Nuclear power plant system

Abstract

The present invention relates to a method for tensioning / untensioning closure studs of a nuclear reactor vessel, the closure studs being spaced around the periphery of the reactor vessel for attaching the reactor vessel's integral head package (IHP) to the body of the reactor vessel. The method includes supporting a first stud pulling device on a trolley, moving the trolley across a moving surface from a stowed position to a deployed position adjacent the reactor vessel, engaging the first stud pulling device with one or more closure studs, and actuating the first stud pulling device to tension / untension the one or more closure studs.

Description

Technical Field

[0001] The present disclosure relates to a method and system for tensioning and / or detensioning studs of a reactor pressure vessel (RPV).

Background Art

[0002] A nuclear power plant converts thermal energy generated by nuclear decay of fissile material contained in a fuel assembly included in a reactor core into electrical energy. Water-cooled nuclear power plants such as pressurized water reactor (PWR) and boiling water reactor (BWR) plants include a reactor pressure vessel that houses the reactor core / fuel assembly, and a turbine for generating electricity from steam (generated by heat from the fuel assembly).

[0003] A PWR plant has a pressurized primary coolant circuit that flows through the RPV and transfers thermal energy to one or more steam generators (heat exchangers) in a secondary circuit. The (low-pressure) secondary circuit includes a steam turbine that drives a generator for power generation. These components of a nuclear power plant have conventionally been housed within an airtight containment building in the form of a concrete structure.

[0004] A reactor-propelled view (RPV) typically comprises a body defining a cavity for housing the reactor (i.e., including fuel assemblies) and a closure head for closing the upper opening to the cavity. The closure head may form part of an integrated head package (IHP) (or integrated head assembly) that further includes a control rod drive mechanism housed within a shroud. The control rod drive mechanism comprises a drive rod that penetrates the closure head and is connected to control rods housed within the core. The control rods are provided to absorb neutron radiation within the core and control nuclear reactions within the core. The drive rods within the control rod drive mechanism are driven by a power source to translate vertically to raise and lower the control rods within the core. The core further includes guide columns for the control rods, which, along with the associated electronics, are typically referred to as the "upper internals." Maintenance and refueling play a crucial role in the operation of nuclear power systems. Regular maintenance is required, such as replacing old or damaged parts of the system. Regular refueling (for example, every 18-24 months) is necessary to replace spent fuel rods in the fuel assemblies.

[0005] During core maintenance / refueling, the IHP (Injection Heat Pump) must be removed from the RPV (Reactor Plant Vehicle) to expose the core. The IHP is typically removably attached to the body by multiple closure studs (formed with nuts and bolts). Each IHP and body has an outwardly projecting circumferential flange with multiple holes spaced circumferentially to extend around the RPV. When attaching the IHP to the body, the holes are aligned, bolts are passed through the holes, and nuts are tightened onto the bolts to secure them in place. The closure studs can then be pulled by a stud tensioning device, which stretches the bolts, allowing the nuts to move further along the bolts toward the flange. In this way, once released, the bolts remain stretched. The tension on the studs can then be released by stretching the studs (using the stud tensioning device) and loosening the nuts from the flange. This allows the studs to be removed (for subsequent removal of the head).

[0006] In nuclear power plants, overhead crane arrangements, such as polar gantry cranes with circular runways, are typically installed within the system's containment structure to perform maintenance and refueling operations. Polar cranes are inherently large and heavy structures to enable the lifting of heavy components in nuclear power plants. Therefore, installing polar cranes is costly.

[0007] During refueling, a slewing crane is typically used to move a stud tensioning device to engage with the RPV in order to tension / release the bolts that attach the IHP to the body. The slewing crane then typically lifts the IHP vertically upward from the RPV body, moves the IHP horizontally away from the RPV body, and then lowers the IHP onto a containment stand installed on the work floor inside the containment building. Next, the slewing crane is used to lift the radioactive upper internal structure, which typically weighs about 15-50 tons. The slewing crane lifts the internal structure vertically, then moves it horizontally, and then lowers it into a water storage pool for immersion. This is to provide gamma shielding around the internal structure during refueling. To provide a refueling cavity above the exposed core inside the reactor vessel body, the reactor vessel body is typically located well below the work floor of the containment structure. While the IHP is being removed from the reactor vessel, the drive rod remains connected to the control rod and protrudes from the reactor vessel cavity into the refueling cavity, which is filled with water to contain any radioactive releases from the drive rod.

[0008] The water in the refueling cavity also acts to shield and cool the spent fuel rods in the exposed core. For effective gamma shielding, a height of 4 meters of water is required above the fuel rods / fuel assemblies. Therefore, filling the refueling cavity requires a very large amount of water and is therefore time-consuming.

[0009] The upper internal structure must clear the vertical height of the drive rod / fueling cavity before moving horizontally and descending into the storage pool; therefore, the vertical extent of the protruding drive rod and fueling cavity is driven by the slewing crane to achieve the required lift height of the upper internal structure.

[0010] The lift height of a slewing crane determines, at least in part, the height of the containment structure (and therefore the cost / time associated with constructing the containment structure). The risks associated with dropping equipment into the reactor core from considerable height are very high. Overhead traveling cranes are necessarily large and heavy, requiring large concrete structures to support them within the containment structure. For this reason, installing such cranes is costly. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 8-122479 [Patent Document 2] U.S. Patent No. 4873760 [Patent Document 3] UK Patent Application Publication No. 2100496 [Patent Document 4] UK Patent Application Publication No. 1346337 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] An improved nuclear power system is needed that mitigates at least some of the problems associated with known systems. [Means for solving the problem]

[0013] In the first aspect, a method for applying / releasing tension to closing studs of a reactor vessel, wherein the closing studs are spaced apart around the reactor vessel to attach the integrated head package of the reactor vessel to the body of the reactor vessel, and the method is Steps include supporting the first stud tensioning device on the trolley, The steps include moving the trolley across a moving surface from a distant storage position to a deployment position adjacent to the reactor vessel, The steps include engaging a first stud tensioning device with one or more closing studs, The steps include: activating a first stud tensioning device to apply / release tension to one or more closing studs; A method is provided that includes the following: By using a trolley instead of a crane to move the stud tensioning device, the nuclear power plant (of which the reactor vessel is part) does not require a crane. This can reduce the height of the containment building that houses the reactor vessel, allowing for faster (and more cost-effective) construction of the containment building. Using a trolley also avoids lifting the stud tensioning device (at least to a significant height), which could pose a safety problem.

