US20130044850A1 - Nuclear reactor refueling methods and apparatuses - Google Patents
Nuclear reactor refueling methods and apparatuses Download PDFInfo
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- US20130044850A1 US20130044850A1 US13/213,389 US201113213389A US2013044850A1 US 20130044850 A1 US20130044850 A1 US 20130044850A1 US 201113213389 A US201113213389 A US 201113213389A US 2013044850 A1 US2013044850 A1 US 2013044850A1
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- fuel assembly
- downwardly extending
- lifting tool
- extending elements
- cra
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C19/00—Arrangements for treating, for handling, or for facilitating the handling of, fuel or other materials which are used within the reactor, e.g. within its pressure vessel
- G21C19/02—Details of handling arrangements
- G21C19/10—Lifting devices or pulling devices adapted for co-operation with fuel elements or with control elements
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C19/00—Arrangements for treating, for handling, or for facilitating the handling of, fuel or other materials which are used within the reactor, e.g. within its pressure vessel
- G21C19/20—Arrangements for introducing objects into the pressure vessel; Arrangements for handling objects within the pressure vessel; Arrangements for removing objects from the pressure vessel
- G21C19/205—Interchanging of fuel elements in the core, i.e. fuel shuffling
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
Definitions
- the following relates to the nuclear reactor arts, electrical power generation arts, nuclear reactor control arts, nuclear electrical power generation control arts, and related arts.
- Nuclear reactors employ a reactor core comprising a critical mass of fissile material, such as a material containing uranium oxide (UO 2 ) that is enriched in the fissile 235 U isotope.
- the fuel rod may take various structural configurations, for example including fissile material as pellets embedded in a ceramic matrix or so forth.
- fissile material As pellets embedded in a ceramic matrix or so forth.
- a set of rods is preassembled to form a fuel assembly.
- the mass of fissile material in the fuel assembly remains below critical mass.
- the fuel assemblies are shipped to the reactor site, and are installed in a grid in the reactor pressure vessel to form the reactor core.
- suitable neutron absorbing material is provided during installation, for example by inserting neutron-absorbing control rods into the fuel assemblies before they are brought together in the pressure vessel, and by omitting the neutron moderator (e.g., water ambient) if employed.
- the neutron moderator e.g., water ambient
- FIG. 1 shows an illustrative fuel assembly 10 including a set of fuel rods 12 secured together with a controlled spacing by mid-spacer grid elements 14 and by end-spacer grid elements 16 , 18 .
- the fuel rods 12 form a 17 ⁇ 17 array.
- the fuel assembly 10 is typically substantially elongated, and is shown in part in FIG. 1 with an indicated gap G.
- the fuel assembly 10 also suitably includes other elements, such as control rod guide tubes or thimbles 20 through which neutron-absorbing control rods may pass.
- control rod guide tubes or thimbles 20 through which neutron-absorbing control rods may pass.
- One or more of these or similar tubes or thimbles may also serve as instrumentation conduits for in-core sensors.
- Upper and lower nozzle plates 22 , 24 may be provided to facilitate coupling of control rods, instrumentation bundles, or so forth into or out of the fuel assembly 10 .
- the illustrative upper and lower nozzle plates 22 , 24 include respective upper and lower alignment pins 26 , 28 at the corners of the respective nozzle plates 22 , 24 for facilitating alignment of the fuel assemblies during installation in the reactor core.
- FIG. 2 shows the assembled reactor core 30 , including a closely packed grid of fuel assemblies 10 disposed in a core former 32 .
- a control rod assembly (CRA) is fully inserted into each fuel assembly 10 .
- the upper support element of each CRA may in be a conventional spider or (as in FIG. 2 ) a larger element (see “Terminal Elements for Coupling Connecting Rods and Control Rods in Control Rod Assemblies For a Nuclear Reactor”, U.S. Ser. No. 12/862,124 filed Aug. 24, 2010, which is incorporated herein by reference in its entirety, for some illustrative examples).
- the illustrative reactor core 30 includes sixty nine (69) fuel assemblies, although in general more or fewer fuel assemblies may be included.
- the reactor core has a designed lifetime, typically in a range of a year to a few years.
- the core lifetime is controlled by the reduction in fissile material caused by operation of the nuclear chain reaction.
- a refueling operation must be performed, in which the spent fuel assemblies are removed and replaced by new fuel assemblies.
- this entails shutting down the reactor, opening the pressure vessel and removing any components in order to gain overhead access to the fuel assemblies, and removing the fuel assemblies with the assistance of a crane.
- each fuel assembly is typically fitted with a box structure with leaf springs mounted on top of the box, or a plate-and-post structure with preloaded helical coil springs mounted between the posts.
- the fuel assembly is lifted by a grappling mechanism that engages the fixed top plate of the box structure or the movable top plate of the plate-and-post structure via hooks that swing laterally under the top plate in four orthogonal directions.
- the hooks swing outward to engage the top plate of the box, while in plate-and-post designs the hooks swing inward to engage the top plate.
- a method comprises performing refueling of a nuclear reactor.
- the refueling includes removing a fuel assembly from a reactor core of the nuclear reactor.
- the removal method includes: connecting a lifting tool of a crane with a top of the fuel assembly, the lifting tool comprising an assembly of downwardly extending elements, the connecting including locking lower ends of the downwardly extending elements with respective mating features located at a top and periphery of the fuel assembly; moving the fuel assembly connected with the lifting tool into a spent fuel pool using the crane; and releasing the lifting tool from the top of the fuel assembly, the releasing including unlocking the lower ends of the downwardly extending elements from the respective peripherally located mating features at the top and periphery of the fuel assembly.
- a method comprises performing refueling of a nuclear reactor.
- the refueling includes removing a fuel assembly having a control rod assembly (CRA) inserted in the fuel assembly from a reactor core of the nuclear reactor.
- the removal method includes: lowering a lifting tool of a crane onto a top of the fuel assembly, the lowered lifting tool including a plurality of downwardly extending elements that surround and vertically overlap a portion of the CRA extending above the top of the fuel assembly; locking the downwardly extending elements of the lowered lifting tool with corresponding mating features at the top of the fuel assembly in order to connect the lifting tool with the fuel assembly; moving the fuel assembly connected with the lifting tool into a spent fuel pool using the crane; and disconnecting the lifting tool from the top of the fuel assembly in the spent fuel pool by unlocking the downwardly extending elements from the corresponding mating features at the top of the fuel assembly.
- CRA control rod assembly
- an apparatus comprises a lifting tool including an upper end configured for attachment with a crane, and a plurality of downwardly extending elements surrounding an open central region disposed below the upper end, lower ends of the downwardly extending elements being configured to mate with mating features at the top of a fuel assembly of a nuclear reactor core.
- an apparatus comprises: a nuclear fuel assembly including mating features at a top of the nuclear fuel assembly; and a lifting tool including an upper end configured for attachment with a crane and a plurality of downwardly extending elements surrounding an open central region disposed below the upper end, lower ends of the downwardly extending elements being configured to mate with the mating features at the top of the nuclear fuel assembly.
