WO2009083675A2

WO2009083675A2 - Nuclear reactor vessel for a fast breeder reactor of the type with loops

Info

Publication number: WO2009083675A2
Application number: PCT/FR2008/052238
Authority: WO
Inventors: Gilles Francois
Original assignee: Areva Np
Priority date: 2007-12-28
Filing date: 2008-12-08
Publication date: 2009-07-09
Also published as: FR2925973B1; FR2925973A1; WO2009083675A3

Abstract

The present invention relates to a nuclear reactor vessel (100) for a fast breeder reactor with loops. The reactor vessel (100) according to the invention comprises a main vessel (1) containing a core (22) made up of fuel assemblies (32), coolant inlet pipe work (10) for letting coolant (25) into the main vessel (1) before it is heated up upon contact with the fuel assemblies (32), coolant (25) outlet pipe work (11) for removing the coolant (25) after it has been heated up upon contact with the fuel assemblies (32), means (5) of supporting the core (22). The inlet (10) and outlet (11) pipe work are arranged concentrically, the inlet pipe work (10) surrounding the outlet pipe work (11) and thus delimiting, with the outer wall of the outlet pipe work (11), an inlet volume (12) for the coolant (25). The reactor vessel (100) further comprises an internal vessel (2), housed inside the main vessel (1), and delimiting with the internal wall of the main vessel (1) an annular manifold (3), the internal vessel (2) being connected to the outlet pipe work (11) in such a way that the inlet volume (12) is in communication with the manifold (3) and means of connection and disconnection (24) between the internal vessel (2) and the coolant (25) hot outlet pipe work (11). FIGURE 1.

Description

NUCLEAR REACTOR REPLACEMENT WAFER WITH BUCKLE TYPE FAST NEUTRONS

The present invention relates to a reactor vessel of a fast neutron type fast neutron nuclear reactor (RNR) with liquid metal cooling such as sodium.

In the framework of the Generation IV International Forum, fast neutron nuclear reactors are experiencing a clear renewal of interest. RNRs first derive their energy from plutonium. Their heart, consisting of plutonium and natural uranium, has a dual function:

- produce heat (fission of plutonium) converted into electricity;

- transform natural or depleted uranium (little fissile) into plutonium (fissile). RNRs are referred to as "regenerator" or

"Breeder" if they produce more plutonium than they consume.

In addition to this dual function, research is being conducted to use this type of reactor to "burn" long-lived radioactive waste, transuranium and actinide, and turn it into short-lived radioactive elements.

An RNR is cooled by a coolant consisting of a liquid metal such as sodium. Sodium, in the liquid state, is a remarkable cooling fluid, thanks in particular to its high boiling point.

In known manner, the primary circuit of a fast neutron nuclear reactor is formed by:

a main vessel containing the reactor core and an internal structure; primary pumps for circulating the cooling fluid and;

intermediate heat exchangers for transmitting the heat of the cooling fluid of the heated reactor in contact with the core to a secondary fluid.

The RNRs are distributed according to two different configurations, characterizing the mode of the primary circuit:

integrated RNRs for which the primary pumps and exchangers are entirely contained inside the main vessel containing the core and are immersed in the cooling fluid of said main vessel through the closure slab of this vessel;

the so-called "loop" RNRs for which the primary pumps and the intermediate heat exchangers are placed in dedicated tanks (called "component tanks") outside the main reactor vessel which now contains only the core and the internal structure; the main tank and the component tank being connected by primary pipes.

The present invention relates solely to loop-type RNRs: its subject is the reactor vessel of a loop-type RNR, that is to say the part of the nuclear reactor formed by the main tank containing the core provided with the fuel assemblies as well as the structure internally placed inside this main tank. The reactor vessel is to be distinguished from

"Component tanks" comprising primary pumps and heat exchangers.

The main vessel of the nuclear reactor contains the core formed by the fuel assemblies, the internal structure, the control rod and fuel handling mechanisms, the instrumentation, and the core support. The internal structure of the main vessel of the nuclear reactor comprises:

an inner vessel formed of one or more ferrules,

- a bed base, - a decking.

The heart of the nuclear reactor is supported by the bed base resting itself on the decking. The decking generally bears on a portion of the inner wall at the bottom of the reactor vessel.

