Supercritical water reactor assembly for radial power flattening

Abstract

The invention discloses a supercritical water reactor assembly for radial power flattening, the supercritical water reactor assembly comprises an assembly box and a plurality of fuel elements, the supercritical water reactor assembly is provided with a first channel and a second channel which are communicated, water flows from top to bottom in the first channel and flows to the bottom of the first channel to reach a subcritical state, and the fuel elements are communicated with the first channel. The water is both a coolant and a moderator, the water flows in the second channel from bottom to top and flows to the top of the second channel to reach a supercritical state, the fuel elements comprise a first fuel element and a second fuel element, and the cross sectional area of the first channel of the first fuel element is larger than that of the first channel of the second fuel element. By adjusting the areas of the first channels of the fuel elements at different positions in the assembly, for the fuel elements with low power values, the moderator channel areas of the elements are enlarged, the moderation capability is improved, the power of the fuel elements at the positions is improved, and thus the radial power distribution of the assembly or a reactor core is flattened.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear power generation, and in particular to a supercritical water reactor assembly for radial power flattening. Background Art

[0002] As a new type of high-efficiency reactor, the supercritical water-cooled reactor (SCWR) has higher outlet temperature and power generation efficiency and is considered to be one of the most promising reactor types in the fourth-generation nuclear energy system. However, the SCWR faces many challenges in its design and operation, especially the problem of uneven radial power distribution, which has an adverse impact on the safe and stable operation of the reactor.

[0003] The design of supercritical water-cooled reactors in related technologies proposes a hexagonal or quadrilateral component design scheme, and a special moderator channel design is designed to achieve neutron moderation. However, due to the different distances between fuel elements at different positions and the moderator channel, the power of the fuel elements near the water channel is high, and the local power peak factor (FL) cannot meet the requirements. In this type of design, in order to achieve radial power flattening, it is generally necessary to load fuels or burnable poisons with different enrichments in the same component, making the component design more complicated. Summary of the invention

[0004] The present invention is based on the inventor's discovery and understanding of the following facts and problems:

[0005] In the related art, a MOX fuel assembly structure suitable for a supercritical water-cooled reactor is provided, wherein a plurality of water boxes form a square shell, a plurality of water rods are arranged in the shell formed by the water boxes, and MOX fuel rods with a diameter of R are arranged in the gaps between the water rods; the water rods are divided into two forms: large water rods and small water rods, the large water rod has a square cross-section, and its length and width are 3R respectively, and the small water rod has a rectangular cross-section, and its length is 3R and its width is R; the spacing between the water rods and between the water rods and the inner wall of the water box is R, which is filled with neatly arranged MOX fuel rods; the gaps between the MOX fuel rods and the water rods or the gaps between the MOX fuel rods and the inner wall of the water box constitute fuel cooling channels.

[0006] This technical solution uses this MOX component structure in a supercritical water-cooled reactor, which can achieve the same effect as the original structure using only UO2 components, and can improve the uneven power distribution factor of the components. It has the characteristics of simple structure and minor improvements to the original supercritical water reactor component design, thus improving the safety of the reactor.

[0007] However, the main problem of this technical solution is that the use of rectangular water channels of different sizes makes the assembly structure complex, and the power distribution of the fuel depends largely on the distance from the water channel. It can be clearly seen that some fuel elements are adjacent to the water channel on one side and fuel elements on three sides, and some fuel elements are adjacent to the water channel on two sides and fuel elements on two sides. The latter are more moderated and have higher power, which may lead to uneven power distribution of the entire assembly.

[0008] In the related art, an annular fuel element and annular fuel supercritical water reactor, the annular fuel element, the annular fuel element is a cylindrical structure with an annular cross section, which is composed of an outer cladding, an outer air gap, a fuel core, an inner air gap and an inner cladding from the outer layer to the inner layer. The water reactor is composed of a pressure vessel, a descending section, a core basket and an annular fuel assembly from the outside to the inside, and the annular fuel assembly is composed of a plurality of square annular fuel assemblies or hexagonal annular fuel assemblies arranged in parallel axially.

[0009] This technical solution can reduce the temperature of the fuel pellets and cladding by effectively increasing the heat transfer area; and because the low-temperature water used as a moderator is in the inner channel of the fuel element, the physical feedback is more uniform, which can effectively reduce the radial power factor. Rectangular and hexagonal assembly designs using annular fuel assemblies and core scheme designs are proposed.

