6 ms·

Sodium is such a nightmarish coolant. Yes, there are advantages in building and engineering a sodium cooled reactor, but from an operating point of view... oh b

Sodium is such a nightmarish coolant. Yes, there are advantages in building and engineering a sodium cooled reactor, but from an operating point of view... oh boy. Sodium catches fire when exposed to air. Sodium reacts violently with water (used in some designs as secondary cooling cycle). Sodium absorbing a neutron creates a strong gamma emitter with a low half time. Sodium reactors have always had low availability times, caused by constant technical problems. However unlike lead as coolant, no advances in material sciences are required to get an operational Gen 4 reactor. On the upside, you can pretty much use Sodium (fast) reactors right now... but maybe you shouldn't?

gus_massa 3y ago
> Sodium absorbing a neutron creates a strong gamma emitter with a low half time. Isn't that a feature? Is it 24Na that decays to 24Mg in 14 hours? In case of an accident, you can run away for a week and it will magically disappear. You don't need a long term storage of the waste.
- wolfram74 3y ago
  for that specific waste, the coolant in a water cooled reactor isn't a huge problem either. The things that are "complicated" are the fuel rods that some people refuse to be convinced we can bury in storage until reprocessing becomes necessary.
- sbaiddn 3y ago
  Run away where? To the next river basin? Na will dissolve into any moisture and be carried away by any moisture.
  - meepmorp 3y ago
    The advantage is 24Na's short (14.9 hour) half-life, not the lack of solubility in water. Half of the original radiation will be gone in 15 hours, and close to 90% in two days.
    - sbaiddn 3y ago
      I understand half life. My point moisture currents can spread water soluble things very far very quickly. Think of it this way, what happens if there's a catastrophic sodium leak? The winds carry it far and the Na gets into everything because it will be diluted into the wind's moisture. Won't you breath the radioactive Na from the air's moisture?
      - meepmorp 3y ago
        The point is that the leaked material stops being dangerous before it can get very far.
        flangola7 3y ago
        Two days of strong winds and storms and you've just dumped sieverts on most of the central US and Canada.
        meepmorp 3y ago
        2 days and ~90% of the original radiation is gone. 3 days and it's ~97%.
        sbaiddn 3y ago
        10% of the radiation of something with a half life measured in hours in a lot od radiation. 10 tons of radioactive Na leak. 1 ton is left after 2 days. Thats a lot!
  - gus_massa 3y ago
    I imagine drinking only bottled water for a week, and perhaps increase the intake of salt for the same time. (Be careful if you have hypertension, it may be more dangerous the additional salt than the radiation.) Beer and salted peanuts looks like a wonderful anti-radiation plan. If you get enough radioactive sodium salts to get covered in a dust layer, you are probably in trouble anyway. It may help that sodium is soluble an it can be washed easily. If the small hidden sodium salts leak to water streams, my guess is that the concentration will be smaller than the natural sodium, and eating some additional non-radioactive sodium may help to remove it from inside the body even faster. Something like the potassium iodine pills.
- credit_guy 3y ago
  Actually this might be sodium's biggest advantage. Everyone knows that Uranium (or Plutonium) can sustain a chain reaction: when hit with a neutron, they split in 2 or 3 lighter atoms, and 2 or 3 new (and fast) neutrons. That can be used to produce a bomb, because the fission events grow exponentially. But it's not all that useful for a reactor, where you want the number of fission events per second to stay constant in time. Which means, on average, each out of the 2 or 3 neutrons produced in a fission event, exactly one will trigger another fission event, and the remaining 1 or 2 neutrons have to find some way to disappear. Roughly speaking they can be absorbed by: 1. by some heavy nucleus like uranium 2. some control rods 3. some neutron poison introduced in the reactor on purpose, such as boron, gadolinium or hafnium, 4. the moderator, like water, or sodium in this case, 5. the walls of the containment vessel. If you think of it, it's such a waste. Many of these options result in radioactive elements. Some result in material embrittlement. Given that, it may very well be that sodium could be the best option out there.
  - RC_ITR 3y ago
    There’s an argument to be made that we should do a much better job of directing those neutrons to make tritium, since fission isn’t even something to discuss until we know how to make abundant tritium.
    - credit_guy 3y ago