- an apparatus comprises: a nuclear fuel assembly including mating features at a top of the nuclear fuel assembly; a control rod assembly (CRA) inserted in the nuclear fuel assembly with an upper end of the CRA extending out of the top of the nuclear fuel assembly; and a lifting tool including an upper end configured for attachment with a crane and a plurality of downwardly extending elements surrounding an open central region disposed below the upper end, lower ends of the downwardly extending elements being configured to mate with the mating features at the top of the nuclear fuel assembly.
- the open central region of the lifting tool that is surrounded by the plurality of downwardly extending elements is configured to receive the upper end of the CRA when the lower ends of the downwardly extending elements mate with the mating features at the top of the nuclear fuel assembly.
- the invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations.
- the drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention.
- FIGS. 1 and 2 show a nuclear fuel assembly and a nuclear reactor core, respectively, according to the prior art.
- FIG. 3 shows a diagrammatic perspective view of a nuclear reactor and selected associated components.
- FIG. 4 shows an exploded perspective view of the pressure vessel of the nuclear reactor of FIG. 3 .
- FIG. 5 shows an exploded perspective view of the lower vessel portion of the pressure vessel of FIG. 4 including selected internal components.
- FIG. 6 shows a perspective view of a nuclear fuel assembly with the fuel rods omitted to reveal the control rod guide tubes or thimbles, with a control rod assembly (CRA) positioned in a withdrawn position above the fuel assembly.
- CRA control rod assembly
- FIG. 7 shows a perspective view of a nuclear fuel assembly with a control rod assembly (CRA) inserted in the fuel assembly.
- CRA control rod assembly
- FIG. 8 shows an isolated perspective view of the upper support element of the CRA of FIGS. 6 and 7 .
- FIG. 9 shows an enlarged perspective sectional view of the CRA focusing on the upper support element and showing a J-lock coupling between the connecting rod and the CRA.
- FIG. 10 diagrammatically shows a refueling process flow including those portions related to unloading spent nuclear fuel assemblies from the reactor.
- FIGS. 11 , 12 , 13 , 14 , 15 , 15 A, 16 , and 16 A show perspective views (with partial cutaway in the case of FIGS. 15A and 16A ) of various operations of the process flow of FIG. 10 .
- FIG. 17 shows an illustrative embodiment of the lifting tool including diagrammatically indicated motors for rotating the lower ends of the downwardly extending elements of the lifting tool to engage the locks.
- FIGS. 18-20 diagrammatically show overhead views of three nuclear fuel assembly embodiments each with an inserted control rod assembly (CRA) and showing the peripherally located mating features at the top of the fuel assembly for connecting with the lifting tool.
- CRA control rod assembly
- FIG. 3 shows the nuclear reactor 40 in conjunction with a diagrammatically indicated spent fuel pool 42 and a diagrammatically indicated crane 44 .
- FIG. 4 shows an exploded view of the pressure vessel of the nuclear reactor of FIG. 3 .
- the pressure vessel includes a lower vessel portion 50 , an upper vessel portion 52 , and a skirt or support structure 54 .
- the pressure vessel is mounted vertically (as shown) with at least part of the lower vessel portion 50 disposed below ground level.
- the bottom of the skirt or support structure 54 is at ground level and supports the pressure vessel and/or biases the pressure vessel against tipping.
- FIG. 3 shows the nuclear reactor 40 in conjunction with a diagrammatically indicated spent fuel pool 42 and a diagrammatically indicated crane 44 .
- FIG. 4 shows an exploded view of the pressure vessel of the nuclear reactor of FIG. 3 .
- the pressure vessel includes a lower vessel portion 50 , an upper vessel portion 52 , and a skirt or support structure 54 .
- the pressure vessel is mounted vertically (as shown) with
- FIG. 5 shows an exploded perspective view of the lower vessel portion 50 including selected internal components.
- the lower vessel 50 contains the nuclear reactor core comprising the core former 32 and an array of fuel assemblies 10 (only one of which is shown by way of example in FIG. 5 ).
- the reactor core is disposed in and supported by the core former 32 which is in turn disposed in and supported by a core basket 56 , which may include radiation shielding, optional emergency coolant tubing (not shown), or so forth.
- the illustrative nuclear reactor includes upper internals 58 which include wholly internal control rod drive mechanism (CRDM) units.
- the upper internals 58 are supported by a mid-flange 60 that also forms a structural joint of the pressure vessel (being disposed at the junction between the lower and upper vessel portions 50 , 52 ).
- Alignment between the fuel assemblies 10 and the upper internals 58 is suitably provided by the upper alignment pins 26 at the corners of the upper nozzle plates 22 of the fuel assemblies 10 . These pins 26 are designed to accommodate the differential thermal expansion between the fuel assembly 10 and the reactor internals 58 and the fuel assembly growth due to irradiation without losing engagement.
- the illustrative nuclear reactor is a thermal nuclear reactor employing light water (H 2 O) as a primary coolant that also serves as a neutron moderator that thermalizes neutrons to enhance the nuclear reaction rate.
- a primary coolant that also serves as a neutron moderator that thermalizes neutrons to enhance the nuclear reaction rate.
- deuterium dioxide (D 2 O) is contemplated as the coolant/moderator.
- the primary coolant optionally contains selected additives, such as optional boric acid which, if added, acts as a neutron poison to slow the reaction rate.
- the pressure vessel suitably includes a cylindrical central riser or other internal compartments or structures (details not shown) to guide circulation of the primary coolant in the pressure vessel.
- the primary coolant circulation may be natural circulation caused by the heating of the primary coolant in the vicinity of the reactor core, or may be assisted or generated by illustrative primary coolant pumps 62 also mounted via the mid-flange 60 .
- the nuclear reactor is intended to generate steam.
- primary coolant heated by the reactor core flows through a primary loop that is in thermal communication with a secondary coolant loop through which secondary coolant flows. Heat transfer from the primary loop to the secondary loop heats the secondary coolant and converts it to steam.
- the thermally coupled primary/secondary coolant loops thus define a steam generator.
- the steam generator is external to the pressure vessel, while in other embodiments the steam generator is internal to the pressure vessel, for example mounted in the upper pressure vessel portion 52 in some contemplated embodiments.
- the steam may for example, be employed to drive a turbine of a generator of an electrical power plant, thus generating electrical power from the nuclear reaction.
- the illustrative nuclear reactor is of a type generally known as a pressurized water nuclear reactor (PWR), in which the primary coolant (water) is maintained in a superheated state during normal operation. This is suitably accomplished by maintaining a steam bubble located at the top of the upper vessel portion 52 at a desired pressure during normal reactor operation.
- the nuclear reactor could be configured as a boiling water reactor (BWR) in which the primary coolant is maintained in a boiling state.
- the illustrative nuclear reactor 40 and other components e.g. spent fuel pool 42 and diagrammatically represented crane 44 , is shown as an example.
- the pressure vessel can have other portioning, such as having a removable top or “cap” section, and can have access manways provided at various points for maintenance or so forth.
- the entire pressure vessel may be located underground.
- the illustrative spent fuel pool 42 is below-ground and surrounds the lower vessel portion 50 , more generally the spent fuel pool can be located anywhere within “reach” of the crane 44 , and may in some embodiments be above-ground (or, conversely, may be buried deep underground with suitable access from above).
- FIG. 6 shows an illustrative fuel assembly with the fuel rods omitted, denoted by reference number 10 ′.
