Nuclear power generation system

Abstract

The present disclosure provides a lifting apparatus for lifting a closure head assembly from a reactor vessel body in a nuclear power system. The lifting apparatus includes at least one lifting element having an engagement surface configured to engage an underside of the closure head assembly. The at least one lifting element is axially adjustable in height between a retracted position, in which the axial height of the lifting element is such that the closure head assembly seals against the reactor vessel body, and an extended position, in which the axial height of the lifting element is such that the closure head assembly is elevated above the reactor vessel body.

Description

Technical Field

[0001] The present disclosure relates to a nuclear power generation system and a method of performing maintenance and refueling operations in a nuclear power generation system.

Background Art

[0002] A nuclear power plant converts thermal energy from the nuclear decay of fissionable materials contained in fuel assemblies within 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 (RPV) containing a 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 in a hermetically sealed containment building, which can be in the form of a concrete structure.

[0004] The RPV typically includes a body that defines a cavity for housing the reactor core / fuel assembly, and a closure head for closing an upper opening to the cavity. The closure head can further form part of an integral head package (IHP) (or integral head assembly) that includes control rod drive mechanisms within a shroud. The control rod drive mechanism includes drive rods that pass through the closure head and are connected to control rods contained within the reactor core. The control rods are provided to absorb neutron radiation within the reactor core and control the nuclear reaction within the reactor core. The drive rods within the control rod drive mechanism are powered by an electric power source and translate vertically to raise and lower the control rods within the reactor core.

[0005] Maintenance and refueling are important parts of the operation of a nuclear power system. For example, maintenance is required regularly to replace old and / or damaged components of the system. Refueling is required regularly (e.g., every 18 - 24 months) to replace spent fuel rods in the fuel assembly.

[0006] When performing core maintenance / refueling, it is necessary to remove at least the closure head assembly from the RPV, thereby exposing the core.

[0007] To perform maintenance and refueling operations in a nuclear power system, an overhead crane device such as a polar gantry crane having a circular runway is usually provided within the storage structure of the system. To enable lifting of heavy components of the nuclear power system, the polar crane is necessarily a large and heavy structure. This makes it expensive to install the polar crane. By housing these within the storage structure, the cost of the storage structure also substantially increases.

[0008] During refueling, the polar crane usually lifts the IHP vertically upward from the RPV (to a lift height of about 10 m to move it away from the refueling cavity), moves the IHP horizontally away from the RPV body, and then lowers it onto a storage stand on the working floor within the storage building. The closure head assembly usually includes a lift frame having a top shackle for connecting to the winch of the polar crane.

[0009] To provide a refueling cavity above the exposed core within the reactor vessel body, the reactor vessel body is usually placed at a considerable distance below the working floor of the storage structure. During removal of the IHP from the reactor vessel body, the drive rods remain connected to the control rods and the fueling cavity filled with water to contain any radioactive emissions from the drive rods protrudes from the reactor vessel cavity into the refueling cavity.

[0010] The water in the refueling cavity also serves to shield and cool the spent fuel rods in the exposed core. For effective gamma shielding, 4 meters of water height is required above the fuel rods / fuel assemblies. Thus, a very large amount of water is required to fill the refueling cavity, and thus it takes time.

[0011] Since the IHP / upper internal structure has to be moved horizontally after passing through the vertical height of the drive rod / refueling cavity and then lowered for storage, the protruding drive rod and the vertical extent of the refueling cavity drive the required lifting height of the upper internal structure by the polar crane.

[0012] The required lifting height of the polar crane determines the height of the storage structure (and thus the cost / time associated with the construction of the storage structure). In addition, if the shackle fails, especially when the closure head assembly is at a fairly high height above the RPV, the dropped load may fall onto the core, which may lead to serious and undesirable consequences.

[0013] There is a need for an improved nuclear power generation system that reduces at least some of the problems associated with the use of a polar gantry crane.

