To begin: I am playing Vanilla 1.89+IC2+JEI, survival. My goal is to suggest the Reactor Pressure Vessel block be made out of less lead. I would even be fine if it was made out of reinforced stone instead of lead, or mixing gold in with the lead. Gold might be less minecraft-rare and more nuclear-ly effective than lead, now that I think about it.
I decided to try to build a fluid reactor... and I can't even get a floor done.
A hollow 5x5 cube is 98 blocks. Each block takes 5 lead.
The cost of a containment wall alone with no ports is 490 lead.
The cost of adding the nuclear reactor, 1 access hatch, 1 fluid port and 1 redstone port is a total of 667 lead.
1 Lead ore = 2 lead. Assume for the moment that washing uranium provides 7 lead at the point you might want to make a fluid reactor.
330 ore needs to be mined.
I'm using an OV miner at level 50. I've mined 37 times and gotten enough lead for 21 RCP blocks, so 105 lead -> about 45 blocks after uranium purifiaction. Perhaps 2 per 9x9 mining column, on a good day.
This means I have 285 lead remaining to make a basic reactor.
This means I need to mine over 200 times to get the remaining lead ore.
If each mining operation takes 5 minutes, I need to play over 16 hours of only mining to get enough lead to make my fluid reactor, and I will have covered something like 60 world chunks, just to mine. I will likely start recycling otherwise "valuable" ore to fuel Lead Ore uu-creation, because it will be that valuable after hour 5 or so.
One lead ore block takes about 10.7 mB of uu-matter, so I will only need the power-equivalent of 3B of uu-matter to make the lead I need. I'm expecting to only spend 1.2B or so, reducing my mining to only 10 hours, roughly.