The internal structure of the main vessel of the nuclear reactor may also include a recuperator disposed under the decking and for protecting the bottom of the tank and recovering the molten core.

The reactor vessel further comprises a horizontal slab for closing the upper part of the main vessel.

The known configurations of loop RNR nuclear reactors, however, pose certain difficulties.

Thus, in the loop RFRs known from the prior art, the elements of the internal structure arranged in the main tank are not removable, either because they are welded together during the production of the reactor block by assembly on site either because their dimensions do not permit their passage through the openings made through the closure slab of the main tank or because the arrangement of the pipes connecting the reactor vessel and the component tank does not allow the disassembly of the internal structures or components of the reactor vessel. Even if such a disassembly operation remains exceptional, it can be useful to allow access to the inside of the tank for interventions, an extension of the inspection in service (ISI), change or repair ex situ internal structures.

When it is necessary to extract the elements of the internal structure, that is to say essentially in the case where the dismantling of the nuclear reactor reached the end of life, it is necessary to completely empty the tank of the nuclear reactor of the liquid metal it contains and perform the cutting of the internal structure of the reactor and the liquid metal supply pipes under an inert gas atmosphere. It is therefore not possible to perform, in the fast loop neutron reactors of the prior art, disassembly of the internal structure members, for example to perform a repair or replacement operation of this organ.

In this context, the present invention aims to provide a loop-type fast neutron nuclear reactor reactor vessel for disassembling the elements forming the internal structure.

To this end, the invention proposes a reactor vessel of a fast loop neutron nuclear reactor comprising a main vessel containing: a core composed of fuel assemblies capable of being cooled by a coolant,

a heat transfer fluid inlet pipe for the inlet of said heat transfer fluid into said main tank before its heating in contact with said fuel assemblies; a coolant outlet pipe for evacuation of said heat transfer fluid after its heating at contact of said fuel assemblies,

- Support means for said core, said reactor vessel being characterized in that - said inlet and outlet piping are concentrically arranged, said inlet pipe surrounding said outlet pipe and thus delimiting with the outer wall of said outlet piping an inlet volume of said heat transfer fluid;

said reactor vessel comprises: an internal vessel housed inside said main vessel and delimiting with the inner wall of said main vessel an annular-shaped collector, said inner vessel being connected to said outlet pipe so that said inlet volume is in communication with said collector o connection and disconnection means between said inner vessel and said heat transfer fluid outlet pipe.

Thanks to the invention, it is possible to disassemble without cutting the devices placed inside the main vessel through the connection and disconnection means connecting the inner vessel and the hot outlet pipe of the coolant. The inner vessel and the hot outlet pipe are not welded but are held together by connection and disconnection means. These connection and disconnection means are for example made by rings of the piston type of circular shapes. The piston seals are pushed axially into the inlet volume of the coolant defined by the outer wall of the outlet pipework and the inlet pipework. The offset of the piston seal thus created frees the connection between the inner vessel and the outlet pipe of the heat transfer fluid. Disconnection between the inner vessel and the primary pipe, allows disassembly of said inner vessel and elements of the internal structure of the main vessel after lifting the closure element of the main vessel.

Thus the present invention provides a solution to the problems mentioned above, namely the disassembly (for example to perform a repair or replacement operation) of all or part of the components of the internal structure of the reactor vessel.

The loop reactor reactor reactor according to the invention comprises a particular arrangement of cooling liquid metal passage pipes connecting the component vessels and the reactor vessel, allowing thus the complete dismantling of the internal structures necessary in case of repair of an element. These pipes are concentric and the flow coming into contact with the main tank is cold, the hot heat transfer fluid leaving the tank being placed in the center. It will be noted that in known configurations of RNR according to the prior art, the pipes for supplying the cold liquid metal under pressure penetrate into the main tank in its upper part and go down to supply the bed base with cold liquid metal. Generally, to avoid placing the taps under the core level, the cold piping passes through the hot heat transfer fluid of the main vessel which causes heat loss, loss of compactness and increases the thermomechanical loadings relatively importantly. The hot liquid metal flows towards the intermediate exchangers of the component tank by hot pipes also placed in the upper part of the main tank. The pipes are usually connected by direct tapping on the main tank. There is a second configuration of inverted U-shaped liquid metal transfer piping passing through the top closure of the main vessel.

