JP2017096953A - Passive starting safety device for nuclear reactor based on abnormal reduction of primary flow rate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a passive starting safety device for a nuclear reactor which is passively activated in cases in which the flow rate of a coolant inside a primary circuit is abnormally reduced.SOLUTION: The present invention relates to a device including an assembly having a sheath 200 which is allowed to pass a coolant in a longitudinal direction and a movable part 100 capable of performing a translating movement along a longitudinal direction 3 inside the sheath 200 and having a neutrophage portion. The movable part 100 includes a first floatation portion 110. The sheath 200 includes a second floatation portion 210. The first and second floatation portions 110 and 210 are arranged so as to face each other in the first and second floatation portions 110 and 210. When the flow rate of the coolant which passes through the sheath 200 in the longitudinal direction exceeds a flow rate threshold value, the coolant is molded in a form adapted to apply a sufficient force to the movable part 100 so as to guarantee a floatation of the movable part inside the sheath 200 and the maintenance by a floatation structure.SELECTED DRAWING: Figure 1

Description

  The present invention relates to the field of nuclear reactors. More particularly, the present invention relates to a passive start-up safety device for interrupting neutron activity in a nuclear reactor when the coolant flow rate in a primary circuit for cooling a nuclear fission core is abnormally reduced.

  A particularly advantageous but non-limiting field of application of the invention is in the field of fast neutron reactors, in particular reactors in which the primary circuit coolant is liquid sodium.

  In nuclear reactors where the core is cooled by coolant, such as sodium-cooled fast neutron reactors (RNR-Na), reactivity control is generally ensured by a plurality of safety devices that can stop the neutron reaction. Due to the redundancy and technical differences of the safety equipment provided in this reactor, it must be possible to make the failure probability of this shutdown function extremely low.

  These safety devices are generally based on the chute and insertion of an absorption control rod, also called a neutrophage control rod, into the fission core. Typically, these absorption control rods are inserted into a nuclear reactor and within a four reaule that forms a single assembly located near the assembly containing the fission material with the absorption control rod. It is assembled in a translational form. These control rods accommodate the absorption needle rods assembled in a bundle.

These absorbent needle bars must be cooled. In practice, the temperature of the absorbent needle bar tends to increase due to irradiation. In particular, the neutron absorption reaction by the isotope ¹⁰ B produces an output in B ₄ C that generally constitutes the absorbing needle bar. However, in order to ensure the functionality and / or mechanical strength of the components of the absorbent needle bar, their temperature must be limited. For this reason, it is necessary to cool the absorption needle bar.

  To date, the main safety device of RNR-Na is an active device in the sense that the insertion of the absorption control rod is activated by external electrical control or by the loss of an electrical signal. For the next generation of RNR-Na, it is contemplated to develop an additional safety device that is a passive device that operates if the primary safety device that is the active device fails. These additional safety devices must be able to retract the control rods without detection means or operator intervention. Conversely, it must be possible to trigger the control rod drop directly on the basis of a physical phenomenon to which the activation means is sensitive (for example, an abnormal drop in coolant flow rate or temperature increase in the primary circuit).

  The present invention relates to this latter type of safety device.

  Several solutions have been proposed to ensure the sinking of the absorption control rod that is passively activated in the event of an abnormal drop in the coolant flow rate in the primary circuit.

  Recall that the primary circuit is a circuit whose coolant directly exhausts the heat generated by the fission core. The primary circuit is in direct contact with the assembly containing the fission material.

  The first solution is described in French patent application No. 13662783. This solution assumes that the control rod is lifted by the flow obtained by the circulation of the coolant through the induction tube which exerts a viscous drag on the absorption control rod. Any reduction in coolant flow allows the control rod to fall in the guide tube until it enters its stop position when there is no flow.

  In practice, this “floating” type of solution does not allow for precise control of the vertical position of the control rod, but provides for inadequate control rod movement and concomitant variability in reactivity. It has become clear that this will not be possible.

  Therefore, this solution cannot guarantee to eliminate the occurrence of accident initiation factors in all situations.

  Another solution is described in Russian patent 2069019. This solution envisions a flotation zone provided above the core, with cooperation between the outer surface of the neurophage portion of the absorption control rod and the inner surface of the sheath.

  In practice, this solution has shown that the absorbent needle bar is not sufficiently cooled by the coolant passing through the assembly. As mentioned above, inadequate cooling can alter the functionality and / or mechanical strength of the absorbent needle bar components.

  Moreover, this solution has been found to be relatively robust.

French Patent Application Publication No. 13626783 Russian patent No. 2069019

Therefore, there is a need to propose a solution that does not have the disadvantages of known solutions, or at least limits them.

The present invention relates to a passive start-up safety device for a reactor in which heat from a fission zone is transferred to a coolant,
A sheath extending along the longitudinal direction, which is substantially vertical in operation, adapted to pass coolant in the longitudinal direction;
A movable part assembled in a form capable of translational movement along the longitudinal direction in the sheath, at least,
-A neurotrophic portion comprising at least one neurotrophic material configured to extend mainly along the longitudinal direction and through which coolant passes in the longitudinal direction;
Including moving parts;
The present invention relates to an apparatus including an assembly including:

The movable portion further includes a first levitation portion positioned longitudinally offset relative to the neurophage portion, and the sheath includes a second levitation portion;
When the first and second levitation parts are in a so-called levitation configuration, facing each other along a transverse direction perpendicular to the longitudinal direction, both the first and second levitation parts have a cross-sectional area A coolant passage space having S1 (or play j1) is defined, and this cross-sectional area S1 is
_{-When the} flow rate Q _{f of the} coolant passing through the sheath in the longitudinal direction exceeds the flow rate Q _{declenchement} , the coolant is guaranteed to move the movable portion in the sheath and maintain the vertical direction in the floating configuration with respect to the movable portion. Apply enough force to do;
_-If Q _f <Q _{declenchement} , the coolant will only exert an insufficient force on the moving part to ensure the floating of the moving part in the sheath and the vertical maintenance in the floating configuration; At this time, the movable part is defined so as to descend by gravity along the sheath until reaching a stroke end position which is a so-called drop-down configuration.
The first and second levitation portions are conformed in such a manner,
If the first and second levitation portions are not facing each other along the transverse direction, both the first levitation portion and the inner wall of the sheath facing the first levitation portion are larger than S1. A coolant passage space having an area S2 is defined, and this cross-sectional area is
The coolant is defined so that it exerts insufficient force on the movable part to re-raise the movable part by translational movement within the sheath, even if it has a flow rate Q _f > Q _{declenchement} ; Yes,
In this manner, the first and second floating portions are molded.

  Thus, the present invention provides a simple and effective solution for passive activation of descent of neurotrophic material, typically an absorber needle bar, into a nuclear fission zone.

Immediately when Q _f <Q _{declenchement} , the flow rate is no longer sufficient to maintain the equilibrium of the movable part, so the movable part falls automatically. The neurophage material stored in the movable part then falls into the fission zone and suppresses the neutron reaction.

  This activation is only performed by a decrease in the coolant flow rate. This is therefore completely passive. Unlike the main safety device, this does not depend on an electrical activation system activated automatically by the inspection-control device or manually by the operator. Thus, safety is further enhanced.

Thus, for example, if the test-control device fails, the control rod drop of the active primary safety device may not be activated and the control rod may not fall. On the other hand, the movable part according to the present invention immediately drops when the flow rate of the coolant is reduced to less than the activation threshold Q _{declenchement} .

  Moreover, the system according to the invention makes it possible to control the vertical position of the moving part in a much more precise manner and even under the influence of flow fluctuations.

  In the above-mentioned solution of the type of FR-A-1362783, the position of the moving part cannot be controlled, and improper movement of this moving part, for example under handling conditions (primary flow is non-zero) Cannot be prepared in advance for the accompanying reactivity fluctuations and power fluctuations (in the case of a decrease in flow rate that induces control rod re-elevation and subsequent sudden re-elevation). In fact, regardless of the vertical position of the control rod, the cross-sectional area of passage between the control rod and the sheath is the same. Thus, for example, if the moving part falls after the flow rate drops, the subsequent increase in flow rate that exceeds the activation threshold will cause the moving part to rise again beyond the fission core, and thus the effect of the safety device on neutron activity. Stops.

