JPH0862360A - Fuel spacer and fuel assembly - Google Patents

Abstract

PURPOSE: To prevent the occurrence of an internal stress resulted from an irradiation growth elongation difference in a fuel spacer, because no irradiation growth elongation difference is caused between zirconium alloy members constituting the fuel space. CONSTITUTION: In the fuel assembly, the fuel spacer is fixed by a plurality of cell materials 8 forming independent unit cells for inserting and supporting fuel elements 2 in the inner part. This assembly also has support plates 10, 11 for forming a cell for inserting and supporting a water rod 3 together with the cell materials, a band 9 forming an outer frame for bundling the cell materials 8, and a spring 12 for elastically supporting the fuel elements 2 and the water rod 3, and the cell materials 8, the support plates 10, 11 and the band 9 are formed out a zirconium alloy. The index showing the <0001> directional orientation ratio of a closest hexagonal lattice, which is the crystal structure of the alloy, is set substantially equal in all the cell material 8, the support plates 10, 11 and the band 9 in the fuel spacer height direction and width direction.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a fuel spacer for a nuclear reactor fuel and a fuel assembly including the fuel spacer.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a fuel assembly 1 used in a boiling water reactor. In the fuel assembly 1, a plurality of fuel elements 2 and a water rod 3 are bundled in a square lattice shape with a plurality of fuel spacers 4 ′ with a constant horizontal interval,
The fuel bundle in which the upper and lower ends of the water rod 3 are supported by the upper tie plate 5 and the lower tie plate 6 is covered by the rectangular channel box 7. In the fuel assembly 1, the fuel spacer 4'holds the fuel element 2 and the water rod 3 at a predetermined horizontal distance and also supports them so as not to vibrate laterally. Fuel spacer 4 '
An example of the structure is disclosed in, for example, Japanese Patent Publication No. 5-12680. The fuel spacer 4'as in this example is used for the fuel element 2
An independent cell for supporting the cell material 8 is formed,
This is a structure in which the cells are bundled in a square lattice and fixed by an outer frame. The cell material 8 is made of a zirconium alloy tube material, and the outer frame is made of a zirconium alloy plate material.

[0003]

It is known that when a zirconium alloy is irradiated with neutrons, it grows due to irradiation growth. Such irradiation growth is affected by fast neutron irradiation, irradiation temperature, cold workability of material, annealing conditions, texture and the like. This basic mechanism is that, as shown in FIG. 3, the hexagonal crystals shrink in the <0001> direction (hereinafter, c-axis direction) due to the accumulation of lattice defects caused by irradiation, and the <1000> direction (hereinafter, It is to spread in the a-axis direction). For example, a tube made of a zirconium alloy has a texture in which the c-axis is perpendicular to the tube axis as shown in FIG. 3, so irradiation growth is observed as elongation of the tube. Therefore, if the texture is different, the growth will also change. Recently, radiation growth data on the high dose side has begun to be reported. For example, as shown in FIG. 4 (Source: Griffiths, M., et a
l .: ASTM STP-1023 (1989), there is a reported example that the growth rate tends to increase on the high irradiation side. It is considered that such rise of the growth rate is related to the structure and properties of the irradiation defect, and is influenced by the texture of the material, alloy components, impurities and the like.

In the fuel spacer 4 of the prior art, the cell material 8 for forming an independent cell for supporting the fuel element 2 is a zirconium alloy tube material (seamless tube), and the cell material 8 is bundled in a square lattice shape. The outer frame called the band 9 for fixing and the support plates 10 and 11 forming the cells around the water rod 3 together with the cell material 8 are made of a zirconium alloy plate material. The zirconium alloy pipe material (seamless pipe) and the zirconium alloy plate material have slightly different textures as described above due to the difference in processing step and processing degree, which causes a difference in irradiation growth elongation. The difference in elongation between the members of the fuel spacer 4 causes internal stress in the fuel spacer 4. In addition, when internal stress is generated in the fuel spacer 4, hydrogen generated by oxidation of the fuel spacer 4 in use in the reactor and radiolysis of the coolant is taken in, and the orientation of the hydride in the fuel spacer 4 is small. Fuel spacer 4
This is not a preferable phenomenon in view of the structural strength of.

