[AngusH]

Uranium is a mineral and can be purchased from many places and stored then used as needed.

15 countries mining it currently: https://en.wikipedia.org/wiki/List_of_countries_by_uranium_p...

There are also more countries with estimated reserves: https://en.wikipedia.org/wiki/List_of_countries_by_uranium_r...

While an undersea cable requires continuous operation and the agreement from a single country where it starts. If they suddenly decide for whatever reason to turn it off (say they're short of electricity) then the supply is immediately stopped.

[caf]

Equally relevant only 13 countries are fabricating nuclear fuel rods.

https://world-nuclear.org/information-library/nuclear-fuel-c...

[preisschild]

You could use a CANDU PHWR (Pressurized Heavy Water Reactor) if supply chain safety is that important to you, but don't want an enrichment industry. CANDU reactors can use natural Uranium.

[belorn]

Sweden do have uranium in the ground and could be mining it, but they created a law forbidding it.