FR3080704A1 - NUCLEAR REACTOR COMPRISING AN ANNULAR CHANNEL - Google Patents

Abstract

The invention relates to a nuclear reactor, comprising: - a vessel containing a fluid, the vessel defining an interior volume; - a heart comprising nuclear fuel, the heart being arranged in the interior volume of the vessel; - At least one clean pump to circulate the fluid through the heart; and - at least one pipe (22) comprising an inlet and an outlet for the circulation of the fluid. The nuclear reactor further comprises an annular channel (42) defining a closed fluid circulation loop. The or each pump is fluidically connected upstream of the annular channel (42) by at least one of the pipes (22). The annular channel (42) is located upstream of the core. The annular channel (42) has a fluid passage restriction (46) at the outlet of the or each pipe (22).

Description

Nuclear reactor including an annular channel

The present invention relates to a nuclear reactor comprising a vessel containing a fluid, the vessel defining an interior volume; a core comprising nuclear fuel, the core being arranged in the interior volume of the vessel; at least one pump capable of circulating the fluid through the heart and at least one piping comprising an inlet and an outlet for the circulation of the fluid.

In particular, the nuclear reactor is a fast neutron nuclear reactor. By "fast neutrons" is meant neutrons which are not moderate, as opposed to thermal neutrons slowed down for example by water in conventional pressurized water reactors. The heat transfer fluid used to extract power from the heart is, in particular, liquid sodium.

Nuclear reactors of the aforementioned type are known, in which the liquid sodium recirculates cyclically in the vessel in order to extract the heat from the heart. The tank is separated into two zones, namely a cold collector and a hot collector. The pumps take the liquid sodium from the cold collector and inject it directly into the heart through a box spring supporting the heart. The liquid sodium heats up on contact with the heart and opens into the hot collector. The hot sodium exchanges its heat with a secondary circuit and recirculates in the cold collector. The heat extracted by the secondary circuit is transformed into electricity in the tertiary circuit using, among other things, a turbine.

Thus, several pipes directly connect the pumps to the box spring. The sodium is injected radially into the box spring and goes up towards the heart. In the event of accidental rupture of one of these pipes, part of the flow injected by unaffected pipes is diverted through the breach of the damaged pipe and returns directly to the cold collector instead of passing through the heart. The flow through the heart is then reduced and therefore the heat extracted from the heart also.

This leads, in known manner, to oversize the number of pumps necessary in order to guarantee a sufficient flow through the core guaranteeing the integrity of the nuclear reactor.

However, this oversizing entails significant construction costs and complicates the internal structure of the nuclear reactor.

The object of the invention is therefore to propose a nuclear reactor in which, in the event of an accidental rupture of a supply pipe of the heart, the diverted flow of the heart is reduced in order to allow a less complex internal structure while guaranteeing a equivalent level of safety and limiting pressure losses.

To this end, the subject of the invention is a nuclear reactor of the aforementioned type, the reactor comprising the nuclear reactor further comprises an annular channel defining a closed loop for circulation of the fluid, the or each pump being fluidly connected upstream of the annular channel by at least one of the pipes, the annular channel being located upstream of the heart, the annular channel having a restriction of passage of the fluid at the outlet of the or each pipe.

Such an annular channel allows rapid circulation of the rotating fluid in the annular channel. In the event of a breach, the fluid present in the annular channel generates a suction at the outlet of the affected piping. In particular, the restriction of passage of the fluid leads to a local acceleration of the fluid and to a significant reduction in the static pressure of the fluid by the Venturi effect. The difference in static pressure between the fluid in the annular channel and the static pressure at the outlet of the breach is therefore greatly reduced, which leads to a reduction in the flow diverted by the breach. The annular channel has a simple structure and causes low pressure losses.