Furthermore, in the reactor vessel according to the invention, the core feed is performed by an annular collector formed by the main vessel and the inner vessel without adding specific structures.

The particular arrangement of the concentric pipes and the annular manifold allows the maintenance of the main vessel and branch pipes of the low temperature inlet piping (ie 400 ⁰ C). The reactor vessel according to the invention may also have one or more of the following characteristics, considered individually or in any technically possible combination:

the connection and disconnection means are made by piston seals; the interface of said at least one piston seal with said outlet pipe is a labyrinth interface;

the connection and disconnection means are made by bellows; - The core support means are formed by a bed base on which the heart is placed, said bed resting on a decking, said decking being supported on an annular flange at the bottom of said main vessel;

- The main vessel comprises a flange and the core support means are formed by a bed base on which the core is placed, said bed resting on a decking, said deck being suspended in said main vessel by said inner shell resting on the flange the main tank;

- The reactor vessel comprises sealing means between said manifold and the internal volume of said inner vessel;

the seal of said annular manifold is formed by at least one piston seal;

said at least one piston seal is associated with a labyrinth system;

- The main vessel comprises a flange and the seal of said annular collector is formed by three unclosed circular piston seals, each opening is oriented at 120 ° from the previous one;

- Sealing said annular collector is achieved by the presence of a metal / metal contact between said inner ring and said flange of said main vessel; - The reactor vessel comprises means for depressurizing the bottom of said main vessel;

the depressurization means comprise at least one labyrinth system and at least one candle;

said means for supporting the core are formed by a bed base on wherein said core is laid, said bed base having an outer ferrule extending said inner ferrule, said outer ferrule having at least one annular supply port of said heat transfer fluid bed; - The reactor vessel comprises sealing means between said manifold and the internal volume of said inner vessel and in that said inner shell forms in its upper part an extension located above said sealing means creating a second annular cooling space with said main tank; the second annular space has at least one orifice allowing the cold coolant to enter an internal volume of said inner vessel receiving the hot heat transfer fluid;

- The second annular cooling space is below the upper level of the heat transfer fluid for all operating regimes of the nuclear reactor.

The present invention also relates to a method of disassembly of the internal structure of a reactor vessel according to the invention comprising the following steps:

disconnecting said inner vessel and said outlet pipe via said connection and disconnection means; disassembly of the inner ferrule;

- dismantling of the bed base;

- disassembly of the decking.

Other features and advantages of the invention will emerge clearly from the description which is given below, as an indication and in no way limiting, with reference to the appended figures, among which:

Figure 1 is a sectional representation along a vertical plane of a reactor vessel of a loop RNR according to a first embodiment of the invention. FIG. 2 is a top view of the reactor vessel of a loop RNR as shown in FIG. 1.

FIG. 3 is a representation in section along a vertical plane of a reactor vessel of a loop RNR according to a second embodiment of the invention.

Figure 4 shows an enlargement of a portion of the reactor vessel shown in Figure 1 showing the connection means and disconnection between the inner vessel and the outlet pipe.

FIG. 1 represents a vertical sectional view of a reactor vessel 100 of a looped RNR comprising:

- A main vessel 1 of substantially cylindrical shape with a central vertical axis (X) having a curved bottom 16;

- A horizontal closing slab 28 of central axis (X) of great thickness, of the order of 800mm; a cylindrical pipework 10 of horizontal central axis (Y) for entering the heat transfer fluid 25:

a cylindrical pipe 1 1 of horizontal central axis (Y) of heat transfer fluid outlet 25.

The main tank 1 closed by the slab 28 in its upper part, contains:

a core 22 formed by fuel assemblies 32;

an internal structure comprising:

An inner vessel 2 of substantially cylindrical shape with a vertical central axis (X) formed of one or more ferrules; A bed base 5 supporting the heart 22;

A decking 14 supporting the bed base 5;

A recuperator 23 resting in the bottom 16 of the tank;

a fuel handling mechanism 19;

a heat transfer fluid of the type liquid-cooling metal 25 such only sodium;

a sealing system provided by piston seals 4;

- a labyrinth system 17;

- candles 18; - Connection and disconnection means 24 between the cylindrical pipe 1 1 and the inner vessel 2.

a heat exchanger 35 of the DRC (Direct Reactor Cooling) type.

