Oxidizers won't help a nuclear explosion get "bigger" under any circumstances. Because a nuclear explosion is not a chemical explosion like TNT or dynamite. What happens is the atoms inside the nuke split apart in the case of a fission bomb, or fuse together in the case of a fusion bomb. Only certain atoms (uranium, hydrogen, plutonium, deuterium, etc.) are useful for weapon purposes. So an oxidizer wouldn't add anything useful to a nuclear explosion unless it also consisted of similar atoms, but then the explosion would be called a pumped up nuclear explosion rather than nuclear explosion with an oxider.
In real life, nuclear weapons like fusion bombs are "enhanced" by surrounding the core with extra uranium. In the stargate universe, it seems that they use Naquadah
As for nuclear weapons in space, as another poster mentioned, any explosion in space isn't very powerful because there is no atmosphere to carry the blast wave. You need some kind of fluid material to carry the wave. Without one, the bulk of the damage comes from the flying shrapnel from the bomb itself.
In real life, a pure chemical explosive will certainly rip you in two at close range but at further range you'll only suffer hearing loss. So military designers pack their explosives in thick metal casings so then the pieces of metal will rip through their targets like bullets.
Nuclear weapons are a little more devasting because they are so powerful that the blast wave alone going through air is enough to cause massive devastation.
In space, without that air, things are a little different. The nuke must be at close range when it goes off to damage its target, but how it does it is not from shrapnel, but from radiation. When the nuclear weapon goes off, it releases a massive burst of radiation that instantly vaporizes any nearby objects. Like getting too close to the sun, you need to be close to the nuclear explosion for this to happen. But when it does happen that vaporized section of the hull is essentially a bubble of superheated gas that explodes outward. This explosion is right on the hull and damages the ship like a normal explosive shockwave. So your nuclear device need not actually TOUCH your target, it just needs to get close enough to vapourize the hull.
In real life, during the hiroshima incident, a sad thing that happened was that people wearing dark clothing died more often than people wearing white clothing. what happened? The sudden burst of radiation, including light, was like a million suns going off. People wearing dark clothing absorbed more of the light and where instantly set ablaze. They then spend the next few agonizing seconds of their lives on fire. People wearing white clothing were still burned, and still had to contend with radiation poisioning and the oncoming blast wave, but suffered less burn damage than those with dark clothing. Their chances of survival (although still slim) were better.
So how do we augment a nuke? a bigger bomb would be nice, then you can either A) have your device further away and do the same damage, or B) get closer and do more damage.
Alternatively the effect may be better if somehow the radiation can be directed toward the target like a beam, greatly extending our range. But that kind of technology is something we do not yet possess, although the Asgard and the ancients probably do.
If we could also tune the radiation energy to be of the right frequency to cause the most damage that would also help.
However doing all of that, its not a nuke anymore, its a beam weapon
