Energy From Thorium Discussion Forum

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PostPosted: Jan 01, 2014 5:31 pm 
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Eino wrote:
I suppose you could put the freeze plug on each side, but I doubt whether a commercial facility will be built that way. Downtime is to be kept to a minimum.


I'm intensely aware how commercial thinking works, and that is precisely why a proactive design approach is needed. I regularly meet companies, who want to shave off ten minutes of downtime, by installing equipment that risks ruining a multi million dollar installation and cause a major media scandal. We must protect the penny wisers from such pound foolishness, and the best way to do it is by design. Equipment that is not there cannot be abused. If there is no rapid isolation option, there is no rapid isolation transient, no pipes bursting due to liquid hammer, and no way for the rapid isolation to fail (which can actually result in a lengthy outage, ironically).

If nuclear energy is to power the world, we can't rely on highly trained operators always doing the right thing. We should count on a coal plant mentality and design for that.


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PostPosted: Jan 01, 2014 7:42 pm 
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Well - It's your imaginary power plant. If you want to leave valves out that's fine with me.


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PostPosted: Jan 02, 2014 5:59 am 
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Eino wrote:
Well - It's your imaginary power plant. If you want to leave valves out that's fine with me.


Unlike your powerplant, of course, which is undoubtedly purring along in your backyard.


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PostPosted: Jan 02, 2014 7:06 pm 
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"Unlike your powerplant, of course, which is undoubtedly purring along in your backyard."

Jeepers! That was supposed to be a secret! It looks just like an outdoor wood boiler.

Here's an idea. How about actually having a project for a public domain power plant? Start off with a size of say 100 MW electric and work backwards to fill in the holes, so to speak. To be honest with you, I think a lot of the "real" MSR companies have little product to offer but vaporware. You guys are pretty smart. It can be amazing what a body can accomplish when the will is there.


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PostPosted: Feb 27, 2014 12:36 pm 
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A piston pump could be driven by the helium sparging system. The helium could be directly vented into the salt after the piston has cycled. Sparge and pump at the same time. XCOR has a cryogenic rocket oxidizer pump that is gas pressure driven.


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PostPosted: Feb 27, 2014 3:59 pm 
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additionally, the heat exchanges could be configured to be fluidic diodes (one directional flow based on fluid dynamics). Integrated piston pumps could move salt without any "valves" to worry about.
microfluidic rectifiers (diodes) are used control fluid movements on many medical diagnostic chips. Integration of the heat exchanger, sparging system and the pumps might make for a simpler repair if all get replaced at the same time. They could be designed for replacement as an integrated unit.


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PostPosted: Mar 17, 2014 3:37 pm 
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Michaelw..where are the advantages of such a system compared to a centrifugal pump?


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PostPosted: Mar 23, 2014 1:30 pm 
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No significant advantage unless centrifugal pumps are not reliable in the reactor environment.
A few possible advantages. The combination of the pump, heat exchanger and sparge system could have some benefit in size and cost. The reactor will have to have the helium pump for the sparging system anyway, might as well use it for more than one purpose. The helium pumps could be located in the hot cell or outside of the hot cell for that matter making replacement easy. The connections in the system should be durable and easily repaired if needed.
Using high pressure helium to pump the salt would make the helium pumps a more critical system. Loss of pressure could be used to scram the reactor ( open dump tanks, etc). Redundant helium pumps could be connected to the pumps and sparge system for safety. An accumulator could also be connected to the system to allow for an extra margin of safety.
sorry for the delay in responding. Pressure sensors could be used to monitor the pumps function


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PostPosted: Mar 25, 2014 11:53 am 
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There is no meaningful advantage over centrifugal because you still have the most difficult issues of sealing you have with a conventional centrifugal pump.

There is a downside with these pulsating pumps because they don't deliver flow continously even with fluidic dampers/rectifiers. This is important for thermal application and possibly important for nuclear stability as well.

One interesting configuration with pulsating pumps, if they are acceptable, is a membrane pump. One could imagine a Hastelloy N or stainless membrane. It might be possible to make the seal be the pump impeller in this way.