According to particular embodiments, the nuclear reactor includes one or more of the following characteristics:

- The fluid is liquid sodium and in which the or each pump is arranged in the interior volume of the tank;

- The nuclear reactor includes a maximum of two pumps capable of circulating the fluid through the heart;

- each pump is connected to the annular channel by at least two pipes;

- The nuclear reactor comprises a box spring supporting the core, the bed base comprising an external ring, the annular channel being arranged in the internal volume defined by the external ring;

- The maximum transverse dimension of the outer shell is greater than the maximum transverse dimension of the heart;

- the base includes a porous inner ferrule capable of being traversed by the fluid and disposed in the interior volume defined by the exterior ferrule, the annular channel being defined by the volume between the exterior ferrule and the interior ferrule, the interior ferrule defining a volume interior placed downstream of the annular canal and upstream of the heart;

- The ratio between the maximum transverse dimension of the outer shell and the maximum transverse dimension of the inner shell is between 120% and 150%;

- the inner shell has a surface porosity of between 10% and%;

- the inner ferrule includes holes, each hole having the shape of a long channel extending along an axis forming an angle between 0 ° and 45 ° with the normal of the inner ferrule;

- The nuclear reactor comprises, for the or each pipe, a deflector placed at the outlet of said pipe directing the fluid tangentially to the annular channel in a plane of horizontal section;

- For the or each pipe, the section of said pipe leading to the annular channel extends along a main axis, the main axis having an angle of incidence relative to the normal to the annular channel of between 30 ° and 90 ° ;

- The nuclear reactor comprises, for the or each piping, an elbow placed at the outlet of said piping in the annular channel and advantageously orienting the fluid tangentially to the annular channel in a plane of horizontal section.

Other characteristics and advantages of the invention will emerge from the detailed description which follows, given only for information and in no way limitative, with reference to the appended figures, among which:

- Figure 1 is a simplified schematic representation of a nuclear reactor according to the invention;

- Figure 2 is a horizontal section of the bed of the nuclear reactor of Figure 1;

- Figure 3 is a horizontal section of the bed of the nuclear reactor of Figure 1 according to an embodiment different from Figure 2;

FIG. 4 is a horizontal section of the bed of the nuclear reactor of FIG. 1 according to an embodiment different from FIGS. 2 and 3.

In what follows, the terms "upstream", "downstream", "inlet" and "outlet" are generally understood with respect to the direction of circulation of the fluid in normal operation of the nuclear reactor. Thus, a first component upstream of a second component is first traversed by the fluid which then flows through the second component.

A nuclear reactor 10 is shown in FIG. 1.

The nuclear reactor 10 advantageously comprises a primary circuit 12, a secondary circuit 13 and a tertiary circuit 14.

As can be seen in FIG. 1, the nuclear reactor 10 comprises a tank 16, a core 18, at least one primary pump 20 and at least one primary pipe 22.

The nuclear reactor 10 advantageously comprises an intermediate exchanger 23. Advantageously, the primary circuit 12 further comprises a bed base 24 supporting the core 18.

The tank 16, the core 18, the at least one primary pump 20, the at least one primary pipe 22 and advantageously the intermediate exchanger 23 and the bed base 24 make up the primary circuit 12.

The tank 16 defines an interior volume. Advantageously, the nuclear reactor 10 is of the integrated type. By "integrated" is meant that all of the components of the primary circuit 12 are contained in the interior volume of the tank 16.

As a variant, the nuclear reactor 10 is a loop reactor in which part of the components of the primary circuit 12 are located outside the interior volume of the vessel 16.

The tank 16 advantageously has a shape of surface of revolution around a vertical main axis A-A ’. In particular, the tank 16 comprises a spherical cap 26, a cylindrical part 28 and a tank cover 30 placed respectively from bottom to top along the axis A-A ’.

“Cylinder” is understood to mean a surface obtained by the union of all the lines having the same direction, called generatrices, and intersecting a given curve, called the director. Advantageously, the director of the cylindrical part 28 has a circle shape and the axis A-A ’is the central axis of the cylindrical part 28.

The tank 16 contains a primary fluid.

The primary fluid is advantageously a heat transfer fluid capable of transporting heat.

The primary fluid is advantageously liquid sodium.

Alternatively, the primary fluid is water, molten lead, or helium.

The internal volume of the tank 16 is separated into two parts by a wall called a step 32. The lower part is called the cold collector 34 and the upper part of the tank 16 is called the hot collector 36. "Upper" and "lower" are defined with respect to the axis A-A '.

The vessel 16 is arranged inside a concrete reactor building, not shown.

The heart 18 is placed in the interior volume of the tank 16. In particular, the heart 18 crosses the step 32. The heart 18 is therefore located between the cold collector 34 and the hot collector 36.

The core 18 includes nuclear fuel.

