WO2023283971A1

WO2023283971A1 - Positioning lattice and fuel assembly

Info

Publication number: WO2023283971A1
Application number: PCT/CN2021/107180
Authority: WO
Inventors: 禹文池; 陈威; 汤阳阳; 鲁亚恒; 李伟才
Original assignee: 中广核研究院有限公司; 中广核工程有限公司; 中国广核集团有限公司; 中国广核电力股份有限公司
Priority date: 2021-07-13
Filing date: 2021-07-19
Publication date: 2023-01-19
Also published as: CN117616513A

Abstract

Disclosed in the present invention are a positioning lattice and a fuel assembly. The positioning lattice is used for the middle position of the fuel assembly, and is made of a material having the same or greater expansion coefficient with respect to a reactor core plate material. The positioning lattice of the present invention is made of the material having the same or greater expansion coefficient with respect to the reactor core plate material, is mainly used for the middle position of the fuel assembly, and effectively reduces a gap between lattices under normal operation conditions, thereby improving the safety performance of a reactor, and reducing the uncertainty of thermal work caused by the gap at the same time.

Description

Positioning grid and fuel assembly

technical field

The invention relates to the technical field of nuclear fuel, in particular to a positioning grid and a fuel assembly.

Background technique

Fuel assemblies in existing reactors generally use bundle-type fuel, with a length and width of about 214mm and a height of about 4m. This slender structure is easily subjected to temperature, radiation, hydraulic and other loads in the reactor, and it will bend, and its typical shape is C-shaped. Considering hoisting, a gap of certain width will be reserved between fuel assemblies.

In existing fuel assemblies, spacers are generally made of zirconium alloys. Considering that the spacer grid will grow after being irradiated, the gap between the fuel assemblies will be appropriately enlarged. Under normal operating conditions, the thermal expansion of the upper/lower core plates (stainless steel) is greater than that of the spacer grid (zirconium alloy), and the gap will be enlarged again. Under severe lateral loads, the individual gaps of a row of fuel assemblies can superimpose. The longer the accumulation of gaps, the longer the acceleration time of the lateral motion of the middle part of the fuel assembly, and the greater the force of the impact of the fuel assembly on the core coaming, the easier it is for the spacer grid of the fuel assembly to be damaged and deformed, which in turn leads to the cooling of the geometric channel (affecting A key indicator of reactor safety) becomes smaller.

technical problem

The technical problem to be solved by the present invention is to provide a spacer grid and a fuel assembly that are resistant to extreme lateral impact loads.

technical solution

The technical solution adopted by the present invention to solve the technical problem is: to provide a fuel assembly, including an upper tube base and a lower tube base arranged oppositely, and a grid set arranged between the upper tube base and the lower tube base; The grid set includes several grids distributed between the upper tube base and the lower tube base at intervals along the axial direction of the fuel assembly; at least one grid located in the middle of the grid set adopts the same expansion coefficient or Spacer grids made of materials greater than the expansion coefficient of the reactor core plate material, and the rest of the grids are zirconium alloy grids;

The positioning grid includes an outer frame surrounded by several outer strips; at least one of the outer strips is provided with a protruding part extending on at least one side of its longitudinal direction, and the protruding part is located on the outer side where it is located. In the middle position of the strip, increase the width of the outer strip in the longitudinal direction;

In the grid group, the distance between the spacer grids adjacent up and down is smaller than the distance between the zirconium alloy grids; and/or, the distance between the spacer grids and the zirconium alloy grids The distance is less than the distance between the zirconium alloy grids.

The present invention also provides another spacer grid, which is used in the middle of the fuel assembly. The spacer grid is made of a material with the same expansion coefficient or greater than the expansion coefficient of the reactor core plate material.

Preferably, the spacer frame is made of stainless steel or nickel-based alloy.

Preferably, the positioning grid includes an outer frame surrounded by several outer strips; at least one of the outer strips is provided with a protrusion extending on at least one side in its longitudinal direction.

Preferably, the protruding portions are respectively extended on opposite sides of the outer strip in the longitudinal direction.

Preferably, in the length direction of the outer strip, the protrusion is located at the middle section of the outer strip, so that the outer strip has a structure in which the center is large and the ends are small.

Preferably, each of said outer strips of said outer frame is provided with said protrusion.

Preferably, the protrusion is an arc-shaped protrusion or a polygonal protrusion.

Preferably, the spacer grid further includes a plurality of parallel spaced first inner strips and a plurality of parallel spaced second inner strips arranged in the outer frame; the first inner strips and the second The inner strips cross each other to form a network-like grid unit.

