In July, 2018, Moltex was selected by New Brunswick Energy Solutions Corporation and New Brunswick Power to progress development of its SSR-W (Stable Salt Reactor – Wasteburner) technology in New Brunswick, with the aim of deploying its first SSR-W at the Point Lepreau nuclear reactor site before 2030.
The agreement provides $5 million of financial support to Moltex for its immediate development activities and Moltex will open its North America headquarters in Saint John and build its development team there.
The Moltex SSR-W reactor will use Candu fuel assemblies for its Canadian prototype.
The design does not use complex controls for managing risks, the Stable Salt Reactor – Wasteburner design eliminates risks.
The non-nuclear portion of the plant uses standard high-temperature natural gas plant turbines and other systems. Those have proven costs and build times from many projects.
The SSR design permits all complex and hazardous high-pressure equipment to be outside the nuclear island, indeed outside the licensed nuclear site in many cases. Thus it has costs similar to those in natural gas-powered stations, which are dramatically lower than in nuclear stations.
The reactor module will generate 150 MWe and weight only 18 tons and take up 50 cubic meters. This is three times the power as the Nuscale 50 MWe reactor module and take less than one-eighth of the volume.
Stable Salt Reactors build on the fundamental safety and simplicity breakthrough of molten salt fuel in essentially standard nuclear fuel tubes.
* The fuel salt is held in vented tubes. Venting is safe because in our reactors the dangerous fission products form stable compounds, not gases.
* The tubes are bundled into fuel assemblies similar to those in a conventional PWR. These are held in the support structure which forms the reactor modules.
* The tank is filled with a safe molten salt coolant, which is not pressurised like gas or water coolants in today’s power reactors and not violently reactive with air and water like sodium in today’s Fast Breeder reactors. A second similar coolant salt system takes heat from the primary coolant salt to steam generators kept well away from the reactor.
* Refuelling is simple: Fuel assemblies are simply moved sideways out of the core and replaced with fresh fuel assemblies. This results in a near on-line refuelling process.
* The entire construction is simple, with no high-pressure systems, few moving parts, and no Pressure Vessel needing specialist foundries.
* The reactor is continuously cooled by natural air flow, giving complete security against overheating
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I don’t believe that convection air cooling can cool down any nuclear reactor unless the reactor has a high negative reaction temperature coefficient.
I don’t believe that convection air cooling can cool down any nuclear reactor unless the reactor has a high negative reaction temperature coefficient.
One of the characteristics of molten salts, is that they have a high coefficient of thermal expansion. A few degrees above the design temperature, fission stops, and you only have to deal with fission daughter decay heat, and lanthanide decay heat.
The proponents of this design seem to think that a bathtub design reactor could not be built without placing fuel salts in many small tubes. I’m not sure why they would believe that.
One of the characteristics of molten salts is that they have a high coefficient of thermal expansion. A few degrees above the design temperature fission stops and you only have to deal with fission daughter decay heat and lanthanide decay heat.
The proponents of this design seem to think that a bathtub design reactor could not be built without placing fuel salts in many small tubes. I’m not sure why they would believe that.
(After discussion of fuel venting in the Dounreay sodium fast reactor, which resulted in a lot of cesium 137 contaminating the sodium) – ‘There seemed a possibility that the stable salt trapping capability of molten salt might clean up the fission gases enough to allow them to be vented. To investigate this, chemical thermodynamic calculations were carried out with the software package HSC8 to quantify the composition of the gas released during fission. The results are shown in Figure 3. At the high temperature of the fuel salt, about 1000°C, there are substantial amounts of gases released. But those gases immediately encounter the cooler walls of the tube above the level of the fuel salt where the temperature is the same as the coolant, 600°C. Since the gas flow is extremely slow, a few ml per day, there is plenty of time for the gases evolved to condense on the cooler walls. The result is that only Xe, Kr, Cd and ZrCl4 are released in significant quantities. None of these are hazardous radioisotopes – Xe-137, which decays to hazardous Cs-137, decays almost entirely (fraction remaining less than 10-6) while still in the tube gas space. The decision was made to vent the tubes therefore as the hazard of pressurising the tubes was seen as greater than that of allowing the gases to vent into the inert gas containment of the reactor (not into the atmosphere). ‘ http://www.modernpowersystems.com/features/featurethe-stable-salt-reactor-transforming-the-promise-of-the-molten-salt-fuel-concept-into-a-viable-technology-5748063/
www.moltexenergy.com/learnmore/An_Introduction_Moltex_Energy_Technology_Portfolio.pdf “The emergency cooling system consists of air ducts around the reactor tank which continually circulate air past the tank purely by natural convection. This is similar to other reactors such as PRISM. The Moltex system is superior however because it can take away the decay heat from small high-power reactors which is not possible for reactors like PRISM. The Moltex system relies on a novel method to capture heat radiated from the hot reactor tank wall on a large surface area of fins which in turn pass the heat to the circulating cool air. This system has been patented and allows passive air cooling to be used on much more powerful and compact reactors than was ever conventionally thought possible.”