[0014] Furthermore, trolleys generally have better transportability than, for example, permanently fixed cranes. Therefore, unlike cranes, trolleys can be transported to multiple nuclear power plants (e.g., by track / rails or loaded onto vehicles) for use in the maintenance processes of those plants.

[0015] Next, we will describe the optional features of this disclosure, which may be applied individually or in any combination with any aspect of this disclosure.

[0016] The movement of the trolley may be on a moving surface. The movement may be such that the trolley remains substantially in contact with the moving surface between the stowed position and the deployed position. This movement may be such that a constant vertical distance is maintained between the moving surface and the first stud tensioning device supported by the trolley as the trolley moves from the stowed position to the deployed position.

[0017] The trolley may move along a path that extends substantially laterally (e.g., radially) relative to the reactor vessel. The term “later” is used here to describe a direction substantially perpendicular to the longitudinal axis of the reactor (i.e., the longitudinal axis is parallel to the elongated axis of the reactor fuel assemblies, if present). A reference plane (e.g., a horizontal reference plane) can be defined, which may intersect the reactor vessel and, in some embodiments, may intersect the IHP of the reactor vessel. The reference plane may be aligned substantially perpendicular to the upper opening of the reactor body (i.e., where the core is housed). The path along which the trolley moves may be aligned perpendicular to the reactor vessel body and / or the opening of the reactor vessel to the IHP.

[0018] Given the scale of the nuclear power generation system, the term "aligned nearly vertically" means that the vertical distance between the work platform and the opening to the cavity (defined by the upper end of the reactor vessel body) is less than 2 meters, for example, 1 meter or 0.5 meters. The trolley can move along one or more tracks or rails. Thus, the moving surface may be defined, for example, by the outer surface of one of the tracks or rails. If the trolley moves along multiple tracks or rails, the trolley moves across the corresponding multiple moving surfaces (i.e., the outer surfaces of the tracks or rails). The trolley can move along two parallel tracks or two parallel rails.

[0019] By moving the trolley along a track or rail, the trolley can be moved along a predetermined path (e.g., a predetermined path by the track or rail), thereby ensuring (consistent) repeatability of the movement. This can facilitate the automation of the method. One or more tracks or rails may independently provide a guidance function to the trolley (i.e., guide the trolley along a predetermined path), or they may additionally support the trolley. The trolley may be supported on one or more tracks or rails, or suspended from one or more tracks or rails.

[0020] The trolley can move along a substantially straight path from a storage position to a deployment position. In this regard, the trolley can move along a substantially straight track or rail. Alternatively, the trolley may be moved along a composite path formed, for example, from straight and non-straight (e.g., curved) portions.

[0021] This method can include attaching a first stud tensioning device to the reactor vessel after the trolley has moved to the deployment position. The reactor vessel can include an attachment structure for receiving the first stud tensioning device, and the method can include attaching the first stud tensioning device to the attachment structure (the attachment structure can be in the form of, for example, a rail or flange extending circumferentially around the reactor vessel). Attachment of the first stud tensioning device can include attaching the first stud tensioning device to the head of the reactor vessel or the body of the reactor vessel, or both.

[0022] Attaching the first stud tensioning device to the reactor vessel can include moving the first stud tensioning device from the trolley to the reactor vessel. In this regard, the attachment can include moving the first stud tensioning device relative to the trolley. Such movement can be performed by a handling device forming part of the trolley or the reactor vessel, or by a handling device separate from the trolley and the reactor vessel (e.g., the handling device can be external to the trolley and the reactor vessel).

[0023] The first stud tensioning device can include a plurality of connected stud tensioning units. In this regard, the first stud tensioning device may be a multi-stud tensioning device. The plurality of connected stud tensioning units can be arranged to draw an arc around the reactor vessel when attached to the reactor vessel. When the first stud tensioning device is in the form of a multi-stud tensioning device, it may be in the form of a minor arc (range and angle less than 180°), a major arc (angle range exceeding 180°), or in the form of a substantially semi-circle.

[0024] This method can include lowering the first stud tensioning device onto one or more closed studs (i.e., for engagement and tensioning / relaxing of the closed studs). The lowering can be performed by a trolley, the first stud tensioning device, the reactor vessel, or a combination thereof. For example, the mounting structure of the reactor vessel can include a hydraulic lift or a winch for lowering the first stud tensioning device.

[0025] This method can further include the step of rotating or moving the first stud tensioning device along the periphery of the reactor vessel before engaging the first stud tensioning device with the stud. The first stud tensioning device can be rotated or moved around the longitudinal (e.g., substantially vertical) axis of the reactor vessel. The first stud tensioning device can be rotated approximately 180° around the outer periphery of the reactor vessel. In some embodiments, rotating or moving the stud tensioning device around the circumference of the reactor vessel can include attaching the stud tensioning device to a rail or flange extending circumferentially around the reactor vessel and moving the stud tensioning device along the flange or rail.

[0026] If the first stud tensioning device is formed from multiple connected elements (for example, to form a chain-like structure), the stud tensioning device can be moved / advanced on and around the reactor vessel in a manner that gradually surrounds (or meanders) the reactor vessel. In this case, the first stud tensioning device can be moved (i.e., surround) the entire circumference of the reactor vessel.