The reactor core 22 and the entire internal structure are immersed in the liquid coolant metal 25, filling the main tank 1 to an upper limit level 26; the level of liquid sodium 25 of the main vessel 1 is a dynamic level which is established in the vicinity of the upper level indicated by the reference 26.

The interior volume of the main tank 1, between the upper level

26 liquid liquid metal 25 consisting of liquid sodium and the lower surface of the closure slab 28 is filled with an inert gas

27 constituted in particular by argon. Argon 27 has the advantage of being denser than air, which limits oxygen inputs into the circuit during the opening of an orifice.

The slab 28 is traversed in its central part by an orifice in which is mounted a rotating plug 21 carrying the loading machine or pantograph 19 of the reactor for handling the fuel assemblies 32 and a set 20 called lid heart cover disposed above the core 22 of the reactor and having instrumentation means for making measurements in the heart 22. The core 22 is formed by hexagonal fuel assemblies

32, arranged in a triangular pitch, whose lower part called foot, is engaged in the welded structure 5 called bed base and more precisely in candles 33. The feet of the fuel assemblies 32 and the candles 33 are provided with calibrated orifices to ensure a suitable distribution of liquid sodium 25 in the different fuel assemblies 32, depending on their power.

The bed base 5 is generally formed by two plates pierced with as many holes as assemblies to supply liquid sodium. It provides the stiffness necessary to maintain the network in the same horizontal plane. The bed base 5 is supported on the second welded structure 14 called deck resting itself on an annular-shaped flange 15 called core support, in the lower part of the main vessel 1. The core support 15 also supports the recuperator 23 disposed below the decking 14: this recuperator 23 makes it possible to recover the molten core (also called corium) in case of fusion of the core 22; a redundant support can also be provided directly under the decking 14.

In this configuration called "heart posed" the heart is carried by the decking 14 itself placed in the lower part of the main vessel 1 on the annular flange 15.

The inner vessel or inner shell 2 of vertical central axis (X), is housed inside the main vessel 1 delimiting with the inner wall of the main vessel 1 an annular collector 3, without adding specific structures. The inner vessel 2 also defines with its inner wall an internal volume 30 containing the liquid sodium 25 coming out of the core 22.

The internal manifold 3 is under an average pressure of 0.6 MPa distributed over the walls so that the inner shell 2 supports an external pressure of 0.6 MPa and the main tank supports an internal pressure of 0.6 MPa.

In the upper part of the annular collector 3, a calibrated leakage flow is provided by a circulation orifice 9 in a second upper annular space 7 extending the annular collector 3. This space is formed by an extension 8 of the inner ferrule 2 at the upper part comprising the orifice 9 allowing the cold liquid sodium to flow into the internal volume 30 above the core 22. The upper annular space 7 thus created, forms a flooded type of weir, located below the upper level 26 of liquid sodium 25 The seal of the annular manifold 3 between said annular manifold 3 and the internal volume 30 is provided by the piston seals 4 in the upper part and by the labyrinths 17 in the lower part of the main vessel 1. The two interfaces of the piston seals 4 in upper part can also present labyrinth systems. A labyrinth designates a succession of chambers and chokes present at the interface of two walls thus limiting the flow rate of a fluid circulating therein.

Piston seals 4, are autoclave piston rings of circular shapes not closed and large diameter of the order of 6.2 meters. To seal between the inner manifold 3 and the internal volume 30 of the main vessel 1, several piston seals are required, ideally three in number. The three piston seals 4, each opening of which is oriented 120 degrees from the previous, make it possible to obtain the required seal. However, the seal is not absolute, piston seals 4 can feed the upper annular collector 7, using a calibrated leakage flow.

The inlet and outlet pipes 10 and 1 1 of the liquid sodium 25 connecting the main vessel 1 and the component tank, not shown, are concentric along the horizontal central axis (Y) perpendicular to the central axis (X) of the main tank 1, and are connected to the main tank 1 above the core 22. The outer inlet pipe 10 surrounds the outlet pipe 1 1 and thus delimits an inlet volume 12 of the cold liquid sodium with the external wall of the outlet pipe 1 1. An outlet volume 13 of the liquid sodium 25 is delimited by the internal wall of the outlet pipe 1 1. The inlet volume 12 communicates with the annular collector 3 and the outlet volume 13 communicates with the internal volume 30.

