Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
  • G21C3/30—Assemblies of a number of fuel elements in the form of a rigid unit
  • G21C3/32—Bundles of parallel pin-, rod-, or tube-shaped fuel elements
  • G21C3/326—Bundles of parallel pin-, rod-, or tube-shaped fuel elements comprising fuel elements of different composition; comprising, in addition to the fuel elements, other pin-, rod-, or tube-shaped elements, e.g. control rods, grid support rods, fertile rods, poison rods or dummy rods
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C9/00—Emergency protection arrangements structurally associated with the reactor, e.g. safety valves provided with pressure equalisation devices
  • G21C9/02—Means for effecting very rapid reduction of the reactivity factor under fault conditions, e.g. reactor fuse; Control elements having arrangements activated in an emergency
  • G21C9/027—Means for effecting very rapid reduction of the reactivity factor under fault conditions, e.g. reactor fuse; Control elements having arrangements activated in an emergency by fast movement of a solid, e.g. pebbles
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C7/00—Control of nuclear reaction
  • G21C7/06—Control of nuclear reaction by application of neutron-absorbing material, i.e. material with absorption cross-section very much in excess of reflection cross-section
  • G21C7/08—Control of nuclear reaction by application of neutron-absorbing material, i.e. material with absorption cross-section very much in excess of reflection cross-section by displacement of solid control elements, e.g. control rods
  • G21C7/12—Means for moving control elements to desired position
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C1/00—Reactor types
  • G21C1/02—Fast fission reactors, i.e. reactors not using a moderator ; Metal cooled reactors; Fast breeders
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C1/00—Reactor types
  • G21C1/04—Thermal reactors ; Epithermal reactors
  • G21C1/06—Heterogeneous reactors, i.e. in which fuel and moderator are separated
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/30—Nuclear fission reactors

Definitions

• the present invention relates to an autonomous device for triggering and inserting at least one element to be inserted.
• the element (s) to be inserted may or may only be absorbing and / or mixing in case of generalized fusion of the heart.
• Mixer means a material capable of forming a eutectic with a low melting point with the material constituting the sheaths of nuclear fuel needles of the assembly and which prevents the formation of plugs which would hinder the evacuation of the molten core or corium absorbing and / or mixer in the heart of a nuclear reactor.
• the autonomous triggering and insertion device is in particular intended to be implemented in a sodium-cooled fast neutron nuclear reactor (known as RNR-Na), and to a nuclear fuel assembly comprising such a device.
• RNR-Na sodium-cooled fast neutron nuclear reactor
• these elements In order to regulate the activity of the core of a nuclear reactor and to limit the consequences of a malfunction of the reactor, it is intended to insert therein elements comprising neutron absorbing materials. In normal operation, these elements may be in the form of control bars suspended above the core. When a need to decrease reactivity of the reactor is detected, the absorbent elements are inserted into the fissile zone.
• a malfunction of the reactor may be a problem in the reactor cooling circuit, for example in the primary circuit, stopping pumps slowing the flow of liquid sodium in the case of a sodium cooled reactor. It can be a loss of cold source, ie that the calories extracted by the primary circuit are not evacuated correctly. In the absence of antireactivity insertion, these malfunctions would then lead to an increase in the temperature of the reactor core, which could lead to a fusion of one or more assemblies, or even a generalized fusion of the core that could lead to a loss. reactor integrity.
• absorbent elements By inserting absorbent elements into the core, it is intended to quench the neutron reaction and stabilize the reactor core at a temperature adapted to the accepted criteria for the malfunctions considered.
• the shutdown systems implemented until today in the RNR-Na are based on active devices, in the sense that the insertion of the absorbing elements is triggered by an external electrical control. or by the loss of the electrical signal.
• EP 0 392 991 describes a mechanism for automatically inserting control rods into a reactor, this mechanism comprises a temperature-sensitive system (hereinafter referred to as a "temperature sensor") and holding means. control bars suspended above the fuel elements.
• the holding means comprise hooks pivotally mounted on a rigid portion of the reactor, pivoting elements articulated on the hooks and on the "temperature sensor". An increase in temperature causes an increase in the length of the "temperature sensor", which causes the rotation of the pivoting elements and the pivoting of the hooks, releasing the control rods which then fall by gravity between the fuel elements.
• this mechanism has several parts articulated to each other, the risk of jamming (by seizing for example) are increased, which is not conducive to the trigger reliability of the bars.
• games are necessarily provided at the axes of rotation. There is therefore a risk of untimely release of the bars, for example during handling the hooks can rotate sufficiently under the effect of shock or vibration.
