Australia

Modern Diesel-Fuel Cell subs like the German/Italian Class 212 have a (minimum) range of 8000nm, can stay submerged for 30 days and are far quieter, which becomes especially relevant in areas with low depth, as you cannot hide in favourable temperature layers that easy there. There is also an option for a "longe version" available which seems to be able to stay submerged even longer and there is always the updated Dolphin class Israel uses as well as the Drakar class or Singapores 218SG. They have been specifically designed to operate in conditions that are very similar to the ones in the yellow sea (that's why SK bought them). There are also alternatives from Sweden(Gotland&Blekinhe class), the updated Soryu from Japan (which is specifically built for a mission profile similar to the Australian one), Spain, South Korea (they even have a nice mixture of hunter-ballistic sub available)etc.

There is a reason that every nation that has a mission profile in the South Chinese sea, the straight or Malacca and the yellow sea has decided to use a non nuclear sub - even nuclear friendly Japan doesn't.

The only good reason beyond Cronyism and bribes for Australia to use nuclear US subs is that OZ might want to use them in support of future US conflicts e.g. in the Gulf of Oman, off the Pakistani shores, etc.

The South China Sea is shallow, a poor operating environment for nuclear subs.

Containment of China to the South China Sea is a US strategy and one which Australia is subsiding, while materially hurting its ability to defend Australia’s coastline.