4 ms·

How hard is it to make FLiBe?

pfdietz 8y ago
The enriched 6Li in a single reactor would correspond to 1/4 of that produced for the entire US hydrogen bomb program. There is no facility in the world that could make the 6Li required, and the technology that was used in the US is now prohibited due to large leakag of elemental mercury into the environment (the plant used thousands of tons of liquid mercury metal.)
- MertsA 8y ago
  As a neat coincidence, molten salt fueled fission reactors also need enriched Lithium. However, those need Lithium 7 which would essentially be the depleted Lithium from enriching Lithium 6.
  - pfdietz 8y ago
    No, MSRs do not necessarily need enriched lithium. For example, Moltex's fast MSR uses no lithium whatsoever. The (barren) coolant salt is zirconium sodium potassium fluoride, and the fuel salt (in tubes, where it does not mix with the coolant) is a mixture of sodium, zirconium, uranium, and plutonium chlorides, as well as fission products. The zirconium does not have to be "nuclear grade", since the design not only tolerates hafnium (a strong thermal neutron absorber) in the coolant salt, it depends on it to shield the reactor structure from thermal neutron degradation. Lithium-7 will still lead to production of some tritium. Any MSR using lithium is going to need a tritium separation and capture system.
    - baking 8y ago
      SPARC's models show a net positive for tritium breeding of 1.08 (tritium produced/tritium consumed) but I'm pretty sure this relies on enriched lithium, although I can't find where they specify the level of enrichment for that model. I'm sure it was a design constraint though.
    - MertsA 8y ago
      MSRs that use lithium in the fuel salt do in fact need enriched lithium. The problem is that lithium 6 has a much larger neutron absorption cross section than lithium 7. It's on the order of 10,000x greater IIRC.
      - pfdietz 8y ago
        Right. It's just that MSRs don't necessarily need lithium.
        MertsA 8y ago
        Not all of them do, you're right about that.
- 08-15 8y ago
  Why do you think it needs to be enriched?
  - philipkglass 8y ago
    The ARC paper proposes that the lithium in the salt should be enriched to 90% lithium 6 to reach a tritium breeding ratio of 1.1. See section 5.3, "Tritium breeding." https://arxiv.org/pdf/1409.3540.pdf https://arxiv.org/pdf/1409.3540.pdf I presume that the breeding ratio would fall below 1.0 with natural lithium.
    - 08-15 8y ago
      For the first proof-of-concept reactor? That's borrowing trouble. If the things works at all and the only remaining problem is the tritium supply, funding won't be a problem anymore.
      - pfdietz 8y ago
        They have to breed tritium if they are to run the reactor for any significant length of time. Buying tritium externally would be very expensive -- it's $100M/kg and up, particularly if you exhaust sources like incidental production in commercial heavy water reactors. DT fusion has the nasty circular dependency that breeding blankets are needed to make tritium, but they cannot be tested without working high intensity DT fusion neutron sources.
      - baking 8y ago
        To clarify, the design that the paper is addressing is the ARC, a full-size pilot reactor intended to put 200MW out on the grid for 9 working years. The demonstration reactor is the SPARC which is based on a scaled down half-sized (but 1/8 the mass and 1/8 the cost) version of ARC. While the main goal of SPARC is to achieve significant net power output, along with a proof-of-concept for many of the design features of ARC, some features may have to be left out for lack of space. So I don't know if SPARC will be able to achieve net tritium breeding, but I presume they will be testing as many of the features as they can along with taking measurements and verifying the model. It is also noteworthy that the ARC/SPARC design allows for replacement of the vacuum vessel and cooling blanket without complete removal of the outside magnetic coils, so they foresee design iteration of those components unlike the ITER design which will be pretty much locked in.

The enriched 6Li in a single reactor would correspond to 1/4 of that produced for the entire US hydrogen bomb program. There is no facility in the world that could make the 6Li required, and the technology that was used in the US is now prohibited due to large leakag of elemental mercury into the environment (the plant used thousands of tons of liquid mercury metal.)

MertsA 8y ago
As a neat coincidence, molten salt fueled fission reactors also need enriched Lithium. However, those need Lithium 7 which would essentially be the depleted Lithium from enriching Lithium 6.
- pfdietz 8y ago
  No, MSRs do not necessarily need enriched lithium. For example, Moltex's fast MSR uses no lithium whatsoever. The (barren) coolant salt is zirconium sodium potassium fluoride, and the fuel salt (in tubes, where it does not mix with the coolant) is a mixture of sodium, zirconium, uranium, and plutonium chlorides, as well as fission products. The zirconium does not have to be "nuclear grade", since the design not only tolerates hafnium (a strong thermal neutron absorber) in the coolant salt, it depends on it to shield the reactor structure from thermal neutron degradation. Lithium-7 will still lead to production of some tritium. Any MSR using lithium is going to need a tritium separation and capture system.
  - baking 8y ago
    SPARC's models show a net positive for tritium breeding of 1.08 (tritium produced/tritium consumed) but I'm pretty sure this relies on enriched lithium, although I can't find where they specify the level of enrichment for that model. I'm sure it was a design constraint though.
  - MertsA 8y ago
    MSRs that use lithium in the fuel salt do in fact need enriched lithium. The problem is that lithium 6 has a much larger neutron absorption cross section than lithium 7. It's on the order of 10,000x greater IIRC.
    - pfdietz 8y ago
      Right. It's just that MSRs don't necessarily need lithium.
      - MertsA 8y ago
        Not all of them do, you're right about that.
08-15 8y ago
Why do you think it needs to be enriched?
- philipkglass 8y ago
  The ARC paper proposes that the lithium in the salt should be enriched to 90% lithium 6 to reach a tritium breeding ratio of 1.1. See section 5.3, "Tritium breeding." https://arxiv.org/pdf/1409.3540.pdf https://arxiv.org/pdf/1409.3540.pdf I presume that the breeding ratio would fall below 1.0 with natural lithium.
  - 08-15 8y ago
    For the first proof-of-concept reactor? That's borrowing trouble. If the things works at all and the only remaining problem is the tritium supply, funding won't be a problem anymore.
    - pfdietz 8y ago
      They have to breed tritium if they are to run the reactor for any significant length of time. Buying tritium externally would be very expensive -- it's $100M/kg and up, particularly if you exhaust sources like incidental production in commercial heavy water reactors. DT fusion has the nasty circular dependency that breeding blankets are needed to make tritium, but they cannot be tested without working high intensity DT fusion neutron sources.
    - baking 8y ago
      To clarify, the design that the paper is addressing is the ARC, a full-size pilot reactor intended to put 200MW out on the grid for 9 working years. The demonstration reactor is the SPARC which is based on a scaled down half-sized (but 1/8 the mass and 1/8 the cost) version of ARC. While the main goal of SPARC is to achieve significant net power output, along with a proof-of-concept for many of the design features of ARC, some features may have to be left out for lack of space. So I don't know if SPARC will be able to achieve net tritium breeding, but I presume they will be testing as many of the features as they can along with taking measurements and verifying the model. It is also noteworthy that the ARC/SPARC design allows for replacement of the vacuum vessel and cooling blanket without complete removal of the outside magnetic coils, so they foresee design iteration of those components unlike the ITER design which will be pretty much locked in.