• a device for triggering and inserting an insert assembly formed of absorbing and / or mixing elements comprising means for suspending an assembly to be inserted over a zone of insertion, locking means of the suspension means, and means for releasing the assembly to be inserted, and a part ensuring both the locking of the holding of the assembly to be inserted, the unlocking and the release of the assembly to be inserted being obtained by a simple movement.
• the trigger and insertion device according to the invention is such that it prevents the inadvertent fall of the assembly to be inserted by avoiding their release if the coolant temperature does not exceed the given threshold.
• the triggering and insertion device is disposed in the upper part of a nuclear fuel assembly, preferably substantially on the axis of the assembly.
• the triggering and insertion device then directly sees all the outflow of the fuel beam of the carrier fuel assembly, which is almost equal to the flow rate of a standard fuel assembly, which improves the accuracy and reliability of triggering the device and release the set to insert.
• the assembly to be inserted is contained in a capsule whose upper part is equipped with the triggering and insertion device according to the present invention.
• a carrier assembly comprising both nuclear fuel and an insert assembly whose insertion is controlled by the device according to the invention, this device being disposed in the upper part of the assembly.
• the triggering of the insertion is faster and more accurate compared to an assembly dedicated exclusively to the absorbent and / or the mixer, since the heat transfer feed rates of those of the fuel assemblies are much greater than those of the absorbent assemblies. .
• the subject of the present invention is therefore a device for triggering and inserting an assembly to be inserted into a fissile zone of a nuclear reactor in which a coolant circulates, having a longitudinal axis intended to be substantially vertical, comprising a fixed part.
• the fixed part comprising means for holding the assembly to be inserted in suspended position above the fissile zone, said assembly to be inserted being releasable under the action of the movable part
• the mobile part comprising locking means, holding means in the suspended position of the assembly to be inserted and means for releasing the assembly to insert holding means, said locking means being formed by at least a first surface, said abutment surface and the means for releasing the insert assembly being formed by at least a second surface, said release surface, and moving means along the longitudinal axis of said abutment (24) and release surfaces, said means displacement being formed by a ferrule adapted to expand longitudinally differentially with respect to the fixed portion under the effect of the rise in temperature the heat transfer surface, said abutment surface and said release surface being arranged so that, during the increase of the coolant temperature, the abutment surface moves axially away from the holding means and the release surface approaches axially.
• the abutment surface being spaced apart from the holding means when the coolant is at the normal operating temperature of the reactor, so that the holding means are unlocked, and the release surface exerting a thrust force on the holding means such that the assembly to be inserted is released when the coolant temperature is greater than a threshold temperature.
• the holding means comprise at least two fingers, preferably three, distributed around the longitudinal axis and mounted articulated in rotation on the fixed part so as to be able to take a position close to the longitudinal axis to maintain the assembly to be inserted between the fingers, and a position spaced from the longitudinal axis in which the assembly to be inserted is released.
• the abutment surface may be a surface disposed radially outside the fingers preventing in the locking position the fingers from moving away from the longitudinal axis.
• the release surface may be a surface perpendicular to the longitudinal axis, and the fingers may include a cam surface with which cooperates the release surface to rotate the fingers away from the longitudinal axis.
• the fixed part may comprise at least a substantially tubular portion coaxial with the longitudinal axis inside which is intended to be suspended the assembly to be inserted, the substantially tubular portion being disposed inside the the movable part, the axes of rotation of the fingers being carried by the outer surface of the substantially tubular portion, said portion having through-holes through the fingers, the free end of the fingers projecting inside the tubular portion.
• the mobile part may for example comprise a head carrying the release and locking surfaces, said head extending through the ferrule, said ferrule being fixed by a longitudinal end on the fixed part opposite the longitudinal end connected to the control head. .
• the ferrule is made of austenitic steel and the fixed part is made of tungsten-based alloy.
• the ferrule may be Z10 CNDT steel 15.15 B and the fixed part in W-5Re.
• a radial clearance is provided between the ferrule and the fixed part so as to delimit a coolant circulation channel between the ferrule and the fixed part, the ferrule having orifices for the circulation of the coolant in said channel.
• the present invention also relates to a triggering and insertion system
• a triggering and insertion system comprising a triggering and insertion device according to the invention, a longitudinal axis capsule forming the fixed part and a neutron absorbent, said capsule comprising a tubular body.
• longitudinal axis in which is housed the assembly to be inserted and a gripping head through which the system can be grasped, the triggering and insertion device being disposed upstream of the gripping head in the direction of flow of the coolant.
• the capsule has coolant supply ports in its lower part.
• the longitudinal dimension of the neutron absorbent is at most equal to half of the total longitudinal dimension of the capsule.
