Fuel assembly handling system and process

Abstract

A fuel assembly handling system for moving fuel assemblies (20) between a reactor chamber (1) configured to house a nuclear reactor (10) and storage chambers (2) configured to store fuel ass emb lies (20) comprising a carousel (30) installed in a transfer chamber (3), said transfer chamber (3) communicating with the reactor chamber (1) via a reactor well (32), with a first storage chamber (2) via a first storage well (34), and with a second storage chamber (2) via a second storage well (36), the carousel (30) comprising housings (40), each housing (40) being configured to accommodate a fuel assembly (20), the carousel (30) being configured to move the housings (40), in the transfer chamber (3) between a reactor location opposite the reactor well (32), a second location opposite the first storage well (34), and a third location opposite the second storage well (36). The use of the same fuel assembly handling system for several nuclear reactors can also be envisaged.

Description

[0001] "FUEL ASSEMBLY HANDLING SYSTEM AND PROCESS"

[0002] Cross-Reference to Related Applications

[0003] This patent appl ication claims priority from Italian patent application no . 102023000017415 filed on August 21 , 2023 , the entire disclosure of which is incorporated herein by reference .

[0004] Technical field

[0005] The invention concerns the nuclear field, and in particular the handling of fuel assembl ies . More speci fically, the invention relates to a fuel assembly system and process for moving fuel assemblies between a reactor chamber configured to house a nuclear reactor and storage chambers configured to store fuel assemblies .

[0006] Technological background

[0007] The core of a nuclear reactor consists of fuel assemblies that group together a bundle of coated rods or needles that enclose fissile or fertile material usually in the form of pellets .

[0008] During the operating time of a nuclear reactor, the nuclear fuel contained in the fuel assemblies runs out , therefore it has to be replaced periodically . Since the depletion of the fuel assemblies depends on their position in the reactor core, the fuel assemblies are not irradiated at the same time . Fuel as semblies that are not completely depleted are generally moved to the reactor core .

[0009] An assembly is designed to remain generally between 2 and 5 years inside the core . The renewal of the irradiated fuel with new fuel is done by periodically ( e . g . between 6 and 24 months) refilling a fraction of the reactor core (between 20 and 50% of the total number of assemblies) , depending on the type of operation and performance level of the assemblies. Hence, the assemblies include a gripping head at their upper end that allows them to be lifted and moved. During this operation, the nuclear reactor must be switched off.

[0010] New fuel assemblies are generally made in a pellet manufacturing plant. They must then be transported to the nuclear power plants where they will be placed in a storage facility before being transferred to the reactor.

[0011] Instead, irradiated fuel assemblies that need to be replaced are removed from the reactor and placed in a dedicated storage facility before being transferred to a dismantling / recycling site.

[0012] The duration of the replacement of these fuel assemblies is an important cost factor, as the reactor is shut down during this period. The invention therefore aims to reduce the time needed for their replacement.

[0013] The loading / unloading of these fuel assemblies is carried out conventionally with assembly elevator systems or articulated or open vessel handling (e.g. for pressurised water reactors: PWR) or a closed vessel with a rotating cap system (e.g. for fast-neutron reactors: FNR) .

[0014] The system for handling assemblies on a fast-neutron reactor, particularly liquid-metal cooled reactors, is more complex than on a water reactor. In fact, in the latter case, it is possible to open the vessel and operate on sight, taking advantage of the neutron protection of the metres of water available to rearrange the reactor core .

[0015] Various systems have been developed to limit reactor downtimes when changing fuel assemblies .

[0016] As an example , patent FR2486297 can be cited . It describes a device for loading and unloading fuel assemblies that allows the assemblies to pass between a primary loading and unloading ramp that communicates with the reactor vessel and a secondary ramp that communicates with a storage or loading area for the assemblies . The handling of fuel assemblies consists of trans ferring the irradiated core assembly into a handling container with a first handling device comprising in particular a handling arm . The second step after the first consists of transporting the handling container containing an irradiated fuel assembly from a second handling device in an upward sloping direction to the outside of the reactor vessel above the closure plate . Then, once extracted from the reactor vessel , the irradiated fuel assembly is transported to an external storage vessel by a handling system such as a handling hood .

[0017] Patent FR2158491 describes an apparatus that moves fuel assemblies by trans ferring them from the reactor core to a storage carousel adj acent to that core . Fuel filling machines are mounted on the inner rotating cap, crossing it . Each loading machine i s equipped with a grappling hook and means to move it vertically upwards or downwards through a corresponding tubular guide or open laterally . Therefore , fuel assemblies can be removed from the core by aligning one of the loading machines above it , lowering the grappling hook of this machine and docking with the fuel assembly into it , then li fting the grappling hook to remove this fuel assembly from the core and li ft it into the corresponding guide . Near the trans fer machine , a fuel assembly storage carousel comprises a rotor equipped on its periphery with a series of fuel assembly holders . A drive shaft enables the rotor to be turned by means of a motor . The fuel assembly can then be stored or removed completely from inside the reactor by rotating the storage carousel to bring it vertically below the guide tube and evacuation passage and to remove it through this tube by another means with a grappling hook . Fuel assemblies are introduced into the core by performing these operations in reverse .

[0018] Finally, patent FR2953319 proposes a device consisting of at least one rotating drum, comprising at least two concentric storage areas , a storage area for new fuel assemblies and a storage area for irradiated fuel assemblies . This device is located inside the vessel , which allows the assemblies to "cool down" , i . e . reduce their residual energy, thus evacuating them from the reactor, and vice versa, allowing new fuels to re-enter the reactor . During the replacement of irradiated fuel assemblies , with the reactor at standstill , the rotating drum positions itsel f at the level of the pantograph arm to accommodate the irradiated fuel assembly, then rotates to make the new fuel assembly available to it . Rotations of the pantograph arm are therefore limited to the bare minimum . This operation can be repeated as many times as necessary .

[0019] State-of-the-art systems do not allow for an ef fective response to the handling of small modular reactor fuel assemblies : ( abbreviated to SMR) that use a liquid metal as a heat carrier, because they are too bulky and require too much maintenance . The development of an ef fective handling system by limiting the volume of the reactor vessel will therefore be an important advantage .

[0020] Presentation of the invention

[0021] The obj ect of the present invention is a system and a process for handling the fuel assemblies of a nuclear reactor, in particular a fast-neutron reactor, using a trans fer carousel that facilitates the trans fer of these assemblies between the reactor and the storage areas . This system allows work to be performed in parallel on several stations , which leads to time savings and thus limits the downtime of the reactor .

