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PostPosted: Feb 12, 2018 11:20 am 
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Canada is part of the Generation IV consortium. Its main nuclear lab, CNL (former AECL), is focusing on developing a supercritical water reactor which uses pressure tubes (1200MWe in power), building upon its experience and its familiarity with CANDUs.

The CNL Nuclear Review dedicated a whole issue (winter 2016) to this specific topic:

http://pubs.cnl.ca/toc/cnr/5/2

It seems an interesting concept, also because it intends to use a Pu-Th-U233 fuel cycle in the future, but I wonder about its viability and how such a pressure tube SCWR stacks up against the SCWR with a regular RPV, considering the high pressure involved (>25 MPa) and temperatures (>600 degrees C).

Any thoughts on this ?


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PostPosted: Feb 12, 2018 8:17 pm 
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The solution to high pressure problem is a low vapor pressure coolant. The moderation could be left to exotic heavy water.
The coolant could be a molten salt, carefully balancing between neutron economy and cost. Stable hydrocarbon could also be selected.
A bigger tank of an economical coolant could act as a heat store and cover load following to an extent.


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PostPosted: Feb 13, 2018 12:24 pm 
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I've been very interested in the PT-SCWR for a long time.

The high efficiency pressure tubes (where the load bearing segment is in thermal contact with the calandria and not the coolant) they propose are far more likely to be practical, in my opinion, than the enormous pressure vessels that pressure vessel SCWRs would require.
Indeed I am not convinced a forged SCWR pressure vessel is even possible, I think prestressed vessels would be required.


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PostPosted: Feb 14, 2018 12:11 am 
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The reaction space, either the vessel or tubes have a high radioactivity and temperature. It would be best to move the high pressure of steam or supercritical water to generation area like the steam generator. The initial heat transfer should best be at a manageable pressure.


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PostPosted: Feb 20, 2018 4:38 pm 
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E Ireland wrote:
I've been very interested in the PT-SCWR for a long time.

The high efficiency pressure tubes (where the load bearing segment is in thermal contact with the calandria and not the coolant) they propose are far more likely to be practical, in my opinion, than the enormous pressure vessels that pressure vessel SCWRs would require.
Indeed I am not convinced a forged SCWR pressure vessel is even possible, I think prestressed vessels would be required.


Agreed on internal insulation & cool calandria water. Many of the issues with CANDU PTs are temperature related: most simply disappear altogether by reducing the operating temperature. It is generally good engineering practise to get the pressure retaining parts of anything as close to room temperature as possible.

PV SCWR seems quite feasible; JSW has indicated they can make about 600 tonnes forgings, which is about twice the weight of typical (US design) proposed SCWR PV's. Though they are limited in the # of forgings a year they can produce.

Still, prestressed is certainly an option too. Taking the concept of internal insulation and extending it to the vessel (where insulation and a cooled liner do the job) makes sense.


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PostPosted: Feb 20, 2018 9:19 pm 
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On a slight aside I am currently looking for someone at my university to let me do my MSc dissertation on a pressure vessel heavy water reactor using a pressure vessel made of prestressed austempered ductile iron.
The vessel ends up sufficiently large, and the price of heavy water in real terms is dropping low enough, to allow a full 3m heavy water reflector around a core.

Burnups of 15MWd/t with natural uranium, using CANDU bundles are within reach I think.

But I am very interested in all things CANDU, and the idea of internal vessel insulation is very interesting, especially when we get to materials like ADI that have relatively low service temperatures.


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PostPosted: Feb 21, 2018 4:04 pm 
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E Ireland wrote:
On a slight aside I am currently looking for someone at my university to let me do my MSc dissertation on a pressure vessel heavy water reactor using a pressure vessel made of prestressed austempered ductile iron.
The vessel ends up sufficiently large, and the price of heavy water in real terms is dropping low enough, to allow a full 3m heavy water reflector around a core.

Burnups of 15MWd/t with natural uranium, using CANDU bundles are within reach I think.

But I am very interested in all things CANDU, and the idea of internal vessel insulation is very interesting, especially when we get to materials like ADI that have relatively low service temperatures.


