Patent Publication Number: US-2023162877-A1

Title: Platform and platform system for nuclear power plant

Description:
The present disclosure relates to a platform for nuclear power plants, in particular for the maintenance of a nuclear reactor. 
     BACKGROUND 
     In a nuclear power plant, the nuclear reactor is immersed in the water of a pool comprising a reactor pool housing the nuclear reactor itself, and a storage pool for the storage and handling of fresh nuclear fuel assemblies prior to their insertion into the core of the nuclear reactor and of spent nuclear fuel assemblies after their removal from the nuclear reactor. 
     An overhead crane spanning the pool is movable along rails for lifting and moving nuclear fuel assemblies, including storing fresh fuel assemblies in the storage pool, transferring fresh fuel assemblies from the storage pool to the nuclear reactor, and transferring spent fuel assemblies from the nuclear reactor to the storage pool. 
     The crane can be equipped with a walkway to accommodate operators, for example to allow them to reach above the pool and carry out maintenance on the nuclear reactor and/or on new or irradiated nuclear fuel assemblies. 
     A movable walkway can be provided separate and apart from the crane, the walkway also being movable along rails, either the same rails as the crane or dedicated rails, the walkway spanning the pool and being intended to accommodate operators to enable them to get above the pool to carry out maintenance operations. 
     SUMMARY 
     However, this requires the provision of a movable walkway in addition to the overhead crane, which takes up some of the relatively small space available around the pool, and which is used for example to store equipment required for the operation of the nuclear reactor or for routine maintenance operations carried out while the nuclear reactor is in operation. 
     One of the purposes of the present disclosure is to provide a platform system comprising a movable platform above the pool of a nuclear power plant, which facilitates the operation of the nuclear reactor. 
     To this end, the present disclosure provides a platform configured to span a pool of a nuclear power plant with being movable along two parallel rails disposed on either side of the pool, the platform having a platform floor for operator traffic and/or equipment storage, the platform comprising at least one platform module, each platform module having a module floor defining at least a portion of the platform floor and two guide assemblies, each guide assembly being configured to mate with a respective one of said rails for guiding the platform along said rails, each platform module being extendable so as to vary the spacing between the two guide assemblies of the platform module, the two guide assemblies being moved towards each other in a storage configuration and away from each other in a service configuration. 
     According to particular embodiments, the platform comprises one or more of the following features taken individually or in any combination that is technically possible:
         each platform module comprises a main part, which has a main plate carried by a main structure, and at least one extension part which comprises an extension plate and guide assembly carried by an extension structure slidably mounted relative to the main structure to move from the storage configuration to the service configuration;   when changing from the service configuration to the storage configuration of each platform module, the extension plate of each extension part slides onto the main plate;   the extension plate of each extension part is mounted on the extension structure so that the extension structure retracts under the main plate, the extension plate passing over the main plate;   each platform module comprises two extension parts, the main part being located between the two extension parts when the platform module is in the service configuration;   the extension structure of each extension part comprises at least one extension beam slidably mounted on a main beam of the main structure;   each extension beam is telescopically mounted on the corresponding main beam;   each platform module comprises at least one actuator assembly, each actuator assembly comprising an actuator and a transmission configured to move the platform module from the storage configuration to the service configuration and vice versa;   each platform module comprises at least one actuator for driving the platform module along the rails;   the platform comprises at least two platform modules, in particular exactly two platform modules, configured to be arranged side by side and assembled to form the platform.       

     The present disclosure also relates to a platform system comprising a platform as defined above and a freight container, the platform being configured for storage in the freight container, each platform module being in a storage configuration. 
     In a particular embodiment, the platform comprises at least two platform modules, which are intended to be stored in a storage configuration in the container by being stacked on top of each other or on top of each other. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
       The present disclosure and its advantages will become apparent upon reading the following description, given only as a non-limiting example, referring to the attached drawings, in which: 
         FIG.  1    is a perspective view of a platform installed above a pool in a nuclear power plant; 
         FIG.  2    is a perspective view of the platform showing the underside of the platform; 
         FIG.  3    is a detailed view of  FIG.  2    showing a platform actuator assembly; 
         FIG.  4    is a schematic cross-section of the platform showing an extension part of a platform module. 
         FIG.  5    is a perspective view of a platform stored in a container. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG.  1   , a nuclear power plant  2  has a pool  4  containing water in which a nuclear reactor (not shown) is immersed. The pool  4  comprises, for example, a reactor basin accommodating the nuclear reactor and/or a storage basin equipped to receive new and/or irradiated nuclear fuel assemblies. 