[0022] The invention thus aims to propose a fuel assembly handling system that makes the loading and unloading of fuel assemblies simpler and quicker, while guaranteeing a high level of safety, in particular by allowing simultaneous unloading or loading via a reactor well that opens in the reactor chamber, loading of a new fuel into a first storage area and unloading of an irradiated fuel assembly into a second storage area .

[0023] For that purpose , the invention proposes a fuel assembly handling system for moving fuel assemblies between a reactor chamber configured to house a nuclear reactor and storage chambers configured to store fuel assemblies characterised in that the handling system comprises a carousel installed in a trans fer chamber, said trans fer chamber communicating with the reactor chamber via a reactor well , with a first storage chamber via a first storage well , and with a second storage chamber via a second storage well , the carousel comprising housings , each housing being configured to accommodate a fuel assembly, the carousel being configured to move the housings , in the trans fer chamber between a reactor location facing the reactor well , a second location facing the first storage well , and a third location facing the second storage well .

[0024] The invention is advantageously complemented by the following di f ferent features taken alone or according to their various possible combinations : the reactor well extends between a plate of the reactor chamber and an upper part of the trans fer chamber, and each storage well extends between a storage chamber and the upper part of the trans fer chamber ; the carousel comprises a shaft about which the housings are configured to rotate , the housings being distributed around the shaft according to an angular of fset in a plane of rotation, and the reactor and storage wells being evenly distributed around the shaft at the same angular of fset ; the carousel comprises a housing support accommodating the housings and displaceable along the shaft in order to alter the height of the housings in the trans fer chamber ;

[0025] - the system comprises cases configured to be received in the housings o f the carousel , each case being configured to contain a fuel assembly and comprising a removable plug configured to seal the case in the presence of a fuel assembly in the case ;

[0026] - the system can be equipped with a suitable heating device adapted to heat the case ;

[0027] - the system comprises a handling hood movable within the reactor chamber and configured to dock with the reactor well , wherein the handling hood comprises a gripping member adapted to extend through the reactor well , grip and li ft the plug of the case or the fuel element , according to the situation;

[0028] - the system comprises a movable member configured to selectively position itsel f in the reactor well below the handling hood when the handling hood is secured to the well , the movable member being configured to receive the plug of the case ;

[0029] - the reactor well comprises two slide valves configured to selectively seal the reactor well , the movable member being arranged between the two slide valves .

[0030] The invention al so relates to a nuclear power plant comprising a reactor chamber housing a nuclear reactor, and at least two storage areas for storing fuel assembl ies , the nuclear power plant comprising a fuel assembly handling system according to the invention .

[0031] The invention also relates to a process for handling fuel assemblies between a reactor chamber configured to house a nuclear reactor and two storage chambers configured to store fuel assemblies , using a fuel assembly handling system according to the invention, comprising the following steps : a ) a fuel assembly, closed in its housing by a cap, is loaded into the housing of the carousel at the second location through a first storage well , b ) the housing is moved by rotation of the carousel from the second location to the reactor location opposite the reactor well , c ) the plug of the case enclosing the fuel element is removed in the reactor well , d) the fuel assembly is unloaded from the housing through the reactor well to the reactor location, e ) another fuel assembly is loaded into the housing at the reactor location through the reactor well , f ) the housing is moved by rotation of the carousel from the reactor location to a third location opposite a second storage well , g) the other fuel assembly is unloaded from the housing at the third location through the second storage well , h) the housing is moved by rotation of the carousel from the third location to the second location opposite the first storage well .

[0032] Preferably, between two successive displacements of housings by the carousel , a fuel assembly is unloaded from a housing at the reactor location, a fuel assembly is loaded into the housing arranged at the reactor location, a fuel assembly is loaded into the housing at the second location, and a fuel assembly is unloaded from a housing at the third location . In addition, preferably, a case received in a housing contains an inert atmosphere at least when a plug closes the case and the case contains a fuel assembly .

[0033] The invention may also relate, in combination with or independently of the trans fer carousel , to a process for handling fuel assemblies , wherein :

[0034] - a case in a trans fer chamber is docked to a well connecting the trans fer chamber and a reactor chamber housing a nuclear reactor, the case being closed by a plug,

[0035] - a gripping member of a handling hood docked to the reactor well in the reactor chamber enters the reactor well and grips the plug,

[0036] - a movable element is positioned in the reactor well below the handling hood and receives the case plug,

[0037] - the movable element is retracted to leave a passage in the reactor well free ,

[0038] - a fuel assembly passes through the reactor well to be removed from or placed in the casing .

[0039] The process may then comprise the following steps :

[0040] - the movable element carrying the plug is positioned in the reactor well below the handling hood,

[0041] - the gripper enters the reactor well and grips the plug,

[0042] - the movable element is retracted to leave a passage in the reactor well free ,

[0043] - the gripper enters the reactor well and replaces the plug to close the case .

[0044] Presentation of Figures

[0045] Further features , purposes and advantages of the invention will emerge from the fol lowing description, which is purely illustrative and not limiting and should be read with reference to the accompanying drawings , in which :

[0046] - Figure 1 schematically illustrates a sectional view of an assembly comprising a reactor chamber housing a nuclear reactor, a storage area and a trans fer device installed in a trans fer chamber, according to a possible embodiment of the invention;

[0047] - Figure 2 is a schematic view from above showing an example of an arrangement of a trans fer device between a reactor chamber and two storage areas , according to a possible embodiment of the invention;

[0048] - Figure 3 is a schematic view from above showing an example of an arrangement of two trans fer devices between three storage areas and four reactor chambers , according to a possible embodiment of the invention;

[0049] - Figure 4 schematically illustrates a sectional view of a housing of the trans fer device at a position opposite the reactor well to which a handling hood is docked;

[0050] - Figure 5 is a diagram showing the steps of the process according to the invention;

[0051] - Figure 6a shows the configuration of the reactor well to which an empty case is attached in the initial step of loading an irradiated fuel assembly into the case ;

[0052] - Figure 6b shows a step of loading an irradiated fuel assembly into a case , following the step shown in Figure 6a ;

[0053] - Figure 6c shows a step of loading an irradiated fuel assembly into a case , following the step shown in Figure 6b ;

[0054] - Figure 6d shows a step of loading an irradiated fuel assembly into a case , following the step shown in Figure 6c ;

[0055] - Figure 6e shows a step of loading a first irradiated fuel assembly into a case , following the step shown in Figure 6d;

[0056] Figure 6f shows a step of loading an irradiated fuel assembly into a case , following the step shown in Figure 6e ;

[0057] - Figure 6g shows a step of loading an irradiated fuel assembly into a case , following the step shown in Figure 6f ;

[0058] - Figure 6h shows a step of loading an irradiated fuel assembly into a case , following the step shown in Figure 6g;

[0059] Figure 7a shows a step of unloading a new fuel assembly from a case ;

[0060] Figure 7b shows a step of unloading a new fuel assembly from a case , following the step shown in Figure 7a ;

[0061] Figure 7c shows a step of unloading a new fuel assembly from a case , following the step shown in Figure 7b ;

[0062] Figure 7d shows a step of unloading a new fuel assembly from a case , following the step shown in Figure 7c .