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PostPosted: Mar 26, 2014 4:50 pm 
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I agree that pulsed flow would be unwelcome in the reactor. A plurality of pumps with overlapping output could generate a "steady flow". The sealing of the pump does not require the pump to contact the salt. The pumping action can be by pressure changes acting on a chamber located between fluid rectifiers. Decrease in pressure pulls salt into chamber. Increase in pressure pushes salt out of the chamber. The rectifiers provide one directional flow. The inflow into the chamber can be provided by hydraulic head if pump is located below salt surface or negative pressure if above. Helium will provide the pressure to move the salt in the chamber. The pressure regulation needed for the pump can occur outside of the reactor transmitted through pipes. The pumps needed for the pressure changes would only touch the helium outside of the reactor. Compressible gas likely makes a poor connecting rod. Efficiency may suffer but is should have high reliability in reactor with no moving parts. All wear items are external to reactor.


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PostPosted: Mar 28, 2014 6:59 am 
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KitemanSA wrote:
Cyril R wrote:
I asked around with a few pump suppliers I've worked with before. They all mentioned the same thing: high temperature hydraulic pumps don't exist. Certainly not for fluoride salts.
If you can make a high temperature pump for FLiBe fuel salt, why not a pump for CLEAN FLiBe?


Maybe dual impeller, i.e. salt turbine, salt impeller pumps don't exist because no one has asked for one. I like the leaking in clean salt, but what about a helium or krypton driven turbine instead of clean salt with guaranteed (higher pressure) in leakage to the fuel salt? That could be your bubbler to help strip Kr & Xe gas from the fuel salt.


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PostPosted: Mar 28, 2014 7:31 am 
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For that matter, why not a helium driven venturi pump? No moving parts in the salt flow. Clean up the gas before sending it back to the compressor.


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PostPosted: Mar 28, 2014 2:44 pm 
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I like the ejector pump idea. What about a molten Lead driven ejector pump/direct contact heat exchanger. Use the ejector pump as the first heat exchanger and allow gravity to separate the lead and salt. Secondary heat exchanger would use lead only. Noble metals would be in lead pool. Lead pool could have a purification loop (if needed) to remove built up fission products. Bismuth extraction of fission products.
You could use direct contact with helium in the ejector pump as the heat exchanger in a Brayton cycle. Compressor- ejector pump/heat exchanger- gas clean up- turbine.


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PostPosted: Mar 29, 2014 12:20 pm 
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In a MSR you will find in more or less realistic designs volume flow rates of a couple of m3/s and a pressure difference of a couple of bars.

Centrifugal pumps for liquid sodium and lead were realized that did operate in reactors at 350 - 550°C for years. Pumps exists as well in chemical facilities.

The best material for gaskets and (radial) slide bearings is graphite. Ceramic roller bearings can be realized out of the salt as well as axial bearings. The potential risk in the long run is carburation at the transition to the metal. Another candidate for sealings is mica.


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PostPosted: Mar 29, 2014 3:26 pm 
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Graphite has some strong points in a gasket application, mainly high temperature and salt compatibility performance, but there are also serious downsides.

Mainly, graphite is not a ductile material and has a low tensile strength to make things worse. It is a bit like mortar.

Furthermore, graphite is soft so this is an instant problem in any bearing application (even for sliders). In fact graphite wants to be more like a lubricant than a bearing.

Carbon based composites/ceramics are more promising for these demanding applications. Tungsten carbide and silicon carbide are excellent candidates. For optimal performance in bearings, typically dissimilar materials are used such as silicoon carbide bearing with tungsten carbide sliders.

Pumps for MSRs are a major developmental issue because of the high radiation carried in the volatile gasses combined with high direct radiation from the fuel salt, combined with high temperature combined with fluoride salt that is incompatible with many materials, combined with... well you get the point. Sodium reactor pumps don't have to deal with radioactive volatiles (other than some trace of Na24 vapor) and noble metals, they have easier cover gas and seal gas requirements, operate with sodium that is not as corrosive as fluoride salt, operate at a lower temperature where canned rotor and magnetic bearing is easier, etc.

Basically the pump is where all the problems of MSRs are magnified. If you can make the pump, you can make the MSR.


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