[0027] In other embodiments, the method may include rotating the first stud tensioning device after engaging the studs to tension / release the studs. In this case, the method may subsequently include engaging the studs aligned with the first stud tensioning device (i.e., studs that have not yet been tensioned or released by the first stud tensioning device) to release / tension the studs. If the first stud tensioning device is not in a semicircular shape, this process may be repeated until all studs attaching the head of the reactor vessel to the body of the reactor vessel are tensioned / released by the first stud tensioning device. The method may further include supporting a second stud tensioning device on a trolley (i.e., so that both the first and second stud tensioning devices are supported on a trolley). In other embodiments, the second stud tensioning device may be supported on another trolley. The second stud tensioning device may be the same as described above with respect to the first stud tensioning device. The second stud tensioning device can be attached to the reactor vessel after the first stud tensioning device has rotated around the reactor vessel. Thus, the rotation of the first stud tensioning device can be performed in such a way that it provides space in the reactor vessel for attaching the second stud tensioning device to the reactor vessel.

[0028] In other embodiments, the first stud tensioning device does not need to rotate around the reactor vessel. In such embodiments, if the first stud tensioning device does not extend completely around the reactor vessel, the method may include supporting a second stud tensioning device on a second trolley (i.e., the trolley on which the first stud tensioning device is supported is the first trolley). The second trolley may be located on the opposite side of the reactor vessel from the first trolley. Thus, the method may include moving another trolley from a storage position to a deployed position adjacent to the reactor vessel (e.g., on the opposite side of the reactor vessel from the other trolley).

[0029] The method described above with respect to the first trolley can be used in conjunction with the second trolley. Thus, this method may include attaching the second stud tensioning device to the reactor vessel and engaging the second stud tensioning device with one or more studs. This method may further include the step of activating the second stud tensioning device to tension / release one or more studs (e.g., aligned with the second stud tensioning device).

[0030] This method may include locking the first and second stud tensioning devices together. Once locked together, the first and second stud tensioning devices may be lowered onto the corresponding closing studs. This method may also include simultaneously operating the first and second stud tensioning devices to release tension on the closing stud. This allows for uniform tensioning / releasing of the closing stud.

[0031] This method may further include removing the studs from the reactor vessel (e.g., removing the bolts and nuts from the reactor vessel). This removal of the bolts and nuts can be performed by each stud tensioning device. This method may also include retracting the studs. For example, the studs may be retracted by the stud tensioning device or each stud tensioning device after the tension has been released. This method may also include removing the reactor vessel head from the reactor vessel body. If the stud tensioning device is attached to the reactor vessel head, the stud tensioning device can be removed from the reactor vessel together with the reactor vessel head (i.e., attached to the reactor vessel head). The reactor vessel head can then be returned to the reactor vessel and attached to the reactor vessel body (with the stud tensioning device still attached there).

[0032] As can be understood, this method may also be performed in reverse to remove the stud tensioning device from the reactor vessel. Thus, this method may then include disengaging the stud tensioning device from one or more studs and removing the stud tensioning device from the reactor vessel and supporting it on the trolley. The trolley or each trolley may be moved from the deployed position to the stowed position.

[0033] If the stud tensioning device is in the form of a chain structure (as described above), the removal process may include pulling the stud tensioning device back from a position where it surrounds the reactor vessel to a position where it is supported on a trolley.

[0034] The reactor vessel body may include a core capable of housing a control rod assembly and an upper internal structure for guiding the control rod assembly. The IHP may include a closed head and a control rod drive mechanism housed within a shroud. The control rod drive mechanism may include at least one drive rod (and preferably more drive rods) extending through the closed head. This method may further include decoupling at least one drive rod from the control rod assembly (for example, after the studs of the IHP have been removed). This method may subsequently include the steps of moving at least one drive rod to a maintenance / refueling position in which it is housed within the IHP, and lifting the IHP from the body with at least one drive unit in the maintenance / refueling position.

[0035] In this way, since there are no radioactive drive rods remaining protruding from the core when the IHP is removed, the need for a flooded fuel replenishment cavity can be eliminated.

[0036] The reactor vessel may be a reactor pressure vessel that forms part of a nuclear power plant of a pressurized water reactor (PWR). A PWR plant may have a plurality of steam generators arranged laterally spaced from the reactor vessel. Movement of the trolley from a stowed position to an deployed position may include moving the trolley between two (adjacent) steam generators. Thus, a rail or track may pass between two (adjacent) steam generators. In a second embodiment, a trolley for transporting one or more stud tensioning devices in a nuclear power plant is disclosed, the trolley comprising a support frame for supporting the stud tensioning devices, a plurality of wheels rotatably mounted on the frame, and a handling device mounted on the frame so as to be movable relative to the frame, the handling device configured to engage and move the stud tensioning devices relative to the support frame.

[0037] As can be understood, the trolley of the second embodiment may be used to carry out the method of the first embodiment. In this regard, by providing the trolley with a handling device, the stud tensioning device (supported by a frame) can be moved from the trolley to the reactor vessel (so that it can be attached to the reactor vessel). In this way, the process of attaching the stud tensioning device (including the process of moving the stud tensioning device to the reactor vessel) can be automated. This can avoid (or at least reduce) manual operation of the stud tensioning device (which may result in a safer process).

[0038] Furthermore, as mentioned above, the portability of trolleys is generally better than, for example, permanently fixed cranes. Therefore, unlike cranes, trolleys can be transported to multiple nuclear power plants (for example, by track / rails or loaded onto vehicles) for use in their maintenance processes.

[0039] The support frame may include an elongated gantry to which a handling device is mounted so as to be movable along the longitudinal axis of the gantry. The handling device may include wheels, and the gantry may include rails or tracks that allow the handling device to move along them. In this regard, the handling device may move along an axis substantially linear with respect to the support frame. The gantry may extend substantially horizontally.

