You're talking about fast-neutron reactors, not about breeder reactors. Fast-neutron reactors can split certain actinides that thermal reactors won't split, but a fast-neutron reactor doesn't have to be a breeder and a breeder doesn't have to be a fast-neutron reactor. In fact, when it comes to fast-neutron reactors, a burner (which consumers fissionable actinides you put in it) is the exact opposite of breeder (which produces more fissionable actinides than you put in it initially). Not quite sure how you mixed that up.
AFAIK most fast-neutron reactors can be used as both burners and breeders depending on loaded blanket. The same neutron flux can be used to split actinides and transform U238. The planned BREST reactor is a good example here: https://en.wikipedia.org/wiki/BREST_(reactor)
What? Different blankets simply produce different results. Load blanket with mostly U238, irradiate it with fast neutron flux for a bit, and finally radio-chemically process the result to extract useful fission elements for new fuel rods to be used in thermal-neutron reactors. Load blanket with waste (stuff which you got after removing Uranium and Plutonium from spent fuel rods) and keep under fast neutron flux for some time and in addition to a bit of energy you will get radioactive, but relatively short-lived waste since almost all actinides will be destroyed.
Then you're reconfiguring a breeder into a burner. You don't have both at the same time.
But I have to say that the part where you concentrate a substantial mass of an unholy mix of medium-lived actinides to be burned into a fairly large structure seems kind of scary. I'm not sure I'd like to work in that part of a nuclear fuel processing plant. Fortunately it's almost certainly an academic question because the probability of this coming into fruition is very low nowadays.
>Then you're reconfiguring a breeder into a burner. You don't have both at the same time.
My point was what the same fast reactor can be used as both breeder and burner without specifying "at the same time". And I am pretty sure (though not 100% confident) that you can mix both breeder and burner rods, thus changing breeder/burner ratio at will.
>the part where you concentrate a substantial mass of an unholy mix of medium-lived actinides to be burned into a fairly large structure seems kind of scary
Yeah, fuel and waste handling is probably the most difficult part of a breeder/burner system, not the reactor itself.
