Patent Number: 047568798
Section: description

DETAILED DESCRIPTION OF THE EMBODIMENTS FIG. 2, which shows in sectional form a sodium-cooled fast neutron nuclear reactor, uses the same reference numerals for the main elements of FIG. 1 according to the prior art and these will not be described again. According to the invention, this reactor is equipped with a core cover plug 15 essentially comprising, above reactor core 1, a deflecting plate 32 suspended on the lower part of an inner small rotary plug 12, either by means of sleeve tubes 26, which is the case in FIG. 2, or by metal tie bolts with rigid sections as will be described hereinafter. These suspension elements 26 are joined together and to the sleeve elements 28 (FIG. 3) the passage of the control rods, in at least one horizontal plane, by a grid 30 formed from intersecting vertical metal plates 43 (FIG. 3). FIG. 3 is a larger scale diagrammatic view of FIG. 2 showing the organization of the core cover plug 15. According to the invention, a certain number of metal sleeves 26 and sleeve elements 28 are linked with the passages 35 of plug 12 and are used for introducing into the core absorbing rods 40, making it possible to regulate the reactor reactivity level. According to the invention, beneath grid 30 and above reactor core 1, certain sleeve elements 28 support a conical deflecting plate 32 which, as explained hereinbefore, makes it possible to deflect the hot sodium jet leaving the assemblies 36 and as indicated by arrows F. Deflecting plate 32 supports sampling tubes 42 used on the one hand for sampling the liquid metal on leaving the core in order to locate the existence of a possible sheath fracture in one of the assemblies 36, and on the other hand to permit the location of thermocouples which directly measure the temperature of the hot sodium leaving core 1. From each of the sampling tubes 42, the information supplied by the thermocouples is passed by sheaths 44 passing through the rotary plug 12 into pipe 45. The hot sodium samples taken at the outlet of assemblies 36 are passed by metal tubes 46 to the sheath fracture locating equipment 47. FIG. 4 shows details of the core cover elements, i.e. sleeves 26, sleeve elements 28, the plates 43 forming grid 30, the deflecting plate 32 with its fixture to certain sleeve elements 28 by a radial clearance expansion system 48, which can best be seen in FIG. 4a, sampling tubes 42 and plates 33, 38 which rigidify this group of tubes and contribute, with plate 32, to the deflection of the sodium jet. FIG. 4 shows in greater detail the respective arrangement of the three deflecting plates 32, 33 and 38 suspended on grid 30 by sleeve elements 28 with a lateral clearance expansion system shown at 48 in FIG. 4a. FIG. 4 also makes it possible to understand how the sampling tubes 42 are fixed to the central deflecting plate 32, as well as to the upper 38 and lower 32 deflecting plates. FIG. 5 is a cross-sectional view in plane YY of FIG. 4 and shows the location, in the particular embodiment described, of sleeves 26 and sleeve elements 28 spaced by the vertical flat plates 43. FIG. 6 shows a special embodiment, where the core cover is suspended on the inner small plug 12 by tie rods. It is possible to see a certain number of sleeves 28 spaced by metal plates 43 and having a three branch star-shape configuration, the lower end 50 of one of the tie rods being connected by vertical spacing plates 51 to plates 43. It is obvious that this tie rod configuration is not limitative and that the cross-section of the tie rods can have a random shape compatible with the necessary rigidity and can in particular have a cross or square configuration.