A nuclear reactor equipped with a core support system
The support system for fast neutron reactors, featuring upper and lower supports and thermal expanders, addresses miniaturization and safety challenges by enabling compact reactor design with integrated heat exchangers and pumps, ensuring safe operation and compactness.
Patent Information
- Application Number
- JP2024573089
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-06-13
- Filing Date
- 2023-06-13
- Publication Date
- 2025-07-03
AI Technical Summary
Existing fast neutron nuclear reactors face challenges in miniaturization and efficient integration of heat exchangers and pumps due to the need for separate fuel element support systems that do not allow vertical placement within the core, limiting reactor compactness and operational flexibility.
A support system for the core of a fast nuclear reactor, comprising an upper and lower support structure extending from the reactor roof, allowing axial and radial constraint of the core, with elastic radial restraints and thermal expanders to ensure safety and compact design, accommodating a heat exchanger above the core.
Enables compact reactor design with integrated heat exchanger and pump placement, enhancing safety through elastic radial restraints and thermal expanders that ensure reactor shutdown in case of overheating, while reducing neutron radiation exposure.
Smart Images
Figure 2025520357000001_ABST
Abstract
Description
Cross - reference to related applications
[0001] This patent application claims the priority of Italian Patent Application No. 102022000012476 filed on June 13, 2022, the entire disclosure of which is incorporated herein by reference.
Technical field
[0002] The present invention relates to nuclear reactors, and in particular to fast nuclear reactors cooled by liquid metals or molten salts.
Background art
[0003] It is known that fast neutron nuclear reactors can be constructed using cores that are small in size and can operate for several years without refueling. This feature enables the construction of plants without replacement systems and spent fuel storage pools, resulting in the advantages of (i) cost reduction of the plant and (ii) reduction of the risk of nuclear proliferation. When the fuel charge is discharged, the core is transported within the reactor vessel to a centralized plant equipped with spent fuel treatment means. Obviously, maximum miniaturization is required to transport the entire vessel.
[0004] Patent application PCT / IB2017 / 052606 describes a solution in which fuel elements are mechanically supported by respective heads joined to each other and joined to a fixed structure by a support device that acts between the fuel elements located around the core that acts between adjacent fuel elements or forms an integral part of the heads of the fuel elements.
[0005] Patent application PCT / IB2017 / 052609 also describes a solution comprising an expander in which fuel elements are characterized by a mechanical coupling of high - thermal - expansion elements that alternately engage with low - thermal - expansion elements to amplify the radial expansion of the respective end elements, which, when a given temperature is exceeded, engage with each other to separate the fuel elements from each other and operate to expand the radial expansion of the core by rotating the fuel elements around their respective legs at their mutually separated heads.
[0006] By combining these last two patents, it becomes possible to form a support system that operates in a zone with reduced neutron radiation, and it also becomes possible to separate the fuel elements when the design temperature is exceeded to shut down the reactor. However, the resulting solution does not allow for the housing of heat exchangers and pumps in the vertical direction of the core, as would be desirable from the perspective of reactor miniaturization. SUMMARY OF THE INVENTION
[0007] The object of the present invention is to provide a nuclear reactor that overcomes the significant drawbacks of known solutions and has construction and safety advantages, particularly a fast nuclear reactor cooled by liquid metal or molten salt.
[0008] Accordingly, the present invention relates to a nuclear reactor, particularly a fast nuclear reactor cooled by liquid metal or molten salt, as defined in claim 1 and its auxiliary features and plant configuration in the dependent claims.
[0009] In summary, the present invention relates to a nuclear reactor, particularly a fast nuclear reactor preferably cooled by heavy liquid metal or molten salt, wherein the core is axially and radially constrained in the upper part and radially constrained in the lower part by an upper support that supports the upper part of the core above the active zone of the fuel elements and a lower support that supports the lower part of the core below the active zone of the fuel elements. At least the upper support is supported by a support structure that extends from the roof of the reactor inside the reactor vessel so as to leave an available space above the core that can accommodate a heat exchanger.