[0063] The drawings are provided as non-limiting examples of the invention . They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily on the scale of practical applications . In particular, the relative dimensions of the di f ferent elements that make up the reactor are not representative of reality .

[0064] Detailed description

[0065] A fuel assembly is a grouping of elements made up of nuclear fuel , and in particular fi ssile material , generally having an elongated shape along a longitudinal axis , and comprising a plurality of nuclear fuel rods or needles . Each rod or needle (between 150 and 300 per group ) is in the form of a sheath inside which a column of pellets of fissile material is stacked ( e . g . MOX ) within which the nuclear reactions that release heat are produced . These groups generally have a hexagonal cross-section of several tens of centimetres on one side and measure several metres in length .

[0066] A fuel assembly can be new or irradiated . There is enough fissile material in a new fuel assembly to maintain the nuclear reactions within a reactor, whereas for an irradiated fuel assembly, the fuel assembly has been irradiated to such an extent that it cannot be used in a reactor without having undergone appropriate treatment . In other words , by irradiated fuel assembly, we mean an assembly that , while still having potentially usable fissile material , the neutron radiation rate of the rod sheaths containing the fissile material and the fission gas pressure inside reach the maximum permissible values beyond which the sheath could crack with the emission of fissile material and fission gas . A fuel assembly can also be a false fuel assembly, or dummy fuel assembly, in which case it is devoid of fissile material .

[0067] In order to gain a good understanding of the invention, various embodiments of a fuel assembly handling system will now be described by way of non-limiting examples , with reference to the accompanying figures . Figure 1 shows a sectional view of nuclear plant comprising a reactor chamber housing the nuclear reactor, a storage area and a trans fer device installed in a trans fer chamber .

[0068] In the example shown, the nuclear reactor in a nonlimiting manner i s a fast-neutron reactor, FNR; the invention can however be applied to other reactor types . By way of example , an FNR can contain between 30 and 600 fuel assemblies . Each fuel assembly needs to be replaced approximately every 2-4 years, resulting in the reactor being shut down for a period of several days.

[0069] The reactor 10 comprises a main vessel 12 having a vertical axis suspended on a horizontal plate 14. The main vessel 12 is here filled with a liquid cooling metal, e.g. lead. The liquid metal level is topped by a layer of an inert gas, commonly argon. The horizontal plate 14 rests on a concrete floor 15. The reactor chamber 1, which houses the nuclear reactor 10, is delimited by a containment cell 16, typically made of concrete, of which floor 15 is a part. The reactor chamber 1 integrates the containment space of nuclear reactor 10 as well as the fuel assembly handling devices. The core 18 of the nuclear reactor 10, which is arranged inside an additional vessel or inner vessel 19, which delimits two separate regions in the main vessel 12, is immersed in liquid metal and essentially consists of fuel ass e mb lies 20.

[0070] The nuclear plant also comprises at least two storage chambers 2 configured to store fuel assemblies. In particular, at least a first chamber 2a can be used to store new fuel assemblies, while at least a second chamber 2b can be used to store irradiated fuel assemblies. For safety reasons, the storage chambers 2 are separate from the reactor chamber 1 and do not communicate with the latter. In particular, the containment cell 16 that delimits the reactor chamber 1 can partially delimit the storage chambers 2. Preferably, the storage chambers 2 are adjacent and contiguous to the reactor chamber 1.

[0071] The nuclear plant also comprises a transfer chamber 3 that houses a transfer carousel 30, or rotating transfer device 30. This transfer chamber 3 communicates with the reactor chamber 1 via a reactor well 32, with the first storage chamber 2a via a supply well 34, and with the second storage chamber 2b via an evacuation well 36. The reactor well 32 serves to transfer fuel assemblies between the reactor chamber 1 and the transfer chamber 3, the supply well 34 serves to transfer fuel assemblies, typically new, from the first storage chamber 2a to the transfer chamber 3, the evacuation well 36 serves to transfer fuel assemblies, typically irradiated, from the transfer chamber 3 to the second storage chamber 2b.

[0072] The transfer chamber 3 is delimited by a chamber 37 and can adopt, for example, a general cylindrical shape around a vertical axis. The upper part 38 of the transfer chamber 3 is enclosed by a material structure that absorbs any radiation that may be emitted, forming the upper part of the cell 37. The wells 32, 34, 36 cross the upper part 38 of the transfer chamber 3. The wells 32, 34, 36 are preferably sealable with removable lids. Each lid is equipped with a system that allows it to be moved, by known means, between a sealing position in which it closes the well 32, 34, 36, and a waiting position in which it leaves the well 32, 34, 36 free. For example, VAT valves (VI, V2, V4) can be used, preferably motorised. The wells 32, 34, 36 are evenly distributed according to a rotation symmetry around a vertical axis.

[0073] The transfer chamber 3 houses the carousel 30, comprising housings 40, each housing 40 being configured to accommodate a fuel assembly 20, the carousel 30 being configured to move the housings 40 into the transfer chamber 3 by rotation. More precisely, the carousel 30 moves each housing 40 between locations 42, 44, 46 which face the wells 32, 34, 36, respectively. Typically, the carousel 30 comprises three housings 40. The carousel 30 is intended to rotate following successive loading / unloading locations of the fuel assemblies 20 so that the housings 40 are each aligned in turn with a loading / unloading well 32, 34, 36 arranged in the transfer chamber cell 3. The carousel 30 is preferably made of radiation-resistant steel.

