An interesting journal from CAEP's warhead design branch with an innocent-looking name "A Numerical Simulation Analysis for Destruct Effect of Blast Load on Large Complex Warship Structure".
Tl;dr
the nuclear warhead designer published an essay roughly estimating how many yields it should take to destory a CVN
Conclusion: even a 1.2kt nuke could easily penetrate the flight deck if groundburst, a 500kt nuke is well enough to punch flight deck onto the flooring of hangar if exploding below 25 meters.
The journal discusses nuclear effect on a certain "large aircraft carrier" with as such specification "the overall length of the carrier is 332.9 meters, deck width about 76.8m, deck to baseline height 30.6m" which is actually Nimitz-class.
The intended nuclear weapons vary with yield from small to high.
Yield: Small x 10 = Medium, Small x 100 = High
Author: "It is worth noting that the distinction between the three yield levels is mainly for the convenience of analysis and elaboration, the nuclear yield corresponds to blast shockwaves of strategic weapons, which are all significantly larger than the equivalent levels of conventional weapons."
I did my own math, it takes around 500kt warhead exploding at 25 meters high to produce an overpressure of 0.2Mpa (30psi) for such shockwave effect which nearly punches the flight deck onto the flooring of hangar.
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The intended impact zone is at the rear end of CVN and shockwave reach every corner of warship in 0.2 seconds.
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