Within the framework of the present invention, the first levitation part is no longer facing the second levitation part as soon as the movable part falls under the action of an abnormal drop in flow rate, and the movable part is then Even when the flow rate rises again exceeding the threshold value Q _{declenchement} , the passage space between the sheath and the first levitation part is too large, and the coolant cannot apply sufficient force on the movable part to re-rise, It can no longer rise again.

Moreover, the present invention assumes that the first levitation part is in a vertically offset position relative to the _neurophage part and the second levitation part is Q _f > Q _{declenchement.} By assuming that the phage portion does not face vertically and that the function of levitation is performed, a number of advantages are provided. In fact, the functions of levitation and cooling of the Neutrophage part are arranged in series. In fact, when the levitation function is performed, the coolant continuously passes first through the passage space defined by the two levitation portions facing each other and then through the neurophage portion, or in some embodiments Pass in reverse.

  Thus, the floating of the movable part is ensured by all the coolant that passes through the sheath.

  Moreover, cooling of the neurotrophic material can be ensured by all or at least a majority of the coolant that passes through the sheath while passing through the portion of the neurotrophic. Thus, the cooling of a neurotrophic material, typically in the form of a needle bar, can be very effective even with a limited coolant flow rate. Typically, a liquid sodium flow rate of about 2.5-3 kg per second is required to cool a bundle of about 19 absorbent needle bars. With a nominal sodium flow rate of 6 kg / sec, the present invention allows the moving parts to be sufficiently cooled and balanced.

  Solutions such as those described in Russian Patent No. 2069019 require splitting the flow rate to perform the levitation and cooling functions of the neurophage control rod. As a result, if the reactor configuration is the same, more flow must be deployed in the assembly, which has two significant disadvantages: That is, the cooling efficiency of the reactor is reduced (total core flow is not optimized) and the risk of thermal cracking of structures above the core increases as long as the assembly is subcooled (adjacent combustible The temperature difference is large compared to the sex assembly).

  Furthermore, according to the present invention, the levitation function is performed by a part that is independent of the part that stores the neurotrophic material, and this levitation function can be performed by a part whose fabrication and dimensions can be controlled with high precision. The accuracy and reliability of levitation is thereby improved. On the other hand, in the solution of the patent document 2 type in which the neutrophage part is hydrodynamically cooperating to generate the levitation function, the neutrophage part itself is a very complicated part in which a plurality of parts intervene, The dimensional control of the floating part is extremely complicated. However, the inaccuracy of several tenths of millimeters of play between the first part and the second part prevents the movable part from being balanced and causes the movable part to drop (impact on reactor availability). Or may delay start-up (failure of the safety function of the device) in flow transients.

Optionally, the present invention may further have at least one of the following features:
The first levitation part is carried by the outer surface of the movable part;
The second levitation part is located on the inner surface of the sheath;
The sheath includes at least one shell retrofitted into the interior of the tube and the second levitation portion is formed by the shell;
The second levitation part, typically a shell, is machined from the block. This makes it possible to produce the second levitation part, for example, by machining it very accurately.
-The first levitation part is machined from the block; This makes it possible, for example, to manufacture the first levitation part by machining it very accurately.
The longitudinal direction is the vertical direction;
The second levitation part extends in the longitudinal direction over only a part of the longitudinal dimension of the sheath; For example, the ratio between the length of the second levitation portion and the length of the sheath above the end track is about 1/12.

Thus, the levitation configuration is only activated for a very precise relative position of the movable part within the sheath.
The neurophage portion comprises a single tube enclosing a plurality of absorbent needle bars extending longitudinally and containing a neurotrophic material.
The movable part includes a thrust wall molded in such a way that the thermal fluid passing through the sheath applies a thrust having one component against the weight of the movable part to the thrust wall;
-The device is configured in such a way that if the coolant flow rate cannot ensure the equilibrium of the moving part within the sheath, it will drop by gravity until the moving part comes into contact with the end-of-stroke stop that defines the dropping configuration. ing.

The device is configured such that in a down configuration, the neurophage portion faces in a transverse direction and faces one zone of the sheath, called the core zone, which itself is intended to face the nuclear fission zone of the reactor. Yes.
The first levitation part is located below the neurophage part in the vertical direction;

In the levitation configuration, the first levitation portion is located below the core zone in the vertical direction. In other words, this levitation part is located upstream of the neurophage part in relation to the coolant flow in the sheath.
The second levitation part is located below the core zone of the sheath in the vertical direction, facing the nuclear fission zone of the reactor.

Thus, the first levitation portion is not located in the neutron flux. As a result, the irradiation dose received by the first levitation portion is limited. However, radiation damage generated on a microscopic scale in a metallic material placed under a neutron flux appears on a macroscopic scale due to dimensional transitions, particularly expansion that increases with irradiation dose. Compared to the solution in which the first levitation part is installed in the neutron flux, the present invention therefore does not affect the geometry of the first levitation zone and thus maintains its functionality and the safety device. It can be made more reliable.
The first levitation part is separated from the neutrophage part by a separation part having a longitudinal length equal to or greater than the longitudinal stroke of the movable part between the levitation configuration and the depression configuration; It is arranged away from.
The movable part includes a stud carrying the first floating part;
The stud is the leg part of the control rod acting in the longitudinal direction as a floating part and acting in the transverse direction as a thrust wall.
-The stud is located at the lower end of the movable part.
The stud has a lower end which is shaped to form a thrust wall for the coolant and to allow the movable part to be balanced;
The first levitation part comprises a levitation zone located on a levitation wall carried by the stud and extending longitudinally;
The floating wall is cylindrical.
The stud is typically formed of a monolithic component made of a material such as grade EM10 ferritic martensitic steel or one of its alloys. It will be appreciated that other grades of steel, as well as other metals (such as refractory metals) could be contemplated depending on the operating conditions of the reactor.
The stud is hollow. This defines a closed internal volume.
The second levitation part is a shell carried or formed by the inner surface of the sheath.
-The inner surface of the shell is cylindrical.
The distance between the inner surface of the shell and the floating part of the stud defines a cross-sectional area S1 and a play j1.

According to one embodiment, the device may have at least one of the following optional features considered alone or in combination:
The separating part preferably comprises at least one tie rod ensuring a mechanical connection between the neurophage part and the first buoyant part.
The separation part is at least two extending radially from the center of the movable part, typically the only tie rod, to the inner wall of the movable part and extending longitudinally from the neurophage part to the first floating part; , Preferably including at least three stiffeners.

  According to the cross-sectional view, the surface area occupied by tie rods and possibly stiffeners is less than 20%, preferably less than 10%, preferably less than 5% of the cross-sectional area of the neurophage portion.

  Thus, this control rod leg structure has an advantageous effect on the passage of coolant inside the device.

  This control rod leg structure with tie rods and preferably three stiffeners arranged at 120 ° provides mechanical guidance throughout the stroke; improved mechanical rigidity; hydraulic robustness for deactivation of the levitation zone; It offers several advantages such as lightness, which is important for maintaining balance; low load loss.

  The isolated portion preferably includes a tube ajoule that ensures mechanical coupling between the levitation portion and the neurotrophic portion.

Preferably, the watermark tube comprises an opening extending mainly in the longitudinal direction,
The openings are distributed throughout the perimeter of the watermark tube,
The openings are distributed over the entire longitudinal dimension of the remote part.

  Thus, this control rod leg structure has an advantageous effect on the passage of coolant inside the device.

The watermark tube has an external cross-sectional area with dimensions approximately equal to the external cross-sectional area of the first levitation portion. Thus, the movable part has a constant external cross-sectional area (including the first levitation part) at least from the neurophage part to the first levitation part.
The first buoyant part is located vertically above the neurophage part.

  In the levitation configuration, the first levitation portion is positioned vertically above the sheath core zone of the sheath.

  In this embodiment, the first levitation portion is further separated from the neutron flux as compared to the case where the first levitation portion is located on the control rod leg, ie, vertically below the core zone of the sheath in the levitation configuration. In the distance. As a result, the radiation dose received by the first levitation portion is limited, thus avoiding its expansion in particular.

The choice between the positioning of levitation on the legs or on the rod is made in particular according to the distance available between the fission zone and the top of the assembly.
The first levitation part is located between the head of the control rod, which forms the upper end of the movable part in the longitudinal direction, and the neurophage part.