Summary of the Invention

Means for Solving the Problems

[0014] In a first aspect, there is provided a lifting device for lifting a closure head assembly from a reactor vessel body in a nuclear power generation system, the lifting device including at least one lifting element having an engaging surface configured to engage the lower surface of the closure head assembly, the at least one lifting element having an axially adjustable height between a retracted position in which its axial height is such that the closure head assembly seals against the body of the reactor vessel and an extended position in which its axial height is such that the closure head assembly is raised above the body of the reactor vessel.

[0015] Provided is an apparatus having at least one lifting element configured to engage a closure head assembly and having an axially adjustable height, such that as it moves from its retracted position to its extended position, the closure head assembly can be lifted above the body of the closure container by at least one lifting element. Thus, the lifting device lifts the closure head by pushing upwardly from below the lower surface of the closure head assembly. By engaging at least one lifting element against the lower surface of the closure head assembly, the storage structure need only accommodate the height of the raised closure head assembly and not any additional height required by the lifting element. This helps to reduce the cost and construction time of the storage structure.

[0016] Here, optional features of the present disclosure are described. These are applicable either alone or in any combination with any aspect of the present disclosure.

[0017] In some embodiments, the apparatus includes a plurality of lifting elements. In some embodiments, the lifting device can have a center of mass that is vertically lower than the center of mass of the closure head assembly.

[0018] This or each lifting element can include a lift jack (e.g., a screw jack, a hydraulic jack, or a pneumatic jack), a ram / piston (e.g., a hydraulic or pneumatic ram), a rack and pinion, a telescopic linear actuator (e.g., a Spiralift® actuator), or a rigid chain actuator.

[0019] This or each lifting element can be operably coupled to a control system so that the movement of the lifting element between the retracted and extended positions can be performed remotely / automatically.

[0020] This or each lifting element has an engagement surface for engaging with the lower surface of the closure head assembly. If there are multiple lifting elements, the lifting device can include one or more engagement platforms, and each engagement platform integrates at least two adjacent engagement surfaces and extends therebetween. For example, the lifting device can include two rows (e.g., two parallel rows) of lifting elements, and two engagement platforms (e.g., two parallel engagement platforms) extend between the lifting elements in each row.

[0021] To further limit any potential damage caused by the dropping of the load (i.e., the dropping of the closure head assembly), this device can further include a failure system for engaging the closure head assembly in the event of a failure of at least one lifting element. The failure system is provided to ensure that the vertical height of the closure head assembly does not drop or does not drop rapidly. The failure system can extend together with at least one lifting element and can include one or more hydraulic or pneumatic elements that support the weight of the closure head assembly if at least one lifting element fails.

[0022] Alternatively, the failure system can include a support frame configured to be coupled to the closure head assembly and extend in the axial height together with the lifting elements. The support frame can include a locking mechanism (e.g., a ratchet locking mechanism) that locks its axial height (and thus the axial height of the closure head assembly). This helps to limit the decrease in the height of the closure head assembly even if the lifting element fails.

[0023] In some embodiments, this device is for lifting the IHP from the reactor vessel body and transporting it horizontally to a storage location. In these embodiments, this device further includes a wheeled frame for guiding the movement of the closure head assembly between the deployment location and the storage location.

[0024] The wheeled frame enables the movement (e.g., horizontal movement) of the closure head assembly (e.g., on the work floor of a storage structure), and the closure head assembly moves between the deployment location and the storage location.

[0025] The wheeled frame can include two parallel and spaced-apart rails and a connecting arm extending between adjacent axial ends of the two spaced-apart rails such that the frame forms a U shape. The connecting arm can be a linear (i.e., perpendicular to the two spaced-apart rails) connecting arm so that the frame forms a square U shape.

[0026] The spaced-apart rails are attached to frame wheels. For example, there can be two rows of frame wheels, and one row can extend along the length of each of the spaced-apart rails. The frame wheels enable the movement of the closure head assembly between the deployment location and the storage location. In some embodiments, the lifting device further includes a motor for driving the frame wheels to move the closure head assembly from deployment to the storage location. The motor can be operable (e.g., automatically operable) by a control system located remotely from the lifting device. The frame wheels can be flanged wheels, i.e., wheels having a reduced-diameter portion axially sandwiched between two flanges. In this way, the frame wheels can be configured to be driven along a rail / track (e.g., a rail / track on the work floor of a storage structure).