In recent years, from the viewpoint of further improving the economical efficiency of nuclear power generation and reducing radioactive waste, the burnup of fuel has been increased. Since the neutron irradiation dose of the fuel spacer 4 increases as the burnup of the fuel increases, the difference in irradiation growth elongation between the members of the fuel spacer 4 increases due to the rise phenomenon of the irradiation growth rate, and Increase internal stress. Since the fuel spacer 4 has sufficient strength against internal stress, the fuel spacer 4 has little substantial effect, but from the viewpoint of ensuring reliability, unnecessary stress is not desirable. It is desirable to prevent the generation of internal stress due to the difference in irradiation growth and elongation as much as possible.

As described above, when the conventional fuel spacer 4 is applied to the high burnup fuel, there is room for improvement from the viewpoint of suppressing an increase in internal stress of the fuel spacer 4.

An object of the present invention is to prevent internal stress from increasing in the irradiation growth elongation difference between the zirconium alloy members constituting the fuel spacer 4 in the high burnup region (that is, the high irradiation amount region). Another object of the present invention is to provide a more reliable fuel spacer 4 which is prevented from occurring and a fuel assembly 1 including the same.

[0008]

In order to achieve the above object, the present invention provides a plurality of cell blanks 8 (each having a circular cross section or a polygonal cross section) each of which forms an independent unit cell for supporting the fuel element 2. May be present), support plates 10 and 11 fixed to the cell material 8 and forming cells for inserting and supporting the water rod 3 together with the cell material 8, cell material 8
In the band 9 which forms the outer frame for bundling, the close-packed hexagonal lattice <
Index indicating the orientation ratio in the 0001> direction (Texture Facto
r) in the fuel spacer height direction (coolant flow direction) and width direction (direction perpendicular to the coolant flow) so that all of the cell material 8, the support plates 10 and 11 and the band 9 are substantially equal. The fuel spacer 4 is formed.

Such a fuel spacer 4 is composed of, for example, a cell material 8 made of zirconium alloy and a support plate 1.
Treatment for randomizing the crystal orientation arrangement of 0, 11 and band 9 (for example, heating to a temperature range of about 960 ° C. or higher at which the zirconium alloy is completely transformed from α phase to β phase, followed by quenching treatment) The fuel spacer 4 is formed of a member, or the cell material 8 is attached to the support plate 1
The fuel spacer 4 is formed by processing a plate material made of a zirconium alloy in the same manner as 0, 11 and the band 9 and aligning the cell material 8 with the rolling directions of the support plate 10, 11 and the material 25 of the band 9 all in the same direction. Assemble to

[0010]

FUNCTION The irradiation growth strain of the zirconium alloy due to neutron irradiation is expressed by the equation 1.

[0011]

[Equation 1] εi = A (φt) · B (T) · C (W) · (1-3 · fi) (Equation 1) where εi: Irradiation growth strain in the i direction A (φt): High speed Function of neutron dose (φt) B (T): Function of irradiation temperature (T) C (W): Cold workability (W) of material, function relating to annealing conditions fi: of close-packed hexagonal lattice in i direction < 0001
Index indicating the orientation ratio in the> direction (Texture Factor) i: rolling direction, rolling right-angle direction, thickness direction From number 1, the smaller the Texture Factor (fi) is, the irradiation growth strain in the i direction due to neutron irradiation of zirconium alloy It turns out to be big. For example, a zirconium alloy tube has a texture in which the c-axis is perpendicular to the tube axis as shown in FIG. 3, so that the tube axis direction (or rolling direction) or the circumferential direction (or rolling direction) is obtained. Right Angle Texture Factor
Is much smaller than that in the radial direction (or the thickness direction), and therefore tends to be easily irradiated and grown in the tube axis direction (or rolling direction) or the circumferential direction (or rolling orthogonal direction).

When the crystallographic orientation of the zirconium alloy is completely randomized, fi = 1/3, and from equation 1, such a zirconium alloy may not cause irradiation growth strain due to neutron irradiation. Recognize.

