My bet it is conventional.
Too fast construction. Building modules with nuclear equipment need time consuming and special raw materials that seems not be employed in this damn fast construction race (it is more like a race build).
A second reason could be the low chinese surface nuclear propulsion experience. Even french navy experienced some nuclear issues in construction of the sole CVN aside US Navy. So my question is, Has the PLAN any other nuclear surface vessel?. Maybe they could gain some experience from a icebreaker or even some AOR first before jumping at a high demanding CVN.
So IMHO, the most logic propulsion could be a low risk COGAG, more powerful than that of the Type 055 for feeding EMALS and sensors & comm, before going to nuclear propulsion.
Here in he west, we´re shocked with this 10 years carrier flotilla buildup. Impressive.