[0010] However, the main problem of this technical solution is that the use of annular fuel elements can indeed flatten the radial power distribution to a certain extent compared to ordinary solid fuel elements, but due to the asymmetry of the fuel elements in the assembly (such as some fuel elements are close to the assembly box or at the outer edge of the core, etc.), when the fuel elements are loaded with fuel of the same enrichment, the assembly close to the assembly box or the fuel elements close to the control rods may have lower power, resulting in an increase in the overall power unevenness of the assembly.

[0011] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0012] To this end, an embodiment of the present invention proposes a supercritical water reactor assembly for radial power flattening to solve the problem of uneven radial power distribution.

[0013] A supercritical water reactor assembly for radial power flattening according to an embodiment of the present invention comprises an assembly box and a plurality of fuel elements uniformly arranged in the assembly box, wherein the fuel element has a first channel arranged in a vertical direction, and a second channel arranged in a vertical direction is provided between adjacent fuel elements, the bottoms of the first channel and the second channel are connected, the first channel and the second channel are used for circulating water, the water flows from top to bottom in the first channel and flows to the bottom of the first channel to reach a subcritical state, the water flows from bottom to top in the second channel and flows to the top of the second channel to reach a supercritical state, the plurality of fuel elements comprises a first fuel element and a second fuel element, the cross-sectional area of ​​the first channel of the first fuel element is larger than the cross-sectional area of ​​the first channel of the second fuel element.

[0014] The supercritical water reactor assembly for radial power flattening of the embodiment of the present invention adjusts the area of ​​the first channel of the fuel elements at different positions in the assembly, expands the moderator channel area of ​​the fuel elements with lower power values, improves the moderation capacity, and achieves an increase in the power of the fuel elements here, thereby flattening the radial power distribution of the assembly or the core.

[0015] In some embodiments, the fuel element is annular in shape, and the first channel is located at the center of the fuel element.

[0016] In some embodiments, the fuel element includes an inner cladding, a fuel pellet, and an outer cladding that are spaced apart from each other in sequence from the inside to the outside, and a central channel of the inner cladding is the first channel.

[0017] In some embodiments, the projection shape of the component box along the vertical direction is a hexagon, and at least the fuel elements located at the hexagons of the component box among the plurality of fuel elements are all the first fuel elements.

[0018] In some embodiments, the fuel elements located at the periphery of the component box are all the first fuel elements.

[0019] In some embodiments, the ratio of the number of layers of the first fuel elements to the number of layers of the second fuel elements in the assembly box is 1:(5-6).

[0020] In some embodiments, the assembly box and the cladding of the fuel element are both made of austenitic stainless steel.

[0021] In some embodiments, the inner side margin of the component box is 20 cm to 21 cm, and the thickness of the component box is 0.15 cm to 0.50 cm.

[0022] In some embodiments, the size of the first fuel element differs from the size of the second fuel element by 0.1 mm to 0.5 mm.

[0023] In some embodiments, the outer diameter of the first fuel element is 8.2 mm, the diameter of the first channel of the first fuel element is 7.2 mm, the outer diameter of the second fuel element is 8.0 mm, and the diameter of the first channel of the second fuel element is 7.0 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of a fuel element according to an embodiment of the present invention.

[0025] Figure 2 Schematic diagram of a supercritical water reactor assembly according to an embodiment of the present invention.

[0026] Figure 3 It is a schematic diagram of the simulation between the radial peak factor change and the burnup days according to an embodiment of the present invention.

[0027] Reference numerals:

[0028] 1-assembly box, 2-fuel element, 21-inner cladding, 22-fuel pellet, 23-outer cladding, 201-first channel, 202-second channel, 203-first fuel element, 204-second fuel element, 205-air gap. DETAILED DESCRIPTION

[0029] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0030] The following describes a supercritical water reactor assembly for radial power flattening according to an embodiment of the present invention in conjunction with the accompanying drawings.

[0031] like Figure 1 and Figure 2 As shown, the supercritical water reactor assembly for radial power flattening according to the embodiment of the present invention includes an assembly box 1 and a plurality of fuel elements 2.

[0032] Among them, multiple fuel elements 2 are evenly arranged in the component box 1, and the fuel element 2 adopts a double-channel design. The fuel element 2 has a first channel 201 set in the vertical direction, and a second channel 202 set in the vertical direction is provided between adjacent fuel elements 2. The bottoms of the first channel 201 and the second channel 202 are connected.

[0033] The first channel 201 and the second channel 202 are used for circulating water. The water flows from top to bottom in the first channel 201. At this time, the temperature of the water is relatively low and the density is relatively large. It serves as both a coolant and a moderator. When it flows to the bottom of the first channel 201, it reaches a subcritical state. Then the water flows into the second channel 202. The water flows from bottom to top in the second channel 202. When it flows to the top of the second channel 202, it reaches a supercritical state.

