Nuclear reactor control system

Abstract

A reactor control system (100) for a nuclear fission reactor system comprising a reactor unit (300) having a core (302) with a central axis (320) extending along the length of the core (302). The reactor unit (300) comprises a first region (310) disposed within the core (302) and a second region (312) disposed outside the core (302). The control system (100) comprises a control duct (200) having a first portion (210) configured to extend through the first region (310) and a second portion (220) configured to extend through the second region (312). The duct (200) is filled with a series of control units (400), each of which is configured to travel along the control duct (200).

Description

Technical Field

[0001] The present disclosure relates to a nuclear reactor control system.

[0002] In particular, the present disclosure relates to a nuclear reactor control system for a nuclear fission reactor system comprising a nuclear reactor unit.

Background Art

[0003] One aspect of all graphite moderated nuclear fission reactor units is that due to the low moderation ability of graphite, their core sizes are proportionally significantly larger for a given power capacity compared to water moderated reactors. Thus, the nuclear reactor unit and associated components, unlike water cooled reactors, generally influence the overall sizing of the power generation package.

[0004] As an example, an example of a graphite moderated nuclear fission reactor 1 (General Atomics GT-MHR) is shown in FIG. 1. Common to many designs, this arrangement has a conventional linear control rod 2 that must be placed on top of the reactor vessel 3. As is well known, the control rod must extend in and out of the nuclear reactor. Thus, a space equal to the core height must be available to enable complete removal of the control rod from the nuclear reactor.

[0005] Removal of the control rod support structure 4 reduces the size and weight of the nuclear reactor unit 1. In addition, reducing the size of the nuclear reactor unit reduces the overall volume of space required to house it, and as a result, reduces the amount of material, and thus the weight, required to house the power unit. In some applications, this is important since space and weight are precious. For example, reducing the size of the nuclear reactor unit within a nuclear powered ship (especially a submarine, e.g., a submarine) contributes to the goal of creating space for other equipment or making the ship smaller and lighter.

[0006] Accordingly, a configuration that enables a more compact reactor unit design for the same power output and control level is highly desirable. SUMMARY OF THE INVENTION

[0007] According to the present disclosure, an apparatus and a system / method as recited in the appended claims are provided. Other features of the present invention will become apparent from the dependent claims and the following description.

[0008] Accordingly, a reactor control system (100) for a nuclear fission reactor system comprising a reactor unit (300) having a core (302) whose central axis (320) extends along the length of the core (302) may be provided. The reactor unit (300) may comprise a first region (310) provided within the core (302) and a second region (312) provided outside the core (302). The control system (100) may comprise a control duct (200) having a first portion (210) configured to extend through the first region (310) and a second portion (220) configured to extend through the second region (312). The duct (200) may be filled with a series of control units (400), each of the control units (400) being configured to travel along the control duct (200).

[0009] The control duct (200) may be configured for the translation of the control units (400) in a first direction D1 and a second direction D2. The first direction D1 may be a traveling direction from the second portion (220) towards the first portion (210). The second direction D2 may be a traveling direction from the first portion (210) towards the second portion (220).

[0010] The control duct (200) may comprise a first arcuate portion (230) extending between the first portion (210) and the second portion (220), and the first portion (210), the first arcuate portion (230), and the second portion (220) of the control duct (200) define a continuous path for the passage of the control units (400) thereby.

[0011] The control duct (200) may comprise a second arcuate portion (240) extending between a first portion (210) and a second portion (220), the second arcuate portion (240) being provided at opposite ends of the first portion (210) and the second portion (220) with respect to the first arcuate portion (230) such that the first arcuate portion (230) is spaced from the second arcuate portion (240) by the first portion (210) and the second portion (220). The first portion (210), the first arcuate portion (230), the second portion (220), and the second arcuate portion (240) of the control duct (200) may thereby define a single continuous loop path for passage of the control unit (400).

[0012] The control system may further comprise a first tank (700) for storing the control unit (400). The control duct (200) may be configured to receive the control unit (400) from the first tank (700) and / or supply the control unit (400) to the first tank (700). The control system may further comprise a second tank (720) for storing the control unit (400). The control duct (200) may be configured to receive the control unit (400) from the second tank (720) and / or supply the control unit (400) to the second tank (720). The first tank (700), the first portion (210), the first arcuate portion (230), the second portion (220), and the second tank (720) may be provided continuously to define a path for passage of the control unit (400).

[0013] Some of the control units (400) may be absorber units (410). Some of the control units may be displacer units (420).