      Yes. But fusion is not quite here yet. It's a difficult business proposition to store large quantities of tritium in the hope that you'll be able to sell to an operator of a fusion reactor three decades down the road (after about 80% of it has decayed). On the other hand, when fusion is ready for prime time, one could use liquid lithium in a reactor. Liquid lithium has quite a number of advantages over sodium: in that temperature range it has more specific heat capacity than any metal, higher even than water. It has excellent conductivity. And if it captures a neutron, it splits in helium and tritium plus energy. It could increase the energy production of a fission reactor by more than 5%. And you get that tritium for free, and ultra-rare helium-3 if you fancy some aneutronic fusion at some point.
  - deleted 3y ago
- hermitcrab 3y ago
  A half-life of a few seconds and it will probably decay before it gets near a human. A half-life of thousands years and it will give out it's energy so slowly you will probably be more worried about it's toxicity (e.g. plutonium). The most dangerous ones are generally those that have half-lives of days or weeks. That is long enough to get into a human body and give out a lot of it's energy. The is particularly the case for elements that are readily absorbed by the human body (such as strontium which replace calcium IIRC). On that basis radioctivity from sodium probably isn't too much of a threat. I would be more worried about it's reactivity. (not an expert on this, but did consultancy for the nuclear industry some time ago)
  - George83728 3y ago
    > The most dangerous ones are generally those that have half-lives of days or weeks. That is long enough to get into a human body and give out a lot of it's energy. The is particularly the case for elements that are readily absorbed by the human body (such as strontium which replace calcium IIRC). You're mistaken, the most dangerous waste is that with half lives measured in decades, like cesium-137 or strontium-90 which both have half lives of about 30 years. That 30 year half life means that it can take centuries for the waste to decay away to safe levels. More than hot enough to kill, and with the longevity to do so for several generations. Strontium-85 and strontium-89 half half lives measured in tens of days, but after a few years you don't have to worry about those anymore. It's the isotopes like strontium-90 that are the major concern.
juliennakache 3y ago
From a link shared in a thread below: “High-temperature properties such as the volumetric storage density, viscosity and transparency are similar to water at room temperature. The major advantages of molten salts are low costs, non-toxicity, non-flammability, high thermal stabilities and low vapor pressures. The low vapor pressure results in storage designs without pressurized tanks (Fig. 1). Molten salts are suitable both as heat storage medium and heat transfer fluid (HTF). In general, there is experience with molten salts in a number of industrial applications related to heat treatment, electrochemical treatment and heat transfer for decades.” I don’t know anything about this but it does seem that things are not as clear cut as your comment made it seem. ref: https://onlinelibrary.wiley.com/doi/10.1002/cite.202000137 https://onlinelibrary.wiley.com/doi/10.1002/cite.202000137 EDIT: From ChatGPT 3.5: “ One of the most commonly used molten salts in nuclear reactors is a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2), commonly referred to as FLiBe. FLiBe is used as both a coolant and a neutron moderator in some types of nuclear reactors, such as molten salt reactors (MSRs) and some advanced small modular reactors (SMRs). FLiBe has several advantages as a coolant in nuclear reactors, including its good heat transfer properties and its ability to operate at high temperatures without evaporating. Additionally, FLiBe is not highly corrosive to many materials commonly used in reactor components, which can help reduce maintenance and replacement costs. However, FLiBe does have some potential disadvantages, such as its relatively high viscosity, which can make it more difficult to pump and circulate, and its high melting point, which can increase startup times for reactor systems. Additionally, FLiBe can be corrosive to some materials, such as aluminum and some types of steels, so care must be taken in selecting materials that are compatible with FLiBe.”
- credit_guy 3y ago