[0034] The plurality of fuel elements 2 include a first fuel element 203 and a second fuel element 204, wherein the cross-sectional area of ​​the first channel 201 of the first fuel element 203 is greater than the cross-sectional area of ​​the first channel 201 of the second fuel element 204. That is, for the fuel element 2 with relatively low power in the assembly, the cross-sectional area of ​​its first channel 201 is enlarged.

[0035] Therefore, the supercritical water reactor assembly for radial power flattening according to the embodiment of the present invention adjusts the area of ​​the first channel 201 of the fuel elements 2 at different positions in the assembly, expands the moderator channel area of ​​the fuel elements 2 with lower power values, improves the moderation capacity, and achieves an increase in the power of the fuel elements 2 here, thereby flattening the radial power distribution of the assembly or the core.

[0036] In some embodiments, Figure 1 As shown, the fuel element 2 is annular, and the first channel 201 is located at the center of the fuel element 2 .

[0037] Alternatively, if Figure 1 As shown, the fuel element 2 includes an inner cladding 21 , a fuel pellet 22 and an outer cladding 23 which are spaced apart from each other in sequence from the inside to the outside, and the central channel of the inner cladding 21 is a first channel 201 .

[0038] It can be understood that the annular fuel element 2 effectively increases the heat transfer area to reduce the temperature of the fuel pellets 22 and the cladding, and because the low-temperature water serving as a moderator is in the inner channel of the fuel element 2, the physical feedback is more uniform, which can effectively reduce the radial power factor.

[0039] Among them, Figure 1 As shown, there is an air gap 205 between the fuel pellet 22 and the inner cladding 21 and the outer cladding 23. The air gap 205 is filled with high-pressure helium to protect the integrity of the fuel rod.

[0040] Furthermore, the cladding of the component box 1 and the fuel element 2 are both made of austenitic stainless steel, which can serve for a long time under high temperature and high pressure.

[0041] In some embodiments, Figure 2As shown, the projection shape of the component box 1 along the vertical direction is a hexagon, and the fuel elements 2 at least located at the hexagons of the component box 1 among the plurality of fuel elements 2 are all first fuel elements 203 .

[0042] It should be noted that the inner and outer diameters of the fuel element 2 are adjusted according to the power distribution. Since the material of the component box 1 has an absorption effect on neutrons, if the size of all fuel elements 2 and the enrichment of the loaded fuel are kept consistent, the low power value will appear at the position of the peripheral fuel element 2, and the lowest point is generally at the hexagon of the hexagon. In order to solve the problem of low power of the peripheral fuel element 2, the inner diameter of the peripheral fuel element 2 is enlarged.

[0043] Therefore, if Figure 2 As shown, the fuel elements 2 located at the periphery of the assembly box 1 are all first fuel elements 203. Without changing the internal structure of the assembly and loading fuels with the same enrichment, the radial power of the assembly is flattened. Moreover, the power flattening can also be achieved for quadrilateral assemblies by a similar method.

[0044] Alternatively, if Figure 2 As shown, the ratio of the number of layers of first fuel elements 203 to the number of layers of second fuel elements 204 in the assembly box 1 is 1:(5-6). For example, the assembly includes 13 layers of 469 fuel elements 2 from the inside to the outside, the fuel elements 2 in the two outermost layers are the first fuel elements 203, and the fuel elements 2 in the eleventh inner layer are the second fuel elements 204.

[0045] In some embodiments, the inner side margin of the component box 1 is 20 cm to 21 cm, and the thickness of the component box 1 is 0.15 cm to 0.50 cm.

[0046] Preferably, the inner side margin of the component box 1 is 20.6454 cm, and the thickness of the component box 1 is 0.3 cm.

[0047] In some embodiments, the size of the first fuel element 203 differs from the size of the second fuel element 204 by 0.1 mm to 0.5 mm.

[0048] Specifically, the outer diameter of the first fuel element 203 is 8.2 mm, the diameter of the first channel 201 of the first fuel element 203 is 7.2 mm, the outer diameter of the second fuel element 204 is 8.0 mm, and the diameter of the first channel 201 of the second fuel element 204 is 7.0 mm.

[0049] In summary, the supercritical water reactor assembly of the embodiment of the present invention has two key points compared with the assembly in the related art.

[0050] First, the assembly adopts an annular fuel element 2, so that the moderator flows through the inside of the fuel element 2, eliminating the design of the moderator waterway in the assembly and simplifying the assembly structure. At the same time, the moderation level of the fuel element 2 is mainly related to the size of its own moderator channel and is independent, thus avoiding the problem of uneven power distribution of the assembly due to the different distances or densities of the fuel element 2 from the moderator waterway in the assembly with a waterway design.

