Do you have a source to support that statement?
It's not entire clear to me that is the case. Nuclear reactors are huge. At the same time, diesel is more energy dense than what people normally think.
It is a fairly well known characteristic between nuclear and conventional carriers.
Nuclear reactors are certainly significant, but conventional carriers have to carry fuel that they themselves must consume which takes up much more volume.
This is a decent study on it, which admittedly compares the CV-67 and CVN-68 which are different in displacement (by 10%) but with very similar volumes to such a degree that the CVN-68 carries almost twice as much aviation fuel as the CV-67.
Page 23:
A good summary of the comparisons regarding conventional and nuclear carriers are basically as follows:
"
Even though the nuclear carriers are newer and larger than the conventional carriers, the two ship types have several common characteristics and capabilities.
They are similar in that they
• are subject to the same operational guidance;
• carry the same number and types of aircraft in their air wing and can generate the same number of sorties;
• have top speeds in excess of 30 knots;
• do not differ with respect to their survivability; and
• can produce adequate supplies of fresh water.
However, there are some differences.
For example, nuclear carriers
• have larger storage areas for aviation fuel and ordnance and
• are better able to recover landing aircraft due to their superior acceleration.
The similarities in these key features have allowed the Navy to employ both types of carriers interchangeably for routine deployments overseas and employment in contingency operations."
Additionally, this is also a good summary of the advantages that nuclear propulsion offer in terms of endurance:
"
By eliminating the requirement for ship propulsion fuel, requirements for replenishment of aviation fuel and ordnance will become the controlling factors, varying directly with the level of aircraft activity and/or combat operations"
... relevant to the PLAN, is that the actual effective endurance in terms of a notional CVN's capability, would be dependent on how much flight sorties and employed combat missions they actually carry out during the time period.
One particular mission set where the PLAN would benefit from CVNs, is if they need a CVN CSG to carry out patrols/presence missions in a certain theater/distance but only need to carry out high intensity sorties and combat missions if combat is joined.
In that case, your lack of need of refuelling the CVN is a major, major advantage which you won't have on a conventional CV because simply by patrolling you'll be needing to count down when your next rendezvous with a refuelling tanker will be.
OTOH, for the above mission set, during the "patrol phase" CVN will only be limited by food, crew endurance, and aviation fuel (which during the patrol phase will be consumed much slower than during the "high intensity conflict phase").
====
Also, I'm going to move this discussion to the 00X carrier thread. Please continue it there.