In particular, the core 18 comprises a plurality of nuclear fuel assemblies.

The heart 18 is suitable for being traversed by the primary fluid. The primary fluid is able to extract the heat produced by nuclear fuel. Thus, the primary fluid coming from the cold collector 34 is able to pass through the core 18 and to heat up in contact with the nuclear fuel and then to emerge in the hot collector 36.

The heart 18 advantageously has a cylindrical shape. Advantageously, the director presents a circle shape and the axis A-A ’is the central axis of the heart 18.

The or each primary pump 20 is capable of circulating the primary fluid through the heart 18.

Advantageously, the or each primary pump 20 has a power between 500 kW and 2500 kW, in particular between 500 kW and 1000 kW.

Advantageously, the or each primary pump 20 is arranged in the interior volume of the tank 16.

In particular, each primary pump 20 is located in the cold manifold 34.

The or each primary pump 20 is therefore placed upstream of the bed base 24.

Advantageously, the nuclear reactor 10 comprises at least two primary pumps 20 in order to ensure a higher primary fluid flow rate through the core 18 and redundancy in the event of an incident on one of the primary pumps 20.

In an advantageous embodiment, the reactor 10 comprises a maximum of two primary pumps 20. This allows a reduction in construction costs while ensuring sufficient safety thanks to the invention as will be explained below.

The intermediate exchanger 23 is a heat exchanger between the primary circuit 12 and the secondary circuit 13.

The intermediate exchanger 23 comprises a primary inlet fluidly connected with the hot manifold 36 and a primary outlet fluidly connected with the cold manifold 34. The intermediate exchanger 23 allows the circulation of the primary fluid from the primary inlet to the primary outlet, the primary fluid yielding its heat to the secondary circuit 13 by circulating from the primary inlet to the primary outlet.

The intermediate exchanger 23 further comprises a secondary inlet and a secondary outlet fluidly connected to each other and fluidly separated from the primary circuit 12.

The bed base 24 is placed in the interior volume of the tank 16.

The bed base 24 supports the assemblies of the heart 18 and ensures their positioning while allowing the circulation of the primary fluid through the heart 18.

The box spring 24 is therefore placed upstream of the heart 18.

The bed base 24 includes an outer ring 38.

The outer shell 38 advantageously has a cylindrical shape. Advantageously, the director has a circle shape and the axis A-A ’is the central axis of the outer shell 38.

The outer shell 38 advantageously has a thickness of between 20 mm and 50 mm.

Advantageously, the outer shell 38 has a diameter in a cross section at the axis A-A ’between 5000 mm and 7000 mm.

In particular, the maximum transverse dimension of the outer shell 38 is advantageously greater than the maximum transverse dimension of the heart 18, as visible in FIG. 1.

The outer shell 38 defines an interior volume.

Advantageously, the bed base 24 further comprises an inner ferrule 40 disposed in the interior volume of the outer ferrule 38.

The inner shell 40 advantageously has a cylindrical shape. Advantageously, the director has a circle shape and the axis A-A ’is the central axis of the inner ring 40.

Advantageously, the lower ferrule 40 has a diameter in a cross section at the axis A-A 'of between 3300 mm and 5300 mm.

In particular, the diameter of the inner ferrule 40 is less than the diameter of the outer ferrule 38.

Advantageously, the ratio between the maximum transverse dimension of the outer shroud 38 and the maximum transverse dimension of the inner shroud 40 is between 120% and 150%.

The inner shell 40 is fluidly porous. The inner shell 40 is therefore suitable for being traversed by the primary fluid.

The inner shell 40 advantageously has a grid shape.

The inner ferrule 40 includes holes 41, each hole 41 being suitable for the primary fluid to pass through.

In one embodiment, as can be seen in FIGS. 2 and 3, each hole 41 has the shape of an elongated channel extending along an axis parallel to the normal of the inner ferrule 40.

In an advantageous variant, as can be seen in FIG. 4, each hole 41 has the shape of an elongated channel extending along an axis forming an angle between 0 ° and 45 ° with the normal of the pore ferrule 40. In particular, each hole 41 is oriented in the direction of circulation of the primary fluid in the annular channel 42.

Thus, the passage of the primary fluid through the porous shell 40 is carried out with reduced pressure drops.

