Let's imagine an Earth clone devoid of naturally occurring fissile materials—and, for comprehensiveness' sake, also devoid of fertile materials like thorium and americium that could be used to produce fissile isotopes artificially.
I suppose the first part of the question is: Could we have gotten to the 1930s or so without significant deviations? I.e., is there any under-appreciated but crucial role that these elements played in the formation of the earth, the biosphere, human civilization, etc.?
And second: what then? Obviously the end of WWII and basically all of world history thereafter would be radically altered. But geopolitics aside, what impact would this have on science and technology? Could it be as simple as, nuclear weapons and nuclear power would be impossible, while the rest of human technological progress would proceed unimpeded? Computing, telecommunications, spaceflight (minus the plutonium-based RTGs)? Even particle physics? How might this "gap" function in the context of our broader knowledge of radioactivity, stellar fusion, etc.? Would scientists have a well-developed theoretical understanding of what fissile elements are and what powerful/destructive properties they have?
Open-ended bonus question just for fun: assuming the above is roughly possible, what might happen if the plucky, naïve denizens of Earth-2 one day landed on Mars-2 and found a big ol' mess of uranium and plutonium there?