Your mention of liking nitride fuels lead me to look at how the Russians were doing on that, as the only ones with any actual fast neutron reactors in service. As I'm sure you know, the BN600 and BN800 run on oxide fuels, UO2 or MOX, but the plan is to eventually move to nitride, or possibly metal fuels. From what I could find, the burnup of nitride fuels they've tried is limited by fuel swelling, or interaction with the rod cladding
-'The performance of nitride fuel pin as well as oxide is limited by irradiation stability of cladding steel, and also by fuel-cladding mechanical interaction (BR-10 reactor experience).The positive BORA-BORA results confirm the possibility to provide at least12at% of burn-up for He-bonded pins at initial fuel porosity increase. '
https://www-pub.iaea.org/mtcd/meetings/PDFplus/2009/cn176/cn176_Presentations/plenary_session_5/INV-02.Zabudko.pdf
I'm surprised that they're using helium for the thermal bond between the fuel meat and the cladding. The USA's Experimental Breeder Reactor II used sodium bonding very succesfully with metal fuels, since the superior thermal conductivity of sodium allows a wider clearance between the fuel and the clad, giving more room for swelling without damage to the rods. Sodium bonding was also considered for light water reactors, as it should keep the rods cooler, but presumably vetoed in case it leaked into the water coolant. For sodium cooled reactors that wouldn't be an issue, so is there some other reason not to use it with UN or PuN ?
Great post, by the way. Go as long as you need to. John O'Neill
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