KeithPickering wrote: Robert Hargraves is fairly down on LiF as a salt for LFTRs in his recent book Thorium: Energy cheaper than coal because the Li produces radioactive tritium inside a LFTR, in quantities higher than can be legally released into the air (in the US, anyway). That means you need a chemical process to capture and sequester the tritium, hence more expense. Instead, Hargraves suggests another fluoride salt be subsituted for LiF, such as NaF for example. Not as good a neutron moderator, but that can be finessed by putting graphite into the core.

Thanks Keith.

I do not have access to Robert’s book, but here is a discussion about lithium-7 usage in LFTRs.

AFAIK, Natural lithium is a mixture of two different isotopes, 7.5% Li-6 and 92.5% Li-7. Because it has a high thermal neutron capture cross section (see ENDF chart), Li-6 is classified as a neutron poison. If Li-6 were present in a LFTR’s LF salt, unwanted tritium would be produced via neutron capture: Li-6 + n -> T + alpha, but if the salt only contained Li-7 this would not be a problem. That is why the advocates of LFTR are suggesting such high levels of enrichment (+99.99% Li-7).

When reading the chart below, it is important to realize that the spallation events on the right side are not expected to occur inside a LFTR because the average kinetic energy coming from prompt neutrons, released by fissioning one atom of U-233 (thorium reactors produce/consume this), is only 4.9 MeV.