     The pool  4  is surrounded by a slab which, on the edges of the pool  4 , is provided with two parallel rails  6  on either side of the pool  4 . 
     A platform system  8  comprises a platform  10  that spans the pool  4  and is movable along the two rails  6 . The platform  10  is for example placed on the rails  6 , which in this case support and guide the platform  10  along the rails  6 . 
     The platform  10 , which is movable along the rails  6 , can be placed at a selected location above the pool  4 . The platform  10  is for example configured to extend over the reactor basin and/or storage basin. 
     The rails  6  are, for example, support and guide rails for an overhead crane (not shown) intended for lifting nuclear fuel assemblies. Alternatively, such a crane is guided along other rails, separate from rails  6  associated with the platform  10 . 
     The two rails  6  are spaced apart in a first direction D 1  and extend in a second direction D 2  perpendicular to the first direction D 1 . The space between the two rails  6  is for example between 8 m and 12 m. 
     Platform  10  is deployable. It has a service state ( FIG.  1   ) in which it is suitable for straddling the pool  4  guided by the rails, and a transport state ( FIG.  5   ) in which the platform  10  is suitable for storage in a freight container  12  of the platform system  8 . 
     A “freight container” here means a container of the type “maritime freight container” or “multimodal freight container”, as defined in particular by the ISO 668 standard or the ISO 1496 standard. The most common freight containers are usually 20 feet, 30 feet or 40 feet long. A freight container is typically about 10 feet (about 3.048 m) wide and about 10 feet (about 3.048 m) high. 
     The freight container  12  of the platform system  8  is advantageously 20 feet long (about 6.096 m) 
     As can be seen in  FIG.  1   , the platform  10  has a platform floor  14  for accommodating operators and/or for storing equipment. Operators can use the platform  10  to position themselves above the pool  4  to carry out maintenance operations on the nuclear reactor and/or on nuclear fuel assemblies. 
     The platform  10  configured to be stored in a 20-foot freight container  12  can be stored and transported in a compact manner, while being able to straddle the pool  4  with a platform floor  14  having an area large enough to accommodate operators and/or to store equipment. 
     Storing equipment on the platform floor  14  means that this equipment does not need to be stored around the pool  4 , limiting the congestion of that area, in particular when the nuclear reactor is undergoing maintenance. 
     The platform floor  14  extends along the first direction D 1  and the second direction D 2 . The platform floor  14  is substantially parallel to the plane defined by the first direction D 1  and the second direction D 2 . 
     The platform  10  comprises at least one platform module  16 , each platform module  16  having a module floor  18  defining at least part of the platform floor  14 . 
     The platform  10  comprises for example at least two platform modules  16  configured to be arranged side by side and connected to form the platform  10 . The platform modules  16  are arranged side by side in the second direction D 2 . Each platform module  16  defines a section of the platform  10  along the second direction D 2 , i.e. the direction of extension of the rails  6 . 
     When the platform modules  16  are arranged side by side, their module floors  18  together define the platform floor  14 . In particular, each platform module  18  defines a section of the platform  14  along the second direction D 2 , i.e. the direction in which the rails  6  extend. 
     The platform  10  comprises for example exactly two platform modules  16  arranged side by side and paired. The module floor  18  of each platform module  16  thus forms approximately half of the platform floor  14 . 
     The module floor  18  of each platform module  16  has, in the second direction D 2 , a dimension of, for example, between 2.50 m and 3.00 m. This facilitates the storage of the platform module  16  in a freight container  12 . 
     In the service state of the platform  10  ( FIG.  1   ), the platform modules  16  are assembled in such a way that they move together along the rails  6 . In the transport state ( FIG.  5   ), the platform modules  16  are separated for storage in the freight container  12 . 
     Each platform module  16  has two guide assemblies  20 . Each guide assembly  20  is configured to mate with a respective one of the two rails  6 , to guide the platform module  16  along the rails  6 . Preferably, each guide assembly  20  is configured to rest on the corresponding rail  6 . The rails  6  guide, and possibly support, each platform module  16 . 
     Each guide assembly  20  comprises, for example, a frame  22  on which wheels  24  are rotatably mounted, by means of which the guide assembly  20  rolls on the corresponding rails  6  when the platform module  16  is placed on the rails  6 . 
     Optionally, each guide assembly  20  comprises a drive actuator  25  arranged to propel the guide assembly  20  along the corresponding rail  6 . 
