Control rod drive mechanism with heat pipe cooling

A representative cooling system for a nuclear reactor control rod drive mechanism (CRDM) includes an evaporation section located within or next to the CRDM and a condensation section fluidly coupled to the evaporation section. The cooling system includes a set of heat fins coupled to drive coils in the CRDM and heat pipes that extend through the drive coils and heat fins. A fluid evaporates while in the evaporation section of the heat pipes from heat generated by the CRDM and moves out of the evaporation section into the condensation section in the heat fins. The fluid cools and condensates while in the condensation section, recirculating back into the evaporation section. This passive natural circulation cooling system reduces or eliminates the number of water hoses, piping, and other water pumping equipment typically used for cooling a CRDM thereby increasing nuclear reactor reliability and simplifying nuclear reactor operation and maintenance.

TECHNICAL FIELD

This disclosure generally relates to a cooling system for a nuclear reactor control rod drive mechanism.

BACKGROUND

A control rod drive mechanism (CRDM) on top of a nuclear reactor pressure vessel (RPV) may maneuver or release drive shafts by gravity during a rapid control rod insertion (SCRAM). The CRDM may be located within an upper containment vessel (CNV) that contains the RPV and may use electrical motors to control movement of the drive shafts. The electrical motors may be driven remotely by electromagnetic force across a pressure vessel boundary.

CRDM electrical motors are typically cooled by Reactor Component Cooling Water Systems (RCCWS) or forced air cooling. The water cooled systems may incorporate a complex arrangement of water hoses to circulate water that removes heat from the electrical motor coils. The hoses are difficult to remove when the RPV is removed from the CNV for refueling. A CRDM failure caused by leaks or blockages in the cooling system hoses may trigger a Containment Evacuation System (CES) to shut down the nuclear reactor. Alternative air cooled systems may not be adequate for some nuclear reactors. For example, an evacuated CNV creates a vacuum environment around the outside of the RPV eliminating convection heat transfer as a cooling option.

DETAILED DESCRIPTION

A simplified cooling system uses heat pipes to cool electrical motors in Control Rod Drive Mechanisms (CRDM) while operating in an evacuated containment vessel (CNV). The cooling system does not rely on active water cooling through a Reactor Component Cooling Water System (RCCWS) and greatly simplifies CRDM, CNV and RCCWS designs avoiding potential Containment Evacuation System (CES) triggers and CRDM failures due to unintended cooling leaks or blockages.

The cooling system overcomes cooling restrictions for CRDMs that operate in vacuum environments that prevent effective convective heat transfer. The heat pipes may transfer heat from CRDM electrical coils to finned heat exchangers located above the CRDM electrical coils increasing the ability to transfer heat through radiation through the vacuum to the surrounding CNV vessel walls. The cooling system may encompass the same or a larger diametrical envelope than the electrical coils and does not need external power or external fluid transfer. In an alternate option, the cold end of the heat pipes may be mounted directly to the CNV vessel wall above the CRDMs to further promote conductive heat transfer.

FIG. 1illustrates a cross-sectional view of an example integral reactor module5comprising reactor pressure vessel52. Reactor core6is shown located near a lower head55of the reactor pressure vessel52. The reactor core6may be located in a shroud22which surrounds reactor core6about its sides. A riser section24is located above the reactor core6surrounded by steam generators30.

When primary coolant28is heated by reactor core6as a result of fission events, primary coolant28may be directed from shroud22up into an annulus23located above reactor core6, and out of riser24. This may result in additional primary coolant28being drawn into shroud22to be heated in turn by reactor core6, which draws yet more primary coolant28into shroud22. The primary coolant28that emerges from riser24may be cooled down by steam generators30and directed towards the outside of the reactor pressure vessel52and then returned to the bottom of the reactor pressure vessel52through natural circulation.

Primary coolant28circulates past the reactor core6to become high-temperature coolant TH and then continues up through the riser section24where it is directed back down the annulus and cooled off by steam generators30to become low-temperature coolant TC. One or more control rod drive mechanisms (CRDM)10are operably coupled to a number of drive shafts20that may be configured to interface with a plurality of control rod assemblies80located above reactor core6.

A reactor pressure vessel baffle plate45may be configured to direct the primary coolant28towards a lower end55of the reactor pressure vessel52. A surface of the reactor pressure vessel baffle plate45may come into direct contact with and deflect the primary coolant28that exits the riser section24. In some examples, the reactor pressure vessel baffle plate45may be made of stainless steel or other materials.

The lower end55of the reactor pressure vessel52may comprise an ellipsoidal, domed, concave, or hemispherical portion55A, wherein the ellipsoidal portion55A directs the primary coolant28towards the reactor core6. The ellipsoidal portion55A may increase flow rate and promote natural circulation of the primary coolant through the reactor core6. Further optimization of the coolant flow28may be obtained by modifying a radius of curvature of the reactor pressure vessel baffle plate45to eliminate/minimize boundary layer separation and stagnation regions.

The reactor pressure vessel baffle plate45is illustrated as being located between the top of the riser section24and a pressurizer region40. The pressurizer region40is shown as comprising one or more heaters and a spray nozzle configured to control a pressure, or maintain a steam dome, within an upper end56or head of the reactor pressure vessel52. Primary coolant28located below the reactor pressure vessel baffle plate45may comprise relatively sub-cooled coolant TSUB, whereas primary coolant28in the pressurizer region40in the upper end56of the reactor pressure vessel52may comprise substantially saturated coolant TSAT.