• the release and insertion system comprising means for damping the fall of the assembly to be inserted.
• the present invention also relates to a nuclear fuel assembly comprising a longitudinal axis housing, a fissile zone, a free central space in the fissile zone extending over at least a portion of the height of the fissile zone from its upper end, and a release and insertion system according to the invention, a lower end of the capsule being inserted into the free central space or a trigger and insertion device (D1) according to the invention, the fixed part being disposed at least above the free central space.
• a nuclear fuel assembly comprising a longitudinal axis housing, a fissile zone, a free central space in the fissile zone extending over at least a portion of the height of the fissile zone from its upper end, and a release and insertion system according to the invention, a lower end of the capsule being inserted into the free central space or a trigger and insertion device (D1) according to the invention, the fixed part being disposed at least above the free central space.
• D1 trigger and insertion device
• the assembly advantageously comprises means for detecting the insertion of the assembly to be inserted by ultrasonic telemetry.
• the detection means comprise for example at least one ultrasonic transducer disposed above the head of the capsule, a reflector mounted on the head of the capsule in front of the transducer, the longitudinal position of the reflector being controlled by the maintenance or not of the neutron absorbent by the holding means, said reflector being connected to the neutron absorbent by an elongate member slidably mounted in a longitudinal bore passing through the capsule head and holding the reflector in a non-insertion state by pressing on the set to insert.
• the nuclear fuel assembly may comprise resilient means compressed in the presence of the neutron absorbent and expandable in the absence of the assembly to be inserted and exerting a tensile force on the elongated member to move the reflector.
• the assembly comprises for example a sheath bordering the free central space and receiving a lower end of the capsule.
• the sleeve may have a hexagonal outer section and a hexagonal or circular inner section.
• the assembly to be inserted may comprise at least one neutron absorbing element and / or mixer.
• the assembly to be inserted comprises a plurality of absorbent elements and / or mixers.
• the present invention also relates to a nuclear reactor, for example a sodium-cooled fast neutron reactor, comprising assemblies containing only nuclear fuel needles and at least one fuel assembly according to the invention.
• a nuclear reactor for example a sodium-cooled fast neutron reactor, comprising assemblies containing only nuclear fuel needles and at least one fuel assembly according to the invention.
• FIG. 1 is a front view of an exemplary embodiment of a trigger and insertion system according to the present invention, for example at a handling temperature,
• FIG. 2A is a longitudinal sectional view of FIG. 1 at the trigger and insertion device at the handling temperature
• FIG. 2B is a view in longitudinal section of FIG. 1 at the trigger and insertion device at the normal operating temperature
• FIG. 2C is a longitudinal sectional view of FIG. 1 at the tripping and insertion device at the tripping temperature just before insertion of the absorbent material into the core;
• Figure 2D is a longitudinal sectional view of Figure 1 at the triggering device and insertion at the trigger temperature during the insertion of the absorbent material in the heart,
• FIG. 3 is a view from above of the system of FIG. 1,
• FIG. 4 is a cross-sectional view of the system of FIG. 1 along the plane AA shown in FIG. 2C
• FIG. 5 is an overall view of an example of integration of the system of FIG. 1 into a nuclear fuel assembly, the set of absorbent elements being suspended above the fissile zone,
• FIG. 6 is a view of the assembly of FIG. 5, the set of absorbent elements being inserted into the fissile zone,
• Figure 7 is a sectional view of the assembly of Figure 6 at the fissile area and through an absorbent member.
• upstream and downstream are to be considered in relation to the circulation of coolant in an assembly, i.e. from the bottom to the top.
• carrier assembly will be used to designate the assembly according to the present invention comprising both nuclear fuel and absorbent elements, and will be designated by “standard assembly” an assembly comprising only nuclear fuel.
• normal operation means the operation of the reactor under normal temperature conditions
• abnormal situation a reactor state in which its temperature exceeds a safety threshold which results in an increase in the temperature of the reactor. coolant beyond a given temperature threshold.
• the assembly to be inserted is described as being a set of elements made of neutron absorbing material, however the invention also applies to the insertion of a set of mitigation elements.
• a nuclear reactor comprises an enclosure in which a plurality of nuclear fuel assemblies, arranged next to each other, are arranged.
• the assemblies form the heart of the reactor.
• the assemblies may have a hexagonal outer cross-section.
• the assemblies may have other types of external cross-sections, such as circular or rectangular sections.
• a coolant circulates in assemblies and between assemblies to extract the heat generated by the nuclear fuel, forming the primary circuit.
• the assemblies contain the nuclear fuel, for example distributed in needles.