Since these pipes 10, 1 1 are concentric, the flow coming into contact with the main tank is cold, the hot liquid sodium leaving the tank being placed in the center.

The cold sodium inlet pipe 10 communicating with the primary pump in the component tank is connected to the main tank 1 by stitching. The welding of the connections on the cold inlet pipe 10 makes it possible to transmit the forces necessary for the displacement of the component (mobile) tanks in order to accommodate the expansions due to the temperature variations between the various operating states of the reactor vessel 100. The positioning of the concentric tappings is in an upper part of the main vessel 1. This particular positioning of the tappings, at the same level as those of the component vessels, makes it possible to limit the axial expansions due to the changes in the state of the liquid sodium 25 and to eliminate the risk of dewatering the heart in liquid sodium in case of breakage at the quilting.

The particular arrangement of the concentric pipes and the annular manifold allows the maintenance of the main vessel and branch pipes of the low temperature inlet piping (ie 400 ⁰ C). In normal operation, this configuration therefore makes it possible to keep the thick structures cold.

The outlet pipe 1 1, hot liquid sodium is connected to the inner vessel 2 by a sealing device 24 forming means of connection and disconnection and composed of joints type circular piston rings placed in the inlet volume 12 An enlargement of this device is shown with reference to FIG. 4. The connection and disconnection means 24 located in the inlet volume 12 are fixed on the inner shell 2 of the main tank 1 by bolting and are support on the outlet pipe 1 1. The pressure of the coolant 25 on the connection and disconnection means 24 ensures their maintenance on the outlet pipe 1 1 and the seal between the inlet volume 12 and the outlet volume 1 1. The sealing device 24 makes it possible to disconnect or connect from the inside of the main tank 1, the hot outlet pipes 1 1 with the inner tank 2. When the sealing device 24 is in place, it ensures also the continuity between the inlet volume 12 and the annular collector 3. The sealing devices 24 are released by pushing along the horizontal central axis (Y) of the pipes 10, 1 1 concentric, thus releasing the connection between the tank internal 2 and the outlet pipe 1 1; disassembly of the inner ferrule 2 and other elements of the internal structures is then possible.

The sealing device 24 formed by the circular piston seal type seals can be associated with a labyrinth system at the interface of the piston seal with the outlet pipe 1 1. It can also be used as connecting means and disconnection of bellows type systems; these systems nevertheless have some disadvantages of space and disassembly.

The primary pumps of the component vessel circulate the liquid sodium 25 in the cold piping 10 and more precisely through the inlet volume 12. The inlet volume 12 communicating with the annular manifold 3, feeds the annular collector 3 into liquid sodium.

The annular collector 3 thus ensures the cooling of the main vessel 1 during operation of the nuclear reactor by the passage of cold liquid sodium. The annular collector 3 also supplies cold liquid sodium to the core 22 of the reactor, by first supplying the bed base 5 situated below the inner shell 2. The bed base 5 is supplied at its periphery with the aid of of orifices 6 in the outer shell 36 of said bed base 5. The bed base 5 then feeds the candles 33 provided with calibrated orifices in which the feet of the assemblies 32 are placed. The calibrated orifices make it possible to ensure a suitable distribution of the liquid sodium 25 in the various fuel assemblies 32. The cold liquid sodium then passes through the core 22 into the vertical direction and from bottom to top by heating in contact with the assemblies 32 of the core 22. Through the fuel assemblies 32, the liquid sodium 25 is heated to an average temperature of 550 ° C.

The hot liquid sodium exiting the core 22 enters the hot piping 11, and more precisely the outlet volume 13 communicating with intermediate exchangers in the component tank, external to the main tank 1. The hot liquid sodium cools in contact with a secondary liquid metal, usually also constituted by liquid sodium, and leaves at a temperature below its inlet temperature in the intermediate exchanger. The secondary liquid sodium heated in contact with the primary liquid sodium is used to produce steam inside steam generators located in a tertiary circuit, outside the component tank.

