuelling machine and the main instrument column.
You don't just build another plant, whenever a component becomes defective !

PS. in this design, the primary sodium pumps and HX's are located INSIDE the pool, next to the core: Maybe you're confusing those with "extra instrumentation" ??


Top
 Profile  
 
PostPosted: Dec 13, 2011 12:20 am 
Offline
User avatar

Joined: Nov 10, 2011 8:13 pm
Posts: 7
Location: Gainesville, FL
To the best of my understanding, they are still very uncertain about the fuel cladding since materials aren't usually tested beyond 500 dpa (because most materials fail before they reach that point). Though the HT9 alloy shows some promise, they are open to the idea of fabricating a new material. They are still testing things. However, neutron irradiation testing is hard to do, so they make an approximation by hitting the material with Fe+, a process that is also referred to as ion implantation.

So much abuse, poor HT9. :-/

_________________
"To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge." ~ Copernicus


Top
 Profile  
 
PostPosted: Dec 13, 2011 2:54 am 
Offline

Joined: Oct 10, 2011 6:22 pm
Posts: 8
Quote:
He mentioned LFTR in one of his online presentations of his traveling wave reactor. He also mentioned property rights. And him being Bill Gates you would assume he wants to make money selling his reactors not Oakridge's reactors.


I find that hard to imagine. Bill Gates is worth, what, $60B? He would have to be incredibly greedy to pass up a superior technology that might literally save our civilization as we know it, just he can make more money. Even if he does not get the IP rights for LFTR, imagine how much he could make just funding it's development. It's a good investment, isn't it?

Until just a few days ago, I did not even realize that Bill Gates was interested at all in nuclear power. Now that I know he is, I'd say Kirk S. or someone should try to talk some sense into him. Or some other rich person. If LFTR is really as good as they say it is -- and I don't doubt it is -- than some major investor should be found. Hell, Bill Gates wouldn't even notice a billion dollars, yet imagine how much push it could give LFTR.

--Russ P.


Top
 Profile  
 
PostPosted: Dec 13, 2011 4:01 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5045
clumma wrote:
Ft St Vrain had prismatic graphite fuel embedded with both fissile and fertile (thorium) TRISO particles. In fact it contained over 20 times more thorium than uranium. The fuel is said to be much cheaper to produce than normal fuel rods. Another spec sheet says it was rated to 100 GWd/t (6 years in the core).


It is more expensive fuel to buy, but the high burnup makes up for that. With a sufficiently high burn the economics become actually better, despite the higher initial fuel investment, due to less downtime for refuelling. Also like you say the fuel operates hotter which makes the power conversion more efficient.

Quote:
The reactor containment was prestressed concrete and the plant achieved 40% thermal efficiency. To my eye, simply iterating on this design would be a better engineering target to what TerraPower are undertaking. General Atomics is currently pushing a design called EM^2, but it is a fast reactor.


This is the philosophy that led to the development of the advanced high temperature reactor at UCB. They swapped out high pressure gas coolant, which is less economical and less safe, for a low pressure fluoride coolant, which is safer and more economical. Dr. Per Peterson's group is working on a pebble bed version.

http://pb-ahtr.nuc.berkeley.edu/index.html


Top
 Profile  
 
PostPosted: Dec 13, 2011 4:21 am 
Offline

Joined: Mar 01, 2010 11:33 pm
Posts: 61
Location: Berkeley, CA
Yeah, I like the FHR/AHTR concepts quite a lot, and I agree the atmospheric-pressure operation (and greater thermal capacity) of molten salt is an advantage. Still, having thousands of spherical fuel elements bobbing around in there concerns me for some reason. I assume the moderation provided by the FLiBe results in a negative void coefficient for the thing... but I guess I should read up on it more. -Carl


Top
 Profile  
 
PostPosted: Dec 13, 2011 7:25 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5045
So far the neutronic analysis of the AHTRs have shown that FLiBe has negative void. More importantly, the total coefficient is negative.

The advantage of pebble fuel is easy shuffeling of pebbles, reducing fissile requirements, and lack of complex core internals and fuel (they are all the same little balls, amenable to mass manufacture). Also the power density is higher for pebble fuel.

Regarding the dpa rates, what do CANDU pressure tubes take? They seem to last quite long (though not 60 years) right in the middle of high flux.


Top
 Profile  
 
PostPosted: Dec 13, 2011 9:32 am 
Offline

Joined: Nov 20, 2011 6:28 pm
Posts: 3
Please not Bill Gates!

Let's try with someone smarter. I think Sergey Brin would be the perfected sponsor of LFTR. He's rich, smart and really likes innovative, crazy and green things like electric automatic cars. Also Google hosted several tech talks about LFTR, also Kirk IIRC.
Google have invested on innovative wind power systems, but I think the Sergey could really appreciate the LFTR and understand its potentials.


Top
 Profile  
 
PostPosted: Dec 13, 2011 12:52 pm 
Offline

Joined: Oct 10, 2011 6:22 pm
Posts: 8
Yeah, getting Sergey Brin to invest is a great idea. I realize that getting the ear of someone like him is not easy, but as you say Kirk has given talks at Google, so you'd think word would get to him. Maybe it has and he is just not sold on the LFTR idea. If that's the case, maybe Kirk and Flibe need to work on a high-level contact there at Google.

Getting back to Bill Gates, I am certainly no big fan of his. I use Linux and I avoid Windows as much as possible. But think about the gigabucks Gates is already putting into his charitable foundation. If just a small portion of that could be diverted to LFTR development, the long-term benefits for Africa alone would probably dwarf the benefits of all his charitable contributions. It's a win-win no-brainer.


Top
 Profile  
 
PostPosted: Dec 13, 2011 1:15 pm 
Offline
User avatar

Joined: Nov 30, 2006 9:18 pm
Posts: 1946
Location: Montreal
Cyril R wrote:
Regarding the dpa rates, what do CANDU pressure tubes take? They seem to last quite long (though not 60 years) right in the middle of high flux.
Can't quote a dpa number off hand.
But the PTs will last at most 25 years (hence the currently on-going refurb projects at several old CANDU plants: Korea's Wolsong-1 restarted a few months ago, with a core full of new PTs)
Also, the neutron flux is likely to be considerably less damaging than an FBR: the fuel is oxide, not metal, and there is light water coolant in the PTs.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 226 posts ]  Go to page Previous  1 ... 8, 9, 10, 11, 12, 13, 14 ... 16  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 0 guests


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