阅读说明：本技术 一种可有效减小燃料组件轴向载荷的压紧系统和燃料组件 (Compression system capable of effectively reducing axial load of fuel assembly and fuel assembly ) 是由 李云 蒲曾坪 张�林 陈平 肖忠 李华 茹俊 朱发文 谷明非 秦勉 李�权 黄 于 2021-06-17 设计创作，主要内容包括：本发明公开了一种可有效减小燃料组件轴向载荷的压紧系统和燃料组件,本发明的压紧系统布置在燃料组件的下部,为燃料组件提供轴向支撑及定位。本发明提供的燃料组件压紧系统可以使得燃料组件在堆内所受轴向压缩载荷显著减小,有利于缓解燃料组件弯曲,并减小各零部件所受应力水平,提高燃料组件的安全裕量。(The invention discloses a compression system capable of effectively reducing axial load of a fuel assembly and the fuel assembly. The fuel assembly compression system provided by the invention can obviously reduce the axial compression load of the fuel assembly in the stack, is beneficial to relieving the bending of the fuel assembly, reduces the stress level of each part and improves the safety allowance of the fuel assembly.)

1. A compression system effective to reduce axial loading of a fuel assembly, the compression system being disposed at a lower portion of the fuel assembly to provide axial support and positioning of the fuel assembly.

2. A compression system for efficiently reducing the axial load on a fuel assembly as set forth in claim 1, wherein the compression system comprises a plurality of sets of elastic members mounted on the lower end of the lower pipe seat (5) of the fuel assembly to provide axial compression and support to the fuel assembly.

3. The hold-down system for reducing axial loading of a fuel assembly of claim 2, wherein the hold-down system comprises one or more of a leaf spring, a coil spring, and a belleville spring.

4. The hold-down system for reducing axial load of a fuel assembly of claim 2, wherein each set of leaf springs is composed of one leaf spring when the elastic member is a leaf spring.

5. The hold-down system for reducing axial load of fuel assembly as claimed in claim 2, wherein when the elastic member is a plate spring, each group of plate springs is composed of a plurality of plate spring pieces which are overlapped, in each group of plate springs, the tail of the uppermost plate spring piece moves the rest of the plate spring pieces together and hooks the tail of the uppermost plate spring piece into the lower tube base, and the root of each group of plate springs is fixed on the lower tube base through a fastener, so as to prevent the spring from loosening or moving to the lower cavity of the lower tube base after the root is broken to affect the distribution of the flow field.

6. The hold-down system for reducing axial loading of a fuel assembly of claim 5, wherein the overlapping leaf springs of each set of leaf springs have a gradually decreasing thickness at their end portions or a locally decreasing width at their end portions.

7. The hold-down system for reducing axial load of fuel assembly of claim 2, wherein when the elastic member is a coil spring, each set of coil springs is composed of one or several concentric coil springs.

8. The hold-down system for reducing axial load of fuel assembly of claim 2, wherein when the elastic member is a disk spring, each set of disk springs is composed of one or several disk spring pieces placed in an overlapping manner.

9. A fuel assembly, characterized in that a compression system according to any one of claims 1-8 is used.

Technical Field

The invention belongs to the technical field of fuel assemblies, and particularly relates to a compression system capable of effectively reducing axial load of a fuel assembly and the fuel assembly.

Background

In pressurized water reactor fuel assembly design, it is generally necessary to design a compression system with elasticity to compensate for manufacturing height differences of the fuel assemblies, different thermal expansion differences between the fuel assemblies and the internals of the reactor, and irradiation growth of the fuel assemblies so as to axially compress the fuel assemblies and maintain their axial positions.

In the case of coolant flowing from bottom to top in the core, the fuel assembly design usually has a hold-down system on its upper header to hold it down axially, preventing it from jumping under hydraulic load. The compression system will apply an axial compressive load to the fuel assembly. In order to resist the hydraulic load borne by the fuel assembly in the existing design, the compression load of the compression system is generally set to be higher, and a larger allowance is reserved.

In a typical design, the maximum compression load of the thermal compression system is approximately equal to the hydraulic load on the fuel assembly, which is much greater than the weight of the fuel assembly. Therefore, the compressive load is much greater than the fuel assembly weight.

When the fuel assembly works in a high-temperature high-pressure and irradiation environment in a reactor, the fuel assembly tends to generate transverse deformation and bending under the action of overhigh axial compression load. Fuel assembly bending tends to make it more difficult for the control rod assembly to be inserted into the core, affecting control rod drop time and, in turn, affecting reactor safety. At the same time, the bending of the fuel assembly also makes loading and unloading more difficult.

To reduce fuel assembly bending, it is necessary to reduce the axial loads to which it is subjected. The usual approach is to reduce the stiffness of the hold-down system springs, but this approach can lead to the fuel assembly jumping due to insufficient hold-down force, which in turn affects the structural integrity of the fuel assembly.