[0074] The carousel 30 comprises a shaft 47 about which the housings 40 are configured to rotate, the housings 40 being evenly distributed around the shaft 47 at an angular offset in a plane of rotation, preferably horizontal. The reactor wells 32 and storage wells 34, 36 are evenly distributed around the shaft 47 at the same angular offset. This angular offset is preferably 120°, if the carousel comprises three housings 40.

[0075] In the example of Figure 2, the transfer chamber 3 ensures the movement of the fuel assemblies 20 between a single reactor chamber 1, a first storage chamber 2a which serves, for example, to store the new fuel assemblies 20, and a second storage chamber 2b which serves, for example, to store the irradiated fuel assemblies 20. In this case, each of the reactor chambers 1 between the first storage chamber 2a and the second storage chamber 2b can only be equipped with one well 32, 34, 36.

[0076] However, the transfer chamber 3 can be equipped with several sets of three wells 32, 34, 36 angularly offset. However, it is possible that one and the same fuel assembly handling system 20 serves several nuclear reactors 10, or has several carousels 30 for one and the same storage chamber 2. In the example of Figure 3, a first carousel 30a housed in a first transfer chamber 3a serves two reactor chambers la, lb, which house two respective reactors 10a, 10b. Reactor wells 32a, 32a' are provided for the first transfer chamber 3a to communicate with each of the two reactor chambers la, lb. Two supply wells 34 make the first transfer chamber 3a communicate with the first storage chamber 2a' : a first supply well 34a that has an angular offset around the carousel 30a, typically 120°, with the first reactor well 32a, and a second supply well 34a' that has the same angular offset, typically 120°, with the second reactor well 32a' . Similarly, two evacuation wells 36 make the first transfer chamber 3a communicate with the second storage chamber 2b: a first evacuation well 36a that has an angular offset around the carousel 30a, typically 120°, with the first reactor well 32a, and a second evacuation well 36a' that has the same angular offset, typically 120°, with the second reactor well 32a' .

[0077] Similarly, a second carousel 30b is housed in a second transfer chamber 3b serves two reactor chambers 1c, Id, which house two respective reactors 10c, lOd. Reactor wells 32b, 32b' are provided to make the second transfer chamber 3b communicate with each of the two reactor chambers 1c, Id. Two supply wells 34 make the second transfer chamber 3b communicate with another first storage chamber 2a' ' : a first supply well 34b that has an angular offset around the carousel 30b, typically 120°, with a first reactor well 32b, and a second supply well 34b' that has the same angular offset, typically 120°, with the second reactor well 32b' . Similarly, two evacuation wells 36 make the second transfer chamber 30b communicate with the second storage chamber 2b: a first evacuation well 36b that has an angular offset around the carousel 30b, typically 120°, with the first reactor well 32b, and a second evacuation well 36b' that has the same angular offset, typically 120°, with the second reactor well 32b' .

[0078] In the example of Figure 3, we therefore have the same storage chamber 2b for two transfer chambers 3a, 3b, a transfer chamber 3a, 3b shared by two reactor chambers la, lb, 1c, Id, or a storage chamber 2a, 2a' shared by two reactors 10a, 10b, 10c, lOd via a single transfer chamber 3a, 3b. The possibilities are therefore manifold, and not limited to this specific example. The arrangement of the series of wells 32, 34, 36 is chosen to allow a reactor chamber 1 to be associated with two storage chambers 2a, 2b, in order to allow the handling of the fuel assemblies 20.

[0079] The current trend in the construction of nuclear reactors 10 is to group these nuclear reactors 10, e.g. for two or four units, at the same site in order to reduce some investments by pooling certain members of these nuclear reactors 10. The use of the same fuel assembly handling system 20 for several nuclear reactors 10 makes it possible not only to reduce the cost of constructing nuclear reactors 10 grouped on the same site, but also to ensure more frequent service of the mechanical elements of the handling system on any of the nuclear reactors 10 located in close proximity to each other . For a single nuclear reactor 10 , a handling system is brought into operation at moments that are spaced apart signi ficantly over time causing very long downtimes which are detrimental to this handling system . Sharing the handling system of fuel assemblies 20 allows more frequent use , and therefore less downtime .

[0080] As can be seen in Figure 1 and Figure 4 , the carousel 30 comprises a housing support 31 which accommodates the housings 40 , for example a disc, or arms extending from the shaft 47 , rotatably mounted on the shaft 47 . This housing support 31 preferably extends into the top part of the carousel 30 and the trans fer chamber 3 , and is preferably movable along the shaft 47 in order to change the height of the housings 40 in the trans fer chamber 3 .

[0081] Preferably, the shaft 47 extends from the upper part 38 of the trans fer chamber 3 , at its lower part 39 opposite the upper part 38 , and is rotationally mounted in the upper part 38 and the lower part 39 . A motor is integrated into the shaft 47 , for example at its upper part 70 ' or lower part 70 , in order to drive the carousel 30 in rotation .

[0082] Each housing 40 is shaped to receive a case 50 that can be installed by a vertical downward translation into the housing 40 and removed from the housing by a vertical upward movement . In particular, the housing may comprise a tubular body 52 that can accommodate a fuel assembly 20 . The housing 40 typically has a through orifice 48 configured to be vertically traversed by the body 52 of the case , and the support means 49 of the case 50 , for example a shoulder on which a portion of the case 50 may rest . The internal diameter of the through ori fice 48 of the housing 40 is greater than the diagonal of the section of the cases 50 so that the latter can be introduced vertically into the housings 40 .

[0083] The support means 49 may be active and comprise a gripper configured to , in a clamping configuration, clamp and hold the case 50 in position, preventing vertical translation thereof , and in a release position, leave the case 50 free to translate vertically into the through ori fice 48 . Preferably, the support means 49 are arranged above the through ori fice 48 .

[0084] Each housing 40 may comprise means for transmitting power to a case and, for example , may include electrical contactors configured to be electrically connected to a case 50 when it is arranged in the housing 40 . The case 50 can then be supplied with electricity from the housing 40 , for example to power a heating device adapted to heat the body 52 of the case 50 .

[0085] Preheating of the fuel assembly 20 prior to its introduction into the reactor core can also be performed by a fixed system, e . g . located below the well 34 , anchored to the wall of the chamber 3 . This system may comprise a motorised heated gripper mechanism that can, i f necessary, rest on the case 50 . This heating device is particularly advantageous for avoiding any thermal shock .

