DE2528120A1 - SUPPORTING STRUCTURE FOR A NUCLEAR REACTOR CORE - Google Patents

Description

Patei.tanwali ΟΠΟΟ1ΟΠ

Dr. Hans Ulrich May Z O Z ö I Z U

8 Munich 22 Thierechstr. 27 - Tel. 225051

CP 517/1384 Munich, June 24, 1975

B 529Ö.3 PG Dr.M./cs

Commissariat ä 1 »Energie Atomique in Paris / France

Support structure for a nuclear reactor core

The invention relates to a support structure for the core of a with fast neutron working nuclear reactor, which in particular has a core catcher and devices for cooling the core catcher, which dissipate the residual power of the nuclear fuel if the core melts partially or completely and is caught in the core catcher will.

As is well known, there is the core catcher (in Anglo-Saxon parlance "core catcher") one that works with fast neutrons Nuclear reactor usually consists of a mechanically connected and welded structure, which is placed under the horizontal grating is, which supports the core-forming fuel assemblies in the vertical direction and even from a substructure Metal is worn. The core catcher is formed by a lateral, cylindrical hoop attached under the grating, the one Has a bottom of generally conical profile inside this tire is an intermediate floor, for example from a series of open circular shells with a conical Cross-section, which together form successive drainage channels from one to the next shell.

509883/0354

In an also common way, the core of the nuclear reactor is inside a first container, the so-called inner container, arranged, which extends above the grating and is itself surrounded by a second, the so-called main container, which holds the liquid metal used to cool the core, generally sodium. This liquid metal flows vertically through the core ascending so that the hot sodium collects at the exit of the core in the primary container, from where it is passed into the heat exchanger where it gives off the absorbed heat. These heat exchangers reach into the inner container and pierce an inclined one in the process Chicane of the same, so that the cooled sodium at the exit of the heat exchanger enters the space between the two tanks, is distributed there and sucked in by primary pumps and pumped under pressure into the interior of the grating, from where it is again flowing through the core. The circuit of the liquid metal serving as a coolant thus has three main manifolds, which are connected to one another connected by the heat exchangers, the primary pumps and the core. The exit of the core and entrance of the heat exchanger form the hot collecting line delimited by the inner container. The outlet of the heat exchanger and the suction chamber of the pumps form the cold Sajrnielleitung, also known as the intermediate tank, the is bounded by the inner tank and the main tank, and finally the outlet of the pumps and the inlet to the core form the high-pressure manifold, which is limited by the grating and the supply lines leading to it from the pumps. Usually between the High-pressure manifold and the cold manifold switched on a secondary circuit, especially to prevent leaks of liquid metal in the grating to catch the level of the feet of the fuel assemblies receiving holes of the same occur, this Ne-

509883/0354

benkreis especially serves the side surface of the main container to cool and the secondary circuit drains through the substructure.

The invention is now based on the object of a support structure to create this kind, which is designed so that a direct cooling of the core catcher in an accident with melting of the core is achieved.

With a supporting structure of this type, this object is achieved by that the tire of the core catcher has at least one partition made of metal which is arranged above the intermediate floor and which divides the space bounded by the tire into two areas, one of which is between the partition and the grating and continuously from the grating in the area of the feet of the fuel element assemblies absorbs leaking amounts of liquid metal, which are directed under the underside of the base to the side surface of the main tank, and of which the other, between the partition wall and the bottom of the core catcher is in communication with the surroundings of the tire through drainage channels, which through the substructure into the area between the main container and the inner container.

During normal operation of the nuclear reactor, the leakage currents from the grating containing the liquid metal under high pressure at the level of the feet of the fuel assembly in the area in the core catcher between the partition and the grating are collected, passed through transverse channels into the main container and continuously cool its inner surface, especially in the area between this inner surface and a parallel baffle. If, on the other hand, the fuel assemblies in a serious accident

509883/0354

of the core melt and the core after destruction of the metallic The partition wall is caught by the intermediate floor of the core catcher, made possible by the substructure supporting the grating Discharge channels the creation of circular currents of the metallic coolant through natural convection between the false floor the core catcher, which is at high temperature because of the molten nuclear fuel assemblies resting on it, and the The area between the main container and the inner container, where the liquid metal has a lower temperature. These cycles thus allow the residual heat generated by the melting of the core to be dissipated in the containers located between the two containers Area and thus a limitation of the consequences of the accident to the interior of the main container, thus ensuring effective protection the parts of the nuclear reactor lying outside this container.

The support structure according to the invention is described with reference to the attached Drawings explained using an exemplary embodiment. Bs demonstrate:

- Fig. 1 is a schematic axial section of a rapid

Neutron working nuclear reactor, which is equipped with an inventive Core support structure is equipped;

- Fig. 2 shows a section on a larger scale showing the particular

Design of the construction under consideration, especially of the substructure and the core catcher shows, and

- Fig. 3 is a partial view in section along the line III-III of

Fig. 2.