Rectangular geometry…. Hmm. The online refueling aspect is a bit of a distraction for them it seems. Not really relevant in trying to prove the other concepts (salt in and outside tubes). It doesn’t seem particularly reasonable to slide shuffle the fuel at power. It’s like a totally new class of NUREG-0800 chapter 15.4 transient to analyze. That’s not how CANDU does it.
The fuel salt is held in vented tubes. Venting is safe because in our reactors the dangerous fission products form stable compounds, not gases.” THEN WHY VENT THE TUBES? Bogus. A total lie. Get almost 1 noble gas fission product atom per fission.
Got your physics mixed up pal.
I’ve got to wonder if a 150MWe module could have an application in ship propulsion?
Rectangular geometry…. Hmm. The online refueling aspect is a bit of a distraction for them it seems. Not really relevant in trying to prove the other concepts (salt in and outside tubes). It doesn’t seem particularly reasonable to slide shuffle the fuel at power. It’s like a totally new class of NUREG-0800 chapter 15.4 transient to analyze. That’s not how CANDU does it.
The fuel salt is held in vented tubes. Venting is safe because in our reactors the dangerous fission products form stable compounds” not gases.””THEN WHY VENT THE TUBES?Bogus. A total lie. Get almost 1 noble gas fission product atom per fission.”””
Got your physics mixed up pal.
I’ve got to wonder if a 150MWe module could have an application in ship propulsion?
One very simple and profound thing hits me as not making sense. If this design can be air cooled by ambient air, how can it develop enough heat in the first place for the standard water boiłing-steam-turbine action? It can’t possibly be that efficient.
Maybe for whaling fleets. If Greenpeace is going to protest you either way, may as well go whole hog.
The British gas cooled reactors were supposed to refuel at power, but they had problems with vibrations. Salt ( and water ) are much better coolants, so velocity is lower. Not sure about BWRs, but don’t PWRs have higher enrichment pellets at the top of the rods, to compensate for the higher temperature there ? With a liquid in the rod, that sorts itself out. Candus shove their fuel assemblies through the pressure tubes in alternate opposite directions, pretty much like Moltex. There’s supposed to usually be a row of the cubic arrangements next to each other, so only the outside ends will be getting less neutrons – convection will equalise everything top to bottom. Ian Scott reckons leaving 2% hafnium in his zirconium fluoride coolant will reduce neutron flux by four orders of magnitude after one metre. There’s no moderator, so shuffling a fuel assembly to the edge of the vat should quench the chain reaction pretty effectively.
From my reading of their documents Xe-137 decays into Cs-137. The diving bell design (borrowed from one of the Dounreay reactors) holds up the Xe-137 long enough for it to decay into Cs-137 and plate out onto the walls of the fuel tube. I think the other noble gasses are vented to avoid pressure build up in the fuel tubes?
The fuel rods split because the pellets have expanded till they interfere with the cladding. That expansion is partly from pressurised fission gas collecting in voids, partly from metals migrating through the oxide because of heat gradients – the temperature at the centre of the pellet is way higher, so more volatile elements move out to where it’s cooler. Moltex’s cladding contains a convecting liquid, so there should be much less stress on it. Most of the volatile metal fission products will stay chemically bound to the salt, but even if some get out into the coolant, they’ll be in tiny grains, and the pumps are filtered. The primary coolant will be radioactive anyway, from activation of the zirconium component of it. That’s why they have a clean salt secondary coolant.
When a fuel rod pops in a BWR we go look for it by sticking rods in/out one at a time over multiple days. When we perturb the area with the leaker we measure elevated FP in the offgas thattis vacuumed from the condenser. We then leave that rod inserted for the remainder of the cycle and take a huge hit in generation because the core will now coast maybe 10 or 20 days early due to suppression of a region in the core. Millions of dollars lost to keep a single fuel rod defect from getting worse because God forbid it gets worse, unzipps and spills it’s pellets. Those pellets would then get chopped up by the pumps and deposit “tramp” uranium from reactor to condenser. So we go to great lengths to make sure 2kg of pellets from one rod doesn’t chrap up the whole plant and increase worker dose. So from that perspective, a core with 30,000 fuel rods all leaking by design is a frickin joke.
One very simple and profound thing hits me as not making sense. If this design can be air cooled by ambient air how can it develop enough heat in the first place for the standard water boiłing-steam-turbine action? It can’t possibly be that efficient.”
Maybe for whaling fleets. If Greenpeace is going to protest you either way may as well go whole hog.
The British gas cooled reactors were supposed to refuel at power but they had problems with vibrations. Salt ( and water ) are much better coolants so velocity is lower. Not sure about BWRs but don’t PWRs have higher enrichment pellets at the top of the rods to compensate for the higher temperature there ? With a liquid in the rod that sorts itself out. Candus shove their fuel assemblies through the pressure tubes in alternate opposite directions pretty much like Moltex. There’s supposed to usually be a row of the cubic arrangements next to each other so only the outside ends will be getting less neutrons – convection will equalise everything top to bottom. Ian Scott reckons leaving 2{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} hafnium in his zirconium fluoride coolant will reduce neutron flux by four orders of magnitude after one metre. There’s no moderator so shuffling a fuel assembly to the edge of the vat should quench the chain reaction pretty effectively.
