I don't know about France but in the U.S. nuclear plants are required to put money aside for decommissioning. They were also required to pay into a fund for long-term waste storage, but since the government shut down its long-term waste facility and companies have to store waste on site, a court decided they shouldn't also have to pay into a fund that's not doing anything.

Regarding Chernobyl, I'll just mention it was used both for power and weapons production, and lacked basic safety features including a containment dome.