[0040] The support frame may include a base for supporting the stud tensioning device. Wheels rotatably mounted on the frame may be mounted on the base. The gantry may be positioned above the base or at a distance from the base.

[0041] Wheels rotatably mounted on a support frame may form part of a wheel assembly for mounting the wheels to a base. Each wheel assembly may include an axle, bearings, etc. The trolley may consist of two sets of wheels spaced apart from each other (e.g., a front wheel pair and a rear wheel pair). In other embodiments, the wheels of the support frame may be configured to engage with rails suspended above the ground (or floor). In this regard, the wheels may be mounted on a base of the support frame. The wheels may be configured to engage with (i.e., roll across) rails or tracks positioned above the trolley so that the trolley is suspended from rails or tracks when in use.

[0042] The handling device may include a winch. The winch may engage with the stud pulling device and include an engaging member for moving the stud pulling device along a substantially vertical axis. When combined with a gantry, the handling device may lift the stud pulling device (so that it is not supported by the support frame) and move the stud pulling device along the support frame (for example, to move it toward the reactor vessel). The winch may include a motor so that it can be controlled electronically (for example, remotely or in a predetermined automated manner).

[0043] Alternatively, the handling device may include a robotic arm (e.g., mounted on the trolley's support frame). Alternatively, the handling device may include a conveyor (e.g., a conveyor belt) for moving the stud tensioning device relative to the trolley. If the stud tensioning device has a chain-like structure (i.e., formed from multiple connecting elements), the handling device may include an unloading means configured to progressively move (i.e., advance) the stud tensioning device from the trolley to the reactor vessel. For example, the unloading means may include one or more driven rollers (for engaging with the stud tensioning device) for progressively attaching (e.g., by pushing) the stud tensioning device to the reactor vessel.

[0044] The trolley may be equipped with drive means (e.g., one or more motors) for driving the wheels. The trolley may further be equipped with a controller for controlling the drive means. The controller may be remotely operated (e.g., via a remote user interface and wired or wireless connection) and / or operated according to predetermined instructions stored in memory. The handling device may be moved in a similar manner (i.e., by one or more remotely controlled motors or according to predetermined instructions). In this way, the trolley can be used as part of an automation process.

[0045] The trolley may be collapsible. That is, the trolley may be configured to move between a collapsible configuration and an expanded configuration. This can be facilitated, for example, by the trolley's structure (frame, etc.) including nesting, pivoting, or hinged components. The trolley may include actuators for deforming the trolley between the collapsible and expanded configurations. In the collapsible configuration, the height and / or width of the trolley may be smaller than in the expanded configuration. The trolley may be movable (e.g., drivable) in the collapsible state. In this way, for example, if it is necessary to move the trolley through an opening in the wall of a structure housing a reactor vessel and / or inside and outside the containment structure, the size of the opening (i.e., the size for housing the equipment) can be minimized. Thus, the trolley can be transported in a collapsible configuration and perform tensioning / releasing operations in an expanded configuration. In a third embodiment, the reactor vessel is, A main body that defines a cavity for housing a nuclear reactor and an IHP for closing the opening to the cavity, The IHP is positioned at intervals around the reactor vessel and is detachably attached to the main body by a plurality of closing studs that extend through openings formed in the outwardly projecting circumferential flanges of the main body and the IHP, respectively. The main unit and A mounting structure for supporting a multi-stud tensioning device that extends circumferentially around the IHP above the closing stud, A reactor vessel equipped with this feature is provided.

[0046] The mounting structure may include rails, tracks, flanges, or projections that extend circumferentially around the IHP. The mounting structure may be positioned vertically spaced above the flange of the IHP. The mounting structure may also be in the form of rails. The rails may be positioned at a distance from the reactor vessel by radially extending supports.

[0047] The mounting structure can be configured to allow the multi-stud tensioning device to move circumferentially around the reactor vessel when the multi-stud tensioning device is mounted on the reactor vessel. The mounting structure may include, for example, a track or rail for guiding the stud tensioning device in circumferential motion around the IHP by engaging with the wheels of the mounted stud tensioning device. Alternatively or additionally, the mounting structure may include wheels for engaging with the track or rail of the stud tensioning device mounted thereon.

[0048] The reactor vessel may include drive means for moving the stud tensioning device circumferentially around the reactor vessel (for example, circumferentially around the IHP) when the stud tensioning device is installed. The drive means may be in the form of one or more motors or actuators. The drive means may be engageable directly with the installed stud tensioning device or, for example, via a mounting structure. The drive means may include, for example, a winch and a cable for engaging with the stud tensioning device, thereby the retraction of the cable (by the winch) providing such movement. Alternatively, the drive means may be configured to move the mounting structure around the IHP. The mounting structure may be operably connected to the IHP via a gear array (i.e., for circumferential movement of the mounting structure).

[0049] The reactor vessel may further include a lowering device for vertically moving a mounted stud tensioning device (i.e., mounted on a mounting structure) in order to engage the stud tensioning device with one or more studs of the reactor vessel. The lowering device may directly engage with the stud tensioning device (for example, by forming part of the mounting structure), or it may lower the mounting structure itself to lower the mounted stud tensioning device, for example, onto one or more studs of the reactor vessel. The lowering device may be in the form of one or more winches.

[0050] In a fourth aspect, a multi-stud tensioning device, A plurality of stud tensioning devices for applying / releasing tension to studs on a reactor vessel, comprising a plurality of stud tensioning devices configured to form an arc, A mounting structure configured to detachably attach a multi-stud tensioning device to the reactor vessel, A multi-stud tensioning device equipped with this feature is provided.

