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 Post subject: Re: LFTR and Water?
PostPosted: Oct 11, 2014 1:08 pm 
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Dave, that's the way that I interpret those figures, they would or should be looking at how many kWhe can be generated from that low level thermal energy that would otherwise be used to heat feed going into the MED. I would expect that low level heat to power efficiency would be some number in the range of 15 - 22% something of that order.

Actually, just checking, the approximate efficiency: steam supply at 1.4 bar abs 120C in the back end of a large efficient turbine has a conversion efficiency of ~17.3% by my calculation which is much higher than one might expect for such a low temperature heat source. Cross-checking, 17.3% thermal eff and 189.9 MJ/m3 thermal energy input comes out to 9.14 kWhe equivalent per m3 freshwater produced as compared to 9.73 quoted in that paper. So yes definitive proof that they have correctly assessed the generation potential of that low temperature thermal energy in a way that correctly accounts for conversion efficiency.

Sidebar: At 1.4 bar abs (just above atmospheric pressure) if we crank the steam temperature all the way up to 347C the gross thermal efficiency rises to 20%


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 11, 2014 3:16 pm 
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That is interesting......

Primary steam circuit at only 1.4 bar might make a single cooling loop MSR practical....


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 13, 2014 1:32 am 
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http://www.iaea.org/OurWork/ST/NE/Downl ... _fs_06.pdf
Nuclear energy and IAEA are already on the job. LFTR could carry it further.


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 16, 2014 9:30 pm 
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E Ireland wrote:
That is interesting......

Primary steam circuit at only 1.4 bar might make a single cooling loop MSR practical....


Single loop? as in direct core to power loop? or as in skipping the intermediary secondary loop?

That would raise issues regarding the containment boundary wouldn't it? One of the things that the secondary loop does is that it makes it so that all 'hot' materials remain in the containment boundary and even things like tritium can be removed before the thermal energy exits the boundary.

If you have a direct cycle system (like the SCWR) then the whole facility needs to be in the containment boundary, granted that it's going to be amazingly efficient, cost is going to become an issue to ensure safety.


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 17, 2014 12:05 am 
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An open water loop in a MSR/LFTR would be very interesting and a replacement for graphite moderator. It could be a dual mode MSR like the Transatomic design. An open water circuit through turbine could make it simpler still. The steam could be just condensed after running the turbine. The nuclear heat in a MSR/LFTR would be quite cheap.


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 17, 2014 4:15 am 
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bensoon wrote:
If you have a direct cycle system (like the SCWR) then the whole facility needs to be in the containment boundary, granted that it's going to be amazingly efficient, cost is going to become an issue to ensure safety.


The entire facility would be in the containment boundary (and it wouldn't be very efficient in energy terms - less so than an existing LWR for example) but it would be inside a <2bar containment boundary.

That is not that expensive really, considering you have to provide some form of containment boundary for the salt regardless.


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 17, 2014 5:11 am 
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The extra loop does not cost that much and it offers you a relatively "clean" depressurization in case of steam leakage. It also avoids precipitating fissile as the fuel salt reacts with steam. Plus you can dabble in natural circulation. Lack of natural circulation is probably the biggest safety issue with SCWR. BWR can operate on level control (inventory control) whereas SCWR needs flow all the time.

Let's use the extra loop please and lets make it a fluoride salt.

Lindsay, just curious, what is the efficiency of a high temperature low pressure steam cycle? Say if you had 600C steam at 2 bar or so? Is this even possible?

p.s. I laughed when you wrote "sidebar". Side-bar, good joke.


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 Post subject: Re: LFTR and Water?
PostPosted: Oct 19, 2014 1:16 am 
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Agree Cyril, but to answer your question I would set a boundary condition that exhaust steam is not allowed to be superheated as this would create major problems with the heat transfer in the condenser.