Part of the cold sodium of the annular collector 3 reaches an annular space, delimited by the inner wall of the main vessel 1 and the outer wall of the decking 14, forming a labyrinth system 17. The labyrinth system 17 seals and maintaining the annular manifold 3 under pressure. The labyrinth system 17 also reduces the pressure present in the bottom of the tank manifold by means of a leakage flow and communication candles (18). The annular space also ensures a centering of the decking 14 in the main vessel 1. The presence of a low pressure (typically 0.02 MPa) in the bottom of tank 16 is necessary in order to avoid a lifting effect of the structure internal, including decking 14. In addition to the labyrinth system 17 for lowering the tank bottom pressure 16, candles 18, located at the feet of the fuel assemblies 32, allow the cold liquid sodium at the bottom of the tank 16 to reach the hot liquid sodium above the core. 22. The residual pressure at the bottom of the tank 16 and in the decking member 14 is thus limited.

The average pressure of 0.6 MPa and the sealing of the annular manifold 3 between the annular collector 3 and the internal volume 30 are provided by the piston seals 4 in the upper part and by labyrinths 17 in the lower part of the main tank 1. this sealing of the manifold 3 is not absolute, because the piston seals 4 and the labyrinths 17 has calibrated leak rates. The calibrated leakage flow of the piston seals 4 in the upper part allows the upper annular collector 7 to be fed. The upper annular space 7 allows cooling of the main vessel 1 in its upper part. As already explained above, the circulation orifice 9 of the upper annular collector 7 located below the limit level 26 of the liquid sodium 25 allows the cold liquid sodium 26 to flow into the internal volume 30 and to join the hot liquid sodium 25 of the core 22 excluding the introduction of argon gas 27 into the liquid sodium 25.

The diameter of the main vessel 1 is most often limited to a value close to 7 meters. This diameter limits the size of the components and internal structures thus promoting the dismantling and transportability of the elements of the internal structure. The total height of the main vessel 1, determined mainly by the axial critical path of the loop RNR, is close to 17 meters, which makes it possible to obtain a large compactness of the main vessel 1.

FIG. 2 shows a top view of the reactor vessel 100 of a loop RNR as shown in FIG. The rotating plug 21 of the reactor vessel 100 is fixed on the slab 28 of the reactor, on a bearing or on rollers, and is provided with rotating seals making it possible to maintain a seal both during a handling regime (reactor stopped). than in normal operation. The rotating plug 21 is traversed by the pantograph 19 at its periphery and by the heart cover plug 20 eccentric with respect to the vertical axis of the rotary plug 21. Thus the rotation of the rotatable cap assembly 21 and heart cover cap 20 and the deployment of the pantograph make it possible to reach all the assembly positions and thus the extraction of the worn assemblies of the core 22 and their replacements by new assemblies.

Slab 28 is traversed in its peripheral portion by heat exchangers 35 type DRC (Direct Reactor Cooling) used for the evacuation of the residual power in case of failure of the primary circuit. In this illustration, the reactor vessel 100 comprises two heat exchangers 35 of the DRC type.

In this representation, the RNR loops removable according to the invention, has three loops B1, B2, B3, that is to say three component vessels connected to the main vessel 1 by three concentric pipe systems 10, 1 1.

FIG. 3 represents a vertical sectional view of a reactor vessel

101 of a loop RNR according to a second embodiment of the invention with a different disposition of the core 22; the heart of the reactor

22 is hung and not laid as we have detailed previously with reference to Figure 1.

The reactor vessel 101 is identical to the reactor vessel 100. The reactor vessel 101 comprises substantially the same elements mentioned above for the vessel 100 but with a different arrangement of the internal structure: the common elements bear the same numbers of the reactor vessel 100. reference.

In this configuration called "hung heart", the heart is carried by the deck 14, suspended in the main vessel 1 by the inner shell 2, itself attached to the main vessel 1 by a flange 34. The bed base 5 is supported on the decking 14, said decking 14 being fixed to the inner ferrule 2. The connection between the decking 14 and the inner ferrule 2 is generally a bolting-type mechanical connection but may also be made by welding. The inner ferrule 2 is supported on the main vessel 1 by means of the flange 34 in the upper part of the main vessel 1.

The flange 34 also makes it possible to ensure the necessary sealing in the annular manifold 3 by means of a metal / metal support generated between the inner shell 2 and the main tank 1.

