Some recipes that use filled barrels can have productivity modules applied, which generate more empty barrels out of nowhere.

Btw, could you put the recipes close to uranium on SEK2 playthrough? It's kind of awkward to be in different tabs.

Could you add a way to use the fluid directly instead of using barrels? like assembly machine does

No, centrifuge doesn't have a fluid input and I don't think it should have one.
This issue is fixable but I've been really busy lately, sorry for delays.

Why do you think it shouldn't have one? You can easily implement it with this.
As far as I've seen, those are the only fluids that have to be barreled to be used.
And you have a fluid "uranium nuclear waste solution" that cannot be used directly anywhere. It's only used as an ingredient in its own barreling.

I think that adding a fluid input/output to a centrifuge is out of scope for this mod, even though it would probably make things simpler. It may also break some other unexpected things.

Can't reproduce the original issue with the two recipes that produce empty barrels: Uranium nuclear waste solution centrifuging and Plutonium-rich nuclear waste solution centrifuging

The empty barrel is not market as catalyst. Each time the productivity bar is filled, it creates a new empty barrel.

But they are marked. I've tested in 1.5.6 and checked the code.

I just backtracked what was going on on my end. It indeed was not marked as catalyst on my end, but it was not because of your mod. Sorry for that! 😅

No worries!