According to one embodiment, the first levitation part is composed of a bulge carried by a movable part between the head of the rod and the neurophage part. The bulge forms an increase in the cross-sectional area of the movable part.
The movable part includes a rod extending from the upper end of the movable part to at least the neurophage part, and the first floating part is formed by a bulge carried by the rod between the upper end part of the movable part and the neurophage part; Has been.
The bulge is placed between the two parts of the rod.
The bulge includes a lower end for forming a thrust surface for the coolant to allow the movable part to remain balanced.
The bulge is hollow and has a passage orifice for the discharge of coolant;
The bulge has a longitudinally extending cylindrical wall, the second levitation portion has a shell formed or carried by the inner surface of the sheath, the outer surface of the bulged cylindrical wall and the shell A space j1 between the inner surfaces defines a cross-sectional area S1.

  According to one embodiment, the device may have at least one of the following optional features considered alone or in combination.

The safety device includes a shock absorber for the movable part when the movable part is dropped.
-A first part carried by the moving part and arranged in contact with the coolant;
A second part carried by the sheath and arranged in contact with the coolant;
The first and second parts are included in the second part when the movable part falls and before the movable part reaches the end position of the stroke in the lowered configuration. The first and second parts cooperate to form a viscous buffer.

  According to one embodiment, the first levitation part and the first part or the second levitation part and the second part are carried by the same mechanism.

  Thus, the same mechanism carried by the sheath or moving part performs the function of a viscous buffer and the function of maintaining balance.

  This provides a great advantage in terms of assembly constraints. Moreover, this also has the advantage of concentrating large dimensional constraints in the same part, in particular. Thus, the present invention can reduce the number of important parts that are to be subjected to, for example, extremely precise machining.

  By reducing the number of critical components, the reliability of passive activation safety devices is improved.

  In addition, the manufacturing cost is also reduced.

  According to one embodiment, which is advantageous but optional, the first levitation part and the first part or the second levitation part and the second part are at least partially positioned at the same level in the longitudinal direction. Yes.

  Optionally, this embodiment with a shock absorber may further have at least one of the following features:

  The first levitation part and the first part or the second levitation part and the second part are at least partially positioned at the same level in the longitudinal direction.

According to one embodiment of the shock absorber, the present invention may have at least one of the following optional features considered alone or in combination:
The second levitation part and the second part are carried by the same mechanism; The sheath includes at least one shell, and the mechanism is formed by the shell.

In this embodiment, the buffer system is deployed on the same fixed part as in the case of maintaining balance. This has several advantages:
-It is not necessary to modify the length and stroke of the moving parts, since the existing parts need to be larger than the height required for the buffering function, so that the balance maintenance function needs to be modified. There is no effect on the height.
-It is unnecessary to deploy a buffer zone elsewhere that is equated with the guidance zone due to its functional play that has been effectively reduced for effective buffering. Thus, this embodiment can eliminate the need to create a new induction zone, which can prevent, hold, and rattle (i.e., slow down) a moving part in the dashpot. This is advantageous from the viewpoint of the reliability of insertion (withdrawal) against the risk of These risks of blocking, gripping, and rattling generally stem from different misalignments / misalignments that can be envisaged concomitant with deformation of the structure under irradiation. The solution according to this embodiment thus has an advantageous effect on the reliability of this entry, since the entry of the movable part of the shock absorber into its female part takes place in the induction zone constituted by the shell. It is.

This embodiment in which the buffering and balancing functions are at least partially performed by the shell can have other advantageous features as follows.
The shell comprises a cavity filled with coolant, the cavity forming said second part; The first part enters the cavity and forms a male part molded to eject the coolant therefrom before the movable part reaches the end of the stroke.
The shell is located in the longitudinal direction between the lower end of the movable part and the neurophage part, preferably between the lower end of the movable part and the head of the movable part.
The first part is shaped to enter into the cavity of the shell; The cavity is circular and has one opening that forms one ring in the transverse direction, through which the first part reaches its end of travel position with the movable part in a lowered configuration. Enter before. The first part forms a tube having one free end that is shaped to enter the cavity through the opening.
The second levitation part is formed by the inner surface of the shell;
The cavity is formed within the thickness of the shell, the cavity having a bottom surface; The second levitation portion is formed by the inner surface of the shell and is arranged at least partially facing the cavity in the longitudinal direction.

According to one embodiment:
The second part forms a female part and has at least one cavity configured to contain the coolant, the first part forms a male part, the male part being a female part It is shaped to enter the at least one cavity and eject the coolant from the movable part before reaching the end of the stroke.

The second part forms a stroke end stopper for the movable part.
The first part is located in the longitudinal direction between the lower end of the movable part, typically a leg, and the head of the movable part; Preferably, the first part is located in the longitudinal direction between the lower end of the movable part and the neurophage part.
The second part forms a female part having a cavity and the first part forms a male part shaped to enter into the cavity; Preferably, according to the cross section, the cavity forms a ring centered on the translation axis of the movable part, and extends from the opening located at the upper end of the cavity in the longitudinal direction to the bottom located at the lower end of the cavity. To do.
The cavity is circular and has one opening that forms a ring in the transverse direction, through which the male part is moved into the lowered configuration before the end of its stroke is reached in the lowered configuration; Enter. Preferably, the male part forms a tube with one free end shaped to enter into the opening of the cavity.
The first part forms a male part shaped to enter into the cavity; Preferably, the first part forms a tube having one end that is free to enter into the cavity. The opposite end forms a bond between the tube and the rest of the movable part. Preferably, the first part is located directly below the neurotrophic portion.
The second part is formed by a shell carried by the inner surface of the sheath and the second floating part is formed by the inner surface of the shell;
The cavity is formed within the thickness of the shell, the cavity has a bottom surface and the second floating part is formed by the inner surface of the shell.
The second levitation part and the cavity are arranged at least partly in the longitudinal direction, ie at the same level in the longitudinal direction.

  According to another embodiment of the shock absorber, the present invention may have at least one of the following optional features that are considered alone or in combination.

According to another embodiment of the shock absorber:
The first levitation part and the first part are carried by the same mechanism, which forms a stud on the movable part;
The stud has an outer surface that simultaneously defines the first floating part and the first part;

The sheath includes at least one guide portion configured to translate the movable portion;
The guiding part comprises at least two and preferably at least three sliding seats regularly distributed in the radial direction about the translation axis of the movable part;
The guiding part comprises a bage porte-patins carrying said sliding seats;
The guiding part is in the sheath such that it faces the Neutrophage part in the transverse direction, preferably at the lower end of the Neutrophage part if the moving part is in a floating configuration, and the moving part is in a recessed configuration In some cases, the upper end is positioned in the longitudinal direction.

  Thus, the cooperation between the outer surface of the neutrophage portion and the sliding seat accurately translates the movable part within the sheath over the entire stroke.

  Another aspect of the present invention relates to a passive stop system comprising a passive activation safety device according to the present invention and an equipment mechanism including a grapple for positioning a moving part. The grapple makes it possible to lift the moving part of the safety device and position it in the levitation position or return it from the lowered position to the levitation position.

  Another aspect of the invention relates to a nuclear reactor comprising a fission zone and a primary circuit through which a coolant circulates and comprising at least one apparatus of the invention.

  This reactor is preferably of the fast neutron reactor type.

  The accompanying drawings are presented by way of example and are not intended to limit the invention. These drawings merely depict one embodiment of the present invention so that the present invention can be easily understood.

