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PostPosted: May 24, 2014 3:35 pm 
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camiel wrote:
jagdish wrote:
The Russian and Indian fast reactors are likely to be completed this year. Will somebody put in a less fire-prone secondary coolant?


That is exactly why I am wondering why the French are building another sodium-cooled fast reactor. They built a couple in the past: Rapsodie, Phenix, Superphenix (been there, seen that, done that). I think it is a duplication of effort. In light of the international R&D of Gen-IV reactors, it would be much better if there would be some division of labor and more coordination, for example the Russians focusing on and building a lead-cooled reactor, the Americans developing a high-temperature gas-cooled reactor, the Chinese building a MSR, etc.

However, the nitrogen power conversion system that is proposed for ASTRID, is interesting. There are some efforts to develop supercritical CO2 turbines for nuclear energy applications, so why go with nitrogen ? What is the largest nitrogen turbine that has ever been developed, if it ever has been developed ?


Nitrogen is the closest to the air based turbines already in widespread use so this choice means lower development cost and the shorter schedule than going with CO2.


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PostPosted: May 24, 2014 10:33 pm 
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A nitrogen based turbine is essentially a gas turbine with all the corrosive stuff taken out.


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PostPosted: May 24, 2014 11:26 pm 
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No sorry, there are no commercial gas turbines working at those pressures, the inlet pressure is 74 bar (compared to 1 bar for normal GT's) that's about double the highest peak pressure used in the high performance industrial gas turbine. This gas turbine will be a very unique machine quite unlike anything in commercial service today. That said the temperature is quite trivial, so all components will be solid without any cooling of any kind.

From an efficiency point of view, a steam cycle with double reheat would make much more sense, but the big challenge is the reactivity of sodium with water and steam.


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PostPosted: May 25, 2014 2:57 am 
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The high pressure is indeed remarkable. I wonder why they did that. Maybe to improve efficiency, reduce pump/compressor power and reduce component size? Lindsay, would you have an idea on this?


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PostPosted: May 25, 2014 6:31 am 
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Lindsay wrote:
From an efficiency point of view, a steam cycle with double reheat would make much more sense, but the big challenge is the reactivity of sodium with water and steam.

If some salt or lead eutectic were used as the secondary coolant, the risk of sodium-water/steam coolant will be eliminated. That is why I wonder when (not if) it will be done.


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PostPosted: May 25, 2014 6:44 am 
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camiel wrote:
the nitrogen power conversion system that is proposed for ASTRID, is interesting. There are some efforts to develop supercritical CO2 turbines for nuclear energy applications, so why go with nitrogen ?

The ASTRID report briefly mentions that SCO2 was considered but rejected, because CO2 does react with high-temperature sodium.


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PostPosted: May 25, 2014 7:18 am 
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Using lead has its own collosal issues.

A sodium derived coolant can be engineered to be molten at room temperature which makes outage planning rather simpler.


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PostPosted: May 25, 2014 10:30 am 
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MOX-fuel is intended to be used in the ASTRID reactor, as well as in the new Russian BN-800 and Indian PFBR sodium-cooled fast reactors. Is metallic fuel, sodium-bonded fuel (U-Pu-Zr), not superior for this type of reactor, as I understand it is easier to reprocess (pyroprocessing)? This type of fuel was proven in the EBR-II and the FFTF reactors in the USA. It also seems to a big selling point of the IFR / GE-Hitachi PRISM reactor. So why keep on using mixed oxide fuel in a sodium-cooled fast reactor ?


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PostPosted: May 25, 2014 11:56 am 
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Cyril R wrote:
The high pressure is indeed remarkable. I wonder why they did that. Maybe to improve efficiency, reduce pump/compressor power and reduce component size? Lindsay, would you have an idea on this?


Because the remarkable feature of closed-cycle gas turbines is that inlet pressure is a "free" parameter you can change to size the turbomachinery components. To first-order, it does not affect cycle efficiency or net work production. This is a fascinating thing you can do---it has no parallel in steam-turbines (where temperature and pressure are connected by phase-change) or open-cycle gas turbines (which are fixed in inlet pressure by the atmosphere).


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PostPosted: May 25, 2014 1:34 pm 
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Cyril R wrote:
The high pressure is indeed remarkable. I wonder why they did that. Maybe to improve efficiency, reduce pump/compressor power and reduce component size? Lindsay, would you have an idea on this?

My best guess is all of the above, but I think the biggest benefit is to reduce the equipment size including the HX. That should in turn reduce pumping losses, helping efficiency. Smaller size also means smaller cost, so multiple benefits from cranking up the pressure throughout the cycle.

Edit: As Kirk says in a closed loop you can dial up whatever cycle pressures you want or can tolerate, it's a unique feature of closed Brayton cycles.


Last edited by Lindsay on May 25, 2014 1:53 pm, edited 1 time in total.

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PostPosted: May 25, 2014 1:52 pm 
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jagdish wrote:
Lindsay wrote:
From an efficiency point of view, a steam cycle with double reheat would make much more sense, but the big challenge is the reactivity of sodium with water and steam.

If some salt or lead eutectic were used as the secondary coolant, the risk of sodium-water/steam coolant will be eliminated. That is why I wonder when (not if) it will be done.

When I made that first post that's what I was thinking, keep sodium in the primary loop if it performs better and run Lead-Bismuth Eutectic (LBE) or something chemically non-reactive in the intermediate loop.

I just did a quick search on corrosion resistance to molten lead and 316 SS came up a number of times, this would also be a good material for making steam generators out of from a corrosion/chemical compatibility perspective on the water/steam side. Others may know a lot more about good material choices for LBE, but the secondary coolant doesn't have to be LBE.


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PostPosted: May 25, 2014 3:59 pm 
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camiel wrote:
MOX-fuel is intended to be used in the ASTRID reactor, as well as in the new Russian BN-800 and Indian PFBR sodium-cooled fast reactors. Is metallic fuel, sodium-bonded fuel (U-Pu-Zr), not superior for this type of reactor, as I understand it is easier to reprocess (pyroprocessing)? This type of fuel was proven in the EBR-II and the FFTF reactors in the USA. It also seems to a big selling point of the IFR / GE-Hitachi PRISM reactor. So why keep on using mixed oxide fuel in a sodium-cooled fast reactor ?


Oxide fuel has the distinct advantage of being easy to license, as opposed as other types of fuels matrices. Otherwise, pyroprocessing is mainly considered as being "non-european" (essentially for historical reasons).


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PostPosted: May 25, 2014 4:04 pm 
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E Ireland wrote:
Using lead has its own collosal issues.

A sodium derived coolant can be engineered to be molten at room temperature which makes outage planning rather simpler.


Are you referring to NaK? The cross-section of K is quite a bit higher, which results in a neutronic penalty and a unwanted (including long-lived) activation. If things go relatively well, decay heat will keep even your pure Na coolant molten.


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PostPosted: May 27, 2014 11:07 am 
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A fast spectrum reactor trhat only has to reach breakeven doesn't really have many neutronics problems - after all it has no need for neutron sucking moderator stacks.

And decay heat implies that the reactor is always going to be sufficiently fueled with used fuel for the decay heat to be significant - which could cause problem during refueling/maintenance outages when the reactor could be defueled for significant periods.


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PostPosted: May 31, 2014 5:46 am 
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E Ireland wrote:
Using lead has its own collosal issues.

A sodium derived coolant can be engineered to be molten at room temperature which makes outage planning rather simpler.

Unfortunately, such coolants are generally chlorides like sodium aluminium chloride. You may have to use separated isotope 37Cl.


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