I don't know how a reactor produces energy without a turbine, since all modern day reactors produce heat, makes steam, move a magnet in a coil of wire, and the produce electricity. The analogy between passive reactor and real life, not applicable.
Yep, Passively cooled Big Reactor Reactors are a mystery.
If we were to embrace our suspension of disbelief: Passively cooled Big Reactors produce RF via "absorbtion". Refer to
RadiationHelper.java - basically each fuel rod emits 4 packets of radiation, each one travelling 4 blocks in a different cardinal direction. Each block the radiation visits first absorbs some of the soft radiation - via the materials absorbtion property, and moderates some of the hard radiation in the packet to soft - via the materials moderation property. The amount absorbed is multiplied by the heat efficiency property to determine the RF generated.
BigReactors.java handles the registration of the matierials - where Cyrotheum is registered with 66% absorption, 95% heat efficiency, and 600% moderation - which makes a few blocks of it in a row insanely good at converting all the available hard radiation to soft, and converting most of the soft radiation to RF. (
Resonant ender is registered with 90% absorption, 75% heat efficiency, 200% moderation - so its a much better absorber, but it converts a lot less of what is absorbed into RF = so it comes out only slightly better at converting radiation into RF than cyrotheum (63% effective conversion for ender vs 62.7% for cyrotheum). At 200%, it is the 2nd best moderator, but can't match cyrotheums moderation ability at all.
Between Gelid Cyrotheum and Resonant Ender, they have the best absorption, heat efficency, moderation - and heat conductivity of all the possible registered reactor interior blocks. Which I think is a shame as it does make (passive) reactor design rather boring: You are using these - or you are doing it wrong.