[0086] The cases 50 are configured to be received in the housings 40 of the carousel 30 , each case 50 being configured to contain a fuel assembly 20 and comprising a removable plug 54 configured to seal the case 50 , in particular, in the presence of a fuel assembly 20 in the case 50 . The plug 54 comprises a circular section with a diameter greater than the internal diameter of the circular section of the body 52 of the case 50 , and is configured to hermetically seal the case 50 . For example , the plug 54 may comprise a protruding part , e . g . circular, shaped to fit into a receiving space such as a groove arranged in the wall thickness of the body 52 of the case 50 . Preferably, the plug 54 comprises a gripping area 56 , taking for example as illustrated the shape of a cavity or recess , typically arranged in the centre of the plug 54 , but which may be any element that allows gripping by the gripping member 62 , such as a protruding part gripped by a gripper, for example in the shape of a mushroom, buckle or handle , or which allows the engagement of the gripping member 62 .

[0087] The plug 54 is typically made of stainless steel , and can be maintained for example by welding with a metal gasket that is applied liquid and then cooled . For example , the body 52 of the case 50 may comprise at its upper end a groove filled with molten metal , typically lead, into which a part of the plug 54 is introduced when the plug 54 closes the case 50 . When the lead is solid, the plug 54 is sealed on the case 50 . When the lead is liquefied, plug 54 is free to be removed or introduced . It is possible to provide heating elements around this groove , e . g . integrated in the reactor well 32 , or in the holders 49 of the housings 42 , 44 and 46, and to be electrically powered by the supports 31 , in order to selectively liquefy the lead, and thus selectively seal or loosen the plug 54 . Preferably, a case 50 received in a housing 40 contains an inert atmosphere at least when a plug 54 closes the case 50 and the case 50 contains a fuel assembly .

[0088] As mentioned above , each case 50 can be equipped with a heating device adapted to heat the body 52 of the case 50 . Typically, this heating device may comprise an electrically conductive element that extends around the body 52 , e . g . by wrapping itsel f , and adapted to heat the case by the ohm ef fect or by electrical induction .

[0089] Each case 50 is intended to contain a fuel assembly 20 , and is therefore compliant to accommodate a fuel assembly 20 in an internal volume . A fuel assembly 20 comprises a body

[0090] 22 extending longitudinally, terminated by a handling head

[0091] 23 through which the fuel assembly 20 can be grasped and moved . As mentioned above , the fuel assemblies 20 must be replaced periodically in the core 18 of the nuclear reactor 10 . A handling hood 60 is used to handle a fuel assembly 20 in the reactor chamber 1 .

[0092] The handling hood 60 is vertically movable , and can move hori zontally, e . g . along a bridge equipped with a rolling track . The handling hood 60 comprises a gripping member 62 , for example a grappling hook or gripper, configured to grasp a fuel assembly 20 , li ft it , move it by hori zontal translation and lower it again . The handling hood 60 is configured to contain a fuel assembly 20 in an internal volume 63 with a lower opening, e . g . closed by shutters . Preferably, a watertight valve closes the lower opening of the internal volume 63 . The handling hood 60 is configured for docking to the reactor 10 and the reactor well 32 , preferably integrally and hermetically . At the same time as the fuel assembly 20 , the internal volume 63 houses the gripping member 62 in its upper part .

[0093] The handling hood 60 comprises a solid body made of an armouring material (biological shield) to stop nuclear radiation in which the internal volume 63 for a fuel assembly 20 is arranged . The fuel assemblies 20 for fast-neutron reactors have a signi ficant length relative to their transverse dimensions . Accordingly, the body of the handling hood 60 may, in this case , have an elongated shape and the housing of the fuel assembly 20 is arranged in the internal volume 63 , preferably in a central position and in a substantially axial direction .

[0094] In order to extract a fuel assembly 20 from the core 18 of the reactor 10 , the handling hood 60 can move above the fuel assembly 20 inside the inner vessel 19 . The hori zontal plate 14 has a circular opening in which a set of two rotatable lids is mounted : a central large rotatable lid 64 and a small rotatable lid 66 , of fset from each other . The large lid 64 covers the upper opening of the inner vessel 19 , and rotates around an axis located in the centre of the large lid 64 , the small lid 66 covers an opening of the large lid 64 and rotates around its axis , the latter being, however, of fset from the axis of the large lid 64 . Therefore , by rotating the large lid 64 and the small lid 65 , it is possible to move a sealable access provided in the small lid 66 to the surface of the inner vessel 19 , giving access to the di f ferent locations of the fuel assemblies 20 within the inner vessel 19 .

[0095] Once the access is sealable opposite the fuel assembly 20 to be extracted, the handling hood 60 can descend to be docked with the sealable access ( 66 ' ) arranged in the small lid 66 . The gripping member 62 of the handling hood 60 is movable in vertical translation with respect to the rest of the handling hood, and descends until it reaches the handling head 23 . The gripping member 62 of the hood then grips the handling head 23 and ascends to bring the fuel assembly into the handling hood 60 . The li fting means of the overhead crane li ft the handling hood 60 away from the small lid 66 . Shutters can close to ensure the containment of the fuel assembly 20 in the handling hood 60 .

[0096] The overhead crane moves the handling hood 60 above the reactor well 32 , where the fuel assembly 20 may be placed in a well 50 of a housing 40 of the carousel 30 , in the case of a fuel assembly trans fer, which will now be described in detail , with reference to Figures 5 , 6a-6h and 7a-7d .

[0097] The fuel assembly 20 handling system allows fuel assemblies 20 to be moved between a reactor chamber 1 and storage chambers 2 , with simultaneous operations being carried out in parallel , saving considerable time .

[0098] The carousel 30 rotates between positions in which the housings 40 in the trans fer chamber 3 are located between a reactor location 42 opposite the reactor well 32 , a supply location 44 opposite the supply well 34 , and an evacuation location 46 opposite the evacuation well 36 . At any given time , a housing 40 therefore faces the reactor well 32 , a housing 40 faces the supply well 34 , and a housing 40 faces the evacuation well 36 . It is therefore possible to simultaneously load or unload fuel assemblies 20 , preferably in cases 50 , through the three wells 32 , 34 , 36.