A fluid level of primary coolant28is shown as being above the reactor pressure vessel baffle plate45, and within the pressurizer region40, such that the entire volume between the reactor pressure vessel baffle plate45and the lower end55of the reactor pressure vessel52may be full of primary coolant28during normal operation of reactor module5.

Shroud22may support one or more control rod guide tubes94that serve to guide control rod assemblies80that are inserted into, or removed from, reactor core6. In some examples, drive shafts20may pass through reactor pressure vessel baffle plate45and through riser section24in order to control the position of control rod assemblies80relative to reactor core6.

Reactor pressure vessel52may comprise a flange by which lower head55may be removably attached to an upper reactor vessel body60of reactor pressure vessel52. In some examples, when lower head55is separated from upper reactor vessel body60, such as during a refueling operation, riser section24, baffle plate45, and other internals may be retained within upper reactor vessel body60, whereas reactor core6may be retained within lower head55.

Additionally, upper reactor vessel body60may be housed within a containment vessel70. Any air or other gases that reside in a containment region74located between containment vessel70and reactor pressure vessel52may be removed or voided prior to or during reactor startup. The gases that are voided or evacuated from the containment region74may comprise non-condensable gases and/or condensable gases. During an emergency operation, vapor and/or steam may be vented from reactor pressure vessel52into containment region74, or only a negligible amount of non-condensable gas (such as hydrogen) may be vented or released into containment region74.

FIG. 2illustrates an upper cross-sectional view of reactor module5and example control rod drive mechanism (CRDM) assemblies10. Reactor module5may comprise an upper containment vessel76housing at least a portion of the CRDM10. A plurality of drive shaft housings77may be located within upper containment vessel76. A plurality of drive shafts20associated with CRDMs10may be located in a reactor pressure vessel52that is housed in main containment vessel70. Drive shaft housings77may be configured to house at least a portion of drive shafts20during operation of reactor module5. In some examples, essentially all of the CRDMs10may be housed within main containment vessel70.

Upper containment vessel76may be removably attached to main containment vessel70. By removing upper containment vessel76, the overall size and/or volume of reactor module5may be reduced, which may affect peak containment pressure and/or water levels. In addition to reducing the overall height of reactor module5, the removal of upper containment vessel76from main containment vessel70may further reduce the weight and shipping height of reactor module5. In some example reactor modules, several tons of weight may be removed for each foot that the overall height of reactor module5is decreased.

Reactor pressure vessel52and/or main containment vessel70may comprise one or more steel vessels. Additionally, main containment vessel70may comprise one or more flanges by which a top head or a bottom head of main containment vessel70may be removed from the containment vessel body, such as during a refueling operation.

During refueling, reactor module5may be relocated from an operating bay into a refueling bay, and a series of disassembly steps may be performed on the reactor module5. The operating bay may be connected to the refueling bay by water, such that reactor module5is transported under water. Main containment vessel70may be disassembled, e.g., the top or bottom head may be separated from the containment vessel body, in order to gain access to CRDM10and/or to reactor pressure vessel52. At this stage of refueling, reactor pressure vessel52may remain completely submerged in the surrounding water in the refueling bay. In some examples, an upper portion of CRDM10, such as the plurality of drive shaft housings77, may be located above water to facilitate access to CRDM10in a dry environment. In other examples, the entire CRDM10may be submerged in the pool of water in the refueling bay.

CRDMs10may be mounted to an upper head of reactor pressure vessel52by nozzles78. Nozzles78may be configured to support CRDMs10when main containment vessel70is partially or completely disassembled during the refueling operation. Additionally, CRDMs10may be configured to support and/or control the position of drive shafts20within reactor pressure vessel52.

Reactor pressure vessel52may comprise a substantially capsule-shaped vessel. In some examples, reactor pressure vessel52may be approximately 20 meters in height. Drive shafts20may extend from CRDMs10, located at the upper head of reactor pressure vessel52, into a lower head of reactor pressure vessel52, so that they can be connected to control rod assemblies80that are inserted into reactor core6(FIG. 1). The distance from the upper head of reactor pressure vessel52to reactor core6, while less than the overall height of reactor pressure vessel52, may therefore result in the length of drive shafts20also being approximately 20 meters in length or, in some examples, somewhat less than the height of reactor pressure vessel52.

FIG. 3is a perspective view of a control rod assembly80held partially above and partially inserted into a nuclear fuel assembly90in reactor core6. As explained above, multiple drive shafts20extend down from rod drive mechanisms10to the top of reactor core6. Control rod assembly80may include a cylindrical hub82that attaches to the bottom end of drive shaft20. Arms84extend radially out from cylindrical hub82and attach at distal ends to top ends of control rods86.

Control rods86extend into a nuclear fuel assembly90that is alternatively referred to as a fuel bundle that forms part of reactor core6. Nuclear fuel assembly90may include a top nozzle92that supports multiple guide tubes94. Guide tubes94extend down from nozzle92and in-between nuclear fuel rods (not shown). Control rods86control the fission rate of the uranium and plutonium in the nuclear fuel rods.

Control rods86are typically held by drive shaft20above nuclear fuel assembly90or held slightly inserted into nuclear fuel assembly90. Reactor core6may overheat. A nuclear SCRAM operation is initiated where control CRDMs10inFIG. 1release drive shafts20dropping control rods86down into guide tubes94and in-between the nuclear fuel rods.