[0014] The absorber unit (410) may not be heavier than the displacer unit (420).

[0015] The control unit (400) is spherical and may have an outer diameter that is the same as or slightly smaller than the diameter of the control duct (200).

[0016] The control system may further include a drive mechanism (600) that is operable to drive the control unit (400) in a first direction D1 along the control duct (200) in a first operating mode and to drive the control unit (400) in a second direction D2 along the control duct (200) in a second operating mode.

[0017] The drive mechanism (600) may include a screw (602) having a track (604) for engagement with the control unit (400) such that when the screw (602) rotates, the control unit (400) is driven along the duct (200).

[0018] The screw (602) may be configured to move between a first position where it is operable to drive the control unit (400) and a second position where a clearance is maintained between the screw (602) and the control unit (400).

[0019] The nuclear reactor control system (100) may further include a check valve mechanism (1100) provided within the control duct (200) and configured to have a first operating mode in which the control unit (400) can move relative to the control duct (200) and a second operating mode in which the control unit (400) is fixed at a predetermined position relative to the control duct (200).

[0020] The control duct (200) may have a substantially constant diameter along its length.

[0021] At least a portion of the second portion (220) of the control duct (200) may have a diameter larger than the diameter of the first portion (210) of the control duct (200). The second portion (220) may be in fluid communication with a pressure source (1000) such that when the screw (602) is in the second position, the control unit (400) is pushed in the first direction D1 by the pressure source.

[0022] A plurality of absorber units (410) may be provided continuously adjacent to each other along the control duct (200) to form a row (416) of absorber units (410). A first plurality of displacer units (420) may be provided continuously adjacent to each other along the control duct (200) to form a first row (422) of displacer units (420). A second plurality of displacer units (420) may be provided continuously adjacent to each other along the control duct (200) to form a second row (424) of displacer units (420). The first row (422) of displacer units (420) may extend from a first end (412) of the row of absorber units (410). The second row (424) of displacer units (420) may extend from a second end (414) of the row of absorber units (410).

[0023] The piston (500) may be provided between the first row (422) of displacer units (420) and the second row (424) of displacer units (420) such that in the first direction D1, the plurality of absorber units (410) are spaced from the piston (500) by the first row (422) of displacer units (420), and in the second direction D2, the plurality of absorber units (410) are spaced from the piston (500) by the second row (424) of displacer units (420).

[0024] The piston (500) can be configured and arranged within the duct (200) such that when the screw (602) is in the second position, the piston (500) acts on the control unit (400) below it to move the control unit (400) along the duct (200).

[0025] The first portion (210) of the control duct (200) can extend substantially parallel to the core central axis (320). The second portion (220) of the control duct (200) can extend substantially parallel to the core central axis (320).

[0026] A fission nuclear reactor system can be provided that includes a nuclear reactor unit (300) and a nuclear reactor control system (100) according to the present disclosure.

[0027] Accordingly, a control system for a fission nuclear reactor is provided that is more compact than conventional designs and significantly reduces the overall size of the included nuclear reactor unit.

[0028] Next, the examples of the present disclosure will be described merely by way of example with reference to the figures.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0030] The present disclosure relates to a reactor control system 100 for a nuclear fission reactor system. The present disclosure also relates to a nuclear fission reactor system comprising a reactor unit 300 and the reactor control system 100 according to the present disclosure.

[0031] For example, the reactor control system of the present disclosure can be used to control a high temperature gas cooled reactor (HTGR). The system can be a direct cycle design in which the core directly heats the working fluid that drives the turbine to generate power. The coolant can be, for example, nitrogen. The features of such a system are well known in the art and thus will not be described in detail herein.

[0032] Accordingly, the reactor control system 100 of the present disclosure can form part of a nuclear fission reactor system. As shown in FIGS. 2 to 6, the nuclear fission reactor system can include a reactor unit 300 having a core 302 that includes a central axis 320 extending along the length of the core 302 from a first end to a second end of the core 302. The figures of the present disclosure relate only to the reactor unit 300, and other features of the nuclear fission reactor system (such as heat exchangers, turbines, etc.) are not shown.

[0033] As shown in FIGS. 2 to 6, the core 302 may be surrounded by a shield 184 (or "core barrel") and a casing shell 180 (defining the "reactor pressure vessel") that houses the core 302 and the shield 184. The casing 180 is spaced from the shield 184 to define a cooling annulus 182, and the shell 180 defines an outer surface 186.

