Using KubeJS to add smelting recipes that require use of the nuclear furnace through the nuclear_furnace crafting type will only function if the configuration options for the nuclear furnace have "nuclear_furnace_custom_type = true" set. Attempting to let the Nuclear furnace perform smelting or blasting operations will completely disable Nuclear Furnace-exclusive operations.

Admittedly I don't know for certain that this is a bug. It is certainly working as designed, but it does not strike me as working as intended. I also do not know if this is a KubeJS issue specifically, as I am incapable of building data packs from scratch.

To reproduce, simply add a custom recipe exclusive to the Nuclear Furnace and try to use it with "nuclear_furnace_custom_type" set to false.