  The reactor that Gates talks about (Natrium) uses sodium as moderator and coolant. In other words, the uranium fuel is submerged in a pool (literally, a pool) of liquid sodium. There are some pipes that circulate the liquid (and very hot) sodium to a separate place, where it heats up a secondary circuit of molten salt. That molten salt then goes on to heat some water and make it steam, which then drives some turbines and generate electricity. Or that molten salt can be left molten for a number of hours, as some form of energy storage solution. So, the molten salt does not get in contact with the nuclear fuel in any way in this design. There are other designs where this happens, and especially, there are designs where the uranium (or thorium) is itself part of the molten salt. Even Gates's company, Terrapower, has such a design in the works. But the Natrium reactor is not that.
credit_guy 3y ago
All of these are true. Sodium catches fire when exposed to air. That's why you don't expose it to air. Generally you fill the reactor with argon, which is an inert gas, and very heavy (dense) compared to air. Leaks can still happen, and the few sodium cooled plants around the world have all experienced them. But the fire the sodium catches when in contact with air is a very mild one. It's nothing like the violent reaction sodium has with water. Which brings up your next point, that sodium reacts with water. For some reason you said "in some designs [water is used] as secondary cooling cycle". Which makes me think you are fully aware that this particular design does not actually use water in its secondary cooling cycle, but rather molten salt (point mentioned by Gates in the article). It's a bit disingenuous of you to bring up this point (arguably the greatest negative point about sodium) when it is actually irrelevant in the reactor discussed here. Sodium absorbs a neutron and becomes a strong gamma emitter with a low half time. To be more precise, the half life of Na-24 is 15 days [1]. It decays in a stable isotope of Magnesium, which is not radioactive. Any leak will result in radioactivity that will naturally completely disappear after about one year. As for the "strong gamma rays" (all gamma rays are strong, by the way), they are contained in the containment vessel. Edit: the half life of Na24 is 15 hours, not 15 days. Even better. [1] https://en.wikipedia.org/wiki/Isotopes_of_sodium#Sodium-24 https://en.wikipedia.org/wiki/Isotopes_of_sodium#Sodium-24
- thuuuomas 3y ago
  It sounds like you’re expecting ideal operating conditions indefinitely?
  - credit_guy 3y ago
    No. But I have a hope that the US engineers can do at least as well as the Russian ones. Russia has been running BN-600 for more than 4 decades now, and BN-800 for 8 years. There were incidents but not huge. Here's what wikipedia has to say [1] In the first 15 years of operation, there have been 12 incidents involving sodium/water interactions from tube breaks in the steam generators, a sodium-air oxidation/"fire" from a leak in an auxiliary system, and a sodium "fire" from a leak in a secondary coolant loop while shut down. All these incidents were classified at the lowest level on the International Nuclear Event Scale, and none of the events prevented restarting operation of the facility after repairs. As of 1997, there had been 27 sodium leaks, 14 of which resulted in sodium-air oxidations/"fires". The steam generators are separated in modules so they can be repaired without shutting down the reactor. As of 2020, the cumulative "energy Availability factor" calculated up to year 2019 and recorded by the IAEA was 75.6%. [1] https://en.wikipedia.org/wiki/BN-600_reactor https://en.wikipedia.org/wiki/BN-600_reactor
pookha 3y ago
"Sodium reacts violently with water (used in some designs as secondary cooling cycle)." Wow. This statement is ludicrous. It's like me saying this wind-turbine is dangerous because of solar-panel hazardous waste...Seemed pretty obvious (guy in the article goes on for a while talking about why water was a bad choice) that the design for this reactor is using some variation of molten-salt as a coolant (not pressurized water).
- jakewins 3y ago
  This seems overly harsh - is there not water involved at the plant to drive the steam turbines? That the design of the plant does not directly heat water from sodium is great, but it still is useful to know the plant becomes sensitive to water issues like flooding.
Iwan-Zotow 3y ago
> Sodium reactors have always had low availability times, caused by constant technical problems BN-800 has between 70 and 80%, looks good to me
deleted 3y ago
[deleted]
RC_ITR 3y ago
Water bombarded with neutrons create tritium, which is it’s own nightmare. The problem is the neutrons, not what they hit.
tremon 3y ago
Are you saying they use raw sodium as the coolant? I thought they used a sodium-based salt liquid? In which case, most of the sodium in the mixture is too tied up to react with air or water. (edit: yes they do, see https://news.ycombinator.com/item?id=35841237 https://news.ycombinator.com/item?id=35841237)
lost_tourist 3y ago
So tell us how this will make the Natrium plant fail? since you are knowledgeable about this area.