In particular, the inner shell 40 has a surface porosity of between 10% and 50%.

The interior shroud 40 defines an interior volume 44. The interior volume 44 of the interior shroud 40 is fluidly connected to the heart 18. The interior volume 44 is located immediately under the heart 18 and communicates fluidically directly with the heart 18.

The nuclear reactor 10 comprises an annular channel 42. As can be seen in FIGS. 2 to 4, the annular channel 42 defines a closed loop for circulation of the primary fluid around the axis A-A ’.

The annular channel is located upstream of the heart 18.

The annular channel 42 is placed in the bed base 24. In particular, the annular channel 42 is located on the periphery of the bed base 24.

The height of the annular channel 42 along the axis A-A ’is between 50% and 100% of the height of the inner ring 40.

The internal volume 44 is therefore placed downstream of the annular channel 42 and upstream of the heart 18.

The annular channel 42 is arranged in the interior volume of the exterior shell 38.

In particular, the annular channel 42 is defined by the volume located between the inner ferrule 40 and the outer ferrule 38.

Alternatively, the annular channel 42 has a toroidal shape.

The or each primary pump 20 is fluidly connected upstream of the annular channel 42 by at least one of the primary pipes 22.

The or each primary pipe 22 is a long, clean conduit for circulating the primary fluid.

The or each primary pipe 22 has an inlet and an outlet for the circulation of the primary fluid.

The inlet of the or each primary pipe 22 is fluidly connected to the respective primary pump 20. The outlet of the or each primary pipe 22 is connected to the annular channel 42.

In the example illustrated in FIGS. 2 and 3, the primary circuit 12 comprises four primary pipes 22 connected to the annular channel 42.

The or each primary pipe 22 comprises different sections. The section connected to the bed base 24 is advantageously cylindrical in shape and extends along a main axis.

As shown in FIGS. 2 and 4, the or each primary pipe 22 is connected orthogonally to the bed base 24. In particular, the main axis of the section connected to the bed base 24 coincides with the normal of the bed base 24.

As a variant, as can be seen in FIG. 3, for the or each primary pipe 22, the main axis of the section of the pipe 22 opening onto the annular channel 42 has, with the normal to the annular channel 42, a non-zero angle of incidence a , advantageously between 30 ° and 90 °.

Advantageously, each primary pump 20 is connected to the bed base 24 by two primary pipes 22. A tee or, as a variant, a Y-shaped connection, not shown, at the outlet of the primary pump 20 separates the primary fluid leaving the primary pump 20 between the two primary pipes 22.

The or each primary pipe 22 advantageously has a circular cross section. The or each primary pipe 22 advantageously has an outside diameter of between 300 mm and 600 mm.

The or each primary pipe 22 is made of a material comprising a metallic material, in particular an austenitic steel.

The annular channel 42 has a restriction on the passage 46 of the primary fluid at the outlet from the or each primary pipe 22.

The passage restriction 46 is a region of the annular channel 42 having a primary fluid passage section smaller than the passage section of the regions adjacent to the annular channel 42. The fluid passage section is defined orthogonally to the direction of circulation of the fluid .

In particular, the passage restriction 46 has a fluid passage section less than 90% of the maximum passage section of the annular channel 42, in particular less than 50% of the maximum passage section of the annular channel 42.

In an advantageous embodiment, as shown in FIG. 2, the or each primary pipe 22 comprises a deflector 48.

The deflector 48 is located at the outlet of the respective primary pipe 22.

The deflector 48 is therefore located downstream of the primary pipe 22.

The deflector 48 is a member making it possible to divert the flow of the primary fluid at the outlet of the primary pipe 22.

In particular, the deflector 48 is capable of orienting the primary fluid tangentially to the annular channel 42 in a plane of horizontal section.

Advantageously, the deflector 48 is of curved shape to limit the pressure drops. In particular, the deflector 48 has a concave shape downstream of the primary pipe 22. As can be seen in FIG. 2, all the deflectors 48 are oriented in the same direction in order to allow the circulation of the primary fluid in a closed loop. annular channel 42.

The deflector 48 projects from the primary pipe 22 and opens into the annular channel 42. The deflector 48 then limits the passage of the primary fluid and thus defines the passage restriction 46 of the primary fluid. The passage restriction 46 is then delimited between the deflector 48 and the inner shell 40.