Longitudinal profile of an embodiment of the passive activation safety device according to the invention when the so-called movable part in a levitation configuration is in an equilibrium state under the action of a levitation force generated by a coolant passing longitudinally through the sheath FIG. FIG. 2 illustrates the safety device of FIG. 1 when a so-called movable part in a drop-down configuration drops due to gravity but does not maintain equilibrium and reaches its stroke end position in the bottom surface of the sheath. 1 illustrates the safety device of FIG. 1 when the movable part is in the middle of falling due to gravity and before reaching the end of the stroke in the bottom surface of the sheath. FIG. 2 is a cross-sectional view of the safety device of FIG. 1, with the cutting being performed at the level of the sheath guiding portion and the moving portion of the neurophage portion. The diagram of FIG. 1 is taken up again. FIG. 2 is a cross-sectional view from below of the safety device according to FIG. FIG. 2 is a cross-sectional view from below of the safety device according to FIG. The diagram of FIG. 1 is taken up again. It is an enlarged view of the lower end part of the movable part of the safety device illustrated in FIG. 1 in the floating configuration. 5b is a perspective view of the end of the movable part of the safety device illustrated in FIG. 5b in a levitation configuration. FIG. The diagram of FIG. 2 is taken up again. FIG. 6b is an enlarged cross-sectional view taken at the level of the shock absorber in the drop configuration of the device of FIG. 6a. FIG. 6b is an enlarged cross-sectional perspective view taken at the level of the shock absorber in the drop configuration of the device of FIG. 6a. Fig. 3 schematically illustrates a plurality of operating steps of the present invention. FIG. 6 is a longitudinal sectional view of another embodiment of a safety device according to the present invention in a levitation configuration. The safety device of FIG. 8a is illustrated in its depressed configuration. The view of FIG. 8b is taken up again. FIG. 8b is an enlarged view of the safety device illustrated in FIG. 8a, taken at the level of the shell and watermark tube in a drop configuration. FIG. 8b is a cross-sectional view of the safety device illustrated in FIG. 8a taken at the level of the shell and openwork tube. FIG. 5 is a longitudinal sectional view of another embodiment of the safety device according to the present invention in which the first levitation part is located above the neurotrophic part, with the movable part represented in a drop configuration. FIG. 10b is an enlarged view of FIG. 10a taken at the level of the first and second levitation portions. FIG. 10b is a cross-sectional perspective view of FIG. 10b. FIG. 6 shows an enlarged view of cooperation between a first levitation portion and a second levitation portion according to one embodiment.

  The drawings are schematic views for facilitating the understanding of the present invention, and are not necessarily the same scale as practical applications. Specifically, the play between the first levitation portion and the inner surface of the sheath or the inner surface of the shell does not necessarily represent reality.

  It should be recalled in advance that there are generally multiple types of aggregates in nuclear reactors where heat from the fission zone is at least transferred to the coolant. Some of these assemblies contain fission materials, and other assemblies contain so-called control rods that allow neutron radioactivity to be controlled. In addition, other assemblies are also contemplated, which form passively activated safety devices that are envisioned to shut down or slow down neutron activity in the event of a reactor malfunction.

  Here, an embodiment of the passive activation safety device according to the present invention will be described in detail with reference to FIGS.

  The apparatus primarily includes a sheath 200 that is adapted to be inserted into the core of a nuclear reactor. The portion of the sheath 200, referred to as the core zone 240, is positioned facing the nuclear fission zone 10 along a transverse direction orthogonal to the longitudinal direction 3. Since the sheath 200 is fixed during the operation of the nuclear reactor, the core zone 240 always remains facing the fission zone 10.

  The sheath 200 extends along a longitudinal direction 3 that is inclined relative to the horizontal in the activated state. Typically, the longitudinal direction 3 is vertical as illustrated in the figures.

  The sheath 200 extends from an upper end 202 provided to grip the assembly being handled, positions the assembly in the end track of the reactor, and replenishes it with a coolant such as liquid sodium, for example. It extends to the assembly leg 204.

  In the sheath 200, the coolant passes in the longitudinal direction from the supply slit 205 provided in the assembly leg 204 to the outlet 203 located at the upper end level 202.

  Preferably, the sheath 200 includes an outer casing formed by a hexagonal tube 201 at the intersection. The longitudinal wall of the sheath 200 is airtight.

  The passive activation safety device also includes a movable part 100 that is housed in the sheath 200 along the longitudinal direction 3 and is assembled for translation. In the nuclear industry, the moving part is also called a control rod. The movable part 100 extends mainly along the longitudinal direction 3, and thus most often during operation, along a vertical line as shown in the figures. The movable part 100 extends from the head 101 to the lower end part 103. The movable part includes a neurotrophic portion 130 containing a neurotrophic material between the head 101 and the lower end 103.

In the case of a liquid metal cooled fast neutron reactor, the neurophage material may be boron carbide (B ₄ C) enriched with ¹⁰ B to some extent. Alternatively, this can be a hafnium-based material. These materials, which have a high density and therefore can reduce the sagging time, do not release gas under irradiation and thus do not induce expansion, greatly reducing the negative reactivity capability of the material under irradiation do not do. Alternatively, the neurotrophic material can also be a refractory boride type absorbent material, such as HfB ₂ and TiB ₂ , having a melting point of approximately 3300 ° C. It is likewise possible to use europium hexaboride EuB6. It can also be envisaged to consider the use of Eu ₂ O ₃ . Eu ₂ O ₃ does not generate a gas product under irradiation. This has a higher absorption capacity.

In the case of a pressurized water reactor, the material used for the absorption element can be, for example, hafnium, Dy ¹¹ B ₆ , Gd ¹¹ B ₆ , Sm ¹¹ B ₆ and Er ¹¹ B ₄ , natural HfB ₂ and natural TiB ₂ .

  The neurophage portion 130 typically includes a body 104 that encapsulates an absorbent needle bar bundle 131. The needle bar 131 extends mainly in the longitudinal direction 3. The neurophage portion 130 is configured to be cooled when the coolant flowing from the assembly leg 204 to the outlet 203 passes in the longitudinal direction. As can be clearly seen from FIG. 3 b, the neurophage portion 130 has mechanical coupling elements 132 between the absorbent needle bars 131, which are in the longitudinal direction of the coolant through the neurophage portion 130. A passage 133 is defined that allows the flow to be directed in a certain direction to cool this portion.

  The head 101 of the movable unit 100 cooperates with the grapple type gripping device 300 to position the movable unit 100 at an appropriate position inside the sheath 200 at the start of operation as described in detail below with reference to FIG. It is configured as follows.

  The movable part 100 also includes a first levitation portion 110 that functions as a first levitation portion 110 when the coolant flow rate falls below a predetermined threshold. Is to make it possible. This function will be described in detail below.

  The movable part 100 also includes a first part 140 that is adapted to cooperate with a second part 220 carried by the sheath 200 to ensure buffering of the movable part 100 when dropped. These first component 140 and second component 220 will be described in detail below.

The passive activation mechanism of the drop of the movable part 100 will now be described. In this mechanism, when the coolant flow rate falls below an abnormal flow rate threshold value called the activation threshold value Q _{declenchement} , the movable unit 100 once drops and drops by causing gravity to drop. Upon reaching its end-of-stroke position, referred to as the configuration, the neurophage portion 130 faces the nuclear fission zone 10 in the transverse direction and thus is positioned facing the core zone 240 of the sheath 200. be able to.

  The first levitation portion 110 carried by the movable unit 100 has an outer wall positioned facing the inner wall of the sheath 200. The inner wall of the sheath 200 has a narrowing of its cross section at the level of the zone of the sheath 200 referred to as the second levitation portion 210. The narrowing of the cross section of the sheath 200 is limited according to its longitudinal dimension. Typically, this second levitation portion 210 extends in the longitudinal direction preferably over less than 1/5 and preferably less than 1/10, and preferably less than 1/15 of the length of the sheath 200. . Typically, the ratio between the length of the second levitation portion 210 and the length of the sheath 200 above the end track is approximately 1/12.

  The space defined between the first levitation portion 110 and the inner surface of the sheath 200 defines a passage cross-sectional area for the coolant flowing inside the sheath 200. Therefore, this passage space is reduced when the first levitation portion 110 is located facing the second levitation portion 210 in the transverse direction.

  Particularly advantageously, the first levitation part 110 is offset in the longitudinal direction in relation to the neurophage part 130. In the example of the embodiment illustrated in FIGS. 1-9 and 11, this first levitation portion 110 is located below the neurotrophic portion 130. The advantages associated with this embodiment are described below. According to another embodiment illustrated in FIG. 10, this first levitation portion 110 can be located above the neurophage portion 130. In each of these embodiments, the first buoyant portion 110 is not located on the neurotrophic portion 130 and is advantageously positioned along the longitudinal direction 3 away from the neurophage portion.

  The first levitation portion 110 and the second levitation portion 210 are in a face-to-face arrangement along a transverse direction orthogonal to the longitudinal direction 3 in which the first and second levitation portions 110 and 210 are in a so-called levitation configuration. The first and second floating portions 110, 210 are both configured to define a coolant passage space. The passage space has a cross-sectional area S1, which can also be defined by the play if the play j1 is regular over the entire circumference of the movable part 100.