[0099] As illustrated in Figure 5 , between two successive movements of hous ings 40 ( step S I ) via the carousel 30 , the same movement step ( step S2 ) is implemented, which includes operations carried out at the three wells 32 , 34 , 36 . A fuel assembly 20 is unloaded from a housing 40 at reactor location 42 opposite the reactor well 32 in order to supply a fuel assembly 20 to the nuclear reactor 10 ( step S32a ) . This step leaves an empty case 50 in the housing 40 , and is followed by another step ( step S32b ) in which a fuel assembly 20 is loaded into the housing 40 arranged in this reactor location . This is an irradiated fuel assembly 20 removed from the core 18 of the nuclear reactor 10 , which is introduced into the case 50 left empty . At the same time , a fuel assembly 20 contained in a case 50 is loaded into a housing at the supply location 44 oppos ite the supply well 34 ( step S34 ) . This is typically a new fuel assembly 20 taken from the first storage chamber 2a and intended for later introduction into the core 18 of the nuclear reactor 10 in a subsequent handling step after a shi ft of the assemblies 40 from the carousel 30 . Simultaneously, a fuel assembly 20 contained in a case 50 is unloaded from a housing 40 at the evacuation location 46 opposite the evacuation well 36 . This is an irradiated fuel assembly 20 , which was previously recovered at the reactor location 42 opposite the reactor well 32 during a previous handling step prior to the displacement of the housings 40 by the carousel 30 (step SI) .

[0100] Following the path of a housing 40 of the carousel 30, the following operations can be described: a) a fuel assembly 20 contained in a case 50 is loaded into the housing 40 from the carousel 30 at the supply position 44 through the supply well 34, typically into a case 50 positioned in the housing 40 (step S34) , b) the housing 40 is moved by rotation of the carousel 30 from the supply position 44 towards the reactor position 42 opposite the reactor well 32 (step SI) c) the fuel assembly 20 is unloaded from its case 50 from the housing 40 at the reactor location 42 through the reactor well 32 (step S32a) , typically leaving an empty case 50 in the housing 40, d) another fuel assembly 20 is loaded into the housing 40 at the reactor location 42 through the reactor well 32 (step S32b) , typically in the empty case 50 in the housing 40, e) the housing 40 is moved by rotation of the carousel 30 from the reactor location 42 to the evacuation location 46 facing the evacuation well 36 (step SI) f) the other fuel assembly 20 is unloaded from the housing 40 at the evacuation location 46 through the evacuation well 36 (step S36) , typically by removing the case 50 containing this other fuel assembly 20, g) the housing 40 is moved by rotation of the carousel 30 from the evacuation location 46 to the supply location 44 facing the supply well 34 (step SI) .

[0101] Thus, three rotations of the carousel 30 bring the housing 40 to three locations 42, 44, 46 corresponding to three loading / unloading locations. At each location 42, 44, 46, a fuel assembly loading or unloading operation can take place, without waiting for the other locations, which significantly reduces the time required to change the fuel assemblies 20 of the core 18.

[0102] Figures 6a-6h show a loading step of an irradiated fuel assembly 20 into an empty case 50 at the reactor location 42 opposite the reactor well 32. These steps can be implemented when using a carousel 30 as described, or can also be implemented directly from the use of such a carousel 30, other means thus being able to be used to connect the case 50 to the reactor well 30.

[0103] The well 32 is equipped with a lower docking station 80, configured to cooperate with the upper part of the case 50, by shape complementarity. Preferably, the lower docking station 80 protrudes into the transfer chamber 3 from its upper part 38. The well 32 is also equipped with an upper docking station 82, configured to cooperate with a lower end of the handling hood 60, by shape complementarity. The lower 80 and upper 82 docking stations must ensure a sealed coupling. Preferably, the upper docking station 82 protrudes into the reactor chamber 1 from the plate 14. A docking station means any well equipment that allows at least the attachment of a handling hood in a plane perpendicular to the axis of the well (typically in the horizontal plane) , and preferably allows hermetic communication with the well. The coupling interface may comprise, for example, flanges, joints, grooves, etc., which act by complementing the shape with a handling hood . Active components such as j aws or fastening elements can also be provided . The lower docking station 80 can be equipped with an electrical device capable of heating and melting the metal that seals the plug 54 .

[0104] In the example described below, an empty case 50 closed and kept under inert gas ( e . g . argon) is placed in a housing 40 of the carousel 30 . The carousel 30 mounts the case 50 up to the lower docking station 80 . This is the situation illustrated in Figure 6a . The case 50 is obstructed by a plug 54 .

[0105] The reactor well 32 comprises two slide valves VI , V2 configured to selectively seal the reactor well 32 . Preferably, a first slide valve VI is arranged below the upper part 38 of the trans fer chamber 3 , while a second slide valve V2 is arranged above the plate 14 of the reactor chamber 1 . In the initial phase il lustrated by Figure 6a the two slide valves VI , V2 are closed, obstructing the reactor well 32 . The two slide valves VI , V2 define between them an intermediate area 84 of the reactor well 32 , which is isolated from both the trans fer chamber 3 and the reactor chamber 1 as long as the slide valves VI , V2 are closed . This intermediate area 84 comprises a recess 86 in which a movable element 90 is arranged in a stowed position . In the illustrated example , the movable element 90 is a motorised trolley, but the movable element 90 may be any device capable of selectively adopting a stowed position in which the movable element 90 leaves the passage in the reactor well 32 free , and an intercepted position in which the movable element is located in the passage of the reactor well 32 , below the handling hood 60 when the handling hood 60 is coupled to the reactor well 32 . The movable element 90 can be , for example , a platform moved by an actuator .

[0106] Once the case 50 is docked to the lower docking station 80 , the handling hood 60 is docked to the upper docking station 82 , as illustrated in Figure 6b, after being moved by the overhead crane and being lowered . The two sl ide valves VI , V2 of the reactor well 32 can then be opened, connecting the lower docking station 80 , the intermediate area 84 and the upper docking station 82 . At the moment illustrated, a slide valve V3 that closes the internal volume 63 of the handling hood 60 is closed, but is subsequently opened, connecting the internal volume 63 of the handling hood 60 , the upper docking station 82 , the intermediate area 84 and the lower docking station 80 .

[0107] The plug 54 closes the case 50 again . The gripping member 62 is then lowered, and crosses the reactor well 32 to reach the plug 54 , and more precisely the gripping area 56 , formed here by a cavity in the centre of the plug 54 . The gripping member 62 cooperates with the gripping area 56 to grip the plug 54 , and overhangs it through the reactor well 32 , at least above the movable element 90 . In the example illustrated in Figure 6c, the plug 54 is raised to the inner volume of the handling hood 60 , but it could remain lower, and for example remain at the level of the upper docking station 82 .

