Superphénix (French pronunciation: [sypɛʁfeniks]; English: Superphoenix, SPX) was a nuclear power station prototype on the Rhône river at Creys-Malville in France, close to the border with Switzerland.

In June 1997, the newly appointed Prime Minister, Lionel Jospin, announced that Superphénix would be closed permanently; this was made official by ministerial decree in December 1998.

At the time, the conventional solution to this problem was to use a graphite moderated air or water cooled reactor fueled with natural uranium.

The graphite is used as a moderator, slowing the neutrons released in the nuclear reactions to a speed that makes other uranium atoms receptive to them.

Ideally the coolant would be both highly efficient, allowing the core size to be reduced, as well as being largely transparent to neutrons.

Plans for a French fast reactor date as far back as 1958's Rapsodie, and followed up in 1964 for a larger design with a power output of 1 GWe.

On the other side of the argument, Andre Giraud, head of French Nuclear Commission (CEA), stated that they should carry on with the buildout, warning that delays would have "catastrophic consequences on the uranium savings that are expected.

The plant was run by the consortium NERSA, 51% owned by EDF, 33% by ENEL and 16% by SBK (Schnell Brüter Kernkraftwerksgesellschaft).

[12][13] This July 1977 protest was finally broken up by the CRS with the death of Vital Michalon and over a hundred serious injuries, with the police using truncheons and firing tear gas grenades to disperse the protestors.

[14][15] Against a background of ongoing protest and low-level sabotage, on the night of January 18, 1982 an RPG-7 rocket-propelled grenade attack was launched against the unfinished plant.

Two rockets hit and caused minor damage to the reinforced concrete outer shell, missing the reactor's empty core.

[16] On May 8, 2003, Chaïm Nissim, who in 1985 was elected to the Geneva cantonal legislature for the Swiss Green Party,[17] admitted carrying out the attack.

As time passed, problems developed from another source: the liquid sodium cooling system suffered from corrosion and leaks.

Power production did not resume until the Direction de la sûreté des installations nucléaires approved it in 1992.

[21] The plant was connected to EDF grid on 14 January 1986 and produced 4,300 GWh of electricity, worth about a billion 1995 Franc, during 10 months of operation, up until 1994.

[20] Superphénix had been a focus point of many groups opposed to nuclear power, including the green party Les Verts, since its planning and construction.

A national network called Sortir du nucléaire was formed, bringing together hundreds of organisations: local committees, ecological associations, citizen movements and parties.

In June 1997, one of the first actions of Lionel Jospin on becoming prime minister was to announce the closure of the plant because of its excessive costs.