Patent Number: 043127045
Section: description

DESCRIPTION OF A PREFERRED ILLUSTRATIVE EMBODIMENT As shown in FIG. 1, a pebble bed 1 within an inner core structure 3, surrounded by a pre-stressed concrete pressure vessel 2 is unloaded in normal operation by discharge conduits 4 distributed around a circle at the core bottom. From the conduits 4, there branch off quick core-emptying ducts 5 that run obliquely and generally radially downward and outward, preferably at an angle of 30.degree. to the horizontal. In the case of an accident, the shut-off device 6 is opened, after release of pressure, by means of the valve combination 7, and the spherical fuel elements from the charge 1 of the core fall into a ring cavity 8 that is surrounded by a water jacket 9 that is closed above by covers 10. According to the invention, the shut-off device is formed from two interfitting rod combs that are arranged and caused to move perpendicularly to the conduit axis, of which one comb 11 is diagrammatically illustrated in FIG. 2. In accordance with a particularly preferred embodiment of the invention, the wall shutting off the conduit cross-section formed by the interfitting rods of the two combs is made up of rods of specially shaped cross-section as illustrated in FIG. 3. In that figure are shown the rods 13 of the comb 14 (see, also, FIG. 4), that are removed from above into the conduit cross-section. These rods have an approximately I-shaped cross-section and form with their sides 15 that are turned towards the column of balls 19 lying against them (i.e., normally all the way to the core), the bottoms of ball grooves, of which the sides 16 are formed respectively by the two adjacent rods 17 of the comb 18 (see, also, FIG. 5), that is arranged to be driven into the conduit cross-section upward from below. The rods 17 are hollow and their connecting surfaces 17' between the surfaces 16 that form the edges or flanks of the ball grooves, have a generally roof-shaped configuration, so that the spontaneous ordering of the spheres 19 in the ball grooves 15 and 16 is promoted thereby. As shown in FIGS. 4 and 5, the rods movable into the conduit cross-section respectively as part of the comb 14 and the comb 18 are held together respectively by connecting bridges 20 and 21, and are disposed outside of the closure wall plane and are each separately actuatable by spindle drives 22 and 23, respectively. For the seating of the connecting bridges 20 and 21, there are provided rails 24,25 along which the combs can ride on roller bearings 24' and 25'. As shown in FIGS. 4a, 4b, and 4c, the rods 13 are prolonged by extensions 26 that fit into corresponding cavities in the lower conduit wall in the closed position of the comb. The correspondingly tapered and closed off ends of the rods 17 of the comb 18 that is movable upwards into the conduit cross-section from below complete the lower duct wall, as is shown in FIGS. 5a, 5b, and 5c, in the open position. The outer rods 27 of this comb 18 carry a slotted cover plate 28 that fills in the upper duct wall and is shown in more detail in FIGS. 6a and 6b. The slotted cover plate 28 has slots 29 corresponding to the cross-section of the rods 13 and is held together by a connecting surface 30 extending above the slots. The surface 30 can be retracted by the thickness of the discharge conduit 5 so that the underside of the slotted cover plate 28 can be flush with the inside wall of the conduit, or else the surface 30 is so narrow that the broadening of the semicircular cut-out of the upper conduit surface beyond the shut-off wall cross-section in order to fit in the connecting surface 30 leaves only a narrow peripheral slit open, through which none of the balls can pass. FIG. 7 shows the arrangement of the first layer of balls with all the ball grooves filled with an integral number of balls that are limited endwise by a corresponding curtaining or profiling of the inner conduit wall, so as to promote a dense and ordered packed seating of the fuel element balls adjacent to the shut-off device. FIG. 8, finally, shows the spatial configuration of the cooperating double pressure vessels which enclose the entire installation made of the interfitting combs of the shut-off device, and are connected by flanges to the quick-emptying conduit 5. An outer casing block 31, encloses an inner casing block 32 that takes up the individual movable parts. Although the invention has been described with reference to a particular illustrated embodiment, it will be understood that variations and modifications may be made within the inventive concept.