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PostPosted: Dec 07, 2011 5:27 pm 
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Jonathan Wyers wrote:
what they're trying to do: eliminate the need to remove, reload, or readjust fuel elements as in LWRs (though TWR's require reshuffling, I still don't know how they physically go about this, he showed us some computer models on some optimal shuffling schemes, but nothing about how that shuffling occurs, and he also said the reactor is supposed to be sealed?

That's the difference between a computer model and a real, engineered gizmo -- in the latter, magic isn't allowed, unfortunately. :lol: :lol: :lol:


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PostPosted: Dec 07, 2011 9:13 pm 
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Jonathan Wyers wrote:
what they're trying to do: eliminate the need to remove, reload, or readjust fuel elements as in LWRs (though TWR's require reshuffling, I still don't know how they physically go about this, he showed us some computer models on some optimal shuffling schemes, but nothing about how that shuffling occurs, and he also said the reactor is supposed to be sealed?

Shuffling solid fuel on the fly? Nice trick, BIG vessel ....or nuclear Rubik's Cube?

Jonathan Wyers wrote:
Right now, Terrapower is very happy with the fact that the coolant it has selected, Sodium (Na), is compatible with its fuel and fuel cladding.

Not thrilled about sodium used as a coolant. A LFTR is looking better and better to me


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PostPosted: Dec 07, 2011 9:19 pm 
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This is something I have always wondered about. How does the the potential of the Travelling Wave Reactor stack up against the potential of LFTR? Does TWR have any shortcomings or potential problems that gives LFTR an advantage?


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PostPosted: Dec 07, 2011 10:03 pm 
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See the other thread but basically TWR is a fast spectrum, uranium burning, solid fuel, long duration, no processing machine.
All nice properties but makes for some extremely demanding materials and controls problems.
Specifically:

First, the cladding that separates the fuel from the coolant has to live in the middle of the neutron flux, that flux is a fast spectrum, and it has to live fo 40-60 years. Typically, in an LWR the lifetime is 6 years and it isn't in the middle of the flux for that time and the spectrum is slower. So this is more than a little challenge.

Second, the reactor is fast spectrum which means the time constants for reactivity changes are very much shorter - you need a fast control mechanism. Being fast doppler does not help you nearly as much as a slow spectrum machine.

Third, the reactor is solid fuel. This means you need to be able to predict the evolution of the fuel and flux intensities over the lifetime of the fuel. This is currently done for LWRs starting with very well known fuel (enriched uranium) and with a 6 year evolution time. It is a pretty challenging problem for LWRs but one that has been satisfactorily solved. Here, you want to start with spent fuel which means there is a bit of uncertainty as your starting point is the ending point for a previous fuel cycle. Now you need to forecast forward 40-60 years of being in the reactor. I would be concerned about hot spots that have a higher reactivity than planned and overstress the cladding thermally.


A LFTR avoids these but has its own challenges.


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PostPosted: Dec 07, 2011 10:28 pm 
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Traveling Wave Reactor is a breeder reactor using solid fuels and liquid sodium as primary coolant. Liquid sodium is explosive if exposed to air, which is a problem. Solid fuels will crumble over time due to radiation and fission products, and they will have to re-clad the solid fuels to extend their shelf life.

These are significant drawbacks, and it is not clear to me why Bill Gates is pushing TWR instead of Molten Salt Reactors.

T. Wang


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PostPosted: Dec 07, 2011 10:38 pm 
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Computing billionaire Bill Gates has confirmed he is discussing developing a new and safer kind of nuclear reactor with China.
"The idea is to be very low cost, very safe and generate very little waste," said the Microsoft co-founder in Peking.

