Factorio Forums

>What did you do?
I added a modded item with a fuel_value, with the fuel_category set to fusion, and a burnt_result item. Then I inserted that item into a fusion reactor.
>What happened?
The fusion reactor consumed the item without returning the burnt_result item.
>What did you expect to happen instead?
I expected the fusion reactor to have a second inventory slot, just like boilers and reactors do, that will contain the optional burnt_result items of whatever fuel it consumes.

Did you remember to add a slot for the burnt item in the reactor itself?

Oh, I did not think about that. Now it works as intended, thank you.

If burner has burnt result inventory of size 0, then it will void the result regardless of burnt_result. That was decided to be a more useful behavior for mods than having burner completly stuck after finishing burning fuel because it could not give the burnt result.