JP3597681B2 - Fuel spacer for nuclear reactor, method of manufacturing the same, and fuel assembly - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel spacer for a nuclear reactor, a method for manufacturing the same, and a fuel assembly.
[0002]
[Prior art]
In a boiling water reactor (BWR), 60 fuel rods and one super-thick water rod are assembled and used as a high burn-up step II fuel (high burn-up 8 × 8 fuel). The fuel assembly has a length of, for example, about 4 m, and spacers are arranged at seven locations in the longitudinal direction to maintain straightness of the fuel rods at predetermined intervals.
[0003]
As the spacer, a plurality of cells formed into a short tube shape, a plurality of cells formed with a stopper portion by pressing a predetermined portion of the outer peripheral surface to be depressed inward by pressing, for example, by laser welding, There is known a structure having a spring member attached to the inside of the cell and holding the fuel rod in cooperation with the stopper.
[0004]
Each of the cells is made of a zirconium alloy of the same material as that of the cladding tube and the water rod which constitute the fuel rod so that the relative position of the fuel rod inserted and held is not shifted. As this zirconium alloy, zircaloy-2 is mainly used, but it is essential that the alloy contains 96% by weight or more of zirconium and has good corrosion resistance. Zircaloy-2 generally contains 1.20 to 1.70% by weight of tin, 0.07 to 0.20% by weight of iron, 0.05 to 0.15% by weight of chromium, and 0.03 to 0.08% of nickel. % By weight and the balance having the composition of zirconium.
[0005]
On the other hand, the spring member is made of elastic Inconel.
However, when a reactor incorporating a spacer having a plurality of cells in which the stoppers are formed by press working is operated for a long time, there is a problem that cracks are generated from the stoppers of the cells.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a fuel spacer for a nuclear reactor capable of suppressing or preventing the occurrence of cracks from a stopper portion of a cell even when the fuel spacer is incorporated in a nuclear reactor and operated for a long period of time, and a method of manufacturing the same.
[0007]
An object of the present invention is to provide a fuel assembly including a fuel spacer for a nuclear reactor capable of suppressing or preventing the occurrence of cracks from a stopper portion of a cell even when the fuel assembly is operated for a long time after being incorporated in a nuclear reactor. is there.
[0008]
[Means for Solving the Problems]
The nuclear reactor fuel spacer according to the present invention is a nuclear reactor spacer having a plurality of cells having a short tube shape, a predetermined portion of the outer peripheral surface is depressed inward by press working to form a stopper portion,
Each of the cells is made of a zirconium alloy, and all the cells including the stop part have a recrystallized structure in which (0001) planes are gathered in parallel with the surface .
[0009]
A method for manufacturing a fuel spacer for a nuclear reactor according to the present invention is directed to a reactor spacer having a plurality of cells in which a predetermined portion of an outer peripheral surface of a short tube made of a zirconium alloy is subjected to press working and is depressed inward to form a stopper portion. In the manufacturing method of
After the cells are subjected to press working, recrystallization annealing is performed so that all the cells including the stopper portion have a recrystallized structure in which the (0001) plane is gathered parallel to the surface .
[0010]
The step of performing recrystallization annealing after performing the press working on the cells may be performed at the cell stage in a state where the plurality of cells are assembled and integrated by laser welding or the like.
A fuel assembly according to the present invention includes the fuel spacer for a nuclear reactor and fuel rods held in each cell of the spacer.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic view showing a spacer incorporated in the fuel assembly according to the present invention, FIG. 2 is a sectional view of a main part of the spacer of FIG. 1, and FIG. 3 is a sectional view taken along line III-III of FIG.
[0012]
The spacer 1 has a plurality of cells 2, and these cells 2 are assembled by, for example, laser welding the outer peripheral surfaces of each other.
As shown in FIGS. 2 and 3, each cell 2 has a stopper portion 4 formed by pressing a predetermined portion of the outer peripheral surface of the short circular tube 3 inward by pressing. For example, two stopper portions 4 are formed in the circumferential direction of the circular tube 3 and two in the longitudinal direction of the circular tube 3, for a total of four stopper portions. The elongated box-shaped spring member 5 is disposed inside the cell 2 through a slit portion 6 opened in the longitudinal direction of two adjacent cells 2. The spring member 5 is inserted into the cell 2 and cooperates with the four stoppers 4 to hold a fuel rod 7 having a cladding tube loaded with nuclear fuel pellets. Are arranged symmetrically with respect to the central axis of
[0013]
Each of the cells 2 is made of a zirconium alloy and all have a recrystallized structure.
The zirconium alloy is preferably an alloy containing 96% by weight or more of zirconium. As such a zirconium alloy gold, for example, 1.20 to 1.70% by weight of tin, 0.07 to 0.20% by weight of iron, 0.05 to 0.15% by weight of chromium, and 0.03 to 0. Zircaloy-2 or Zircaloy-4 having a composition of 08% by weight and a balance of zirconium, or 1 to 2% by weight of Sn, 0.20 to 0.35% by weight of Fe, 0.03 to 0.16% by weight of Ni and substantially the balance It is preferable to use a composition of zirconium and having a Fe / Ni ratio of 1.88.0.