In this way, for example, a process of randomizing the crystal orientation arrangement of the cell material 8 made of zirconium alloy, the support plates 10 and 11 and the band 9 which form the fuel spacer 4 (for example, the zirconium alloy changes from α phase to β phase). After heating to a temperature range of about 960 ° C or higher where the phase is completely transformed,
By performing the rapid cooling treatment), irradiation growth due to neutron irradiation generated in these members can be made zero, and the fuel spacer 4 in which internal stress is not generated can be obtained.

On the other hand, in the conventional fuel spacer 4 ', the cell material 8 is made of a zirconium alloy pipe material, and the band 9 and the support plates 10 and 11 are made of a zirconium alloy plate material. Typical of these zirconium alloy components in the fuel spacer height direction (coolant flow direction)
The texture factor is Fl = 0.06 for the pipe material and Fl = 0.10 for the plate material. Therefore, assuming that A (φt), B (T), and C (W) in Formula 1 are the same in the tube material and the plate material, [irradiation growth strain of the tube material] / [irradiation growth strain of the plate material] = (1-3 X 0.06) / (1-3 x 0.10) = 1.17, which means that the irradiation growth strain of the tube material is about 17% larger than the irradiation growth strain of the plate material. As a result, a compressive internal stress is generated in the cell material 8 made of a tubular material, and a tensile internal stress is generated in the band 9 made of a plate material and the support plates 10 and 11 based on the difference in irradiation growth strain of these members. However, when the cell material 8 is made of a plate material like the band 9 and the support plates 10 and 11 and the textures are aligned, the difference in irradiation growth strain between the cell material 8 and the band 9 and the support plates 10 and 11 is different. Can be prevented, and the generation of internal stress can be prevented.

As a method for producing the cell material 8 from a plate material as described above, it is conceivable to use, for example, a welded joint pipe obtained by bending the plate material and then welding the bent ends to form a tubular shape.

FIG. 8 shows a material processing step diagram of the zirconium alloy component of the fuel spacer 4.

In FIG. 8, the material processing flow of the cell material 8 is on the left side, and the band or support plate material 27 is on the right side.
Represents the material processing flow. The cell material 8 is made of a zirconium alloy plate material 25 like the band or support plate material 27. For the cell material 8, a zirconium alloy plate material 25 is bent, for example, in a direction perpendicular to the rolling direction, and thereafter, bent ends of the plate material 25 are butted and the partial seam welding is performed to form a welded joint pipe. After that, the welded joint pipe is cut into a length corresponding to the size of the cell material 8. On the other hand, the band or support plate material 27 is produced by cutting the zirconium alloy plate material 25 in the direction perpendicular to the rolling direction, for example. In the example of the cell material 8 and the band or the support plate material 27 produced in this way, the zirconium alloy sheet material 25 of the fuel spacer 4 is oriented so that the rolling direction of the zirconium alloy plate material 25 is oriented in the fuel spacer height direction (coolant flow direction). The orientation of parts is uniform. At the same time, the parts of the fuel spacer 4 are uniformly arranged so that the zirconium alloy plate 25 is oriented in the direction perpendicular to the rolling direction in the fuel spacer width direction (direction perpendicular to the coolant flow).

By configuring the fuel spacer 4 with zirconium alloy parts as described above, an index (indicating the orientation ratio in the <0001> direction of all zirconium alloy parts in the height and width directions of the fuel spacer). Te
xture Factor) becomes the same. As a result, the difference in irradiation growth elongation caused by the difference in the texture between the zirconium alloy parts constituting the fuel spacer 4 does not occur, and the generation of internal stress due to the difference in elongation can be prevented.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the fuel spacer 4 of the present invention. The fuel spacer 4 shown in FIG.
A plurality of cell materials 8 each of which forms an independent unit cell for inserting and supporting water, and support plates 10 and 11 fixed to the cell material 8 to form cells for inserting and supporting the water rod 3 together with the cell material 8. , The band 9 forming the outer frame for bundling the cell material 8, the fuel element 2 and the water rod 3
And a spring 12 for elastically supporting the.

