Weird, I thought that Wikipedia page used to cite the costs of retrofitting Diablo Canyon's cooling to move away from once through water, but I don't see it there anymore. The history of that page shows scars of manipulating the narrative, but I stil didn't find it. Here's a PDF from PG&E that puts the cost at $2.6B:

https://www.waterboards.ca.gov/water_issues/programs/ocean/c...

These days you can buy a lot of solar, wind, and storage for $2.6B, so I'm not sure that closing the reactor is merely "not liking" nuclear. At this point we get more carbon free energy from solar and storage for the same amount of money, so if one is concerned about carbon it makes more sense to chug it down and build newer cheaper infrastructure.