[0034] As shown in FIGS. 3 to 6, the reactor unit 300 includes a first region 310 provided within the core 302 and a second region 312 provided outside the core 302. Thus, the second region 312 is located outside the outer periphery of the core 302. That is, the first region 310 is provided within the core 302 inside the core shield 184, and the second region 312 is outside the core shield 184 of the core 302. The second region 312 may be adjacent to the core shield 184 of the core 302. The second region 312 may be adjacent to the outer surface 186 of the shell 180. The second region 312 may be adjacent to the shell 180. The first region 310 is located between the central axis 320 and the second region 312, and the second region 312 is outside the first region 310. The second region 312 may include the cooling annulus 182. For example, the first region 310 is the region within the dashed line labeled "310" (i.e., surrounded by the dashed line) in FIGS. 3 to 6 defined by the shield 184, and the second region 312 surrounds (i.e., is outside of) the first region 310 (i.e., outside the region surrounded by the dashed line labeled "310"). That is, the second region 312 is outside the volume defined by the shield 184 and defines the volume that defines the boundary of the first region 310.

[0035] The control system 100 includes a control duct 200. As shown in FIG. 2, the control system 100 may include a plurality of control ducts 200 spaced apart around the core central axis 320. Each of these control ducts, i.e., each control duct, may be provided as a passage, pipe or tube, and may have a circular cross-section, for example forming a cylindrical passage. Each of these control ducts, i.e., each control duct 200, may include a first portion 210 configured to extend through a first region 310 and a second portion 220 configured to extend through a second region 312.

[0036] The second portion 220 of the control duct may extend through the cooling annulus 182. The second portion 220 of the control duct 200 may be housed within the cooling annulus 182. That is, the second portion 220 of the control duct 200 may be located entirely within the cooling annulus 182.

[0037] The first portion 210 of the control duct 200 may extend substantially parallel to the core central axis 320. The second portion 220 of the control duct 200 may extend substantially parallel to the core central axis 320. Thus, the second portion 220 of the control duct 200 may extend substantially parallel to the first portion 210 of the control duct 200.

[0038] In an alternative example (not shown), the first portion 210 of the control duct 200 may extend at an angle with respect to the core central axis 320, and / or the second portion 220 of the control duct 200 may extend at an angle with respect to the core central axis 320. Thus, the second portion 220 of the control duct 200 may extend at an angle and / or parallel to the first portion 210 of the control duct 200.

[0039] The duct 200 is filled with a series of control units 400, each of the control units 400 being configured to travel along the control duct 200.

[0040] The control duct 200 is configured for the translation of the control unit 400. That is, the control duct 200 is configured to enable the control unit 400 to travel along the control duct 200. The control duct 200 is configured for the translation of the control unit 400 in a first direction D1 and a second direction D2. The first direction D1 is the traveling direction from the second portion 220 of the control duct to the first portion 210 of the control duct. The second direction D2 is the traveling direction from the first portion 210 of the control duct to the second portion 220 of the control duct.

[0041] The control duct 200 may include a first arcuate portion 230 extending between the first portion 210 of the control duct and the second portion 220 of the control duct such that the first portion 210, the first arcuate portion 230, and the second portion 220 of the control duct 200 define a continuous path for the passage of the control unit 400.

[0042] The first arcuate portion 230 of the control duct 200 may be semi-circular. That is, the first arcuate portion 230 may be configured to define a path for the control unit 400 that rotates 180 degrees from one of the first portion 210 or the second portion 220 of the control duct (from which the first arcuate portion 230 extends) to the other of the first portion 210 or the second portion 220 of the control duct.

[0043] As shown in the examples of FIGS. 2 to 4, the control duct 200 may include a second arcuate portion 240 extending between the first portion 210 of the control duct 200 and the second portion 220. In this example, the second arcuate portion 240 of the control duct 200 is provided at opposite ends of the first portion 210 and the second portion 220 with respect to the first arcuate portion 230 such that the first arcuate portion 230 is spaced apart from the second arcuate portion 240 by the first portion 210 and the second portion 220.

[0044] The second arcuate portion 240 of the control duct 200 may be semi-circular. That is, the second arcuate portion 240 of the control duct 200 may be configured to define a path for the control unit 400 to rotate 180 degrees from one of the first portion 210 or the second portion 220 of the control duct 200 (from which the second arcuate portion 240 extends) to the other of the first portion 210 or the second portion 220.

[0045] Accordingly, as shown in the examples of FIGS. 2 to 4, the first portion 210, the first arcuate portion 230, the second portion 220, and the second arcuate portion 240 of the control duct 200 define a single continuous loop path for the passage of the control unit 400.