In the fuel spacer 4 of the first embodiment of the present invention, a process for randomizing the crystal orientation arrangement of the cell material 8, the support plates 10 and 11, and the band 9 made of zirconium alloy (for example, zirconium alloy is α phase). To a β-phase is completely transformed into a temperature range of about 960 ° C. or higher, followed by quenching treatment). As a result, cell material 8,
Since the support plates 10 and 11 and the band 9 do not cause irradiation growth / expansion due to neutron irradiation, it is possible to eliminate the possibility that internal stress is generated in the fuel spacer 4 due to the difference in irradiation growth / expansion between these members.

In the fuel spacer 4 of the second embodiment of the present invention, the cell material 8 made of zirconium alloy is formed by processing a plate material made of zirconium alloy in the same manner as the support plates 10 and 11 and the band 9. The cell material 8 is assembled to the fuel spacer 4 by aligning the rolling directions of the support plates 10 and 11 and the material 25 of the band 9 in the same direction. As a result, the fuel spacer 4 is formed of a zirconium alloy member having the same texture, and the fuel spacer 4 has the same index (Texture Factor) indicating the orientation ratio of the crystals of all the members in the <0001> direction. A structure can be obtained in which the difference in irradiation growth and elongation resulting from the difference in the texture between the zirconium alloy parts constituting No. 4 does not occur, and the generation of internal stress due to the difference in elongation can be prevented. Such a fuel spacer 4 can be realized, for example, by bending the cell material 8 into a zirconium alloy plate material and then forming a welded joint tube manufactured by welding the bent ends. FIG. 8 shows an example of the material processing flow of the cell material 8, band 9 and support plates 10 and 11 applied to this embodiment.

In FIG. 8, the left side is the material processing flow of the cell material 8, and the right side is the band or support plate material 27.
Represents the material processing flow. The cell material 8 is made of a zirconium alloy plate material 25 like the band or support plate material 27. For the cell material 8, a zirconium alloy plate material 25 is bent, for example, in the direction perpendicular to the rolling direction, then the bent ends of the plate material 25 are butted, and a welding torch 26 is made to face this portion and seam welded to form a welded joint pipe. , Cell material 23. After this, the welded joint tube is made of cell material 8
It is cut to a length corresponding to the dimensions of. On the other hand, the band or support plate material 27 is produced by cutting the zirconium alloy plate material 25 in the direction perpendicular to the rolling direction, for example. In the example of the cell material 8 and the band or the support plate material 27 produced in this way, the zirconium alloy sheet material 25 of the fuel spacer 4 is oriented so that the rolling direction of the zirconium alloy plate material 25 is oriented in the fuel spacer height direction (coolant flow direction). The orientation of parts is uniform. At the same time, the parts of the fuel spacer 4 are uniformly arranged so that the zirconium alloy plate 25 is oriented in the direction perpendicular to the rolling direction in the fuel spacer width direction (direction perpendicular to the coolant flow).

The second embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 5 shows a pair of cell materials 8 of the fuel spacer 4.
2 is a plan view (lower surface of the fuel spacer 4) of FIG. FIG. 6 shows a perspective view of an embodiment of the cell material 8 of the fuel spacer 4 according to the present invention. Further, FIG. 7 shows a side view of another embodiment of the cell material 8 of the fuel spacer 4 according to the present invention.

The fuel element 2 is provided at the center of the pair of cell materials 8.
A spring 12 for elastically supporting the
A cell stop 13 for supporting the fuel element 2 in combination with the spring 12 is provided at a position of the cell material 8 facing the spring 12. Also, the spring 12
There are spot welds 14 above and below the cell material 8 at positions immediately above, and at positions of ± 90 ° and 180 ° with respect to the cell material 8 and thereby the cell materials 8 are fixed to each other. Further, a U-shaped cell opening 16 for engaging the spring 12 is provided on the end surface of the cell material 8 (the U-shaped cell opening 16 is shown in FIGS. 6 and 7; However, a semicircular index notch 15 is provided in order to accurately align the () may be used) with the pair of cell materials 8.

The cell material 8 of one embodiment of the present invention shown in FIGS. 6 and 7 is a support plate 10, 11 and a band 9.
In order to prevent a difference in growth between irradiation and growth due to neutron irradiation, a welded joint pipe made of a zirconium alloy plate is used, for example, as shown in FIG.
Since the once welded portion coincides with the spot welded portion 14 for further fixing the cell blanks 8 and re-welding is not preferable in terms of material characteristics, the present invention shown in FIG. 6 and FIG. The weld seam 20 of the cell material 8 of the embodiment is characterized in that it does not coincide with the spot weld portion 14.