- the diagrammatic element 10 ′ reveals that the control rod guide tubes or thimbles 20 through which neutron-absorbing control rods may pass extend through the entire (vertical) height of the fuel assembly.
- Corresponding control rods 72 of the CRA 70 are shown in the fully withdrawn position in FIG. 6 (that is, fully withdrawn out of the guide tubes or thimbles 20 ).
- FIG. 7 shows the CRA 70 fully inserted into the fuel assembly 10 . It will be noted in FIG. 7 that a portion of the CRA 70 , including at least the upper support element 74 , extends above the top of the fuel assembly 10 in the fully inserted position.
- the opposite upper end of the connecting rod 76 is not illustrated, but is connected with a suitable control rod drive mechanism (CRDM) unit.
- CRDM control rod drive mechanism
- the CRDMs are wholly internal and are part of the upper internals 58 contained within the pressure vessel.
- the CRDMs may be mounted externally above the pressure vessel (as is typical in a PWR) or externally below the pressure vessel (as is typical in a BWR), with the connecting rods passing through suitable vessel penetrations to connect with the corresponding CRA.
- the reactor core has a sufficient quantity of fissile material to support reactor operation for a designed operational time period, which is typically of order one to a few years, although shorter or longer designed periods are also contemplated.
- the nuclear reactor 40 is refueled and then restarted.
- the crane 44 includes or is operatively connected with lifting tool 80 that is designed to connect with one of the fuel assemblies.
- the crane 44 operating in conjunction with the lifting tool 80 transfers spent fuel assemblies out of the lower vessel 50 and deposits the spent fuel assemblies in the spent fuel pool 42 .
- FIG. 3 shows several spent fuel assemblies 10 spent which have been transferred into the spent fuel pool 42 .
- the illustrative spent fuel pool 42 is below-ground and surrounds the lower vessel portion 50 , more generally the spent fuel pool can be located anywhere within “reach” of the crane 44 , and may in some embodiments be above-ground.
- the crane 44 operating in conjunction with the lifting tool 80 also transfers (i.e., loads) new fuel assemblies into the lower vessel 50 , and more particularly into the core former 32 .
- the reactor is shut down preparatory to the refueling.
- the shutdown S 1 includes inserting each CRA 70 into its corresponding fuel assembly 10 , producing the inserted configuration shown in FIG. 7 .
- a suitable time delay is allowed in order for the reactor to cool down to a sufficiently low temperature to allow opening of the pressure vessel. Some primary coolant may also be removed from the pressure vessel in order to reduce the water level.
- the upper vessel portion 52 is removed (for example, using the crane 44 ). The effect of the operation S 2 is to provide access to the (now spent) fuel assemblies 10 disposed in the core former 32 .
- an operation S 3 for each fuel assembly 10 the connecting rod 76 is detached from the corresponding CRA 70 so as to leave the combination of the fuel assembly 10 and the inserted CRA 70 , as shown in FIG. 11 .
- a bayonet, J-lock, or other “quick-release” type rotatable coupling can be employed to enable the operation S 3 to be quickly performed, with the “groove” and “pin” or other retaining combination being variously disposed (e.g., with the groove on the connecting rod and the pin or pins on the CRA receptacle, or vice versa).
- the resulting unit includes the fuel assembly 10 with the CRA 70 inserted, with a top portion of the CRA 70 including the upper support element 74 extending above the top of the fuel assembly 10 .
- the lifting tool 80 is lowered onto the top of the fuel assembly 10 .
- the lifting tool 80 includes an upper end 81 configured for attachment with the crane 44 .
- the upper end 81 includes a loop for attachment with the cable or arm of the crane 44 .
- the upper alignment pins 26 of the fuel assembly 10 located at the corners of the upper nozzle plate 22 also serve as the mating features 26 (namely lifting pins 26 in the illustrative example) at a top and periphery of the fuel assembly 10 .
- the mating features can be protrusions, openings, or recesses at a top and periphery of the fuel assembly.
- the mating features are designed to be weight-bearing such that the entire fuel assembly 10 can be raised upward by lifting on the mating features.
- this is accomplished by constructing the upper and lower nozzle plates 22 , 24 , the control rod guide tubes or thimbles 20 , and the spacer grid elements 14 , 16 , 18 as a welded assembly of steel or another suitable structural material (best seen as the structure 10 ′ in FIG. 6 ).
- the lifting pins 26 at a top and periphery of the fuel assembly 10 are secured to the upper nozzle plate 22 by welding, a threaded connection, a combination thereof, or another suitably load-bearing connection.
- connection operation S 5 includes locking the lower ends 82 L of the downwardly extending elements 80 with the respective peripherally located mating features, e.g. lifting pins 26 , at the top and periphery of the fuel assembly 10 .
- mating features e.g. lifting pins 26
- FIG. 15 shows an enlarged view of the lower end 82 L fully lowered over the lifting pin 26 .
- FIG. 15A shows the view of FIG. 15 with partial cutaway of the lower end 82 L to reveal internal components of the (unlocked) locking configuration.
- FIG. 16 shows an enlarged view of the lower end 82 L after a rotation of about 90°. This rotation causes the narrowed region 92 to move into the groove 86 to form the lock.
- FIG. 16A shows the view of FIG. 16 with partial cutaway of the lower end 82 L to reveal internal components of the (locked) locking configuration.
- FIG. 9 for coupling the connecting rod 76 with the CRA upper support element 74 can be used in coupling the lower end of the downwardly extending rod or bar with a mating recess at the top and periphery of the fuel assembly.
- Another rotationally locking quick-release configuration contemplated for use in the lower ends of the downwardly extending elements of the lifting tool are threaded connections.
- the lower ends have threads that mate with threaded holes located at the top periphery of the nuclear fuel assembly. The locking in this case is a frictional lock obtained by rotating the lower ends to thread into the threaded holes until a designed torque is reached.
- each downwardly extending rod or bar 82 includes a diagrammatically indicated motor 94 providing the motorized rotation of the lower end 82 L .
- FIG. 17 illustrates a separate motor 94 for each downwardly extending rod or bar 82
- rotational locks e.g., bayonet or J-lock couplings
- other types of locks including non-rotational locks
- the locks may employ motorized clamps that clamp onto respective mating features at the top of the fuel assembly.
- an operation S 6 the fuel assembly 10 connected with the lifting tool 80 is moved into the spent fuel pool 42 using the crane 44 .
- the lifting tool 80 is released from the top of the fuel assembly.
- the release operation S 7 includes unlocking the lower ends 82 L of the downwardly extending elements 82 from the respective peripherally located mating features (e.g. lifting pins 26 ) at the top and periphery of the fuel assembly 10 .
- this entails rotating the lower ends 82 L in the opposite direction to that used in the locking operation and then lifting the unlocked lifting tool 80 upward away from the spent fuel assembly now residing in the spent fuel pool 42 .
- Other unlocking operations may be employed depending upon the nature and configuration of the locking coupling.
- the reactor core typically includes a number of fuel assemblies 10 (see the example of FIG. 2 in which the reactor core 30 includes sixty nine fuel assemblies). Accordingly, after the release operation S 7 , an operation S 8 is performed in which the next fuel assembly to be unloaded is selected, and the process repeats beginning at operation S 4 . Once all fuel assemblies have been unloaded, an operation S 9 is performed in which the lifting tool 80 is parked in a storage location.
