Cooling water considerations for nuclear and the relative cost is not going to decide if nuclear is any more viable than coal fired power.
The costs of the containment, safety, and heat exchange systems for nuclear are going to be different to a PF coal boiler. Also the costs of the fuel and safe management of nuclear fuel differ from traditional coal or oil or gas fuels.
All these costs are greater for nuclear compared with coal or other fossil fuels used in a traditional steam turbine power plant. I’ll boldly suggest it is this short term economic reasoning, and no other that has genuinely prevented Australia from ever going down the path of nuclear power generation. Apologies to any one opposed to nuclear power for many many other critical reasons.
Sea water cooling is not that great an added expense compared with fresh water used in an open loop cooling solution. As already noted the main consideration is how much hotter the water returned to a river, or lake or ocean is after being used for cooling and the significant volume of this hot water.
Other than places like Sydney Harbour etc, which is salt any way Australia has few mighty fresh water rivers and lakes to heat up to bath temperature. Power stations such as those at Gladstone in Qld, and those on Lake Macquarie in NSW or Pyrmont in Sydney all used open loop cooling returning the waste power station heat to the sea or lake. All salt or saline water. Newer power stations such as Bayswater NSW or Tarong Qld in more inland areas rely on closed loop cooling and evaporative cooling using fresh water to loose the waste heat to the atmosphere. They have large cooling towers that blow clouds of water vapour skywood and draw large volumes of fresh water from the nearby environment.
A polite caution, noting I’ve avoided filling the space with selectively chosen data or sources. There are many sources all of which can be reliable, however these need a degree of detail to support the basis and relevance. The differences are irrelevant if you are to argue which outcome is best. Eg one teaspoon full of mercury with dinner each night is better than two spoons full. None is best!
Over time neither the continued reliance on fossil fuels or alternate use of the nuclear alternative can be good.