• the part of the assemblies comprising the nuclear fuel is called the fissile zone. In order to regulate the operation of the reactor core, it is planned to insert anti-reactivity into the fissile zone by introducing a neutron absorbing material.
• the absorbent materials of the control rods remain in the assemblies (more precisely their stroke is ensured in the assemblies and it is their insertion mechanisms which make the connection between the assemblies and the heart cover cap or BCC).
• the absorbent materials are either partially inserted in the fissile zone (control rods), or suspended above the fissile zone (complementary stop bars), and to stop the reactor, they are introduced totally into the zone. fissile within the needle beam.
• the absorbent materials are for example in the form of control rods, complementary stop bars or advantageously in the form of strings of elements of absorbent material, for example oblong, cylindrical, or preferably of spherical shape.
• FIGS. 1 to 4 show an exemplary embodiment of a trigger and insertion system SI according to the present invention comprising a trigger and insertion device D1 intended to hold a set of absorbent elements 2 at above the fissile zone when the temperature is below a threshold temperature (FIGS. 1, 2A to 2C), to release the set of absorbent elements 2 beyond the threshold temperature (FIGS. 2D and 2E).
• the assembly 4 comprises a plurality of elements 4 in neutron absorbent material of spherical shape threaded onto a cable 6 (shown in dotted line) providing a certain flexibility.
• the assembly 2 comprises at its upper end an upper end element 2.1, which is distinguished from the other elements, in that it is intended to cooperate with the triggering device and insertion.
• the element 2.1 has a frustoconical shape formed of a large base oriented towards the spherical elements and a lateral surface.
• the "set of absorbent elements" 2 will be referred to hereafter as “the set” 2, and the piece 2.1 will be designated as "hanging head”.
• the system SI comprises a capsule 10 formed by a tubular body of longitudinal axis X in which is housed the assembly 2, as can be seen in FIG.
• the capsule 10 has an upper zone ZI, in which is located the absorbent assembly 2 in the suspended position, which is above the fuel needles, when the system is mounted in an assembly as can be seen in FIG.
• the capsule 10 also has a lower zone Z11 located in the fissile zone within the fuel needles. The lower zone Z11 receives the assembly when it has been released (FIG. 6).
• the assembly formed by the tripping and insertion device D1 and the capsule 10 forms a trigger and insertion system SI which will be described later.
• Means for damping the fall of the neutron absorber material at the end of stroke are provided in the lower zone Z11 of the capsule. For example, the inside diameter of the capsule at the lower zone Z11 is reduced.
• the capsule 10 also comprises a gripping head 13 intended to allow manipulation of the capsule and more generally of the trigger and insertion system SI.
• the gripping head 13 comprises means for gripping the system by an external handling device (not shown).
• the coolant for example liquid sodium, circulates in the assembly along the longitudinal axis X from bottom to top.
• the capsule 10 in its lower part, has supply ports to ensure its filling with the coolant, the lower feed ports are provided with porous vents that have very high pressure losses. This allows the filling without generating significant flow, and this regardless of the size of the upper outlet openings.
• the assembly 2 having a low mass and the sodium having a significant viscosity, the coolant flow in the capsule is the lowest possible so as not to slow down the fall of the neutron material and thus not penalize the time of fall .
• the trigger and insertion device D1 is arranged around the upper zone ZI of the capsule.
• the device D1 comprises holding means 11 of the assembly 2, locking means of the holding means 11 and passive activation means which ensure the release of the assembly 2 in abnormal situation.
• the trigger and insertion device D1 has a shape of revolution of longitudinal axis X.
• the triggering and insertion device D1 comprises in the lower part a ferrule 19 fixed by its upstream end to the capsule 10, considering the flow direction of the coolant from bottom to top, and in the upper part a control head 18 in the extension of the shell and secured axially thereof.
• the control head 18 is mounted capable of sliding around the capsule 10. A radial clearance is provided between the outer diameter of the capsule and the internal diameter of the control head 18.
• the holding means 11 comprise fingers 20 mounted articulated on an upper part of the body of the capsule 10.
• the control head 18 and the fingers 20 are advantageously located in the upper part of the capsule 10 in an area remote from the fissile core where the neutron flux is minimal.
• the fingers 20 are three in number 20 distributed substantially at 120 ° from one another providing a uniform support for the assembly. One could, however, provide only two fingers, or three fingers or more.
• the fingers 20, in the holding position, are inclined towards the longitudinal axis X.
• Each finger 20 has a first longitudinal end 20.1 articulated in rotation on the capsule body 10 about a Y axis orthogonal to the longitudinal axis X and a second longitudinal end 20.2 forming a support surface in contact with the attachment head 2.1.
