Energy From Thorium Discussion Forum

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PostPosted: Sep 04, 2014 11:35 pm 
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E Ireland wrote:
I assume there is no way to make use of the almost absurdly low air temperatures during the winter?
Would the equipment to take advantage be too expensive and complex to operate?

I imagine there might be some issues with the water intakes from the bay freezing if the design was not careful.
(Probably a second set of outfalls next to the intakes through which some of the outlet water can be cycled to make sure the intakes stay above freezing).

What's the lowest condenser temperature you know of having been used in service?
There is. If you use an air breathing Brayton open cycle you can use that cold heat sink. If you run a binary cycle with iso-pentane as the bottoming cycle on an air cooled condenser you can get benefits well below zero and no freezing problem.

The lowest temperature that I recall was somewhere in Scandinavia where once through cooling with sea water at about 4.5C, enhanced output and efficiency, the turbine and condenser have to be specified for those conditions to get the benefits.


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PostPosted: Sep 05, 2014 5:15 am 
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If you use an air breathing Brayton open cycle you can use that cold heat sink.


These cycles are not very suitable to molten salt reactors. Only interesting for FHRs. You lose a barrier. Even for FHRs it is a tritium containment issue.

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If you run a binary cycle with iso-pentane as the bottoming cycle on an air cooled condenser you can get benefits well below zero and no freezing problem.


Would you really want a highly flammable working fluid?

Freezing doesn't appear to be an issue if you have once through cooling. The intake water would freeze before the condensate could. During shutdowns you just drain the condensate from the hotwell.

It seems pretty tough to beat just a steam turbine, no bottoming cycles. Just a higher vacuum in the condenser. I still think water-ammonia could be attractive because it avoids high vacuum. Really compact condensers too.


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PostPosted: Sep 05, 2014 7:40 am 
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Tritium management is an obvious challenge, maybe that will get easier if and when we collectively get a little more realistic about the risks associated with ionising radiation.

Isopentane, totally agree, as a thermodynamic fluid I really dislike the stuff, but that doesn't stop people using it all around the world as the working fluid in a binary Rankine cycle in the bottoming cycle. Do a search for Ormat binary or organic Rankine cycle.

Yes it is hard to beat a good steam turbine, I've been looking at power cycles for MSR's for 5+ years and I've had to come back to the humble yet effective STG, but the steam generator is a challenge. When MSR's start running at 900+C Braytons and combined cycles will float to the top, but that seems so far away today.


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PostPosted: Sep 05, 2014 8:09 am 
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Isopentane, totally agree, as a thermodynamic fluid I really dislike the stuff, but that doesn't stop people using it all around the world as the working fluid in a binary Rankine cycle in the bottoming cycle. Do a search for Ormat binary or organic Rankine cycle.


Yes I know, part of my internship in Indonesia was on improvements on Binary cycle plants. They were pretty rare though - they like simple flash steam plants wherever the temperature is high enough. Since MSRs involve much higher temperatures my guess would be there isn't a solid case for bottoming cycles. I think if they made sense someone would have strapped one to a modern supercritical coal plant, some are already over 620C peak supercritical water as you know.


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but the steam generator is a challenge


I was under the impression your proprietary SG had tackled the issues? I understand if you don't want to talk about this here.


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PostPosted: Sep 05, 2014 10:19 am 
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Cyril R wrote:
Quote:
If you use an air breathing Brayton open cycle you can use that cold heat sink.


These cycles are not very suitable to molten salt reactors. Only interesting for FHRs. You lose a barrier. Even for FHRs it is a tritium containment issue.


Those cycles are not very suitable for any salt-based reactor with a tritium issue. The tritium problem for FHRs is MORE pronounced than it is for MSRs, since the tritium is generated in the coolant. In the open-cycle Brayton the only barrier between tritium and the environment is the salt/air heat exchanger (gas heater).


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PostPosted: Sep 05, 2014 10:59 am 
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Kirk Sorensen wrote:
Cyril R wrote:
Quote:
If you use an air breathing Brayton open cycle you can use that cold heat sink.


These cycles are not very suitable to molten salt reactors. Only interesting for FHRs. You lose a barrier. Even for FHRs it is a tritium containment issue.


Those cycles are not very suitable for any salt-based reactor with a tritium issue. The tritium problem for FHRs is MORE pronounced than it is for MSRs, since the tritium is generated in the coolant. In the open-cycle Brayton the only barrier between tritium and the environment is the salt/air heat exchanger (gas heater).


