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PostPosted: Oct 16, 2013 6:20 am 
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Because I could not past sheet, I upload their comparation as jpg file


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File comment: References
[4] BETTIS E, SCHROEDER R, CRISTY G, et al. The Aircraft Reactor Experiment-Design and Construction,1957. NSE_ARE_design
[5] R. C. Robertson, MSRE design and operations report,1965. ORNL-TM-0728
[6] E.S. Bettis, Roy C. Robertson, The design and performatnce features of a single-fluid molten salt breeder reactor,1969. NAT_MSBRdesign
[7] MSR-FUJI General Information, Technical Features, and Operating Characteristics CTS-31-92: 1991-02-18
[8] Merle-Lucotte, E. et al.,.Optimized transition from the reactors of second and third generation to the Thorium Molten Salt Reactor[R]. Proceedings of the ICAPP 2007
[9] Charles W. Forsberg,Oak Ridge National Laboratory.Thermal- and Fast-Spectrum Molten Salt Reactors for Actinide Burning and Fuel Production.2007
[10] TalkENEN-Gen4Seminar_MSFR_nov2010, Introduction to the Physics of Molten Salt Reactors, conference presentation, 2010
[11] E. Merle-Lucotte, D. Heuer, M. Allibert, X. Doligez, V. Ghetta.Minimizing the fissile inventory of the molten salt fast reactor.Advances in Nuclear Fuel Management IV .2009
[12] Ignatiev, V., Feynberg, O., Gnidoi, I., Merzlyakov, A., Smirnov, V., Surenkov, A.,Tretiakov, I., Zakirov, R., Progress in development of Li,Be,Na/F molten saltactinide recycler & transmuter concept.2007. In: Proceedings of the ICAPP 2007 International Conference
[13] Da-Lin, ZHANG,Sui-Zheng, QIU,Chang-Liang, LIU,Guang-Hui, S U,steady state investigation on neutronics of a molten salt reactor considering the flow effect of fuel salt[J],2008
[14] E.S. Bettis, L.G. Alexander, and H.L. Watts, Design Studies of a Molten-Salt Reactor Demonstration Plant, ORNL-TM-3832 .1972

MSR and PWR temperature comparation.jpg
MSR and PWR temperature comparation.jpg [ 145.63 KiB | Viewed 1507 times ]
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PostPosted: Oct 16, 2013 9:21 pm 
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What kind of MSR plant is the best candidate for the future?
1. fuel salt-helium-electricity
2. fuel salt-coolant salt-electrocity
3. fuel salt-coolant salt-steam generator-electricity
4. fuel salt-coolant salt I-coolant salt II-steam generator-electricity
5. fuel salt- helium-steam generator-electricity

Which one is promising?


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PostPosted: Oct 16, 2013 9:23 pm 
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longwei1221 wrote:
What kind of MSR plant is the best candidate for the future?
1. fuel salt-helium-electricity
2. fuel salt-coolant salt-electrocity
3. fuel salt-coolant salt-steam generator-electricity
4. fuel salt-coolant salt I-coolant salt II-steam generator-electricity
5. fuel salt- helium-steam generator-electricity

Which one is promising?


sorry, the second is :
2. fuel salt-coolant salt-helium-electrocity

the 1 and 2 is high temperature Helium Brayton cycle produce electricity


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PostPosted: Oct 16, 2013 11:54 pm 
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In a fuel salt-cooling salt configuration, any gas should do (incl N2/CO2) as the radioactivity problem is reduced. It is best to transport the heat from reactor with a secondary, clean salt. This salt can also be stored outside the core as heat store to cover daily demand variation.
Salt, equivalent to a lower volatility substitute for water in a PWR, will work at a higher temperature for higher thermal efficiency of generation.


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PostPosted: Oct 17, 2013 3:11 am 
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jagdish wrote:
In a fuel salt-cooling salt configuration, any gas should do (incl N2/CO2) as the radioactivity problem is reduced. It is best to transport the heat from reactor with a secondary, clean salt. This salt can also be stored outside the core as heat store to cover daily demand variation.
Salt, equivalent to a lower volatility substitute for water in a PWR, will work at a higher temperature for higher thermal efficiency of generation.


But the coolant salt system make the reactor more complex. I tend to support suel salt-helium system, though the tritium will migrate from fuel to helium gas through the heat exchanger. We could add another tritium-off system to separate tritium from helium by chemical method, it is easierthan tritium in steam.


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PostPosted: Oct 17, 2013 5:58 am 
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Helium certainly has a few advantages - easy tritium removal and negligible chemical corrosion.

But there are massive downsides to a helium secondary loop. First of all helium is a poor coolant, it requires very high pressure to get any sort of efficiency in heat transfer and reasonable pumping powers, and even then it's poor. High pump power, big thick walled heat exchangers. The thicker HX wall means much poorer heat transfer, so more fuel salt is needed in the HX. That's bad. The primary HX will be very large. Also bad.

