[marmarama]

> How did the UK and France solve it?

Remove the fuel elements, reprocess what's useful, and store the reprocessed materials and nuclear waste somewhere "temporarily" that isn't really suitable for long-term storage.

Remove intermediate and low level waste from site and also store it "temporarily".

Remove any non-contaminated plant and sell for scrap.

Punt the main part of the problem (scrapping the main reactors and reactor buildings) down the road for a hundred years or so until radiation levels are acceptable for demolition to proceed.

Re-use other parts of the site for projects that can use the existing HV connection, like another reactor, or battery storage.

That's essentially all you can do unless you want to risk a radiological accident.