It is a claim. I also agree that F18 can fly from STOBAR. But the payload is suspect. If the payload is too low or if F18 needs to be refueled mid air after take off, then also it is problematic. F18 hasn't demonstrated its ability to take off with 5 ton payload and full tank as if now. So, it is simply not proven.
Lets be clear. UK has no indigenous carrier worthy plane and it wanted to go with F35 from the beginning. Hence it didn't get CATAPULT. There was never a problem with CATAPULT on diesel. UK carrier doesn't even have arrestor wires as it was always designed for F35 which is STOVL.
As I said, catapult needs steam and that is from the heat of boiler. Electric power need is not much. You can check examples of USS independence launched in 1959 that had steam catapult.
Today, you can see type 002 of China that even has EMALS in conventional power.
Despite all these evidence, why insist that nuclear power is a must for catapult? If 1950s technology can have catapult with boiler propulsion, why can't 2020 Technology use it?
India is not going for nuclear submarine by discarding diesel ones. Look at UK or France and tell me whether they have any Diesel submarine at all? But India is not going their path and even encouraging more diesel submarine design.
Nuclear submarine is also being developed at the same time because of advantage like long duration of submergence. But in aircraft carrier, these don't stay hidden and hence are easy target. They have higher risk of getting hit and the long endurance of these carrier is irrelevant for short distance from Indian shores to IOR. Submarine, on the other hand has to stay hidden waiting yo ambush. This difference of role is what makes nuclear submarine useful at times. But nuclear carrier is more a liability with no advantage.
Cost of fueling etc are all low as the reactors are fueled once in 20 years. But the real problem is in repair duration and lack of real advantage.
INS Vishal will be diesel powered as it is mainly for IOR. It will be having CATAPULT, however. It will be able yo carry any plane including F18 & Rafale. But by then NMWF would be ready. It appears that MWF will be able to fly even in STOBAR of Vikrant. With such versatile MWF capable of being flown from all types of carrier, there will be no need to get any other plane. If NAMCA can be developed (it is difficult to have stealth Naval plane with arrestor landing), then even that can be used on it.
Overall, Vishal will be Catapult but even then it will select only Indian planes