From my reading of their documents Xe-137 decays into Cs-137. The diving bell design (borrowed from one of the Dounreay reactors) holds up the Xe-137 long enough for it to decay into Cs-137 and plate out onto the walls of the fuel tube.I think the other noble gasses are vented to avoid pressure build up in the fuel tubes?
The fuel rods split because the pellets have expanded till they interfere with the cladding. That expansion is partly from pressurised fission gas collecting in voids partly from metals migrating through the oxide because of heat gradients – the temperature at the centre of the pellet is way higher so more volatile elements move out to where it’s cooler. Moltex’s cladding contains a convecting liquid so there should be much less stress on it. Most of the volatile metal fission products will stay chemically bound to the salt but even if some get out into the coolant they’ll be in tiny grains and the pumps are filtered. The primary coolant will be radioactive anyway from activation of the zirconium component of it. That’s why they have a clean salt secondary coolant.
When a fuel rod pops in a BWR we go look for it by sticking rods in/out one at a time over multiple days. When we perturb the area with the leaker we measure elevated FP in the offgas thattis vacuumed from the condenser. We then leave that rod inserted for the remainder of the cycle and take a huge hit in generation because the core will now coast maybe 10 or 20 days early due to suppression of a region in the core. Millions of dollars lost to keep a single fuel rod defect from getting worse because God forbid it gets worse unzipps and spills it’s pellets. Those pellets would then get chopped up by the pumps and deposit tramp”” uranium from reactor to condenser. So we go to great lengths to make sure 2kg of pellets from one rod doesn’t chrap up the whole plant and increase worker dose. So from that perspective”” a core with 30″”000 fuel rods all leaking by design is a frickin joke.”””
Proper heat recovery works wonders. The coolant never changes state. That is the major efficiency loss in a steam cycle. Coolant does not have to change state in order to re-enter the coolant cycle. I suppose that is one very simple and profound difference when liquid salts are used to get heat out of the reaction. It CAN be that efficient!
Proper heat recovery works wonders. The coolant never changes state. That is the major efficiency loss in a steam cycle. Coolant does not have to change state in order to re-enter the coolant cycle. I suppose that is one very simple and profound difference when liquid salts are used to get heat out of the reaction. It CAN be that efficient!
I thought that long sealed fuel salt tubes with a vacuum that pulls out Xe in to the void could work but what do I know.
The cladding splits because entropy happens. Again: I too just can’t buy the “open fuel rod” design. Entropy happens and the rods don’t seem to be locked in place. What happens during an earthquake? What happens if the fuel handler machine falls on the open rods?
They want to get the Xeon and Krypton out of the fuel salt. I’m sorry but I just cant accept that some fuel won’t find its way out of the open tubes and settle in the coolant salt. You have hundreds of assemblies and the fuel salt is hot for years. Some fuel ions will escape and foul the coolant salt. Entropy is just a bltch that way.
I don’t like that if a fuel assembly tips over while shuffling (hey stuff happens) then it mixes the fuel salt with the cooling salt. Just mix the two and design for that up front. So I guess i’m partial to the chloride salt fast reactor designs.
I thought that long sealed fuel salt tubes with a vacuum that pulls out Xe in to the void could work but what do I know.
The cladding splits because entropy happens.Again: I too just can’t buy the open fuel rod”” design. Entropy happens and the rods don’t seem to be locked in place. What happens during an earthquake? What happens if the fuel handler machine falls on the open rods?”””
They want to get the Xeon and Krypton out of the fuel salt.I’m sorry but I just cant accept that some fuel won’t find its way out of the open tubes and settle in the coolant salt. You have hundreds of assemblies and the fuel salt is hot for years. Some fuel ions will escape and foul the coolant salt. Entropy is just a bltch that way.
I don’t like that if a fuel assembly tips over while shuffling (hey stuff happens) then it mixes the fuel salt with the cooling salt.Just mix the two and design for that up front. So I guess i’m partial to the chloride salt fast reactor designs.
A liquid like molten salt has a far higher heat capacity than air. Air flowing by natural convection around the outside of the tub carries a lot less heat away than salt pumped from right next to the fuel rods. It just has to be able to take away decay heat after the chain reaction stops, probably a few tens of megawatts max, compared to ~ 500 MW thermal during normal operation. The reactor is designed to shut down when the temperature goes much above its normal range. Air convection will get faster with higher temperature, and there is enough thermal inertia to keep the salts well below boiling point.