As a variant, as visible in FIG. 3, one end 50 of the primary piping 22 situated on the side of the outlet is inserted into the annular channel 42.

The end 50 projects from the primary pipe 22 in the annular channel 42.

The end 50 extends in the same direction as the section of the primary pipe 22 connected to the directory channel 42.

The end 50 then limits the passage of the primary fluid and thus defines the restriction of passage 46 of the primary fluid.

The passage restriction 46 is then delimited between the end 50 and the inner shell 40.

As a variant, as visible in FIG. 4, the primary piping 22 comprises an elbow 51.

It is connected orthogonally to the bed base 24.

The elbow 51 is located at the outlet of the respective primary pipe 22.

The elbow 51 advantageously has the same diameter as the respective primary pipe 22.

As visible in FIG. 4, the elbow 51 is located in the annular channel 42.

The elbow 51 makes it possible to deflect the flow of the primary fluid leaving the primary pipe 22.

Advantageously, the elbow 51 is capable of orienting the primary fluid tangentially to the annular channel 42 in a plane of horizontal section.

The elbow 51 then limits the passage of the primary fluid and thus defines the restriction of passage 46 of the primary fluid. The passage restriction 46 is then delimited between the elbow 51 and the inner ring 40.

As a variant, the passage restriction 46 at the outlet of the primary pipe 22 is produced by any device limiting the passage section of the annular channel 42.

Obviously, the passage restriction 46 is located, as a variant, in the vicinity of the outlet of the primary pipe 22.

The secondary circuit 13 is suitable for circulating a secondary fluid. The secondary fluid is advantageously a heat transfer fluid capable of transporting heat.

The secondary fluid is advantageously liquid sodium.

Likewise, the tertiary circuit is suitable for circulating a tertiary fluid. The secondary fluid is advantageously a heat transfer fluid capable of transporting heat.

The tertiary fluid is advantageously water.

Alternatively, the tertiary fluid is a gas.

As can be seen in FIG. 1, the secondary circuit 13 comprises a steam generator 52, at least one secondary pipe 54 and at least one secondary pump 56.

The secondary piping 54 fluidly connects the secondary part of the intermediate exchanger 23, the steam generator 52 and the secondary pump 56.

The steam generator 52 is a heat exchanger between the secondary circuit 13 and the tertiary circuit 14.

The steam generator 52 comprises a secondary inlet fluidly connected with the secondary outlet of the intermediate exchanger 23 and a secondary outlet fluidly connected to the secondary pump 56.

The steam generator 52 allows the circulation of the secondary fluid from the secondary inlet to the secondary outlet, the secondary fluid yielding its heat to the tertiary circuit 14.

The steam generator 52 further comprises a tertiary inlet and a tertiary outlet fluidly connected to each other and fluidly separated from the tertiary circuit 14.

The steam generator 52 allows the circulation of the tertiary fluid from the tertiary inlet to the tertiary outlet. In particular, the steam generator 52 is capable of evaporating the water which enters the liquid state at the tertiary inlet in order to obtain water vapor at the tertiary outlet.

The secondary pump 56 is able to circulate the secondary fluid in the secondary circuit 13.

As visible in FIG. 1, the tertiary circuit 14 comprises at least one tertiary piping 58, a turbine 60, an alternator 62, a condenser 64 and a tertiary pump 66.

The tertiary piping 58 fluidly connects the tertiary part of the steam generator 52, the turbine 60, the condenser 64 and the tertiary pump 66.

The turbine 60 is fluidly connected to the tertiary outlet of the steam generator 52. The turbine 60 is a rotary device capable of transforming the kinetic energy of the tertiary fluid, in particular water vapor into mechanical energy to rotate a central shaft 68.

The central shaft 68 is linked to the alternator 62.

The alternator 62 is capable of transforming the mechanical energy of the central shaft 68 into electrical energy. The alternator 62 is suitable for sending electrical energy to an electrical network.

The condenser 64 is capable of condensing the vapor by heat exchange with a cold source external to the reactor 10, such as for example a river, a sea or an air cooler, not shown.

The tertiary pump 66 is able to circulate the tertiary fluid in the tertiary circuit 14.

The circulation of the primary fluid in the primary circuit 12 in normal operation will now be described.