gus_massa 3y ago

> Sodium absorbing a neutron creates a strong gamma emitter with a low half time. Isn't that a feature? Is it 24Na that decays to 24Mg in 14 hours? In case of an accident, you can run away for a week and it will magically disappear. You don't need a long term storage of the waste.

wolfram74 3y ago
for that specific waste, the coolant in a water cooled reactor isn't a huge problem either. The things that are "complicated" are the fuel rods that some people refuse to be convinced we can bury in storage until reprocessing becomes necessary.
sbaiddn 3y ago
Run away where? To the next river basin? Na will dissolve into any moisture and be carried away by any moisture.
- meepmorp 3y ago
  The advantage is 24Na's short (14.9 hour) half-life, not the lack of solubility in water. Half of the original radiation will be gone in 15 hours, and close to 90% in two days.
  - sbaiddn 3y ago
    I understand half life. My point moisture currents can spread water soluble things very far very quickly. Think of it this way, what happens if there's a catastrophic sodium leak? The winds carry it far and the Na gets into everything because it will be diluted into the wind's moisture. Won't you breath the radioactive Na from the air's moisture?
    - meepmorp 3y ago
      The point is that the leaked material stops being dangerous before it can get very far.
      - flangola7 3y ago
        Two days of strong winds and storms and you've just dumped sieverts on most of the central US and Canada.
        meepmorp 3y ago
        2 days and ~90% of the original radiation is gone. 3 days and it's ~97%.
        sbaiddn 3y ago
        10% of the radiation of something with a half life measured in hours in a lot od radiation. 10 tons of radioactive Na leak. 1 ton is left after 2 days. Thats a lot!
- gus_massa 3y ago
  I imagine drinking only bottled water for a week, and perhaps increase the intake of salt for the same time. (Be careful if you have hypertension, it may be more dangerous the additional salt than the radiation.) Beer and salted peanuts looks like a wonderful anti-radiation plan. If you get enough radioactive sodium salts to get covered in a dust layer, you are probably in trouble anyway. It may help that sodium is soluble an it can be washed easily. If the small hidden sodium salts leak to water streams, my guess is that the concentration will be smaller than the natural sodium, and eating some additional non-radioactive sodium may help to remove it from inside the body even faster. Something like the potassium iodine pills.
credit_guy 3y ago
Actually this might be sodium's biggest advantage. Everyone knows that Uranium (or Plutonium) can sustain a chain reaction: when hit with a neutron, they split in 2 or 3 lighter atoms, and 2 or 3 new (and fast) neutrons. That can be used to produce a bomb, because the fission events grow exponentially. But it's not all that useful for a reactor, where you want the number of fission events per second to stay constant in time. Which means, on average, each out of the 2 or 3 neutrons produced in a fission event, exactly one will trigger another fission event, and the remaining 1 or 2 neutrons have to find some way to disappear. Roughly speaking they can be absorbed by: 1. by some heavy nucleus like uranium 2. some control rods 3. some neutron poison introduced in the reactor on purpose, such as boron, gadolinium or hafnium, 4. the moderator, like water, or sodium in this case, 5. the walls of the containment vessel. If you think of it, it's such a waste. Many of these options result in radioactive elements. Some result in material embrittlement. Given that, it may very well be that sodium could be the best option out there.
- RC_ITR 3y ago
  There’s an argument to be made that we should do a much better job of directing those neutrons to make tritium, since fission isn’t even something to discuss until we know how to make abundant tritium.
  - credit_guy 3y ago
    Yes. But fusion is not quite here yet. It's a difficult business proposition to store large quantities of tritium in the hope that you'll be able to sell to an operator of a fusion reactor three decades down the road (after about 80% of it has decayed). On the other hand, when fusion is ready for prime time, one could use liquid lithium in a reactor. Liquid lithium has quite a number of advantages over sodium: in that temperature range it has more specific heat capacity than any metal, higher even than water. It has excellent conductivity. And if it captures a neutron, it splits in helium and tritium plus energy. It could increase the energy production of a fission reactor by more than 5%. And you get that tritium for free, and ultra-rare helium-3 if you fancy some aneutronic fusion at some point.
- deleted 3y ago
hermitcrab 3y ago
A half-life of a few seconds and it will probably decay before it gets near a human. A half-life of thousands years and it will give out it's energy so slowly you will probably be more worried about it's toxicity (e.g. plutonium). The most dangerous ones are generally those that have half-lives of days or weeks. That is long enough to get into a human body and give out a lot of it's energy. The is particularly the case for elements that are readily absorbed by the human body (such as strontium which replace calcium IIRC). On that basis radioctivity from sodium probably isn't too much of a threat. I would be more worried about it's reactivity. (not an expert on this, but did consultancy for the nuclear industry some time ago)
- George83728 3y ago
  > The most dangerous ones are generally those that have half-lives of days or weeks. That is long enough to get into a human body and give out a lot of it's energy. The is particularly the case for elements that are readily absorbed by the human body (such as strontium which replace calcium IIRC). You're mistaken, the most dangerous waste is that with half lives measured in decades, like cesium-137 or strontium-90 which both have half lives of about 30 years. That 30 year half life means that it can take centuries for the waste to decay away to safe levels. More than hot enough to kill, and with the longevity to do so for several generations. Strontium-85 and strontium-89 half half lives measured in tens of days, but after a few years you don't have to worry about those anymore. It's the isotopes like strontium-90 that are the major concern.