• the capsule 10 comprises longitudinal slots in which the fingers 20 are mounted so that the second end 20.2 of the fingers 20 is located inside the capsule 10.
• the second end 20.2 of each finger has a notch 22 delimited by two surfaces 22.1, 22.2 particularly visible in Figure 2D.
• One 22.1 of the surfaces is intended to bear against the large base of the attachment head 2.1 and the other surface 22.2 is intended to bear against the lateral surface, as is particularly visible in Figures 2A to 2C.
• the control head 18 carries the finger locking means 20 in the holding position of the assembly 2, i.e. in an inclined position towards the longitudinal axis X.
• the locking means comprise stops 24 arranged radially outside the fingers 20 so as to prevent them from moving away from their holding position.
• each finger 20 has a spout on its edge 20.3 opposite their abutment surface 24.
• a radial clearance is advantageously provided between the spout and the abutment surface 24, avoiding friction and risk of seizure.
• the abutment surfaces 24 are carried by a single annular surface of axis X formed inside the control head 18. In the example shown, this surface is located downstream with respect to the axes of rotation of the fingers on the capsule 10.
• control head 18 carries the activation means of the assembly 2 in abnormal situation.
• the release means are formed by thrust surfaces 26 oriented in a transverse plane, for example perpendicular to the longitudinal axis, intended to bear against the fingers 20 to exert a thrust on them and cause their pivoting about their axis of rotation.
• the thrust surfaces 26 are intended to bear against cam surfaces 28 of the fingers located radially inwardly with respect to the axis of rotation of the fingers 20.
• the thrust surfaces 26 are located upstream with respect to the axes of rotation of the fingers 20 on the capsule 10.
• control head 18 has in its inner periphery cavities 30 for accommodating the fingers 20.
• the tubular body of the capsule 10 has on its radially projecting outer surface three tabs 32 carrying the axes of rotation of the fingers 20.
• the passive activation means are formed by the ferrule 19 and by the control head 18.
• the ferrule 19 and the control head 18 are made of a material having a high coefficient of expansion, greater than that of the material of the capsule 10 .
• the inner diameter of the ferrule is chosen so as to provide a channel between the ferrule and the outer face of the capsule 10 to ensure the flow of coolant. Openings 36 are made in the shell 19 and in the upstream and downstream parts to allow the heat transfer and its evacuation. The difference in diameter between the outer surface of the capsule 10 and the inner surface of the shell 19 is chosen to be large enough for a significant portion of the coolant flow to flow in this channel.
• the axial dimension of the shell 19 is chosen very large.
• the first advantage resulting from this important axial dimension of the ferrule is to have a large axial expansion.
• the second advantage is that the ferrule has a very large heat exchange surface with the coolant, which allows to integrate the local thermal heterogeneities that can provide and thus improve the reliability of tripping.
• the large axial dimension of the ferrule is very interesting in terms of tripping reliability.
• the ferrule is positioned sufficiently above the fissile area to overcome any risk of swelling of materials related to the neutron flux.
• the SI release and insertion system is mounted in a nuclear fuel assembly, called a carrier assembly.
• the assembly according to the present invention comprises a housing 40 of longitudinal axis XI of cylindrical shape hexagonal section.
• This hexagonal section is in no way limiting and a rectangular or circular section is within the scope of the present invention.
• the casing 40 comprises a central part 42, called the fissile zone, receiving the nuclear fuel needles 41.
• the casing 40 comprises a lower part called an assembly foot 44 ensuring the maintenance of the assembly in the reactor, the foot of assembly 44 being intended to be mounted in a support called bedspring.
• the housing 40 also has an upper portion 48 open.
• the assembly foot also includes supply ports 46 heat transfer.
• the assembly A is traversed from bottom to top by the coolant symbolized by the arrow F, which is circulated by means of pumps, the coolant extracting the heat produced by the needles.
• the coolant also flows outside the assembly, between the assemblies in so-called inter-assemblies zones.
• the assembly according to the present invention also comprises a housing 52 of axis XI extending over the entire height of the fissile zone.
• This housing 52 is delimited by a sleeve 54 whose outer section is homothetic to that of the housing.
• the sleeve 54 ensures the integration of the tripping and insertion device D1 in the needle beam and the coherence of the architecture of the needle beam.
• the sleeve 54 has a hexagonal outer section such as the housing.
• the inner section of the sleeve 54 is circular like that of the capsule 10.
• the inner section of the sleeve 54 could be hexagonal.