[0046] Accordingly, the first portion 210, the first arcuate portion 230, the second portion 220, and the second arcuate portion 240 of the control duct 200 may be continuously provided so as to define a single continuous loop path for the passage of the control unit 400.

[0047] In an alternative example shown in FIGS. 5 and 6, instead of the second arcuate portion 240 of the example of FIGS. 2 to 4, the control duct 200 is configured to receive the control unit 400 from the first tank 700 and / or supply the control unit 400 to the first tank 700, and a first tank 700 for storing the control unit 400, and the control duct 200 is configured to receive the control unit 400 from the second tank 720 and / or supply the control unit 400 to the second tank 720, and a second tank 720 for storing the control unit 400 may be provided.

[0048] Accordingly, in the example of FIGS. 5 and 6, the first tank 700, the first portion 210, the first arcuate portion 230, the second portion 220, and the second tank 720 of the control duct 200 are continuously provided so as to define a path for the passage of the control unit 400 between the first tank 700 and the second tank 720.

[0049] The core 302 and its central axis 320 can extend vertically (as shown in the figure). Thus, in the examples of FIGS. 2 to 4, when the reactor unit 300 is attached to a horizontal substrate, such as the floor of a building, the core 302 and its central axis 320 extend such that the second arcuate portion 240 is vertically above the first arcuate portion 230.

[0050] Alternatively, in the examples of FIGS. 5 and 6, when the reactor unit 300 is attached to a horizontal substrate, such as the floor of a building, the core 302 and its central axis 320 extend such that the first tank 700 and the second tank 720 are vertically above the first arcuate portion 230.

[0051] In a further example having a configuration similar to the examples of FIGS. 2 to 4, the reactor may be horizontally attached. In such an example, when the reactor unit 300 is attached to a horizontal substrate, such as the floor of a building, the core 302 and its central axis 320 extend horizontally such that the second arcuate portion 240 is at the same height as the first arcuate portion 230 above the substrate.

[0052] Some of the control units 400 are absorber units 410. At least some of the remainder of the control units 400 are displacer units 420.

[0053] The absorber unit 410 can be configured to absorb radiation energy. For example, the absorber unit 410 can be configured to absorb particles that contribute to the operation of the nuclear chain reaction. For example, the absorber unit 410 can be configured to absorb neutrons. The absorber unit 410 can comprise boron carbide particles. The displacer unit 420 is configured to have lower absorption characteristics than the absorber unit 410. The displacer unit 420 can comprise graphite.

[0054] In the illustrated example, a plurality of absorber units 410 are provided continuously adjacent to each other (i.e., in a row) along the control duct 200 to form a row 416 of absorber units 410. A first plurality of displacer units 420 are provided continuously adjacent to each other (i.e., in a row) along the control duct 200 to form a first row 422 of displacer units 420. A second plurality of displacer units 420 are provided continuously adjacent to each other along the control duct 200 to form a second row 424 of displacer units 420. The first row 422 of displacer units 420 extends along the duct 200 in a first direction D1 from a first end 412 of the row of absorber units 410, and the second row 424 of displacer units 420 extends along the duct 200 in a second direction D2 from a second end 414 of the row of absorber units 410.

[0055] The absorber unit 410 may not be heavier than the displacer unit 420. The absorber unit 410 may be at least 2% lighter than the displacer unit 420, but not more than 80% lighter than the displacer unit. The absorber unit 410 may be at least 10% lighter than the displacer unit 420, but not more than 50% lighter than the displacer unit. The absorber unit 410 may be at least 20% lighter than the displacer unit 420, but not more than 30% lighter than the displacer unit.

[0056] The control unit 400 may be spherical. The control unit 400 may have an outer diameter that is the same as or slightly smaller than the diameter of the control duct 200.

[0057] The control unit 400 may have a diameter that is at least 10 mm and does not exceed 300 mm. The control unit 400 may have a diameter that is at least 50 mm and does not exceed 150 mm. The control unit 400 may have a diameter that is at least 90 mm and does not exceed 110 mm. The control unit 400 may have a diameter of approximately 100 mm.

[0058] As shown in the examples of FIGS. 2 to 7, in the first operating mode, a drive mechanism 600 may be further provided that is operable to drive the control unit 400 in a first direction D1 along the control duct 200, and in the second operating mode, is operable to drive the control unit 400 in a second direction D2 along the control duct 200.