The first and second levitation portions 110, 210, or rather their facing surfaces, in the levitation configuration, have this cross-sectional area S1 (or this play j1)
_-If the coolant flow rate Q _f passing through the sheath 200 in the longitudinal direction exceeds a predetermined flow rate Q _{declenchement} , the coolant _floats with _respect to the movable part 100 in the movable part 100 in the sheath 200 and its floating configuration. Defined in such a way as to apply sufficient force to oppose the weight of the movable part 100 to ensure vertical maintenance;
It is configured as follows.

More precisely, the movable part 100 also includes at least one thrust wall 117, the surface of which is along a protrusion perpendicular to the coolant advancement direction, ie along a transverse protrusion. It is non-zero. The coolant applies a force against the apparent weight of the movable part 100 on the thrust wall 117.
If Q _f <Q _{declenchement} , the coolant has insufficient force to move the moving part 100 to ensure the floating of the moving part 100 in the sheath 200 and the vertical maintenance in the floating configuration. Do not add. At this time, the movable part 100 descends by gravity along the sheath 200 until reaching the stroke end position which is a so-called drop-down configuration. In this position, the neurotrophic portion 130 faces the fission core 10 and can therefore stop or slow down the neutron activity.

The first and second levitation portions 110, 210, or rather their facing surfaces, similarly, if the first and second levitation portions 110, 210 are not face-to-face along the transverse direction, 1 levitation portion 110 and the inner wall of the sheath 200 facing the first levitation portion 110 together define a coolant passage space having a cross-sectional area S2 greater than S1 (or play j2 greater than j1). Molded in shape. The cross-sectional area S2 or the play j2 is coolant, even if having a much greater flow rate Q _f than _Q declenchement (criteria considered in the reactor is 110% of the flow rate at the nominal output) But The movable part 100 is defined so as to apply an insufficient force to re-raise the movable part 100 by translational movement in the sheath 200. Thus, after an abnormal drop in flow rate, the absorption control rod cannot withdraw from the fission zone 10 again unless it is intentionally pulled out of it by the grapple 200.

  Thus, the present invention provides a hydraulic levitation zone that is deployed by cooperation between the first levitation portion 110 and the second levitation portion 210, which in this non-limiting embodiment is located below the fission core. Based on the proposed solution. When the movable part 100 is in its depressed configuration, the hydraulic levitation zone is not activated.

The present invention makes the safety device extremely robust, high performance and effective. In fact, this safety device has the following advantages in particular:
-Since the hydraulic cooperation zone formed partly by the first levitation part 110 is located below the neurophage part 130, the hydraulic function (equilibrium maintenance) and the thermal hydraulic function (bundle cooling) are not connected. Are arranged in series. In particular, this allows you to:
○ Good control of cooling possibility of needle bar bundle 131 and maintaining balance of movable part 100:
-In fact, the entire flow allocated to the aggregate can be used for cooling as well as maintaining equilibrium. As a result, when the diameter play at the buoyancy zone level is equivalent, the concept of the buoyancy zone on the control rod leg is smaller than the concept of the buoyancy zone located on the neurophage partial level, ie the control rod body. Expected to require only the flow of coolant in the body (or can lift a larger mass in an equivalent manner);
In the insertion phase, the cooling of the needle bar bundle 131 is the same regardless of its longitudinal position;
O Flexibility with respect to manufacturing tolerances of the components of the levitation zone: complying with a radial play of approximately a few millimeters at the levitation zone level (with a manufacturing tolerance of approximately 1/10) It is easy when the second levitation portion 210 is formed by an integral short part.
A certain degree of freedom at the concept level of the needle bar bundle 131: Even if the dimensions of the needle bar bundle 131 are corrected, the dimensions of the levitation zones 110 and 210 are not affected. This can be extremely useful both in the development situation (working within the project) and in predicting the useful life of the reactor.
O Ease of view from a computational point of view, and thus from any proof of view that might be necessary
• Can control mechanical problems of moving part guidance when moving parts are dropped or equipped.

  The present invention is not limited to cylindrical walls in order to define the passage cross section S1 of the coolant. The present invention extends to any other form capable of performing its levitation function and descent activation function.

  Most advantageously, the sheath 200 includes a shell 211 retrofitted into the hexagonal tube 201, which shell 211 forms a second levitation portion 210. This allows dimensional constraints to be limited to this shell 211 retrofitted onto the hexagonal tube 201, which limits the dimensional constraints to the hexagonal tube 201 with respect to manufacturing complexity and thus cost. This is an advantage over existing solutions. The shell 211 can be machined from a block, for example, so that its dimensions can be completely controlled.

  Advantageously, as illustrated in the embodiments of FIGS. 1-9 and 11, the first levitation portion 110 is defined by a stud 112 carried by the movable part 100. The stud 112 is located at the lower end 103 of the movable unit 100. The stud 112 has a lower end portion 103 molded so as to form at least a part of the thrust wall 117. In the illustrated embodiment, the thrust wall 117 is formed by a flat surface that forms the end 103 and a chamfer that extends from the end 103 to the longitudinal wall of the stud 112.

  As described above, the thrust wall 117 is molded in such a manner that the coolant passing through the sheath 200 applies a thrust having one component that opposes the weight of the movable portion 100 to the wall. This thrust depends on the surface area occupied by the transverse protrusion of the thrust wall 117 and the pressure difference between the upstream and downstream sides of the first levitation portion 110.

  It is this stud 112 that defines the cross section of passage between the movable part 100 and the sheath 200. In the illustrated embodiment, the first levitation portion 110 is cylindrical. The stud 112 is preferably formed of a one-piece component typically made of grade EM10 ferritic-martensitic steel or one of its alloys. It will be appreciated that other grades of steel, as well as other metals (eg, refractory metals) could be contemplated depending on the reactor operating conditions.

  Equally advantageously, the stud 112 is machined from the block in such a way that its dimensions, in particular the dimensions allowing the cross-sectional area S1 to be defined, can be finely controlled.

  According to one embodiment, the stud may be a solid part.

  According to another advantageous embodiment, the stud is hollow, so that it can be made lighter. The stud may or may not be manufactured by machining. If you want to avoid the recessed part on the upstream side of the stud, add a stopper at the bottom.

  Very advantageously, according to the embodiment illustrated in FIGS. 1-9 and 11, the first levitation portion 110 is located vertically below the neurophage portion 130. Thus, in the levitation configuration, the stud 112 is under the fission core. At this time, the first levitation portion 110 is located upstream of the neurophage portion 130 with respect to the flow of the coolant 5 in the sheath 200.

  An alternative embodiment in which the first levitation portion 110 is located vertically above the neurotrophic portion 130 will be described with reference to FIG.

  Embodiments in which the first levitation portion 110 is located vertically below the neurotrophic portion 130 has many advantages.

  In practice, the first levitation portion 110 is not located in the neutron flux. As a result, the irradiation dose received by the first levitation portion 110 is limited. However, irradiation damage produced on a microscopic scale in a metallic material placed under a neutron flux appears on a macroscopic scale in the form of a dimensional transition, in particular an expansion that increases with the irradiation dose. Thus, compared to a solution in which the first levitation part is placed in the neutron flux, the described solution can preserve its functionality without affecting the geometry of the first levitation zone, and thus The safety device becomes more reliable.

  An example of the determination of the force generated by the coolant to induce equilibrium maintenance is described in detail below with reference to FIG.

FIG. 11 shows a second levitation portion 210 formed by the shell 211, where the stud 112 of the movable part 100 defines the first levitation portion 110, whose longitudinal wall is the longitudinal length of the shell 211. Facing the directional wall, its thrust wall 117 receives an equilibrium maintaining force generated by the coolant. In this figure, the diameter D _{112 of} the stud and the diameter D ₂₁₁ of the internal flow path formed by the shell are represented, and the play j1 between these two diameters is also represented. Similarly, this figure also shows the coolant flow direction 5 and the pressure P ₁ upstream of the shell 211 and the pressure P ₂ downstream of the shell 211. The length L ₂₁₁ is the longitudinal dimension on which the first levitation portion 110 faces the second levitation portion 210 defined by the shell 211 in the levitation configuration.