FIG. 4Ashows a cross-sectional view of an example reactor pressure vessel52. CRDMs10may be mounted to an upper head96of reactor pressure vessel52and configured to support a plurality of drive shafts20that extend through the length of an upper reactor vessel body60of reactor pressure vessel52towards reactor core6located in a lower head98of reactor pressure vessel52. In some examples, lower head98may be removably attached to upper reactor vessel body60at a flange100, such as by a plurality of bolts.

In addition to housing a number of nuclear fuel rods, reactor core6may be configured to receive a plurality of control rod assemblies80that may be movably inserted between the fuel rods to control the power output of reactor core6. When reactor core6is generating power, lower ends102of drive shafts20may be connected to control rod assemblies80. Additionally, CRDMs10may be configured to control the location of control rod assemblies80within reactor core6by moving drive shafts20either up or down within reactor pressure vessel52.

Upper ends104of drive shafts20may be housed in CRDM pressure housing77located above upper head96of reactor pressure vessel52, such as when control rod assemblies80are removed from reactor core6. In some examples, CRDM pressure housing77may comprise a single pressure vessel configured to house upper ends104of drive shafts20. In other examples, CRDM pressure housing77may comprise individual housings for each of the drive shafts20.

Lower ends102of drive shafts20are shown disconnected from control rod assemblies80, such as may be associated with a refueling operation of reactor core6. During an initial stage of the refueling operation, lower head98may remain attached to upper reactor vessel body60while drive shafts20are disconnected from control rod assemblies80. Reactor pressure vessel52may remain completely sealed to the surrounding environment, which in some examples may comprise a pool of water that at least partially surrounds reactor pressure vessel52, during the initial stage of the refueling operation.

CRDMs10may comprise remote disconnect mechanisms by which drive shafts20may be disconnected from control rod assemblies80without opening or otherwise disassembling reactor pressure vessel52. In some examples, reactor pressure vessel52may form a sealed region106that surrounds reactor core6, control rod assemblies80, and lower ends102of drive shafts20. By remotely disconnecting drive shafts20, control rod assemblies80may remain within reactor core6when drive shafts20are withdrawn, at least partially, into CRDM pressure housing77.

FIG. 4Billustrates the example reactor pressure vessel52ofFIG. 4Apartially disassembled. During the refueling operation, lower head98may be separated from upper reactor vessel body60of reactor pressure vessel52. In some examples, lower head98may be held stationary in a refueling station while upper reactor vessel body60is lifted up by a crane and moved away from lower head98to facilitate access to reactor core6.

Drive shafts20are shown in a retracted or withdrawn position, such that lower ends102may be completely retained within upper reactor vessel body60and/or CRDM pressure housing77. For example, CRDMs10may be configured to raise lower ends102of drive shafts20above a lower flange108used to mount upper reactor vessel60together with an upper flange110of lower head98. Withdrawing lower ends102of drive shafts20into upper reactor vessel body60may provide additional clearance between lower flange108and upper flange110during the refueling operation and further may keep drive shafts20from contacting external objects or getting damaged during transport and/or storage of upper reactor vessel body60. Additionally, upper ends104of drive shafts20may similarly be housed and/or protected by CRDM pressure housing77when drive shafts20are in the retracted or withdrawn position.

As discussed above, control rod assemblies80may remain completely inserted in reactor core6during some or all of the refueling operation. In some examples, maintaining the insertion of control rod assemblies80within reactor core6may be dictated by nuclear regulatory and/or safety considerations.

Single-Hinge Type Control Rod Drive Mechanism

FIG. 5is a side view andFIG. 6is a plan view of a single-hinge type control rod drive mechanism88that includes a remote disconnect mechanism. Referring toFIGS. 5 and 6, a drive shaft housing77extends over the top end of drive shaft20and around the latch mechanism138. Drive shaft housing77is alternatively referred to as an upper pressure boundary.

As described above, drive shaft20enters reactor pressure vessel (RPV)52inFIG. 2through a nozzle78connected on top to the bottom end of drive shaft housing77. A bottom end of drive shaft20detachably connects to control rod assembly80as shown in more detail below.

Control rod drive mechanism88includes a drive assembly122that raises and lowers drive shaft20and attached control rod assembly80. Control rod drive mechanism88also includes a disconnect assembly120that disconnects drive shaft20from control rod assembly80. Both drive assembly122and disconnect assembly120may be remotely activated and controlled from outside of the RPV52via electrical control signals.

FIG. 7is a side sectional view of control rod drive mechanism88andFIG. 8is a more detailed sectional view of a single-hinge latch assembly138used in control rod drive mechanism88. Referring toFIGS. 7 and 8, through-holes158are provided in drive shaft housing77and nozzle78. Bolts (not shown) may be inserted into holes158to connect drive shaft housing77to nozzle78that extends up from the upper head of RPV52as shown above inFIG. 2.

A disconnect rod132extends through the entire length of drive shaft20and a cylindrical disconnect magnet134is attached to a top end of disconnect rod132. Disconnect magnet134extends up into drive shaft housing77and annular disconnect coils136extend around drive shaft housing77and disconnect magnet134. When activated, disconnect coils136may hold disconnect magnet134in a raised position allowing disconnect rod132to retract vertically upwards within drive shaft20.