A cell material 8 according to an embodiment of the present invention shown in FIG.
Then, the welding seam 20 is located on the right side of the center 21 (represented by the one-dot chain line) of the spring corresponding to the position where the spring 12 is arranged, and most of the welding seam 20 is deleted by punching the cell opening 16. It is characterized by being. In the base material part of the cell material 8 and the welding seam 20,
For example, physical properties such as Young's modulus and coefficient of thermal expansion are slightly different. The proportion of the weld seam 20 itself in the cell material 8 is sufficiently small that the influence of these differences in physical properties can be ignored,
By minimizing the weld seam 20 as in the embodiment of the present invention shown in FIG. 6, it is possible to further reduce the influence due to the difference in the physical property values between the base metal part of the cell material 8 and the weld seam 20. it can.

Further, in the cell material 8 according to the embodiment of the present invention shown in FIG. 7, the position of the welding seam 20 is made to coincide with the position of the index notch 15, and the position of the welding seam 20 is assembled when the fuel spacer 4 is assembled. There is an advantage that it is easy to confirm.

In the above embodiment, it is important to confirm the position of the weld seam 20 in relation to the spot welded portion 14. Therefore, an example of a method for confirming the welding seam 20 in the material of the cell material 8 of the embodiment of the present invention shown in FIGS. 6 and 7 will be described with reference to FIGS. 9 to 11.

FIG. 9 shows an example of the cell material 23 according to the embodiment shown in FIG. The holes 22 are formed at the positions of the weld seams 20 at equal intervals in the pipe length direction. The hole 22 is a cell material 23
Corresponding to the length of the cell material 8, for example, after being cut as shown in FIG. 10, it is utilized as the index notch 15 described above. FIG. 11 is an example of the cell material 23 of the embodiment shown in FIG. In this case, holes 22 are bored at equal intervals in the pipe length direction in a fixed direction with respect to the weld seam 20. Also in this case, the hole 22 for identifying the position of the welding seam 20 is utilized as the index notch 15 after the cell material 23 is cut corresponding to the length of the cell material 8 as in the case of FIG. 9.

In the above description, the case where the cross-sectional shape of the member forming each independent unit cell is circular (cell material) is mainly described, but the cross-sectional shape of this member is, for example, an octagon. The same effect can be obtained with polygons such as
Within the scope of the present invention.

The fuel spacer 4 is suitable for ensuring the mechanical soundness in the high burnup region, and when applied to the fuel spacer 4 of the fuel assembly 1 for high burnup, the reliability is further improved. Can contribute.

[0034]

EFFECTS OF THE INVENTION According to the present invention, even in a high burnup region (that is, a high irradiation amount region), the irradiation growth elongation difference does not occur between the zirconium alloy members forming the fuel spacer 4, so that the irradiation growth elongation in the fuel spacer 4 is not generated. Generation of internal stress due to the difference is prevented.

[Brief description of drawings]

FIG. 1 is a plan view of a fuel spacer according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a fuel assembly.

FIG. 3 is an illustration of irradiation growth and texture of Zircaloy.

FIG. 4 is a characteristic diagram of accelerated irradiation growth of zircaloy (annealed material).

FIG. 5 is a plan view of a fuel spacer cell.

FIG. 6 is a perspective view of a fuel spacer cell of one embodiment of the present invention.

FIG. 7 is a side view of a fuel spacer cell of one embodiment of the present invention.

FIG. 8 is a material processing step diagram of a fuel spacer component of the fuel spacer of the present invention.

FIG. 9 is a perspective view of an embodiment of a fuel spacer cell material of the present invention.

FIG. 10 is a perspective view of a second embodiment of the fuel spacer cell material of the present invention.

FIG. 11 is a perspective view of a third embodiment of the fuel spacer cell material of the present invention.

