The problem is that western nuclear tech isn't very vertically integrated.

If you buy a Russian nuclear power plant, Rosatom takes care of absolutely everything.

If you buy a powerplant from anywhere else, you've got to juggle hundreds of various contractors and companies at various stages.

So if you've built your system, there will be only very few fuel suppliers left, whose fuel product is approved for usage with all the components.

And if one of those suppliers has problems or goes bankrupt (since nuclear fuel is an aweful product to make money with: Very low numbers, extremely strict regulations, very expensive handling and processing, a very unstable and slow growing market, constantly new requirements and all of your customers have huge legal teams and deep pockets), you're going to have a lot of difficulty finding a replacement.