[0014]
The recrystallized structure of all the cells 2 made of the zirconium alloy means that the (0001) crystal plane is parallel or almost parallel to the surface at any position including the stopper 3. To be more specific, the recrystallized structure means that in a plane perpendicular to the longitudinal direction of the circular tube 3 constituting the cell 2, a direction inclined by 30 ° from a direction perpendicular to the surface is the most frequent direction of the [0001] axis, In a plane parallel to the longitudinal direction of the circular tube 3, a direction perpendicular to the surface is the most frequent direction of the [0001] axis.
[0015]
The spring member 5 is made of, for example, elastic Inconel.
When the fuel rods 7 loaded with nuclear fuel pellets in cladding tubes are inserted into the plurality of cells 2 constituting the spacer 1 as shown in FIGS. Straightness is maintained at predetermined intervals by a spring member 5 disposed inside the cell 2 and a stopper 3 formed in each of the cells 2.
[0016]
Next, a method for manufacturing the spacer of the present invention will be described.
First, a short tube made of a zirconium alloy is prepared and quenched, and then cold rolling and annealing are repeated to prepare a short circular tube. Subsequently, a predetermined portion on the outer peripheral surface of the short circular tube is pressed to be depressed inward to form a stopper portion. Subsequently, after the cells are annealed at a temperature equal to or higher than the recrystallization temperature of the zirconium alloy, the spring members are attached to these cells, and the cells are joined together by laser welding or the like, assembled, integrated, and a spacer is manufactured. .
[0017]
In the manufacture of the spacer, a spring member may be attached to the plurality of pressed cells, and the cells may be joined by laser welding or the like, assembled, integrated, and then subjected to recrystallization annealing. According to such a method, the recrystallization annealing also has the effect of improving the corrosion resistance by reducing the tensile strain of the welded portion and the heat-affected zone by the laser welding of the cells, and as described above, at the cell stage. The effectiveness of the annealing operation can be further enhanced as compared with the case where recrystallization annealing is performed.
[0018]
It should be noted that, after the cell which has been recrystallized in advance is pressed and the stopper portion is carried, the cell may be recrystallized again to have a recrystallized structure.
According to the present invention described above, it is possible to provide a fuel spacer for a nuclear reactor that can suppress or prevent the occurrence of cracks from the stopper portion of the cell even when the fuel spacer is operated for a long time after being incorporated in the nuclear reactor.
[0019]
That is, when the present inventors have operated a reactor incorporating a spacer having a plurality of cells made of a zirconium alloy in which the stopper portion is formed by press working for a long period of time, a crack is generated from the stopper portion of each cell. After various investigations, hydrides of zirconium having inferior toughness were gradually accumulated in the stopper portion of the cell in a direction perpendicular to the surface, that is, in the inside of the cell, and the hydride generation point was at the crack initiation point. I decided to become. However, it has been determined that hydrides are not parallel to the surface of the cell portion except for the stopper portion, so that the hydride does not start cracks.
[0020]
Based on such an investigation result, the present inventors measured the crystal orientation of the stopper portion of the cell and the other portion by X-ray diffraction. As a result, in the cell portion other than the stopper portion, the (0001) plane was on the surface. In contrast, the stoppers have different crystal orientations, and the (0001) plane is aligned in the thickness direction of the short tube-shaped cell, that is, the (0001) plane is aligned in the radial direction of the tube. It turned out to be parallel to. This is considered to be due to the fact that the stopper had a working structure by press working.
[0021]
The present inventors have performed a process such as annealing the cell having the stopper portion at a temperature equal to or higher than the recrystallization temperature of the zirconium alloy to make all the cells have a recrystallized structure. It has been found that the cell portion can be formed into a structure in which the (0001) plane is gathered in parallel with the surface.
[0022]
Even when a fuel assembly incorporating a spacer having a plurality of cells having the stoppers of the present invention is loaded into a nuclear reactor and operated, the hydride absorbed in the cells includes the stoppers. In all the cells, the cells were arranged parallel to the surface, did not become the starting point of the crack, and could prevent the crack from being generated over a long period of operation.
[0023]
Further, according to the present invention, a predetermined portion of the outer peripheral surface of the short tube made of a zirconium alloy is subjected to press working, and after forming a stopper portion by being depressed inward, annealing at a temperature equal to or higher than the recrystallization temperature of the zirconium alloy. By doing so, a spacer having a plurality of cells, all of which have a recrystallized structure, can be manufactured. As described above, by incorporating the fuel assembly into the spacer and loading it into the nuclear reactor, the generation of cracks in the cell can be prevented during long-term operation.