Hydro cooperating zones, and through the load losses that occur during the cross-section of the stud diameter D _112, the equilibrium maintained force is based on a plurality of parameters (length L ₁₁₂ ~ _211, the diameter D _211, the diameter play j ₁ = D ₂₁₁ ~D _112). Furthermore, there is room for L ₁₁₂ ~ ₂₁₁ virtually, is needed by the contact process of the movable part after the disengagement / separation of the grapple 300 of positioning for the mechanism of the movable portion 100. All of these will react advantageously in the vicinity of a corresponding decro- ment condition and create an equilibrium concept that increases its reliability and robustness.

Stall is a levitation zone sufficient to make the moving part 100 inevitable even if the value of the flow rate Q _{f in} the assembly remains larger than the value of the starting flow rate Q _{declenchement} after the stall. Must be understood as exposure. This notion of stall is a manifestation of system instability, especially due to geometric mechanical causes (eg possible misalignment or misalignment of moving parts within the sheath), hydraulic power It can be a cause (e.g. hydraulic disturbance, vibration) or other (e.g. the accidental presence of impurities in the play between the stud and shell).

Accordingly, depending on the nominal flow rate Q _N and the threshold value Q _{declenchement at} which the moving part 100 is desired to start dropping, the _{person skilled} in the _art will _know the dimensions of the first levitation part 110 and the second levitation part 210, in particular their The cross-sectional area and length can be determined.

More specifically, on the movable part, a thrust F _poussee that allows the movable part to maintain equilibrium when Q _f is _larger than Q _{declenchement} and the first levitation part 110 and the second levitation part 210 face each _other. Is added. This thrust F _poussee can be defined as follows:
F _poussee = F _{resultante des forces de pression} + F _frottement
Where
-“F _frottement ” is the wear force derived from the viscous drag at the hydraulic cooperation zone level. In the non-limiting example of FIG. 11, F _frottement depends in particular on length L ₂₁₁ , coolant viscosity and play j1 (j1 = D ₂₁₁ −D ₁₁₂ ).
-"F _{resultante des forces de pression} " depends on the planned surface area (typically the thrust wall 117 of the stud 112) on which the coolant pressure is exerted and the coolant pressure P ₁ exerted on this planned surface. The On the non-limiting example of FIG. 11, the planned surface area on which the coolant pressure is exerted depends on the diameter D ₁₁₂ and the pressure is noted as P ₁ .

Therefore, F _poussee must at least equilibrate the apparent weight of the control rod, ie its weight minus buoyancy.

  According to one embodiment, the first levitation portion 110 is separated from the neurophage portion 130 by a separation portion 120 having a longitudinal length equal to or greater than the longitudinal stroke of the movable portion between the levitation configuration and the depression configuration. The neurotrophic portion 130 is spaced apart in the longitudinal direction. Thus, regardless of the position of the first levitation portion 110, it can be ensured that the first levitation portion 110 is never located at the level of the fission core, in particular the first levitation portion 110 is It offers the advantages mentioned above in terms of the reduction of the radiation imposed on the first levitation part 110 compared to the solution located in the bundle.

  The spacing portion 120 can be implemented according to different embodiments. The first embodiment is illustrated with reference to FIGS. According to this embodiment, a tie rod 122 with stiffener 121 ensures mechanical coupling between the neurophage portion 130 and the first levitation portion 110. Preferably, as illustrated in FIG. 4 b, which is a cross-sectional view of the assembly, the separation portion 120 extends radially from the center of the movable portion 100 and extends from the neurophage portion 130 to the first levitation portion 110. 3 stiffeners 121 are included. This control rod leg structure with one tie rod and three stiffeners can deactivate the hydraulic cooperating zone under control rod drop conditions. This structure also provides the advantages of mechanical guidance throughout the stroke; improved mechanical stiffness; lightness that is important for maintaining balance; low load loss; and no complex hydraulic sizing.

  8 and 9 illustrate another embodiment of the separation portion 120 where this separation portion 120 includes a watermark tube 123. The watermark tube 123 includes an opening 124 extending in the longitudinal direction. These openings 124 are distributed along the entire watermark tube 123. These openings are distributed throughout the longitudinal dimension of the spaced apart portion 120. Thus, the coolant can migrate through these openings 124 to reach the inside of the neurotrophic portion 130 with little load loss and cool the neurotrophic portion.

  This embodiment with watermark tube 123 has the above-mentioned advantages with respect to control rod legs with tie rods and stiffeners. Instead, this embodiment requires more advanced hydraulic and mechanical sizing.

  The equipment of the movable part 100 in its nominal operating position is assisted through a mechanism commonly referred to as a control rod mechanism that includes the gripping grapple 300 of the head 101 of the movable part 100. Within the framework of the present invention, the mechanism has only the equipment function for the only passive activation of the drop of the movable part 100.

  The operating principle of the passive safety device according to the present invention will now be described with reference to FIG.

  In the retracted position illustrated in FIG. 7a, the hydraulic cooperating zone between the movable part 100 and the sheath 200, more precisely between its respective floating part 110, 210, is in an inactive state.

  It is through its control rod mechanism that includes the grapple 300 that the moving part 100 is equipped before the critical state, i.e., at the start of the reactor activity. When the absorbent part 130 of the movable part 100 is positioned above the fission core 10, it is described as “equipped”. The grapple catches the head 101 (FIG. 7b) and lifts the movable part 100 until it is guided vertically up in its floating configuration, as illustrated in FIG. 7c.

During the above steps, the coolant flow rate Q _f is maintained at a reactor handling flow rate value that is less than the discharge flow rate referred to below.

At this time, the flow rate Q _{f of the} coolant is increased while maintaining the movable unit 100 suspended by the control rod mechanism (FIG. 7d).

As illustrated in FIG. 7, Q _{declenchement} ≦ Q _lacher , preferably Q _{declenchement} <Q _lacher for higher safety, the grapple 300 opens immediately when Q _f reaches at least Q _lacher and the control rod mechanism Releases the movable part 100. Q _lacher <Q _N.

Preferably, the movable part 100 has its levitation part 110 at the level of the second levitation part 210 of the sheath 200 in its position suspended from the grapple 300. The balance maintaining force generated by the flow rate Q _lacher enables the movable portion 100 to be balanced.

At this time, the flow rate Q _f continues to increase and can reach its nominal value Q _N , so long as Q _{declenchement} <Q _f , the movable part 100 will then remain in its floating configuration illustrated in FIG. 7e.

Instead, as soon as Q _f <Q _{declenchement} , the equilibrium maintaining force generated by the flow rate Q _f no longer allows the movable part 100 to maintain equilibrium, which is due to gravity (FIG. 7f), Drop until it reaches its drop configuration at the end of the stroke as illustrated in FIG.

  Thus, hydraulic cooperation stops at a value below the appropriate flow rate value reached in the aggregate during an unprotected transient during an abnormal drop in the flow rate in the primary circuit, and thus the drop of the movable part 100 occurs. Passive activation and gravitational insertion of the absorbent charge 130 in the fission core 10 are driven.

  With reference to FIGS. 10 a, 10 b, 10 c, an alternative embodiment is illustrated in which the first levitation portion 110 is positioned vertically above the neurophage portion 130. Thus, the first levitation portion 110 is positioned vertically above the core zone 240 of the sheath 200 and thus above the nuclear fission core 10 of the reactor. More precisely, the first levitation part 110 is located between the head 101 of the movable part 100 and the neurophage part 130.

  According to one embodiment, the first levitation portion 110 is formed by a bulge 115 carried by the rod 102 and extending between the head 101 and the neurophage portion 130. Thus, the bulge 115 is positioned between the two sections of the rod 102. As illustrated in FIG. 10 a, the spacing portion 120 maintains the bulge 115 carrying the first levitation portion 110 away from the neurophage portion 130. The bulge 115 includes a lower end portion that forms a thrust wall 117 for the coolant so that the movable portion 100 can be maintained in equilibrium.

  Advantageously, the bulge 115 is hollow. This bulge has coolant passage orifices 116,118. Among these orifices, the upper hole 118 is located at the upper end level of the bulge 115, and at least one hole 116 is disposed at the lower end of the bulge 115. The bulge 115 has a cylindrical wall extending in the longitudinal direction. The second levitation portion 210 is formed by a shell 211. The space between the outer surface of the cylindrical wall of the bulge 115 and the inner surface of the shell 211 defines a coolant passage cross section S1.

