The BV238 was a 6-propeller blades large plane made for long distance flight and able to airdrop some bombs & fire some cannons. The BV 238’s name hints on the main fuel, uranium 238, but it’s also man fuel, since obviously the core was fuelled with partially cooked products from Birkenau, with the pistons for propulsion involved both in plutogenization and propulsion. It’s a mix of thermal and fast neutrons achieved in a subcritical mode but with flaws related to, first, the human flakes in (see link above) and secondly to the complexity of the loop with, in addition, I think, the need to consume oceanwater regularly to stream it inbetween the pistons as attempt to thermalize (so the plane… regularly takes water like any modern firefighting plane but for its core’s thermalization).
There certainly was a lateral heating exactly as in Birkenau ovens where it’s under… for initial pressurization (start and control of the subcritical chain reaction which also needs waterflow inbetween the tiny pistonned cores, 6 of them, one per blade, to get better fission rates). A small diesel unit I think.
Here’s a part of the core :
So you can see the quite heavy black plume identical to Zyklon B bombs (see again link above).