[Explanation of symbols]

2 ... Fuel element, 3 ... Water rod, 4 ... Fuel spacer, 8 ...
Cell material, 9 ... band, 10, 11 ... support plate, 12 ... spring, 13 ... cell stop.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Tomita 3-2-1, Sachimachi, Hitachi City, Ibaraki Prefecture, Hitachi Engineering Co., Ltd. 1-1-1, Hitachi Ltd., Hitachi Works (72) Inventor Masafumi Imai 3-2-1, Saiwaicho, Hitachi City, Ibaraki Hitachi Engineering Co., Ltd.

Claims (8)

[Claims] 1. A fuel assembly comprising a plurality of fuel elements, a water rod, and a fuel spacer that bundles these together and elastically supports them to maintain an interval between them, wherein the fuel spacer has a fuel inside. A plurality of tubular members forming independent unit cells for respectively inserting and supporting the elements, a plate fixed to the tubular members and forming cells for inserting and supporting the water rod together with the tubular members, A band forming an outer frame for bundling the tubular members and a spring for elastically supporting the fuel element and the water rod are included, and the tubular member, the plate and the band are made of zirconium alloy, The index indicating the orientation ratio in the <0001> direction of the close-packed hexagonal lattice having a crystal structure is the height direction and the width direction of the fuel spacer, and And fuel spacer for a nuclear reactor fuel, characterized in that approximately equal in both the bands. 2. A fuel assembly comprising a plurality of fuel elements, a water rod, and a fuel spacer that bundles these together and elastically supports them to maintain a mutual distance between them, wherein the fuel spacer has a fuel inside. Cylindrical members made of zirconium alloy forming independent unit cells for inserting and supporting elements, and cells for inserting and supporting water rods fixed to the cylindrical members together with the cylindrical members. A zirconium alloy plate to be formed, a zirconium alloy band forming an outer frame for bundling the tubular members, a fuel element, and a spring for elastically supporting a water rod, wherein the tubular member is the plate. And a zirconium alloy plate material is processed similarly to the band, and the material rolling directions of the tubular member, the plate and the band are all the same direction. Fuel spacer for a nuclear reactor fuel, characterized by being assembled collated by the fuel spacer. 3. The tubular member forming an independent unit cell for inserting and supporting the fuel element according to claim 2, wherein a plate material made of a zirconium alloy is bent into a tubular shape,
A fuel spacer formed by a welded joint tube in which bent ends are welded. 4. The welding seam of the tubular member according to claim 2 or 3, which forms an independent unit cell for inserting and supporting the fuel element, by inserting a spring for elastically supporting the fuel element. The tubular member is positioned at an opening formed by cutting a partial surface of the tubular member into a U-shape or a U-shape so that a part or most of the weld seam is formed by the formation of the opening. Fuel spacers have been removed. 5. The tubular member according to claim 2, 3 or 4, wherein the tubular members, which are welded joint tubes forming independent unit cells for inserting and supporting the fuel element, are fixed to each other by spot welding. A fuel spacer in which a weld seam portion of the tubular member is arranged at a position that does not coincide with the spot weld portion. 6. A fuel spacer for a nuclear reactor fuel, wherein an independent unit cell for supporting a fuel element is formed of a tubular member made of a zirconium alloy, wherein the tubular member is a long welded joint pipe. It is made by cutting into a size that fits the spacer and then performing various processing.For the long weld seam pipe, at fixed positions in the pipe circumferential direction based on the weld seam, and at equal intervals in the pipe length direction. Perforated and the perforated portion or a part thereof is formed at one or both ends in the longitudinal direction of the tubular member, which is produced by cutting the welded joint pipe into a size suitable for the fuel spacer. A fuel spacer for a nuclear reactor fuel, which is formed by using a material perforated in a welded joint pipe. 7. The cylindrical member according to claim 6, wherein one end or both ends in the longitudinal direction of the cylindrical member forming an independent unit cell for supporting the fuel element, is arranged in a circumferential direction of the cylindrical member when a fuel spacer is assembled. A fuel spacer is formed, which has a notch that functions as a positioning and rotation fixing portion, and the notch corresponds to a perforated portion of the welded joint pipe, which is a material of the tubular member. 8. A fuel assembly comprising the fuel spacer according to claim 1, 2, 3, 4, 5, 6 or 7.