An upper end of drive shaft20includes a threaded outside surface140. In one example, threads140may comprise ACME® type threads for linearly displacing drive shaft20. Of course, any other type of threading or gearing also may be used. Drive shaft20extends from underneath disconnect magnet134, through drive shaft housing77and nozzle78, and into the upper head of RPV52(FIG. 1). Drive shaft20further extends through the length of RPV52and a bottom end includes a grapple126that connects to control rod assembly80. Disconnect magnet134and disconnect coils136encompass the disconnect assembly120.

An annular arrangement of drive coils128may extend around the outside of drive shaft housing77and an annular arrangement of drive magnets130inside of drive shaft housing77may extend around drive shaft20. Continuously activating drive coils128may raise drive magnets130. Alternating activation of alternating drive coils128inFIG. 8also may rotate drive magnets130around a center axis156of drive shaft20. Drive coils128, drive magnets130and latch assembly138form the drive assembly122.

A single-hinge latch assembly138is coupled on the bottom end to the drive shaft housing77and coupled on top to drive magnets130. Latch assembly138includes an annular base142that includes a central opening that extends around drive shaft20. A lip143extends out from an outside bottom end of base142and seats into a recess formed between the bottom end of drive shaft housing77and the top end of nozzle78. Lip143functions as a hold-down holding base142down against the top surface of nozzle78.

An annular collar148is rotationally attached to base142and includes a step144that attaches on top of bearings154that extend around the top of base142. Collar146also includes a center opening that receives and extends around drive shaft20. Collar146is held vertically/elevationally down onto base142but rotates about central axis156of drive shaft20on top of bearings154and base142.

The outside end of a gripper150is pivotally attached to an upper end of collar148with a first pin152A. The inside end of gripper150is pivotally attached to a bottom end of a latch146by a second pin152B. A top end of latch146is attached to drive magnets130. When drive magnets130are lowered a bottom end of latch146may sit on top of step144of collar148.

When activated, drive coils128lift drive magnets130vertically upwards also lifting latch146. Lifting latch146causes the inside ends of grippers150to rotate upwards engaging with threads140on drive shaft20. The outside ends of grippers150rotate about pins152A which are held vertically in place by collar148.

After raising the inside ends of grippers150, drive coils128may start rotating drive magnets130about central axis156of drive shaft20. The bottom ends of drive magnets130start rotating raised latch146and attached gripper150around the outside circumference of drive shaft20. Rotating gripper150also rotates collar148over the top of base142and around central axis156while remaining elevationally held down in place by base142.

The inside end of grippers150rotate within threads140moving drive shaft20axially and linearly upwards inside of drive shaft housing77and nozzle78. Drive coils128may rotate drive magnets130in an opposite direction, also rotating attached grippers150within threads140in an opposite direction. Accordingly, grippers150axially and linearly move drive shaft20in an upward or downward direction as directed by an electrical control system.

Deactivating drive coils128drops drive magnets130vertically downwards. Inside ends of grippers150also rotate downwards about pins152B, disengaging from threads140. Now released from grippers150, drive shaft20is free to drop vertically downwards via gravity.

FIG. 9is a cross-sectional plan view of drive assembly122. Annular drive coils128extend around the outside of drive shaft housing77and annular drive magnets130extend around the inside of drive shaft housing77. Drive shaft20extends through a central opening formed in drive magnets130and disconnect rod132extends through a hole formed along the central axis of drive shaft20. Threads140extend around the outside surface of drive shaft20.

When continuously activated, drive coils128generate an electromagnetic field that vertically lifts up drive magnets130. When drive coils128are activated in an alternating pattern, the electromagnetic field also rotates drive magnets130around the central axis causing drive assembly122to operate effectively like an electrical motor. For example, the electrical control system may activate drive coils A during a first period and activate drive coils B during an alternating second period. The alternating activation of drive coils A and B cause drive magnets M to rotate about a vertical axis that extends through drive shaft20.

FIG. 10is a cross-sectional plan view of single-hinge latch assembly138. Disconnect rod132extends through the center of drive shaft20. Threads140extend around the outside surface of drive shaft20. Latch146has an annular cross-sectional shape and attaches to the inside end of gripper150via pin152B. Collar148also includes an annular cross-sectional shape and attached to the outside end of gripper150via pin152A. As explained above, latch146is attached to drive magnets130and can move vertically up and down. Drive shaft housing77also has an annular cross-sectional shape concentrically aligned with drive shaft20. Also note that any number of grippers150may be located around drive shaft20. For example, four grippers150may be located 90 degrees apart around drive shaft20.

FIGS. 11A-11Eare side sectional views showing different operating positions of control rod drive mechanism88. Referring toFIG. 11A, drive assembly122is shown in a lowered state. Drive coils128are deactivated and drive magnets130are in a lowered position, with the control rod assembly80fully inserted into reactor core6(FIG. 1). Lowered drive magnets130with attached latch146released grippers150from threads140of drive shaft20.

During a loss of electric power or forced SCRAM, drive coils128may deactivate, allowing gravity to drop drive shaft20downward, disconnected from latch assembly138. Attached control rod assembly80accordingly drops into fuel assembly90neutralizing reactor core6(seeFIGS. 1 and 3). Thus, CRDM88has the advantage of automatically scramming reactor core6whenever deactivated during a power failure.

