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. Construction of the Rapsodie facility started in 1962 and went critical on 28 January 1967. It did not have power producing systems, but its 22 MW of thermal output (MWth) would translate to perhaps 9 MW of electrical output (MWe). Experiments on core configurations were carried out in the "Masurca" facility starting in 1966, and design of a larger power-producing facility was already well underway.