[0027] In some embodiments, at least one lifting element can be attached to the wheeled frame. In this way, the wheeled frame enables the movement (e.g., horizontal movement) of the lifting element (e.g., on the work floor of a storage structure), and the lifting element moves from storage to the deployment location. For example, one of each of two rows (e.g., two parallel rows) of lifting elements with the two engaging platforms (e.g., two parallel engaging platforms) described above can be attached to each of the spaced-apart rails.

[0028] This device can be made foldable. That is, this device can be configured to be movable between a folded configuration and an extended configuration. This can be facilitated, for example, by the structure of the device including nested, pivoting or hinged components. This device can include an actuator for moving the device between its folded and extended configurations. In the folded configuration, the height and / or width of the device can be made less than in the extended configuration. This device can be made movable (e.g., drivable) in the folded configuration. Thus, when the device is required to move through an opening, for example, enter or exit a storage structure, the size of the opening (i.e., for accommodating the device) can be minimized. Accordingly, this device can be transported in the folded configuration and can perform a refueling operation in the extended configuration.

[0029] In some embodiments, the lifting device can be configured to pivot the closure head assembly from its upright (e.g., vertical) orientation, i.e., the orientation fixed to the reactor vessel, to an inclined (e.g., horizontal) position. This will result in a reduction in the vertical height of the lifting device / inclined closure head assembly, enabling the device to be moved through an opening with a minimized vertical dimension, for example, to enter or exit a storage structure.

[0030] In some embodiments, the lifting device can include a gamma shield that reduces gamma emissions from the closure head assembly. The gamma shield can be configured to be disposed vertically below the closure head assembly, for example, vertically below an inclined (horizontal) closure head assembly.

[0031] In a second aspect, a closure head assembly for sealing a reactor vessel body in a nuclear power generation system is provided, the closure head assembly having a closure head with a sealing surface at its axial lower end and an opposite axial upper end for sealing against the pressure vessel body, the closure head assembly further including at least one seating element vertically spaced below the axial upper end of the closure head assembly and having a lower surface for abutting an engagement surface of at least one lifting element.

[0032] The closure head assembly can be an integrated head package (IHP) further including a control rod drive mechanism housed within a shroud. The control rod drive mechanism includes at least one drive rod (and preferably a plurality of drive rods) extending through the closure head, each of which has a coupling element (such as a pneumatic coupling element) for releasably coupling to a control rod assembly within the reactor core. At least one drive rod is movable to a maintenance / fuel refueling position where the at least one drive rod is detached from the control rod assembly and at least partially (preferably completely) retracts into the IHP (such as into the shroud). The IHP further includes at least one locking element for locking at least one drive rod in the maintenance / fuel refueling position.

[0033] This IHP enables the drive rod to be removed from the reactor core together with the IHP. Thus, the need to flood the fuel refueling cavity is eliminated because the radioactive drive rod no longer protrudes from the reactor core.

[0034] The closure head can further include a fixing flange (such as an annular fixing flange) for receiving studs for fixing the closure head to the reactor vessel body.

[0035] The seating element can project radially / transversely from the closure head assembly. Thus, this / each lifting element of the lifting device, as it extends from its contracted state to its extended position, pushes the closure head assembly upward from below (with respect to the lower surface of the seating element) to an elevated position where the closure head assembly seats on the engagement surface of the lifting element rather than on the reactor vessel body.

[0036] In some embodiments, at least one seating element can extend radially / transversely from the closure head, for example, it can project proximal to the axial lower end of the closure head assembly. In other embodiments, at least one seating element can project radially / transversely at an axial position intervening between the axial lower end and the axial upper end of the closure head assembly. The intervening axial position can be closer to the axial lower end than to the axial upper end of the closure head assembly.

[0037] A plurality of seating elements can be provided on the closure head assembly, each for seating on one of the plurality of lifting elements of the lifting device. The plurality of seating elements can be circumferentially spaced around the closure head assembly at a vertical spacing intervening between the axial upper end and the axial lower end, for example, they can be circumferentially spaced closer (e.g., proximal) to the axial lower end of the closure head assembly.

