Patent Description:
Nuclear fission reactors generate heat via a process of neutron chain reaction. The operating state of the reactor is adjusted by changing the neutron absorption rate in the reactor core. In general terms, this is referred to as reactivity control. One of the established methods for reactivity control is to use movable control rods containing neutron absorbing material, such as cadmium or boron. Inserting the control rods deeper into the reactor core increases, and withdrawing the rods reduces neutron absorption.

The conventional technical solution for control rod systems is to place the rod drive mechanisms (i.e. the electric motors that move the rods up and down) outside the reactor pressure vessel. In pressurized water reactors (PWRs) the rod drives are attached on the top lid of the vessel. Control rods of boiling water reactors (BWRs) are operated from below, with the drive shafts penetrating the vessel bottom.

In some reactor concepts the control rod drive mechanisms are placed inside the pressure vessel. One of the advantages of using in-vessel rod drives is that the possibility of fast control rod ejection transients is eliminated by design, due to the lack of pressure differential over the drive mechanism. This is not a common solution, however, since the operating conditions can be challenging for electric components. The operating temperature in conventional light water reactors is around <NUM>. PWRs operate at <NUM>-<NUM> MPa, and BWRs at around <NUM> MPa pressure, respectively.

In conventional PWRs core reactivity is in addition adjusted by changing the concentration of boric acid in the coolant water. This method, also known as boron shim, is in particular used for compensating the excess reactivity of fresh fuel assemblies placed in the reactor core at the beginning of each operating cycle. As the fuel is consumed, boron concentration is slowly reduced.

Some PWR concepts are designed to operate without soluble boron. The advantage of this approach is that the chemical and volume control system of the reactor is somewhat simplified, and reactivity transients related to boron dilution eliminated by design.

The drawback of boron-free operation is that reactivity control has to be managed by control rods alone, which complicates the core design. Further, maintaining the core in a sub-critical safe shut-down state during reloading operations becomes a technical challenge, since disassembling the core requires removing the control rod drives and associated structures before the fuel assemblies can be accessed. This is not an issue in conventional PWRs, in which the safe shut-down state is instead maintained by soluble boron, or in BWRs, in which control rods are inserted from below, and remain in place when the core is accessed from above.

In addition to reactivity control systems, the state of the reactor should be constantly monitored by various sensors and detectors that measure the relevant operating parameters, such as neutron flux and coolant temperature. In-core neutron detectors are placed in hollow instrumentation tubes that are part of the fuel assembly structure. Ex-core neutron detectors and temperature sensors are placed outside the core.

Nuclear reactors subject to boron-free operations are challenging due to managing reactivity control by control rods alone and tedious disassembling of the control rod mechanism while maintaining the reactor in safe shut-down state during refueling operations. In-vessel control rod drives may be a preferred solution for many reactors operating under natural circulation, in which case maintaining sufficient coolant flow requires considerable elevation between the reactor core and primary heat exchangers, which is also reflected in the overall height of the reactor pressure vessel and the length of the control rod shafts. This is in particular the case for low-temperature reactors, in which the operating conditions are less challenging for electric components. There is therefore a need to improve in-vessel control rod systems in reactor types where such configuration is an attractive option.

<CIT> discloses a method which comprises the refuelling of a nuclear reactor and includes removing a fuel assembly having a control rod assembly inserted in the fuel assembly.

A novel fuel and control system is therefore herein proposed.

According to a first aspect of the present disclosure, there is provided a fuel and control system featuring a drive motor, a control rod assembly, a fuel unit and a frame. The frame attaches the drive assembly to the fuel unit and provides a space for control movement of the control rod assembly so that the frame, the fuel unit, the drive assembly and the control rod assembly are integrated so that the fuel and control system is configured to be loaded into and unloaded out of the nuclear reactor as one unit.

One or more embodiments of the first aspect may include one or several features from the following itemized list:.

According to a second aspect of the present disclosure, there is provided a nuclear reactor featuring a reactor core, a pressure vessel and a plurality of fuel and control system where the fuel and control system is contained inside the pressure vessel.

One or more embodiments of the second aspect may include one or several features from the following itemized list:.

According to a third aspect of the present disclosure, there is provided a method for refueling a nuclear reactor featuring unloading a first fuel unit by removing a fuel and control system as one unit from the reactor core, and reloading a second fuel unit by inserting a fuel and control system as one unit into the reactor core.

One or more embodiments of the third aspect may include one or several features from the following itemized list:.

According to a fourth aspect of the present disclosure, there is provided a method of operating the nuclear reactor featuring the fuel and control system where the reactor core is subject to a boron free operation.

Considerable benefits are gained with the aid of the novel fuel and control system. The fuel and control system ensures that at least the control rod assembly, the drive motor and the fuel unit move as one unit to allow for convenient removal of the fuel unit. The fuel and control system mitigates the criticality safety challenges associated with reactors operating without soluble boron primarily by eliminating the need to remove individual components such as the drive assembly, which could lead to the inadvertent removal of the neutron-absorbing control rods. This enables the fuel and control rod system to be designed in such way, that the reactor cannot become critical during reloading operations. This is ensured by two factors. First, the control rod assembly is maintained in the fuel unit when the fuel and control system is moved as a single unit. Second, the design of the components prevents the control rod assembly to be withdrawn from the fuel unit by actuating the drive unit, since the electric connections have to be disconnected before accessing the core. Further, the fuel and control system simplifies the reloading operations by integrating all reactivity control and instrumentation systems into a single modular component. The fuel and control system enables combining various attractive options in reactor design: boron-free operation and in-vessel control rod drives, the combination of which has been previously limited by conflicting constraints in known solutions.

