I've been playing with this mod for a while (in a legit game, to get an appreciation of the balance). I was about to come in and make a few suggestions, but I've just read the commits on the github repo, so I'm going to list those changes to put my comments in appropriate context.
From what I can tell from looking at the code (I'm not really a programmer)
-> base reactor speed has been slightly nerfed to 0.02 (from 0.025)
-> pellets themselves are now much cheaper to 5 units of UF6 gas each (from 25)
-> fuel assemblies now require 50 pellets (from 35)
-> uraninite and fluorite deposits are richer
-> researching nuclear tech nolonger requires Science Pack 3s
Overall, assemblies cost ~29% as much uranium as they used to. The downside, however, is that the time and electricity cost has gone up. So if you were short on uraninite/fluorite before, this should help a lot. Personally, I've always had a large excess of ores and a lack of enrichment throughput, which has now been worsened. That's compounded by the need for more reactors, too.
My problems with the balance so far is that my reactor produced very modest amounts of power. According to some tests I did ingame with accumulators, I'm getting about ~9MJ per reactor cycle, depending on tanks and generator layout. With 3.5% fuel assemblies, each cycle takes 28.6 seconds yielding an output of 315kW. With the new reactor speed nerf it will now take 35.7 seconds, for 252kW. For comparison, a solar panel is far cheaper and produces 60kW during the day. I'd wager it's capacity factor is around 0.7 given that days in factorio are longer than nights. It's about as effective as 6-8 solars.
I understand that since fuel assemblies last forever, reactors have to be expensive to prevent being overpowered and that the payoff will take a while. But given how much power I poured into chemical reactors for enrichment (>3MW for quite a while), it would take ages to get a return on that investment. Even with the reduced uranium costs, they're just not worth it compared to solars.
EDIT: I forgot to even include the running cost of the reactor, 210kW. Accounting for that it's even more dismal. I have a feeling that I'm missing something in my setup and that 9MJ is far less than I should be getting, but I'm not just how.
Chemical plants feeding back into themselves can be a little bit tricky. A single chain of plants going from 0.7% to 3.5% will eventually clog itself. This happens when plants lower in the chain become full in their input slots (and associated piping), then the plants higher up the chain can't output their lower-enriched product back down, and clog up their output slot. Essentially both upper and lower plants are waiting for each other to operate, which will not happen unless additional fluid capacity is added to the clogged lines. The way to avoid this is, of course, to use multiple plants until you have so much more throughput than could possibly be saturated by the fluorinator. More plants are needed for the lower concentrations than the higher concentrations, so my enrichment facility is somewhat pyramid shaped.
For example, for each plant combining yellowcake and fluorine, I have 4 plants making 1.1%, 3 plants making 1.5%, 3 plants making 1.9%, and 2 plants making 2.1%, and 2 plants making Depleted. The rest are all singles. My throughput bottleneck appears to be the 1.5% plants, but at least three is sufficient to prevent blocking.
The uranite slurry recipe is a little irritating, given that the operation takes far less time than an Inserter can feed 5 uranite ore. That little inserter was the bottleneck for my whole enrichment facility until I noticed it and replaced it with a Fast Inserter, which is still a bit too slow. A longer recipe time would help make it more obvious that multiple assemblers are needed to create slurry in order to keep pace with the fluorine.