Withstanding extreme thermal energy and pressure across a wide area isn't comparable to a focused punch in one spot. It would be better to base it on the fact that .50 cal rounds can't dent it. Also, in The Flood Wraith mortars boiled Wraiths apart and left only the slagged skeletal remains of the tank. At least for the nuke, he was 800 meters away from the epicenter, away from the 20 psi overpressure shockwaves by 300 meters and and well far away from the fireball. He would have only felt the thermal and ionizing radiation, not the main brunt of the explosion. https://www.atomicarchive.com/science/effects/energy.html That makes up 50% of a nuclear bomb's energy, or 6 kilotons but also using inverse square law, well 4,068,344 m^2/2.52 m^2 = 15,549,835.5 joules