It is apparently cheaper because in France, as in many countries, the nuke was and remains heavily subsided, decommission costs under evaluated ( take a look at https://news.ycombinator.com/item?id=18686703 ), mishaps hidden...

The French public financial auditing institution (la Cour des Comptes) published in 2012 that public nuke investments are opaque, and that it costed around 228 10e9 euros, plus nowadays 3.4 10e9 euros per year for the sole maintenance. Nuke risk is what it is, and even financially it is not sound. Read there, starting folio 269: https://www.ccomptes.fr/sites/default/files/EzPublish/Rappor...

It is so expensive it cannot be hidden anymore. Electricity in France is absolutely not cheap, its price there is average in Europe. Source: https://ec.europa.eu/eurostat/statistics-explained/index.php...

Germany now pays in order to solve the problem.

France isn't completely dumb and a state law (2015-992, from 2015, the "loi relative à la transition énergétique pour la croissance verte") states that the part of nuke-produced electricity must fall to less than 50% in 2025, from 72% then, and that renewables must replace it. However those are only words, until now.

Meanwhile... Germany solves its problem by switching to more adequate energy sources.