Patent Number: 047987006
Section: description

DETAILED DESCRIPTION OF THE PRESENT INVENTION The invention, together with advantageous examples of the embodiments and improvements, will become more apparent and are described in more detail below, with references to the figures in which two different embodiments are illustrated. FIG. 1 shows a cross-section through a core 14, enclosed by circular cylindrical reactor pressure vessel 10, against the inner wall 11 whereof ceramic installations, in particular graphite blocks built up in the shape of a wall, are set as the side reflector 12, and into which four projections 13 are radially projecting in mutually opposing pairs. The projections consist of individual nose stones 20, 30 set upon each other and positively joined to the side reflector 12. The nose stones 20, 30, which are made of graphite, as is the side reflector 12, comprise in their free frontal side 17 projecting into the core 14, a vertically arranged cavity with an elongated cross-section extending parallel to the external surfaces facing the core 14. In the area of its frontal side 17 a vertically oriented continuous gap or opening 23, 33 is formed in each nose stone 20, 30, said gap connecting the cavity 18 with the core 14. While the core is intended to receive the fuel elements 15, the vertical cavity 18 is to receive the absorber elements 16. FIG. 2 shows an individual nose stone in a lateral or side elevation. The surface 21 of the nose stone 20 projecting into the core 14 is provided with a plurality of vertical grooves 22 close to the horizontal surface and laid out in a grid-like pattern, intended for the division of the external surfaced exposed to neutron radiation into small surface units to make possible the equalization of neutron-induced volume changes. From the slit lateral surface 21 of the nose stone 20, into which the continuous gap 23 connecting the core 14 with the cavity 18 extends, the support surface 24 is offset by means of a step 25, whereby the nose stone 20 is joined both upward and downward with the next nose stone or the bottom or roof reflector respectively. The height of the step 25 corresponds to one-half the width of a surface gap 22, so that a gap 22 is again formed in case of nose stones set upon each other in the area of the adjacent surfaces 24. The rear part of the nose stone 20, which is attached into the side reflector 12, comprises a groove 27 formed in the lateral surface 26 for anchoring purposes, with the side reflector 12 entering the said groove to form a positive joint. The surface 26, which is otherwise without gaps, joins the slit surface 21 in alignment. With the exception of the lateral layout of the gap 23, which establishes the connection of the cavity 18 with the core 14, the lateral view of a nose stone 20 shown in FIG. 2 is identical with that of a nose stone 30 comprising a frontal gap opening. Therefore, no separate figure is shown to display this difference. FIG. 3 shows a nose stone 20 in a top view. In a supplementation of the view in FIG. 2, the configuration of the gap 22 close to the surface 21 facing the core 14 and of the support surface 24 offset by the center step 25 may be seen, together with the smooth surface 26 in the rear part of the nose stone 20, interrupted only by a groove 27 arranged vertically on each of the two sides. The groove 27 is rectangular, but according to the present invention a groove with a cylindrical profile may be provided in order to reduce stresses in the bottom of the groove, particularly in the corners. The cavity 18 has a longitudinal cross-section and is connected at its narrow frontal side 19 through a gap 23 with the core 14. The gap 23 is thereby extended as a continuation of the narrow frontal side 19 of the cavity 18 through one of the two longitudinal sides of the nose stone 20 to the outside and expands at an angle from inside to the outside, with the gap surfaces being straight. However, according to the invention, the gap surfaces may also be curved away from the center portion of the core in an involute manner. FIG. 4 shows a top view of a nose stone 30 with a gap 33 on its frontal side, i.e., the gap 33 centrally passes through the narrow frontal side 19 of the elongated cavity 18. The nose stone 30 is thereby divided by the vertically continuous gap 33, the gap surfaces of which define the grooves 38 to receive a graphite blocking element 39, into two equal halves, which laterally surround the cavity 18 in the form of cheeks. The lateral surface 31 projecting into the core 14 is provided in the manner shown in FIG. 3 with slit-like recesses 32 close to the surface. The support surface 34 is similarly offset from the slit area by a step 35. The rear area of the nose stone again has a smooth surface 36, into which on both sides a vertical groove 37 is set, said groove 37 being intended for anchoring in the side reflector 14.