I second this and dug around to add it. Note that I have no coding experience whatsoever and while it seems to work for me, I give no guarantee that this doesn't brick your computer or something. Though that'd amaze me.
Find your mod folder, unpack the smr_030.zip
Open data.lua (I used notepad++ but frankly the text editor works), find line 113. It should be the only line under "results" for the recharge recipe and contain this:
{ type = 'item', name = name, amount = 1 },
Mind that the crafting recipe above it is for making the actual SMR in the first place, it contains the same line so make sure you get the correct recipe. Again, you want line 113.
Add a new line under it and add this in it:
{ type = 'item', name = 'used-up-uranium-fuel-cell' , amount = recharge },
Save the file, repack the folder as a .zip, done.
You should now get the same amount of used fuel cells you spend new ones throwing in there. Not ideal I suppose but it's something.
Any mod update probably wipes this change so you can make a local copy with a similar name if you want to keep it. Or just add it again.