[0051] A multi-stud tensioning device can be configured to move circumferentially around the reactor vessel on which it is installed. Therefore, the multi-stud tensioning device may include wheels, tracks, or rails for moving the device around the reactor vessel.

[0052] A multi-stud tensioning device, when mounted on a reactor vessel, may include drive means for moving the multi-stud tensioning device circumferentially around the reactor vessel. In this regard, the multi-stud tensioning device may include one or more actuators or motors for moving the multi-stud tensioning device circumferentially around the reactor vessel. The actuators or motors may be operably connected to wheels for moving the multi-stud tensioning device.

[0053] A multi-stud tensioning device may additionally or alternatively include a plurality of connected (series-connected) chain elements to form a chain-like structure. Each element may be rotatably or pivotably connected to an adjacent element by a link. Thus, each element may be rotatable (with respect to one or more axes) or pivotable with respect to an adjacent element. Each element may include one or more stud tensioning devices. In this way, the stud tensioning device can surround (or meander) the reactor vessel when moved over it. That is, the leading element of the plurality of chain elements can engage with a track or rail on the reactor vessel, and the subsequent chain elements can advance over the reactor vessel and follow the circumferential movement of the leading element (e.g., by engagement with the track or rail) as the leading element moves around the reactor vessel.

[0054] Alternatively, the (chain-like) multi-stud tensioning device may be self-supporting, and each element may be equipped with an actuator configured to move (e.g., rotate or pivot) the element relative to an adjacent chain element. The multi-stud tensioning device may include (or be connectable to) a controller configured to control the actuators to surround or meander the chain elements around the reactor vessel. In another embodiment, the chain elements may be biased (e.g., by springs) to hold the multi-stud tensioning device to the reactor vessel.

[0055] A multi-stud tensioning device may include a descent device for moving the multi-stud tensioning device vertically when mounted on the reactor vessel. The descent device may allow the multi-stud tensioning device to descend onto (and engage with) the studs of the reactor vessel. The descent device may be in the form of one or more winches.

[0056] The multi-stud tensioning device may include a stud removal mechanism for removing studs from the reactor vessel after tension has been released. The stud removal mechanism may include a storage compartment for housing one or more removed studs.

[0057] In the fifth aspect, a nuclear power plant system is provided, which nuclear power plant system is - A reactor vessel, A body defining a cavity for housing the core of a nuclear reactor and an IHP for closing the opening to the cavity, wherein the IHP is detachably attached to the body by a plurality of closing studs that are spaced apart around the reactor vessel and extend through openings formed in the outwardly projecting circumferential flanges of the body and the IHP, respectively. A mounting structure for receiving a stud tensioning device, comprising a mounting structure positioned at intervals above the circumferential flange and extending circumferentially around the IHP, A reactor vessel equipped with, - A trolley according to the second embodiment, the trolley being movable from a storage position to a deployed position adjacent to the reactor vessel, - A stud tensioning device configured to apply / release tension to the closing stud and having a mounting portion for attaching to the mounting structure of the reactor vessel, - A containment structure surrounding the reactor vessel, comprising one or more tracks or rails extending between the containment area and the reactor vessel, wherein the wheels of the trolley engage with the one or more tracks or rails in order to move the trolley between the containment area and the reactor vessel, It is equipped with.

[0058] The containment structure may include a primary enclosure containing the reactor vessel and a secondary enclosure defining the containment location. In some embodiments, the secondary enclosure may be external to the containment structure (e.g., an annex). The primary and secondary enclosures may be separated by a separation wall of the containment structure. One or more tracks or rails may extend from the secondary enclosure to the reactor vessel through an opening in the separation wall. The containment structure may include doors for sealing the opening in the separation wall. A trolley and / or multi-stud tensioning device is detachable from the secondary enclosure so that the trolley and / or multi-stud tensioning device can be used with a vehicle.

[0059] The system of the fifth embodiment may include a further containment structure, which includes a further reactor vessel and one or more rails extending from the containment to the further reactor vessel. In this way, the trolley (and multi-stud tensioning device) is moved from the containment to the further reactor vessel, and the multi-stud tensioning device is attached to the further reactor vessel. Thus, the trolley and multi-stud tensioning device can service multiple reactor vessels. The containment can be centrally located relative to the reactor vessel.

[0060] Each of the reactor vessel's IHP and body may include mounting sections for attaching the IHP to the body. Each mounting section may include a circumferential flange projecting outward. Each flange may include through-holes for receiving closing studs to mount the flange (and thus the IHP and body) together. The IHP may include a pressure seal at its lower end to seal the IHP at the upper end of the body.

[0061] As described above with respect to the first embodiment, the core may include a control rod assembly and an upper internal structure for guiding the control rod assembly. The IHP may include a closed head and a control rod drive mechanism housed within a shroud. The control rod drive mechanism may include at least one drive rod (and preferably more drive rods) extending through the closed head. Each drive rod may include a coupling element (e.g., a pneumatic coupling element) for releasably coupling to the control rod assembly within the core. At least one drive rod may be movable to a maintenance / refueling position, in which case at least one drive rod is discoupled from the control rod assembly and retracted at least partially (preferably completely) into the IHP (e.g., within the shroud). The IHP may further include at least one locking element for locking at least one drive rod in the maintenance / refueling position.

[0062] The present invention may include a nuclear reactor power plant, may be included as part of a nuclear reactor power plant, or may be used together with a nuclear reactor power plant (hereinafter referred to as a nuclear reactor). In particular, the present invention relates to a pressurized water reactor. The nuclear reactor power plant may have an output of 250 to 600 MW or 300 to 550 MW. The nuclear reactor power plant may be a modular reactor. A modular reactor can be thought of as a reactor composed of a number of modules manufactured off-site (e.g., in a factory), which are then assembled into a nuclear reactor power plant on-site by connecting the modules to each other. The primary, secondary, and / or tertiary circuits may all be formed in a modular structure.