[0108] The gripping member 62 releases or rests the plug 54 on the movable element 90 , which is then withdrawn to its stowed position, in the recess 86 , leaving the passage of the reactor well 32 at the level of the intermediate area 84 free , as illustrated by Figure 6d . The gripping member 62 is removed in the inner volume 63 of the handling hood 60 , and the slide valve V3 of the handling hood 60 is closed again . The second slide valve V2 is also closed again, isolating the intermediate area 84 and allowing the handling hood 60 of the reactor well 32 to be disengaged . The handling hood 60 is then moved to collect an irradiated fuel assembly 20 in the core 18 of the nuclear reactor 10 and return it opposite the reactor well 32 , as shown in Figure 6e .

[0109] The handling hood 60 is lowered back down and docked to the handling well 32 from the upper docking station 82 , and the third slide valve V3 is opened, as is the second valve V2 , connecting the internal volume 63 of the handling hood 60 in which the fuel assembly 60 i s located and retained by the gripping member 62 and the handling well 32 . The fuel assembly 60 is lowered down through the reactor well 32 by the gripping member 62 to the case 50 , as illustrated by Figure 6f .

[0110] Once the fuel assembly 60 rests in the case 50 , the gripping member 62 releases the fuel assembly 60 and ascends into the handling hood 60 . The movable element 90 , also carrying the plug 54 , is then positioned in the reactor well 32 below the handling hood 60 by rolling its wheels , as illustrated in Figure 6g . The gripping member 62 then descends to grip the plug 54 on the movable element 90 in the same manner as explained above . The movable element 90 is then removed, preferably after the li fting of the plug 54 by the gripping member 62 . The gripping member 62 is then lowered to pass through the reactor well 32 and reposition the plug 54 on the case 50 as shown in Figure 6h and release it . All that remains now is to reassemble the gripping member 62 in the handling hood 60 . The slide valves VI , V2 of the reactor well 32 and the slide valve V3 of the handl ing hood 60 are then closed . The case 50 can be disconnected from the reactor well 32 , e . g . disengaged from the lower docking station 80 . The carousel 30 may then move the housing that carries the case 50 towards the evacuation location 46 facing the evacuation well 36 to allow evacuation of the irradiated fuel assembly 20 .

[0111] The rotation of the carousel 30 allows a case 50 containing a new, already preheated fuel assembly 20 to be placed below the reactor well 32 , ready to be removed with the handling hood 60 and introduced into the reactor 10 . Once this new fuel assembly 20 is removed, the case 50 is empty and can be used for the process described above . Only for the first irradiated fuel assembly 20 removed from the core 18 is it necessary to carry an empty case 50 in order to free a location o f the core 18 that will allow a fuel assembly 20 to be inserted, which will leave a case 50 empty .

[0112] With reference to Figures 7a-7d, an example of unloading a new fuel assembly 20 from a case 50 will be described . Many of the characteristics that were previously described are not described again, but may be present . As before , these steps can be implemented when using a carousel 30 as described, or can also be implemented directly from the use of such a carousel 30 , other means thus being able to be used to connect the case 50 to the reactor well 30 . As shown in Figure 7a, a case 50 containing a new fuel assembly 20 is brought to the reactor position opposite the reactor well 32 . The case 50 is docked to the lower docking station 80 , the slide valve V3 of the handling hood 60 is open, as is the second slide valve V2 of the reactor well 32 . The first valve VI can remain temporarily closed .

[0113] Once the first valve VI has been opened, the gripping member 62 grasps and reassembles the plug 54 , as illustrated in Figure 7b . The movable element 90 is then pos itioned in the passage of the reactor well 32 below the handling hood 60 to recover the plug 54 released or deposited by the gripping member 62 and to release the plug 54 from the passage , withdrawing, as illustrated in Figure 7c . The gripping member 62 is then lowered to grasp the fuel assembly 20 and reassemble it in the handling hood 60 . The valve V3 of the handling hood 60 is then closed again, as is the second valve V2 of the reactor well 32 , as shown in Figure 7d . The handling hood 60 can then be disconnected from the reactor well 32 to bring the fuel assembly 20 into the core 18 of the nuclear reactor 10 . Another irradiated fuel assembly 20 can then be brought back and loaded into the case 50 as explained above with reference to Figures 6e- 6h .

[0114] In these examples , the gripping member 62 is used both to handle the fuel assemblies 20 and to remove the plug 54 of the case . However, it is possible to use two dedicated gripping members 62 : one gripping member to handle the plug 54 , and another gripping member to handle the fuel assembly

[0115] 20 .

[0116] Similar handling is carried out at the level of the supply well 34 and the evacuation well 36 . However, insofar as the storage areas 2 do not house nuclear reactors 10 , the procedures may be simpli fied . In particular, handling through the supply well 34 and the evacuation well 36 does not imply the need to remove the plug 54 : it is the case 50 containing the fuel assembly 20 and closed by its plug 54 that is loaded into the housing 40 through the supply well 34 , and unloaded through the evacuation well 36.

[0117] To do this , a trans fer station 100 is provided in each storage area 2 , allowing the trans fer of fuel assemblies , typically in a case 50 , between the inside of the housing 40 of the carousel 30 and a location in the storage area 2 , for example a receiving basket . Each trans fer station 100 comprises means for li fting and moving the cases 50 , such as a winch and a gripping device attached to the free end of a winch chain, or an overhead crane .

[0118] For example , the trans fer station 100 may consist of the following main elements : - an upper part 102 for docking with the overhead crane 104 comprising a hook connected by chains or cables to the overhead crane 104 ,

[0119] - a body 106 forming a receiving sheath for the case 50 or the fuel assembly 20 during its trans fer,

[0120] The case 50 , containing the fuel assembly 20 , is grasped by a grappling hook and gradually raised / lowered by chains driven by the winch . The li fting chains are adapted to handle fuel assemblies / cases and have high reliability . The winch is particularly equipped with overload and overspeed detectors . To access a well 34, 36, the grappling hook of the transfer station 100 is gradually lowered to the level of the housing 40 so as to bring the case 50 into contact with a support edge arranged around the opening of the well 34, 36. The transfer station 100 that has gripped the case 50, containing the fuel assembly 20, is moved horizontally by the overhead crane 100 and carried towards the storage equipment 110, e.g. baskets, in the storage area 2.