Disconnect assembly120is also shown in a lowered state. Disconnect coils136are deactivated and disconnect magnet134is in a lowered position sitting on top of drive shaft20. In the lowered position, the bottom end of disconnect rod132extends in-between reciprocating arms127A and127B of grapple126. Spread-apart grapple arms127A and127B press against and lock into grooves in cylindrical hub82of control rod assembly80.

FIG. 11Bshows drive assembly122in a raised state. Drive coils128are activated and drive magnets130are in a raised position. Raised drive magnets130raise attached latch146moving inside ends of grippers150upward, interlocking with threads140of drive shaft20. Locked grippers150can raise or lower drive shaft20based on the rotational direction of drive magnets130.

Disconnect assembly120is still shown in a lowered state where the bottom end of disconnect rod132remains inserted in-between grapple arms127A and127B. Spread-apart grapple arms127A and127B remain locked inside of cylindrical hub82locking the bottom end of drive shaft20to control rod assembly80.

FIG. 11Cshows drive assembly122in a raised state. Drive coils128are activated and drive magnets130are raised, moving attached latch146upward engaging inside ends of grippers150with threads140. Drive coils128also may start rotating drive magnets130causing grippers150to rotate around engaged threads140of drive shaft20. Rotating grippers150force drive shaft20axially and linearly upwards into drive shaft housing77and lift connected control rod assembly80by a short distance that does not cause a reactivity insertion into the reactor core (within a so-called dead band).

Raising drive shaft20also raises disconnect magnet134, maintaining the bottom end of attached disconnect rod132in-between grapple arms127A and127B. In other words, raising drive shaft20and disconnect rod132together keeps the bottom end of drive shaft20attached to control rod drive mechanism80, prior to the disconnection discussed below.

FIG. 11Dshows drive assembly122in a lowered state and disconnect assembly120in a raised state. Disconnect coils136are activated when drive shaft20and disconnect magnet134are in the raised position shown inFIG. 11C. Drive coils128then may rotate drive magnets130in an opposite direction lowering drive shaft20vertically downward. At the same time, disconnect coils136hold disconnect magnet134in a raised position. As grippers150continue to move drive shaft20linearly downward, the bottom end of disconnect rod132slides up and out from in-between grapple126. Grapple arms127A and127B accordingly reciprocate inwards disconnecting from control rod assembly80, which drops a short distance. Alternatively, drive coils128are deactivated dropping drive shaft20and disconnecting control rod assembly80, with disconnect coils136holding disconnect magnet134in a raised position.

FIG. 11Eshows disconnect assembly120and drive assembly122both in a lowered state. Deactivating disconnect coils136releases disconnect magnet134causing the bottom end of disconnect rod132to slide in-between grapple arms127A and127B. Drive coils128then may deactivate disconnecting grippers150from drive shaft20. Spread-apart grapple126then sits on the top of control rod assembly80.

Thus, drive coils128and disconnect coils136can be remotely activated and deactivated to linearly displace drive shaft20and also to disconnect drive shaft20from control rod assembly80during a reactor core refueling operation. Reconnecting the control rod assembly80after completion of refueling and re-assembly of reactor vessel52(FIGS. 4A and 4B) may be performed in reverse order of the steps shown inFIG. 11A to 11D.

Dual-Hinge Type Control Rod Drive Mechanism

FIG. 12is a side view of a dual-hinge type control rod drive mechanism159.FIGS. 13A and 13Bare side sectional views of control rod drive mechanism159.FIG. 14is a more detailed view of the dual-hinge latch assembly160.

Referring toFIGS. 12, 13A, 13B, and 14, drive assembly122and disconnect assembly120in control rod drive mechanism159include substantially the same drive and disconnect coils and magnets as described above. Drive shaft housing77and nozzle78are also all substantially the same as those described above. Disconnect rod132, drive shaft20, and threaded outside surface140are also similar to those described above.

Similar to above, continuously activating drive coils128may raise and align drive magnets130with annular drive coils128. Alternating activation of adjacent drive coils128also may rotate drive magnets130around a central axis156of drive shaft20, to force linear motion of drive shaft20and attached control rod assembly80.

Dual-hinge latch assembly160is coupled at a bottom end to drive shaft housing77and coupled at a top end to drive magnets130. Latch assembly160includes a similar base142at described above that includes a central opening that extends around drive shaft20. A similar lip143extends out from an outside bottom end of base142and seats into a recess formed between the bottom end of drive shaft housing77and the top end of nozzle78. Lip143functions as a hold-down holding base142down against a top surface of nozzle78.

Referring toFIG. 13A, drive assembly122is shown in a raised state. Activating drive coils128raises drive magnets130and attached latch162. The lower ends of grippers164move upwards and inwards engaging with threads140of drive shaft20. Locked grippers164can then raise or lower drive shaft20based on the rotational direction of drive magnets130.

Disconnect assembly120is shown in a lowered position where the bottom end of disconnect rod132is inserted in-between arms127A and127B of grapple126. Spread-apart arms127A and127B lock inside of cylindrical hub82locking the bottom end of drive shaft20to control rod assembly80.

Disconnect assembly120is still shown deactivated where the bottom end of disconnect rod132remains inserted in-between arms127A and127B of grapple126. Spread-apart arms127A and127B remain locked inside of cylindrical hub82locking the bottom end of drive shaft20to control rod assembly80.