The primary fluid, initially in the cold manifold 34, is sucked in by one of the primary pumps 20.

At the outlet of the primary pump 20, the primary fluid circulates in the associated primary pipe (s) 22 then opens into the annular channel 42.

In particular, the primary fluid is deflected by the deflector 48 and then circulates circumferentially in a direction substantially tangential to the outer shell 38.

Said primary fluid then mixes with the primary fluid injected by the other primary pipes 22 into the annular channel 42.

The annular channel 42 therefore makes it possible to homogenize the primary fluid before it is introduced into the heart 18. In fact, in a state-of-the-art reactor, the supply by the primary pumps 20 can be asymmetrical and cause heterogeneities. of temperature and speed in the bed base 24, and thus causing cooling of the nuclear fuel assemblies of the core 18 less efficient.

For example, the speed of the fluid in the annular channel 42 is, in normal operation, between 5 m / s and 12 m / s.

Part of the primary fluid flowing in the annular channel 42 passes through the porous inner shroud 40 and opens into the interior volume 44 of the inner shroud 40.

Then, the primary fluid rises along the axis A-A ’towards the heart 18.

For example, the speed of the primary fluid in the interior volume 44 is, in normal operation, less than 1 m / s.

The primary fluid then penetrates into the heart 18 and rises along the axis A-A ’.

The primary fluid heats up in contact with the nuclear fuel assemblies and opens into the hot manifold 36.

The primary fluid circulates from the primary inlet of the intermediate exchanger 23 to the primary outlet and exchanges its heat with the secondary circuit 13.

The primary fluid then recirculates in the cold collector 34.

The heat extracted by the secondary circuit 13 is transferred to the tertiary circuit 14 by the circulation of the secondary fluid from the secondary part of the intermediate exchanger 23 to the steam generator 52.

The tertiary fluid, in particular water, vaporizes in the tertiary part of the steam generator 52 and circulates towards the turbine 60. The turbine 60 and the alternator 62 transform the kinetic energy of the steam into mechanical energy then into energy sent to the electrical network.

The circulation of the primary fluid in the primary circuit 12 in the event of a breach on a primary pipe 22 will now be described.

The static pressure in the cold manifold 34 being lower than the static pressure in the primary piping 22, the breach in the primary piping 22 known as damaged causes a leakage of a part of the primary fluid towards the outside of the primary piping 22 directly in the cold collector 34 without passing through the core 18.

In the event of a major breach, part of the primary fluid present in the bed base 24 rises in the damaged primary pipe 22 up to the breach.

However, this phenomenon of rising fluid is greatly reduced thanks to the invention.

Indeed, the primary fluid flowing in the annular channel 42 with a high tangential speed, the suction through the gap is limited, the primary fluid being mainly driven in the annular channel 42.

In a state-of-the-art reactor, the speed of the primary fluid in the bed base 24 being much lower and not tangential, the primary fluid rises more easily towards the breach and the leakage rate is greater.

In addition, the primary fluid flowing in the annular channel 42 locally accelerates at the passage restrictions 46. The speed of the primary fluid increasing, the static pressure of the primary fluid decreases due to the Venturi effect.

The static pressure difference of the primary fluid between the outlet of the damaged primary pipe 22 and the outlet of the breach is thus reduced. The primary fluid flow going up the primary pipe 22 is thus also particularly reduced.

The invention therefore makes it possible to limit the leakage rate of the primary fluid in the event of a breach in a primary pipe 22 and thus makes it possible to guarantee a flow rate of primary fluid flowing in the core 18 sufficient to allow cooling of the nuclear fuel assemblies. The invention therefore provides increased safety in the event of an accident.

In addition, in a state-of-the-art reactor, it is necessary to install three or four primary pumps 20 in order to guarantee a sufficient primary flow in the core 18 in the event of a breach in a primary pipe 22.

The present invention makes it possible to use only two primary pumps 20 while guaranteeing an equivalent level of safety, thus allowing significant savings in construction costs and a simplification of the internal structure of the primary circuit 12.

In addition, the addition of the annular channel 42 adds limited pressure drops in the primary circuit 12 due to its rounded shape.