Fig. 1 shows a nuclear reactor operating with fast neutrons, which in a conventional manner has a thick-walled outer protective container T, especially made of concrete, which occupies an interior 2

509883/0354

borders, in which a container 3 is held, the entirety of the Includes components of the nuclear reactor. This container 3, the so-called main container, is open at the top and on a closure lid 4 suspended, which rests on the protective container 1 with its lateral support surfaces. The main container 3 is outside within the cavity 2 surrounded by a container 5, the security container, and contains a corresponding volume of a liquid metal as Coolant, generally sodium, which flows particularly in contact with the core 6 of the nuclear reactor which is inside this main container is arranged and supported in this by a grating 7. The grating extends horizontally under the core and is itself supported by a substructure 8, which is formed by an openwork metal structure, which extends with its periphery on the main container 3 supports. Under the grating 7 a core catcher 9 is attached, which the core in the case of partial or complete Melting the same catches and has a tire 10, which laterally pierced at 10a and through a conical bottom 11 is closed with holes 11a and one inside the tire Contains intermediate or collecting tray 12. In the embodiment shown, this intermediate floor is successive from a row Shells formed with a conical cross-sectional profile, which are arranged from one to the other in a series of cascading Form drainage channels. These bowls have holes 12a at their bottom (FIG. 2), which allow the liquid sodium to flow freely through them allow through the intermediate floor 12, while the edges of the trays are arranged so that each hole in the bottom of a tray from the edge of the overlying tray before the overflow of this Shell is protected from cascading sodium flowing down. Of the The interior of the core catcher 9 is relatively thin

S09883 / 035A

horizontal metal wall 13 divided into two zones 14 and 15, from which the first between the wall 13 and the bottom of the grating 7 and the second between the partition 13 and the conical bottom 11 of the core catcher lies.

The core 6 consists in a known manner of a group next to one another standing fuel assemblies 16, each having a lower Have foot 17 which can be inserted into correspondingly distributed holes in the grating 7 in order to hold the fuel assembly vertically. The cooling sodium flows through the core 6 from bottom to top in contact with the fuel elements 16 and is at the exit of the core collected in a first collecting line 18 which is delimited in the interior of the main container 3 by an inner container 19. That hot sodium is then fed to the inlet ports 20 of heat exchangers 21 which are carried by the closure cover 4 and their Housing extends downward through an inclined baffle 22 of the inner container 19 so that the outlet openings 23 this heat exchanger is located in a second collecting line 24. In this, from the main container 3 and inner container 19 limited collecting line 24, the cold sodium is taken from the inlet openings 25 of the primary circuit pumps 26 and through lines 27 of large Cross-section pumped back into the grating 7, the inner region 28 of which thus forms a high-pressure manifold.

Fig. 2 shows in more detail the particular one according to the invention Execution of the core catcher and the supporting structure. As can be seen from this figure, the inside of the tire 10 of the core catcher 9 and in this the two zones 14 and 15 separating partition wall 13 made of metal an expedient and permanent Separation of the cold sodium inside the core catcher. The area

§09883 / 0354

14 takes the from the high pressure manifold 28 in the area of the Insertion of the feet 17 of the fuel assemblies serving holes exiting Sodium leaks up and runs this cold under pressure standing sodium through lines 29 (see left part of Fig. 2), which are under the substructure 8, to an annular space 30, which of the Inner surface of the main container 3 and a shielding wall parallel to it 31 is limited * In area 15 this is used at lower pressure cold sodium present during normal operation of the reactor for cooling the intermediate floor 12 and the substructure 8.

The operating conditions are of course different in the event of an accident with the core 6 melting and the fuel assemblies being caught 16 of the core on the intermediate floor 12 after the partition 13 has been destroyed. in this case one cares according to an essential one Feature of the invention that in the core catcher 9 around this intermediate floor 12 around a natural convection flow of sodium by connecting the area 15 below the intermediate floor with the area between the containers 3 and 19 lying collecting area 24 for cold sodium by a series of vertical exhaust ducts 32, which through the substructure 8 pass through (see the right part of Fig. 2). These ducts, which are shown in Fig. 3 in section, allow through their Distribution around the axis of the nuclear reactor a continuous circulating current of the sodium, around which by the melting of the core in the height of the intermediate floor 12 to dissipate residual heat output. These drainage ducts through the substructure are distributed so that some of them carry the hot sodium to the cold plenum area flows and through others the same sodium after it has cooled on its way to the collection area and mix in it,

509883/0354

is returned to the intermediate floor. Fig. 2 shows the outflow on the left the hot and on the right the backflow of the cold sodium. Of course, the ducts do not necessarily need all of them to run perpendicular, but at least some of them may also have a different direction, depending on the particular design the substructure, the core catcher and the grating

509883/0354

Claims (3)

^ 9 claims 25281 1.) Support structure for the core of a working with fast neutrons Nuclear reactor with a horizontal grating into which the feet of the fuel assemblies forming the core are inserted and the one high pressure saramel line. for a liquid metal as Forms coolant for these fuel assemblies, which flows from bottom to top through the core and collects in an inner container, with a perforated substructure supporting the grating Metal, which is firmly connected at its periphery to the inner surface of a main container surrounding the inner container, and with a held under the grating, which has a lateral cylindrical hoop and a bottom and delimits an area, one of them catching the core with melts in the event of an IM case Contains intermediate floor, characterized in that that the tire (10) of the core catcher (9) at least one Has partition (13) made of metal, which is above the intermediate floor (12) is arranged and the space bounded by the tire in two zones (14,15) divides, one of which is a zone (14) between the partition (13) and the grating (7) is and permanently that of the grids rust in the area of the feet (17) of the fuel assemblies (16) coming Absorbs leakage quantities of liquid metal and conducts it under the underside of the substructure (8) to the surface of the main container (3), while the other zone (15) between the partition (13) and the bottom (11) of the core catcher (9) and with the environment of the Tire is in communication by drainage channels (32) which are formed through the substructure (8) and to the between the Main container (3) and inner container (19) lead in the lying area « 609883/0354 -ίο. 252812Ü 2. Support structure according to claim 1, characterized in that the drainage channels (32) extend perpendicularly through the substructure (8). 3. Support structure according to claim 1, characterized in that the drainage channels (32) at an angle of less than or extend equal to 90 ° to the vertical. BG9883 / 0354