- operations analogous to operations S 4 , S 5 , S 6 , S 7 , S 8 are performed to pick up new fuel assemblies from a loading dock or other source location and place the new fuel assemblies into the core former 32 , followed by performing control rod reattachment (analogous to operation S 3 ), replacement of the upper vessel portion 52 (analogous to operation S 2 ), and restarting the reactor (analogous to operation S 1 , and optionally further including performing various integrity or safety checks prior to the restart).
- control rod reattachment analogous to operation S 3
- replacement of the upper vessel portion 52 analogous to operation S 2
- restarting the reactor analogous to operation S 1 , and optionally further including performing various integrity or safety checks prior to the restart.
- these analogous loading operations are not shown in FIG. 10 .
- the reloading may include performing other maintenance such as replacing the connecting rods or other internal reactor components, various inspection and/or cleanup operations, or so forth.
- An advantage of the lifting tool 80 is that it accommodates a CRA inserted into the fuel assembly 10 that extends substantially above the top of the fuel assembly 10 . Because no swing action is required to engage the lifting mechanism; the fuel assembly can be lifted even when most or all of the inboard volume above the fuel assembly is occupied by the upper portion 74 of the inserted CRA.
- the peripherally arranged downwardly extending elements 80 accommodate the exposed portion of the CRA by surrounding the exposed upper end of the inserted CRA (e.g., the upper support element 74 ) when the fuel assembly 10 is connected with the lifting tool.
- the downwardly extending elements 82 surround an open central region disposed below the upper end 81 of the lifting tool 80 , such that the open central region can accommodate the upward extension of the inserted CRA out of the top of the fuel assembly 10 .
- the CRA vertically overlaps the lifting tool 80 when the fuel assembly 10 is connected with the lifting tool 80 (see FIG. 13 ).
- the overlap is at least one-half of the vertical height of the lifting tool 80 .
- the overlap between the CRA and the lifting tool 80 is at least one-half of the vertical height of the downwardly extending elements 82 of the lifting tool 80 .
- FIG. 18 shows the illustrative geometry of the fuel assembly 10 , which has a rectangular cross-section when viewed from above as per FIG. 18 , with the CRA including the upper support element 74 inserted in illustrative FIG. 18 .
- FIG. 19 illustrates a hexagonal fuel assembly 22 H having six sides, with the same CRA including the same upper support element 74 inserted.
- the illustrative six mating features 26 H are the same as the lifting pins 26 of the fuel assembly 10 .
- the corresponding lifting tool suitably includes six downwardly extending elements, e.g. six downwardly extending rods or bars, arranged in a hexagonal pattern to mate with the respective six lifting pins 26 H .
- FIG. 20 illustrates a triangular fuel assembly 22 T having three sides, with a conventional spider 74 T with six branches serving as the upper support element of the CRA.
- there are three mating features 26 T which in this embodiment are embodied as recesses or openings 26 T .
- the corresponding lifting tool suitably includes three downwardly extending elements, e.g. three downwardly extending rods or bars, arranged in an equilateral triangular pattern to mate with the respective three openings 26 T .
- the geometry of the fuel assembly preferably promotes a closely packed arrangement.
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Abstract
Description
- The following relates to the nuclear reactor arts, electrical power generation arts, nuclear reactor control arts, nuclear electrical power generation control arts, and related arts.
- Nuclear reactors employ a reactor core comprising a critical mass of fissile material, such as a material containing uranium oxide (UO2) that is enriched in the fissile 235U isotope. The fuel rod may take various structural configurations, for example including fissile material as pellets embedded in a ceramic matrix or so forth. To promote safety, it is conventional to assemble the core as rods containing the fissile material. A set of rods is preassembled to form a fuel assembly. Preferably, the mass of fissile material in the fuel assembly remains below critical mass. The fuel assemblies are shipped to the reactor site, and are installed in a grid in the reactor pressure vessel to form the reactor core. To prevent a premature chain reaction, suitable neutron absorbing material is provided during installation, for example by inserting neutron-absorbing control rods into the fuel assemblies before they are brought together in the pressure vessel, and by omitting the neutron moderator (e.g., water ambient) if employed.
- With reference to
FIGS. 1 and 2 , an illustrative example of such an assembly is shown.FIG. 1 shows anillustrative fuel assembly 10 including a set offuel rods 12 secured together with a controlled spacing bymid-spacer grid elements 14 and by end-spacer grid elements fuel rods 12 form a 17×17 array. Thefuel assembly 10 is typically substantially elongated, and is shown in part inFIG. 1 with an indicated gap G. Thefuel assembly 10 also suitably includes other elements, such as control rod guide tubes or thimbles 20 through which neutron-absorbing control rods may pass. One or more of these or similar tubes or thimbles may also serve as instrumentation conduits for in-core sensors. Upper andlower nozzle plates fuel assembly 10. The illustrative upper andlower nozzle plates lower alignment pins respective nozzle plates -
FIG. 2 shows the assembledreactor core 30, including a closely packed grid offuel assemblies 10 disposed in a core former 32. InFIG. 2 , a control rod assembly (CRA) is fully inserted into eachfuel assembly 10. In the view ofFIG. 2 , only an upper support element 34 of the CRA is visible extending above eachcorresponding fuel assembly 10. The upper support element of each CRA may in be a conventional spider or (as inFIG. 2 ) a larger element (see “Terminal Elements for Coupling Connecting Rods and Control Rods in Control Rod Assemblies For a Nuclear Reactor”, U.S. Ser. No. 12/862,124 filed Aug. 24, 2010, which is incorporated herein by reference in its entirety, for some illustrative examples). Theillustrative reactor core 30 includes sixty nine (69) fuel assemblies, although in general more or fewer fuel assemblies may be included. - The reactor core has a designed lifetime, typically in a range of a year to a few years. The core lifetime is controlled by the reduction in fissile material caused by operation of the nuclear chain reaction. To continue operation, a refueling operation must be performed, in which the spent fuel assemblies are removed and replaced by new fuel assemblies. Typically, this entails shutting down the reactor, opening the pressure vessel and removing any components in order to gain overhead access to the fuel assemblies, and removing the fuel assemblies with the assistance of a crane. To enable coupling with the fuel assembly, each fuel assembly is typically fitted with a box structure with leaf springs mounted on top of the box, or a plate-and-post structure with preloaded helical coil springs mounted between the posts. The fuel assembly is lifted by a grappling mechanism that engages the fixed top plate of the box structure or the movable top plate of the plate-and-post structure via hooks that swing laterally under the top plate in four orthogonal directions. In box designs, the hooks swing outward to engage the top plate of the box, while in plate-and-post designs the hooks swing inward to engage the top plate.
- These refueling approaches have substantial disadvantages. The swinging motion of the grappling hooks calls for a large working space proximate to the top of each fuel assembly. However, this working space is constrained by the presence of closely adjacent neighboring fuel assemblies in the array disposed in the core former. Moreover, if the CRA is left fully inserted into the fuel assembly during refueling (which is desirable to maintain suppression of the neutron population in the fuel assembly during the refueling process), then either the spider must be removed entirely (a process entailing individually detaching each of the numerous control rods from the spider), or the spider must be of sufficiently low profile to enable the grappling hooks to operate above the spider.
