1, I'm interested.
2, Okay, so you're not counting the 80% first draft as a first draft at all. How complete is the new draft? Regardless of how complete it is or even what draft you're counting it as, write it out anyway. Make completion the first priority, because the entire point of a first draft (or a second first draft, or a third....) is to suck donkey nuts while you hash out what it is your story is saying. After you've gotten what the story says, you can chisel out how it's said. Sometimes it's difficult to think of a problem if it's still in your head, and writing it out is the of the plot and its mechanics. Put anything you're not sure of in [brackets] with some text like FIGURE THIS OUT LATER (for goofy bonus points, if you're typing out the draft and can Ctrl+F the text, put [MOOOOOOOO] or something ridiculous in there so you can find it easier.).
3, Put the story in perspective a bit. Is this for a general audience that likes science fiction, or is this aimed at actual experts on gamma radiation and dystopian settings? Because the average reader is A) not an expert on these things enough to call you out: as you've said, they can't prove it wrong, and in general B) they're coming in with a basic suspension of disbelief because the setting is not real life, only imitating it in certain parts. The reader expects at a basic level, compelling characters and a good plot, and that the setting has internal consistency with itself. If teleporters and fast methods of travel haven't been invented, characters shouldn't cross entire continents within a day even under harsh weather because that's "basically teleporting". Something like that.
The average Star Wars fan didn't (and still doesn't) care enough to pull out their nasally nerd voice about how "actually, parsecs are a unit of distance and not time, so there's no way that the Millenium Falcon could clear the Kessel Run in "12 parsecs" because it's like saying it cleared a mile in two feet", but they were still invested in Obi Wan successfully recruiting Han and how well the Millenium Falcon could fly in the interests of getting Luke from point A to point B. Adding midichlorians in the prequels to justify Anakin's power in the Force made the worldbuilding worse. So just don't say anything blatantly stupid like " " and you're good. Don't overexplain worldbuilding that doesn't matter to the immediate settings and the characters, and you're good.
Or you know, figure out what exactly it is you're prioritizing. Is the science a pivotal character in its own right in the plot, more than the people with the names and going the places and doing the things? Some things need to be in the background where they belong. and even then, they bent the rules a bit to land jokes because "one of the first rules that Matt Groening and [David Cohen] agreed upon for writing Futurama was, “Science shall not outweigh comedy.”". Is, and should, the science outweigh the drama of the story? If it's the science, how willing are you to get into contact with physicists in real time and pick their brain?
I'm feeling a bit sick (once again) but I just came by to say thanks. I've read this like 4 or 5 times to let it sink in. Being a coward in terms of writing facts is a major problem for me. Let's be honest: I'd love to write historical fiction, but I'm terribly afraid of historical inaccuracies – and even historical accuracies that sound like an inaccuracy, such as nipple piercing in Medieval Era (Yeah, it was a thing faaaaar before 1960s).
Rubber duck debugging is great. I use Silent Husband Debugging instead of that. I just explain my problem to him, he doesn't get the chance to say a word, and I'm like "Oh NOW I know how to do it!" and rush to the keyboard shouting "Thanks love" over my shoulder It works like a charm!