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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

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.
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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

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