Patent Number: 047449411
Section: description

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a building 1 of a fast neutron nuclear reactor, whose pile block 2 comprises a main vessel 3 and a safety vessel 4 in a well 5 of building 1. Pile block 2 and vessel 3 of the reactor are sealed in conventional manner by a concrete slab 6. In the lower part of building 1 are provided two floors, namely an upper floor 7 and a lower floor 8, separated from one another by elastic supports 9 made from fretted elastomer. These supports 9 permit an oscillatory horizontal displacement, with return to the initial position, of the upper part of building 1 with respect to the lower floor 8, which can be very useful for absorbing seismic shocks having horizontal components of a certain magnitude. Pile block 2 rests on building 1 in the following way. A lateral cylindrical concrete structure 19 integral with and peripherally and terminally extending the slab of reactor 6, serves as a support for pile block 2, via the series of elastic supports 10 placed between the bottom of cylindrical structure 19 and upper floor 7. In this embodiment, the vertical guidance means 12 are laterally distributed between supports 12a in the upper part and supports 12b in the lower part of block 2. The guidance means 12 are rigid in the horizontal plane and flexible in the vertical plane. The distribution of the vertical guidance means of the reactor block in well 5 between the top and bottom thereof makes it possible to completely prevent any rocking or oscillation of the reactor block assembly in the case of seismic shocks. The structure operates in the following way: the horizontal movement of the assembly is imposed by paraseismic supports 9 positioned beneath building 1; PA1 the vertical movement of reactor block 2 is regulated by the characteristics of the elastic supports and absorbers 10; PA1 the overall vertical movement of the remainder of buidling 1 is a function of its natural frequencies, which are dependent on the characteristics of the ground. The building of reactor 1 and the reactor block 2 are connected by pipes, cables, etc., which must have sufficient flexibility to accept the vertical differential movements occurring, in the case of an earthquake, between these two parts. FIG. 2 shows the second embodiment of the support structure according to the invention and has, with the same reference numerals, most of the components of the embodiment of FIG. 1. However, in this embodiment, the elastic supports 10 and guidance means 12 are positioned at the coupling slab 6 in the following way. According to the invention the absorbing elastic supports 10 are positioned between the upper ends of slab 6 and the vertical concrete caisson 11 directly surrounding the pile block 2. These absorber means make it possible to absorb the vertical components of a possible seismic wave, by preventing the rocking of the reactor vessel 3 with respect to building 1. The vertical elastic guidance means 12, positioned vertically between the peripheral ends of reactor slab 6 and the structures of building 1, enable pile block 2 to be guided in well 5 in a vertical direction, while preventing any horizontal displacement of block 2, as well as any rocking thereof under the effect of the horizontal components of a possible seismic wave, because it is then substantially integral with building 1. FIG. 3 is a plan view of reactor slab 6, which is peripherally provided with a certain number of support tenons, such as 13, which cooperate with mortises 14, cut from the concrete of the building of reactor 1, so as to laterally enclose the vertical elastic guidance means 12, preventing any horizontal rotation of slab 6 with respect to the building 1, under the effect of the horizontal component of a seismic wave. The constructional detail of the sector surrounded by a circle and designated A in FIG. 2 is shown in FIGS. 4 and 5, where it is possible to see the main components referred to hereinbefore and, in addition, the circular gallery 15 positioned beneath slab 6 and more particularly giving access to the first elastic support 10 and to the flexible tight joints 16, which obviate any leaks of radioactive material coming from the main vessel 3 and towards the outside thereof. Manholes 17, distributed over the periphery of the installation, permit the introduction of the individuals necessary for the different manipulations and the like in said gallery 15. FIG. 4 shows at 10, the elastic supports for absorbing the vertical components and the elastic guidance means 12, positioned vertically between tenons 13 and mortises 14, belonging respectively to slab 6 and to the concrete of reactor building 1. The guidance means 12 are rigid in the horizontal direction (in order to permit the displacement of slab 6 by building 1) and flexible in their vertical parallel planes (to permit the freedom of vertical movement of vessel 3). Between tenon 13 and mortise 14, there is a space forming an expansion joint 18 permitting, when the reactor temperature rises, the radial expansion of the slab. This arrangement, which is a consequence of the existence of tenons 13 and mortises 14 is very interesting, because it very simply solves the hitherto difficultly solvable problem of the radial expansion of the vessel and the slab supporting the same. Thus, by associating the three means constituted by supports 9, 10 and 12, it is possible to obtain a maximum, effective protection against the seismic wave of a certain magnitude, no matter whether their components are mainly horizontal or vertical. The antiseismic support structure according to the invention thus provides a double horizontal and vertical filtering of the seismic stresses, which considerably reduce the acceleration to which the slab and the components of the pile block are exposed in the case of an earthquake. Thus, it permits a simplified and much less costly construction than those available hitherto. Moreover, this structure very simply permits the construction of the system oscillating with three degrees of freedom (2 horizontal and one vertical), whose rigidity and absorbing or damping characteristics are accurately known. Thus, there is a very good knowledge of the dynamic response in the case of a shock, which is also very satisfactory from the reactor safety standpoint. FIG. 6 shows in greater detail the absorber 10 of FIG. 1. This viscoelastic absorber 10 has between its ends 20, 21, a series of springs 22 and a viscous absorber 23. This association makes it possible to increase the filtering qualities of the vertical component of a seismic shock, above a frequency of approximately 1 to 1.7 Hz. FIG. 7 diagrammatically shows the application of the invention to the seismic protection of a solid block 24, such as exists in buildings. As a result of the means according to the invention and which carry the same references as in FIG. 1, this block is stabilized and is protected against rocking or oscillating movements through the double filtering of the horizontal and vertical components above approximately 1 Hz.