[0063] A nuclear reactor may comprise a primary circuit comprising a reactor pressure vessel, one or more steam generators, and one or more pressurizers. The primary circuit circulates a medium (e.g., water) through the reactor pressure vessel, extracting heat generated by nuclear fission in the core, which is then sent to the steam generators and transferred to the secondary circuit. The primary circuit may comprise one to six steam generators, or two to four steam generators, or three steam generators, or any of the aforementioned numerical ranges. The primary circuit may comprise one, two, or two or more pressurizers. The primary circuit may include circuits extending from the reactor pressure vessel to each of the steam generators, which can transport a high-temperature medium from the reactor pressure vessel to the steam generators and a cooling medium from the steam generators back to the reactor pressure vessel. The medium may be circulated by one or more pumps. In some embodiments, the primary circuit may comprise one or two pumps per steam generator in the primary circuit.

[0064] In some embodiments, the circulating medium in the primary circuit may include water. In some embodiments, the medium may include a neutron-absorbing material (e.g., boron, gadolinium) added to the medium. In some embodiments, the pressure in the primary circuit is at least 50, 80, 100, or 150 bar during full-power operation, and the pressure may reach 80, 100, 150, or 180 bar during full-power operation. In some embodiments, when water is the medium in the primary circuit, the hot water temperature of the water leaving the reactor pressure vessel may be between 540K and 670K, between 560K and 650K, or between 580K and 630K during full-power operation. In some embodiments where water is the medium in the primary circuit, the cold water temperature of the water returning to the reactor pressure vessel may be between 510 and 600K, or between 530 and 580K, during full-power operation.

[0065] A nuclear reactor may have a secondary circuit comprising a water circulation loop that extracts heat from a primary circuit in a steam generator to convert water into steam to drive a turbine. In an embodiment, the secondary loop may comprise one or two high-pressure turbines and one or two low-pressure turbines. The secondary circuit may also comprise a heat exchanger that condenses the steam into water when the steam is returned to the steam generator. The heat exchanger may be connected to a tertiary loop that can contain a large amount of water to act as a heat sink.

[0066] The reactor vessel may include a steel pressure vessel, which may be 5–15 m in height or 9.5–11.5 m in height and 2–7 m in diameter or 3–6 m in diameter or 4–5 m in diameter. The pressure vessel may comprise a reactor body and a reactor head positioned vertically above the reactor body. The reactor head may be connected to the reactor body by a series of studs that pass through flanges on the reactor head and corresponding flanges on the reactor body.

[0067] The reactor head may include an integrated head assembly in which numerous elements of the reactor structure are combined into a single element. The integrated elements may include the reactor vessel head, cooling shroud, control rod drive mechanism, missile shield, lifting rig, hoist assembly, and cable tray assembly.

[0068] The reactor core can consist of numerous fuel assemblies, each containing fuel rods. Fuel rods can be formed from pellets of fissile material. Fuel assemblies can also contain spaces for control rods. For example, a fuel assembly can provide housing for 17x17 grid rods, i.e., a total of 289 spaces. Of these 289 spaces, 24 can be reserved for the reactor's control rods, each of which can be formed from 24 control rods connected to the main arms, and one can be reserved for the instrumentation tubes. Control rods are movable in and out of the core to provide control of the fission process the fuel undergoes by absorbing neutrons released during fission. The core can contain 100 to 300 fuel assemblies. Fully inserting the control rods can typically result in a subcritical state, which would shut down the reactor. Up to 100% of the fuel assemblies in the core can contain control rods.

[0069] The movement of the control rod can be performed by a control rod drive mechanism. The control rod drive mechanism can command and power actuators to lower and raise the control rod inside and outside the fuel assembly and to maintain the position of the control rod relative to the core. The control rod drive mechanism can also rapidly insert the control rod to rapidly shut down (i.e., scram) the reactor.

[0070] The primary circuit can be contained within a containment structure to retain steam from the primary circuit in the event of an accident. The containment structure can have a diameter of 15 to 60 m, or 30 to 50 m. The containment structure can be made of steel, concrete, or steel-backed concrete. The containment structure may include water tanks for emergency cooling of the reactor, either internally or externally. The containment structure may include equipment and facilities to enable refueling of the reactor, storage of fuel assemblies, and transport of fuel assemblies between the inside and outside of the containment structure.

[0071] A power plant may include one or more civil structures to protect its reactor elements from external hazards (e.g., missile attacks) and natural hazards (e.g., tsunamis). These civil structures may be constructed from steel, concrete, or a combination of both. [Brief explanation of the drawing]

[0072] [Figure 1A] This is a side view of the trolley and reactor vessel according to the first embodiment. [Figure 1B] This is a top view of the trolley according to the first embodiment. [Figure 1C] This is a top view showing a method for attaching a multi-stud tensioning device to a reactor vessel according to the first embodiment. [Figure 1D] This is a top view showing a method for attaching a multi-stud tensioning device to a reactor vessel according to the first embodiment. [Figure 1E] This is a top view showing a method for attaching a multi-stud tensioning device to a reactor vessel according to the first embodiment. [Figure 1F] This is a top view showing a method for attaching a multi-stud tensioning device to a reactor vessel according to the first embodiment. [Figure 2] This is a schematic top view showing a trolley, multi-stud tensioning device, and reactor vessel according to the second embodiment. [Modes for carrying out the invention]

[0073] Next, embodiments will be described only as examples, with reference to the drawings.