[0059] As best shown in FIG. 7, the drive mechanism 600 may include a screw 602 having a track 604 for engagement with the control unit 400 such that when the screw 602 rotates, the control unit 400 is driven along the duct 200. The track 604 may be provided as a thread so as to form an Archimedean screw type arrangement. The screw 602 may be rotatable about an axis 610 and drivable by a drive motor 606. A drive arm 608 may extend from the drive motor 606 to the screw 602. Thus, the drive motor 606 may be operable to rotate the screw 602 about the axis of rotation 610, thereby moving the control unit 400 along the duct 200.

[0060] As shown in FIG. 7, the screw 602 is configured to move between a first position (shown in FIG. 7) where it is operable to drive the control unit 400 and a second position (not shown) where a clearance is maintained between the screw 602 and the control unit 400. That is, in the second position, the screw 602 is spaced apart from the control unit 400. The screw 602 can be configured to move in a first displacement direction (indicated by arrow D3 in FIG. 7) between a first position (shown in FIG. 7) where the screw 602 is operable to drive the control unit 400 and a second position where a clearance is maintained between the screw 602 and the control unit 400 so that the control unit 400 does not engage with the screw 602 when the control unit 400 passes by the screw 602. The screw 602 can be configured to move in a second displacement direction (indicated by arrow D4 in FIG. 7) between a second position where the screw 602 is spaced apart from the control unit 400 and a first position (shown in FIG. 7) where the screw 602 is operable to drive the control unit 400.

[0061] The piston 500 is provided between the first row 422 of the displacer unit 420 and the second row 424 of the displacer unit 420 such that in a first direction D1, a plurality (i.e., a row) of absorber units 410 are spaced apart from the piston 500 by the first row 422 of the displacer unit 420, and in a second direction D2, a plurality (i.e., a row) of absorber units 410 are spaced apart from the piston 500 by the second row 424 of the displacer unit 420.

[0062] The piston 500 is configured and disposed within the duct 200 such that when the screw 602 is in a second position (with a clearance maintained between the screw 602 and the control unit 400), the piston 500 acts on the control unit 400 therebelow to move the control unit 400 along the duct 200. Thus, the piston 500, by itself and / or when combined with the weight of at least some of the displacer units 420 of the first row 422 of the displacer unit 420, causes the second row 424 of the displacer unit 420 to travel in a first direction D1 along the duct 200 such that the absorber unit 410 is located (i.e., moves) in the first region 310 of the core 302 (for example, when the reactor is mounted vertically as shown in the figure).

[0063] The screw 602 may be attached, for example, by a spring, while being biased toward a second position in which the screw 602 is spaced apart from the control unit 400. The screw 602 may be maintained in a first position in which the screw 602 is operable to drive the control unit 400 by pressure from an actuator and / or a pressure source. In the event of a system failure, the actuator and / or the pressure source releases the screw 602 such that the screw 602 assumes the second position, thereby enabling the control unit 400 to move along the duct 200.

[0064] As shown in FIGS. 8 and 9, the reactor control system 100 may further include a check mechanism 1100 provided within the control duct 200 and configured to have a first operating mode in which the control unit 400 can move relative to the control duct 200 and a second operating mode in which the control unit 400 is fixed at a predetermined position relative to the control duct 200.

[0065] The check mechanism 1100 may be provided in the second portion 220. The check mechanism 1100 may be provided in the first portion 210.

[0066] As shown in FIGS. 8 and 9, the check mechanism 1100 may include a ratchet component 1102. In a first configuration (i.e., the operating configuration shown in FIGS. 3, 5, and 9), the control unit 400 can push / pass the ratchet component 1102 in a first direction D1 and / or a second direction D2. In a second configuration (i.e., the stop configuration shown in FIGS. 4, 6, and 8), the ratchet component 1102 allows the control unit 400 to pass the ratchet component 1102 in the first direction D1, but does not allow the control unit 400 to pass the ratchet component 1102 in the second direction D2.

[0067] Accordingly, in normal operation (i.e., the operating configuration), the check mechanism 1100 is in its first configuration. However, when a stop is required, the check mechanism 1100 is converted to its second configuration to allow the absorber unit 410 to move in the first direction D1 (i.e., within or towards the first region 310) towards the core, but prevent movement in the second direction D2 (i.e., within or towards the second region 312).

[0068] As shown in FIGS. 3 to 6, the control duct 200 may have a substantially constant diameter.

