Uranium Tweaks is a simple mod that rebalances nuclear reactor fuel processing to be more forgiving in the early game, and less overpowered after unlocking Kovarex Enrichment.

The "uranium-processing" recipe now requires 20 pieces of uranium-ore, and has a 5% chance to result in U-235 and only 95% chance to produce U-238.
The "uranium-fuel-cell" recipe now requires 10 iron-plate, 1 U-235 and 5 U-238, and produces only a single fuel cell
The result is that uranium processing setups generally consume ore at a faster speed, produce slightly more fuel cells, and far, far less spare U-238.

The "kovarex-enrichment-process" recipe now requires 7 U-238, so it will consume your backlog of U-238 (which is already reduced...) much more quickly. It's still a very powerful recipe.