Rapsodie is an originally 24 MWt system cooled by up-flowing sodium which has been uprated to 40 MWt in 1970. It is fueled with mixed pluto­nium-uranium oxide, stainless steel clad, and wire wrapped in 37-pin hexa­gons. The power rating is 340 W/cm3. Figure 4.31 gives the reactor cross section.

The vessel is hung for bottom entry, the loops are nonelevated but are all doubly contained. The two loops join before vessel entry and come in as a single saxophone pipe. Figure 4.31 shows a cross section of the reactor vessel and its nitrogen filled guard vessel. All the circuits have up to 4% natural circulation capability, and they are provided with EM pumps with double check valves.

Six control rods are driven in, and a digital computer is used for trip analysis since there are: 15 scrams on high flux, one each on у activity in vaults, power-to-flow ratio, thermocouples at the reactor outlets, seismic disturbance, and manual trips. In addition there are 84 trips derived from each thermocouple of each subassembly outlet.

Failed fuel detection instrumentation takes the form of delayed neutron detectors in the primary sodium circuit and within the argon cover gas system.

The fuel handling equipment was a very complex machine handling more assemblies than one at one time. This was eventually changed for a simpler device, another instance in which simplicity improved reliability and safety. Emergency cooling is provided inside the double containment.