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Traveling Wave Reactor
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Author:  David [ Dec 16, 2011 3:19 pm ]
Post subject:  Re: Traveling Wave Reactor

Quote:
Everyone talks about different fuels in Calandria configuration but the only coolants considered have been water or heavy water.


Not true, AECL came pretty close to implementing a low pressure, high temperature (425 outlet) oil as the coolant (cool heavy water still the moderator). They even ran a reactor with it in the 60s. Great stuff overall, many still lament it being abandoned. The fact that the stuff burns always threw me off but I never really looked into it too deeply.

David LeBlanc

Author:  Lars [ Dec 16, 2011 7:10 pm ]
Post subject:  Re: Bill Gates in talks with China on TWR

700C is pretty toxic.
Intense radioactivity is pretty toxic.
So I'm not sure there is significant additional precautions required if beryllium is present.
No graphite in the core helps the with graphite lifetime and waste flow, it also helps with the slow rate positive thermal reactivity.

But going without graphite and looking for breeding means you have to use either 1.5 or 2 fluid. This brings in the challenge of lifetime of the first wall (between fuel and blanket salt). A 1.5 fluid design is less stressful on the first wall since most of the neutrons used for fertile conversion to fissile happen in the fuel salt. But there are still enough neutrons flowing through the wall to require some improvement from the state of the art in 1970. The 1.5 fluid approach is what the French are pursuing. Using this makes the first wall problem more solvable. The French believe they have a different metal formulation that they believe will handle the neutron flux better. But this then needs to tested and qualified. Second with a 1.5 fluid design they have thorium in the fuel salt and separating the thorium from the fission products is a bit of a challenge. The French are planning to use liquid metal exchange with bismuth to do this - which ORNL was hopeful for but I was not impressed by the early test results. Still, good work going on there!

Author:  jagdish [ Dec 17, 2011 12:22 am ]
Post subject:  Re: Traveling Wave Reactor

It may have been abandoned due to instability of oils at high temperature. I read about it once and then proceeded to search for more of less volatile moderator/coolants to reduce the pressure in tubes/reactor vessels. A per-fluorocarbon lubricant, Krytox (poly hexa-fluoro propyl ether) came nearest. I have not been able to convince many about it. Mg and Al have higher ignition points than Sodium and I have had some encouraging feedback. Tin or lead di-fluorides would be non-moderating but no more corrosive than other fluorides. Tetra-fluorides could be oxidizing. You could always have Nickel or copper coating if found necessary.

Author:  Cyril R [ Dec 17, 2011 6:32 am ]
Post subject:  Re: Traveling Wave Reactor

Tin and lead fluorides are very corrosive. In fact you'd be better of with pure lead coolant than lead fluoride.

Lead is a pretty good coolant for a fast reactor. Lead is corrosive to nickel alloys but not to zirconium, niobium, molybdenum with proper oxygen control. Would be nice for a CANDU as well, especially if using radiogenic lead, from thorium deposits, when thorium decays it eventually becomes Pb-208, the best lead isotope for reactor coolant. Lead doesn't moderate, so in a lead cooled heavy water moderated CANDU it means you have a bimodal spectrum and can breed much better with both U-Pu and Th-U. Lead is compatible with the zirconium alloys used in CANDUs so you can just make the entire primary loop out of that, and maybe a TZM steam generator tubing.

Author:  Lindsay [ Dec 19, 2011 3:08 pm ]
Post subject:  Re: Bill Gates in talks with China on TWR

I would just add, that however you approach it the barrier and barrier service life is and issue, so my suggestion is to keep the geometry simple, the wall thickness as thin as possible and just replace as required. With additional work there may even be some opportunity for recycling the barrier material so that it does not have to become waste.

Author:  djw1 [ Dec 29, 2011 3:29 pm ]
Post subject:  Re: Bill Gates in talks with China on TWR

If Terrapower were making good progress,
Gates would never have gone to China,
where he knows he will get ripped off.

Gates has about 200 countries at his disposal
including several that owe him big time.

Gates going to China tells me he doesn't think
he has enough money to develop the TWR,
and if he doesnt, nobody does.

Author:  Lars [ Dec 29, 2011 4:28 pm ]
Post subject:  Re: Bill Gates in talks with China on TWR

OR that his concern isn't making money. Maybe he wants the world to build fewer coal power plants and Terrawatt is the way he sees this happening.

Author:  jagdish [ Dec 29, 2011 7:38 pm ]
Post subject:  Re: Bill Gates in talks with China on TWR

There is probably no scope of starting physical construction of new design in the US due to regulatory hurdles. One US reactor design has been built in China and then approved in the US. He is in all probability doing the same.
For a long burn up, that he aims at, you require not only a high conversion/breeding ratio but also removal of neutron poisons. Liquid fuel helps in escape of gaseous fission product poisons. It is more difficult in solid fuels.

Author:  Ed P [ Mar 02, 2013 12:22 am ]
Post subject:  Re: Traveling Wave Reactor

So, basically this is a Na IFR, but much bigger because they load all the fuel in at beginning of life (and pay for it then, i.e. one of the problems with current PWRs is initial cost). This is especially costly for a fast reactor.