• the sleeve 54 besides the fact that it delimits a housing for the capsule 10, improves the mechanical decoupling between the trigger and insertion system SI and the assembly, insofar as it protects thanks to its rigid structure the system triggering and insertion SI of the swelling of the needles under irradiation. It thus contributes in a general way to the mechanical decoupling with the pitch of the network.
• the sleeve 54 has at its lower end one or more coolant supply ports, which provide the coolant supply of the integrated capsule.
• the sleeve 54 replaces two crowns of needles.
• the capsule 10 is inserted into the sleeve 54, the outer diameter of the capsule 10 is slightly less than the inner diameter of the sleeve 54 to allow its insertion.
• the capsule 10 is held in the carrier assembly at its head.
• Figure 7 a cross-section of the assembly of Figures 5 and 6 can be seen at the fissile area and through an absorbent member.
• the relative arrangement of the needles 41, the sleeve 54, the capsule 10 and an element of the absorbent assembly 2 can be seen.
• Triggering state at the threshold temperature, for example of the order of 660 ° C in the present invention to which it is desired to insert the absorbent material in the fissile core.
• the mounting state is not shown but is very close to that shown in Figure 2A.
• the various elements of the trigger and insertion system are not deformed by the thermal expansion.
• the fingers 20 support the assembly 2.
• the abutment surfaces are opposite the jaws of the fingers 20 and the thrust surfaces 26 are remote from the cam surfaces 28.
• the fingers 20 are thus locked and the assembly 2 can not be closed. released. The manipulation of the system can then be done safely without risk of unwanted insertion into the needle beam.
• the trigger and insertion system is mounted in the carrier assembly which is disposed in the reactor. Due to the temperature in the reactor and the difference in coefficients of expansion between the material of the capsule 10 and the material of the ferrule 19 and the control head 18, a differential expansion appears between the capsule 10 and the assembly. ferrule 19 and control head 18. There is therefore a differential deformation between the capsule 10 and the ferrule assembly 19 and control head 18, and a relative displacement of the abutment surfaces 24 and the thrust surfaces 26 carried by the head 18 relative to the fingers 20.
• the differential expansion is such that the abutment surfaces 24, although having moved relative to the fingers 20, are still partially facing the beaks of the fingers 20 and ensure again a locking of the fingers in the holding position of the assembly 2.
• the fingers 20 thus support the assembly 2.
• the assembly can not be released. The handling of the system can then be done safely without risk of insertion into the fissile core.
• the operating state is shown in Figure 2B.
• the different elements of the trigger and insertion system are immersed in the coolant at the operating temperature.
• the shell 19 is surrounded by coolant through the channel formed between the shell 19 and the capsule 10, and is therefore sensitive to the operating state of the assembly.
• the increase in temperature of the coolant leads to the continuation of the increase of deformation of the elements of the trigger system and insertion by thermal expansion.
• the Differential expansion between the ferrule 19 and the capsule 10 is such that the abutment surfaces 24 are no longer opposite the beaks of the fingers 20, the fingers 20 are thus unlocked.
• the thrust surfaces 26 just come into contact with the cam surfaces 28, the fingers 20 are thus still inclined towards the longitudinal axis in the holding position of the assembly 2.
• FIG. 2C the triggering state is represented, the fingers 20 are then in the final phase of rotation and the assembly 2 is almost free.
• Figure 2D the fingers have finished tilting, the assembly 2 is released and is falling towards the fissile heart.
• the insertion of the absorbent elements ensures the neutron quenching of the chain reaction so as to avoid melting of the core in the short term, with a temperature compatible with the maintenance of the integrity of the support structures of the core, for a sufficient period of time. to implement corrective actions.
• the trigger and insertion system is immersed in the coolant through the channel between the ferrule and the capsule, the temperature of the system is close to the coolant temperature, resulting in a high accuracy trigger system.
• the ferrule 19 and the control head 18 are made of a material offering a high coefficient of expansion, for example a steel, more particularly an austenitic steel such as that used for the needle sheaths, such as Z10 steel CNDT 15.15 B ( 15/15 Ti) hardened.
• tungsten-based alloy for example alloy W-5Re, i.e. which is a tungsten alloy with 5% rhenium.
• W-ODS An alloy such as W-ODS can also be envisaged.
• tungsten has the advantage of swelling slightly under irradiation at the temperatures considered because of its refractory nature.
• the W-5Re alloy also offers an acceptable ductility with respect to the dimensioning rules considered.
• the Z10 CNDT15.15 B alloy could be chosen for the capsule and the W-5Re alloy for the shell, adapting the trigger and insertion device accordingly.
• abutment surfaces 24 form a radial surface and the thrust surface 26 forms a surface perpendicular to the longitudinal axis.
• this configuration is in no way limiting.