- Disclosed herein are improvements that provide various benefits that will become apparent to the skilled artisan upon reading the following.
- In one aspect of the disclosure, a method comprises performing refueling of a nuclear reactor. The refueling includes removing a fuel assembly from a reactor core of the nuclear reactor. The removal method includes: connecting a lifting tool of a crane with a top of the fuel assembly, the lifting tool comprising an assembly of downwardly extending elements, the connecting including locking lower ends of the downwardly extending elements with respective mating features located at a top and periphery of the fuel assembly; moving the fuel assembly connected with the lifting tool into a spent fuel pool using the crane; and releasing the lifting tool from the top of the fuel assembly, the releasing including unlocking the lower ends of the downwardly extending elements from the respective peripherally located mating features at the top and periphery of the fuel assembly.
- In another aspect of the disclosure, a method comprises performing refueling of a nuclear reactor. The refueling includes removing a fuel assembly having a control rod assembly (CRA) inserted in the fuel assembly from a reactor core of the nuclear reactor. The removal method includes: lowering a lifting tool of a crane onto a top of the fuel assembly, the lowered lifting tool including a plurality of downwardly extending elements that surround and vertically overlap a portion of the CRA extending above the top of the fuel assembly; locking the downwardly extending elements of the lowered lifting tool with corresponding mating features at the top of the fuel assembly in order to connect the lifting tool with the fuel assembly; moving the fuel assembly connected with the lifting tool into a spent fuel pool using the crane; and disconnecting the lifting tool from the top of the fuel assembly in the spent fuel pool by unlocking the downwardly extending elements from the corresponding mating features at the top of the fuel assembly.
- In another aspect of the disclosure, an apparatus comprises a lifting tool including an upper end configured for attachment with a crane, and a plurality of downwardly extending elements surrounding an open central region disposed below the upper end, lower ends of the downwardly extending elements being configured to mate with mating features at the top of a fuel assembly of a nuclear reactor core.
- In another aspect of the disclosure, an apparatus comprises: a nuclear fuel assembly including mating features at a top of the nuclear fuel assembly; and a lifting tool including an upper end configured for attachment with a crane and a plurality of downwardly extending elements surrounding an open central region disposed below the upper end, lower ends of the downwardly extending elements being configured to mate with the mating features at the top of the nuclear fuel assembly.
- In another aspect of the disclosure, an apparatus comprises: a nuclear fuel assembly including mating features at a top of the nuclear fuel assembly; a control rod assembly (CRA) inserted in the nuclear fuel assembly with an upper end of the CRA extending out of the top of the nuclear fuel assembly; and a lifting tool including an upper end configured for attachment with a crane and a plurality of downwardly extending elements surrounding an open central region disposed below the upper end, lower ends of the downwardly extending elements being configured to mate with the mating features at the top of the nuclear fuel assembly. The open central region of the lifting tool that is surrounded by the plurality of downwardly extending elements is configured to receive the upper end of the CRA when the lower ends of the downwardly extending elements mate with the mating features at the top of the nuclear fuel assembly.
- The invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention.
-
FIGS. 1 and 2 show a nuclear fuel assembly and a nuclear reactor core, respectively, according to the prior art. -
FIG. 3 shows a diagrammatic perspective view of a nuclear reactor and selected associated components. -
FIG. 4 shows an exploded perspective view of the pressure vessel of the nuclear reactor ofFIG. 3 . -
FIG. 5 shows an exploded perspective view of the lower vessel portion of the pressure vessel ofFIG. 4 including selected internal components. -
FIG. 6 shows a perspective view of a nuclear fuel assembly with the fuel rods omitted to reveal the control rod guide tubes or thimbles, with a control rod assembly (CRA) positioned in a withdrawn position above the fuel assembly. -
FIG. 7 shows a perspective view of a nuclear fuel assembly with a control rod assembly (CRA) inserted in the fuel assembly. -
FIG. 8 shows an isolated perspective view of the upper support element of the CRA ofFIGS. 6 and 7 . -
FIG. 9 shows an enlarged perspective sectional view of the CRA focusing on the upper support element and showing a J-lock coupling between the connecting rod and the CRA. -
FIG. 10 diagrammatically shows a refueling process flow including those portions related to unloading spent nuclear fuel assemblies from the reactor. -
FIGS. 11 , 12, 13, 14, 15, 15A, 16, and 16A show perspective views (with partial cutaway in the case ofFIGS. 15A and 16A ) of various operations of the process flow ofFIG. 10 . -
FIG. 17 shows an illustrative embodiment of the lifting tool including diagrammatically indicated motors for rotating the lower ends of the downwardly extending elements of the lifting tool to engage the locks. -
FIGS. 18-20 diagrammatically show overhead views of three nuclear fuel assembly embodiments each with an inserted control rod assembly (CRA) and showing the peripherally located mating features at the top of the fuel assembly for connecting with the lifting tool. - With reference to
FIGS. 3-5 , an illustrative nuclear reactor is shown.FIG. 3 shows thenuclear reactor 40 in conjunction with a diagrammatically indicated spentfuel pool 42 and a diagrammatically indicatedcrane 44.FIG. 4 shows an exploded view of the pressure vessel of the nuclear reactor ofFIG. 3 . The pressure vessel includes alower vessel portion 50, anupper vessel portion 52, and a skirt orsupport structure 54. In the illustrative arrangement, the pressure vessel is mounted vertically (as shown) with at least part of thelower vessel portion 50 disposed below ground level. The bottom of the skirt orsupport structure 54 is at ground level and supports the pressure vessel and/or biases the pressure vessel against tipping. In the illustrative example ofFIG. 3 , the spentfuel pool 42 is a below-ground pool containing water and optional additives such as, by way of illustrative example, boric acid (a soluble neutron poison).FIG. 5 shows an exploded perspective view of thelower vessel portion 50 including selected internal components. Thelower vessel 50 contains the nuclear reactor core comprising the core former 32 and an array of fuel assemblies 10 (only one of which is shown by way of example inFIG. 5 ). The reactor core is disposed in and supported by the core former 32 which is in turn disposed in and supported by acore basket 56, which may include radiation shielding, optional emergency coolant tubing (not shown), or so forth. - The illustrative nuclear reactor includes
upper internals 58 which include wholly internal control rod drive mechanism (CRDM) units. In the illustrative example, theupper internals 58 are supported by a mid-flange 60 that also forms a structural joint of the pressure vessel (being disposed at the junction between the lower andupper vessel portions 50, 52). Alignment between thefuel assemblies 10 and theupper internals 58 is suitably provided by the upper alignment pins 26 at the corners of theupper nozzle plates 22 of thefuel assemblies 10. Thesepins 26 are designed to accommodate the differential thermal expansion between thefuel assembly 10 and thereactor internals 58 and the fuel assembly growth due to irradiation without losing engagement. - The illustrative nuclear reactor is a thermal nuclear reactor employing light water (H2O) as a primary coolant that also serves as a neutron moderator that thermalizes neutrons to enhance the nuclear reaction rate. Alternatively, deuterium dioxide (D2O) is contemplated as the coolant/moderator. The primary coolant optionally contains selected additives, such as optional boric acid which, if added, acts as a neutron poison to slow the reaction rate. The pressure vessel suitably includes a cylindrical central riser or other internal compartments or structures (details not shown) to guide circulation of the primary coolant in the pressure vessel. The primary coolant circulation may be natural circulation caused by the heating of the primary coolant in the vicinity of the reactor core, or may be assisted or generated by illustrative primary coolant pumps 62 also mounted via the mid-flange 60.