[0010] In a preferred embodiment, the support structure extending from the roof of the reactor branches into an upper core restraint branch with an upper support and a lower core restraint branch with a lower support. Overall, the support structure appears like a double-bottom cylinder with incomplete bottoms at both ends. Since the above-mentioned upper and lower bottoms are separated from the active part of the core due to the intervening upper and lower gas regions, the core is restrained only at two ends within the lower neutron flux zone.
[0011] In other embodiments, instead of being integrally joined to each other, the two branches of the support structure are formed by respective separate bodies, both supported by the roof of the reactor, for example, one being concentric with the other (the branches support the upper support radially within the branch carrying the lower support). Or, while the upper support is supported by a support structure suspended from the roof of the reactor, the upper support is supported by a body extending downward from the bottom wall of the main vessel of the reactor.
[0012] The upper cylindrical portion of the support structure above the upper core restraint bottom is perforated to allow for the passage of the cold primary coolant at the heat exchanger outlet and to direct that primary coolant towards the inlet of the core within the annular conduit defined externally by the reactor vessel and internally by the support structure.
[0013] The bottom of the lower support that supports the core internally reproduces the outer shape of the core to be accommodated. The bottom of the upper support that supports the core has, on the inside, a plurality of jaws, preferably six jaws in the case of a core having a hexagonal cross-section, for accommodating the heads of the fuel elements that interact with the end elements forming part of the bottom of the upper support. The jaws are provided with movable elements that act on the heads of the fuel elements by means of elastic thrust elements formed, for example, by helical springs or leaf springs. The head of the fuel element includes, on the inside, a bimetallic element that expands, creating a spacing that allows the head of the fuel element to overcome the reaction of the elastic elements of the jaws when the design temperature is exceeded.
[0014] The upper support that supports the core is provided with a cavity for accommodating a cam for vertically supporting the fuel elements and an elastic radial storage system for the heads of the fuel elements, which interacts with the system of bimetallic spacing expanders for the heads of the fuel elements in the event of accidental overheating of the core, causing a reactor shutdown. The lower support structure ends with a hexagonal contour for the radial storage of the legs of the fuel elements. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention will be described in detail in the following non-limiting embodiments with reference to the figures in the accompanying drawings.
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Figure 8A
Figure 8B
Mode for Carrying Out the Invention
[0016] Description of Embodiment Referring to FIGS. 1 and 2, the nuclear reactor 1 includes a main vessel 2 that houses a primary cooling fluid F and has its top closed by a roof 3.
[0017] Inside the vessel 2, a core 4 formed by a plurality of fuel elements 5 and immersed in the primary fluid F, and a support structure 6 that supports the core 4 supported by the roof 3 are accommodated.
[0018] For example, although not essential, the fuel elements 5 have a hexagonal cross-section and are arranged adjacent to each other so as to form a core 4 having a substantially hexagonal shape as a whole.
[0019] In the preferred embodiment shown, the support structure 6 is formed as a double bottom shell and has a substantially cylindrical side wall 7 supported by the roof 3, and an upper bottom 8 and a lower bottom 9 that branch radially inward of the side wall 7 and are spaced apart from each other in the vertical direction.
[0020] The side wall 7 includes a perforated upper portion 70 disposed above the upper bottom 8 and having a plurality of through radial holes 71 that allow the passage of the primary fluid F, and a lower portion 72 located below the upper bottom 8 from which the lower bottom 9 branches.
[0021] The side wall 7 and the bottom 9, together with the container 2, define an annular conduit 10 for supplying the core 4.
[0022] The bottom 8 defines an upper support 80 for supporting the core 4, and the bottom 9 defines a lower support 90 for supporting the core. Preferably, the support 80 is configured to support the core 4 in the axial direction (vertical direction) and to achieve elastic radial restraint of the core 4, while the support 90 is configured to define radial restraint of the core 4.
[0023] In particular, the bottom 9 has a central through opening defined by a peripheral portion 11 having an outer shape corresponding to the outer periphery of the core 4 so as to form radial restraint of the core 4.
[0024] The bottom 8 has a central through opening defined by an end element 16 having a plurality of jaws 14 on the inside for vertical support and elastic radial restraint of the fuel element 5.