     The drive actuator  25  is for example a hydraulic motor or an electric motor. 
     The drive actuator  25  is for example configured to rotate at least one of the wheels  24  of the guide assembly  20   
     The two guide assemblies  20  of each platform module  16  are spaced apart in the first direction D 1 . 
     Each platform module  16  has a storage configuration and a service configuration. The storage configuration corresponds to the transport state of the platform  10  and the service configuration corresponds to the service state of the platform  10 . 
     Each platform module  16  is expandable along the first direction D 1  from the storage configuration to the service configuration. 
     In the storage configuration, the two guide assemblies  20  are close together along the first direction D 1 , and in the service configuration, the two guide assemblies  20  are spaced apart along the first direction D 1 . 
     In the storage configuration, the spacing between the two guide assemblies  20  is strictly less than that between the two rails  6 , and in the service configuration, the spacing between the two guide assemblies  20  corresponds to that between the two rails  6 , so that the guide assemblies  20  can mate with the two rails  6 . 
     In the storage configuration, each platform module  16  has a length (taken along the first direction D 1  corresponding to the direction along which the guide assemblies  20  are spaced apart), which is strictly less than the length available within the freight container  12 . This available length is approximately 5.90 m for a 20-ft freight container  12 . 
     Furthermore, each platform module  16  has a width (taken in the second direction D 2  corresponding to the direction of movement of the guide assemblies  20  along the rails  6 ) which is strictly less than the width available inside the freight container  12 . This available length is approximately 2.35 m for a freight container  12 . 
     This allows each platform module  16  to be stored in the freight container  12 , and the platform modules  16  to be stacked on top of each other. 
     Each platform module  16  comprises a main portion  26 , comprising a main plate  28  carried by a main structure  30 , and at least one extension part  32 , each extension part  32  comprising an extension plate  34  and one of the guide assemblies  20  carried by an extension structure  36 . 
     Each extension structure  36  is slidably mounted in the first direction D 1  on the main structure  30  so as to change the spacing between the two guide assemblies  20 . 
     Each extension structure  36  is slidably mounted relative to the main structure  30  between a retracted position, corresponding to the storage configuration of the platform module  16 , and an extended position, corresponding to the service configuration of the platform module  16 . 
     In the service configuration, the main plate  28  and each extension plate  34  each form a respective part of the module floor  18 . 
     Each extension structure  36  carries a guide assembly  20 , so that movement of the extension structure  36  relative to the main structure  30  changes the spacing between the two guide assemblies  20 . 
     In the retracted position of the extension structure  36 , the guide assembly  20  carried by the extension structure  36  is drawn back against the main part  26 . In the extended position of the extension structure  36 , the guide assembly  20  carried by the extension structure  36  is moved away from the main part  26 . 
     Each platform module  16  comprises, for example, two extension parts  32  located on either side of the main part  26  along the first direction D 1 , each extension part  32 . In the storage configuration, both extension structures  36  are in their retracted positions, and in the service configuration, both extension structures  36  are in their extended positions. 
     In another embodiment, each platform module  16  has a single extension part  32 , one of the two guide assemblies  20  being carried by the extension structure  36  of that extension part  32  and the other being fixedly mounted to the main structure  30 . The extension structure  36  is then arranged to extend to one side of the main part  26 , with the guide assembly  20  carried by the main part  26  located on the opposite side of the main part  26 . 
     The main structure  30  comprises for example at least one main beam  38  extending in the first direction D 1 . The main structure  30  comprises, for example, a plurality of parallel main beams  38  extending in the first direction D 1 . The main structure  30  here comprises four main beams  38 . 
     Each extension structure  36  has for example at least one extension beam  40  slidably mounted along the first direction D 1  on the main structure  30 . 
     Each extension beam  40  is for example telescopically mounted on a main beam  38 . The guide assembly  20  of the extension part  32  is carried at the end of each extension beam  40  that is opposite the main part  26 . 
     In one example embodiment, the extension structure  36  has a respective extension beam  40  associated with each main beam  38  and slidably mounted on that main beam  38 , in particular telescopically mounted on that main beam  38 . 
     The main structure  30  here comprises four main beams  38 , including two central main beams  38  located between two lateral main beams  38 . For example, the central main beams  38  have a larger cross-section than the lateral main beams  38 . Each extension structure  36  has four extension beams  40 , each extension beam  40  being telescopically mounted on a respective main beam  38 . 
     As can be seen in  FIG.  3   , each platform module  16  advantageously has at least one actuator assembly  42  for moving the platform module  16  from the storage configuration to the service configuration, and vice versa. 