A liquid like molten salt has a far higher heat capacity than air. Air flowing by natural convection around the outside of the tub carries a lot less heat away than salt pumped from right next to the fuel rods. It just has to be able to take away decay heat after the chain reaction stops probably a few tens of megawatts max compared to ~ 500 MW thermal during normal operation. The reactor is designed to shut down when the temperature goes much above its normal range. Air convection will get faster with higher temperature and there is enough thermal inertia to keep the salts well below boiling point.
It could, but this way you don’t have to pump the fissile material through the heat exchangers. That means you need a lot less of it – molten salt designs pumping fuel around usually have a third to a half of the fissile outside the area where fission is supposed to happen. Also, the fuel only touches the inside of the fuel tubes, which are simple to swap out. The pumps, heat exchangers and tank walls are only exposed to a fraction of the fission products that would otherwise be able to corrode them, plate out on them, or get absorbed into them. Everything except the consumable fuel assemblies is protected from neutron flux by a metre of hafnium-containing coolant.
The fuel assemblies have a spike at the bottom that sits in a locator, and flanges at the top that sit on rails running across the top of the tank. Make the flanges wider than the gap between the rails, and they shouldn’t fall over. The attachments at the top of the fuel assemblies are visible above the surface of the coolant. If the fuel handler machine fell on the bell capped rods, I guess you’d just have to get it off again. Probably easier than the one at Monju, in liquid sodium.
It could but this way you don’t have to pump the fissile material through the heat exchangers. That means you need a lot less of it – molten salt designs pumping fuel around usually have a third to a half of the fissile outside the area where fission is supposed to happen. Also the fuel only touches the inside of the fuel tubes which are simple to swap out. The pumps heat exchangers and tank walls are only exposed to a fraction of the fission products that would otherwise be able to corrode them plate out on them or get absorbed into them. Everything except the consumable fuel assemblies is protected from neutron flux by a metre of hafnium-containing coolant.
The fuel assemblies have a spike at the bottom that sits in a locator and flanges at the top that sit on rails running across the top of the tank. Make the flanges wider than the gap between the rails and they shouldn’t fall over. The attachments at the top of the fuel assemblies are visible above the surface of the coolant.If the fuel handler machine fell on the bell capped rods I guess you’d just have to get it off again. Probably easier than the one at Monju in liquid sodium.
Rankine cycle works BECAUSE change in state. Christ all mighty.
shutdown decay heat is 6% in the first hour and 1% after 24 hours.
Rankine cycle works BECAUSE change in state. Christ all mighty.
shutdown decay heat is 6{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} in the first hour and 1{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} after 24 hours.
Radioactive sodium choride salts at sea. Maybe not such a great idea?
Radioactive sodium choride salts at sea. Maybe not such a great idea?
Just how much heat per square metre can be radiated by the system at the temperatures to be expected, and how much airflow will be required to absorb the energy , and, given a purely passive ie convection system, how big a chimney stack system to take the hot air away? I can`t get my head round this, would like to see a beermat calculation showing how it`s done.
Just how much heat per square metre can be radiated by the system at the temperatures to be expected and how much airflow will be required to absorb the energy and given a purely passive ie convection system how big a chimney stack system to take the hot air away? I can`t get my head round this would like to see a beermat calculation showing how it`s done.
Several points you mention here are incorrect. PWR enrichment is typically flat for 11 feet with a 6″ reduced enrichment ‘cutback’ at the top and the bottom. PWR do not have higher enrichment pellets at the top to compensate; instead, they simply tolerate a 1-5% power tilt (top vs. bottom) for most of the cycle, which flips and becomes ~5% top peaked in coast down at EOC. Same with BWR enrichment although BWR tend to reduce poison load in the top of the fuel assembly to balance significantly voided top of the fuel. If “with liquid rod… sorts itself out” you mean that there is no enrichment gradient – then I would agree, but don’t see what you are driving at. With your comment about slide-shuffle BS for Moltex you don’t really appreciate how the system would be coupled. Remove an assembly and you will reduce regional power density significantly and could even shut the whole thing down. CANDU is huge with large radial distance between fuel assemblies compared to more closely assembled Moltex power point reactor. Removing a fuel assembly would be similar to dropping a control rod in a PWR – push the peak all out of joint. Why would anyone leave a strong epi-thermal absorber in the coolant? Sounds really silly since Hf is about 30X more absorbing than iron. Don’t really get the “quench chain reaction pretty effectively” comment, but ok whatever.
Several points you mention here are incorrect. PWR enrichment is typically flat for 11 feet with a 6 reduced enrichment ‘cutback’ at the top and the bottom. PWR do not have higher enrichment pellets at the top to compensate; instead they simply tolerate a 1-5{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} power tilt (top vs. bottom) for most of the cycle” which flips and becomes ~5{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} top peaked in coast down at EOC. Same with BWR enrichment although BWR tend to reduce poison load in the top of the fuel assembly to balance significantly voided top of the fuel. If “”with liquid rod… sorts itself out”””” you mean that there is no enrichment gradient – then I would agree”””” but don’t see what you are driving at. With your comment about slide-shuffle BS for Moltex you don’t really appreciate how the system would be coupled. Remove an assembly and you will reduce regional power density significantly and could even shut the whole thing down. CANDU is huge with large radial distance between fuel assemblies compared to more closely assembled Moltex power point reactor. Removing a fuel assembly would be similar to dropping a control rod in a PWR – push the peak all out of joint.Why would anyone leave a strong epi-thermal absorber in the coolant? Sounds really silly since Hf is about 30X more absorbing than iron. Don’t really get the “”””quench chain reaction pretty effectively”””” comment”””” but ok whatever.”””
