5. Fuel assembly and handling

5.1 Fuel assembly

The fuel is made up of assemblies of 36 rods containing annular UO ₂ pellets wrapped in a ribbed steel envelope, then inserted and clad on a steel cladding so as to obtain the best heat transfer to the coolant gas, the remaining void being filled with helium. The rods are assembled by grids at the ends and held together by strapping, all positioned inside a double cylindrical graphite liner whose clearance serves to limit heat leakage from the hot fluid to the graphite blocks (figures 8 , 9 and