     Each actuator assembly  42  is configured to move the extension structure  36  of at least one extension part  32  between its retracted position and its extended position. 
     In one example embodiment, each platform module  16  has a respective actuator assembly  42  associated with each extension part  32 , which actuation assembly  42  is configured to move the extension structure  36  of that extension part  32  between its retracted position and its extended position. 
     In another example embodiment, each platform module  16  has a single actuator assembly  42  configured to move the extension structures  36  of two extension parts  32  between their respective retracted and extended positions. 
     Each actuator assembly  42  comprises an actuator  44  and a transmission  46  configured to transmit movement generated by the actuator  44  to each extension structure  36  operated by that actuator assembly  42 . 
     The actuator  44  of each actuator assembly  42  is for example a motor, in particular an electric motor. 
     The transmission  46  of each actuator assembly  42  comprises, for example, at least one screw/nut assembly comprising a screw  48  and a nut  50 , the screw  48  extending in the first direction D 1 , and the actuator  44  being coupled to one of the screw  48  and the nut  50  to rotate it so as to move the other in translation. 
     In one example embodiment, the screw  48  of each screw/nut assembly is rotatably mounted on the main structure  30 , and the nut  50  is mounted on the extension structure  36 , with rotation of the screw  48  caused by the actuator  44  causing the nut  50  to move along the screw  48  and thereby sliding the extension structure  36  relative to the main structure  30 . 
     In an example embodiment in which the extension part  32  comprises at least two extension beams  40 , the transmission  46  comprises for example two screw/nut assemblies, each interposed between the actuator  44  and a respective extension beam  40  for driving that extension beam  40  in translation, both extension beams  40  thus being driven in translation by means of the same actuator  44 . 
     Each extension plate  34  is configured to extend the main plate  28  by being supported by the corresponding extension structure  36 . In the service configuration, each extension plate  34  extends between the guide assembly  20  carried by the extension part  36  and the main plate  38 . 
     As shown in  FIG.  4   , each extension plate  34  is for example mounted on the corresponding extension structure  36  so as to pass over the main plate  28  when the extension structure  36  is retracted, with the extension structure  36  passing under the main plate  28 . 
     To this end, each extension plate  34  has its end adjacent to the guide assembly  20  linked to the extension structure  36  or to the frame  22  of the guide assembly  20  by at least one connection  52  so as to allow upward movement of the extension plate  34  relative to the extension structure  36 . 
     In one embodiment, the link  52  is formed by a slider  54  slidably received in a guide  56  having a lower end and an upper end. When the slider  54  is at the lower end, the extension plate  34  is placed on the extension structure  36 . When the slider  54  is at the top end, the extension plate  34  is vertically spaced away from the extension structure  36 . 
     For example, the guide  56  has an arcuate shape, with the lower end of the guide  56  offset horizontally towards the central portion  28  from the upper end. 
     The end of each extension plate  34  adjacent to the main plate  28  is simply supported on the corresponding extension structure  36 . 
     When the extension structure  36  is retracted, the end of the extension plate  34  adjacent to the main plate  28  passes over the main plate  28 , the other end being able to shift upwards by the linkage  52  configured for this purpose, to facilitate the passage of the extension plate  34  over the main plate  28 . 
     Optionally the platform module  16  has at least one ramp  58  associated with each extension plate  34  and arranged to raise the end of the extension plate  34  adjacent to the main plate  28  above the main plate  28 . Each ramp  58  is for example fixed to the main structure  30 . 
     Optionally, the platform module  16  has a rolling device  60  attached to the extension plate  34  and configured to roll on a corresponding ramp  58  to raise the end of the extension plate  34  adjacent to the main plate  28  above the main plate. 
     Each rolling device  60  comprises rolling elements, such as wheels or rolls or rollers, by means of which the extension plate  34  is supported on the ramp  58 . 
     Returning to  FIG.  1   , the platform  10  has at least one connecting device  62 , each connecting device  62  allowing two adjacent platform modules  16  to be connected, such that the platform modules  16  move together along the rails  6 . 
     Each assembly device  62  comprises, for example, an assembly plate  64  provided with slots receiving assembly rods attached to the platform modules  16 . Here the assembly plates  64  are arranged on the side of the guide assemblies  20 . 
     Advantageously, the platform system  8  has removable equipment, which can be detachably mounted on the platform  10 . 