Interesting project Ed. If you're going for a prestressed vessel, it is likely you will be insulting the vessel & having a cooled liner for heat loss through the insulation. That way you can operate the vessel cold and pretty much isothermal. It avoids thermal stress and other problems. The liner cooling system can be your back up heat sink if all else fails. (meltable insulation?)


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PostPosted: Feb 21, 2018 4:11 pm 
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Cyril R wrote:
E Ireland wrote:
On a slight aside I am currently looking for someone at my university to let me do my MSc dissertation on a pressure vessel heavy water reactor using a pressure vessel made of prestressed austempered ductile iron.
The vessel ends up sufficiently large, and the price of heavy water in real terms is dropping low enough, to allow a full 3m heavy water reflector around a core.

Burnups of 15MWd/t with natural uranium, using CANDU bundles are within reach I think.

But I am very interested in all things CANDU, and the idea of internal vessel insulation is very interesting, especially when we get to materials like ADI that have relatively low service temperatures.


Interesting project Ed. If you're going for a prestressed vessel, it is likely you will be insulting the vessel & having a cooled liner for heat loss through the insulation. That way you can operate the vessel cold and pretty much isothermal. It avoids thermal stress and other problems. The liner cooling system can be your back up heat sink if all else fails. (meltable insulation?)


The highest grades of austempered ductile iron have a continuous service temperature of 260C or so, and if we use Atucha as an example the maximum moderator temperature will be about 220C, so in theory no insulation is needed inside the vessel.
Passive insulation can be provided between the compressed segment and the wrapping cables to keep the cables from creeping by allowing them to operate close to ambient.

The only places that require ative cooling would be the charge tubes that will put reactor coolant directly into contact with the vessel, I assume with yttrium-stabilised zirconia insulation as it i resistant to supercritical water.
I am thinking about lining the reactor vessel with YSZ anyway just to reduce the susceptibility of the vessel to overheating in a LOCA - but it should be feasible to cool the vessel without active cooling systems inside the vessel, rather than just spraying water onto the cables on the outer surface.

Projections indicate the side of the (cylindrical) vessel being 100mm of ADI and about 100mm of Cables, with a safety factor of about 2.5 or so.


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PostPosted: Feb 24, 2018 10:18 pm 
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Quote:
The highest grades of austempered ductile iron have a continuous service temperature of 260C or so, and if we use Atucha as an example the maximum moderator temperature will be about 220C, so in theory no insulation is needed inside the vessel.
Passive insulation can be provided between the compressed segment and the wrapping cables to keep the cables from creeping by allowing them to operate close to ambient.


If you insulate the vessel on the inside, it does take care of the thermal stress problems, esp. from load cycling. From an analysis and design viewpoint, being able to analyze everything at low temperature isothermal is going to make your life a lot easier.

Quote:
The only places that require ative cooling would be the charge tubes that will put reactor coolant directly into contact with the vessel, I assume with yttrium-stabilised zirconia insulation as it i resistant to supercritical water.


another option is to just thermally sleeve everything. just provide some stainless steel liners with a gap, the gap will fill with coolant and insulate. Avoids issues with possible solid insulation deteriorating. Stagnant water is pretty decent insulation.

Quote:
I am thinking about lining the reactor vessel with YSZ anyway just to reduce the susceptibility of the vessel to overheating in a LOCA - but it should be feasible to cool the vessel without active cooling systems inside the vessel, rather than just spraying water onto the cables on the outer surface.


Yes, I was thinking just put the whole thing in a giant pool of water. That way you have nice passive liner cooling, shielding, and a big source of water in any sort of accident or in case you need to flush the primary loop for maintenance. It would also provide pressure suppression in a LOCA like a BWR, but better as it is inherent pressure suppression (can't be bypassed and needs no valves).


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PostPosted: Feb 27, 2018 12:22 am 
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I feel that supercritical water should be produced in a separated heat exchanger.
The heat should be transferred to this device by a low pressure molten salt or an organic fluid, just like a PHWR, only with a fluid changed. The tubes can be designed for high temperature and a lower pressure.
Th Pu or Th leu fuel could have a life of 2000-2500 FP days. A thorium radial blanket in outer tubes could be irradiated for 500 days and replaced with every fuel change and result in a thermal breeder, which could be used to create U233 fissile for a thermal thorium breeder.


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