Patent Number: 041860497
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The prior art components which have already been described with reference to FIG. 1 will not be described relative to FIG. 2 and in addition the same reference numerals will be used. FIG. 2 shows in a more explicit manner an autonomous heat transfer module 14 suspended on the upper slab 16 of the reactor by elastic means 15 which permit a limited angular displacement of the assembly about its vertical axis. Autonomous module 14 comprises a primary circuit 17, designated by arrows F for the circulation of the combustible salt which when heated on leaving core 4 penetrates the module via an opening 18 provided in the upper part thereof and then after cooling is forced back by a pump 19 located in the lower part thereof. A secondary salt circuit whose inlets and outlets are designated by reference numeral 20 receives the calories from the combustible salt in the primary circuit and finally transfers them to a not shown water circuit where the steam produced is finally used to operate an also not shown turbine. The lower part of autonomous module 14 has, if necessary, a non-return valve for the molten salt flow, said valve not being shown in FIG. 2. According to the invention, between reactor skirt 5 and main vessel 3 a conical ferrule 21 is provided which by one end is fixed to reactor skirt 5 and whose other end 22 is mounted freely in the immediate vicinity of main vessel 3 in the solidified salt layer 13. According to the invention, the surface of conical ferrule 21 has openings 23 distributed around the core axis, each being surrounded by a planar bearing surface 24 and cooperating in the present embodiment with a spherical bearing surface 25 in the lower part of autonomous module 14. The bearing of spherical bearing surface 25 on planar bearing surface 24 makes it possible to support the weight of module 14, whilst ensuring the relative displacements of the said members relative to one another in accordance with the different thermal operating cycles of the reactor, whilst providing the sealing relative to the pressure of the cold salt delivered by pump 19 at the base of autonomous module 14. In the embodiment of FIG. 2 a delivery pipe 26 directly links the base of module 14 through opening 23 and the lower part of the reactor core via an opening 27 made in wall 5 of the reactor skirt below conical ferrule 21. Pipe 26 is made from the same material as the reactor skirt 5 and ferrule 21, said members being at the same temperature during normal operation of the reactor. This makes it possible to avoid all differential expansion problems encountered in prior art solutions using transverse connections between the base of each exchanger shaft and the base of each pump shaft, said two components being completely separate. A second embodiment of the invention will now be described with reference to FIG. 3. In this embodiment each autonomous heat transfer module 14 provided with its pump 19 is supported, as in the previous embodiment, on a conical ferrule 21 having openings 23 for the passage of the cold salt delivered by the corresponding pump 19. As in the previous embodiment, the cooperation between a spherical bearing surface 25 at the base of module 14 and a planar bearing surface 24 surrounding opening 23 leads to a tightly sealed support and permits the relative movements of module 14 and ferrule 21. In this embodiment the space below ferrule 21 between main vessel 3 and reactor skirt 5 is subject to the pressure of pump 19, whereby the cold salt flows through channels 33 made in carbonaceous mass 7 connecting the outlet of the pumps to openings 29 made in the lower part of skirt 5 to the reactor core and in accordance with arrow F. Channels 33 are obtained by an appropriate shaping of the carbonaceous material in the absence of any metallic element connecting the opening of the pumps to those of the reactor skirt. Thus, the mass of carbonaceous material ensures the filling of space 28, whilst piping the combustible salt between the pumps and openings 29. This space is not tightly sealed and construction joints can exist between the carbonaceous elements and there can be tolerances between said elements and the metallic structures defining space 28. Cracks may also occur in the carbonaceous mass. Therefore the delivery pressure of the pumps can be exerted on the periphery of this space which from then on should be sealed. With regard to vessel 23 and ferrule 21, this sealing is more particularly obtained by the cooperation of a boss 30 and the free end 31, which is preferably slightly tapered, of conical ferrule 21 which moves freely beneath boss 30, the assembly being located in area 13 which is filled by the neutral solid salt crust which is voluntarily maintained against the inner surface of main vessel 3. This arrangement which is essential for the second embodiment of the invention is described in greater detail with reference to FIG. 4. FIG. 4a illustrates the reciprocal arrangement of boss 30 on main vessel 3 and the free end 31 of ferrule 21 when, with the reactor shut down, the different members are at the same ambient temperature, for example about 20.degree. C. The external diameter of ferrule 21 is then below the inner bore of boss 30 providing a given clearance between said members permitting a one piece fitting of the ferrule during assembly. In FIG. 4b the respective position of the different members corresponds to the formation stage of salt crust 13, i.e. when vessel 3 is heated to a temperature of about 300.degree. C. whilst ferrule 21 is at a temperature of about 400.degree. C. Under these conditions boss 30 connected to vessel 3, and on which it is suspended by its upper part, drops slightly relative to the position which it occupied in FIG. 4a, whilst conical ferrule 21 has expanded transversely towards the outside of the reactor by a distance sufficient to bring about a partial covering of said boss by said ferrule measured by the distance j'. Simultaneously, the upward vertical expansion of ferrule 21 causes the engagement of its end 31 beneath boss 30, approaching the latter in the area of solid salt 13. In FIG. 4c which corresponds to the normal operation of the reactor, the main vessel 3 is still at a temperature of 300.degree. C. necessary for maintaining the crust of solid salt 13 against its surface, whilst conical ferrule 21 has reached a temperature of about 560.degree. C., its expansion in both the radial and vertical directions having increased further. Therefore its free end 31 engages beneath boss 30, permitting if necessary the fitting of a piece of graphite 32 located in a groove made in the upper part of end 31 so as to increase the sealing between the latter and boss 30. It should also be noted that the cooperation between end 31 of ferrule 21 and boss 30 of main vessel 3 is beneficial from the thermal standpoint because the tapered portion constitutes a significant impedance for the calories which would otherwise tend to escape directly from the core towards the periphery. Moreover, boss 30 constitutes a mass whose thermal impedance is very low and via which it is possible to evacuate very rapidly the calories from conical ferrule 21 towards the air-conditioning fluid 9 contained between main vessel 3 and outer vessel 8. It is clear that the solidification of salt crust 13 takes place automatically even when occasional cracks occur in said crust, for example during the sliding of the two metal members 30 and 31. In the extreme case where a break in the sealing could occur due to cracks in the crust 13 between boss 30 and end 31 as a result of said two members sliding, e.g. due to a change in the thermal operating cycle, combustible salt could possibly pass through the carbonaceous lining and flow between ferrule 21 and vessel 3. This mixture which would have to pass into the cold area adjacent to the main vessel 3 where the temperature is lower than its melting point would then be rapidly solidified again which would automatically re-establish the sealing. In other words, the device according to the invention permits a certain relative movement between the metal members as a result, for example, of a change in the thermal state of the ferrule, but the sealing is automatically restored by solidification of the liquid salt coming into contact with the cold metal parts. The invention is not limited to the embodiments described and represented hereinbefore, and various modifications can be made thereto without passing beyond the scope of the invention.