Energy From Thorium Discussion Forum

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PostPosted: Feb 22, 2012 5:41 pm 
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The past couple of weeks I have been reading "Atomic America", a book written by Todd Tucker. What struck me is me how important the role of the U.S. Navy has been as a pioneer of nuclear technology. Especially worth mentioning is, of course, the pivotal role played by Admiral Hyman Rickover overseeing the development of light-water reactors and the nuclear Navy.

Nowadays, the U.S. Navy is the largest operator of nuclear reactors in the world. The U.S. Navy seems to be a satisfied user of PWR reactors for their aircraft carriers and submarines. These naval reactors have long core lives (>30 years) thanks to the highly enriched fuel that is used. This naval HEU fuel is reprocessed from nuclear weapons by the DOE Y-12 Facility in Oak Ridge, Tennessee.

Although the Navy seems to be satisfied with the status quo, I wonder what could be a good Generation IV reactor replacement for the current naval reactors. Would a LFTR/MSR be appropriate for use in a submarine ? Or would other Gen-IV reactor types be better ? I guess a S-CO2 power conversion system would also be of great benefit in a submarine. Is it possible that the U.S. Navy will take on its role as a nuclear technology pioneer again ? It has two research laboratories dedicated to naval reactors at its disposal, the Bettis and Knolls Atomic Power Labs, which could be of great help developing Gen-IV reactor technologies


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PostPosted: Feb 23, 2012 9:49 am 
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For the submarine community the radiated noise levels is of paramount concern. Not just peak noises but the frequencies and their distribution. The aircraft carriers would have an easier time of it, and they would love having more space (I'm figuring LFTR & its associated support equipment is smaller in volume). I can picture most of the surface fleet switching over to LFTRs since it would dramatically change their refuelling requirements and their operations tempo. Also, having a reactor will be handy if their rail guns and laser developments work out and they need the electrical power.

The Navy (or DoD) is interested in powering remote bases without the need to resupply them with diesel fuel. And since wind and solar have intermittency issues that really shortens up the list where small compact reactors (such as LFTR) are the list. An intriguing projection would be: Navy contracts a company to make such a reactor for its bases overseas, then decides it would be great for its ships. Then it will be fairly obvious that US bases can be powered by the same/similar technology reactor. Finally it will dawn on the masses that civilian power can use the same tech. Probably after purchasing excess electricity from Naval/DoD installations! At this point I think the number of trained and experienced personnel would be available to train/work for power companies.

Just some thoughts,
Jim L.


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PostPosted: Feb 24, 2012 9:57 am 
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Most compact reactor I can visualize is a fast spectrum MSR.
To avoid diesel replenishment requirements on bases, have some buried RTGs fueled by fission products Cs and Sr.


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PostPosted: Mar 04, 2012 8:06 pm 
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Alas, most navy nukes think MSRs are too weird to bother with. They never get to the specific power specs, or other information about MSR's objective superiority for vehicle engineering. If we really wanted to get their attention, the thing to develop would be a LFTR that was perfectly noiseless. And, maybe it's possible. No water means no boiling. Maybe a supercritical CO2 turbine with gas bearings could be dirctly coupled to a centripetal injection pump with an external laminar-flow venturi: No turbine noise, no propeller noise, reduced wake noise (ever heard a Dyson fan? Same principle.), a very small power plant, and power to burn.


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PostPosted: May 21, 2012 12:00 pm 
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Seems to me that the best selling point for Naval nukes is the lack of a need for an accident pressure containment vessel, being has how the LFTR has no pressure driver.

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PostPosted: May 21, 2012 7:47 pm 
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what would be the effect of getting sea water into the LFTR on a sub?


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PostPosted: May 22, 2012 8:28 am 
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A lead cooled fast reactor fuelled with some sort of TRISO using HEU or Pu fuel would probably be a better fit for a submarine. You don't want to do all sorts of fuel processing in a tiny submarine. SCO2 would also be a good coolant, with TRISO fuel, with a direct cycle into a compact tubine. Magnetic and gas bearings.

Fast spectrum is attractive due to the compact core and high burnup, and you don't really care about fissile cost.


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PostPosted: Feb 23, 2013 4:53 pm 
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I think a sub-LFTR would not need a lot of exotic fuel cleaning. It would have to be drained and refilled, but existing subs have service items as well. For example, they have to change deionization resins, and this is sometimes done at sea via tenders.

I think a LFTR is an excellent fit because it has a very high energy density, and a more stable fuel configuration, less prone to hot spots. A special, very nice feature is that the fuel can be replaced without removing or rebuilding the core. Since the energy required is relatively small, and the requirements for fissionables are relaxed (90% HEU or U233 is just fine), it should be possible to build a core with no graphite, as well, so the Navy's apparent requirement for a long lifetime would be met, as well.

The whole game in this application is how to make a stealth powerplant. I think a supercritical CO2 plant is just the thing. The entry and exit temperatures match a LFTR. The specific power of both items is very high. The smaller equipment can be better isolated and operate with high frequencies that are easier to damp and isolate. The real question is how to couple that small equipment efficiently to drive the hull. I think the trick is to convert high pressures at low volume into reaction forces. That's why I suggested a laminar-flow driver. The turbine could also power a hydraulic or electric drive, which would work very well with a conventional screw, or Voith-Schneider drives.


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PostPosted: Feb 24, 2013 7:45 am 
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Low mass and volume are a definite advantage in a submarine power plant. One without graphite would be useful. Thorium fuel is good for a long fuel life. So is molten salt. A fast LFTR using FNaZr would be the right power plant.


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PostPosted: Feb 24, 2013 8:11 am 
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Would a LFTR made less noise than a PWR ? AFAIK a PWR on a sub uses natural circulation for the coolant at least on low power and
iirc we had a discussion here on the board that natural circulation is very difficult for a molten salt reactor.
So a mrs must use their pumps all the time or ?


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PostPosted: Feb 24, 2013 8:59 am 
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I highly doubt that an MSR would end up being a superior reactor for a military submarine, mostly due to space constraints and noise issues. For a civilian (or even military) surface vessel, on the other hand, an MSR might be a very attractive choice.


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PostPosted: Feb 24, 2013 9:00 am 
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Aren't MHD pumps viable for molten salts?

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PostPosted: Feb 24, 2013 9:13 am 
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KitemanSA wrote:
Aren't MHD pumps viable for molten salts?


No, insufficient electrical conductivity.


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PostPosted: Feb 24, 2013 10:17 am 
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Kirk Sorensen wrote:
KitemanSA wrote:
Aren't MHD pumps viable for molten salts?
No, insufficient electrical conductivity.
Really? Molten salt? aluminum smelting? Hmm...

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PostPosted: Feb 24, 2013 10:34 am 
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Kirk Sorensen wrote:
I highly doubt that an MSR would end up being a superior reactor for a military submarine, mostly due to space constraints and noise issues. For a civilian (or even military) surface vessel, on the other hand, an MSR might be a very attractive choice.

Why should pumping the fuel salt around generate more noise than pumping coolant water?


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