There are a lot of unknown factors with regards to 003. Like what is the total power consumption. In the case of the Ford-class it has two 700 MWt reactors while the previous Nimitz class had two 550 MWt reactors. Which makes it seem that EMALS and other electric systems have actually increased the power requirements versus steam. After all electric systems might be more compact, lower maintenance, have performance which leads to less aircraft airframe stress on launch, but they led to more power generation losses because you are converting heat into electricity instead of using the steam directly. Because it was unknown, when 003 was designed, which catapult system would be available, and there is no known Chinese naval nuclear reactor with the required power, it is quite likely they simply decided to go with boilers. I think it is unlikely they went for gas turbine technology because steam allows them to gain experience with the future nuclear reactor, which will also output steam, and in case EMALS turns out not to work in practice having steam boilers allows the PLAN to backpedal into the steam catapults just in case. Also the Chinese have limited experience with high enough powered naval gas turbines. The Ford class EMALS so far has not proven to work all that well. It simply does not have enough reliability and the medium time between failures is too low. While the Chinese might not have these problems with their EMALS because they did more ground testing with actual aircraft, they might run into similar issues. I suspect the EMALS on the Ford class will have to be completely replaced in a decade or less for an improved system and only then will it have the required performance, if it is possible to refit it at all without a new ship.
Using submarine naval reactors is implausible because of the displacement of the 003 which is much larger than, say, the Charles de Gaulle. Purchasing the technology abroad is also implausible because the closest reactor to the requirements is the Russian RITM-400 reactor which is supposed to have 315 MWt but it is still not in production. The smaller RITM-200 with half the power has only recently started naval propulsion tests on the Arktika Project 22220 icebreaker. While the Chinese nuclear industry should have know-how to make their own reactor they have limited experience with such large naval reactors and such a project in itself might take like 8 years to achieve if you compare it with other nuclear reactor programs. Contrary to what others said here though I do not think the nuclear icebreaker is a pre-requisite. The Chinese nuclear industry has enough expertise to directly design the required reactor and test it and its components in ground test stands I think. It would still be useful to do subscale testing on another platform but it doesn't need to be an icebreaker. They could simply use a modified hull of some other ship they can build quickly like the Type 071 hull if they do need to perform actual ship testing I think. Anyway I see little reason to think the Chinese have deviated from the supposed plan where they build two conventional powered EMALS carriers first and only afterwards build two nuclear powered EMALS carriers.