Disclosure of Invention

Aiming at the problems of the existing compression system, the invention provides a compression system capable of effectively reducing the axial load of a fuel assembly. The invention can ensure the axial compression and positioning of the fuel assembly, and can obviously reduce the axial compression load borne by the fuel assembly, thereby reducing the transverse bending of the fuel assembly, and being beneficial to relieving the difficulty that the control rod assembly cannot be completely inserted or the material is loaded and unloaded due to the bending of the fuel assembly.

The invention is realized by the following technical scheme:

a compression system for effectively reducing the axial load on a fuel assembly is arranged at the lower part of the fuel assembly to provide axial support and positioning for the fuel assembly.

Preferably, the compression system of the present invention is comprised of a plurality of sets of elastic elements mounted at the lower end of the lower pipe seat of the fuel assembly to provide axial compression and support to the fuel assembly.

Preferably, the compression system of the invention employs one or more of a plate spring, a coil spring, and a disc spring.

Preferably, when the plate springs are used as the elastic members of the present invention, each set of plate springs is composed of one plate spring piece.

Preferably, when the elastic element adopts plate springs, each group of plate springs is composed of a plurality of plate spring pieces which are overlapped, in each group of plate springs, the rest spring pieces are strung together through the tail part of the uppermost spring piece and hooked into the lower pipe seat, and the root part of each group of plate springs is fixed on the lower pipe seat through a fastener, so that the influence of the loosening of the springs or the movement of the root part to the lower cavity of the lower pipe seat after the root part is broken on the flow field distribution is avoided.

Preferably, the thickness of the end position of the overlapped spring piece in each group of plate springs is gradually reduced, or the width of the end position is locally gradually narrowed.

Preferably, when the elastic element of the present invention is a coil spring, each set of coil springs is composed of one or several concentric coil springs.

Preferably, when the elastic element of the present invention is made of disc springs, each set of disc springs is made of one or several disc spring pieces placed in an overlapping manner.

In another aspect, the invention also provides a fuel assembly, which adopts the compaction system.

The invention has the following advantages and beneficial effects:

1. the fuel assembly compression system provided by the invention can obviously reduce the axial compression load of the fuel assembly in the stack, is beneficial to relieving the bending of the fuel assembly, reduces the stress level of each part and improves the safety allowance of the fuel assembly.

2. The fuel assembly is typically subjected to a thermal hydraulic load that is much greater than its weight. The upper end of the fuel assembly will abut the upper core plate due to the hydraulic load. The fuel assembly can not jump up due to overlarge hydraulic load. The higher the hydraulic load, the higher the force of the fuel assembly on the upper core plate, and the more firmly the fuel assembly is axially positioned. This provides conditions for increasing the core coolant flow rate, increasing the hot work allowance and increasing the reactor power.

3. The axial compression system of the fuel assembly is arranged at the bottom of the fuel assembly and plays a supporting role for the fuel assembly. In a cold installation state, the compression system only needs to compress a small deformation amount, enough spring force is generated to support the weight of the fuel assemblies, and the upper core plate does not apply axial load or only applies small axial load to the fuel assemblies. As the temperature increases, the compression system stiffness decreases, and its compression will also decrease much due to the difference in material thermal expansion between the fuel assembly guide tube and the spider cylinder. The compression force of the compression system from cold state to hot state is greatly reduced, and the compression load of the fuel assembly is far less than the weight of the fuel assembly. And in the running process of the reactor, the pressing force of the pressing system tends to be constant, the integrity of the pressing system is not endangered due to excessive hydraulic load, and the phenomenon that the pressing system is subjected to cyclic load and fatigue caused by fluctuation of the hydraulic load in the traditional design is avoided.

4. When the fuel assembly pressing system adopts the plate spring, the plate spring can work in an elastic range or slightly exceeds the elastic range because the working state of the plate spring is greatly reduced compared with the traditional design, the risk of fracture and failure of the root part of the plate spring is lower, and the structural integrity of the plate spring is favorably ensured.

5. The axial pressing force of the fuel assembly pressing system is small, the axial load of the fuel assembly on the components in the stack is small, and the safety allowance of the components in the stack is increased.

6. The fuel assembly hold-down system of the invention is arranged at the bottom of the fuel assembly and is not in the range of the motion stroke of the control rod assembly, and the normal action of the drive wire can not be influenced even if individual springs of the hold-down system are broken or loosened.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:

FIG. 1 is a schematic view of a fuel assembly hold down system arrangement of the present invention.

FIG. 2 is a schematic view of a lower tube seat structure of the fuel assembly of the present invention.

Fig. 3 is a schematic view of the fuel assembly hold-down spring structure of the present invention.

Reference numbers and corresponding part names in the drawings:

1-upper tube seat, 2-location grid, 3-fuel rod, 4-guide tube, 5-lower tube seat, 6-compression system, 7-spring screw, 8-first spring piece, 9-second spring piece, 10-third spring piece and 11-fourth spring piece.