juliennakache 3y ago

From a link shared in a thread below: “High-temperature properties such as the volumetric storage density, viscosity and transparency are similar to water at room temperature. The major advantages of molten salts are low costs, non-toxicity, non-flammability, high thermal stabilities and low vapor pressures. The low vapor pressure results in storage designs without pressurized tanks (Fig. 1). Molten salts are suitable both as heat storage medium and heat transfer fluid (HTF). In general, there is experience with molten salts in a number of industrial applications related to heat treatment, electrochemical treatment and heat transfer for decades.” I don’t know anything about this but it does seem that things are not as clear cut as your comment made it seem. ref: https://onlinelibrary.wiley.com/doi/10.1002/cite.202000137 https://onlinelibrary.wiley.com/doi/10.1002/cite.202000137 EDIT: From ChatGPT 3.5: “ One of the most commonly used molten salts in nuclear reactors is a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2), commonly referred to as FLiBe. FLiBe is used as both a coolant and a neutron moderator in some types of nuclear reactors, such as molten salt reactors (MSRs) and some advanced small modular reactors (SMRs). FLiBe has several advantages as a coolant in nuclear reactors, including its good heat transfer properties and its ability to operate at high temperatures without evaporating. Additionally, FLiBe is not highly corrosive to many materials commonly used in reactor components, which can help reduce maintenance and replacement costs. However, FLiBe does have some potential disadvantages, such as its relatively high viscosity, which can make it more difficult to pump and circulate, and its high melting point, which can increase startup times for reactor systems. Additionally, FLiBe can be corrosive to some materials, such as aluminum and some types of steels, so care must be taken in selecting materials that are compatible with FLiBe.”

credit_guy 3y ago
The reactor that Gates talks about (Natrium) uses sodium as moderator and coolant. In other words, the uranium fuel is submerged in a pool (literally, a pool) of liquid sodium. There are some pipes that circulate the liquid (and very hot) sodium to a separate place, where it heats up a secondary circuit of molten salt. That molten salt then goes on to heat some water and make it steam, which then drives some turbines and generate electricity. Or that molten salt can be left molten for a number of hours, as some form of energy storage solution. So, the molten salt does not get in contact with the nuclear fuel in any way in this design. There are other designs where this happens, and especially, there are designs where the uranium (or thorium) is itself part of the molten salt. Even Gates's company, Terrapower, has such a design in the works. But the Natrium reactor is not that.

