The Orphee reactor is a small research reactor of a power of 14MW that operates around 40°C. In case of incident, the reactor is automatically stopped. 4 control rods fall down by gravity within less than 2 seconds inside the core. This stops the nuclear reaction.

The residual heat remaining can be evacuated only by natural convection within the water of the pool that surrounds the core of the reactor. Thus, even in case of loss of all external power supply or water supply, the reactor is controlled and maintained at a low temperature.