The present invention also provides a fuel assembly, which includes an upper nozzle seat and a lower nozzle seat arranged oppositely, and a grid group arranged between the upper nozzle seat and the lower nozzle seat; the grid group includes several The grids distributed between the upper tube base and the lower tube base at axial intervals; at least one grid located in the middle of the grid set is the spacer grid described in any one of the above.

Preferably, the grid set includes 1-3 positioning grids.

Preferably, the rest of the grids in the grid group are zirconium alloy grids;

The distance between the spacer grids adjacent up and down is smaller than the distance between the zirconium alloy grids; and/or, the distance between the spacer grids and the zirconium alloy grids is smaller than the distance between the zirconium alloy grids Distance between grids.

Beneficial effect

The spacer grid of the present invention is made of a material with the same expansion coefficient or greater than that of the reactor core plate material, and is mainly used in the middle of the fuel assembly, avoiding the spacer grid made of conventional zirconium alloys from being damaged by radiation. The growth causes the gap between the fuel assemblies to enlarge, effectively reducing the gap between the grids under normal operation, thereby improving the safety performance of the reactor (guaranteeing a coolable geometry), and reducing the thermal uncertainty caused by the gap (such as A row of fuel assemblies bends to one side, resulting in increased water gaps and uneven distribution of moderating material).

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment, in the accompanying drawing:

Fig. 1 is a schematic structural view of a fuel assembly according to an embodiment of the present invention;

Fig. 2 is the structural representation of the outer strip of spacer frame in Fig. 1;

Fig. 3 is a schematic diagram of overlapping outer strips of two adjacent spacer grids in the present invention.

Embodiments of the present invention

In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation manners of the present invention will now be described in detail with reference to the accompanying drawings.

As shown in Figure 1, the fuel assembly according to one embodiment of the present invention includes an upper nozzle 10 and a lower nozzle 20 arranged oppositely, a grid group 30 arranged between the upper nozzle 10 and the lower nozzle 20, and several Fuel rods 40 etc.

The grid group 30 includes several grids distributed between the upper tube base 10 and the lower tube base 20 at intervals along the axial direction of the fuel assembly; the fuel rods 40 axially pass through several grids, and the upper and lower ends of the fuel rods 40 Inserted on the upper tube base 10 and the lower tube base 20 respectively.

At least one of the grids located in the middle of the grid group 30 is a spacer grid 31 for resisting lateral ultimate impact load, and the rest are zirconium alloy grids 32 . The spacer grid 31 is made of a material whose expansion coefficient is the same as or greater than that of the reactor core plate material. For example, the spacer grid 31 is made of stainless steel or nickel-based alloy (Inconel).

From the perspective of neutron economy, combined with the number of grids in the grid group 30 , the number of positioning grids 31 in the grid group 30 is 1-3, and they are located in the middle of the grid group 30 .

Structurally, the spacer grid 31 includes an outer frame surrounded by several outer strips 310 , a plurality of parallel spaced first inner strips and a plurality of parallel spaced second inner strips arranged in the outer frame. The first inner strips and the second inner strips cross each other to form a network grid unit. The grid unit includes a plurality of adjacently connected cells in sequence, and the cells are hollow, through which the fuel rods and guide tubes of the fuel assembly respectively pass.

In order to prevent the material of the spacer grids 31 from affecting the neutron economy, in the fuel assembly, the distance between the spacer grids 31 or between the spacer grids 31 and the zirconium alloy grid 32 can be reduced compared with the conventional distance. For example, the distance between the up and down adjacent zirconium alloy grids 32 is set with the spacing between the grids in the conventional fuel assembly, the distance between the up and down adjacent spacer grids 31, the up and down adjacent spacer grids 31 At least one of the distances between the zirconium alloy grids 32 is reduced so that the distance between the spacer grids 31 and/or the distance between the spacer grids 31 and the zirconium alloy grids 32 is smaller than the aforementioned zirconium alloy grids 32. The distance between the alloy grids 32.

In addition, in order to avoid the difference in the growth and manufacture of adjacent fuel assemblies in the fuel assembly, the grid will be misaligned, resulting in insufficient overlapping area of the grid, which will seriously affect the lateral positioning (normal operation) of the fuel assembly and the transmission of lateral load ( ACCIDENT). As shown in FIG. 2 , on the outer frame, at least one outer strip 310 is provided with a protruding portion 311 extending on at least one side in the longitudinal direction, the main function of which is to increase the width of a part of the outer strip 310 in the longitudinal direction. The protrusion 311 may be an arc protrusion or a polygon protrusion.