     Advantageously, the platform system  8  comprises a removable lifting tool  66  configured to be mounted on the platform. The lifting tool  66  is, for example, in the form of a jib, having a mast and a boom mounted on the mast. 
     The platform system has, for example, removable guardrails  68  configured to be mounted on the platform  10  at the periphery of the platform floor  4 , possibly leaving access openings for access to the platform from the edge of the pool  4 . 
     The platform system comprises for example one or more removable steps  70 . Each step  70  makes it easier for operators to climb onto the platform  10 . 
       FIG.  5    shows the platform  10  stored in the freight container  12 . Two panels of the freight container  12  are omitted to make the platform  10  stored in the container  12  visible. 
     As illustrated in  FIG.  5   , in a stored state of the platform, the platform modules  16  are separated, with each platform module  16  being placed in a storage configuration, with each platform module being disposed in the freight container  12 . 
     More specifically, the transport modules  16  are superimposed on each other or on each other. 
     Advantageously, the platform system  8  comprises a storage plate  72 , the storage plate being intended to be inserted inside the freight container  12  by being superimposed with the platform modules  16 , and to receive for example removable equipment (lifting tool, guardrail, step(s)) intended to be mounted on the platform modules  16 . 
     During the normal operation of the nuclear reactor, the platform system  8  is not installed and might not be on-site at the nuclear power plant. 
     When maintenance operations are planned on the nuclear reactor and the operator wishes to have a platform available during these maintenance operations, for example to provide additional storage space and/or to allow operators to reach the top of the pool  4 , the platform system  8 , comprising the platform  10  in its stored state, stored in the freight container  12 , is brought to the site ( FIG.  5   ). 
     The platform modules  16  in storage configuration are removed from the freight container  12 . Each platform module  16  thus has its extension parts  32  in their retracted positions and its guide assemblies  20  in their proximate positions. 
     Each platform module  16  is then brought into a service configuration, by moving the extension structure  36  of each extension part  32  from its retracted position to its extended position, for example using the associated actuator assembly  42 . The guide assemblies  20  are thus spaced apart so that the distance between them corresponds to that between the rails  6 . 
     In so doing, each extension plate  34 , initially located on the main plate  28 , moves in conjunction with the associated guide assembly  20  and comes to rest adjacent to the main plate  28  on the corresponding extension structure  36 . 
     The platform modules  16  are arranged on the rails  6  and connected to each other by means of the connecting devices  62 , thus forming the platform  10 . 
     The platform  10  is then fitted with its removable equipment (lifting tool  66 , guardrail  68 , step(s)  70 ) ( FIG.  1   ). 
     For the dismantling and storage of the platform system  8 , the reverse operations are performed. 
     During a nuclear reactor unit outage, the operation of the nuclear reactor is interrupted, and the operator proceeds to unload spent fuel assemblies, load fresh fuel assemblies, reposition some spent fuel assemblies that are kept in the nuclear reactor, and perform maintenance operations. 
     During a unit outage, there is usually a lack of space on the slab surrounding the nuclear power plant pool to allow for co-activity and reduce the duration of the unit outage. 
     The platform system  8  provides the operator with more available floor space during unit outages, allowing that person to optimise the use of maintenance equipment, in particular the overhead crane. 
     The platform system  8  increases the usable area by partially covering the pool  4  without interfering with unit shutdown operations. 
     The platform  10  can be installed and dismantled quickly. It is movable along rails  6  to allow access to elements stored at the bottom of the pool, such as fresh or spent fuel assemblies. 
     The platform system  8  in its disassembled state, when stored in the freight container  12 , is compact, which reduces transport and storage costs. 
     The transport modules  16  with a storage configuration and a service configuration facilitate transport by allowing compact storage, and use, by allowing the platform  10  to be deployed for mounting on the rails  6  with an appropriate spacing between the guide assemblies  20 . 
     The platform  10  in the service state is preferably intended to carry a substantial load, for example for storage of material and/or to provide an additional working surface. 
     Advantageously, the platform  10  in the service state has a platform floor  14  with a surface area of at least 20 m 2 , in particular a surface area of at least 30 m 2 , for example a surface area of approximately 32 m 2 . 
     Advantageously, the platform  10  in the service state has a load capacity of at least 400 kg/m 2 , preferably at least 500 kg/m 2 , in particular about 600 kg/m 2 . 
     Preferably, the platform  10  is designed to rest on the rails  6  of the crane provided for handling the nuclear fuel assemblies. Thus, no modifications to the nuclear power plant are required to allow the use of the platform system  8 .