The DFR is a 60 MWt system cooled with down-flowing NaK. When built, the system used the present state-of-the-art which led to the use of small electromagnetic pumps and 6-in. diameter main loops. There are thus 24 loops of all welded construction doubly contained throughout. There are no valves or seals, and even the control rod drive is transmitted through the vessel by an electromagnetic clutch. The fuel element had a

TABLE 4.7 Reactor Characteristics and Safety Features Reactor Power (MWt) Fuel loading (kgm) Fuel Heat transport and auxiliary cooling (ACS) DBA Containment EBR-II 62.5 363 U Pool 440 MW-sec (1) Reinforced concrete (2) Steel Enrico Fermi 300.0 2000 u 3 loop 1900 MW-sec (1) Steel SEFOR 20.0 1920 Pu-UO, 1 loop, ACS 20 MW-sec (1) Reinforced concrete (2) Steel FFTF 400-0 3000 Pu-UOj 3 loop — — FARET 50.0 260 Pu-U 1 loop, ACS 60 MW-sec (1) Reinforced concrete PFR 600.0 6000 Pu-UOa Pool, cooler Limited melt-down (1) Primary tank (2) Containment building SNR 730.0 5000 Pu-UOa 3 loop, ACS? 2400 MW-sec (total) (1) Reinforced concrete and dome (2) Steel shell Rapsodie 20.0 300 Pu-UOj 2 loop (1) Disruption (2) Sodium fire (1) Concrete blast shield (2) Steel shell Phenix 560.0 3500 Pu-UOj Pool, cooler (1) Disruption (2) Sodium fire (1) Concrete blast shield (2) Steel shell

safety design with a niobium outer cladding and a vanadium inner cladding that was designed to fail first, in the event of any overheating, to allow any fuel debris to run down the center of the annular element. The fuel pins are restrained from bowing. All the control rods are worth less than $ 1; they are moving fuel assemblies inserted from beneath.

There is a thermal siphon capability for decay heat removal upon shut­down. The containment sphere is designed for a pressure range of from + 18 psig to —4 psig. Final dispersal facilities are provided by niobium — plated cones inside and outside the reactor vessel, leading finally into a series of cylinders terminating in the bedrock. Figures 4.30 and 5.16 show reactor cross sections.