With Jonathan's insight in regards to his post on vessel metallurgy questions, coupled with sodium as a coolant.
How in the wildest stretch of the imagination could this be considered as "very safe"?
I think Jonathan's right, they weren't using a 1024 Xeon possessor. More like S.W.A.G. :lol:


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PostPosted: Dec 07, 2011 11:35 pm 
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Lars wrote:
First, the cladding that separates the fuel from the coolant has to live in the middle of the neutron flux, that flux is a fast spectrum, and it has to live fo 40-60 years.

Trying to be more objective, I would have to say that, by definition, the neutron flux in a traveling wave reactor will NOT be constant for 40-60 years, at every location in the reactor: Depending on the width of the "wave", which can be designed to be more or less wide, mostly by selecting less dense or more dense materials for fuel & coolant (respectively), the exposure of the spent fuel to neutron flux could, theoretically, be minimized.
Of course, not knowing the details of the TWR design, this all just speculation...


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PostPosted: Dec 08, 2011 2:07 am 
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EnergyUser wrote:
Traveling Wave Reactor is a breeder reactor using solid fuels and liquid sodium as primary coolant. Liquid sodium is explosive if exposed to air, which is a problem. Solid fuels will crumble over time due to radiation and fission products, and they will have to re-clad the solid fuels to extend their shelf life.
These are significant drawbacks, and it is not clear to me why Bill Gates is pushing TWR instead of Molten Salt Reactors.
T. Wang

China is the place where nuclear systems are being constructed and new ones get a chance. AP-1000 has already been proved in China.
http://www.chinadaily.com.cn/cndy/2011- ... 223281.htm
His Terrapower is developing a TWR and China is the place to develop it at a low cost and to prove it before selling it elsewhere.


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PostPosted: Dec 08, 2011 2:19 am 
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Sodium coolant is what gave fast reactors a bad name. A lot of people want to throw away the fast reactor baby with its sodium bath.
A salt coolant is the best anti-dote to sodium allergy. Let someone try out a moderately priced SnF2-PbF2 mixture.


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PostPosted: Dec 08, 2011 5:04 am 
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Someone please correct me if I'm wrong, but I thought that I read somewhere recently TerraPower had admitted that the TWR would have to be a fuel shuffler. Perhaps it should be TFR, Travelling Fuel Reactor.


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PostPosted: Dec 08, 2011 10:18 am 
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Your right Lindsay. As far as I know it is no longer a traveling wave reactor. So what exactly is it now if they just shuffle fuel into and out of the higher power region. Hmmm, an extra large fast breeder core that stores its decades of spent fuel in the active core. Wow, that sounds like a wonderful idea to me.

David LeBlanc


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PostPosted: Dec 08, 2011 3:38 pm 
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David wrote:
Your right Lindsay. As far as I know it is no longer a traveling wave reactor. So what exactly is it now if they just shuffle fuel into and out of the higher power region. Hmmm, an extra large fast breeder core that stores its decades of spent fuel in the active core. Wow, that sounds like a wonderful idea to me.

David LeBlanc

Yes, an advanced materials testing lab for highly irradiated fuel undergoing further irradiation for 60 years, what could possibly go wrong :shock:


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PostPosted: Dec 09, 2011 5:11 pm 
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"All these new designs are going to be incredibly safe," Mr Gates said. "They require no human action to remain safe at all times."

What if you get a sodium leak? I like the design except for the requirement for using sodium.


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PostPosted: Dec 09, 2011 9:15 pm 
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One would think that before investing a billion dollars, an investor would investigate all the various types of reactors and invest in the one that best meets the target criteria, which is LFTR. That is, unless one has a billion dollars to burn.


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PostPosted: Dec 10, 2011 12:52 am 
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Steve Brown wrote:
One would think that before investing a billion dollars, an investor would investigate all the various types of reactors and invest in the one that best meets the target criteria, which is LFTR. That is, unless one has a billion dollars to burn.


Bill Gates knows about LFTR. Maybe he thinks his design is less expensive. I would like to know what he thinks will be the cost of electricity with the TWR.

It is sad that he has to go to China to get it built.


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