If you had a time machine and unlimited resources, in what way would you unwisely interfere in the time stream? The Aztecs get AKs and smallpox vaccine? The Roman empire plus Communism? Solar panels at the dawn of the industrial revolution? Jimi Hendrix gets an iPhone? Introducing elephants to North America before people make it there? Go wild.
If we adjust things so there's fewer fossil fuels—but there's way more U-235. Imagine if instead of coal and oil, our industrial revolution was powered by cheap and easy to build nuclear reactors?
And of course, this would cause the conversation about responsible disposal of nuclear waste to look a lot different...though since coal is actually much worse for people's health per watt generated, even 'dump the nuclear waste in a random hole in the ground' would still result in a healthier populace.
Though, this assumes we'd also get much more advanced electricity transmission and battery storage to move the nuclear power, rather than everyone running unsafe tiny personal reactors. Hopefully people are smart enough to not use shitty reactors with insufficient shielding for personal home heating, cars and planes, etc.
In the time period between discovery of nuclear power and good electricity transmission and electric motors, we'd probably see nuclear steam turbine powered line shaft millworks.
I'd also expect that in this timeline, islands and remote arctic areas would use small nuclear reactors instead of giant diesel generators. For reference, small commercial reactors today can be made with a generation capacity as low as 5 MW, and Kotzebue, population 3,10, averages 2.2 MW usage and the town's electricity grid has up to 12 MW of generating capacity.
