1) Recapture 40 of the 41 produced u-235
2) Remove the 1 extra from the loop to Fuel Cell production
3) Remove the need to hold 120 U-235 at each station allowing better early u-235 generation.
4) Be tile-able
How it works.
Requester chest is set to request a stack of u-238 (do not request u-235)
Wired Inserter is set to stack size =10 and a condition of u-238 >9 (obviously this could be 1 but w/e)
Priming is simple as dropping 40 u-235 once.
The simple version
Because of the inserter stack size being set to 10 and the wire condition there should always be 1 left over for bots to grab and dump.
Late game with lots of bot speed there may be a chance bots interfere with the loop. My fix was simply to place the roboport a bit further away. If you find that bots are a problem for you, changing the Active Provider to a Steel chest wired to a filter inserter "u-235 <10" should remove any chance.
Update 5/21 to use bots making everything simpler.