Patent GB-1412279-A (GB)
Title: Restraint system for core elements of a reactor core
IPC: G21C5/10
Filed: 1972-12-05
Abstract: 1412279 Reactors GES FUR KERNFORSCHUNG mbH 5 Dec 1972 [15 Dec 1971]  56057/72 Heading G6C A core of a sodium-cooled, fast breeder reactor consists of an assembly of core elements each with an hexagonal cross-section, these core elements comprising fuel elements 7, blanket elements 8, shim rods 9, and shutdown rods 10. Around the core element assembly, sodium hydraulic expansion elements 12 are arranged within a core shell 11. Space 13 between the expansion elements 12 and the blanket rods 8 is subjected to the sodium outlet pressure whereas the inner space of the expansion elements 12 is subjected to the sodium inlet pressure. The core elements are in contact with one another at specific planes of restraint via bearing elements such as spheres, rollers, or ball or roller bearing s or alternatively via elastically deformable elements. As shown in Fig. 4, in the planes of restraint 4, 5, a tubular box 15 is inserted into the cladding wall 14 of core elements 7, 8, 9, 10 and welded to it. The box 15, just as the core elements, has an hexagonal cross-section and is provided with recesses 17 in its outer surfaces. The recesses 17 each contain a roller 19 the ends of which are equipped with shaft journals 20 slightly spherical at their ends 21 and supported by needle roller bearings 22 in bushes 23, 24. The external diameter of the rollers 19 is such that they protrude beyond the outer surface 18 of the tubular box 15. The rollers 19 are laterally offset with respect to the centre of the surface 18 and act upon each of the opposed surfaces 18 of the other fuel element boxes in pairs together at a spring 25. The spring 25 is supported at two points like a bending bar by means of bolts 26, 27 in a recess 29. The wall section 28 of the box 15 behind the spring 25 is adapted to the bending line of the spring in such a way that a maximum restraining force will cause the spring to abut the wall section 28. Under certain conditions, the rollers 19 may be replaced by spring elements, they may also be supported in spring elements. The expansion elements 12 (Fig. 6) also have an hexagonal cross-section and are longitudinally subdivided over the area of the planes of restraint 4, 5. In this area, each restraining element 12 consists of two parts 30 and 31, part 30 being situated opposite the core elements and part 31 being supported on the core shell 11 by distance elements 32. The inner part 30 comprising a cavity 35 is movable perpendicular to the longitudinal axis of the restraining element and is sealed in the outer part 31 by means of gaskets 38. The travel of the part 30 is limited by means of distance pads 39 and limiting pins in oblong holes (Fig. 5, not shown). Behind the part 30 is a cavity connected with a duct by means of which the cavity is kept at sodium inlet pressure so that the resultant pressure difference between the cavity and the space 13 causes the core elements to be restrained. The inner part 30 abuts the core elements at rollers 44. Flexural springs 46 are installed between the two parts 30 and 31 to retract the inner part 30 to its original position as soon as the pressure difference ceases to exist.