- Although not illustrated, in some embodiments the nuclear reactor is intended to generate steam. Toward this end, primary coolant heated by the reactor core flows through a primary loop that is in thermal communication with a secondary coolant loop through which secondary coolant flows. Heat transfer from the primary loop to the secondary loop heats the secondary coolant and converts it to steam. The thermally coupled primary/secondary coolant loops thus define a steam generator. In some embodiments, the steam generator is external to the pressure vessel, while in other embodiments the steam generator is internal to the pressure vessel, for example mounted in the upper
pressure vessel portion 52 in some contemplated embodiments. The steam may for example, be employed to drive a turbine of a generator of an electrical power plant, thus generating electrical power from the nuclear reaction. - The illustrative nuclear reactor is of a type generally known as a pressurized water nuclear reactor (PWR), in which the primary coolant (water) is maintained in a superheated state during normal operation. This is suitably accomplished by maintaining a steam bubble located at the top of the
upper vessel portion 52 at a desired pressure during normal reactor operation. Alternatively, the nuclear reactor could be configured as a boiling water reactor (BWR) in which the primary coolant is maintained in a boiling state. - The illustrative
nuclear reactor 40 and other components, e.g. spentfuel pool 42 and diagrammatically representedcrane 44, is shown as an example. Numerous variations are contemplated. For example, the pressure vessel can have other portioning, such as having a removable top or “cap” section, and can have access manways provided at various points for maintenance or so forth. In some embodiments the entire pressure vessel may be located underground. Similarly, while the illustrative spentfuel pool 42 is below-ground and surrounds thelower vessel portion 50, more generally the spent fuel pool can be located anywhere within “reach” of thecrane 44, and may in some embodiments be above-ground (or, conversely, may be buried deep underground with suitable access from above). Thereactor 40 andauxiliary components crane 44 is diagrammatically shown, and may in general have any suitable configuration that provides the desired horizontal and vertical travel, lifting capacity, and so forth while fitting within the containment structure. Some suitable crane configurations include an overhead crane configuration, a gantry crane configuration, a tower or hammerhead crane configuration, or so forth. - With continuing reference to
FIGS. 3-5 and with further reference toFIGS. 6-9 , reactivity control is suitably achieved using a control rod assembly (CRA) 70 associated with eachfuel assembly 10.FIG. 6 shows an illustrative fuel assembly with the fuel rods omitted, denoted byreference number 10′. By omitting the fuel rods for illustrative purposes, thediagrammatic element 10′ reveals that the control rod guide tubes orthimbles 20 through which neutron-absorbing control rods may pass extend through the entire (vertical) height of the fuel assembly. Correspondingcontrol rods 72 of theCRA 70 are shown in the fully withdrawn position inFIG. 6 (that is, fully withdrawn out of the guide tubes or thimbles 20). TheCRA 70 also includesupper support element 74 that secures the bundle ofcontrol rods 72 together in a pattern matching that of the guide tubes orthimbles 20. Theupper support element 74 may be a conventional spider; in the illustrative example, however, theupper support element 74 is a larger element intended to provide various benefits such as a longer (vertical) length over which to secure the upper ends of thecontrol rods 72, and optionally increased mass for theCRA 70. The illustrativeupper support element 74 is shown in isolation inFIG. 8 , and in side sectional view inFIG. 9 . The illustrativeupper support element 74 is further described in “Terminal Elements for Coupling Connecting Rods and Control Rods in Control Rod Assemblies For a Nuclear Reactor”, U.S. Ser. No. 12/862,124 filed Aug. 24, 2010, which is incorporated herein by reference in its entirety.FIG. 7 shows theCRA 70 fully inserted into thefuel assembly 10. It will be noted inFIG. 7 that a portion of theCRA 70, including at least theupper support element 74, extends above the top of thefuel assembly 10 in the fully inserted position. - With continuing reference to
FIGS. 6-9 , theCRA 70 is inserted into the fuel assembly 10 (as perFIG. 7 ), or withdrawn from the fuel assembly 10 (as perFIG. 6 ) in order to control the reaction rate of reactivity of the reactor core. Thecontrol rods 72 comprise a neutron-absorbing material—accordingly, as thecontrol rods 72 are inserted further into thefuel assembly 10 the reaction rate is reduced. In the fully inserted position (FIG. 6 ) the reaction is typically extinguished entirely. A connectingrod 76 is employed in order to raise or lower theCRA 70. As illustrated inFIGS. 6 , 7, and 9, the lower end of the connectingrod 76 is connected with theupper support element 74 of theCRA 70. The opposite upper end of the connectingrod 76 is not illustrated, but is connected with a suitable control rod drive mechanism (CRDM) unit. In the illustrative embodiment (seeFIG. 5 ) the CRDMs are wholly internal and are part of theupper internals 58 contained within the pressure vessel. Alternatively, the CRDMs may be mounted externally above the pressure vessel (as is typical in a PWR) or externally below the pressure vessel (as is typical in a BWR), with the connecting rods passing through suitable vessel penetrations to connect with the corresponding CRA. - With returning reference to
FIGS. 3-5 , the reactor core has a sufficient quantity of fissile material to support reactor operation for a designed operational time period, which is typically of order one to a few years, although shorter or longer designed periods are also contemplated. Thereafter, thenuclear reactor 40 is refueled and then restarted. Toward this end, thecrane 44 includes or is operatively connected with liftingtool 80 that is designed to connect with one of the fuel assemblies. During refueling, thecrane 44 operating in conjunction with thelifting tool 80 transfers spent fuel assemblies out of thelower vessel 50 and deposits the spent fuel assemblies in the spentfuel pool 42. By way of diagrammatic illustration,FIG. 3 shows several spentfuel assemblies 10 spent which have been transferred into the spentfuel pool 42. (It should be noted that while the illustrative spentfuel pool 42 is below-ground and surrounds thelower vessel portion 50, more generally the spent fuel pool can be located anywhere within “reach” of thecrane 44, and may in some embodiments be above-ground.) Thecrane 44 operating in conjunction with thelifting tool 80 also transfers (i.e., loads) new fuel assemblies into thelower vessel 50, and more particularly into the core former 32. - With reference to
FIGS. 10-16 , the refueling process is described. In an operation S1, the reactor is shut down preparatory to the refueling. The shutdown S1 includes inserting eachCRA 70 into its correspondingfuel assembly 10, producing the inserted configuration shown inFIG. 7 . A suitable time delay is allowed in order for the reactor to cool down to a sufficiently low temperature to allow opening of the pressure vessel. Some primary coolant may also be removed from the pressure vessel in order to reduce the water level. In an operation S2 (see alsoFIGS. 3-5 ), theupper vessel portion 52 is removed (for example, using the crane 44). The effect of the operation S2 is to provide access to the (now spent)fuel assemblies 10 disposed in the core former 32. In an operation S3, for eachfuel assembly 10 the connectingrod 76 is detached from the correspondingCRA 70 so as to leave the combination of thefuel assembly 10 and the insertedCRA 70, as shown inFIG. 11 . - With brief reference to