In the following certain exemplary embodiments are described in greater detail with reference to the accompanying drawings, in which:.

"Fuel unit" is known as a fuel assembly in the field of nuclear engineering. "Electrical connector" refers to an electrical connection, for example electrical leads or wires which may connect to a socket or other leads of another component. "Electrical connector counterpart" refers to a socket or another electrical connection, for example an electrical connection meant to connect the ends of electrical leads. "Attachment" without the connotation of "electrical" may refer to a physical attachment between surfaces or components and may refer to mating surfaces between surfaces or components.

In the present context expressions "fuel and control system" and "fuel and control module" can be used interchangeably.

<FIG> illustrates a nuclear reactor <NUM> in accordance with at least some embodiments. The nuclear reactor <NUM> comprises a reactor core <NUM> encased in a pressure vessel <NUM>, which in turn comprises a lid <NUM>. The reactor core <NUM> is located at a lower section of the pressure vessel <NUM>. The pressure vessel <NUM> defines an inner volume of the nuclear reactor <NUM>. The reactor core <NUM> is located inside the pressure vessel <NUM>. A plurality of fuel and control systems <NUM> are located inside the pressure vessel <NUM>. The fuel and control system <NUM> comprises a drive assembly <NUM> and a fuel unit <NUM>. According to this illustrated embodiment the drive assembly <NUM> is located inside the pressure vessel <NUM>. While in operation, the fuel unit <NUM> of each fuel and control system <NUM> is located in the lower section of the pressure vessel <NUM>, in which the fuel units <NUM> are gathered together to make up the reactor core <NUM>.

<FIG> and <FIG> illustrate the fuel and control system <NUM>. The fuel and control system <NUM> has the drive assembly <NUM>, as mentioned before, a frame <NUM>, a control rod assembly <NUM>, and the fuel unit <NUM>.

<FIG> illustrates the drive assembly. According to the illustrated embodiment, the drive assembly <NUM> has a drive motor frame <NUM> and a drive motor <NUM> located inside the drive motor frame <NUM>. The drive motor frame <NUM> surrounds the drive motor <NUM> to hold the drive motor <NUM> in place and provides drive motor frame <NUM> attachments to other components. The drive motor frame <NUM> is rigidly attached to a drive flange <NUM>. The drive motor frame <NUM> and the drive flange <NUM> may be attached by welding or the drive motor frame <NUM> and drive flange <NUM> may be cast as a single component or may be assembled with bolts or other fasteners. The drive flange <NUM> enables an attachment between the drive assembly <NUM> and the frame <NUM>. The drive flange <NUM> has a first frame attachment <NUM> that provides the attachment, which is a temporary attachment. The drive flange <NUM> has a drive motor <NUM> electrical connector <NUM> and an instrumentation opening <NUM>. The electrical connector <NUM> may be an inductive connector.

According to the illustrated embodiment <FIG>, the drive assembly <NUM> has a linear translator <NUM> coaxially attached to the drive assembly. The drive assembly <NUM> has a linear translator opening <NUM> located coaxially with the drive motor. The linear translator opening <NUM> extends through the drive motor <NUM> where the linear translator <NUM> translates through. The linear translator opening <NUM> extends through the drive motor <NUM> so that the drive motor <NUM> is wrapped around the outer surface of the linear translator <NUM>. The linear translator <NUM> has a shaft opening <NUM> which extends from at a first linear translator end to a second linear translator end. At the second linear translator end, there is an electromagnet <NUM> in which the shaft opening <NUM> extends through.

<FIG> illustrates the frame <NUM>. According to the illustrated embodiment the frame <NUM> has a profile <NUM>, a frame upper section <NUM> and a frame lower section <NUM>. The frame <NUM> has a frame height, which is the distance between the frame upper section <NUM> and the frame lower section <NUM>. The frame <NUM> has an instrumentation guide <NUM>, which may be in the form of a hollow tube, rod or a cover. The instrumentation guide <NUM> acts as a guide for the instrumentation electrical wires, or wiring, and holds them in place. According to at least some embodiments, instrumentation guide <NUM> is permanently attached to the frame <NUM> or is incorporated into the frame <NUM>, and the instrumentation guide <NUM> may be manufactured as part of the frame <NUM>. The instrumentation guide <NUM> also serves the purpose to not disrupt the movement of other components such as the control rod assembly <NUM>. For example, if the instrumentation electrical wires were loose they could tangle with a plurality of control rods <NUM> and cause an unsafe malfunction in the control rod assembly <NUM>, such as preventing the control rods <NUM> from travelling downwards. At a first instrumentation guide end there is an instrumentation electrical connector <NUM>, which is attached to the instrumentation electrical wires. The instrumentation guide <NUM> continues through the frame lower section <NUM>. At a second instrumentation guide end there is an instrumentation for taking measurements. The second instrumentation guide end and the instrumentation may be located in the fuel unit <NUM>. The instrumentation guide end may be split to accommodate for the attachments between components, such as the fuel unit <NUM> and the frame <NUM>. The instrumentation guide <NUM> may branch into different branches to provide passage for electrical wiring to other sensors, such as a temperature sensor in other locations in the fuel and control system <NUM>. For example, a temperature sensor may be located near the frame <NUM>. At the frame lower section <NUM> there are a plurality of control rod openings <NUM> and there may be a mesh <NUM>.

