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PostPosted: Dec 10, 2011 1:28 am 
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Bill Gates knows about LFTR. Maybe he thinks his design is less expensive.


His reasons most probably are based on intellectual property rights.

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PostPosted: Dec 10, 2011 2:39 am 
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I think the selection of design was a fast spectrum. It has been stated that the Terrapower has moved to another fast neutron design.
The regulatory regime in China is more developer-friendly. The way to do it in the US was to call it a waste incinerator with the DOE blessings. Position it as an alternative to Yucca!


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PostPosted: Dec 10, 2011 4:28 pm 
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Christopher Calder wrote:
Bill Gates knows about LFTR....


I'm curious as to how you know that. I wonder if he actually listened to any of Kirk Sorensen's lectures. It's difficult to imagine an intelligent person doing so without being convinced LFTR is the best way forward in nuclear reactor design.


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PostPosted: Dec 10, 2011 6:45 pm 
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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.


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PostPosted: Dec 10, 2011 8:30 pm 
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Except ORNL designs are not patent protected- well and truly expired and his LTFR design would actually be new (unlikely to be the original) and so patentable.


The Chinese will rip him off.


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PostPosted: Dec 11, 2011 10:44 am 
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I just watched this video:
http://www.intellectualventures.com/new ... culty.aspx

Are they really going to have more materials problems than other SFRs? What I understood is that they plan to put fuel rods worth 60 years of operation into the core. A few rods in the center are enriched to 11%. As plutonium in the rods next to the center is bread, a fuel shuffling robot shuffles the exhausted rods out of the center and irradiated ones in. As the inner fuel rods serve as a shield for the outer ones the total neutron load for the individual rod should not be higher than with conventional SFRs. Note that this also provides an effective shielding for the reactor vessel. They could populate the outer region more densely for good shielding and the inner region more sparsely to allow for easy sodium flow.

If they really get their reactor running for 60 years, why bother about reprocessing now? 60 years should be enough time to develop GANEX.


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PostPosted: Dec 11, 2011 2:46 pm 
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Burghard wrote:

Thanks !

The reactor design looks an awful lot like France's old Phenix & Superphenix reactors : a big steel dome over the reactor deck, with offset rotating plugs to switch between the instrument column and the refuelling mechanism.
I don't see anything different in it, other than fuel material (U-Zr alloy) and a great big core load in which the spent fuel is not removed for ~40 years.


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PostPosted: Dec 11, 2011 6:38 pm 
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Thanks Jaro, I'll try to watch that later tonight. Probably it has a lot of the same info as this paper

http://lumma.org/temp/Ellis_et_al-TWRs_ ... source.pdf

which was taken down from the site hosting it, but not before I could yank it from the Google cache. Get it while it's hot - Gates and Myhrvold are both coauthors! I read it last night and made these notes:

* The TerraPower TWR is one of an emerging class of once-through fast reactors, which aim to achieve high burnup without reprocessing. A good review is
http://www.ipd.anl.gov/anlpubs/2010/09/67863.pdf

* Pool-type, sodium-cooled fast reactor

* Some design choices made in order to minimize technical and regulatory risk

* Design is still changing rapidly

* Does use a breed-and-burn "wave", but fuel shuffling will be used to keep the critical region stationary, presumably to simplify cooling and other systems.

* Fuel shuffling will take ~ 2 wks and will require an outage, but will not require opening the core. Secrecy over the details of this is explicitly mentioned. I expect a robotic arm of some kind.

* Like all fast rectors, serious materials questions remain with respect to the target 40-60yr core lifetime.

* Fuel will be U-Zr metal with steel cladding

* For a long time I thought Gates' objection to LFTR must be the lack of fuel cladding as an FP barrier. But in the TWR the steel cladding is apparently not sealed, and involves "fission gas plenums" that allow gaseous FPs to leave the fuel, travel out of and collect above the coolant in an space designated for that purpose!

* That's just the start. Design complexity seems to be multiplying like crazy. Mentioned are various types coolant orifices - some fixed and others adjustable - which delineate different classes of fuel assembly (which were already divided into active and reserve assemblies).

* One of the benefits of breed-and-burn fast reactors is that they don't have lots of extra reactivity and therefore don't need control rods or other shims. No wait- TWR has control rods now too! In fact these are planned to be long-life hafnium hydride, and are currently under development "in Japan".

* Many details of their core simulations are mentioned, which may be of interest to readers here.

If you ever wondered what it would take to get an IFR to 40% burnup without reprocessing, this paper gives a taste.

-Carl

Edit: Sorry Burghard, I see you found the video. I wrongly attributed it to Jaro since he also posted it to facebook. Apparently they've revealed the robots then!


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PostPosted: Dec 11, 2011 8:21 pm 
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Thanks Carl,

Good of you to have saved the paper & made it available to others !