Agree! The pebble bed designs actually make much more tritium per unit power output than MSRs, due to the high salt and high Be fractions.

However, Dr. Peterson is quite convinced that aluminium barrier coatings will work and will self heal and give decades plus lifetime without tritium leaks. The argument apparently is that without a radiation (neutron) flux, the aluminium is self healing, combined with rapid in salt removal of tritium by sorption in carbon particle beds.


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PostPosted: Sep 05, 2014 12:03 pm 
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Cyril R wrote:
However, Dr. Peterson is quite convinced that aluminium barrier coatings will work and will self heal and give decades plus lifetime without tritium leaks. The argument apparently is that without a radiation (neutron) flux, the aluminium is self healing, combined with rapid in salt removal of tritium by sorption in carbon particle beds.


Are you talking about an aluminum barrier on the salt-to-air heat exchanger? If so, wouldn't that solution be equally applicable to an MSR?


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PostPosted: Sep 05, 2014 12:32 pm 
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If you went for a brayton cycle helium turbine you could avoid a bottoming cycle I suppose.

Additionally you could have 400+Hz generators feeding the HVDC stack directly.


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PostPosted: Sep 05, 2014 12:43 pm 
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Kirk Sorensen wrote:
Cyril R wrote:
However, Dr. Peterson is quite convinced that aluminium barrier coatings will work and will self heal and give decades plus lifetime without tritium leaks. The argument apparently is that without a radiation (neutron) flux, the aluminium is self healing, combined with rapid in salt removal of tritium by sorption in carbon particle beds.


Are you talking about an aluminum barrier on the salt-to-air heat exchanger? If so, wouldn't that solution be equally applicable to an MSR?


Yes, theoretically. That is, IF it works at all reliably over decades; plus IF you have some pretty impressive heat exchangers (in stead of ORNLs 165C dT you are left with less than 30C)

Even with that, I probably still wouldn't bother; it needs the added cost and complexity of a bottoming cycle to be efficient, and you lose most some natural circulation/defence in depth heat sinks like boiling off steam generator inventory or running a little steam turbo pump. And any tube failure means you have fluoride emissions, beryllium (if Be secondary salt is used), and tritium plus any neutron activated salt. If there's a dual primary and secondary tube failure you get fission products going into the air.


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PostPosted: Sep 05, 2014 12:45 pm 
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E Ireland wrote:
If you went for a brayton cycle helium turbine you could avoid a bottoming cycle I suppose.


Brayton cycles are actually good candidates for bottoming cycles because they are inefficient at low temperatures.


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PostPosted: Sep 05, 2014 12:46 pm 
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E Ireland wrote:
Additionally you could have 400+Hz generators feeding the HVDC stack directly.
Why isn't anyone working on an HVDC generator?

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PostPosted: Sep 05, 2014 12:54 pm 
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KitemanSA wrote:
E Ireland wrote:
Additionally you could have 400+Hz generators feeding the HVDC stack directly.
Why isn't anyone working on an HVDC generator?


A high voltage commutator is rather impractical and a solid state switching system (for a non brushed DC generator) on the back is precisely what I am proposing.


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PostPosted: Sep 06, 2014 12:17 am 
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Cyril R wrote:
Yes I know, part of my internship in Indonesia was on improvements on Binary cycle plants. They were pretty rare though - they like simple flash steam plants wherever the temperature is high enough.
Amen, I really don't like the use of any hdrocarbon in a power cycle.
Cyril R wrote:
Since MSRs involve much higher temperatures my guess would be there isn't a solid case for bottoming cycles. I think if they made sense someone would have strapped one to a modern supercritical coal plant, some are already over 620C peak supercritical water as you know.
Agreed, I was just trying to answer the question of what power cycle options can make use of very low (sub-zero) ambient temperatures.

Cyril R wrote:
Lindsay wrote:
but the steam generator is a challenge

I was under the impression your proprietary SG had tackled the issues? I understand if you don't want to talk about this here.
Yup, totally sorted and very compatible with typical or low feedwater temperatures, and somewhat oddly it does like the feedwater too warm (~300C or more), but around 250 - 275C it is very happy, also very happy at any lower temperature. The simulations at 15C (fully cold start) are quite remarkable and very stable.


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