Several points you mention here are incorrect. PWR enrichment is typically flat for 11 feet with a 6″ reduced enrichment ‘cutback’ at the top and the bottom. PWR do not have higher enrichment pellets at the top to compensate; instead, they simply tolerate a 1-5% power tilt (top vs. bottom) for most of the cycle, which flips and becomes ~5% top peaked in coast down at EOC. Same with BWR enrichment although BWR tend to reduce poison load in the top of the fuel assembly to balance significantly voided top of the fuel. If “with liquid rod… sorts itself out” you mean that there is no enrichment gradient – then I would agree, but don’t see what you are driving at. With your comment about slide-shuffle BS for Moltex you don’t really appreciate how the system would be coupled. Remove an assembly and you will reduce regional power density significantly and could even shut the whole thing down. CANDU is huge with large radial distance between fuel assemblies compared to more closely assembled Moltex power point reactor. Removing a fuel assembly would be similar to dropping a control rod in a PWR – push the peak all out of joint. Why would anyone leave a strong epi-thermal absorber in the coolant? Sounds really silly since Hf is about 30X more absorbing than iron. Don’t really get the “quench chain reaction pretty effectively” comment, but ok whatever.
Several points you mention here are incorrect. PWR enrichment is typically flat for 11 feet with a 6 reduced enrichment ‘cutback’ at the top and the bottom. PWR do not have higher enrichment pellets at the top to compensate; instead they simply tolerate a 1-5{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} power tilt (top vs. bottom) for most of the cycle” which flips and becomes ~5{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} top peaked in coast down at EOC. Same with BWR enrichment although BWR tend to reduce poison load in the top of the fuel assembly to balance significantly voided top of the fuel. If “”with liquid rod… sorts itself out”””” you mean that there is no enrichment gradient – then I would agree”””” but don’t see what you are driving at. With your comment about slide-shuffle BS for Moltex you don’t really appreciate how the system would be coupled. Remove an assembly and you will reduce regional power density significantly and could even shut the whole thing down. CANDU is huge with large radial distance between fuel assemblies compared to more closely assembled Moltex power point reactor. Removing a fuel assembly would be similar to dropping a control rod in a PWR – push the peak all out of joint.Why would anyone leave a strong epi-thermal absorber in the coolant? Sounds really silly since Hf is about 30X more absorbing than iron. Don’t really get the “”””quench chain reaction pretty effectively”””” comment”””” but ok whatever.”””
Several points you mention here are incorrect.
PWR enrichment is typically flat for 11 feet with a 6″ reduced enrichment ‘cutback’ at the top and the bottom. PWR do not have higher enrichment pellets at the top to compensate; instead, they simply tolerate a 1-5% power tilt (top vs. bottom) for most of the cycle, which flips and becomes ~5% top peaked in coast down at EOC. Same with BWR enrichment although BWR tend to reduce poison load in the top of the fuel assembly to balance significantly voided top of the fuel. If “with liquid rod… sorts itself out” you mean that there is no enrichment gradient – then I would agree, but don’t see what you are driving at.
With your comment about slide-shuffle BS for Moltex you don’t really appreciate how the system would be coupled. Remove an assembly and you will reduce regional power density significantly and could even shut the whole thing down. CANDU is huge with large radial distance between fuel assemblies compared to more closely assembled Moltex power point reactor. Removing a fuel assembly would be similar to dropping a control rod in a PWR – push the peak all out of joint.
Why would anyone leave a strong epi-thermal absorber in the coolant? Sounds really silly since Hf is about 30X more absorbing than iron. Don’t really get the “quench chain reaction pretty effectively” comment, but ok whatever.
Just how much heat per square metre can be radiated by the system at the temperatures to be expected, and how much airflow will be required to absorb the energy , and, given a purely passive ie convection system, how big a chimney stack system to take the hot air away? I can`t get my head round this, would like to see a beermat calculation showing how it`s done.
Just how much heat per square metre can be radiated by the system at the temperatures to be expected and how much airflow will be required to absorb the energy and given a purely passive ie convection system how big a chimney stack system to take the hot air away? I can`t get my head round this would like to see a beermat calculation showing how it`s done.
Just how much heat per square metre can be radiated by the system at the temperatures to be expected, and how much airflow will be required to absorb the energy , and, given a purely passive ie convection system, how big a chimney stack system to take the hot air away? I can`t get my head round this, would like to see a beermat calculation showing how it`s done.
Radioactive sodium choride salts at sea. Maybe not such a great idea?