[0121] It is possible, in particular when loading a new fuel assembly 20 into the housing 40 at the supply location 44, to provide for heating the case 50. Preferably, a temperature of at least 200 °C is reached in the case 50 before it is moved to the reactor location 42. Such heating makes it possible, in particular, to avoid thermal shocks for the fuel assembly 20 when it is introduced into the core 18 of the nuclear reactor 10.

[0122] The invention is not limited to the embodiment described and depicted in the accompanying figures. Modifications, in particular from the point of view of constituting different technical features or by substituting technical equivalents, remain possible without departing from the scope of protection of the invention.

Claims

CLAIMS1. A fuel assembly handling system for moving fuel assemblies (20) between a reactor chamber (1) configured to house a nuclear reactor (10) and storage chambers (2) configured to store fuel assemblies (20) , characterized in that the handling system comprises a carousel (30) installed in a transfer chamber (3) , said transfer chamber (3) communicating with the reactor chamber (1) via a reactor well (32) , with a first storage chamber (2a) via a first storage well (34) , and with a second storage chamber (2b) via a second storage well (36) , the carousel (30) comprising housings (40) , each housing (40) being configured to accommodate a fuel assembly (20) , the carousel (30) being configured to move the housings (40) , in the transfer chamber (3) between a reactor location (42) facing the reactor well (32) , a second location (44) facing the first storage well (34) , and a third location (46) facing the second storage well (36) .

2. The system according to claim 1, wherein the reactor well (32) extends between the reactor chamber (1) and an upper part (38) of the transfer chamber (3) , and each storage well (34, 36) extends between a storage chamber (2) and an upper part (38) of the transfer chamber (3) .

3. The system according to any one of the preceding claims, wherein the carousel (30) comprises a shaft (47) about which the housings (40) are configured to rotate, the housings (40) being evenly distributed around the shaft (47) at an angular offset in a plane of rotation, and the reactor (32) and storage wells (34, 36) are evenly distributed aroundthe shaft (47) at the same angular offset.

4. The system according to any one of the preceding claims, wherein the carousel (30) comprises a housing support(31) accommodating the housings (40) and displaceable along the shaft (47) in order to alter the height of the housings (40) in the transfer chamber (3) .

5. The system according to any one of the preceding claims, comprising cases (50) configured to be received in the housings (40) of the carousel (30) , each case (50) being configured to contain a fuel assembly (20) and comprising a removable plug (54) configured to seal the case (50) in the presence of a fuel assembly (20) in the case (50) .

6. The system according to claim 5, wherein each case (50) is provided with a heating device adapted to heat the case ( 50 ) .

7. The system according to any one of claims 5 to 6, comprising a handling hood (60) movable within the reactor chamber (1) and configured to dock with the reactor well(32) , wherein the handling hood (60) comprises a gripping member (62) adapted to extend through the reactor well (32) , grip and lift the plug (54) of the case (50) .

8. The system according to claim 7, comprising a movable member (90) configured to selectively position itself in the reactor well (32) below the handling hood (60) when the handling hood (60) is secured to the well (32) , the movable member (90) being configured to receive the plug (54) of the case ( 50 ) .

9. The system according to claim 8, wherein the reactor well (32) comprises two slide valves (VI, V2 ) configured toselectively seal the reactor well (32) , the movable member(90) being disposed between the two slide valves.

10. A nuclear power plant comprising a reactor chamber (1) housing a nuclear reactor (10) , and at least two storage areas (2) for storing fuel assemblies (20) , the nuclear power plant (10) comprising a fuel assembly (20) handling system according to any one of the preceding claims.

11. A process of handling fuel assemblies (20) between a reactor chamber (1) configured to house a nuclear reactor and two storage chambers (2) configured to store fuel assemblies (20) , using a fuel assembly handling system according to any one of claims 1 to 9, comprising the following steps: a) a fuel assembly (20) is loaded into the housing (40) of the carousel (30) at the second location (44) through a first storage well (34) , b) the housing (40) is moved by rotation of the carousel (30) from the second location (44) to the reactor location (42) opposite the reactor well (32) , c) the fuel assembly (20) is unloaded from the housing (40) through the reactor well (32) to the reactor location (42) , d) another fuel assembly (20) is loaded into the housing (40) at the reactor location (42) through the reactor well (32) , e) the housing (40) is moved by rotation of the carousel (30) from the reactor location (42) to a third location (46) opposite a second storage well (36) , f) the other fuel assembly (20) is unloaded from thehousing (40) at the third location (46) through the second storage well (36) , g) the housing (40) is moved by rotation of the carousel (30) from the third location (46) to the second location (44) opposite the first storage well (34) .

12. The process according to claim 11, wherein between two successive displacements (SI) of housings (40) by the carousel (30) , a fuel assembly (20) is unloaded (S32a) from a housing (40) at the reactor location (42) , a fuel assembly (20) is loaded (S32b) into the housing (40) disposed at the reactor location (42) , a fuel assembly (20) is loaded (S34) into the housing (40) at the second location (44) , and a fuel assembly (20) is unloaded (S36) from a housing (40) at the third location (46) .

13. The process according to any one of claims 11 to12, wherein a case (50) received in a housing (40) contains an inert atmosphere at least when a plug (54) closes the case (50) and the case (50) contains a fuel assembly.

14. The process according to any one of claims 11 to13, wherein :- a case (50) in a transfer chamber (3) is docked to a well connecting the transfer chamber (3) and a reactor chamber (1) housing a nuclear reactor (10) , the case (50) being closed by a plug (54) ,- a gripping member (62) of a handling hood (60) docked to the reactor well (32) in the reactor chamber (1) enters the reactor well (32) and grips the plug (54) ,- a movable element (90) is positioned in the reactor well (32) below the handling hood (60) and receives the caseplug ( 54 ) ,- the movable element (90) is retracted to leave a passage in the reactor well (32) free,- a fuel assembly (20) passes through the reactor well (32) to be removed from or placed in the casing (50) .

15. The process according to claim 14, then comprising the following steps:- the movable element (90) carrying the plug (54) is positioned in the reactor well (32) below the handling hood (60) ,- the gripper (62) enters the reactor well (32) and grips the plug (54) ,- the movable element (90) is retracted to leave a passage in the reactor well (32) free, - the gripper (62) enters the reactor well (32) and replaces the plug (54) to close the case (50) .

Images