It is not not a known fact, it is in fact not true. France has over 1 million m3 of waste, and I assure you they have not been operating nuclear plants for over a million years. :)

Sources:

https://www.ompe.org/en/france-doesnt-know-what-to-do-with-i...

The La Manche facility had 527 000m3 of waste in 1994:

https://www.neimagazine.com/features/featuredisposal-of-shor...