  Advantageously, the safety device includes a buffering mechanism of the movable part 100 for buffering the drop when the movable part 100 arrives at the end of the stroke.

  The buffer mechanism includes a first part 140 carried by the movable part 100 and arranged in contact with the coolant, and a second part 220 carried by the sheath 200 and similarly arranged in contact with the coolant. .

  The first part 140 and the second part 220 have the first part 140 dropped into the second part 220 before the movable part 100 is lowered and before the movable part 100 reaches its stroke end position in the lowered configuration. The first part 140 and the second part 220 cooperate to form a viscous buffer.

  The second part 220 preferably forms a stroke end stopper for the movable part 100. Thus, the movable portion 100 does not collide with the bottom wall 206 located at the lower end portion of the sheath 200.

  According to the embodiment illustrated in FIGS. 1 to 6, 8 and 9, the first part 140 has a longitudinal direction in which the lower end 103 of the movable part 100 and the neurophage part 130, more precisely the neurophage part 130. It is located between the lower ends of the. In this embodiment, the second part 220 forming the female part has a cavity 225. The cavity 225 forms an annulus centering on the translation axis of the movable part 100 along the transverse section, and extends from the opening 226 located at the upper end of the cavity 225 to the bottom surface 227 forming the lower end of the cavity 225. Extend in the direction.

  The first part 140 forming the male part is molded so as to enter the cavity 225 before the movable part drops and the end point of the stroke is reached.

  The male part forms a tube having a wall shaped to be inserted into the cavity 225. One end 141 of the tube is free. The other end of the tube ensures a mechanical connection between the tube and the moving part. Preferably, this end of the tube is located proximate the lower end of the neurophage portion 130. This embodiment is clearly visible in FIGS. 6b and 6c.

  The cavity 225 is approximately centered on the translational axis of the movable part 100, and the male part has a dimension complementary to the cavity 225, so that the male part and the female part are inserted into the cavity 225 during the relative insertion of the male part and the female part. The existing fluid is ejected out of the cavity and generates a viscous force that opposes the insertion of the male part into the female part. More precisely, the transverse and longitudinal dimensions of the cavity 225 and the male part are selected in such a way as to produce a viscous buffer against the drop of the movable part 100 until the end of the stroke.

  Preferably, the cavity 225 is formed by a shell 211 that is itself carried by the inner surface of the sheath 200. Similarly, the second levitation portion 210 is preferably formed by the shell 211 as well.

Thus, the only identical part, shell 211, carries two walls that each perform the following specific functions:
-If the flow rate is sufficient, one wall of the shell 211 cooperates with the floating part carried by the movable part to maintain the equilibrium of the movable part;
-If the flow rate drops abnormally, the other wall of the shell 211 buffers the moving part when the moving part drops and the end of the stroke is reached.

  Preferably, the second part 220, whose function is viscous buffering, and the second floating part 210, whose function is balancing, are at least partly facing longitudinally, ie they are longitudinally At the same level. The advantage of this is that in particular large dimensional constraints are concentrated inside the same part. This can be seen from FIGS. 4c and 5b, which clearly show the play j1 and the cavity 225 that allow the movable part 100 to remain balanced. According to this embodiment, the number of very important parts to be machined very precisely is thus reduced. Moreover, this saves a lot of space.

Moreover, this embodiment with the shell 211 serving the function of buffering and balancing has the following advantages:
-It is not necessary to modify the length and stroke of the moving parts, since the existing parts need to be higher in height than required by the buffering function, so that the length of the moving part and the stroke need not be modified. There is no effect on the height.
-It is unnecessary to deploy a buffer zone elsewhere that is equated with the guidance zone due to its functional play that has been effectively reduced for effective buffering. Thus, this embodiment can eliminate the need to create a new guidance zone, which is the prevention of movement of the moving part within the dashpot, gripping and rattling (and hence slowing down). This is advantageous from the point of view of reliability of insertion (and withdrawal) against risk. These risks of blocking, gripping, and rattling generally stem from different misalignments / misalignments that can be envisaged associated with deformation of the structure under irradiation. The solution according to this embodiment thus has an advantageous effect on the reliability of this entry, since the entry of the movable part of the shock absorber into its female part takes place in the induction zone constituted by the shell 211. Is brought about.

  According to another embodiment not illustrated, the cushioning function is performed by the cooperation of the stud 112 and the wall of the sheath 200, preferably the bottom wall 206.

  Thus, the first levitation portion 110 and the first portion 140 are defined by the outer surface 113 of the stud 112 of the movable part 100. Thus, in this embodiment, the two functions of maintaining balance and buffering are performed by the same mechanism carried by the movable part 100, which can be the stud 112. This bottom wall 206 is preferably retrofitted onto the inside of the sheath, for example on its legs 204.

  According to one advantageous embodiment illustrated in each of FIGS. 1 to 6 and 8 to 10, the safety device is at least one configured to guide the movable part 100 in its translational movement within the sheath 200. Two guiding portions 230 are included. As illustrated in FIG. 3 b, the guiding portion 230 is at least one formed by at least two, preferably three sliding seats 231 that are regularly and radially distributed about the translation axis of the movable part 100. A guide portion 230 is included. In FIG. 3b, the sliding seats 231 are distributed at 120 ° intervals. Preferably, the guide portion 230 is formed by a sliding seat carrying ring that defines the sliding seat 231 on one of its inner surfaces.

  The guiding portion 230 is positioned in the sheath 200 to be at the level of the neurophage portion 130 in the longitudinal direction when the movable part 100 is in the floating configuration. Thus, the cooperation between the outer surface of the neurophage portion 130 and the sliding seat 231 ensures accurate and reliable translational guidance of the movable part 100 inside the sheath 200.

  However, this embodiment is not limiting.

  In view of the above description, the present invention provides an extremely reliable and reliable solution to allow the passive control rod to drop completely passively when the coolant flow rate is abnormally reduced. You can clearly see that you are proposing.

  The invention is not limited to the embodiments described above, but extends to all embodiments covered by the claims.

DESCRIPTION OF SYMBOLS 1 Apparatus 3 Longitudinal direction 5 Coolant flow zone 10 Fission zone 100 Movable part 101 Head 102 Rod 103 Lower end part 104 Control rod main body 110 First floating part 112 Stud 113 External surface 115 Swelling 116 Hole 117 Thrust wall 118 Upper hole 120 Separation part 121 Stiffener 122 Tie rod 123 Opening pipe 124 Opening part 130 Neutrophage part 131 Needle bar 132 Coupling element 133 Passage channel for coolant 140 First part 141 End of pipe 200 Sheath 201 Hexagonal pipe 202 Upper end 203 Exit 204 Assembly leg 206 Wall 210 Second levitation portion 211 Shell 212 Internal wall 220 Second part 225 Cavity 226 Opening 227 Cavity bottom surface 230 Guiding portion 231 Sliding seat 240 Core zone 300 Grapples

Claims (36)