There are also a great many safety implications. High pressure helium means leaks will result in pressurizing the primary loop, detracting from one of the major advantages of molten salt (that it is always low pressure). Voiding of helium into the core provides added nuclear safety issues.

So in my opinion you want a low pressure second loop, and it has to be compatible with the fuel salt, so another fluoride salt is an obvious choice.

For a steam power cycle or process steam loop, in my opinion the most attractive is fuel salt - fluoride coolant salt - nitrate salt - water/steam.

For a helium/nitrogen Brayton or S-CO2 loop, the most attractive in my opinion would be fuel salt - fluoride salt - working fluid gas/supercritical fluid.


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PostPosted: Oct 17, 2013 11:32 am 
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Cyril R wrote:
Helium certainly has a few advantages - easy tritium removal and negligible chemical corrosion.

But there are massive downsides to a helium secondary loop. First of all helium is a poor coolant, it requires very high pressure to get any sort of efficiency in heat transfer and reasonable pumping powers, and even then it's poor. High pump power, big thick walled heat exchangers. The thicker HX wall means much poorer heat transfer, so more fuel salt is needed in the HX. That's bad. The primary HX will be very large. Also bad.

There are also a great many safety implications. High pressure helium means leaks will result in pressurizing the primary loop, detracting from one of the major advantages of molten salt (that it is always low pressure). Voiding of helium into the core provides added nuclear safety issues.

So in my opinion you want a low pressure second loop, and it has to be compatible with the fuel salt, so another fluoride salt is an obvious choice.

For a steam power cycle or process steam loop, in my opinion the most attractive is fuel salt - fluoride coolant salt - nitrate salt - water/steam.

For a helium/nitrogen Brayton or S-CO2 loop, the most attractive in my opinion would be fuel salt - fluoride salt - working fluid gas/supercritical fluid.

Cyril R,
I like you because you are smarter than me. But I think you wrote this entire post wrong.

There are 4 reasons why helium is the worst coolant,
1 leaks
2 leaks
3 leaks
4 helium has poor thermal conductivity requiring high pressure which again leads to the first three reasons

HELIUM AS A COOLANT CAN ONLY WORK IN ACADEMIC LAND OR UNECONOMIC LAND. (YES I KNOW I REPEAT MYSELF)


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PostPosted: Oct 18, 2013 11:38 pm 
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And I was thinking of cost and availability.


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PostPosted: Oct 19, 2013 11:30 am 
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Lets say you have a PCHE or similar (which would be rather compact) in the reactor with pumps forcing the salt through it.

Lets say you spring a leak in the heat exchanger, you now have helium leaking out of the secondary loop into the fuel loop because the former is obviously at a far far higher pressure.

Is this a catastrophic issue?
The helium certainly won't react with anything in the core or even do anything except exclude some fuel from the core, which with proper design of the reactor geometry, should tend to cause a negative reactivity alteration, rather than allowing some horrendous positive power excursion.

With a PCHE the amount of helium that can practically leak from a single failure is v. small, which will allow the reactor to potentially continue operating despite the leak, with the helium being re-trapped from the cover gas system.


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PostPosted: Oct 19, 2013 12:04 pm 
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Yes, but even with PCHE you get a high pressure differential across the HX. Low pressure on the fuel salt side, high pressure on the helium side. This is a problem because of high temperature creep. It will force quite thick PCHE walls which isn't ideal for heat transfer.

If you have a molten fluoride salt as secondary loop, then you can have a pressure-equalized primary HX. No driving force for any leaks. No voids to deal with, no helium removal from the primary side, primary pumps cavitation etc. Two phase phenomena is something a molten salt reactor can avoid, that's one of its selling points.


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PostPosted: Oct 19, 2013 12:17 pm 
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Cyril R wrote:
Yes, but even with PCHE you get a high pressure differential across the HX. Low pressure on the fuel salt side, high pressure on the helium side. This is a problem because of high temperature creep. It will force quite thick PCHE walls which isn't ideal for heat transfer.


Well you will eventually have those problems anyway at the secondary loop heat exchanger, so I don't think that is something you can really chalk up as a problem for the single salt loop design.

Cyril R wrote:
If you have a molten fluoride salt as secondary loop, then you can have a pressure-equalized primary HX. No driving force for any leaks. No voids to deal with, no helium removal from the primary side, primary pumps cavitation etc. Two phase phenomena is something a molten salt reactor can avoid, that's one of its selling points.


But then you end up with having to add a whole suite of new systems including a gas cleanup system for the secondary salt loop, salt loop pumps and god knows what else.
I'm sure you really gain anything by having this salt loop.


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PostPosted: Oct 19, 2013 12:44 pm 
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The secondary HX is subjected to far fewer constraints than the primary HX. Much less activity (just actived activity), fewer space/volume requirements. Check the activity of the primary loop. It's ridiculous. If you can ease the mechanical environment there, such as by going for pressure-equalized HX design, then you've gained a lot. Optimize for the most difficult system.

