France began construction of the Phénix demonstration plant in November 1968, only a year after Rapsodie went critical. It was fueled with 931 kg of highly enriched plutonium, around 77% Pu-239. The fuel load is capable of running for about 90 days maximum, but in practice it normally ran for two month periods. Due to its design, refueling required the reactor to be shut down. As a result, it had a low capacity factor (CF), on the order of 65%. As a prototype plant, a high CF was not a design goal, although any practical design would have to improve this. Phénix demonstrated a breeding ratio of 1.16, meaning it produced 16% more fuel than it consumed, while also producing 233 MWe in normal operation.