• a first technique may be to detect the insertion of the antireactivity in the heart, either directly through the neutron chambers, or indirectly through the "heart temperature treatment" (TRTC) which consists of measuring by means of thermocouples arranged above assemblies the coolant outlet temperature. If absorbent material falls, the power of the carrier assembly drops and the coolant outlet temperature of the carrier assembly drops. Therefore, by detecting a drop in the coolant temperature, the antireactivity insertion is detected.
• TRTC heart temperature treatment
• Another technique is to detect the suspended state or not of the set of absorbent elements.
• the detection device DT for implementing this technique is shown in FIGS. 2A to 2D. It is an ultrasonic telemetry device for measuring the distance between one or more transducers disposed above the assembly heads and a reflector whose position relative to the transducer (s) is dependent on the inserted state or not of the set of absorbent elements.
• the device DT comprises a pin 64 slidably mounted in a longitudinal bore 65 formed in the gripping head 13 of the capsule 10.
• the length of the pin 64 is such that its lower end bears against the attachment head 2.1 of the assembly 2 of absorbent element and an upper end protrudes from the upper end of the gripping head 13.
• the upper end of the peg 64 comprises a reflector 66.
• the lower end of the peg 64 is simply resting on the attachment head of the absorbent assembly, if the freeze was to be blocked, it would not prevent not the insertion of the rosary, insofar as it is not in solidarity.
• the weak section of the rod 64 being insufficient to form the reflector, the upper end of the rod 64 then has a shape such that its section is greater than the section of the rod in the bore and forms a reflector 66.
• it is a cone of conicity oriented upwards, the base of the cone forming the reflector. The cone comes into abutment against the upper part of the bore when the fall of the rod.
• the reflector 66 carried by the rod which passes through the gripping head
• Transducers 67 are disposed above the assembly head.
• the axial displacement of the reflectors during a insertion of the set 2 allows its detection and its location.
• the transducers are attached to the gates of the heart cover plug.
• a spring 68 mounted in compression between the lower end of the rod and the lower end of the bore.
• This spring is compressed in normal operation, ie when the assembly 2 is in the non-inserted position, the gripping head being held by the fingers 20.
• the spring 68 relaxes, causing the downward movement of the pin 64.
• This spring 68 advantageously prevents the pin 64 is prevented from falling.
• the rod 64 having a low mass, galling due to a corrosion phenomenon or the presence of impurities, for example, could prevent it from falling. Thanks to the force applied by the spring 68 during its expansion, such blockage is overcome, the pin 64 drops and the device detects the fall of the string 2.
• the force applied by the spring is not likely to be relaxed by the irradiation creep due to the position of the spring remote from the fissile core.
• the spring 68 thus improves the detection robustness of the telemetry device.
• the transducers are not arranged vertically above the reflector.
• Fixed mirrors are arranged on the internal face of the assembly head, in order to direct the ultrasound beam towards the reflector 66.
• the reflector 66 carried by the rod 64 may have a surface with several facets, to form a triplane mirror for example, to improve the directivity of the beam.
• the rod 64 When the assembly is unhooked (FIG. 2D) when the threshold temperature is reached or in the event of a nuisance tripping, the rod 64 does not rest on the attachment head, under the action of the spring 68 and the gravity detent, the rod 64 slides downwards in the bore 65, driving with it the reflector 66 which takes a second position resting on the The transducer 67 measures an elongation of the distance between the transducer 67 and the reflector 66 and thus makes it possible to detect the insertion of the assembly 2.
• the rod 64 having a small section, it is flexible in bending and a large mechanical clearance is provided with the bore; any risk of mechanical blockage can be avoided, even in case of significant deformation of the gripping head 13 due to the distortion of the axis and / or the crushing of the bore.
• This detection device makes it possible to guarantee the detection and localization in the heart of the fall of the set of absorbent elements in any situation and without in any way penalizing the reliability of triggering and insertion of this string.
• This detection device can be used in addition to the TRTC and / or fission chambers in order to diversify the detection means of the antireactivity insertion, or to replace these techniques.
• the trigger and insertion system is reported in the assembly, it is completely independent of the carrier assembly, and can therefore be advantageously managed independently of the fuel assembly.
• the triggering and insertion device according to the present invention is particularly suitable for a trigger and removable insertion system. Indeed, thanks to the triggering and insertion device, more particularly thanks to the stop 24 which ensures a locking up to the handling temperature, any risk of unlocking the fingers in handling situation is avoided, thus during the assembly of the capsule in the carrier assembly, and for example in case of shock, the set of absorbent elements can not fall, unless a break of the fingers, the attachment head or the cable. This advantage also appears during the integration of the assembly in the core (handling state described above).