I didn't get the part about gas cleanup systems. Helium loops need gas cleanup systems as well, in case of contamination. And everything happens at high pressure so your gas cleanup is hard. Gas cleanup with fluoride salt occurs at low pressure. It's more of a cover gas cleanup system, at atmospheric pressure. The other side of the HX already sees fluoride salt, and much dirtier fluoride salt at that, so your HX doesn't get subjected to new constraints. Only the piping does, but the piping is low pressure.

If you're worried about salt pumps, then check out the power rating on helium circulators... scary! Gasses are compressible and have low volumetric heat capacity, that's exactly what you don't need. Secondary salt pumps are a heck of lot more economical than helium circulators.

There are major pressure management advantages with a secondary salt loop, even with a low leak probability HX. If the power cycle loop leaks, then you can depressurize in a clean non-nuclear salt loop. Do you want to depressurize fuel salt? This is going to make a big mess and a billion dollar decommissioning on your hands. Penny wise, pound foolish.


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PostPosted: Oct 19, 2013 1:49 pm 
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Cyril R wrote:
I didn't get the part about gas cleanup systems. Helium loops need gas cleanup systems as well, in case of contamination. And everything happens at high pressure so your gas cleanup is hard. Gas cleanup with fluoride salt occurs at low pressure. It's more of a cover gas cleanup system, at atmospheric pressure. The other side of the HX already sees fluoride salt, and much dirtier fluoride salt at that, so your HX doesn't get subjected to new constraints. Only the piping does, but the piping is low pressure.


Having an extra salt loop means you need two cleanup systems instead of one because you have to protect against a radiological leak from the primary loop into the secondary loop and you probably still need the loop on your gas system.
Gas cleanup could also be sited at the low pressure part of the gas loop where the gas it at or relatively near atmospheric pressure and temperature.

(I am proposing a direct Brayton cycle turbine rig with multiple reheats - much literature work talks about 100atm or 200atm peak gas pressures in such systems, which are not particularily high by PCHE standards, manufacturers listing characteristics for 500atm gas/water gas coolers)

Cyril R wrote:
If you're worried about salt pumps, then check out the power rating on helium circulators... scary! Gasses are compressible and have low volumetric heat capacity, that's exactly what you don't need. Secondary salt pumps are a heck of lot more economical than helium circulators.


The circulators are still going to be necessary if you are going for a Brayton cycle turbine system, as I am suggesting would yield the simplest reactor that does not have water inside the core heat exchanger (which would be rather bad I imagine in case of a leak).

Cyril R wrote:
There are major pressure management advantages with a secondary salt loop, even with a low leak probability HX. If the power cycle loop leaks, then you can depressurize in a clean non-nuclear salt loop. Do you want to depressurize fuel salt? This is going to make a big mess and a billion dollar decommissioning on your hands. Penny wise, pound foolish.


But why would we need to "depressurise" the helium?
The helium is essentially insoluble in the fuel salt, unlike the heavier noble gasses, and will just bubble out apart from a negligible quantity that is probably overwhelmed by the alpha emission going on in the fuel salt as a matter of course.

The leak is unlikely to be large enough, with a properly designed heat exchanger using PCHE technology, to cause the pressure in the overall containment to rise, and even if it did the gas will just build up in the cover gas space and can be drawn off from there.


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PostPosted: Oct 19, 2013 3:37 pm 
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First let me say that this might be an option for the configuration you're describing - helium Brayton and PCHE. Simplicity is a worthy goal and LFTRs aren't the most simple reactor around to say the least. Let me follow that up by saying that helium Braytons are complete vapourware at the moment, or should I say gassyware. Further, helium as a secondary loop means no natural circulation heat removal of any decay heat removal significance to speak of. Consider that all major groups working on MSRs, even groups favoring Brayton (Berkeley), have gone for intermediate fluoride salt loops, even for the AHTRs where there are fewer activity issues. And oddly, many people seem to think PCHEs aren't going to work due to transient thermal stresses, even though my discussions with the major manucturer of PCHEs in the UK suggest otherwise.

So my focus is on steam systems, and these have all sorts of chemical compatibility problems, including H2O reacting with UF4 to precipitate fissile and making lots of HF, needless to say that's bad. Plus they have freezing problems that are not easy to solve with PCHE. Hence I'd rather have more loops. Salt loops are compact and you'd be surprised how little they add to total capital costs, only a 5-10 percent more for the nitrate third loop for example. Nitrate is also great for process steam applications where you have even lower feedwater temperatures.


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PostPosted: Oct 19, 2013 9:50 pm 
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academia and their helium pipedreams!

http://www.periodictable.com/Properties ... ius.v.html
helium has the smallest atomic radius


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