[0038] The seating elements on the closure head assembly can each include a lug, plate or flange that extends laterally / radially / horizontally from the closure head assembly. If there are four seating elements, these can be formed by a horizontal square plate where the closure head or shroud intersects vertically. The square plate can be positioned substantially vertically, for example proximal to the axial lower end of the closure head, such as the closure head assembly, and the sealing surface (or annular fixing flange) of the closure head is inscribed within the square plate, leaving the four corners of the square plate as seating elements for seating on the lifting elements. The square plate can be formed integrally with the closure head. The seating elements can be welded, riveted or attached to the closure head by known fixing means.

[0039] In a third aspect, an apparatus according to the first aspect, and a reactor vessel comprising a reactor vessel body defining a cavity for accommodating a core, a closure head assembly according to the second aspect, and a nuclear power generation system including a reactor vessel having the same is provided.

[0040] Thus, in some embodiments, the system includes a storage structure, and the working floor of the storage structure surrounds the opening to the reactor vessel body cavity and is substantially vertically aligned therewith.

[0041] Considering the scale of the nuclear power generation system, the term "substantially vertically aligned" means that the vertical distance between the working floor and the opening to the reactor vessel cavity (defined by the upper end of the reactor vessel body) is less than 2 meters, for example 1 meter or 0.5 meters above the opening to the cavity within the reactor vessel body.

[0042] In some embodiments, the working floor includes at least one path extending from near the reactor vessel to a (remote) storage location, and the at least one path is substantially vertically aligned with the opening to the reactor vessel cavity. The remote storage location can be provided outside the storage structure, for example, in a shielded enclosure.

[0043] In some embodiments, the at least one path can be a linear path extending between the reactor vessel body and the storage location. In some embodiments, the at least one path can be a substantially horizontal path.

[0044] In some embodiments, the at least one path can include a track / rail extending from between the reactor vessel body and the storage location, and the frame wheels of the lifting device are attached to the track / rail. The track / rail can be substantially vertically aligned with the opening to the cavity within the reactor vessel body. The use of the track / rail can facilitate the automation of the movement of the lifting device along the at least one path, thereby reducing the number of workers required to perform refueling / maintenance (thereby reducing the safety risks associated with these processes).

[0045] In some embodiments, the lifting elements of the lifting device are vertically spaced and attached below the opening to the reactor vessel body cavity within the storage structure. These can be horizontally / radially aligned with the body of the reactor vessel. If there are multiple lifting elements, they can be circumferentially arranged around the reactor vessel body.

[0046] In some embodiments, the deployment location is vertically above the reactor vessel body.

[0047] In some embodiments, the system includes a control system for actuating at least one lifting element and / or for sending control signals for driving the frame wheels. The control system (and any associated user interface) can be remote from the reactor vessel.

[0048] In an embodiment, when the lifting element and the engagement surface / platform are attached to a wheeled trolley, a seating element (e.g., a square plate) on the closure head assembly projects radially / transversely from the closure head assembly at a vertical height higher than the vertical height of the engagement surface / platform when the lifting element is in the retracted position.

[0049] A plurality of seating elements can be provided on the closure head assembly, each seating element being for seating on a respective one of the plurality of lifting elements of the lifting device.

[0050] In some embodiments, the system is a pressurized water reactor system.

[0051] In a fourth aspect, a method is provided for exposing the core in a nuclear power generation system according to the third aspect (e.g., to enable maintenance / fuel replenishment), the method including adjusting the axial height of at least one lifting element from a retracted position in which the closure head assembly is sealed against the body of the reactor vessel to an extended position in which the lower surface of the closure head assembly has risen above the body of the reactor vessel.

[0052] In some embodiments, the method includes pushing the closure head assembly vertically upward from below the axial upper end of the closure head assembly (e.g., proximally from the axial lower end). The method can include providing an upward force to the lower surface of one or more seating elements that can project radially / transversely from the closure head assembly (e.g., radially / transversely from proximally to the axial lower end of the closure head assembly) using an engagement surface / platform of a lifting device.