InFIG. 14an annular collar148similar in design toFIG. 8is attached, but rotationally de-coupled, to base142and includes a similar step144that attaches on top of bearings154that extend around the top of base142. Collar146also includes a center opening that receives and extends around drive shaft20. Collar146is held vertically/elevationally down onto base142but rotates about central axis156of drive shaft20on top of bearings154and base142.

The outside end of a hinge168is pivotally attached to a top end of collar148with a first pin166A. The inside end of hinge168is pivotally attached to a lower end of a gripper164by a second pin166B. The top end of a latch162is attached to drive magnet130and a bottom end of latch162is pivotally attached to a top end of gripper164by a third pin166C.

When activated, drive coils128lift drive magnets130vertically upwards also raising latch162. Gripper164and the inside end of hinge168also move upwards, moving the bottom end of gripper164inwards engaging with threads140of drive shaft20.

After engaging the lower ends of grippers164, drive coils128may start rotating drive magnets130about central axis156of drive shaft20. The bottom ends of drive magnets130also start rotating raised latch146and engaged grippers164around drive shaft20. Rotating grippers164also rotates collar148about central axis156while being held vertically down by base142.

The inside ends of grippers164rotate within engaged threads140moving drive shaft20linearly upwards inside of drive shaft housing77and nozzle78. Drive coils128may rotate drive magnets130in an opposite direction, thus rotating grippers164within threads140in an opposite direction axially moving drive shaft20downward.

Deactivating drive coils128drops drive magnets130and inside ends of grippers164downwards. Hinges168also rotate downwards and outwards disengaging the lower ends of grippers164from threads140. Drive shaft20is now released from grippers150and is free to drop vertically downwards via gravity.

FIG. 15is a cross-sectional plan view of dual-hinge latch assembly160. Disconnect rod132extends through a centerline of drive shaft20. Threads140extend around the outside surface of drive shaft20. Latch162has an annular cross-sectional shape and attaches at the bottom end to the top end of gripper164. Collar148also includes an annular cross-sectional shape and attaches to the outside end of hinge168via pin166A. As explained above, collar146is attached to drive magnets130and can move vertically up and down. Drive shaft housing77also has an annular cross-sectional shape concentrically aligned with drive shaft20.

FIGS. 16A-16Gare simplified schematic diagrams showing different operations of the single-hinge type control rod drive mechanism88or double-hinge type control rod drive mechanism159described above, focusing on the primary elements to attain the CRDM functions described herein. For explanation purposes, the following abbreviations are used below.

Drive shaft housing77=I

Control rod assembly80=CRA

Concentric electromagnetic coils A and F extend on the outside of drive shaft housing I, alternatively referred to as pressure boundary. Coils A and F on the outside interact to move cylindrical magnets B and G, respectively, inside pressure boundary I.

Referring toFIG. 16A, drive coils A are initially de-energized. Latch C is fixed to annular drive magnets B and rests on base J inside drive shaft housing I.

Referring toFIG. 16B, drive coils A are energized, lifting drive magnet B upwards until aligned with drive coils A. This lifts latch C and engages grippers E that pivot around pins that are vertically fixed with respect to the inside of pressure boundary I, yet allow for rotation of latch C. Grippers E fit into threaded grooves of drive shaft D.

Referring toFIG. 16C, by operating drive coils A in a specific sequence, drive magnet B and latch C are set into rotary motion, while at the same time still maintaining a same elevation as drive coils A. This precludes disengagement of grippers E. The rotary motion of grippers E translates into linear drive shaft motion that raises drive rod D and the attached CRA.

Referring back toFIG. 16A, upon a SCRAM signal or loss of electric power, drive coils A release drive magnet B causing grippers E to pivot down and outwards due to the drop of latch C. This provides a safety feature where a gravity-driven drop of drive shaft D drops attached CRA into the reactor core.

FIGS. 16D-16Gshow how to remotely disconnect drive shaft D from the CRA prior to disassembly of reactor pressure vessel52inFIGS. 4A and 4B. Drive coils A are initially de-energized and latch C is resting on base J. This may be similar to the initial drive shaft engagement configuration shown inFIG. 16A.

Referring toFIG. 16D, drive coils A are activated raising drive magnets B and latch C causing grippers E to engage with drive shaft D. As shown above inFIG. 11C, drive coils A then set drive magnet B and latch C into rotary motion, while at the same time maintaining a same elevation as drive coils A. Rotating grippers E move drive shaft D and disconnect magnet G linearly upwards into raised positions, lifting the attached CRA by a short distance that does not cause a reactivity insertion into the reactor core (within a so-called dead band).

Referring toFIG. 16E, drive coils A are still energized holding drive magnet B, drive shaft D, disconnect magnet G, and disconnect rod K in raised positions. Disconnect coil F is energized holding disconnect magnet G and attached disconnect rod K vertically in place. Drive coils A then may rotate drive magnet B, latch C, and gripper E in an opposite direction linearly lowering drive shaft D. Grapple H on the bottom end of drive shaft D currently holds the CRA, and the bottom end of disconnect rod K starts moving up and out from the grapple arms. The arms of grapple H contract causing the CRA to drop by a short distance, until it rests again on top of the nuclear fuel assembly top nozzle92inFIG. 3.