According to the illustrated embodiment <FIG>, at the frame upper section <NUM> there is a first frame attachment counterpart <NUM> that attaches, temporarily, to the first frame attachment <NUM> of the drive assembly. According to the illustrated embodiment, the first frame attachment counterpart <NUM> is the form of a pin and the first frame attachment <NUM> is in the form of a hole which guides the first frame attachment counterpart <NUM> into the first frame attachment <NUM>. This manner of attaching provides a temporary attachment that hold the drive assembly <NUM> and the frame <NUM> in place when the reactor is in operation.

As is shown in <FIG>, the frame <NUM> is a distinct component from the fuel unit <NUM>. The frame lower section <NUM> is used to attach the frame <NUM> to the fuel unit <NUM>. More specifically, the frame <NUM> sits atop the fuel unit <NUM>. The fuel unit <NUM> preferably contains a top crate best shown in <FIG> for attachment to the frame lower section <NUM>.

<FIG> illustrates the control rod assembly <NUM>. The control rod assembly <NUM> has a shaft <NUM> at a first control rod assembly end, a plate <NUM> and a plurality of control rods <NUM> at a second control rod assembly end. The control rods <NUM> are rigidly attached to the shaft <NUM> by a plurality of supports <NUM>. The plate <NUM>, which is made of a material known to attach to electromagnets, for example, a ferromagnetic material, attaches at least temporarily to the electromagnet <NUM> of the drive assembly. Thus, the attachment between the plate <NUM> and the electromagnet <NUM> provide an attachment between the control rod assembly <NUM> and the drive assembly. In at least some embodiments, at least a portion of the shaft <NUM> is coaxially located inside the shaft opening <NUM> of the drive assembly. The length of the shaft <NUM> is approximately the same length as the range of movement, i.e. the height of the fuel unit <NUM>. The control rods <NUM> are arranged so that they are guided through the control rod openings <NUM> of the frame <NUM>.

<FIG> illustrates a view of the fuel unit <NUM>. According to at least some embodiments, the control rods <NUM> interact with the fuel unit <NUM> and are placed inside the fuel unit <NUM>. The control rods <NUM> may be placed inside the fuel unit <NUM> where most of a length of the control rods <NUM> are inside the fuel unit <NUM>. The length of the control rods <NUM> may be the same or slightly less as the height of the fuel unit <NUM>. The length of the control rods <NUM> must be long enough to be able to cover the entirety of an active height of the fuel unit <NUM>. As shown in <FIG>, a fuel unit upper section is attached to the frame lower section <NUM>. This attachment is secured to allow the fuel unit <NUM> to be moved with the frame <NUM>.

<FIG> illustrate a view of a radial reflector <NUM>. The nuclear reactor <NUM> comprises the radial reflector <NUM> surrounding the reactor core <NUM>. The radial reflector <NUM> may have a radial reflector upper surface <NUM>. During operation, a support grid plate <NUM> may be located on top of the radial reflector upper surface <NUM> and above the reactor core <NUM>. The support grid plate <NUM> has support grid plate openings, which are located above each fuel and control system <NUM>. The support grid plate <NUM> provides structural support for other components, therefore the nuclear reactor <NUM> may have another arrangement known per se to support the fuel and control systems <NUM>. According to the illustrated embodiment, a connector grid plate <NUM> is placed on top of the support grid plate <NUM>. According to another embodiment, the connector grid plate <NUM> is located below the support grid plate <NUM>. The connector grid plate <NUM> is a component with a body that is at least partially solid and at least partially hollow. The connector grid plate <NUM> has a plurality of wires for distributing electric power and electric connections to a plurality of fuel and control systems <NUM>, where the wires may be located within the hollow portions of the connector grid plate <NUM>. According to at least some embodiments, the plurality of wires of the connector grid plate <NUM> run along and inside the body of the connector grid plate <NUM>. The connector grid plate <NUM> has a plurality of connector grid plate openings <NUM> where each opening <NUM> is located above a fuel and control system <NUM>. The support grid plate openings may be the same or similar size than the connector grid plate openings <NUM>. The connector grid plate <NUM> has a plurality of drive motor and instrumentation electrical connector counterparts <NUM>, in which each connector grid plate opening <NUM> has one drive motor and instrumentation electrical connector counterpart <NUM>. Each drive motor and instrumentation electrical connector counterpart <NUM> is configured to connect to the drive motor electrical connector <NUM> and the instrumentation electrical connector <NUM> of each fuel and control system <NUM>. According to at least some embodiments, the drive motor and instrumentation electrical connector counterpart <NUM> has one socket or appropriate counterpart for each of the drive motor electrical connector <NUM> and the instrumentation electrical connector <NUM>. In other words, the drive motor and instrumentation electrical connector counterpart <NUM> may have two sockets or appropriate counterparts.