Radioactive sodium choride salts at sea. Maybe not such a great idea?
Radioactive sodium choride salts at sea. Maybe not such a great idea?
At the BWR we have a standing plan to reduce power to 85% and back to 100% as needed; we revisit and tweak as necessary (usually good for 6 weeks). This standing plan requires no oversight because predictions indicate adequate margins to all parameters. You have to admit that 15% power reduction should be adequate for load follow, but evidently the germans put themselves in the position and their reactor engineers caved to generation pressure and broke fuel.
At the BWR we have a standing plan to reduce power to 85{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} and back to 100{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} as needed; we revisit and tweak as necessary (usually good for 6 weeks). This standing plan requires no oversight because predictions indicate adequate margins to all parameters. You have to admit that 15{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} power reduction should be adequate for load follow but evidently the germans put themselves in the position and their reactor engineers caved to generation pressure and broke fuel.
I heard a German reactor had had fuel damage from trying to load follow peaky unreliables, so they’ve been relegated to strictly baseload again.
I heard a German reactor had had fuel damage from trying to load follow peaky unreliables so they’ve been relegated to strictly baseload again.
At the BWR we have a standing plan to reduce power to 85% and back to 100% as needed; we revisit and tweak as necessary (usually good for 6 weeks). This standing plan requires no oversight because predictions indicate adequate margins to all parameters. You have to admit that 15% power reduction should be adequate for load follow, but evidently the germans put themselves in the position and their reactor engineers caved to generation pressure and broke fuel.
I heard a German reactor had had fuel damage from trying to load follow peaky unreliables, so they’ve been relegated to strictly baseload again.
99% of the time fuel rod defect is due to debris fretting (wire bristle, swarf, turnings). 1% of the time defect occurs to pellet-cladding interaction you described, but the actual root cause there would be not following ramp rate guidelines. In other words, the station nuclear engineer “had one job to do” and he didn’t do it right. When defect does occur then you get hydriding UO2 becomes U3O8 again, etc.
99{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} of the time fuel rod defect is due to debris fretting (wire bristle swarf turnings). 1{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} of the time defect occurs to pellet-cladding interaction you described but the actual root cause there would be not following ramp rate guidelines. In other words the station nuclear engineer had one job to do”” and he didn’t do it right.When defect does occur then you get hydriding UO2 becomes U3O8 again”””” etc.”””
‘The cladding splits because entropy happens. ‘ No, because the fuel pellets swell. They could leave more room for them by having a wider clearance between the pellets and the inside of the fuel tubes, but the helium that fills the gap isn’t a very good heat conductor, so the pellets would get even hotter, and swell faster. The Experimental Breeder Reactor II in Idaho ran for thirty years with metal fuel, instead of uranium oxide pellets. Metal is a better heat conductor than UO2, but it still swells. They left more clearance, and filled the gap with a liquid sodium ‘bond’, the same as the coolant on the outside of the fuel tube. This allowed much longer burn-up than a light water reactor. A sodium bond was proposed for LWR fuel, but presumably the regulators frowned on it. Lightbridge want to use metal fuel with a cross-section rather like a star shape, instead of round, which, with a higher enrichment level, could accommodate more swelling without splitting the casing.
‘The cladding splits because entropy happens. ‘ No because the fuel pellets swell. They could leave more room for them by having a wider clearance between the pellets and the inside of the fuel tubes but the helium that fills the gap isn’t a very good heat conductor so the pellets would get even hotter and swell faster. The Experimental Breeder Reactor II in Idaho ran for thirty years with metal fuel instead of uranium oxide pellets. Metal is a better heat conductor than UO2 but it still swells. They left more clearance and filled the gap with a liquid sodium ‘bond’ the same as the coolant on the outside of the fuel tube. This allowed much longer burn-up than a light water reactor. A sodium bond was proposed for LWR fuel but presumably the regulators frowned on it. Lightbridge want to use metal fuel with a cross-section rather like a star shape instead of round which with a higher enrichment level could accommodate more swelling without splitting the casing.
Moltex calculate that with loss of heat sink without scram, fission will shut down when the coolant goes over 800C- well below boiling point of the salt, or failure of the steel. Coolant temperature will peak below 900C after 13 or 14 hours, but stay above 800C for at least 35 hours post trip. After that, if the boron blades still won’t come down, they could move enough fuel assemblies away from the core to keep it subcritical.
Moltex calculate that with loss of heat sink without scram fission will shut down when the coolant goes over 800C- well below boiling point of the salt or failure of the steel. Coolant temperature will peak below 900C after 13 or 14 hours but stay above 800C for at least 35 hours post trip. After that if the boron blades still won’t come down they could move enough fuel assemblies away from the core to keep it subcritical.
99% of the time fuel rod defect is due to debris fretting (wire bristle, swarf, turnings). 1% of the time defect occurs to pellet-cladding interaction you described, but the actual root cause there would be not following ramp rate guidelines. In other words, the station nuclear engineer “had one job to do” and he didn’t do it right.