[0074] Figure 1 shows a trolley 10 and a reactor pressure reactor vessel (RPV) 12, which in the illustrated embodiment form part of a pressurized water reactor (PWR) nuclear power plant. The RPV includes a reactor body 14 and an integrated head package (IHP) 16. The RPV 12 is positioned through an opening formed in the floor structure such that only the IHP 16 extends above the floor structure. The IHP 16 is removably attached to the reactor body 14 by a number of studs 18 spaced apart around the RPV 12. The studs 18 extend vertically through openings formed in outwardly projecting circumferential flanges 20, 22 of the reactor body 14 and the IHP 16, respectively. As will be described in more detail below, the IHP 16 further includes a mounting structure in the form of an outwardly projecting mounting flange 24 for attaching a multi-stud tensioning device to the IHP 16.

[0075] In the illustrated embodiment, the trolley 10 comprises a support frame 26 supporting a first multi-stud tensioning device (MST) 28a and a second multi-stud tensioning device 28b, which will be described in more detail below. The trolley 10 further includes four wheels 30 (arranged at rectangular intervals) rotatably mounted to a base 32 of the support frame 26. The wheels 30 are housed in a pair of spaced-apart straight tracks 34 (only a portion of the tracks 34 is shown in the figure), which are in the form of parallel grooves formed in the floor structure. In this way, the movement of the trolley 10 is restricted to the path defined by the tracks 34. Although not shown, the wheels 30 can be operably connected to motors that drive the wheels 30 in order to move the wheels 30 toward and away from the RPV 12 along the tracks.

[0076] In the illustrated embodiment, the support frame 26 includes a plurality of horizontal and vertical elongated members 36 formed in a box-shaped frame. However, it should be understood that the support frame 26 can take many different forms. The base 32 of the support frame 26 also includes a plurality of platforms 38 that can support two MSTs 28a, 28b.

[0077] The support frame 26 is also positioned vertically above the base 32 and includes a horizontally extending gantry 40 that extends approximately through the center between the opposing lateral sides of the trolley 10. The gantry 40 extends beyond the base 32 (i.e., overhangs). As will be further described below, this facilitates the movement of the MSTs 28a, 28b from the trolley 10 to the RPV 12.

[0078] The handling device 42 is movably mounted to the gantry 40 via rollers and is movable horizontally along the gantry 40. The handling device 42 includes a winch 46 having an engaging member 44 (e.g., an electromagnet, a locking mechanism, or a hook) for engaging the MSTs 28a, 28b. The winch 46 is operable to move the engaging member 44 along a vertical axis (e.g., via a wire). Thus, the combination of the gantry 40 and the winch 46 allows the handling device 42 to engage with the MSTs 28a, 28b and move along two axes. In the illustrated embodiment, the second MST 28b is engaged by the engaging member 44. The second MST 28b is lifted by the winch 46 and moved along the gantry 40 by the handling device 42. This movement of the handling device 42 may be provided by one or more motors (e.g., remotely controlled or following predetermined instructions) that form part of the handling device 42 and / or the gantry 40.

[0079] Therefore, the trolley 10 can be used to attach the MSTs 28a and 28b to the RPV 12 for the purpose of removing the IHP 16 from the reactor body 14. The MSTs 28a and 28b are configured to apply / release tension to the closing studs 18 of the RPV 12. Each MST 28a and 28b comprises a plurality of stud tension units connected to each other and arranged in a semicircle. In this way, each MST 28a and 28b can apply / release tension to half of the closing studs 18 of the RPV 12 when attached to the RPV 12.

[0080] An exemplary method for doing this is shown in Figures 1C to 1F. For clarity, these figures do not show the closing studs 18 or flanges 20, 22, 24 of the RPV12.

[0081] In Figure 1C, the trolley 10 is in the process of being moved along the parallel track 34 from a storage position (not shown). The trolley 10 supports two MSTs 28a, 28b on the platform 38 at the base 32 of the support frame 26. As described above, the trolley 10 may be remotely controlled or move along the track 34 according to predetermined instructions (i.e., in an automated manner).

[0082] In Figure 1D, trolley 10 has reached a position adjacent to RPV 12. Winch 46 is used to lift the second MST 28b from platform 38 and is moved horizontally along gantry 40 to move the second MST 28b toward RPV 12.

[0083] In Figure 1E, the second MST 28b is attached to the flange 24 of the RPV 12 (see Figures 1A and 1B) and rotated 180° around the RPV 12. This rotation may be performed manually, or the second MST 28b may be moved by a drive mechanism (motor, winch, geared mechanism, etc.). In this figure, the winch 46 is also moved horizontally along the gantry 40 from the RPV 12 to the first MST 28a. The winch 46 is then used to lift the first MST 28a from the platform 32 and returned to its position on the gantry 40 close to the RPV 12.

[0084] In Figure 1F, the first MST 28a is attached to the RPV 12, and both MSTs 28a and 28b are locked together. Although not shown, the MSTs 28a and 28b can then be engaged with (e.g., lowered over) a closing stud 18 and used to tension / release the stud 18. Subsequently, the stud 18 can be removed, thereby allowing the head 16 of the RPV 12 to be removed from the body 14. Figure 2 shows a trolley 10' and a multi-stud tensioning device 28' according to a second embodiment. The multi-stud tensioning device 28' includes a plurality of chain elements 48 connected to each other by links 50. Each chain element 48 (except for the front chain element 48 and the rear chain element 48) is pivotably engaged with two links 50. In this way, the chain elements 48 are pivotable relative to each other. Thus, the multi-stud tensioning device 28' can be made to surround or meander around the reactor vessel 12 (as shown in the figure).

[0085] In this embodiment, this enclosure around the reaction vessel 12 is facilitated by a removal means 54 provided on the trolley 10'. The removal means 54 includes a linear guide structure (e.g., rail, track, etc.) 54 and an actuator or roller (not shown) for progressively moving or advancing the multi-stud tensioning device 28' along the guide structure 54.

[0086] Although not shown, the trolley 10' may also be provided with means for housing the multi-stud tensioning device 28' (for example, by winding the multi-stud tensioning device 28' around it).