[0053] In some embodiments, the method can include lifting the closure head assembly using a plurality of lifting elements.

[0054] In these embodiments, the method can include providing an upward force to a plurality of seating elements on the closure head assembly, each seating element being for seating on a respective one of the engagement surfaces of a plurality of lifting elements (e.g., on an engagement platform).

[0055] The method can include lifting the closure head assembly using one or more of a lift jack (e.g., a screw jack, a hydraulic jack, or a pneumatic jack), a ram / piston (e.g., a hydraulic or pneumatic ram), a rack and pinion, a telescopic linear actuator, or a rigid chain actuator.

[0056] In some embodiments, the method further includes moving the closure head assembly to a storage position (e.g., a storage position on a work floor of a storage structure), for example horizontally.

[0057] When the lifting element is vertically spaced and attached below the opening to the reactor vessel body cavity within the storage structure (e.g., horizontally / radially aligned with the reactor vessel body), the (horizontal) movement can be performed by inserting a wheeled frame between the reactor vessel body and the closure head assembly such that the axial lower end of the closure head assembly can be lowered and placed on the wheeled frame. The lifting element can then be removed from the closure head assembly. The lifting element can then be contracted to reduce its axial (vertical) height.

[0058] In an embodiment where at least one lifting element is attached to the wheeled frame, the method can include moving the lifting device to the deployment position with at least one lifting element in its contracted position and disposed below the lower surface of the closure head assembly (e.g., below the lower surface of the seating element). The at least one lifting element is then extended such that the engagement surface / engagement platform engages the lower surface of the closure head assembly and pushes upward to lift the closure head assembly from the reactor vessel body.

[0059] In any alternative method, the wheeled frame can be moved (e.g., horizontally) to move the closure head assembly to the storage position. The wheeled frame can be moved to the storage position, for example, along rails or tracks provided on the working floor of the storage container.

[0060] The present invention can be included as part of, or used with, a nuclear power plant (referred to herein as a nuclear reactor). In particular, the present invention can relate to a pressurized water reactor. The nuclear power plant can have an output between 250 and 600 MW, or between 300 and 550 MW.

[0061] The nuclear power plant can be a modular nuclear reactor. The modular nuclear reactor can be regarded as a nuclear reactor composed of a number of modules manufactured off-site (for example, in a factory), and then these modules are assembled on-site into a nuclear power plant by connecting these modules together. Any of the primary, secondary, and / or tertiary circuits can be formed in a modular structure.

[0062] The nuclear reactor can include a primary circuit including a nuclear reactor pressure vessel, one or more steam generators, and one or more pressurizers. The primary circuit circulates a medium (for example, water) through the nuclear reactor pressure vessel to extract the heat generated by nuclear fission in the core, and the heat is then delivered to the steam generator and transferred to the secondary circuit. The primary circuit can include a steam generator between 1 and 6, or between 2 and 4, or three steam generators, or can include any range of the aforementioned numerical values. The primary circuit can include one, two, or more than two pressurizers. The primary circuit can include a circuit extending from the nuclear reactor pressure vessel to each of the steam generators, and the circuit can carry a high-temperature medium from the nuclear reactor pressure vessel to the steam generator and return a cooling medium from the steam generator to the nuclear reactor pressure vessel. The medium can be circulated by one or more pumps. In some embodiments, the primary circuit can include one or two pumps for each steam generator within the primary circuit.

[0063] In some embodiments, the medium circulating within the primary circuit can include water. In some embodiments, the medium can include neutron absorbing substances (e.g., boron, gadolinium) added to the medium. In some embodiments, the pressure within the primary circuit can be at least 50, 80, 100, or 150 bar during full power operation, and the pressure can reach 80, 100, 150, or 180 bar during full power operation. In some embodiments, when water is the medium of the primary circuit, the heated water temperature of the water exiting the reactor pressure vessel can be between 540 and 670 K, or between 560 and 650 K, or between 580 and 630 K during full power operation. In some embodiments, when water is the medium of the primary circuit, the cooled water temperature of the water returning to the reactor pressure vessel can be between 510 and 600 K, or between 530 and 580 K during full power operation.