The recuperator 23 is disposed below the decking 14 which is supported on a redundant support 29 formed by an annular flange located on the lower cylindrical portion of the main vessel 1. The redundant support 29 doubles the support of the heart in the case of a possible incident.

We will now describe an example of disassembly of the elements of the internal structure of a reactor vessel as shown in Figure 1 or 2.

The slab 28 can be lifted only after unloading the core 22, lifting the heat exchangers 35 of the DRC type, the pantograph 19, the core lid 20, and the plug. These disassembly operations are carried out possibly after complete emptying of the liquid sodium 25 of the main vessel 1 and preferably in an inert gas atmosphere.

At first, it is necessary to disconnect the outlet pipe 1 1 and the inner shell 2 held together by the means of 24. The piston seals are pushed axially into the inlet volume 12. The offset of the piston seal thus created frees the connection between the inner shell 2 and the outlet pipe 1 1 of the liquid sodium 25. it is possible to lift and extract the inner shell 2 by simple lifting, because this element does not support other elements of the internal structure; it is however necessary to remove the connection between the bed base 5 and the inner shell 2, in the case of a RNR with hinged-core loops (Figure 2), which is usually a bolt-type mechanical connection; this operation requires laying the bed base 5 / decking 14 on the redundant support 29. The extraction of the bed 5 then poses no difficulty, the bed base 5 resting freely on the deck 14. After dismounting the elements mentioned, it is it is possible to disassemble the decking 14 resting solely on the flange 15 of the main tank 1. In the case of a RNR with hung-core loops, the bed base 5 and the deck 14 are mechanically secured by a bolting system. They can then be extracted together or disconnected. Finally, it is possible to disassemble the recuperator 23 which rests on the flange of the support 15 (or 29) secured to the bottom of the main vessel 1. The extraction of the elements of the internal structure can be carried out without dismantling welded or mechanical connections (except in the case of a hung heart, which requires the dismantling of a mechanical link). Indeed, each of the elements of the internal structures rests with the aid of a holding part or support on another element of the internal structures or on part of the inner surface of the main vessel 1. The surfaces of the parts likely to come into bearing contact or in rubbing contact with other parts generally comprise an aluminizing treatment of the surfaces or a coating of a stellite alloy containing cobalt. However, aluminization treatment will be preferable to stellite type coating because it is desirable to avoid as much as possible the presence of cobalt inside the tank of a nuclear reactor.

It should be noted that the support planes of the internal structural elements on the inner surface of the main tank 1 are located in the lower part of the main tank 1, in which the liquid sodium 25, during the operation of the nuclear reactor, is at a temperature of 400 ° C.

Thus, the object of the invention is to provide a reactor vessel of a compact loop RNR enabling a change or replacement of all or part of the elements of the internal structure for the purpose of a repair operation. .

For this, the architecture of the loop RNR according to the invention is based on an annular collector configuration for supplying the core and for cooling the periphery of the main vessel, on short and concentric primary pipes as well as on removable sealing devices and sliding sealing systems equipped with piston seals and labyrinths.

Claims

1. Reactor tank (100) of a nuclear fast loop neutron reactor comprising a main tank (1) containing: - a core (22) composed of fuel assemblies (32) able to be cooled by a coolant (25). )

- a heat transfer fluid inlet pipe (10) for the inlet of said heat transfer fluid (25) into said main tank (1) before its heating in contact with said fuel assemblies (32), - an outlet pipe (1 1 ) heat transfer fluid (25), for the evacuation of said coolant (25) after its heating in contact with said fuel assemblies (32),

support means (5) for said core (22), said reactor vessel (100) being characterized in that - said inlet (10) and outlet (1 1) piping are arranged in a concentric manner, said piping inlet (10) surrounding said outlet pipe (1 1) and thus delimiting with the outer wall of said outlet pipe (1 1) an inlet volume (12) of said coolant (25); said reactor vessel (100) comprises: an internal vessel (2) housed inside said main vessel;

(1) and delimiting with the inner wall of said main vessel

(1) an annular shaped collector (3), said inner vessel (2) being connected to said outlet pipe (1 1) so that said inlet volume (12) is in communication with said collector (3), o connection and disconnection means (24) between said inner vessel (2) and said outlet pipe (1 1) of the coolant (25).

