1. A fuel rod to overcome pellet cladding mechanical interaction, comprising cladding and fuel pellets, wherein a gap between the cladding and the fuel pellets contains a predetermined thermal expansion difference space.

2. A fuel rod to overcome pellet cladding mechanical interaction according to claim 1, wherein the clearance between the cladding and the fuel pellets is δ 1+ Δ r2- Δ r 1;

where δ 1 is the fuel rod gap, Δ r1 is the maximum thermal expansion of the fuel pellets, and Δ r2 is the cladding corresponding thermal expansion.

3. A fuel rod to overcome pellet cladding mechanical interaction according to claim 1, wherein said fuel pellets employ high thermal conductivity fuel pellets, lowering the temperature of the fuel pellets.

4. A fuel rod to overcome pellet cladding mechanical interaction according to claim 1, wherein the fuel pellets are equivalent fuel pellets made of uranium dioxide fuel placed in a metal of high thermal conductivity.

5. A fuel rod to overcome pellet cladding mechanical interaction according to claim 4, wherein the metallic phase of the uranium dioxide fuel matrix has a coefficient of thermal expansion less than the coefficient of thermal expansion of the cladding.

6. A fuel rod for overcoming pellet cladding mechanical interaction according to claim 4, wherein said cladding is of zirconium alloy material and said uranium dioxide fuel matrix is of tungsten material.

7. A fuel rod to overcome pellet cladding mechanical interaction according to claim 4, wherein said high thermal conductivity metal is stainless steel.

8. A fuel assembly, characterized in that a fuel rod according to any one of claims 1-7 is used.

9. A nuclear reactor, characterized in that a fuel assembly according to claim 8 is used.

Background

The fuel rods are used to contain nuclear fuel and fission products. Conventional fuel rod designs often employ uranium dioxide ceramic fuel, zirconium alloy cladding for neutron economy. Because the ceramic fuel is the place where the nuclear reaction occurs, the temperature of the ceramic fuel is higher, and the thermal expansion coefficient of uranium dioxide is larger than that of zirconium alloy, when rapid power change occurs, the zirconium alloy cladding generates larger strain due to radial push-pull of ceramic fuel pellets, so that fatigue failure is generated, the structural integrity of the fuel rod is damaged, and the most important function of shielding the nuclear fuel and fission products is lost. Currently nuclear power fuel assemblies accommodate this requirement by limiting the power variation of the reactor, but this limits the range of applicability of the fuel assembly.

The prior art proposes the use of chromium oxide Cr₂O₃As an additive to fuel pellets, it improves the thermal creep performance of the fuel pellets and the cladding performance through control of the cladding materials and processes, and limits the motion power to reduce the loading of the pellet cladding upon mechanical interaction to reduce the risk of cladding failure, but it still does not fundamentally alleviate or eliminate the pellet cladding mechanical interaction and is difficult to adapt to reactors with fast power change requirements.

Disclosure of Invention

In order to solve the problems that the prior art cannot fundamentally relieve or eliminate the mechanical interaction of the pellet cladding and is difficult to adapt to the fuel rod with the requirement of rapid power change, the invention provides the fuel rod which overcomes the mechanical interaction of the pellet cladding and solves the problems. The invention relieves and eliminates the mechanical interaction of the core block cladding of the fuel rod by reducing the thermal expansion difference of the core block and the cladding, so that the fuel rod has the capability of adapting to rapid power conversion, further has wider adaptability, simplifies the operation of a reactor and reduces the operation limitation of the reactor.

The invention is realized by the following technical scheme:

a fuel rod that overcomes pellet cladding mechanical interaction includes a cladding and fuel pellets with a gap between the cladding and the fuel pellets containing a predetermined thermal expansion difference space.

The invention can avoid the mechanical interaction of the pellet cladding under larger power variation range by presetting the thermal expansion difference space in the fuel rod.

Preferably, the gap between the cladding of the present invention and the fuel pellets is δ 1+ Δ r2- Δ r 1;

where δ 1 is the fuel rod gap, Δ r1 is the maximum thermal expansion of the fuel pellets, and Δ r2 is the cladding corresponding thermal expansion.

Preferably, the fuel pellets of the present invention employ fuel pellets of high thermal conductivity to reduce the temperature of the fuel pellets.

Preferably, the fuel pellet of the present invention is an equivalent fuel pellet made by placing uranium dioxide fuel in a metal of high thermal conductivity.

Preferably, the coefficient of thermal expansion of the metal phase of the uranium dioxide fuel matrix of the invention is less than the coefficient of thermal expansion of the cladding.