[0069] In an alternative example, as shown for example in FIG. 10, at least a portion of the second portion 220 of the control duct 200 has a diameter larger than the diameter of the first portion 210 of the control duct 200. This region of enlarged diameter may be arranged such that the first portion 210, the region of enlarged diameter, and the drive mechanism 600 are provided continuously in the second direction D2.

[0070] In this example, the second portion 220 is in fluid communication with the pressure source 1000 such that when the screw 602 is in the second position, the control unit 400 is pushed in the first direction D1 by the pressure source.

[0071] Accordingly, in this example, the piston 500 and the control duct 200 are enlarged such that there is an area difference between the diameter of the control unit 400 and the piston 500. Thus, the diameter of the enlarged region 250 may be 5% to 10% larger than the diameter of the control unit 400. When the control unit 400 enters the enlarged region 250 of the control duct 200, it acts as a valve, thereby restricting the leakage of gas from the control duct 200 using the piston 500, and the control duct 200 is vented in the drive mechanism. Then, when gas pressure is applied to the enlarged cross-section 250, the differential pressure between the piston 500 and the control unit 400 ensures that the piston 500 is driven downward of the control duct 200 in the first direction D1 to stop the core reaction.

[0072] During normal operation (i.e., operating configuration) of the nuclear fission reactor system, the control unit 400 is moved along the control duct 200 in the first direction D1 and the second direction D2 as needed to decelerate the reaction in the core 302 as needed by using the drive mechanism 600.

[0073] The drive mechanism 600 can move the control unit 400 between an operating configuration arrangement shown in FIGS. 3 and 5, where most of the control unit 400 in the first region 310 of the core 302 is the displacer unit 420, and a shutdown configuration arrangement shown in FIGS. 4, 6, and 7, where most of the control unit 400 in the first region 310 of the core 300 is the absorber unit 410. The drive mechanism 600 is operable to position the control unit 400 at a position between the position shown in FIGS. 3 and 5 and the position shown in FIGS. 4, 6, and 7.

[0074] However, as described above, the reactor control system 100 is configured such that during a shutdown scenario, the drive mechanism is operable to allow the control unit to adopt the arrangement shown in FIGS. 4, 6, and 7.

[0075] Accordingly, a control system for a nuclear fission reactor is provided that is more compact than conventional designs and that significantly reduces the overall size of the contained reactor units as compared to examples of related art.

[0076] Since the reactor control and / or shutdown components of the present disclosure extend radially outward from the core rather than longitudinally from the ends of the core, this enables a substantial potential for improvement to the overall control system package design.

[0077] In some examples, the arrangement of the present disclosure enables placement of the entire control system within the reactor housing (e.g., casing 180), and thus does not increase the volume of the overall reactor.

[0078] Using spherical control units instead of control rods has a further significant safety advantage since control rods are prone to warping due to temperature differences and neutron irradiation. This has in the past caused jamming of shutdown rods that prevent automatic shutdown in a failed situation. In contrast, spherical control units are less susceptible to such jamming due to the inherently segmented nature of the design and only point and line contacts within the control ducts 200.

[0079] The use of, for example, an Archimedes screw to move the control units enables precise drive control of the control units, allows for inherent gearing from the drive motor, and reduces the need for a control drive motor gearbox.

[0080] The control system 100 may also enable a horizontally mounted reactor. Horizontal mounting may have advantages in space - constrained environments, including within the hull of a submarine. However, when a horizontal arrangement is considered, gravity - induced shutdown is no longer practical and hydraulic or pneumatic insertion of the shutdown elements may be required (as described, for example, with respect to FIG. 10).

[0081] Attention is directed to all papers and documents filed in connection with this application and published prior to or simultaneously with this specification and made available to the public with this specification, and the contents of all such papers and documents are hereby incorporated herein by reference.

[0082] All of the features disclosed in this specification (including any appended claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0083] Each feature disclosed in this specification (including any appended claims, abstract and drawings) may, unless otherwise specified, be replaced by alternative features serving the same, equivalent or similar purpose. Accordingly, unless otherwise specified, each feature disclosed is only an example of a general series of equivalent or similar features.