[0025] Advantageously, in order to reduce neutron damage to the bottom 8 and the bottom 9, the bottom 8, and thus the support 80, acts on the upper part of the core 4 above the active zone 12 of the fuel element 5, and the bottom 9 and the support 90 act on the lower part of the core 4 below the active zone 12 of the fuel element 5. Outside the active zone 12 of the fuel element 5, actually, both ends of the fuel rod contain gas and do not contain fuel, so the neutron flux is low.
[0026] Referring also to FIGS. 3 to 5, the jaw 14 is, for example, six in number with respect to the core 4 having a hexagonal cross-section, and is movably supported by the end elements 16 and is movable so as to radially clamp the head 15 of the fuel element 5. The jaw 14 acts on the head 15 of the fuel element 5 by means of a pressing element 18 which comprises, for example, an elastic member 19 such as a spring, in particular a coil spring, and an element 20 for applying a pre-tension to the elastic member 19.
[0027] The jaw 14 vertically supports the outermost uppermost fuel element 5 of the core 4 by means of a cavity 21 in which the cam 22 of the fuel element 5 engages. The outermost uppermost fuel element 5 vertically fixes the fuel element 5 belonging to the innermost uppermost using the same cam system 22 as described in patent application PCT / IB2017 / 052606.
[0028] The jaw 14 is pressed against the head 15 of the fuel element 5 by the thrust element 18 and is guided in their compressive action by one or more cylindrical bodies 23 or other shapes, which slide within the respective housings 24 of the end elements 16 and are hydraulically connected to the primary fluid F by means of calibration holes 25. The calibration holes 25 connect the inside of the housing 24 to the mass of the primary fluid F, allowing for the expansion of the core 4 and also defining a damping system against possible seismic shocks.
[0029] FIG. 6 shows an alternative solution for the jaw 14, which comprises an elastic member 26 in the form of a leaf spring that bends when horizontally engaged by the force of the thrust of the head 15 of the fuel element 5 and the ends of which slide along the respective supports 27, and a pressing element 18 that presses the head 15 of the fuel element 5.
[0030] FIG. 7 shows details of the jaw 14 in which holes 28 of a suitable shape (for example, rectangular) are made in the central part and the radial ends. Inside the holes 28, a release cam 29 is arranged, which is integral with the end element 16 and is operated by an operating shaft 30 which can be rotated so as to move the jaw 14 inside the holes 28, selectively reducing / increasing the compressive action exerted by the jaw 14 on the head 15 of the fuel element 5.
[0031] Referring to FIGS. 8A and 8B, each fuel element 5 is provided with a plurality of thermal expanders 31 (for example, six thermal expanders in the case of a fuel element 5 having a hexagonal cross section) arranged on each side of the fuel element 5 on the head 15 of the fuel element 5, similar to those shown in Patent PCT / IB2017 / 052609.
[0032] Each thermal expander 31 (for example, six belonging to each head 15 of the fuel element 5) is formed by alternately arranging a first element "a" having a high coefficient of thermal expansion and a second element "b" having a low coefficient of thermal expansion. In particular, it is connected to the opposite side of each lateral expander element 33 having a small thermal expansion and is coupled to other elements having a large thermal expansion. The thermal expander 31 includes a central expander element 32 having a large thermal expansion. Finally, each box element 34 is formed, and they are hooked to each other by joints 35 to complete the whole.
[0033] This type of thermal expander is already known from PCT / IB2017 / 052609 where a gap occurs due to the deformation of the fuel element. In addition to what is already provided in PCT / IB2017 / 052609, the thermal expander 31 has a return joint 36 that also enables the thermal expander 31 to pull down radially and ensure expansion according to temperature.
[0034] Next, the nuclear reactor 1 is provided with a heat exchanger 40 (FIG. 1), which removes heat from the primary fluid F through a secondary fluid circulating within the heat exchanger 40. According to the present invention, the heat exchanger 40 is arranged centrally above the core 4. Thanks to the support structure 6, in fact, the space above the core 4 is available for accommodating the heat exchanger 40.