• the fuel volume fraction is little reduced, and in fact the neutron performances of the core as well.
• the design of the assembly according to the invention makes it possible to apply the fuel cycle of the assemblies of the state of the art with a minimum of modifications and thus to optimize costs.
• the structure of the assembly according to the invention has little impact on the pressure drop of the carrier fuel assembly and therefore on the optimization of the thermal hydraulics of the core.
• the assembly according to the invention optimally uses the flow rate of the fuel assembly which ensures maximum speed and accuracy of triggering. Indeed, because of the central location of the ferrule in the assembly and its structure, it sees a flow very close to the flow of a Standard fuel assembly, its expansion is therefore representative of the coolant temperature and therefore the state of the assembly.
• the reliability of insertion of antireactivity is optimized.
• the capsule is mechanically decoupled from the deformations of the needle beam because it is protected by the sleeve which has a significant stiffness and in which it is also inserted with a large radial clearance.
• the presence of the needle bundle between the sleeve and the hexagonal tube also allows the capsule to be decoupled mechanically from the deformations affecting the pitch of the grating, insofar as the needle bundle has a certain capacity to accommodate the deformations of the hexagonal tube. , due to the presence of play between the needles and spacers son.
• the absorbent elements may be made of any neutron absorbing material.
• it may be boron carbide (B 4 C) more or less enriched in 10 B.
• hafnium-based materials may be hafnium-based materials. These materials have a high density, which reduces the time of fall, do not emit gas under irradiation, and therefore do not cause swelling, and do not see their ability to antireactivity under irradiation significantly reduce.
• refractory boride absorbent materials for example HfB 2 and TiB 2 , which have melting temperatures of the order of 3300 ° C. It is also possible to use europium hexaboride EuB6. We can also consider using Eu 2 0 3 . It does not generate gaseous products under irradiation. It also has a significant absorbency.
• the materials of the absorbent elements may for example be the following: Hafnium, Dy B 6 , Gd B 6 , Sm B 6 and Er B 4 , HfB 2 natural and natural TiB 2 .
• the assembly to be inserted can have a mitigation effect, for example Hafnium could serve as a mixing agent in case of generalized fusion of the heart.
• the coolant may be formed by any suitable liquid metal, for example sodium.
• suitable liquid metals that can be envisaged in a fast reactor are lead and lead-bismuth.
• the medium liquid metal avoids the potential problems of setting pressure of speakers (needle, capsule or other) by the helium coming from the 10 B.
• the viscosity The high metal medium also allows a sharp progressive deceleration at the end of the drop stroke which greatly limits the risk of fragmentation of the absorbent ceramic.
• the trigger temperature considered 660 ° C and a ferrule height of about 800 mm with the dimensions of selected components. It is possible to calculate the differential axial displacement of the ferrule with respect to the capsule:
• the displacement of the head of an actuator finger can be calculated between the operating temperature and the tripping temperature: the finger has a linear displacement of 5.4 mm and an angular displacement of 7.2 °.
• the fastening head of the assembly 2 then has an axial displacement between the operating temperature and the tripping temperature of 3.5 mm.
• the release and insertion device is simple in structure and very robust and has a reduced number of parts, in particular a reduced number of moving parts.
• the device comprises three fingers movable in rotation and a movable ring in translation.
• the triggering and insertion device, the triggering and insertion system and the carrier assembly according to the present invention are particularly suitable for use in sodium cooled fast neutron reactors. They can also be applied to other types of nuclear reactors (fast reactors cooled with other liquid metals such as lead or lead-bismuth, fast reactors cooled by gas, pressurized or boiling water reactors).

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Monitoring And Testing Of Nuclear Reactors (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=47257850

Family Applications (1)

Country Status (6)

Cited By (3)

Families Citing this family (11)

Citations (3)

Family Cites Families (14)

• 2011
  • 2011-12-02 FR FR1161104A patent/FR2983625B1/fr active Active
• 2012
  • 2012-11-30 CN CN201280068931.4A patent/CN104094359B/zh not_active Expired - Fee Related
  • 2012-11-30 JP JP2014543913A patent/JP6173334B2/ja active Active
  • 2012-11-30 WO PCT/EP2012/074101 patent/WO2013079664A1/fr active Application Filing
  • 2012-11-30 KR KR1020147018274A patent/KR20140097551A/ko not_active Application Discontinuation
  • 2012-11-30 RU RU2014126883/07A patent/RU2603128C2/ru not_active IP Right Cessation

Patent Citations (3)

Also Published As

Similar Documents

Legal Events