[0084] The invention is not limited to the details of the above embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any appended claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The following is appended as it is the matter described in the claims of the original application at the time of filing. [1] A reactor control system for a nuclear fission reactor system comprising a reactor unit having a core whose central axis extends along the length of the core, wherein the reactor unit includes a first region provided within the core and a second region provided outside the core, wherein the reactor control system includes a control duct, and the control duct has a first portion configured to extend through the first region, and a second portion configured to extend through the second region and the control duct is filled with a series of control units, each of the control units being configured to travel along the control duct. [2] The control duct is configured for the translation of the control units in a first direction D1 and a second direction D2, wherein the first direction D1 is a traveling direction from the second portion toward the first portion, and the second direction D2 is a traveling direction from the first portion toward the second portion, the reactor control system according to [1]. [3] The control duct includes a first arcuate portion extending between the first portion and the second portion, and the first portion, the first arcuate portion, and the second portion of the control duct define, thereby, a continuous path for the passage of the control units, the reactor control system according to [1] or [2]. [4] The control duct includes a second arcuate portion extending between the first portion and the second portion and the second arcuate portion is provided at opposite ends of the first portion and the second portion with respect to the first arcuate portion such that the first arcuate portion is spaced apart from the second arcuate portion by the first portion and the second portion, and the first portion, the first arcuate portion, the second portion, and the second arcuate portion of the control duct define, thereby, a single continuous loop path for the passage of the control units, the reactor control system according to [3]. [5] A first tank for storing the control units, wherein the control duct is configured to receive control units from and / or supply control units to the first tank, a second tank for storing the control unit, wherein the control duct is configured to receive the control unit from and / or supply the control unit to the second tank further comprising the nuclear reactor control system according to any one of [1] to [3], wherein the first tank, the first portion, the first arcuate portion, the second portion, and the second tank are provided continuously so as to define a path for the passage of the control unit [6] Some of the control units are absorber units Some of the control units are displacer units the nuclear reactor control system according to any one of [1] to [5] [7] the nuclear reactor control system according to [6], wherein the absorber unit is not heavier than the displacer unit [8] the nuclear reactor control system according to any one of [1] to [7], wherein the control unit is spherical and has an outer diameter equal to or slightly smaller than the diameter of the control duct [9] the nuclear reactor control system according to any one of [1] to [8], further comprising a drive mechanism operable to drive the control unit in a first direction D1 along the control duct in a first operating mode and operable to drive the control unit in a second direction D2 along the control duct in a second operating mode

[10] the nuclear reactor control system according to [9], wherein the drive mechanism comprises a screw having a track for engagement with the control unit such that when the screw rotates, the control unit is driven along the control duct

[11] the nuclear reactor control system according to

[10] , wherein the screw is configured to move between a first position operable to drive the control unit and a second position in which a clearance is maintained between the screw and the control unit

[12] the nuclear reactor control system according to any one of [9] to

[11] , further comprising a check mechanism provided in the control duct configured to have a first operating mode in which the control unit can move relative to the control duct and a second operating mode in which the control unit is fixed at a predetermined position relative to the control duct

[13] The control duct has a substantially constant diameter and is the nuclear reactor control system according to any one of [1] to

[12] .

[14] At least a part of the second portion of the control duct has a diameter larger than the diameter of the first portion of the control duct. The second portion is in fluid communication with a pressure source such that when the screw is in the second position, the control unit is pushed in the first direction D1, and is the nuclear reactor control system according to any one of [1] to

[12] .

[15] A plurality of absorber units are provided continuously adjacent to each other along the control duct to form a row of absorber units. A first plurality of displacer units are provided continuously adjacent to each other along the control duct to form a first row of displacer units. A second plurality of displacer units are provided continuously adjacent to each other along the control duct to form a second row of displacer units. The first row of displacer units extends from the first end of the row of absorber units, and the second row of displacer units extends from the second end of the row of absorber units, and is the nuclear reactor control system according to any one of [1] to

[14] .

[16] In the first direction D1, a piston is provided between the first row of displacer units and the second row of displacer units such that a plurality of absorber units are separated from the piston by the first row of displacer units, and in the second direction D2, the plurality of absorber units are separated from the piston by the second row of displacer units, and is the nuclear reactor control system according to any one of [1] to

[15] .

[17] The piston is configured and arranged in the control duct such that when the screw is in the second position, the piston acts on the control unit below it to move the control unit along the control duct, and is the nuclear reactor control system according to

[16] dependent on

[11] .

[18] The first portion of the control duct extends substantially parallel to the core central axis. The second portion of the control duct extends substantially parallel to the core central axis, and is the nuclear reactor control system according to any one of [1] to

[17] .

[19] A nuclear reactor unit, A nuclear fission reactor system comprising the reactor control system according to any one of [1] to

[18] and being provided with.