Detailed Description

Hereinafter, the term "comprising" or "may include" used in various embodiments of the present invention indicates the presence of the invented function, operation or element, and does not limit the addition of one or more functions, operations or elements. Furthermore, as used in various embodiments of the present invention, the terms "comprises," "comprising," "includes," "including," "has," "having" and their derivatives are intended to mean that the specified features, numbers, steps, operations, elements, components, or combinations of the foregoing, are only meant to indicate that a particular feature, number, step, operation, element, component, or combination of the foregoing, and should not be construed as first excluding the existence of, or adding to the possibility of, one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing.

In various embodiments of the invention, the expression "or" at least one of a or/and B "includes any or all combinations of the words listed simultaneously. For example, the expression "a or B" or "at least one of a or/and B" may include a, may include B, or may include both a and B.

Expressions (such as "first", "second", and the like) used in various embodiments of the present invention may modify various constituent elements in various embodiments, but may not limit the respective constituent elements. For example, the above description does not limit the order and/or importance of the elements described. The foregoing description is for the purpose of distinguishing one element from another. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of various embodiments of the present invention.

It should be noted that: if it is described that one constituent element is "connected" to another constituent element, the first constituent element may be directly connected to the second constituent element, and a third constituent element may be "connected" between the first constituent element and the second constituent element. In contrast, when one constituent element is "directly connected" to another constituent element, it is understood that there is no third constituent element between the first constituent element and the second constituent element.

The terminology used in the various embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the various embodiments of the invention. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments of the present invention belong. The terms (such as those defined in commonly used dictionaries) should be interpreted as having a meaning that is consistent with their contextual meaning in the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein in various embodiments of the present invention.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.

Example 1

The embodiment provides a compression system 6 which can effectively reduce the axial load of the fuel assembly, and the compression system 6 is arranged at the lower part of the fuel assembly of the reactor and provides axial support and positioning for the fuel assembly.

As shown in fig. 1, the compression system 6 is comprised of a plurality of sets of resilient members mounted to the lower end of the lower nozzle 5 of the fuel assembly to provide axial compression and support to the fuel assembly as it is installed in the reactor.

The hold-down system 6 of the present embodiment may be implemented by a plate spring, a coil spring, a disc spring, other elastic elements, or a combination thereof.

The stiffness and stroke (range of deformation) of the compression system 6 of the present embodiment should be compatible with the weight of the fuel assembly and its operating environment and parameters (temperature, pressure, coolant flow, stack cavity height, etc.) to provide suitable axial compression forces.

The elastic element adopted by the pressing system 6 of the present embodiment is a plate spring, that is, the pressing system 6 of the present embodiment is composed of a plurality of groups of plate springs installed at the lower end of the lower tube seat, and each group of plate springs is composed of one or a plurality of plate springs placed in an overlapping manner; and each leaf spring can gradually reduce the thickness of the end part position or gradually narrow the width of the end part position, so that the spring group has proper rigidity characteristics. The root of each group of plate springs is fixed on the lower tube seat through bolts or pins; the tail part of the uppermost plate spring of each group of plate springs leads the rest springs to be connected together and hooked into the lower pipe seat, so that the situation that the springs are loosened or the roots of the springs are broken and then move to the lower cavity of the lower pipe seat to influence the distribution of a flow field is avoided; after the fuel assembly is installed in the reactor core, the spring is compressed under the action of the gravity of the fuel assembly to generate axial force, and the bottom of the fuel assembly is supported.

As shown in fig. 2 to 3, the hold-down system 6 of the present embodiment is constituted by a set of plate springs mounted on each of the four sides of the lower end of the lower tube seat 5 of the fuel assembly, that is, the hold-down system 6 of the present embodiment is constituted by four sets of plate springs each constituted by 4 plate-like spring pieces placed in an overlapping manner.

The second spring piece 9, the third spring piece 10 and the fourth spring piece 11 are arranged together to form a whole body at the tail part of the first spring piece 8, the root part of the plate spring is fixed on the lower tube seat 5 through the screw 7 when the tail part of the first spring piece 8 is hooked inside the lower tube seat 5, and the situation that the spring is loosened or the root part is broken and then moves to the lower tube seat lower cavity to influence flow distribution is avoided.

Example 2

The present embodiment is different from embodiment 1 in that the elastic element adopted by the pressing system 6 of the present embodiment is a coil spring, that is, the pressing system 6 of the present embodiment is composed of a plurality of groups of coil springs installed at the lower end of the lower pipe seat 5 of the fuel assembly, and each group of coil springs is composed of one or several concentric coil springs; each set of coil springs may be provided with guides, the compressive load generated by the coil springs providing support for the bottom of the fuel assembly.

Example 3

The difference between the present embodiment and embodiment 1 is that the elastic element adopted by the pressing system 6 of the present embodiment is a disc spring, that is, the pressing system 6 of the present embodiment is composed of a plurality of groups of disc springs mounted at the lower end of the lower pipe seat 5, and each group of disc springs is composed of one or a plurality of overlapped disc spring pieces; each set of belleville springs may be provided with a guide means, the compressive load generated by the belleville springs providing support for the bottom of the fuel assembly.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.