According to at least some embodiments, at least a portion of the fuel and control system <NUM> is located under the grid plates <NUM>, <NUM>. A portion of the drive assembly <NUM> and the control rod assembly <NUM> may be located above the grid plates <NUM>, <NUM>, however the connector grid plate opening <NUM> and the support grid plate opening are openings where the entire structure of each of the drive assembly, the frame <NUM>, the fuel unit <NUM>, and the control rod assembly <NUM>, cannot go through due to the size of these openings. According to at least some embodiments, the width of the grid plate opening <NUM> is smaller than the width of the frame <NUM> and the width of the drive flange <NUM>.

The connector grid plate <NUM> has a main electrical connector <NUM>, which connects to a main electrical connector counterpart <NUM>. The nuclear reactor <NUM> may have a connector block <NUM> where, according to the illustrated embodiment <FIG>, the main electrical connector counterpart <NUM> is located on. The main electrical connector counterpart <NUM> may be an inductive connector. The nuclear reactor <NUM> has electric cables <NUM> which are connected to a power source on a first electric cable end and to the connector block <NUM> at a second electric cable end. A portion of these electric cables <NUM> are the cables used to transmit data from the instrumentation.

The following paragraphs describe the usage of components of the fuel and control system <NUM>.

The nuclear reactor <NUM> as illustrated in <FIG> has the pressure vessel <NUM> in which the fuel and control system <NUM> has a drive assembly <NUM> located inside the pressure vessel <NUM>. This means that the drive assembly <NUM> is operated in a fluid contained in the pressure vessel <NUM>. The fluid acts as the coolant for the reactor core.

During operation, the drive motor and instrumentation electrical connector counterpart <NUM> is connected to the drive motor electrical connector <NUM> and the instrumentation electrical connector <NUM>. While these connectors are connected, the main electrical connector <NUM> and the main electrical connector counterpart <NUM> are connected and therefore power and electrical connections are being supplied by the electric cables <NUM> to the drive motor <NUM> and the instrumentation via the main connector and the drive motor electrical connector <NUM>. As a result, the connector grid plate <NUM>, when installed, provides an electrical connection to the drive motor <NUM> and the electromagnet <NUM>, provides transmission of data and other signals to and from the instrumentation, and provides electric current to power the instrumentation. The connector grid plate <NUM> has a body that is at least partially solid. According to at least some embodiments, when the connector grid plate <NUM> is installed, each of the drive motor and instrumentation electrical connector counterparts <NUM> connects to the corresponding drive motor electrical connector <NUM> and the instrumentation electrical connector <NUM> of each fuel and control system <NUM>. This manner of connecting allows the electrical connections to be made all at once (due to the at least partially solid body of the connector grid plate <NUM>), rather than having to connect the electrical connection individually. As a result, a function of the connector grid plate <NUM> is to make electric connections time-efficient. The connector grid plate <NUM> acts as a bridge between the electric cables <NUM> and the drive motor electrical connector <NUM> with the instrumentation electrical connector <NUM>. Therefore, the installment and detachment of the connector grid plate <NUM> determines whether the electrical connections provided to the drive motor <NUM> and the instrumentation are connected or not. When the connector grid plate <NUM> is installed and providing power and electric connections, the connector grid plate <NUM> is in a connected state.

The connector grid plate <NUM> also allows signals of data to transmit from the instrumentation to a receiving device for receiving data which is located outside of the nuclear reactor <NUM>.

The electric cables <NUM> may be connected directly to the main electrical connector counterpart <NUM> so that when the main electrical connector counterpart <NUM> is in connection with the main electrical connector <NUM>, the electric cables <NUM> provide electric power to the connector grid plate <NUM> from the power source.

When the coolant is a liquid, the electric connectors and electric connector counter parts are "wet-mated", meaning that the connection can be established while submerged in the coolant.

When the grid plates <NUM>, <NUM> are attached to the nuclear reactor <NUM> and are therefore electrically connected and in operation, the grid plates <NUM>, <NUM> prevent the drive assembly, the frame <NUM>, and the fuel unit <NUM> from being transported. In other words, the grid plates <NUM>, <NUM> and the fuel and control system <NUM> are arranged where the fuel and control system <NUM> cannot be removed from the pressure vessel <NUM> unless the grid plates <NUM>, <NUM> are removed first. Therefore the grid plates <NUM>, <NUM> hold the drive assembly <NUM>, the frame <NUM>, and the fuel unit <NUM> in place. The drive assembly <NUM> may cause the control rod assembly <NUM> to be at least partially withdrawn from the fuel unit <NUM>, however the grid plates <NUM>, <NUM> hold the drive assembly <NUM> in place, and the control rod assembly <NUM> is unable to travel through the drive assembly <NUM> due to the electromagnet <NUM> and supports <NUM> not fitting through the linear translator opening <NUM>. Further, the control rod assembly <NUM> can move the distance of the active height within the fuel unit <NUM>.