Claims

1. A reactor control system for a nuclear fission reactor system comprising a reactor unit having a core with a central axis extending along the length of the core, wherein the reactor unit comprises a first region provided within the core and a second region provided outside the core, the reactor control system comprising a control duct, the control duct comprising a first portion configured to extend through the first region, a second portion configured to extend through the second region and having, the control duct being filled with a series of control units, each of the control units being configured to travel along the control duct, the reactor control system comprising a first tank for storing control units, wherein the control duct is configured to receive control units from and / or supply control units to the first tank, a second tank for storing control units, wherein the control duct is configured to receive control units from and / or supply control units to the second tank, the reactor control system, wherein the first tank, the first portion, the first arcuate portion, the second portion, and the second tank are provided continuously to define a path for the passage of control units.

2. the control duct being configured for the translation of the control units in a first direction D1 and a second direction D2, the first direction D1 being a traveling direction from the second portion towards the first portion, the second direction D2 being a traveling direction from the first portion towards the second portion, the reactor control system according to claim 1.

3. the control duct comprising a first arcuate portion extending between the first portion and the second portion, the first portion, the first arcuate portion, and the second portion of the control duct defining thereby a continuous path for the passage of control units, the reactor control system according to claim 1 or 2.

4. the control duct comprising a second arcuate portion extending between the first portion and the second portion and having, The second arcuate portion is provided at opposite ends of the first portion and the second portion with respect to the first arcuate portion such that the first arcuate portion is spaced from the second arcuate portion by the first portion and the second portion. The first portion, the first arcuate portion, the second portion, and the second arcuate portion of the control duct define a single continuous loop path for passage of the control unit, the nuclear reactor control system of claim 3. **Claim 5** Some of the control units are absorber units. Some of the control units are displacer units. The nuclear reactor control system according to claim 1 or 2. **Claim 6** The absorber unit is not heavier than the displacer unit, the nuclear reactor control system of claim 5. **Claim 7** The control unit is spherical and has an outer diameter that is the same as or slightly smaller than the diameter of the control duct, the nuclear reactor control system of claim 1 or 2. **Claim 8** In a first operating mode, it is operable to drive the control unit in a first direction D1 along the control duct, and in a second operating mode, a drive mechanism is further provided that is operable to drive the control unit in a second direction D2 along the control duct, the nuclear reactor control system of claim 1 or 2. **Claim 9** The drive mechanism includes a screw having a track for engagement with the control unit such that when the screw rotates, the control unit is driven along the control duct, the nuclear reactor control system of claim 8. **Claim 10** The screw is configured to move between a first position operable to drive the control unit and a second position in which a clearance is maintained between the screw and the control unit, the nuclear reactor control system of claim 9. **Claim 11** The control duct further includes a check mechanism provided therein and configured to have a moving operating mode in which the control unit can move relative to the control duct and a fixed operating mode in which the control unit is fixed at a predetermined position relative to the control duct, the nuclear reactor control system of claim 8. **Claim 12** The control duct has a substantially constant diameter, the nuclear reactor control system of claim 1 or 2. **Claim 13** At least a part of the second portion of the control duct has a diameter larger than the diameter of the first portion of the control duct. The nuclear reactor control system according to claim 10, wherein the second portion is in fluid communication with a pressure source such that when the screw is in the second position, the control unit is pushed in the first direction D1. **Claim 14** A plurality of absorber units are provided adjacent to each other continuously along the control duct to form a row of absorber units. A first plurality of displacer units are provided adjacent to each other continuously along the control duct to form a first row of displacer units. A second plurality of displacer units are provided adjacent to each other continuously along the control duct to form a second row of displacer units. The nuclear reactor control system according to claim 1 or 2, wherein the first row of displacer units extends from a first end of the row of absorber units, and the second row of displacer units extends from a second end of the row of absorber units. **Claim 15** The piston is provided between the first row of displacer units and the second row of displacer units such that in the first direction D1, a plurality of absorber units are separated from the piston by the first row of displacer units, and in the second direction D2, the plurality of absorber units are separated from the piston by the second row of displacer units. The nuclear reactor control system according to claim 2. **Claim 16** The nuclear reactor control system according to claim 15, wherein the piston is configured and arranged in the control duct such that when the screw is in a second position where a clearance is maintained between the screw and the control unit, the piston acts on the control unit below it to move the control unit along the control duct. **Claim 17** The first portion of the control duct extends substantially parallel to the core central axis. The nuclear reactor control system according to claim 1 or 2, wherein the second portion of the control duct extends substantially parallel to the core central axis. **Claim 18** A nuclear reactor unit, The nuclear reactor control system according to claim 1 or 2, and A nuclear fission reactor system comprising the same.

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