... it was shut down in 1998, relevant section from German Wikipedia as the English version is lacking details:

In June 1997, Prime Minister Lionel Jospin announced the closure of the power plant as one of his first official acts. He justified this step by pointing to the enormous costs the plant incurred. In the preceding ten years, it had produced no electricity for most of the time due to malfunctions. It even consumed considerable amounts of electricity to keep the sodium in the cooling system above its melting temperature. Each pipe carrying sodium and every tank was equipped with heaters and thermal insulation for this purpose.

... so it used a lot of energy while being shut down because of malfunctions for most of those 10 years. Seems like shutting it down was the best course of action.

It had problems but it was new technology. That’s always the case. Now only China, Russia and India have Fast Breeder Reactors.

Plus there was the pressure from Les Verts and Sortir du nucléaire, the Molotov cocktail attacks by the Fédération Anarchiste, the RPG attack by the Cellules Communistes Combattantes etc.

It was a highly political decision.