2. reactor vessel (100) of a fast loop neutron nuclear reactor according to claim 1 characterized in that said connection and disconnection means (24) are formed by piston seals.

3. reactor vessel (100) of a fast loop neutron nuclear reactor according to claim 2 characterized in that the interface of said at least one piston seal with said outlet pipe is a labyrinth interface.

4. reactor vessel (100) of a fast loop neutron nuclear reactor according to claim 1 characterized in that said connection and disconnection means are formed by bellows.

5. reactor vessel (100) of a nuclear fast neutron loop reactor according to one of claims 1 to 4 characterized in that said support means (5) of the core are formed by a bed base on which said core (22). ) is placed, said bed base (5) resting on a deck (14), said deck being supported on an annular flange

(15) housed at the bottom of said main tank (1).

6. reactor vessel (100) of a fast neutron nuclear reactor with loops according to one of claims 1 to 4 characterized in that said main vessel comprises a flange (34) and said support means (5) of the core are formed by a bed base on which said core (22) is laid, said bed base (5) resting on a deck (14), said deck (14) being suspended in said main tank (1) by said inner shell (2) in support on said flange (34) of said main vessel (1) -

7. reactor vessel (100) of a fast neutron nuclear reactor loop according to one of claims 1 to 6 characterized in that it comprises sealing means between said collector (3) and the internal volume (30). ) of said inner vessel (2).

8. reactor vessel (100) of a fast neutron nuclear reactor with loops according to claim 7 characterized in that the seal of said annular collector (3) is formed by at least one piston seal

(4).

9. reactor vessel (100) of a fast loop neutron nuclear reactor according to claim 8 characterized in that said at least one piston seal (4) is associated with a labyrinth system (17).

10. reactor vessel (100) of a fast loop neutron nuclear reactor according to claim 9 characterized in that the seal of said annular collector (3) is formed by three piston rings (4) circular not closed each opening is oriented at 120 ° from the previous one.

1. A reactor vessel (100) of a fast loop neutron nuclear reactor according to claim 7, characterized in that said main vessel comprises a flange (34) and the sealing of said annular manifold (3) is achieved by the presence a metal / metal contact between said inner shell (2) and said flange (34) of said main tank (1) -

12. reactor vessel (100) of a nuclear fast neutron loop reactor according to one of claims 1 to 1 1 characterized in that said reactor vessel (100) comprises means for depressurizing the bottom of said main vessel (1). ).

13. reactor vessel (100) of a fast loop neutron nuclear reactor according to claim 12 characterized in that said depressurization means comprise at least one labyrinth system and at least one candle (18).

14. Reactor tank (100) of a nuclear reactor fast neutron loop according to one of claims 1 to 13 characterized in that said support means (5) of the core are formed by a bed base on which said core (22). ) is placed, said bed base (5) having an outer shell (36) extending said inner shell (2), said outer shell

(36) having at least one annular orifice (6) for supplying said bed base (5) with heat transfer fluid (25).

15. reactor vessel (100) of a fast loop neutron nuclear reactor according to one of claims 1 to 14 characterized in that it comprises sealing means between said collector (3) and the internal volume (30). ) of said inner vessel (2) and in that said inner shell (2) forms in its upper part an extension (8) located above said sealing means creating a second annular cooling space (7) with said main vessel (1).

16. Reactor tank (100) of a fast loop neutron nuclear reactor according to claim 15, characterized in that said second annular space (7) has at least one orifice (9). allowing the cold coolant (25) to enter an internal volume (30) of said inner vessel (2) receiving the hot heat transfer fluid (25).

17. reactor vessel (100) of a fast loop neutron nuclear reactor according to one of claims 15 to 16 characterized in that said second annular cooling space (7) is below the upper level (26) of the heat transfer fluid (25) for all operating modes of the nuclear reactor.

18. A method of disassembling the elements of the internal structure of a reactor vessel (100) of a fast loop neutron nuclear reactor according to one of claims 1 to 17, said internal structure comprising: - a bed base (5) ;

- a decking (14); said disassembly method being characterized in that it comprises the following steps:

disconnection of said inner tank (2) and of said outlet pipe (1 1) via said connection and disconnection means

(24); disassembly of the inner ferrule (2);

- dismantling of the bed base (5);

- disassembly of the decking (14).