[0064] The reactor can include a secondary circuit including a water circulation loop that extracts heat from the primary circuit in a steam generator to convert water into steam to drive a turbine. In an embodiment, the secondary loop can include one or two high pressure turbines and one or two low pressure turbines.

[0065] The secondary circuit can include a heat exchanger that condenses steam into water when returned to the steam generator. The heat exchanger can be connected to a tertiary loop that can include a large body of water acting as a heat sink.

[0066] The reactor vessel can include a steel pressure vessel, the pressure vessel having a height of 5 to 15 m, or 9.5 to 11.5 m, and a diameter between 2 and 7 m, or between 3 and 6 m, or between 4 and 5 m. The pressure vessel can include a reactor body and a reactor head disposed vertically above the reactor body. The reactor head can be connected to the reactor body by a series of studs passing through a flange on the reactor head and a corresponding flange on the reactor body.

[0067] The reactor head can include an integral head assembly that can integrate a number of elements of the reactor structure into a single element. Among the elements to be integrated are a pressure vessel head, a cooling shroud, a control rod drive mechanism, a missile shield, a lifting lug, a hoist assembly, and a cable tray assembly.

[0068] The nuclear core can be composed of a number of fuel assemblies, and the fuel assemblies include fuel rods. The fuel rods can be formed of pellets of fissile material. The fuel assemblies can also include spaces for control rods. For example, the fuel assemblies can provide a housing for 17×17 grid rods, i.e., a total of 289 spaces. Of these total 289 spaces, 24 can be reserved for control rods for the reactor, each of which can be formed by 24 control rods connected to a main arm, and 1 can be reserved for an instrumentation tube. The control rods are movable in and out of the core to control the nuclear fission process received by the fuel by absorbing neutrons released during nuclear fission. The core can include between 100 and 300 fuel assemblies. Completely inserting the control rods can usually lead to an undercritical state where the reactor stops. Up to 100% of the fuel assemblies in the core can include control rods.

[0069] The movement of the control rods can be moved by a control rod drive mechanism. The control rod drive mechanism can command and power an actuator to lower and raise the control rods inside and outside the fuel assemblies and to hold the position of the control rods relative to the core. The control rod drive mechanism rods can be able to rapidly insert the control rods to quickly stop the reactor (i.e., scram).

[0070] The primary circuit can be housed within a containment structure that holds steam from the primary circuit in the event of an accident. The containment vessel can have a diameter between 15 and 60 m, or between 30 and 50 m. The containment structure can be formed from steel, or concrete, or concrete lined with steel. The containment vessel can house a water tank for emergency cooling of the reactor, or support it externally. The containment vessel can include equipment and facilities that enable refueling of the reactor, storage of fuel assemblies, and transportation of fuel assemblies between the inside and outside of the containment vessel.

[0071] This power plant can include one or more civil structures that protect the reactor core from external hazards (such as missile attacks) and natural disasters (such as tsunamis). The civil structures can be made from steel, or concrete, or a combination of both.

[0072] Here, embodiments will be described by way of example with reference to the accompanying drawings.

Brief Description of the Drawings

[0073]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0074] Figures 1 and 2 show a pressurized reactor vessel 1 used in a pressurized water reactor (PWR) type nuclear power generation system. The reactor vessel 1 has a removable closure head assembly 2 which is an integral head package (IHP) having a closure head 3 for closing the upper opening in the reactor vessel body 4 and thereby sealing a fuel assembly / core (not shown) in a cavity 5 within the reactor vessel body 4. The IHP further includes a control rod drive mechanism 10 within a shroud 11.

[0075] As shown in FIG. 3, the closure head 3 has a sealing surface 6 at its axial lower end for sealing against the body 4. The closure head assembly has an opposite axial upper end 13 (visible in FIGS. 1 and 2). The sealing surface 6 is annular and is surrounded by an annular flange 7 having a hole 14 for receiving studs for sealing the closure head 3 onto the reactor vessel body. The annular flange 7 is inscribed within a square plate 8 such that four corners 8a, 8b, 8c, 8d of the plate 8 extend laterally from the proximal side of the lower surface 6 / annular flange 7.