Referring toFIG. 16F, drive coils A remain energized and therefore hold drive magnet B in place. Disconnect coil F is then de-energized. This releases disconnect magnet G causing the bottom end of disconnect rod K to insert into and expand grapple H on the bottom of drive shaft D.

Referring toFIG. 16G, drive coils A are de-energized releasing annular drive magnet B and latch C. Drive shaft D drops by a short distance until grapple H rests on top of the CRA cylindrical hub without being engaged. This allows the upper and lower sections of the reactor pressure vessel to be separated for refueling without removing the CRA.

Re-connection of grapple H to the CRA is performed in reverse order. Drive coils A may move drive shaft D and disconnect magnet G vertically up into raised positions. Disconnect coils F may activate holding disconnect magnet G and disconnect rod K in the raised position. Drive coils A then may lower drive shaft D contracting and inserting grapple H into the CRA. Disconnect coils F then may be deactivated dropping disconnect magnet G and the bottom of disconnect rod K in-between grapple H. Grapple H expands locking into the CRA.

Alternatively, grapple H is reengaged with the CRA by pulling up disconnect magnet G using the electromagnetic force of disconnect coil F. Disconnect magnet G is moved into the raised position without simultaneously energizing drive coil A. The weight of drive shaft D may be large enough so that only disconnect rod K moves upwards inside of drive shaft D. Grapple H contracts inserting into the CRA cylindrical hub. Disconnect coils F are then deactivated so the bottom of disconnect rod K drops back down into grapple H. Grapple H expands locking into the CRA.

CRDM Cooling System

FIG. 17illustrates an upper cross-sectional view of reactor module5with an example control rod drive mechanism (CRDM)88with an integrated cooling system180.FIG. 18is a isometric perspective view showing CRDM88and cooling system180in further detail. Reactor module5includes the same upper containment vessel76housing described above. A plurality of drive shaft housings77are located within upper containment vessel76. As also described above, a plurality of drive shafts20extend down into RPV52through nozzles78connected on top to the bottom end of drive shaft housing77.

Drive shaft housings77may retain any of the CRDM88, disconnect assembly120, drive assembly122, single-hinge latch assembly138, or double-hinge type control rod drive mechanism159described above. As explained above, drive assembly122may raise and lower drive shaft20and disconnect assembly120may disconnect drive shaft20from control rod assembly80(FIG. 3). Both drive assembly122and disconnect assembly120may be remotely activated and controlled from outside of RPV52via electrical control signals.

As also mentioned above, any air or other gases that reside in containment region74located between containment vessel70and reactor pressure vessel52may be removed or voided prior to or during reactor startup. The gases that are voided or evacuated from the containment region74may comprise non-condensable gases and/or condensable gases.

Cooling system180includes a set of heat fins184that extend up from the top of drive coils128and around disconnect assembly120. Heat fins184may have a tabular shape and may be formed from any heat sink material, such as aluminum, copper, stainless steel, or any other heat conducting metal. Heat fins184have an improved path for radiative heat transfer to the CNV surfaces with cooler temperatures within containment region74formed between RPV52and CNV70. Heat fins184may remove heat generated by drive coils128without substantially increasing the footprint of CRDM88.

In one example, heat fins184may be attached or formed with an outside metal enclosure185that retains drive coils128. For example, drive coils128and heat fins184may be formed into a same modular annular enclosure that can slide over drive shaft housing77.

FIG. 19is a cross-sectional plan view of a lower portion of CRDM cooling system180. As described above inFIG. 9, annular drive coils128extend around the outside circumference of drive shaft housing77and annular drive magnets130extend around the inside of drive shaft housing77. Drive shaft20extends through a central opening formed in drive magnets130and disconnect rod132extends through a hole formed along the central axis of drive shaft20. Threads140extend around the outside surface of drive shaft20.

Cooling channels186extend vertically through and/or in-between drive coils128and either form or retain heat pipes190. For example, channels186may retain metal tubes that retain a fluid that together operate as a heat pipe190. In this example, four pairs of outer heat pipes190A and inner heat pipes190B extend in a half-loop through each drive coil128. Outer heat pipes190A and inner heat pipes190B are alternatively referred to as heat pipes190.

FIG. 20is a cross-sectional plan view of an upper portion of CRDM cooling system180andFIG. 21is an expanded plan cross-sectional view of the upper portion of CRDM cooling system180. Cooling channels188extend vertically through heat fins184and again either form or retain tubes that operate as heat pipes190. Cooling channels188connect or are continuously formed with channels186in drive coils128to form heat pipe loops190.

As described above inFIGS. 5-7, cylindrical disconnect magnet134is attached to a top end of disconnect rod132(FIG. 7). Disconnect magnet134extends up into drive shaft housing77and annular disconnect coils136extend around drive shaft housing77and disconnect magnet134. Heat fins184extend radially out from disconnect coils136and in one example contain the upper sections of heat pipes190. Heat pipes190A and190B extend in half-loops up through each heat fin184.

Evaporation sections of heat pipes190A and190B extend along the inner side of heat fin184and are covered by insulation196in heat fin184. In one example, insulation196may be any type of mineral wool, calcium silicate, fiberglass, microporous refractory, glass fiber felt, reflective metallic insulation (RMI), or any other material normally used for insulating pipes in nuclear power plants.