When the fuel units <NUM> are ready to be replaced, the refueling operation commences. The nuclear reactor <NUM> is first manually shut down, by driving the control rods <NUM> to the lowered position. The lid <NUM> of the pressure vessel <NUM> can be opened to access the reactor core <NUM> and the fuel and control system <NUM>. Subsequently, the grid plates <NUM>, <NUM> are removed and thereafter the grid plates <NUM>, <NUM> are in a disconnected state. The disconnection of the connector grid plate <NUM> causes the plurality of drive motor and instrumentation electrical connector counterparts <NUM> to disconnect from the drive motor electrical connector <NUM> and the instrumentation electrical connector <NUM> of each fuel and control system <NUM> in the reactor core <NUM> in one instance. Further, the main electrical connector <NUM> and the main electrical connector counterpart <NUM> are no longer connected and therefore no power is being supplied by the electric cables <NUM>. This ensures that there is no electric power in the fuel and control system <NUM> and in the reactor core <NUM> when the connector grid plate <NUM> is removed. To summarize, the disconnected state of the grid plate <NUM> causes no power to be provided to the drive motor, the electromagnet <NUM> and the instrumentation, and prevents the instrumentation to transmit or receive signals.

As there is no power provided to the drive motor <NUM> and the electromagnet <NUM> is no longer energized, the control rods <NUM> cannot be withdrawn from the lowered position, inadvertently or otherwise. This is crucial because this ensures that all control rods <NUM> are fully inserted, and the reactor remains in a safe shutdown state. It is also crucial that the control rods <NUM> are in a lowered position while the core is being disassembled, and the fuel and control system <NUM> is being transported, or more specifically unloaded and loaded.

A reloading machine, not shown in the figures, can make contact with the frame <NUM> in order to remove the fuel and control system <NUM> out of the reactor core <NUM>. The removal of the fuel and control system <NUM> out of the reactor core <NUM> is called a first transportation state. In other words, when the reloading machine is lifting the frame <NUM>, the following components are being lifted also: the drive assembly, the control rod assembly <NUM> and the fuel unit <NUM>. Therefore the drive assembly, the frame <NUM>, the control rod assembly <NUM> and the fuel unit <NUM> move as one single unit during the first transportation state. This is accomplished by the attachment the frame <NUM> makes between the drive assembly <NUM> and the fuel unit <NUM>. According to at least some embodiments, the reloading machine moves the fuel and control system <NUM> in the direction indicated as Z in <FIG>. According to at least some embodiments, the reloading machine removes one fuel and control system <NUM> at a time.

As mentioned previously, the frame <NUM> has a frame height. The frame <NUM> creates a space which is open or preferably at least partially enclosed. The frame height is a certain length to allow the control rod assembly <NUM> to travel at least partially within the space of the frame <NUM> while the fuel and control system <NUM> is in operation in the pressure vessel <NUM>. The frame height therefore affects the range of movement of the control rod assembly <NUM> and the control rods <NUM>. The movement of the control rod assembly <NUM> and the control rods <NUM> while in operation is for changing the neutron absorption rate in the reactor core <NUM>. This movement may be referred to as control movement.

According to at least some embodiments, the reloading machine is designed in such way that it cannot make contact with and lift the drive assembly, thereby disconnecting it from the frame <NUM> Also, the reloading machine is designed to make contact with and lift the frame <NUM>. According to <FIG>, <FIG>, <FIG>, the drive assembly <NUM> has four reloading machine openings <NUM> through which the reloading machine reaches into and then subsequently attaches to the frame <NUM> at the frame upper section <NUM>. The drive assembly <NUM> may have no reloading machine openings <NUM> or less than four or more than four reloading machine openings <NUM> in order to accommodate the prongs or attachment mechanism of the reloading machine to the frame <NUM>. The reloading machine openings <NUM> also serve the function to let coolant flow through the fuel and control system <NUM>. The shape of the reloading machine is designed where the reloading machine avoids making an attachment with the drive assembly <NUM> so that when the reloading machine is moved upwards, the reloading machine does not cause a situation where the drive assembly <NUM> is lifted out of the reactor core <NUM> without the frame <NUM>. In other words, a function of the reloading machine is to lift the frame <NUM> and cause the drive assembly <NUM> to move with the frame <NUM>. At this stage, the electromagnet <NUM> would be disconnected, however the manner in which the reloading machine avoids making an attachment with the drive assembly, ensures that the drive assembly <NUM> is unable to be removed from the frame <NUM> and possibly cause the control rods <NUM> to be withdrawn away from the fuel unit <NUM> while the fuel unit <NUM> is in the reactor core <NUM>, which would compromise criticality safety.

The arrangement of the fuel and control system <NUM> is designed to ensure criticality safety because the fuel and control system <NUM> is lifted as the frame <NUM> is lifted by the reloading machine. The reloading machine comes into contact with the frame <NUM> at a contact point, not shown in the figures. The contact point may be at the frame upper section <NUM>. Since the frame <NUM> is attached to the drive assembly, the drive assembly <NUM> moves with it. According to the illustrated embodiments <FIG>, <FIG>, and <FIG>, the drive assembly <NUM> is placed on top of the frame <NUM> and attached at the first frame attachment <NUM> and at the first frame attachment counterpart <NUM>. Since the drive assembly <NUM> is on top of the frame <NUM> and since the attachments keep the frame <NUM> and drive assembly <NUM> secure, the drive assembly <NUM> moves with the frame <NUM>. The fuel unit <NUM> is attached to the frame <NUM>, and therefore the fuel unit <NUM> also moves with the frame <NUM> when the frame <NUM> is being transported by the reloading machine.

