Safety concerns related to the operation of the Superphenix reactor were a key objection of the critics of the project from its very early stages. Over 5,000 tons of highly reactive sodium combined with several tons of highly toxic plutonium raised numerous safety issues. After the Chernobyl accident, which occurred only three months after connection of Superphenix to the grid, the question of the positive void coefficient inherent in the design, theoretically favoring power — excursion accidents, only increased the concerns of a number of scientist-critics. Safety concerns played a significant role in generating the opposition, including its most extreme forms.41

The first exceptional event took place at Creys-Malville before construction of the reactor was completed. A group of anti-nuclear activists succeeded in obtaining an RPG-7 (Rocket Propelled Grenade launcher) and eight warheads ("bonbons") from the German terrorist organization Rote Armee Fraktion (RAF) via the Belgian counterpart Cellules Communistes Combattantes (CCC). On 18 January 1982, five missiles were fired against the Superphenix construction site (three other pieces of ammunition had been discarded prior to the attack). There was little material damage but significant political and media attention. The authors of the attack were never caught until the confession of the key person, Chaim Nissim, 22 years later.42

The internal incident database of the French Nuclear Safety Authorities only refers to a single event during the operational period of Superphenix: a sodium leak from the main fuel storage tank. The tank was a key element of the plant since it was intended to serve as a transfer and storage tank for new and spent fuel assemblies. The leak was detected on 3 April 1987 and led to a 10-month shutdown. Worse, it became evident that it would be impossible to repair the tank. The leak was determined to be the result of a design error (wrong material). An entirely new fuel loading and unloading scheme had to be developed. It is interesting to note that the original design of the transfer tank did not have double walls. The consequences of the leak would most likely have been much more dramatic if that design had been used.

The National Assembly’s Enquiry Committee on Superphenix and the fast breeder reactor line also discussed the three previously mentioned significant events: the sodium pollution of July 1990, the turbine hall roof collapse of December 1990, and the argon gas leak in December 1994.43

At present the Superphenix reactor is undergoing various decommissioning operations. The dismantling of its reactor block is planned to begin in 2014 and continue for a period of eight years. The entire installation is to be dismantled by 2025.

After four decades of R&D, design and operation of LMFRs, with no imminent new breeder project, CEA, EDF and AREVA agreed in 2000 to preserve the breeder knowledge-base.44