As steam temperature increases the minimum pressure required to meet that exhaust boundary condition increases as does the cycle efficiency. The results are plotted in the following chart. Running higher pressures than these permits higher efficiency and provides better regenerative feedwater heating options which is also very important. These figures have no feedwater heating as little is possible from such low pressures.
Attachment:
Min Pressure vs Steam Temperature.jpg
Min Pressure vs Steam Temperature.jpg [ 55.69 KiB | Viewed 2837 times ]


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 Post subject: Re: LFTR and Water?
PostPosted: Nov 04, 2014 6:27 am 
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I just wanted to check my understanding of co-generation.

Large MSF facilities are already paired with existing power generation facilities for water desalination. Am I correct in understanding that what makes it more advantageous to use the waste heat from a nuclear system like the LFTR lies in the total thermal energy available in the waste heat?

The temperature of distillation systems is kept at 70C or less to avoid problems with corrosion and scale formation, so higher temperatures in such systems is actually a disadvantage, but the total amount of water you can desalinate is a function of the total amount of thermal energy you put into the system.

Anyone?


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 Post subject: Re: LFTR and Water?
PostPosted: Nov 05, 2014 12:23 am 
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bensoon wrote:
I just wanted to check my understanding of co-generation.

Large MSF facilities are already paired with existing power generation facilities for water desalination. Am I correct in understanding that what makes it more advantageous to use the waste heat from a nuclear system like the LFTR lies in the total thermal energy available in the waste heat?

The temperature of distillation systems is kept at 70C or less to avoid problems with corrosion and scale formation, so higher temperatures in such systems is actually a disadvantage, but the total amount of water you can desalinate is a function of the total amount of thermal energy you put into the system.

Anyone?
Cogeneration provides a more efficient way of delivering thermal and electrical energy than is possible by generating those two products independently. It doesn't really matter whether the heat supply is nuclear, solar or fossil based, cogeneration improves the overall efficiency and economics.


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 Post subject: Re: LFTR and Water?
PostPosted: Nov 05, 2014 3:10 am 
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Lindsay wrote:
bensoon wrote:
I just wanted to check my understanding of co-generation.

Large MSF facilities are already paired with existing power generation facilities for water desalination. Am I correct in understanding that what makes it more advantageous to use the waste heat from a nuclear system like the LFTR lies in the total thermal energy available in the waste heat?

The temperature of distillation systems is kept at 70C or less to avoid problems with corrosion and scale formation, so higher temperatures in such systems is actually a disadvantage, but the total amount of water you can desalinate is a function of the total amount of thermal energy you put into the system.

Anyone?
Cogeneration provides a more efficient way of delivering thermal and electrical energy than is possible by generating those two products independently. It doesn't really matter whether the heat supply is nuclear, solar or fossil based, cogeneration improves the overall efficiency and economics.


Yup that much is evident, but is there any reason to say that the use of nuclear waste heating is superior to traditional fossil fuel plants apart from the fact that it doesn't generate CO2 emissions? In that case desalination should be pursued anywhere there is a power plant located next to the ocean, and that it matters little if the plant is nuclear, gas or coal.

In fact a CCGT plant with an open cycle steam turbine stage combined with an MSF/MED plant would produce even more desalinated water theoretically (though admittedly I haven't actually tried to run any numbers to check for efficiency issues yet).


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 Post subject: Re: LFTR and Water?
PostPosted: Nov 06, 2014 11:59 pm 
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bensoon wrote:
Yup that much is evident, but is there any reason to say that the use of nuclear waste heating is superior to traditional fossil fuel plants apart from the fact that it doesn't generate CO2 emissions?
No, you've just described the only benefit. Low cost to supply would be another benefit.

The only thing where there is a connection is if the high temperature reactor uses a Brayton power cycle, then we can say that waste can be applied to desalination will have no adverse effect on the efficiency power generation; that waste heat is truly free, whereas any other power cycle would suffer a drop in electrical conversion efficiency if connected to a MSF evaporator system.


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