Nuclear reactor fuel element design - esp. a head for fuel rod assembly of a sodium cooled fast neutron reactor

In a nuclear reactor fuel element assembly, particularly a sodium-cooled, fast neutron reactor, containing some assemblies of fuel elements containing both fissile and fertile material, each assembly has a standard head which is the same for all assemblies. Each heat is mounted on the axial extension of the upper part of a polygonal and especially a hexagonal, elongated hollow casing forming the body of the assemblage. The head consists of a cylindrical sleeve, terminating in a conical bearing and has an internal circular opening for gripping the assembly. The cylindrical sleeve has a roughened external surface, which has a constant reflecting power with respect to ultrasonic radiation. Ensures that all the fuel elements are at the same level for gripping by the remote control unit. A single type of head facilitates manufacture and the geometry of the head avoids damage during changing the core of the spherical sealing bearing at the lower end of the casing of the assembly and its locating foot. Finally, any assembly which is out of position can be detected by the usual ultrasonic methods and the transverse holes through the head in this case ensure that it is cooled by natural convection.