The fuel unit <NUM> has a plurality of control rod guide tubes for the control rods <NUM> to travel into, and where the control rods <NUM> can travel at least most of the height of the fuel unit <NUM>. Located at the bottom of each control rod guide tube, is a dashpot or stopping surface that defines an end of the control rod guide tube. The stopping surface prevents each control rod <NUM> from travelling further downward. The control rod assembly <NUM> may move downward until a bottom end of the control rod comes into contact with the stopping surface. When the control rods <NUM> come into contact with the stopping surface, the control rods <NUM> are in a lowered state and thus rest at the stopping surface. As a result, the stopping surface allows each control rod <NUM> to stay in place by gravity. Therefore, when the fuel unit <NUM> is transported, the control rods <NUM> and the control rod assembly <NUM> is transported with the fuel unit <NUM>. The active height of the fuel unit <NUM> may determine the frame height since the control movement range within the fuel unit <NUM> may be the same or substantially the same as the control movement range within the space of the frame <NUM>.

To summarize the attachments within the fuel and control system <NUM> during the first transportation state, the frame <NUM> is attached to both the drive assembly <NUM> and the fuel unit <NUM>. Further, the control rod assembly <NUM> is in connection with the fuel unit <NUM> when the control rods <NUM> are in the lowered state. As a result, when the frame <NUM> is transported, the transporting of the frame <NUM> causes the drive assembly, the fuel unit <NUM>, and the control rod assembly <NUM> to be transported also. The structural integrity of the frame <NUM> or the profile <NUM> enables the fuel and control system <NUM> to transport as a one unit.

Once the reloading machine has a secured attachment with a fuel and control system <NUM>, an unloading stage commences and therefore the reloading machine transports the fuel and control system <NUM>, during the first transportation state, out of the reactor core <NUM> and out of the pressure vessel <NUM>. According to at least some embodiments, the reloading machine lifts the fuel and control system <NUM> upwards while exiting the reactor core <NUM> and the pressure vessel <NUM>. Then, the reloading machine may transport the fuel and control system <NUM> in a direction necessary to place the fuel and control system <NUM> onto a support rack, not shown in the figures, to hold the fuel and control system <NUM> in place. Once the support rack holds the fuel and control system <NUM> in place, the attachment between the reloading machine and the fuel and control system <NUM> may be detached and thus defines the end of the process of the first transportation state, according to at least some embodiments.

The reloading machine can repeat this process and cause other fuel and control systems <NUM> to be in a first transportation state and thus be unloaded from the pressure vessel <NUM> to the support rack.

The support rack may hold many fuel and control systems <NUM> in place. The support rack is designed in such way, that criticality safety is ensured by geometry. This means that there is enough distance between the fuel units <NUM> to prevent the neutron chain reaction from being started even when the control rod assemblies <NUM> are removed from the fuel units <NUM>. Alternatively, criticality safety can be ensured by placing neutron absorbing materials in the structures of the support rack. <FIG> illustrates that the fuel and control systems <NUM> may be positioned to their sides, however <FIG> is for illustration purposes and the figure does not depict the distance in which each of the fuel and control system <NUM> may be distanced from each other while outside of the reactor core <NUM>.

During the refueling process, the fuel units <NUM> of the fuel and control system <NUM> that are removed from the reactor core <NUM> are fuel units that may be used again for the loading process or spent fuel units <NUM>, which become waste. This depends on the amount of cycles of usage the fuel unit <NUM> has been subject to, until the fuel unit <NUM> becomes waste, which may be, for example, <NUM> times. The fuel unit <NUM> that has been used for at least one cycle or is subject to become waste as a spent fuel unit, is referred to as a first fuel unit <NUM>. <FIG> depicts a plurality of first fuel units <NUM>. The drive assembly <NUM> and the control rod assembly <NUM> may be reused. After the fuel and control system <NUM> has been removed from the reactor core <NUM>, and placed on the support rack, the drive assembly <NUM> and the control rod assembly <NUM> are separated from the frame <NUM> and the first fuel units <NUM>.

<FIG> illustrates the drive assembly <NUM> and the control rod assembly <NUM> being separated from the fuel unit <NUM> and fuel assembly. When the drive assembly <NUM> and the control rod assembly <NUM> are transported away from the fuel unit <NUM>, the drive assembly <NUM> and the control rod assembly <NUM> are in a second transportation state.