[0076] The lifting device includes four lifting elements 9 circumferentially spaced around the reactor vessel body 4 (only two of which are shown in FIGS. 1 and 2). The lifting elements 9 are vertically spaced below the closure head assembly 2, i.e., below the lower surface 6 of the closure head 3, such that each of the four corners 8a, 8b, 8c, 8d seats on a respective one of the lifting elements 9.

[0077] Figure 1 shows the lifting element 9 in the retracted position where the lower surface 6 of the closure head 3 is sealed against the body 4. When it becomes necessary to open the reactor vessel 1 (for example, to replace spent fuel rods in the fuel assembly / core), the studs are removed from the annular flange 7 and the axial height of the lifting element 9 increases, i.e., the lifting element moves to its extended position. Due to the extension of the lifting element 9, a vertically upward force is applied to the seated corners 8a, 8b, 8c, 8d of the plate 8, and the closure head assembly 2 rises vertically from below (rather than being lifted vertically upward from above), so that the seal between the lower surface 6 of the closure head 2 and the reactor vessel body 4 is broken.

[0078] When lifted vertically by the lifting element, the closure head assembly 2 moves horizontally along the working floor 12 of the storage container to the storage position. This (horizontal) movement can be achieved by inserting a wheeled frame (not shown) between the reactor vessel body 4 and the closure head assembly 2 such that the lower surface 6 of the closure head 3 rests on the load carrier. The lifting element 9 is then removed from the closure head assembly 2 by contraction that reduces its axial (vertical) height. The wheeled frame can then be moved along the tracks / rails on the working floor 12 to move the closure head assembly 2 to the storage position.

[0079] The wheeled frame can be used to move the closure head assembly 2 from the storage position to a position vertically above the reactor vessel body 4, and the core can be resealed by extending the lifting element 9 so that it engages the four corners 8a, 8b, 8c, 8d of the plate 8. The lifting element 9 then extends further to support the weight of the closure head assembly 2 so that the wheeled frame can be removed from between the reactor vessel body 4 and the closure head assembly 2. The lifting element 9 then contracts to lower the closure head assembly 2 onto the reactor vessel body 4 such that the sealing surface 6 of the closure head 3 seals the cavity within the reactor vessel body 4.

[0080] An alternative lifting device 1' is shown in FIG. 4. Two rows of lifting elements 9a, 9b are attached to a wheeled frame 15.

[0081] The wheeled frame 15 includes two parallel and spaced rails 16a, 16b and a linear vertical connecting arm 17 extending therebetween such that the frame 15 forms a square U-shape. The spaced rails 16a, 16b are attached to frame wheels 18 extending in two rows, with one row supporting each of the spaced rails 16a, 16b. The wheeled frame 15 further includes a motor (not shown) for driving the frame wheels 18. The motor can be automatically actuated by a control system located remotely from the lifting device 1'.

[0082] The lifting device 1' includes two engagement platforms 19a, 19b, each of which integrates adjacent engagement surfaces of adjacent lifting elements 9a, 9b and extends therebetween. The two parallel engagement platforms 19a, 19b extend parallel to and vertically above the spaced rails 16a, 16b.

[0083] Using this device 1', the lifting device 1' is moved to the deployment position by driving the frame wheels 18 with the lifting element 9 in its retracted position, and engaging platforms 19a, 19b are placed directly below the lower surface of the closure head assembly 2. A shroud 11, horizontally attached and vertically spaced between the axial upper end 13 and the axial lower end of the closure head assembly 2, vertically intersects a square plate 8 (by engaging, for example, the lower surfaces of four corners 8a, 8b, 8c, 8d thereof), such that the engaging platforms 19a, 19b engage the lower surface of the closure head assembly 2. The lifting element 9 then extends so that the lower surface is pushed upward and the closure head assembly 2 rises from the reactor vessel body 4 and seats on the engaging platforms 19a, 19b vertically above the reactor vessel body 4. The frame wheels 18 can then be driven to move the closure head assembly 2 horizontally away from the deployment position. In this case, the working floor can be at or below the height of the flange.