[0035] Advantageously, the heat exchanger 40 is an annular exchanger that internally houses a pump 41 for circulating the primary fluid F within the nuclear reactor 1.
[0036] In this way, the heat exchanger 40 is arranged above the center of the core 4 inside the upper perforated portion 70 of the support structure 6 provided with the radially extending through holes 71, enabling the passage of the primary fluid F exiting the heat exchanger 40 and guiding the primary fluid F towards the inlet of the core 4 within the annular conduit 10 defined externally by the vessel 2 and internally by the support structure 6.
[0037] Finally, it is understood that further modifications and variations can be made to the nuclear reactor described and illustrated herein without departing from the scope of the appended claims.
Claims
**Claim 1** A container (2) with a top closed by a roof (3) and containing a core (4), wherein the core (4) comprises a bundle of fuel elements (5) and is immersed in a primary fluid (F) to cool the core (4); and a heat exchanger (40) for removing heat from the primary fluid (F) via a secondary fluid circulating within the heat exchanger (40). The core (4) is supported by a lower support (90) that supports the lower part of the core (4) below the active zone (12) of the fuel elements (5) and an upper support (80) that supports the upper part of the core (4) above the active zone (12) of the fuel elements (5). The nuclear reactor (1) is characterized in that the upper support (80) extends from the roof (3) and is joined to the roof (3) by a support structure (6) having end elements (16). The end elements (16) have a central opening and are provided inside with a plurality of jaws (14) for vertical support and elastic radial restraint of the fuel elements (5). **Claim 2** The nuclear reactor according to claim 1, wherein the support structure (6) is formed as a double-bottom shell and comprises a substantially cylindrical side wall (7) supported by the roof (3), and an upper bottom (8) and a lower bottom (9) extending radially inward from the side wall (7) and spaced apart in a direction perpendicular to each other. The lower bottom (9) has a central opening defined by a peripheral portion (11) that defines the lower support (90) for radially restraining the fuel elements (5) of the core (4), and the upper bottom (8) comprises the end element (16) provided inside with the plurality of jaws (14) for vertical support and elastic radial restraint of the fuel elements (5). **Claim 3** The nuclear reactor according to claim 1 or 2, wherein the heat exchanger (40) is disposed centrally above the core (4) inside an upper part (70) and above the upper support (80), and is provided with a radially through hole (71) to allow passage of the primary fluid (F) exiting the heat exchanger (40), and guides the primary fluid (F) towards the inlet of the core (4) within an annular conduit (10) defined outside by the container (2) and inside by the support structure (6). **Claim 4** The reactor according to any one of claims 1 to 3, wherein the jaw portions (14) are supported by the end elements (16) via respective bodies (23) and vertically support the fuel elements (5) via respective cavities (21) engaged by respective cams (22) which are part of respective fuel elements (5).
5. The reactor according to claim 4, wherein the fuel elements (5) have respective upper heads (15) disposed above the active zones (12) of the fuel elements (5), and the jaw portions (14) radially compress the heads (15) by pressing elements (18) operated by elastic members (19, 26).
6. The reactor according to claim 4 or 5, wherein the bodies (23) are received in respective housings (24), the housings (24) connect the inside of the housings (24) to the primary fluid (F), enable expansion of the core (4), and are provided with calibration holes (25) defining a damping system against possible seismic loads.
7. The reactor according to any one of claims 4 to 6, wherein each fuel element (5) is provided with a plurality of thermal expanders (31) disposed on each side of the fuel element (5) on the head (15) of the fuel element (5), each thermal expander (31) comprising a first high coefficient of thermal expansion element (a) arranged alternately with a second low coefficient of thermal expansion element (b), and the elements (a, b) of the thermal expander (31) are interconnected by a return joint (36) which reliably returns to the initial position when the temperature decreases.
8. The reactor according to any one of claims 1 to 7, wherein the end elements (16) have release cams (29) cooperating with respective jaw portions (14), each release cam (29) being operated by an operating shaft (30) to rotate and push the jaw portion (14), and selectively reducing and increasing the compressive action exerted by the jaw portion (14) on the head (15) of the fuel element (5).