credit_guy 3y ago

All of these are true. Sodium catches fire when exposed to air. That's why you don't expose it to air. Generally you fill the reactor with argon, which is an inert gas, and very heavy (dense) compared to air. Leaks can still happen, and the few sodium cooled plants around the world have all experienced them. But the fire the sodium catches when in contact with air is a very mild one. It's nothing like the violent reaction sodium has with water. Which brings up your next point, that sodium reacts with water. For some reason you said "in some designs [water is used] as secondary cooling cycle". Which makes me think you are fully aware that this particular design does not actually use water in its secondary cooling cycle, but rather molten salt (point mentioned by Gates in the article). It's a bit disingenuous of you to bring up this point (arguably the greatest negative point about sodium) when it is actually irrelevant in the reactor discussed here. Sodium absorbs a neutron and becomes a strong gamma emitter with a low half time. To be more precise, the half life of Na-24 is 15 days [1]. It decays in a stable isotope of Magnesium, which is not radioactive. Any leak will result in radioactivity that will naturally completely disappear after about one year. As for the "strong gamma rays" (all gamma rays are strong, by the way), they are contained in the containment vessel. Edit: the half life of Na24 is 15 hours, not 15 days. Even better. [1] https://en.wikipedia.org/wiki/Isotopes_of_sodium#Sodium-24 https://en.wikipedia.org/wiki/Isotopes_of_sodium#Sodium-24

thuuuomas 3y ago
It sounds like you’re expecting ideal operating conditions indefinitely?
- credit_guy 3y ago
  No. But I have a hope that the US engineers can do at least as well as the Russian ones. Russia has been running BN-600 for more than 4 decades now, and BN-800 for 8 years. There were incidents but not huge. Here's what wikipedia has to say [1] In the first 15 years of operation, there have been 12 incidents involving sodium/water interactions from tube breaks in the steam generators, a sodium-air oxidation/"fire" from a leak in an auxiliary system, and a sodium "fire" from a leak in a secondary coolant loop while shut down. All these incidents were classified at the lowest level on the International Nuclear Event Scale, and none of the events prevented restarting operation of the facility after repairs. As of 1997, there had been 27 sodium leaks, 14 of which resulted in sodium-air oxidations/"fires". The steam generators are separated in modules so they can be repaired without shutting down the reactor. As of 2020, the cumulative "energy Availability factor" calculated up to year 2019 and recorded by the IAEA was 75.6%. [1] https://en.wikipedia.org/wiki/BN-600_reactor https://en.wikipedia.org/wiki/BN-600_reactor

pookha 3y ago

"Sodium reacts violently with water (used in some designs as secondary cooling cycle)." Wow. This statement is ludicrous. It's like me saying this wind-turbine is dangerous because of solar-panel hazardous waste...Seemed pretty obvious (guy in the article goes on for a while talking about why water was a bad choice) that the design for this reactor is using some variation of molten-salt as a coolant (not pressurized water).

jakewins 3y ago
This seems overly harsh - is there not water involved at the plant to drive the steam turbines? That the design of the plant does not directly heat water from sodium is great, but it still is useful to know the plant becomes sensitive to water issues like flooding.

Iwan-Zotow 3y ago

> Sodium reactors have always had low availability times, caused by constant technical problems BN-800 has between 70 and 80%, looks good to me

deleted 3y ago

[deleted]

RC_ITR 3y ago

Water bombarded with neutrons create tritium, which is it’s own nightmare. The problem is the neutrons, not what they hit.

tremon 3y ago

Are you saying they use raw sodium as the coolant? I thought they used a sodium-based salt liquid? In which case, most of the sodium in the mixture is too tied up to react with air or water. (edit: yes they do, see https://news.ycombinator.com/item?id=35841237 https://news.ycombinator.com/item?id=35841237)

lost_tourist 3y ago

So tell us how this will make the Natrium plant fail? since you are knowledgeable about this area.