[0084] It will be understood that the present disclosure is not limited to the above-described embodiments, and various modifications and improvements can be made without departing from the concepts described herein. Except in cases where they are mutually exclusive, any of these features can be used individually or in combination with any other feature, and the present disclosure extends to and includes all combinations and sub-combinations of one or more of the features described herein.

Explanation of Reference Numerals

[0085] 1 Reactor vessel 1' Lifting device 2 Closure head assembly 3 Closure head 4 Reactor vessel body 5 Cavity 6 Sealing surface 7 Annular flange 8a Corner 8b angle 8c angle 8d angle 9 lifting element 9a lifting element 9b lifting element 10 control rod drive mechanism 11 shroud 12 work floor 13 axial upper end 14 hole 15 wheeled frame 16a spaced rails 16b spaced rails 17 connecting arm 18 frame wheel 19a engaging platform 19b engaging platform

Claims

1. A lifting device for lifting a closure head assembly from a reactor vessel body in a nuclear power generation system, the lifting device including at least one lifting element having an engagement surface configured to engage the lower surface of the closure head assembly, the at least one lifting element having an axially adjustable height between a retracted position in which its axial height is such that the closure head assembly seals against the body of the reactor vessel and an extended position in which its axial height is such that the closure head assembly is lifted above the body of the reactor vessel, In the retracted position, a sealing surface at the axial lower end of the closure head assembly seals against the body of the reactor vessel, and the lifting device is vertically spaced below the sealing surface, The lifting device further includes a wheeled frame for guiding the horizontal movement of the closure head assembly between a deployment location and a storage location, the wheeled frame including two parallel and spaced rails attached to frame wheels and a connecting arm extending therebetween to form a U-shaped frame, the at least one lifting element being attached to the wheeled frame. Lifting device.

2. The device according to claim 1, wherein the at least one lifting element includes a lift jack, a ram / piston, a rack and pinion, a telescopic linear actuator or a rigid chain actuator.

3. The device according to claim 1 or 2, wherein the at least one lifting element is operably coupled to a control system such that the movement of the lifting element between the retracted and extended positions can be performed remotely / automatically.

4. The device according to any one of claims 1 to 3, including a plurality of lifting elements, the lifting device including one or more engagement platforms, each engagement platform integrating at least two adjacent engagement surfaces and extending therebetween.

5. The device according to any one of claims 1 to 4, further including a failure system including at least one pneumatic or hydraulic element for engaging the closure head assembly in the event of a failure of the at least one lifting element.

6. The apparatus according to any one of claims 1 to 5, and a reactor vessel, A reactor vessel main body defining a cavity for accommodating a reactor core, A closure head assembly having a lower surface for abutting against an engagement surface of the at least one lifting element, A reactor vessel having the same, and a nuclear power generation system including the same.

7. The system according to claim 6, including a storage structure, wherein a working floor of the storage structure surrounds an opening of the reactor vessel main body into the cavity and is substantially vertically aligned therewith.

8. The system according to claim 7, including at least one linear path extending between the reactor vessel main body and a storage location, the at least one path including a track / rail, and frame wheels of the lifting device being attached to the track / rail.

9. A method for exposing a reactor core in the nuclear power generation system according to any one of claims 6 to 8, the method including the step of adjusting an axial height of the at least one lifting element from a contracted position where the closure head assembly is sealed against the main body of the reactor vessel to an extended position where the lower surface of the closure head assembly is raised above the main body of the reactor vessel.

10. The method according to claim 9, including the step of pushing the closure head assembly vertically upward from a proximal position of an axial lower end of the closure head assembly.

11. The method according to claim 9 or 10, further including the step of horizontally moving the closure head assembly from a deployed position to a storage position.

12. Moving the lifting device, in which the at least one lifting element is attached to a wheeled frame, to the deployed position with the at least one lifting element in its contracted position; Placing the engagement surface vertically below a lower surface of the closure head assembly; Extending the at least one lifting element such that the engagement surface / engagement platform engages the lower surface of the closure head assembly and pushes upward to vertically lift the closure head assembly from the reactor vessel main body; The method according to claim 11, including the same.

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