You just got to be able to make neutron stars collide - or the right kind of supernovae . That'd help you create uranium from hydrogen (with some extra steps).

Or you could skip that and go for fusion.

Eventually, of course, the universe will run down. somewhere between 10^13 to 10^23 years .. you don't want to wait until 10^67 or beyond...

At which point you got to learn how to create a new universe.

In other words, it is just that you don't have the tech to make nuclear renewable right now .