A passive start-up safety device (1) for a nuclear reactor, wherein the nuclear reactor includes a fission zone in which heat is at least partially transferred to the coolant;
A sheath (200) extending along the longitudinal direction (3), which is substantially vertical in operation, with the coolant passing in the longitudinal direction;
Assembled in a sheath (200) so as to be able to translate along the longitudinal direction (3), at least
A neurotrophic portion (130) comprising at least one neurotrophic material, configured to extend mainly along the longitudinal direction (3) and through which coolant passes in the longitudinal direction;
Including an assembly including a movable part (100),
The movable portion (100) includes a first levitation portion (110) located longitudinally offset relative to the neurophage portion, the sheath (200) includes a second levitation portion (210), And the second levitation portion (110, 210) is
If the first and second levitation portions (110, 210) are in a so-called levitation configuration, facing each other along a transverse direction perpendicular to the longitudinal direction (3), the first and second The floating portions (110, 210) together define a coolant passage space having a cross-sectional area S1, which is
_{-If the} flow rate Q _{f of the} coolant passing through the sheath (200) in the longitudinal direction exceeds the flow rate Q _{declenchement} , the coolant floats up the movable portion in the sheath (200) _relative to the movable portion (100) and Applying sufficient force to ensure maintenance in a floating configuration;
If Q _f <Q _{declenchement,} it is not possible for the coolant to guarantee the floating of the movable part (100) in the sheath (200) and its maintenance in the floating configuration relative to the movable part (100). Only a sufficient force is applied, at which time the movable part (100) descends by gravity along the sheath until reaching the stroke end position, which is a so-called drop configuration;
Is defined as
It is molded in such a form,
If the first and second levitation portions (110, 210) are not facing each other along the transverse direction, they face the first levitation portion (110) and the first levitation portion (110) Both the inner walls (212) of the sheath (200) define a coolant passage space having a cross-sectional area S2 that is larger than S1, and this cross-sectional area S2 is
_-Even if the coolant has a flow rate Q _f > Q _{declenchement} , it _applies only enough force to the movable part (100) to re-raise the movable part by translational movement in the sheath (200). Absent,
Is defined as
Molded in a shape like this,
Features a safety device.   Safety device arranged according to claim 1, characterized in that the first levitation part (110) is carried by the outer surface of the movable part (100).   The safety device according to claim 1 or 2, characterized in that the sheath (200) comprises at least one shell (211) and the second levitation part (210) is formed by the shell (211).   The safety device according to any one of claims 1 to 3, characterized in that the first levitation part (110) is located vertically below the neurophage part (130).   The second levitation portion (210) is located vertically below the core zone (240) of the sheath (200) adapted to face the nuclear fission zone (10) of the nuclear reactor. The safety device according to any one of claims 1 to 4.   The first levitation portion (110) is separated from the neurophage portion (130) by a separation portion (120) having a longitudinal length equal to or greater than the longitudinal stroke of the movable portion between the levitation configuration and the depression configuration. 6. A safety device according to any one of the preceding claims, characterized in that it is arranged in the longitudinal direction away from this neurotrophic part (130).   A safety device according to any one of the preceding claims, characterized in that the movable part comprises a stud (112) carrying the first levitation part (110).   The stud (112) is positioned at the lower end (103) of the movable part (100), and the stud (112) forms a thrust wall (117) for the coolant so that the movable part (100) is kept in equilibrium. The safety device according to claim 7, wherein the safety device has a lower end portion that is molded so as to enable the following.   The stud (112) has a cylindrical longitudinal wall and is formed of a monolithic component made of a material such as ferritic-martensitic steel, grade EM10 ferritic-martensitic steel, refractory metal or alloys thereof. The safety device according to claim 7 or 8, characterized in that:   The second levitation portion (210) is a shell (211) carried or formed by the inner surface of the sheath (200), and the distance between the inner surface of the shell (211) and the levitation wall of the stud (112) is 10. A safety device according to any one of claims 7 to 9, characterized in that it defines a cross-sectional area S1.   11. A safety device according to any one of claims 7 to 10, characterized in that the stud (112) is hollow and defines a closed internal volume.   A first levitation portion (110) is separated from the neurophage portion (130) by a spacing portion (120) and is spaced longitudinally from the neurophage portion (130), the spacing portion (120). Comprises at least one and preferably only one tie rod (122) and preferably at least one stiffener ensuring mechanical coupling between the neurotrophic part (130) and the first levitation part (110). The safety device according to claim 1, characterized in that:   At least three stiffeners in which the separation portion (120) extends radially from the center of the movable portion (100) and extends longitudinally from the neurophage portion (130) to the first levitation portion (110) 13. The safety device according to claim 12, comprising (121).   The first buoyant portion (110) is disposed longitudinally away from the neurophage portion (130) by being separated from the neurophage portion (130) by the spacing portion (120). 120) comprises an openwork tube (123) ensuring a mechanical coupling between the levitation part and the neurophage part (130). Safety device.   The watermark tube (123) includes a primarily longitudinally extending opening (124) distributed throughout the perimeter of the watermark tube (123) and distributed throughout the longitudinal dimension of the spacing portion (120). The safety device according to claim 14, characterized in that:   The safety device according to any one of claims 1 to 3, characterized in that the first levitation part (110) is located above the neurotrophic part (130) in the vertical direction.   17. The levitation configuration, wherein the first levitation portion (110) is positioned vertically above the core zone (240) of the sheath (200). Safety device according to any one of the above.   The first levitation part (110) is located in the longitudinal direction between the head (101) forming the upper end of the movable part (100) and the neurophage part (130), The safety device according to claim 16 or 17.   The movable part includes a rod (102) extending from the upper end part of the movable part (100) to at least the neurophage part (130), and the first floating part (110) is connected to the upper end part of the movable part (100) and the 19. Safety device according to any one of claims 16 to 18, characterized in that it is formed by a bulge (115) carried by a rod (102) between phage parts (130).   20. The bulge (115) includes a lower end for forming a coolant thrust wall (117) to allow the movable part (100) to remain balanced. Safety equipment.   21. Safety device according to claim 19 or 20, characterized in that the bulge (115) is hollow and has a passage orifice (116, 118) for the discharge of coolant.   The bulge (115) has a longitudinally extending cylindrical wall and the second levitation portion (210) has a shell (211) formed or carried by the inner surface of the sheath (200); The space j1 between the outer surface of the cylindrical wall of the bulge (115) and the inner surface of the shell (211) defines a cross-sectional area S1, according to any one of claims 19-21 Safety device as described. The movable part (100) includes a shock absorber for the movable part at the time of dropping.
A first part (140) carried by the movable part (100) and arranged in contact with the coolant;
A second part (220) carried by the sheath (200) and arranged in contact with the coolant;
When the movable part (100) is lowered and before the movable part (100) reaches the stroke end position in the lowered configuration, the first part (140) is the first and second parts. The first part (140) and the second part (220) cooperate with each other to form a viscous buffer. The safety device according to any one of claims 1 to 22.   That the first levitation portion (110) and the first part (140) or the second levitation portion (210) and the second part (220) are carried by the same mechanism (112, 211). 24. A safety device according to claim 23, characterized in that:   The first levitation portion (110) and the first part (140) or the second levitation portion (210) and the second part (220) are at least partially positioned at the same level in the longitudinal direction. 25. The safety device according to claim 24, wherein:   The second levitation portion (210) and the second part (220) are carried by the same mechanism (112, 211), the sheath (200) includes at least one shell (211), which mechanism includes the shell (211). 26. The safety device according to any one of claims 23 to 25, wherein the safety device is formed by:   The second part (220) is a female part, has a cavity (225) filled with coolant, and the first part (140) enters the cavity (225) of the female part and enters the movable part ( 24. A safety device according to claim 23, characterized in that it forms a male part molded to eject coolant from it before reaching the end of stroke.   The first part (140) is longitudinally located between the lower end (103) of the movable part (100) and the neurophage part (130), and preferably, the lower end (103) of the movable part (100). ) And the head of the movable part (100), the safety device according to claim 27.   The second part (220) forms a female part having a cavity (225) and the first part (140) forms a male part (145) shaped to enter the cavity (225); The cavity (225) is circular and has an opening (226) that forms an annulus in the transverse direction, through which the male part (145) is retracted by the movable part (100). The male part (145) forms a tube having a free end that is shaped to enter the cavity (225) through the opening (226) before entering its end-of-stroke position. 29. A safety device according to claim 28, characterized in that:   The second part (220) is formed by the shell (211) carried by the inner surface of the sheath (200), and the second floating part (210) is formed by the inner surface of the shell (211). 30. A safety device according to claim 28 or 29, characterized in that   A cavity (225) is formed within the thickness of the shell (211), this cavity has a bottom surface (227), a second levitation portion (210) is formed by the inner surface of the shell (211), and is 31. Safety device according to claim 30, characterized in that it is arranged at least partly facing this cavity (225) in the direction.   32. A safety device according to any one of the preceding claims, characterized in that the sheath (200) comprises at least one guiding part (230) configured to translate the movable part.   The guide part comprises a sliding seat (231), preferably three sliding seats (231) distributed regularly and radially around the translation axis of the movable part (100), Item 33. The safety device according to Item 32.   A passive shutdown system for a reactor, comprising a passive start-up safety device (1) according to any one of the preceding claims and an equipment mechanism including a grapple (300) for positioning a movable part (100).   Reactor comprising a fission zone (10) and a primary circuit in which a coolant circulates and comprising at least one device (1) according to any one of claims 1 to 33.   36. A nuclear reactor according to claim 35 of the fast neutron reactor type.

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