Preferably, the outer strip 310 is provided with protrusions 311 extending on opposite sides in the longitudinal direction thereof.

Even if the spacer grids 31 of adjacent fuel assemblies are offset laterally and axially, the arrangement of the protrusions 31 on the outer strip 310 can still ensure that there is an overlapping area 312 in the transverse direction between the spacer grids 31 of adjacent fuel assemblies , to ensure lateral positioning between fuel assemblies (normal operation) and transfer of lateral loads (accident).

Further, in the length direction of the outer strip 310, the protruding part 311 is located at the middle position of the outer strip 310, so that the outer strip 310 has a structure with a large middle and small ends. materials to improve neutron economy.

In addition, according to the fact that the fuel assemblies in the reactor are arranged adjacent to each other, and there are adjacent fuel assemblies on each side of each fuel assembly, it is preferable that each outer strip 310 of the outer frame of the positioning grid 31 is provided with a protruding Section 311.

The fuel assembly of the present invention, through the arrangement of the positioning grid 31 in the middle of the grid group, reduces the gap between the grids under normal operation, thereby improving the safety performance of the reactor (guaranteeing a coolable geometry), and reducing the gap caused by the gap Generated thermal uncertainties (such as a row of fuel assemblies bent to one side, resulting in increased water gaps, non-uniform distribution of moderating material); reduced lateral impact loads on the fuel assembly grid under accident conditions.

In addition, the setting of the protruding portion 311 on the spacer grid 31 solves the problem of grid dislocation caused by component growth differences of the lower spacer grid 31 under different fuel consumption (dislocation easily leads to difficulty in lateral load transmission).

The above is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technologies fields, all of which are equally included in the scope of patent protection of the present invention.

Claims

A fuel assembly, characterized in that it includes an upper tube base and a lower tube base arranged oppositely, and a grid set arranged between the upper tube base and the lower tube base; the grid set includes several The axial interval is distributed between the grids between the upper tube base and the lower tube base; at least one grid located in the middle of the grid group is made of a grid with the same expansion coefficient or greater than the expansion coefficient of the reactor core plate material The positioning grid made of materials, and the rest of the grids are zirconium alloy grids;

The positioning grid includes an outer frame surrounded by several outer strips; at least one of the outer strips is provided with a protruding part extending on at least one side of its longitudinal direction, and the protruding part is located on the outer side where it is located. In the middle position of the strip, increase the width of the outer strip in the longitudinal direction;

In the grid group, the distance between the spacer grids adjacent up and down is smaller than the distance between the zirconium alloy grids; and/or, the distance between the spacer grids and the zirconium alloy grids The distance is less than the distance between the zirconium alloy grids.
A spacer grid, characterized in that it is used in the middle of the fuel assembly, and the spacer grid is made of a material with the same expansion coefficient or greater than the expansion coefficient of the reactor core plate material.
The spacer grid according to claim 2, wherein the spacer grid is made of stainless steel or nickel-based alloy.
The spacer grid according to claim 2, wherein the spacer grid comprises an outer frame surrounded by several outer strips; at least one of the outer strips extends on at least one side in its longitudinal direction A protrusion is provided.
The spacer grid according to claim 4, wherein the protrusions are respectively extended on opposite sides of the outer strip in the longitudinal direction.
The positioning grid according to claim 5, characterized in that, in the length direction of the outer strip, the protrusion is located at the middle position of the outer strip, so that the outer strip is in the middle Large structures with small ends.
The spacer grid according to claim 4, wherein each of said outer strips of said outer frame is provided with said protrusion.
The spacer grid according to claim 4, wherein the protrusions are arc-shaped protrusions or polygonal protrusions.
The spacer grid according to any one of claims 4-8, wherein the spacer grid further comprises a plurality of parallel spaced first inner strips and a plurality of parallel spaced The second inner strip; the first inner strip and the second inner strip intersect each other to form a network grid unit.
A fuel assembly, characterized in that it includes an upper tube base and a lower tube base arranged oppositely, and a grid set arranged between the upper tube base and the lower tube base; the grid set includes several The axial spacing is distributed between the upper tube seat and the lower tube seat; at least one grid located in the middle of the grid group is the spacer grid described in any one of claims 2-9.
The fuel assembly according to claim 10, wherein the grid set includes 1-3 spacer grids.
The fuel assembly according to claim 11, wherein the remaining grids in the grid group are zirconium alloy grids;

The distance between the spacer grids adjacent up and down is smaller than the distance between the zirconium alloy grids; and/or, the distance between the spacer grids and the zirconium alloy grids is smaller than the distance between the zirconium alloy grids Distance between grids.