I'll be speaking from M20, because that's the one that I have the most recent experience with. I also acknowledge that I might be getting some of this a bit wrong, but I'm pretty sure that it's at least close.
There's... not a lot.
Mages aren't amazing at force-against-force, and "point blank of a nuclear explosion" is about as close to an irresistable force as you get. They're good at cheating. There's a bunch of ways to decide that you don't want to be here after all, or that you want to stop existing briefly and come back, but the constraints you've put in place even go so far as to prevent even things like Time-triggered self-resurrection rotes.
Your only real remaining options are going to be toughening yourself to the point that the blast can't kill you, making yourself temporarily into something that doesn't interact with explosions, and using Forces to tell the blast to pass you by. Let's start with the last.
If you want to try to redirect the bit of the blast that's coming for you personally, you're going to need 4 Forces bare minimum, just to be able to play. You'll probably want 5. Correspondence 5 would help, for the bit where you're warping the shape of reality. Matter 5 (and possibly prime 2) would be really handy if you're willing to create/modify a wall to hide behind... in order to allow that wall to be made of some sort of mystical material that can actually block some of the blast without being annihilated. So... Forces 4 if you want to try to part the blast with raw will, and thus use the rote as a contested action, multiple times in quick succession, against a much higher dice pool, while your storyteller laughs. Forces 5, Correspondence 5, Matter 5, Prime 2 if you want to arrange for a physical shield of some magical material that might give you an actual decent chance of survival if you hunker behind it.
If you want to turn yourself into something that can survive the blast, that's Matter 5 (for Alter Properties) and Life 5 (for Perfect Metamorphosis). In essence, you come up with a magical material that can ignore nuclear blasts, and then turn yourself into a living statue composed of such material. This one is actually pretty straightforward, as the hard part isn't a contested roll against the bomb's absurd-tier dice pool, but it's super-paradoxical. If you want this effect to persist, that paradox is going to be permanent paradox, and you're also going to want to have Time 5, so that you can stretch those 10 minutes out into enough time to perform a major ritual. You could also do crazier versions of this one, like temporarily transforming yourself into a spirit of nuclear fire (using Spirit and Forces, rather than Matter) but you're going to need Life 5 anyway, and the other component probably isn't going to be easier than Matter 5.
It all starts making a lot more sense mechanically when you start thinking of a nuclear bomb as a Technocracy Forces/Prime/??? effect that involved multiple powerful mages with a lot of infrastructure behind them doing dangerous ritual work for an extended period of time at a notable cost in resources.