Regarding a couple of the notes you made, the presentation video addresses some of the issues - either directly or in replies to questions from the audience....
clumma wrote:
* Fuel shuffling will take ~ 2 wks and will require an outage, but will not require opening the core. Secrecy over the details of this is explicitly mentioned. I expect a robotic arm of some kind.
No "robotic arm."
Instead, its the old combination using offset rotating plugs and a pretty ordinary fuelling machine: the same system was used in the French FBRs, only more complex, in that it also moved spent fuel to a storage bay, instead of just shuffling it around in the core.

clumma wrote:
* For a long time I thought Gates' objection to LFTR must be the lack of fuel cladding as an FP barrier. But in the TWR the steel cladding is apparently not sealed, and involves "fission gas plenums" that allow gaseous FPs to leave the fuel, travel out of and collect above the coolant in an space designated for that purpose!
The TP engineers said the opposite: NO fuel venting.
Maybe it depends on which day of the week you ask them :lol:


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PostPosted: Dec 11, 2011 10:40 pm 
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clumma wrote:

* Fuel shuffling will take ~ 2 wks and will require an outage, but will not require opening the core. Secrecy over the details of this is explicitly mentioned. I expect a robotic arm of some kind.



Perhaps the reason for secrecy is, they don't have a clue how to do it. With the cascading level of complexity within the vessel, I'd be surprised if they had room for offset rotating plugs to move the fuel around.
If it were some type of portal mounted robot within the reactor vessel they would have other issues. Want to take a guess how many minutes cameras or position sensors last in a high radiation environment?

OK, I'm just a lowly machinist with nothing higher than a H.S. diploma, and it's so freaking obvious there would be a better chance of commercial fusion power before a TWR will happen, and that wont be in my lifetime.

Maybe Mr Gates is trying to kill nuclear innovation with thinking like -Look, I tried to build a safe reactor, and it couldn't be done, so therefore don't bother.


Last edited by Prothor on Dec 11, 2011 10:52 pm, edited 1 time in total.

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PostPosted: Dec 11, 2011 10:51 pm 
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Perhaps they plan to return to vacuum tube electronics. That survives radiation better than solid state electronics.


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PostPosted: Dec 12, 2011 2:11 am 
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They talked about recladding plutonium enriched fuel rods as a potential "advantage" of the Traveling Wave Reactor. I have no idea where Gate's promise of this is all very safe comes from. Smells very risky to me; perhaps more dangerous than a Light Water Reactor.

T. Wang


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PostPosted: Dec 12, 2011 4:29 am 
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Working in the field of industrial safety myself, I have serious doubts about sodium's wonderful safety advantage. Using a fuel to cool a reactor, several hundred degrees above its flash point, in contact with an extreme oxidizer (steam in the power cycle), even with a second non-radioactive loop, is a serious pain. Even without any radioactivity involved, a fire in the primary components of a nuclear plant is really bad publicity. There was a sodium fire near here, in Delfzijl, recently. It had inerted cover gas systems and everything, still had a fire.

I talked to a nuclear engineer about it that had experience in EBR reactors design. He had a funny joke about it; I don't remember it exactly but it went something like this:

Sodium is easy to master by the cubic yard
It's less than pleasant by the cubic foot
And an inch sodium filled tube is always a nightmare

The pool type design suddenly made a lot of sense to me. Sodium reactors really have to avoid fuel dry out in all cases, since if there is gross fuel melting, there will be a likely critical reconfiguration, the fuel being heavier, will slump to a critical assembly.

However some of the issues mentioned upthread would be fairly easy to solve. Fiber optics for the cameras, ultrasound for looking into the sodium pool. Attach steel rods to the fuel elements, extending out of the sodium pool, to allow shuffeling of the fuel in the cover gas rather than trying to manipulate in an opaque pool of sodium. Etc. All fairly easy to solve, I'd think.

The high burnup is still a worry. Even if not 60 years, but 20 (due to shuffeling) that is difficult to test for longevity. Anyone know the burnup in GWd/ton they are aiming for?


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PostPosted: Dec 12, 2011 4:53 am 
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For a long time I thought Gates' objection to LFTR must be the lack of fuel cladding as an FP barrier. But in the TWR the steel cladding is apparently not sealed, and involves "fission gas plenums" that allow gaseous FPs to leave the fuel, travel out of and collect above the coolant in an space designated for that purpose!


This is called "vented fuel". In stead of a sealed plenum, there are a bunch of holes in the plenum. There is also some kind of siphon or capillary trap, and/or filter plugs (like a cigarette filter) to trap the reactive stuff so that mostly noble gasses are vented.

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.

While vented fuel does increase the radiological burden in the coolant, oddly enough, vented fuel is actually safer in an accident. The excess gas release during an accident is vented rather than causing the internal pressure to rupture completely sealed fuel elements. This means the cladding doesn't balloon, avoiding flow blockage that could exagerbate the accident. The cladding integrity is largely maintained.


I wonder how they will remove the gasses and volatile fission products from the coolant. Cesium is very similar to sodium, and iodine's behaviour in sodium is very complex.


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PostPosted: Dec 12, 2011 6:01 am 
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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.


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