This is a misunderstanding of radioactive material. The atoms already exist & they are already spread all throughout the world. Building a reactor allows us to harness the energy of atoms decaying in a useful way.
As for the end product France is able to recycle up to 96% of spent fuel. The remaining 4% is being prepped & placed back in the ground at a site they are currently building. If you want to read more this Stanford student wrote a well cited paper.
http://large.stanford.edu/courses/2024/ph241/friedman2/ Or you can read this this science insite article. https://scienceinsights.org/what-does-france-do-with-nuclear-waste/