https://mods.factorio.com/mod/NuclearScienceRebalanced

Why This Rebalance?
Uranium-235 Dependency: The original nuclear science pack required uranium-235, making Kovarex enrichment almost mandatory to produce it at scale, especially with higher science cost multipliers. Switching to uranium-238 reduces this bottleneck.

Nuclear Power Progression: The uranium-235 requirement delayed nuclear power, pushing it later in the game. This rebalance allows earlier access to nuclear science, making nuclear power more viable sooner (without Kovarex enrichment).

I don't see it as rebalance, but potential issue

When making this mod recipe had 238 before but then after testing it was changed to 235.

Switching to u 238 creates situation where after setting up kovarex and after filling all buffers and chests you eventually will have only 235 and no or almost no 238 left. Which will block science production.
It is highly probable that previous mod did so for same reason

So you create new issue, trying to solve inconsistency made by the fact that to make reasonable ammount of science you need kovarex.

It would probably be better to lock whole science behind kovarex instead

moved science pack to kovarex because it's needed anyway