Is a mining machine that goes on forever not effectively renewable?
*Chuckles* You have no idea of the train of throught triggered by that comment. That I don't consider those equal is part of how I approach games like this, namely, as a simulation of a fictional world rather than just a game. Call it a playstyle preference. Please note, yet again, that I am not complaining and approve the design choice. This is strictly my perspective.
(1) There is a difference between infinite resources and renewable resources. Everything you take out of the world permanently and which can't be replaced is by definition not renewable. It may not make a difference for gameplay, but I always consider the MC world as a fictional world, and I am reluctant to exploit a trait like infinite resources if it's a gameplay convenience rather than a design decision rooted in the lore of a fictional world.
(2) There is the matter of realism to consider, especially in mods like yours which are designed to be realistic. I feel it is against the spirit of how to use ReactorCraft if I use mechanics that exist as gameplay conveniences to get around problems that almost define the technology in the real world, namely, scarcity of fuel and waste disposal.
(3) If you think through (1) a little deeper, you'll realize that everything we call renewable comes down to some resource being effectively unlimited (like sunlight on Earth, or hydrogen in the solar system), and considering thermodynamics you might say nothing is truly renewable and we're all deceiving ourselves. Still, nuclear fission is a real-world technology, if you didn't want real-world problems like scarcity of fuel to be associated with it, why make the mod that way in the first place, rather than, say, calling your resource "yellorium"? If I'm using scarcity of resources to drive some of my decisions, then I feel I'm acting like I'm supposed to when using ReactorCraft.
(4) For some reason, I am unable to take off my (moderate) enviromentalist's hat when I play Minecraft. When I enter a pristine new world, I inevitably feel that it would be a sacrilege to destroy parts of it just for convenience. I hate nothing more than to create large holes in the world, I do not like to leave poisonous stuff behind and my constructions aim to integrate themselves naturally into the landscape where that's possible. Yes, we have mining ages, but it doesn't matter. Every time I see those large holes created by mining machines in dimensions with any life at all, I think "I don't want this", even in the Nether because it makes things look ugly. The only place where I don't care is the Deep Dark, but unfortunately, pitchblende does not spawn there.