During the second transportation state the drive assembly <NUM> and the control rod assembly <NUM> are transported by a replacing machine. The replacing machine comes into contact at a second contact point located on the drive assembly. The replacing machine transports the drive assembly <NUM> and the control rod assembly <NUM>. As the drive assembly <NUM> and the control rod assembly <NUM> are transported during the second transportation state, the drive assembly <NUM> and the frame <NUM> are detaching. As a result, the first frame attachment <NUM> and the first frame attachment counterpart <NUM> detach. According to at least some embodiments, the first frame attachment <NUM> and the first frame attachment counterpart <NUM> are in the form of a hole and a pin, respectively. Therefore, as the drive assembly <NUM> is transported during the second transportation state, the hole <NUM> moves out of the pin <NUM> and therefore the drive assembly <NUM> detaches from the frame <NUM>. Therefore, the first frame attachment <NUM> and the first frame attachment counterpart <NUM> achieve an attachment during the first transportation state, and they are able to detach during the second transportation state.

The drive assembly <NUM> and the control rod assembly <NUM> are designed to be transported as one unit during the second transportation state. Thus, there is an attachment made between the drive assembly <NUM> and the control rod assembly <NUM> during the second transportation state. According to at least some embodiments, the replacing machine provides power to the drive assembly <NUM> and causes the electromagnet <NUM> to attach to the plate <NUM> of the control rod assembly <NUM>. This way, as the replacing machine transports the drive assembly, the control rod assembly <NUM> is transported also. In addition, the replacing machine may mechanically attach, even if electric power is lost, to the control rod assembly <NUM> or shaft <NUM>, where the shaft <NUM> protrudes through the shaft opening <NUM>, in order to avoid the control rod assembly <NUM> from falling down in case electric power is lost during the second transport state.

According to the illustrated embodiment <FIG>, the replacing machine transports the drive assembly <NUM> and the control rod assembly <NUM> in a direction, noted as Y, away from the frame <NUM> and the first fuel unit <NUM>. According to <FIG>, the drive assembly <NUM> and the control rod assembly <NUM> are transported, in the second transportation state, into a fuel unit, which will be loaded into the reactor core <NUM>, and into a new frame <NUM>. This fuel unit is referred to as a second fuel unit <NUM>. The second fuel unit <NUM> may be a fresh fuel unit or a fuel unit that has previously been used or cycled through unless it is at the end of its designed life. The second fuel <NUM> unit differs from the first fuel unit <NUM> in that the second fuel unit <NUM> is prepared to be loaded or is loaded into the reactor core <NUM> in the third transportation state, whereas the first fuel unit <NUM> is unloaded from the reactor core <NUM> in the first transportation state. A first fuel unit <NUM> that is not at the end of its designed life may become a second fuel unit <NUM> after the drive assembly <NUM> and the control rod assembly <NUM> are removed. The new frame <NUM> may be a reused frame <NUM>. The frame <NUM> may be reused or may be waste. According to at least some embodiments, the frame <NUM> is not detached from the fuel unit <NUM> and both the frame <NUM> and the fuel unit <NUM> are relocated for waste management.

During the second transportation state, the replacing machine guides the drive assembly <NUM> and the control rod assembly <NUM> into the other frame <NUM> and the corresponding second fuel unit <NUM>. According to at least some embodiments, the replacing machine lowers the drive assembly <NUM> and the control rod assembly <NUM> where the control rods <NUM> are guided into the control rod guides and then further lowered and guided into the second fuel unit <NUM>. As the control rods <NUM> are guided into the second fuel unit <NUM>, the first frame attachment <NUM> and first frame attachment counterpart <NUM> will be attached. According to at least some embodiments, the first frame attachment <NUM> and the first frame attachment counterpart <NUM> are in the form of a hole and a pin, respectively, and the hole is guided to surround the pin. The function of the first frame attachment <NUM> and the first frame attachment counterpart <NUM> is to provide an attachment, or a mating of surfaces, where the drive assembly <NUM> can be moved with the frame <NUM> and moved without falling to one side or shifting to one side when the frame <NUM> is moved. After the control rods <NUM> are in the second fuel unit <NUM> and the first frame attachment <NUM> and the first frame attachment counterpart <NUM> are attached, the replacing machine is detached from the drive assembly, causing the end of the second transportation state. If the replacing machine provides power to the drive assembly, detaching the replacing machine will ensure that there is no power provided which could cause the control rods <NUM> to move out of the fuel unit <NUM>.

The replacing machine can repeat this process and cause other drive assemblies <NUM> and control rod assemblies <NUM> to be in the second transportation state and thus be moved from other first fuel units <NUM> to other second fuel units <NUM>.

The new fuel and control system <NUM>, which has the second fuel unit <NUM>, the drive assembly, the control rod assembly <NUM>, and the frame <NUM>, is ready to be transported in a third transportation state to be loaded into the pressure vessel <NUM>. This is the loading stage. The reloading machine comes into contact with the new fuel and control system <NUM> in the same or similar manner as in the unloading stage. The reloading machine transports the new fuel and control system <NUM> from the support rack to a location above the pressure vessel <NUM> and lowers the new fuel and control system <NUM> into the pressure vessel <NUM> and into the reactor core <NUM>. Once the new fuel and control system <NUM> is accurately placed into the correct position inside the reactor core <NUM>, the reloading machine detaches from the new fuel and control system <NUM>. The reloading machine can transport more new fuel and control systems <NUM> into the pressure vessel <NUM>. The grid plates <NUM>, <NUM> are out of the way, and do not interfere, while the fuel and control systems <NUM> are loaded and unloaded.