This would seem to require a massive Na inventory as well. Coolant is flammable and reacts with water.

Many coolant flow paths are a nightmare and require extra pumping power.

They have refueling shutdowns just like PWR's or normal IFR's, they just don't open the Reactor.

They have massive burnup and neutron fluence problems to overcome, with several work arounds like metalic fuel, sodium filled cladding, vented fuel (not too happy about that one). This is the reason I prefer LFTR's, even higher burnup, but no fuel damage concerns.

They keep the spent fuel inventory around the core and keep it activated, so any accident scenario would include it.

The design is still going through significant changes from candle TWR, to pebble in a pond TWR, to standing wave by shuffling fuel. Technically, CANDU is a standing wave reactor with water instead of sodium.

Author:  FRE [ Mar 02, 2013 12:48 am ]
Post subject:  Re: Traveling Wave Reactor

Cyril R wrote:
Tin and lead fluorides are very corrosive. In fact you'd be better of with pure lead coolant than lead fluoride.

Lead is a pretty good coolant for a fast reactor. Lead is corrosive to nickel alloys but not to zirconium, niobium, molybdenum with proper oxygen control. Would be nice for a CANDU as well, especially if using radiogenic lead, from thorium deposits, when thorium decays it eventually becomes Pb-208, the best lead isotope for reactor coolant. Lead doesn't moderate, so in a lead cooled heavy water moderated CANDU it means you have a bimodal spectrum and can breed much better with both U-Pu and Th-U. Lead is compatible with the zirconium alloys used in CANDUs so you can just make the entire primary loop out of that, and maybe a TZM steam generator tubing.


Some of the Russian nuclear submarines used Pb as a coolant.

Author:  Ed P [ Mar 02, 2013 1:07 am ]
Post subject:  Re: Traveling Wave Reactor

And where are those reactors now............................?

Defunct? Most Decommissioned in 1990. According to wikipedia they were expected to have a short life, probably due to PbBi corrosion of the vessel.

http://en.wikipedia.org/wiki/Alfa_class_submarine

Author:  FRE [ Mar 02, 2013 2:06 am ]
Post subject:  Re: Traveling Wave Reactor

Ed P wrote:
And where are those reactors now............................?

Defunct?


At least one sunk with its submarine. I think that the others are defunct.

I got the information from the book Plentiful Energy by Till & Chang. They strongly support the IFR and strongly defend the Na cooling. However, the reprocessing of the fuel to me seems somewhat awkward. They have to chop up the fuel rods, including the stainless steel cladding, before using what amounts to a modified electroplating process. Making the fuel rods includes a casting process. And, unlike the LFTR, it has to be shut down for refueling. The IFR may well be practical, but the LFTR approach seems much simpler to me. However, I think that it would be a mistake to rule out the IFR approach completely until it can be established that the LFTR can be scaled up and have a long trouble-free life; it could have serious problems which are not yet apparent. I seem to recall something about putting all of one's eggs into one basket. We've already made that mistake with the PWR.

Actually, I don't have the right degree to understand this sort of thing so probably I'm not qualified to have an opinion.

Author:  jagdish [ Mar 02, 2013 4:49 am ]
Post subject:  Re: Traveling Wave Reactor

I am sure an enamel to protect a reactor material from any coolant can be found. It could be silica or pyrolytic carbon or SiC. Fire prone sodium needs replacement as heat transport agent.

Author:  Ed P [ Mar 02, 2013 8:35 am ]
Post subject:  Re: Traveling Wave Reactor

jagdish wrote:
I am sure an enamel to protect a reactor material from any coolant can be found. It could be silica or pyrolytic carbon or SiC. Fire prone sodium needs replacement as heat transport agent.


@jjagdish, Everything is relevant. Would you rather have a coolant that burns (Na) on contact with air or one that vaporizes on contact with air, causing immediate loss of cooling, producing hydrogen gas, that explodes.............................. :lol:

Author:  FRE [ Mar 02, 2013 3:50 pm ]
Post subject:  Re: Traveling Wave Reactor

jagdish wrote:
I am sure an enamel to protect a reactor material from any coolant can be found. It could be silica or pyrolytic carbon or SiC. Fire prone sodium needs replacement as heat transport agent.


Depending on a coating that could be breached is also risky. Even a scratch that would enable the coolant to contact the base metal could create serious problems. In earlier times, cars had chrome trim, which was actually plated steel. Bumpers (fenders in British English) were chrome. In areas where salt was used for melting ice, even the slightest scratch to chrome plated parts resulted in rust.

Na for cooling does have it's problems, but the authors of Plentiful Energy, i.e., Till & Chang, believe that dealing with the reactivity of Na is a problem that can easily be dealt with. They provide examples. Even so, I'd think that it would be inconvenient. Surely it would complicate refueling since the entire operation would have to be done within an Ar blanket. If too much Ar escaped, there would be a risk of suffocation.

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