FIG. 9 , a suitable approach for performing the removal S3 of the connectingrod 76 is described. In this embodiment, thelower end 76 L of the connectingrod 76 terminates in a bayonet or (illustrated) J-lock coupling that is designed to lock into a mating receptacle 76 M (seeFIG. 8 ) of theupper support element 74 of theCRA 70. The perspective sectional view ofFIG. 9 shows thelower end 76 L of the connectingrod 76 in the locked position biased by a spring SS against a retaining feature RR inside themating receptacle 76 M of the CRAupper support element 74. Thus, by pressing the connectingrod 76 downward against the bias of the spring SS and rotating the connectingrod 76 to disengage from the retaining feature RR, the connectingrod 76 is released from the CRAupper support element 74. More generally, a bayonet, J-lock, or other “quick-release” type rotatable coupling can be employed to enable the operation S3 to be quickly performed, with the “groove” and “pin” or other retaining combination being variously disposed (e.g., with the groove on the connecting rod and the pin or pins on the CRA receptacle, or vice versa). Some further illustrative description is set forth in “Terminal Elements for Coupling Connecting Rods and Control Rods in Control Rod Assemblies For a Nuclear Reactor”, U.S. Ser. No. 12/862,124 filed Aug. 24, 2010, which is incorporated herein by reference in its entirety. Although a quick-release approach is advantageous, it is also contemplated to employ a different approach for performing the operation S3—for example, the connecting rod may be permanently connected with the CRA (for example, by a weld or the like), and the operation S3 may entail cutting the connecting rod at a point at or near its junction with the CRA. - With continuing reference to
FIG. 10 , after completion of the operation S3 the resulting unit includes thefuel assembly 10 with theCRA 70 inserted, with a top portion of theCRA 70 including theupper support element 74 extending above the top of thefuel assembly 10. This is illustrated inFIG. 11 . In an operation S4 (see alsoFIG. 12 ), thelifting tool 80 is lowered onto the top of thefuel assembly 10. As seen inFIG. 12 , thelifting tool 80 includes anupper end 81 configured for attachment with thecrane 44. In theillustrative lifting tool 80, theupper end 81 includes a loop for attachment with the cable or arm of thecrane 44. Thelifting tool 80 also includes a plurality of downwardly extendingelements 82, namely four downwardly extending rods or bars 82 in the illustrative example, that surround and vertically overlap the portion of theCRA 70 extending above the top of the fuel assembly 10 (e.g., the upper support element 74). The illustrative downwardly extendingelements 82 are vertical rods or bars that are aligned such that lower ends 82 L of the downwardly extendingelements 82 of the loweredlifting tool 80 align with respective peripherally located mating features at a top and periphery of thefuel assembly 10. In the illustrative embodiment, the upper alignment pins 26 of thefuel assembly 10 located at the corners of theupper nozzle plate 22 also serve as the mating features 26 (namely liftingpins 26 in the illustrative example) at a top and periphery of thefuel assembly 10. However, other mating features are also contemplated. For example, the mating features can be protrusions, openings, or recesses at a top and periphery of the fuel assembly. - The mating features (e.g., lifting pins 26) are designed to be weight-bearing such that the
entire fuel assembly 10 can be raised upward by lifting on the mating features. In the case of theillustrative fuel assembly 10, this is accomplished by constructing the upper andlower nozzle plates thimbles 20, and thespacer grid elements structure 10′ inFIG. 6 ). The lifting pins 26 at a top and periphery of thefuel assembly 10 are secured to theupper nozzle plate 22 by welding, a threaded connection, a combination thereof, or another suitably load-bearing connection. - With continuing reference to
FIG. 10 and with further reference toFIGS. 14 , 15, 15A, 16, and 16A, in an operation S5 the loweredlifting tool 80 is connected with the top of thefuel assembly 10. The connection operation S5 includes locking the lower ends 82 L of the downwardly extendingelements 80 with the respective peripherally located mating features, e.g. lifting pins 26, at the top and periphery of thefuel assembly 10. In the illustrative approach (seeFIGS. 14 , 15, 15A, 16, and 16A), the locking operation is performed by rotating at least the lower ends 82 L of the downwardly extendingelements 80 to lock the lower ends disposed over (as illustrated) or inside the respective lifting pins 26 with the respective lifting pins 26. Toward this end, the lower ends 82 L and the respective lifting pins 26 define a lockable bayonet coupling.FIG. 14 shows an enlarged view of one of the lower ends 82L aligned with and being lowered over therespective lifting pin 26. In this view agroove 86 in the liftingpin 26 is visible, as well as a narrowedportion 88 of the liftingpin 26. These features 86, 88 are designed to cooperate with arecess 90 in thelower end 82 L with a narrowedregion 92 to form a rotationally engaging lock.FIG. 15 shows an enlarged view of thelower end 82L fully lowered over the liftingpin 26.FIG. 15A shows the view ofFIG. 15 with partial cutaway of thelower end 82 L to reveal internal components of the (unlocked) locking configuration.FIG. 16 shows an enlarged view of thelower end 82L after a rotation of about 90°. This rotation causes the narrowedregion 92 to move into thegroove 86 to form the lock.FIG. 16A shows the view ofFIG. 16 with partial cutaway of thelower end 82 L to reveal internal components of the (locked) locking configuration. - In other embodiments, other rotationally locking “quick-release” configurations can be employed. For example, in another contemplated embodiment the J-lock coupling shown in
FIG. 9 for coupling the connectingrod 76 with the CRAupper support element 74 can be used in coupling the lower end of the downwardly extending rod or bar with a mating recess at the top and periphery of the fuel assembly. Another rotationally locking quick-release configuration contemplated for use in the lower ends of the downwardly extending elements of the lifting tool are threaded connections. In this embodiment, the lower ends have threads that mate with threaded holes located at the top periphery of the nuclear fuel assembly. The locking in this case is a frictional lock obtained by rotating the lower ends to thread into the threaded holes until a designed torque is reached. - With reference to
FIG. 17 , in any embodiment employing a rotational lock, the downwardly extending elements, or at least their lower ends, should include motorized rotation capability. In an illustrative example shown inFIG. 17 , each downwardly extending rod orbar 82 includes a diagrammatically indicatedmotor 94 providing the motorized rotation of thelower end 82 L. AlthoughFIG. 17 illustrates aseparate motor 94 for each downwardly extending rod orbar 82, in other embodiments it is contemplated to employ a single motor that drives rotation of all lower ends via a suitable drive train (e.g., geared rotating shafts or the like). It is also noted that since thelifting tool 80 is not disposed inside the pressure vessel except when the reactor is shut down, the lifting tool 80 (including the motors 94) does not need to be rated for operation at the operating temperature of the nuclear reactor. Themotors 94 should be robust against immersion in the primary coolant and in the fluid of the spent fuel pool 42 (seeFIG. 3 ), for example by being hermetically sealed. - While various embodiments of rotational locks (e.g., bayonet or J-lock couplings) are disclosed herein, other types of locks, including non-rotational locks, are also contemplated. For example, in another contemplated embodiment the locks may employ motorized clamps that clamp onto respective mating features at the top of the fuel assembly.