After the reloading operation has been completed, the grid plates <NUM>, <NUM> are placed above the fuel and control systems <NUM>. The grid plates <NUM>, <NUM> are installed and are thereafter in a connected state. Now the control rod assembly <NUM> is able to translate within the fuel unit <NUM> to regulate the neutron absorption rate. As mentioned before, the installment of the connector grid plate <NUM> enables power and electrical connections to be provided to the drive motor <NUM> and the instrumentation, enables the electromagnet <NUM> to be energized and allows the instrumentation to transmit and receive signals.

A person skilled in the art may foresee several variants of the above described embodiment.

For example, another embodiment comprises the reloading machine having prongs that reach into the reloading machine openings <NUM>. The reloading machine may make the attachment to the frame <NUM> via a known mechanism for grasping frames. According to an embodiment, the reloading may have prongs that reach into the reloading machine openings <NUM> and subsequently each prong will translate outward to grasp onto the frame <NUM>. The prongs may reach under a lip located on the frame <NUM> that when the loading machine is lifted the prongs are lifting the frame <NUM> via the lip. According to an embodiment, the drive assembly <NUM> may not have a reloading machine opening <NUM>, and the reloading machine may reach around to an outer side surface of the frame <NUM> in order to attach to and lift the frame <NUM>. According to another embodiment, the reloading machine may make an attachment with the frame <NUM> via a snap fit.

The operations performed during the third transportation state may be similar or the same as the reverse order of operations performed during the first transportations state.

The drive motor frame may have the first frame attachment <NUM> and thus a drive flange <NUM> may not be necessary to make an attachment between the drive assembly <NUM> and the frame <NUM>.

The linear translator <NUM> may be a lead screw, the drive motor <NUM> joined with the linear translator <NUM> may make up a linear actuator or another device for translating linearly known per se. The linear translator <NUM> may have a threaded section. The drive motor <NUM> may be a brushless DC motor, such as a step motor. The drive unit may include a reduction gear to increase the torque.

The first frame attachment <NUM> may be a hole and the first frame attachment counterpart <NUM> may be a pin so that the frame <NUM> and the drive assembly <NUM> may be attached to one another, but also allow them to separate. The attachment between the first frame attachment <NUM> and the first frame attachment counterpart <NUM> may also be in the form of a temporary attachment known for attaching two parts. This attachment may be rigidly attached temporarily or may be where a surface of the drive flange <NUM> rests on a surface of the frame <NUM>. This attachment may be made by a fastener which is unfastened before the second transportation state to allow the drive assembly <NUM> to be transported when the frame <NUM> is transported and to allow the drive assembly <NUM> to detach from the frame <NUM> during the second transportation state.

The instrumentation electrical connector <NUM> connects to the instrumentation electrical connector counterpart, in which the instrumentation electrical connector counterpart is located in the drive motor and instrumentation electrical connector counterpart <NUM>. The drive assembly <NUM> may have the instrumentation opening <NUM> to allow these connections to meet, or may have more connectors and connector counterparts to provide electrical connections without the use of an opening. The instrumentation may comprise a plurality of sensors.

The cross section of the fuel unit <NUM> may have four sides or may be hexagonal or other known shapes for fuel units. Thus, the frame <NUM> and other components, for example the drive flange <NUM>, may have an outer surface shape, such as a hexagonal shape, which may conform to the shape of the fuel unit <NUM>.

The frame <NUM> lower section may be at a bottommost surface of the frame <NUM> or above the bottommost surface of the frame <NUM>.

The subcomponents of the frame <NUM> may be manufactured as one solid component. The profile <NUM> may have a profile as illustrated in <FIG> or may be a plate having enough structural integrity to prevent the frame <NUM> from falling to one side, or brake, and be able to transport the fuel and control system <NUM> without the profile <NUM> or frame from fracturing significantly.

The fuel and control system <NUM> may be powered by the connector grid plate <NUM>, wires, or by other known methods.

The fuel unit upper section and the frame lower section <NUM> may be attached by a weld, fasteners, or other attachments known per se for attaching metal parts. The attachment between the fuel unit upper section and frame lower section <NUM> may be temporary where the attachment is secured during the normal operation of the nuclear reactor <NUM>, the first transportation state, and the second transportation state and where the attachment can be detached and thus the frame can be reused and the fuel unit <NUM> taken to waste management.

In addition, various embodiments and examples of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention, which is defined by the claims.

Claim 1:
A fuel and control system (<NUM>) for a nuclear reactor (<NUM>), comprising:
- a control rod assembly (<NUM>),
- a drive assembly (<NUM>), which is attached to the control rod assembly (<NUM>) for reactivity control, and
- a fuel unit (<NUM>),
characterized by a frame (<NUM>), which attaches the drive assembly (<NUM>) to the fuel unit (<NUM>) and provides a space for reactivity control movement of the control rod assembly (<NUM>) so that the frame (<NUM>), the fuel unit (<NUM>), the drive assembly (<NUM>) and the control rod assembly (<NUM>) are integrated as one unit, and so that the fuel and control system (<NUM>) is configured to be loaded into and unloaded out of the nuclear reactor (<NUM>) as one unit.