Preferably, the cladding of the invention is made of zirconium alloy material, and the uranium dioxide fuel matrix is made of tungsten material.

Preferably, stainless steel is used as the high thermal conductivity metal of the present invention.

The fuel rod of the invention adopts the fuel material with lower thermal expansion coefficient and the cladding material with higher thermal expansion coefficient, for example, uranium dioxide and other conventional fuels are put into metal with high thermal conductivity to prepare equivalent fuel pellets, so that the equivalent thermal expansion coefficient of the pellets is close to that of the base metal, and the thermal expansion of the pellets can be effectively reduced; or the current zirconium alloy cladding is doped and modified to improve the thermal expansion coefficient, which can relieve or eliminate the mechanical interaction of the core block cladding.

In a second aspect, the invention provides a fuel assembly incorporating a fuel rod according to the invention.

In a third aspect, the present invention provides a nuclear reactor employing a fuel assembly according to the present invention.

The invention has the following advantages and beneficial effects:

1. the invention overcomes the mechanical interaction of the pellet cladding of the fuel rod, ensures that the fuel rod has the capability of adapting to rapid power change, enlarges the application range of the fuel assembly adopting the fuel rod, simplifies the operation of a reactor, reduces the operation limitation of the reactor, and improves the economy of the fuel assembly and even the reactor.

2. The invention overcomes the mechanical interaction of the pellet cladding of the fuel rod, thereby eliminating the failure mechanism of PCI (pellet cladding interaction) and improving the reliability of the fuel rod;

3. the invention adopts the measure of the fuel pellet with high thermal conductivity, can also reduce the thermal energy storage of the fuel assembly and reduce the safety risk after the accident occurs.

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 rod of the present invention.

FIG. 2 is a partial cross-sectional view of a fuel rod structure of the present invention.

Fig. 3 is a schematic view of a high thermal conductivity fuel pellet of the present invention.

Reference numbers and corresponding part names in the drawings:

1-clad, 2-fuel pellet, 3-clad-fuel pellet gap, 4-fuel, 5-high thermal conductivity matrix.

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

Compared with the conventional fuel rod structure which cannot fundamentally relieve or eliminate the mechanical interaction of the pellet cladding and is difficult to use in the reactor with the requirement of rapid power change, the embodiment provides the fuel rod for overcoming the mechanical interaction of the pellet cladding.

As shown particularly in fig. 1-3, the fuel rod of the present embodiment includes a cladding 1, fuel pellets 2, and cladding-fuel pellet gaps 3;

the clad-fuel pellet gap 3 of the present embodiment includes a preset thermal expansion difference space, and the present embodiment includes a fuel pellet gap 3 of δ 1+ Δ r2- Δ r 1;

where δ 1 is the fuel rod gap, Δ r1 is the maximum thermal expansion of the fuel pellets, and Δ r2 is the cladding corresponding thermal expansion.

Example 2

To further mitigate or eliminate pellet cladding mechanical interactions, the fuel rod of this example employs high thermal conductivity fuel pellets, based on example 1 above, reducing the temperature of the fuel pellets. Such as by placing conventional fuels such as uranium dioxide in a metal of high thermal conductivity to make equivalent fuel pellets.

The metal with high thermal conductivity of the present embodiment may be made of stainless steel.

Example 3

To further mitigate or eliminate pellet cladding mechanical interactions, this embodiment uses a lower coefficient of thermal expansion fuel material and a higher coefficient of thermal expansion cladding material on the basis of the above-described embodiments. If the conventional fuel such as uranium dioxide is put in metal with high thermal conductivity to prepare an equivalent fuel pellet, the equivalent thermal expansion coefficient of the pellet is close to that of the base metal, and the thermal expansion of the pellet can be effectively reduced; or the current zirconium alloy cladding is doped and modified to improve the thermal expansion coefficient, which can relieve or eliminate the mechanical interaction of the core block cladding.

The thermal expansion coefficient of the metal phase of the uranium dioxide fuel matrix of the embodiment is smaller than that of the cladding, for example, the cladding is made of zirconium alloy material, and the matrix metal is made of tungsten material.

The invention overcomes the mechanical interaction of the pellet cladding of the fuel rod, so that the fuel rod has the capability of adapting to rapid power change, the application range of a fuel assembly adopting the fuel rod is enlarged, the operation of a reactor is simplified, the operation limit of the reactor is reduced, and the economy of the fuel assembly and even the reactor is improved; meanwhile, the failure mechanism of PCI (pellet cladding interaction) is eliminated, and the reliability of the fuel rod is improved; the thermal energy storage of the fuel assembly can be reduced, and the safety risk after an accident occurs is reduced.

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.