The invention therefore makes it possible, in the event of a breach or accidental rupture of a primary pipe 22, that the diverted flow from the core 18 is reduced. The invention allows the installation of only two primary pumps 20 making the internal structure of the primary circuit 12 less complex while guaranteeing an equivalent level of safety and limiting pressure losses.

The invention is a particularly simple system to implement and easily adaptable and integrable within the bed base 24. In fact, the invention does not require moving parts which can cause wear or seizure.

Finally, the invention also makes it possible to significantly improve the kinetics of slowing down of the primary fluid in the event of failure of the primary pumps 20. Indeed, the large volume of primary fluid present in the annular channel 42 as well as the significant speed of the primary fluid cause a great inertia of the primary fluid in the annular channel 42. Thus in the event of accidental stopping of the primary pumps 20, the decrease in the primary flow is much less significant due to the phenomenon of "flywheel" of the primary fluid in the annular channel 42. Thus the cooling of the core 18 is ensured longer and the safety of the reactor 10 is improved.

Claims (13)

1. - Nuclear reactor (10), comprising: - a tank (16) containing a fluid, the tank (16) defining an interior volume; - A core (18) comprising nuclear fuel, the core (18) being arranged in the interior volume of the tank (16); - at least one pump (20) capable of circulating the fluid through the heart (18); - at least one pipe (22) having an inlet and an outlet for the circulation of the fluid; characterized in that the nuclear reactor (10) further comprises an annular channel (42) defining a closed loop for circulation of the fluid, the or each pump (20) being fluidly connected upstream of the annular channel (42) by at least the one of the pipes (22), the annular channel (42) being located upstream of the heart (18), the annular channel (42) having a restriction of passage (46) of the fluid at the outlet of the or each pipe (22 ). 2. - Nuclear reactor (10) according to claim 1, in which the fluid is liquid sodium and in which the or each pump (20) is arranged in the interior volume of the tank (16). 3. - Nuclear reactor (10) according to claim 1 or 2, comprising at most two pumps (20) adapted to circulate the fluid through the heart (18). 4. - Nuclear reactor (10) according to any one of the preceding claims, in which each pump (20) is connected to the annular channel (42) by at least two pipes (22). 5. - Nuclear reactor (10) according to any one of the preceding claims, comprising a bed base (24) supporting the heart (18), the bed base (24) comprising an outer ring (38), the annular channel (42) being arranged in the interior volume defined by the exterior ferrule (38). 6. - Nuclear reactor (10) according to claim 5, wherein the maximum transverse dimension of the outer shell (38) is greater than the maximum transverse dimension of the heart (18). 7. - nuclear reactor (10) according to claim 5 or 6, wherein the base (24) comprises an inner ferrule (40) porous suitable for being traversed by the fluid and disposed in the interior volume defined by the exterior ferrule (38 ), the annular channel (42) being defined by the volume between the outer ferrule (38) and the inner ferrule (40), the inner ferrule (40) defining an interior volume (44) placed downstream of the annular channel (42) and upstream of the heart (18). 8. - Nuclear reactor (10) according to claim 7, wherein the ratio between the maximum transverse dimension of the outer shell (38) and the maximum transverse dimension of the inner shell (40) is between 120% and 150%. 9. - Nuclear reactor (10) according to claim 7 or 8, wherein the inner shell (40) has a surface porosity between 10% and 50%. 10. - Nuclear reactor (10) according to one of claims 7 to 9, in which the inner shell (40) comprises holes (41), each hole (41) having the shape of an elongated channel extending along an axis forming an angle between 0 ° and 45 ° with the normal of the inner shell (40). 11. - Nuclear reactor (10) according to any one of the preceding claims, comprising, for the or each pipe (22), a deflector (48) placed at the outlet of said pipe (22) orienting the fluid tangentially to the annular channel ( 42) in a horizontal section plane. 12. - Nuclear reactor (10) according to any one of the preceding claims, in which, for the or each pipe (22), the section of said pipe (22) opening onto the annular channel (42) extends along a main axis, the main axis having an angle of incidence (a) relative to the normal to the annular channel (42) of between 30 ° and 90 °. 13. - Nuclear reactor (10) according to any one of the preceding claims, comprising, for the or each pipe (22), an elbow (51) placed at the outlet of said pipe (22) in the annular channel and advantageously orienting the fluid tangential to the annular channel (42) in a horizontal section plane.