Patent Number: 044951388
Section: description

DESCRIPTION OF PREFERRED EMBODIMENT The drawing shows the bottom portion 1 of the volute casing of a primary pump disposed inside the vessel of a liquid sodium cooled fast neutron nuclear reactor. The vessel of this nuclear reactor also contains the core support of the reactor, on which are disposed the fuel element assemblies forming the core. On this core support or bed is fixed a duct for injecting liquid sodium at the base of the assemblies; the inlet end 2 of this duct can be seen in the drawing. This vertically disposed inlet end 2 leads into a hollow sphere, on which is fixed the outlet portion of the duct joined to the core support. This outlet portion is horizontal and permits the distribution of the sodium to the bottom portion of the core assembly. The bottom portion of the volute casing 1 is connected at its periphery to a junction ring 4. The bottom portion of the volute casing and this ring 4 constitute the delivery duct of the pump. The junction device between the pump delivery duct and the inlet portion 2 of the duct joined to the core support is composed of a sleeve 6, a connecting member 7 disposed at the pump delivery duct end, and a sealing and retaining assembly 8 disposed at the end adjoining the duct joined to the bed. The entire junction device is symmetrical in revolution about the vertical axis 5 of the pump. The connecting member 7 is welded to the smaller base of the frusto-conical sleeve 6, at a point near the pump delivery duct. This connecting member 7 has a peripheral portion 9 machined to form a spherical surface complementary to a spherical surface machined on the outer surface of the ring 4. These two spherical surfaces in contact with one another assure leak-tightness at the junction between the pump delivery duct and the sleeve with the aid of a labyrinth seal 10 disposed between the connecting member 7 and the ring 4. The connecting member 7 also has a central portion connected to the peripheral portion by means of a cross-piece 12. This central portion is composed of the movable portion 14 of a ball joint whose fixed portion 6 is carried by the bottom portion of the pump volute casing in its central portion, near the axis of symmetry 5. The shaft 15 of this ball joint is fixed to the threaded central portion of the fixed portion 6 of the joint. The frusto-conical sleeve 6 widens out from its inlet end near the outlet of the delivery duct towards its outlet end near the inlet end of the duct joined to the bed. The sealing and retaining assembly 8 is fixed to the end of the sleeve 6, at the larger base of the latter, and is provided with a ring on which are fixed, on the one hand, frusto-conical elastic sectors 16 carrying at their ends spherical bearing surfaces 17 and, on the other hand, an assembly of sealing segments 18. The end of the sleeve 6 and the ring 9 penetrate inside the inlet of the duct 2, which has a diameter greater than the diameter of the larger base of the sleeve 6. The segments 18 are inserted between the ring 8 and the inner surface of the duct 2, while the elastic sectors 16 bear through the spherical portions 17 against the surfaces locally machined to a spherical shape and integral with the duct 2. It can be seen that the outlet end of the sleeve 6 and the ring 8 are free to move in the direction of the axis 5 inside the inlet of the duct 2. When liquid sodium is circulating inside the sleeve 6 at the outlet of the pump delivery duct, the excess pressure of this sodium in relation to the sodium contained in the vessel gives rise to forces applied to the wall of the sleeve, the resultant of these forces being a force axially directed toward the pump. The central joint connection 6, 14 enables this axial force to be resisted. In addition, between the peripheral portion of the connecting member 7 and the junction portion of this member on the sleeve 6, at the smaller base of the latter, an annular surface 20 exists which is perpendicular to the axis 5 and to which is applied the pressure of the liquid sodium delivered by the pump. This pressure produces an axial force opposed to the force produced by the pressure of the sodium inside the sleeve 6. In the embodiment illustrated in the drawing, these two forces cancel one another, so that during the operation of the pump the equilibrium of the sleeve is completely stable in the axial direction. The transverse forces applied to the junction device may give rise to a displacement of the latter, so that it will assume an inclination relative to the axis 5. The arrangement of the articulated connections permits this displacement, and the complementary sealing surfaces carried by the sleeve and the ducts to which the sleeve is connected enable these displacements to be made while assuring perfect continuity of flow of the liquid sodium. The junction device therefore undergoes no excessive stresses either in the axial direction or in the transverse directions. Nevertheless, the junction is always maintained perfectly. In addition, both longitudinal and transversal expansions are possible without the subjection of the junction device to any considerable stresses. The transverse displacements are moreover limited by the elasticity of the sectors 16 completely surrounding the end of the sleeve and assuring the recentering and lateral retention of the latter. A frusto-conical insertion slope 21 permits easy mounting of the sleeve inside the duct 2. It can be seen that the main advantages of the device according to the invention are the fact that it permits a perfect junction between the pump delivery duct and the duct joined to the core support bed of the reactor, while permitting expansions and displacements of this junction device through the action of various stresses, and thus preventing overstresses. Moreover, the balancing of axial forces is possible by modifying the diameter of the peripheral portion of the connecting member 7. It is thus possible to obtain a completely balanced system like the one described above, or else to obtain a system in which the resultant of the axial forces is directed towards the pump or else directed towards the bed. The suspension and attachment of the junction device by an articulated connection disposed in its central portion permit displacement under the action of transverse forces, while assuring perfect support of the junction device in the longitudinal direction. The invention is not limited to the embodiment described above, but on the contrary includes all variants. Thus, for the articulated device for securing the sleeve to the pump delivery duct, it is possible to use an articulated connection means other than a ball joint. It is also possible to conceive the construction of the connecting member 7 in a different form, while the balancing surface 20 of the sleeve could have a shape differing from the annular shape. It is likewise possible to conceive a different form of construction of the sealing and retention assembly 8, and the elastic device inserted between the end of the sleeve and the bed could be made in a form different from an assembly of frusto-conical sectors. Finally, the junction device according to the invention can be used in all cases where a primary pump of a liquid metal cooled fast neutron nuclear reactor is used for injecting this liquid metal into a duct joined to a fixed part of the reactor.