When defect does occur then you get hydriding UO2 becomes U3O8 again, etc.
‘The cladding splits because entropy happens. ‘ No, because the fuel pellets swell. They could leave more room for them by having a wider clearance between the pellets and the inside of the fuel tubes, but the helium that fills the gap isn’t a very good heat conductor, so the pellets would get even hotter, and swell faster. The Experimental Breeder Reactor II in Idaho ran for thirty years with metal fuel, instead of uranium oxide pellets. Metal is a better heat conductor than UO2, but it still swells. They left more clearance, and filled the gap with a liquid sodium ‘bond’, the same as the coolant on the outside of the fuel tube. This allowed much longer burn-up than a light water reactor. A sodium bond was proposed for LWR fuel, but presumably the regulators frowned on it. Lightbridge want to use metal fuel with a cross-section rather like a star shape, instead of round, which, with a higher enrichment level, could accommodate more swelling without splitting the casing.
Moltex calculate that with loss of heat sink without scram, fission will shut down when the coolant goes over 800C- well below boiling point of the salt, or failure of the steel. Coolant temperature will peak below 900C after 13 or 14 hours, but stay above 800C for at least 35 hours post trip. After that, if the boron blades still won’t come down, they could move enough fuel assemblies away from the core to keep it subcritical.
Rankine cycle works BECAUSE change in state. Christ all mighty.
shutdown decay heat is 6% in the first hour and 1% after 24 hours.
It could, but this way you don’t have to pump the fissile material through the heat exchangers. That means you need a lot less of it – molten salt designs pumping fuel around usually have a third to a half of the fissile outside the area where fission is supposed to happen. Also, the fuel only touches the inside of the fuel tubes, which are simple to swap out. The pumps, heat exchangers and tank walls are only exposed to a fraction of the fission products that would otherwise be able to corrode them, plate out on them, or get absorbed into them. Everything except the consumable fuel assemblies is protected from neutron flux by a metre of hafnium-containing coolant.
The fuel assemblies have a spike at the bottom that sits in a locator, and flanges at the top that sit on rails running across the top of the tank. Make the flanges wider than the gap between the rails, and they shouldn’t fall over. The attachments at the top of the fuel assemblies are visible above the surface of the coolant.
If the fuel handler machine fell on the bell capped rods, I guess you’d just have to get it off again. Probably easier than the one at Monju, in liquid sodium.
A liquid like molten salt has a far higher heat capacity than air. Air flowing by natural convection around the outside of the tub carries a lot less heat away than salt pumped from right next to the fuel rods. It just has to be able to take away decay heat after the chain reaction stops, probably a few tens of megawatts max, compared to ~ 500 MW thermal during normal operation. The reactor is designed to shut down when the temperature goes much above its normal range. Air convection will get faster with higher temperature, and there is enough thermal inertia to keep the salts well below boiling point.
I thought that long sealed fuel salt tubes with a vacuum that pulls out Xe in to the void could work but what do I know.
The cladding splits because entropy happens.
Again: I too just can’t buy the “open fuel rod” design. Entropy happens and the rods don’t seem to be locked in place. What happens during an earthquake? What happens if the fuel handler machine falls on the open rods?
They want to get the Xeon and Krypton out of the fuel salt.
I’m sorry but I just cant accept that some fuel won’t find its way out of the open tubes and settle in the coolant salt. You have hundreds of assemblies and the fuel salt is hot for years. Some fuel ions will escape and foul the coolant salt. Entropy is just a bltch that way.
I don’t like that if a fuel assembly tips over while shuffling (hey stuff happens) then it mixes the fuel salt with the cooling salt.
Just mix the two and design for that up front. So I guess i’m partial to the chloride salt fast reactor designs.
Proper heat recovery works wonders. The coolant never changes state. That is the major efficiency loss in a steam cycle. Coolant does not have to change state in order to re-enter the coolant cycle. I suppose that is one very simple and profound difference when liquid salts are used to get heat out of the reaction. It CAN be that efficient!
One very simple and profound thing hits me as not making sense. If this design can be air cooled by ambient air, how can it develop enough heat in the first place for the standard water boiłing-steam-turbine action? It can’t possibly be that efficient.
Maybe for whaling fleets. If Greenpeace is going to protest you either way, may as well go whole hog.
The British gas cooled reactors were supposed to refuel at power, but they had problems with vibrations. Salt ( and water ) are much better coolants, so velocity is lower. Not sure about BWRs, but don’t PWRs have higher enrichment pellets at the top of the rods, to compensate for the higher temperature there ? With a liquid in the rod, that sorts itself out.
Candus shove their fuel assemblies through the pressure tubes in alternate opposite directions, pretty much like Moltex. There’s supposed to usually be a row of the cubic arrangements next to each other, so only the outside ends will be getting less neutrons – convection will equalise everything top to bottom.