- With returning reference to
FIG. 10 , in an operation S6 thefuel assembly 10 connected with thelifting tool 80 is moved into the spentfuel pool 42 using thecrane 44. In an operation S7 thelifting tool 80 is released from the top of the fuel assembly. The release operation S7 includes unlocking the lower ends 82 L of the downwardly extendingelements 82 from the respective peripherally located mating features (e.g. lifting pins 26) at the top and periphery of thefuel assembly 10. In the illustrative embodiment, this entails rotating the lower ends 82 L in the opposite direction to that used in the locking operation and then lifting theunlocked lifting tool 80 upward away from the spent fuel assembly now residing in the spentfuel pool 42. Other unlocking operations may be employed depending upon the nature and configuration of the locking coupling. - Since the reactor core typically includes a number of fuel assemblies 10 (see the example of
FIG. 2 in which thereactor core 30 includes sixty nine fuel assemblies). Accordingly, after the release operation S7, an operation S8 is performed in which the next fuel assembly to be unloaded is selected, and the process repeats beginning at operation S4. Once all fuel assemblies have been unloaded, an operation S9 is performed in which thelifting tool 80 is parked in a storage location. Alternatively, if new fuel is to be loaded into the reactor, operations analogous to operations S4, S5, S6, S7, S8 are performed to pick up new fuel assemblies from a loading dock or other source location and place the new fuel assemblies into the core former 32, followed by performing control rod reattachment (analogous to operation S3), replacement of the upper vessel portion 52 (analogous to operation S2), and restarting the reactor (analogous to operation S1, and optionally further including performing various integrity or safety checks prior to the restart). Note that these analogous loading operations are not shown inFIG. 10 . Additionally, the reloading may include performing other maintenance such as replacing the connecting rods or other internal reactor components, various inspection and/or cleanup operations, or so forth. - An advantage of the
lifting tool 80 is that it accommodates a CRA inserted into thefuel assembly 10 that extends substantially above the top of thefuel assembly 10. Because no swing action is required to engage the lifting mechanism; the fuel assembly can be lifted even when most or all of the inboard volume above the fuel assembly is occupied by theupper portion 74 of the inserted CRA. The peripherally arranged downwardly extendingelements 80 accommodate the exposed portion of the CRA by surrounding the exposed upper end of the inserted CRA (e.g., the upper support element 74) when thefuel assembly 10 is connected with the lifting tool. The downwardly extendingelements 82 surround an open central region disposed below theupper end 81 of thelifting tool 80, such that the open central region can accommodate the upward extension of the inserted CRA out of the top of thefuel assembly 10. In this way, the CRA vertically overlaps thelifting tool 80 when thefuel assembly 10 is connected with the lifting tool 80 (seeFIG. 13 ). In some embodiments the overlap is at least one-half of the vertical height of thelifting tool 80. In some embodiments the overlap between the CRA and thelifting tool 80 is at least one-half of the vertical height of the downwardly extendingelements 82 of thelifting tool 80. - With reference to
FIGS. 18-20 , it is to be appreciated that the fuel assemblies, CRA, and lifting tool can have various geometries.FIG. 18 shows the illustrative geometry of thefuel assembly 10, which has a rectangular cross-section when viewed from above as perFIG. 18 , with the CRA including theupper support element 74 inserted in illustrativeFIG. 18 .FIG. 19 illustrates ahexagonal fuel assembly 22 H having six sides, with the same CRA including the sameupper support element 74 inserted. In this embodiment there are six mating features 26 H located at a top and periphery of the fuel assembly. The illustrative six mating features 26 H are the same as the lifting pins 26 of thefuel assembly 10. The corresponding lifting tool (not shown) suitably includes six downwardly extending elements, e.g. six downwardly extending rods or bars, arranged in a hexagonal pattern to mate with the respective six lifting pins 26 H. Finally, as a further example,FIG. 20 illustrates atriangular fuel assembly 22 T having three sides, with aconventional spider 74 T with six branches serving as the upper support element of the CRA. In this embodiment there are three mating features 26 T, which in this embodiment are embodied as recesses oropenings 26 T. The corresponding lifting tool (not shown) suitably includes three downwardly extending elements, e.g. three downwardly extending rods or bars, arranged in an equilateral triangular pattern to mate with the respective threeopenings 26 T. In general, the geometry of the fuel assembly preferably promotes a closely packed arrangement. - The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (24)
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US13/213,389 US20130044850A1 (en) | 2011-08-19 | 2011-08-19 | Nuclear reactor refueling methods and apparatuses |
CN2012101117672A CN103000237A (en) | 2011-08-19 | 2012-04-16 | Nuclear reactor refueling methods and apparatuses |
KR1020147007215A KR20140068075A (en) | 2011-08-19 | 2012-07-18 | Nuclear reactor refueling methods and apparatuses |
PCT/US2012/047171 WO2013028286A1 (en) | 2011-08-19 | 2012-07-18 | Nuclear reactor refueling methods and apparatuses |
CA2845700A CA2845700C (en) | 2011-08-19 | 2012-07-18 | Nuclear reactor refueling methods and apparatuses |
EP12825470.3A EP2745297B1 (en) | 2011-08-19 | 2012-07-18 | Nuclear reactor refueling methods and apparatuses |
JP2014526008A JP2014524575A (en) | 2011-08-19 | 2012-07-18 | Reactor fuel supply method and apparatus |
ARP120102933A AR087511A1 (en) | 2011-08-19 | 2012-08-10 | METHODS AND APPLIANCES FOR FUEL RECHARGING OF NUCLEAR REACTORS |
TW101129367A TW201327577A (en) | 2011-08-19 | 2012-08-14 | Nuclear reactor refueling methods and apparatuses |
US15/970,316 US10490311B2 (en) | 2011-08-19 | 2018-05-03 | Nuclear reactor refueling methods and apparatuses |
US16/692,177 US10878970B2 (en) | 2011-08-19 | 2019-11-22 | Nuclear reactor refueling methods and apparatuses |
US17/134,730 US11887739B2 (en) | 2011-08-19 | 2020-12-28 | Nuclear reactor refueling methods and apparatuses |
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US10878970B2 (en) | 2011-08-19 | 2020-12-29 | Bwxt Mpower, Inc. | Nuclear reactor refueling methods and apparatuses |
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US10062461B2 (en) | 2015-10-20 | 2018-08-28 | Kepco Engineering & Construction Company, Inc. | Spent fuel transfer device for transferring spent fuel between storage pools |
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Also Published As
Publication number | Publication date |
---|---|
EP2745297A1 (en) | 2014-06-25 |
AR087511A1 (en) | 2014-03-26 |
EP2745297A4 (en) | 2015-04-08 |
US20200105427A1 (en) | 2020-04-02 |
CA2845700A1 (en) | 2013-02-28 |
US20210118583A1 (en) | 2021-04-22 |
US11887739B2 (en) | 2024-01-30 |
WO2013028286A1 (en) | 2013-02-28 |
EP2745297B1 (en) | 2018-09-12 |
TW201327577A (en) | 2013-07-01 |
US10490311B2 (en) | 2019-11-26 |
JP2014524575A (en) | 2014-09-22 |
US10878970B2 (en) | 2020-12-29 |
CN103000237A (en) | 2013-03-27 |
CA2845700C (en) | 2021-05-04 |
US20180277270A1 (en) | 2018-09-27 |
KR20140068075A (en) | 2014-06-05 |
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