[0087] As indicated by the arrows in the figure, the multi-stud tensioning device 28' advances over the reaction vessel 12, and then the removal means 54 pushes the multi-stud tensioning device 28' out of the trolley 10', gradually encircling the reaction vessel 12. To encircle the reaction vessel 12, the multi-stud tensioning device 28' includes actuators that pivot the individual chain elements 48 relative to each other to form a curved / circular shape. These actuators may be controlled by controllers that form part of the multi-stud tensioning device 28' and the trolley 10', or they may be separate from the trolley 10' and the multi-stud tensioning device 28'.

[0088] Each chain element 48 of the multi-stud tensioning device 28' is equipped with two tensioning devices 52. Thus, once the multi-stud tensioning device 28' completely surrounds the reactor vessel 12 (so that the tensioning devices 52 are aligned perpendicularly to the studs of the reactor vessel 12), the multi-stud tensioning device 28' can be lowered over the studs of the reactor vessel 12 to apply / release tension to the studs.

[0089] The present invention is not limited to the embodiments described above, and it will be understood that various modifications and improvements can be made without departing from the concepts described herein. Any feature may be used separately or in combination with any other feature, except where mutually exclusive, and the disclosure extends to and includes all combinations and subcombinations of one or more features described herein.

Claims

1. A trolley for transporting one or more stud tensioning devices in a nuclear power plant, Support frame that supports the stud tensioning device and Multiple wheels rotatably mounted on the aforementioned frame and A handling device attached to the frame so as to be movable with respect to the frame, the handling device being configured to move by engaging a stud tensioning device with respect to the support frame, Equipped with, The handling device includes a winch, the winch engages with the stud pulling device and includes an engaging member for moving the stud pulling device along a substantially vertical axis. Trolley.

2. The trolley according to claim 1, wherein the support frame is equipped with an elongated gantry, and the handling device is mounted on the gantry so as to be movable along the longitudinal axis of the gantry.

3. The trolley according to claim 2, wherein the gantry extends substantially horizontally.

4. The trolley according to claim 2 or 3, wherein the support frame comprises a base for supporting the stud tensioning device, and the gantry is spaced apart above the base.

5. The trolley according to claim 4, wherein the wheel is rotatably mounted on the base.

6. The trolley according to any one of claims 1 to 5, wherein the support frame includes nesting, pivoting, or hinged components and is configured to be movable between a folded configuration and an extended configuration.

7. It is a nuclear power plant system, - Reactor vessel A body defining a cavity for housing the core of a nuclear reactor and an integrated head package (IHP) for closing the opening to the cavity, wherein the integrated head package is detachably attached to the body by a plurality of closing studs that are spaced apart around the reactor vessel and extend through openings formed in outwardly projecting circumferential flanges of the body and the integrated head package, respectively. A mounting structure for receiving a stud tensioning device, comprising a mounting structure positioned at intervals above the circumferential flange and extending circumferentially around the integrated head package, A reactor vessel equipped with, - A trolley according to any one of claims 1 to 6, which is movable from a storage position to a deployed position adjacent to the reactor vessel, - A stud tensioning device configured to apply / release tension to the closing stud, comprising a mounting portion for attaching to the mounting structure of the reactor vessel, - A containment structure surrounding a reactor containment vessel, comprising one or more tracks or rails extending between the containment area and the reactor vessel, wherein the wheels of the trolley engage with the one or more tracks or rails in order to move the trolley between the containment area and the reactor vessel, A nuclear power plant system equipped with these features.

8. The nuclear plant system according to claim 7, wherein the containment structure comprises a primary enclosure containing the reactor vessel and a secondary enclosure defining the containment location, the primary enclosure and the secondary enclosure being separated by a separation wall of the containment structure, and the one or more tracks or rails extending from the secondary enclosure to the reactor vessel through an opening in the separation wall.

9. A method for applying / releasing tension to closing studs of a reactor vessel, wherein the closing studs are spaced apart around the reactor vessel to attach the integrated head package (IHP) of the reactor vessel to the body of the reactor vessel, and the method is The steps include supporting the first stud tensioning device on the trolley, The steps include moving the trolley across a moving surface from a distant storage position to a deployment position adjacent to the reactor vessel, The steps include engaging the first stud tensioning device with one or more of the closing studs, The steps include: activating the first stud tensioning device to apply / release tension to one or more of the closing studs; A method that includes this.

10. The method according to claim 9, wherein the movement of the trolley is carried out along a path that extends substantially laterally with respect to the reactor vessel.

11. The method according to claim 10, wherein the path extends along a substantially horizontal reference plane defined by the moving surface, and the reference plane is aligned substantially perpendicularly to the upper opening of the body of the reactor vessel.

12. The method according to any one of claims 9 to 11, wherein the movement of the trolley is performed along one or more tracks or rails, and the moving surface is the surface of the one or more tracks or rails.

13. The method according to any one of claims 9 to 12, comprising attaching the first stud tensioning device to the reactor vessel after the trolley has been moved to the deployed position.

14. The method according to claim 13, comprising rotating the first stud tensioning device around the outer circumference of the reactor vessel before engaging the first stud tensioning device with the stud.

15. The method according to claim 14, comprising the steps of supporting a second stud tensioning device on the trolley, and then attaching the second stud tensioning device to the reactor vessel after rotating the first stud tensioning device around the reactor vessel.

16. The method according to claim 15, further comprising the steps of engaging a second stud tensioning device with the closing studs and simultaneously operating the first stud tensioning device and the second stud tensioning device to apply / release tension to a plurality of the closing studs.

17. The method according to any one of claims 14 to 16, wherein the step of rotating the first stud tensioning device includes the step of attaching the first stud tensioning device to a mounting structure around the reactor vessel and moving the stud tensioning device along the mounting structure.

18. The method according to any one of claims 9 to 17, wherein the stud tensioning device is a multi-stud tensioning device.

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