Ian Scott reckons leaving 2% hafnium in his zirconium fluoride coolant will reduce neutron flux by four orders of magnitude after one metre. There’s no moderator, so shuffling a fuel assembly to the edge of the vat should quench the chain reaction pretty effectively.
From my reading of their documents Xe-137 decays into Cs-137. The diving bell design (borrowed from one of the Dounreay reactors) holds up the Xe-137 long enough for it to decay into Cs-137 and plate out onto the walls of the fuel tube.
I think the other noble gasses are vented to avoid pressure build up in the fuel tubes?
The fuel rods split because the pellets have expanded till they interfere with the cladding. That expansion is partly from pressurised fission gas collecting in voids, partly from metals migrating through the oxide because of heat gradients – the temperature at the centre of the pellet is way higher, so more volatile elements move out to where it’s cooler. Moltex’s cladding contains a convecting liquid, so there should be much less stress on it. Most of the volatile metal fission products will stay chemically bound to the salt, but even if some get out into the coolant, they’ll be in tiny grains, and the pumps are filtered. The primary coolant will be radioactive anyway, from activation of the zirconium component of it. That’s why they have a clean salt secondary coolant.
When a fuel rod pops in a BWR we go look for it by sticking rods in/out one at a time over multiple days. When we perturb the area with the leaker we measure elevated FP in the offgas thattis vacuumed from the condenser. We then leave that rod inserted for the remainder of the cycle and take a huge hit in generation because the core will now coast maybe 10 or 20 days early due to suppression of a region in the core. Millions of dollars lost to keep a single fuel rod defect from getting worse because God forbid it gets worse, unzipps and spills it’s pellets. Those pellets would then get chopped up by the pumps and deposit “tramp” uranium from reactor to condenser. So we go to great lengths to make sure 2kg of pellets from one rod doesn’t chrap up the whole plant and increase worker dose. So from that perspective, a core with 30,000 fuel rods all leaking by design is a frickin joke.
(After discussion of fuel venting in the Dounreay sodium fast reactor, which resulted in a lot of cesium 137 contaminating the sodium) – ‘There seemed a possibility that the stable salt trapping capability of molten salt might clean up the fission gases enough to allow them to be vented. To investigate this, chemical thermodynamic calculations were carried out with the software package HSC8 to quantify the composition of the gas released during fission. The results are shown in Figure 3. At the high temperature of the fuel salt, about 1000°C, there are substantial amounts of gases released. But those gases immediately encounter the cooler walls of the tube above the level of the fuel salt where the temperature is the same as the coolant, 600°C. Since the gas flow is extremely slow, a few ml per day, there is plenty of time for the gases evolved to condense on the cooler walls. The result is that only Xe, Kr, Cd and ZrCl4 are released in significant quantities. None of these are hazardous radioisotopes – Xe-137, which decays to hazardous Cs-137, decays almost entirely (fraction remaining less than 10-6) while still in the tube gas space.
The decision was made to vent the tubes therefore as the hazard of pressurising the tubes was seen as greater than that of allowing the gases to vent into the inert gas containment of the reactor (not into the atmosphere). ‘
http://www.modernpowersystems.com/features/featurethe-stable-salt-reactor-transforming-the-promise-of-the-molten-salt-fuel-concept-into-a-viable-technology-5748063/
www.moltexenergy.com/learnmore/An_Introduction_Moltex_Energy_Technology_Portfolio.pdf
“The emergency cooling system consists of air ducts around the reactor tank which continually circulate
air past the tank purely by natural convection. This is similar to other reactors such as PRISM. The
Moltex system is superior however because it can take away the decay heat from small high-power
reactors which is not possible for reactors like PRISM. The Moltex system relies on a novel method to
capture heat radiated from the hot reactor tank wall on a large surface area of fins which in turn pass
the heat to the circulating cool air. This system has been patented and allows passive air cooling to be
used on much more powerful and compact reactors than was ever conventionally thought possible.”
Rectangular geometry…. Hmm. The online refueling aspect is a bit of a distraction for them it seems. Not really relevant in trying to prove the other concepts (salt in and outside tubes). It doesn’t seem particularly reasonable to slide shuffle the fuel at power. It’s like a totally new class of NUREG-0800 chapter 15.4 transient to analyze. That’s not how CANDU does it.
“The fuel salt is held in vented tubes. Venting is safe because in our reactors the dangerous fission products form stable compounds, not gases.”
THEN WHY VENT THE TUBES?
Bogus. A total lie. Get almost 1 noble gas fission product atom per fission.
Got your physics mixed up pal.
I’ve got to wonder if a 150MWe module could have an application in ship propulsion?
One of the characteristics of molten salts, is that they have a high coefficient of thermal expansion. A few degrees above the design temperature, fission stops, and you only have to deal with fission daughter decay heat, and lanthanide decay heat.
The proponents of this design seem to think that a bathtub design reactor could not be built without placing fuel salts in many small tubes. I’m not sure why they would believe that.
I don’t believe that convection air cooling can cool down any nuclear reactor unless the reactor has a high negative reaction temperature coefficient.