[0051] Second, annular fuel elements 2 with different inner and outer diameters are used, while ensuring that the weight of nuclear fuel loaded on each fuel element 2 is basically the same. Because the moderator density of supercritical water reactors is generally lower than that of ordinary pressurized water reactors, there is generally a problem of insufficient moderation. By increasing the area of ​​the water channel, the local neutron energy spectrum can be effectively softened and the element power can be increased. This is a feature that ordinary pressurized water reactors do not have. Therefore, in supercritical water reactors, the method of changing the moderator flow rate of the inner channel can be used to control the power distribution of the fuel element 2, without having to load the fuel element 2 with fuels of different enrichments or combustible poisons in order to flatten the assembly power.

[0052] Due to the neutron absorption of the assembly box 1, the low power point of the assembly generally appears around the outermost fuel element 2 or control rod of the assembly. Therefore, by expanding the moderator channel of the fuel element 2 at the corresponding position, the power of the fuel element 2 is effectively increased, thereby achieving the goal of power flattening. At the same time, since the fuel loading amount of each fuel element 2 is basically the same, the fuel element 2 with high power consumes fuel quickly, and the fuel element 2 with low power consumes fuel slowly. Therefore, at the later stage of burnup, the power peak will gradually transfer from the high-power fuel element 2 at the beginning to the low-power fuel element 2, thereby achieving radial power flattening throughout the life cycle.

[0053] like Figure 3 As shown in the figure, through simple burnup calculation of a single component, the local power peak factor of a single component can be maintained below 1.02 during the entire life cycle. Considering that the reactivity control system and the asymmetric factors of the core have not yet been introduced, the actual radial peak factor of the component will be higher than the current simulation value, but it can be seen that the present invention has a significant effect on the radial power flattening of the component.

[0054] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0055] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0056] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0057] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0058] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0059] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. A supercritical water reactor assembly for radial power flattening, characterized in that: It includes a component box and a plurality of fuel elements uniformly arranged in the component box, wherein the fuel element has a first channel arranged in the vertical direction, and a second channel arranged in the vertical direction is provided between adjacent fuel elements, the bottoms of the first channel and the second channel are connected, the first channel and the second channel are used for flowing water, the water flows from top to bottom in the first channel and flows to the bottom of the first channel to reach a subcritical state, the water flows from bottom to top in the second channel and flows to the top of the second channel to reach a supercritical state, the plurality of fuel elements include a first fuel element and a second fuel element, and the cross-sectional area of ​​the first channel of the first fuel element is larger than the cross-sectional area of ​​the first channel of the second fuel element.

2. The supercritical water reactor assembly for radial power flattening according to claim 1, characterized in that: The fuel element is annular in shape, and the first channel is located at the center of the fuel element.

3. The supercritical water reactor assembly for radial power flattening according to claim 2, characterized in that: The fuel element comprises an inner cladding, a fuel pellet and an outer cladding which are sequentially spaced from the inside to the outside, and a central channel of the inner cladding is the first channel.

4. The supercritical water reactor assembly for radial power flattening according to any one of claims 1 to 3, characterized in that: The projection shape of the component box along the vertical direction is a hexagon, and at least the fuel elements located at the hexagons of the component box among the plurality of fuel elements are all the first fuel elements.

5. The supercritical water reactor assembly for radial power flattening according to claim 4, characterized in that: The fuel elements located at the periphery of the component box are all the first fuel elements.

6. The supercritical water reactor assembly for radial power flattening according to claim 5, characterized in that: The ratio of the number of layers of the first fuel elements to the number of layers of the second fuel elements in the assembly box is 1:(5-6).

7. The supercritical water reactor assembly for radial power flattening according to claim 3, characterized in that: The assembly box and the cladding of the fuel element are both made of austenitic stainless steel.

8. The supercritical water reactor assembly for radial power flattening according to claim 4, characterized in that: The inner side margin of the component box is 20 cm to 21 cm, and the thickness of the component box is 0.15 cm to 0.50 cm.

9. The supercritical water reactor assembly for radial power flattening according to claim 8, characterized in that: The size of the first fuel element differs from the size of the second fuel element by 0.1 mm to 0.5 mm.

10. The supercritical water reactor assembly for radial power flattening according to claim 9, characterized in that: The outer diameter of the first fuel element is 8.2 mm, and the diameter of the first channel of the first fuel element is 7.2 mm. The outer diameter of the second fuel element is 8.0 mm, and the diameter of the first channel of the second fuel element is 7.0 mm.

Images