Condensation sections of heat pipes190A and190B are fluidly coupled to the insulation sections of heat pipes190A and190B, extend along the outer lateral sides of heat fins184, and are surrounded by condensation channels198. In one example, condensation channels198are a group of highly heat conductive metal strips or slots that extend radially out from the outer surface of heat pipes190. Condensation channels198expose more outer surface area of the condensation sections of heat pipes190to the cooler containment region74formed by CNV70(FIG. 17). Any other type of heat fin or heat sink may be formed within heat fins184around the condensation portions of heat pipes190to further increase the rate of heat transfer.

FIG. 22is an isometric side-sectional view of cooling system180andFIG. 23is a more detailed isometric side-sectional view of cooling system180. In this example, multiple pairs of outer and inner circular heat pipes loops190A and190B, respectively, extend through each drive coil128and heat fin184. Outer heat pipes190A extend along the inner and outer lateral sides of drive coils128and heat fins184. Inner heat pipes190B extend through drive coils128and heat fins184inside of outer heat pipes190A.

Heat pipes190extend from the bottom ends up through top ends of drive coils128and then extend further up through the bottom ends to the top ends of heat fins184. The top ends of heat pipes190extend radially out from disconnect coils136, and the bottom ends of heat pipes190extend radially inward toward drive shaft housing77forming continuous loops.

An alternate option is to mount the colder upper sections194of heat pipes190directly to the inside wall of CNV70above CRDMs88where heat is transferred to the CNV surfaces by conduction. For example, heat pipes190may include loops that extend further up and out of the top of heat fins184or drive coils128and contact the inside wall of CNV70. In both the alternatives once the heat is transferred to the CNV it is dissipated to the environment outside of the CNV.

The inner portions of heat pipes190A and190B located closer to the inner lateral sides of drive coils128and heat fins184are referred to as evaporation sections208and the outer portions of heat pipes190A and190B that extend closer to the outer lateral sides of heat fins184are referred to as condensation sections210. Evaporation sections208and condensation sections210are fluidly coupled together.

Heat pipes190may comprise any round, oval, or flat shaped tube or orifice formed from any material, such as copper, aluminum, stainless steel, or any other heat conductive metal. Heat pipes190may contain any fluid200capable of transferring heat, such as water, ammonia, methanol, liquid sodium, or the like. When heated, fluid200may transform into an evaporated state200A and when cooled may transform back into a condensed state200B.

Evaporation and condensation of fluid200creates a fluid flow through heat pipes190that removes heat from drive coils128. For example, drive coils128while in operation create heat that evaporates fluid200A. Evaporated fluid200A rises up through the evaporation section208of heat pipes190transferring heat away from drive coils128.

As explained above, insulation material196in upper condensation section210of heat pipes190transfer evaporated fluid200A. Condensation channels198in the upper condensation section210of heat pipes190coagulate evaporated fluid200A into droplets of condensed fluid200B. Other types of porous media may be used in heat pipes190to help coagulate evaporated fluid200A into condensed fluid200B.

Condensed fluid200B drops vertically downward via gravity or capillary action through the condensation section210of heat pipes190. Drive coils128then reheat condensed fluid200B back into evaporated fluid200A, recirculating fluid200back through heat pipes190and further removing heat from drive coils128. A flow restrictor (not shown) may be located in heat pipes190upstream of drive coils128to control the flow direction and flow rate of fluid200.

Passive cooling system180reduces or eliminates the number of water hoses, piping, and water pumping equipment normally used in active RCCWS systems. The simplified cooling system180also embeds heat pipes190in integrated drive coils128and heat fins184to provide a modular CRDM88design where electrical drive coils128can be more easily swapped out during maintenance operations. Cooling system180also overcomes limitations of convective heat cooling in Pressurized Water Reactor (PWR) CRDM designs where CRDM electrical coils128are located on the outside of the CRDM pressure boundary in a vacuum environment.

Having described and illustrated the principles of a preferred embodiment, it should be apparent that the embodiments may be modified in arrangement and detail without departing from such principles. Claim is made to all modifications and variation coming within the spirit and scope of the following claims.

Some of the operations described above may be implemented in software and other operations may be implemented in hardware. One or more of the operations, processes, or methods described herein may be performed by an apparatus, device, or system similar to those as described herein and with reference to the illustrated figures.

It will be apparent to one skilled in the art that the disclosed implementations may be practiced without some or all of the specific details provided. In other instances, certain process or methods have not been described in detail in order to avoid unnecessarily obscuring the disclosed implementations. Other implementations and applications also are possible, and as such, the following examples should not be taken as definitive or limiting either in scope or setting.

References have been made to accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific implementations. Although these disclosed implementations are described in sufficient detail to enable one skilled in the art to practice the implementations, it is to be understood that these examples are not limiting, such that other implementations may be used and changes may be made to the disclosed implementations without departing from their spirit and scope.

Although the examples provided herein have primarily described a pressurized water reactor and/or a light water reactor, it should be apparent to one skilled in the art that the examples may be applied to other types of power systems. For example, the examples or variations thereof may also be made operable with a boiling water reactor, sodium liquid metal reactor, gas cooled reactor, pebble-bed reactor, and/or other types of reactor designs.

It should be noted that examples are not limited to any particular type of reactor cooling mechanism, nor to any particular type of fuel employed to produce heat within or associated with a nuclear reaction. Any rates and values described herein are provided by way of example only. Other rates and values may be determined through experimentation such as by construction of full scale or scaled models of a nuclear reactor system.