[0024]
【Example】
(Example 1)
First, a short circular tube made of Zircaloy-2 having an outer diameter of 16 mm, an inner diameter of 14.8 mm, and a length of 30.5 mm is punched in the vicinity of both ends to form a slit in the circumferential direction, and then pressed on the outer peripheral surface facing the slit. A cell was fabricated by processing and indenting inward to form a stopper. Subsequently, the cell was subjected to vacuum annealing at 580 ° C. for 1 hour. X-ray measurement of the stopper portion of the annealed cell confirmed that the (0001) plane had gathered on the surface, similarly to the cell portion other than the stopper portion.
[0025]
Next, a plurality of the cells are assembled, and a spring member made of Inconel is attached to a slit of an adjacent cell. Then, the cells are laser-welded and integrated to form the structure shown in FIGS. 1 to 3 described above. Was manufactured.
[0026]
A fuel assembly was assembled using the obtained spacers and loaded into a nuclear reactor. After operating the reactor for five years, the internal spacers were examined. As a result, it was confirmed that hydrides were accumulated in each cell of the spacer in parallel with the surface, and the initial toughness was maintained.
[0027]
(Comparative Example 1)
After punching out the vicinity of both ends of a short circular tube made of Zircaloy-2 similar to that in Example 1 to form a slit in the circumferential direction, the outer peripheral surface facing the slit is subjected to press working, and is depressed inward to form a stopper portion. Was formed to form a cell. X-ray measurement of the stopper portion of this cell confirmed that the (0001) plane was gathered in a direction perpendicular to the surface.
[0028]
Next, a plurality of the cells were assembled without vacuum annealing, and a spring member made of Inconel was attached to a slit of an adjacent cell, and then the cells were integrated by laser welding to produce a spacer.
[0029]
A fuel assembly was assembled using the obtained spacers, loaded into a nuclear reactor, and operated. As a result, when the internal spacers were examined after one year of operation, hydrides accumulated in the cells of the spacers in a direction perpendicular to the surface, and appeared to cause cracking when any stress was applied.
[0030]
(Example 2)
First, a short circular tube having an outer diameter of 16 mm, an inner diameter of 14.8 mm, and a length of 30.5 mm, made of 0.25% by weight of Fe, 0.1% by weight of Ni, 0.1% by weight of Cr, 1.3% by weight of Sn, and the remainder made of zirconium. After forming a slit in the circumferential direction by punching out the vicinity of both ends, a pressing process was performed on the outer peripheral surface facing the slit, and a concave portion was formed inward to form a stopper portion, thereby producing a cell. Subsequently, the cell was subjected to vacuum annealing at 580 ° C. for 1 hour. X-ray measurement of the stopper portion of the annealed cell confirmed that the (0001) plane had gathered on the surface, similarly to the cell portion other than the stopper portion.
[0031]
Next, a plurality of the cells are assembled, and a spring member made of Inconel is attached to a slit of an adjacent cell. Then, the cells are laser-welded and integrated to form the structure shown in FIGS. 1 to 3 described above. Was manufactured.
[0032]
A fuel assembly was assembled using the obtained spacers and loaded into a nuclear reactor. After operating the reactor for five years, the internal spacers were examined. As a result, it was confirmed that hydrides were accumulated in each cell of the spacer in parallel with the surface, and the initial toughness was maintained.
[0033]
(Example 3)
First, a short circular tube made of Zircaloy-2 having an outer diameter of 16 mm, an inner diameter of 14.8 mm, and a length of 30.5 mm is punched in the vicinity of both ends to form a slit in the circumferential direction, and then pressed on the outer peripheral surface facing the slit. A cell was fabricated by processing and indenting inward to form a stopper. Subsequently, a plurality of the cells are assembled, a spring member made of Inconel is attached to a slit of an adjacent cell, and then the cells are integrated by laser welding to form the structure shown in FIGS. Was manufactured. This spacer was subjected to vacuum annealing at 580 ° C. for 1 hour. X-ray measurement of the stopper portion of the annealed cell confirmed that the (0001) plane had gathered on the surface, similarly to the cell portion other than the stopper portion.
[0034]
A fuel assembly was assembled using the obtained spacers and loaded into a nuclear reactor. After operating the reactor for five years, the internal spacers were examined. As a result, it was confirmed that hydrides were accumulated in each cell of the spacer in parallel with the surface, and the initial toughness was maintained.
[0035]
【The invention's effect】
INDUSTRIAL APPLICABILITY As described above in detail, according to the present invention, a highly reliable and long-life nuclear reactor capable of suppressing or preventing the occurrence of cracks from a stopper portion of a cell even when incorporated in a nuclear reactor and operated for a long time. A fuel spacer and a method for manufacturing the same can be provided.
[0036]
The present invention relates to a highly reliable and long-life fuel assembly provided with a fuel spacer for a nuclear reactor capable of suppressing or preventing the occurrence of cracks from a stopper portion of a cell even when the fuel assembly is incorporated in a nuclear reactor and operated for a long time. Can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a spacer incorporated in a fuel assembly according to the present invention.
FIG. 2 is a sectional view of a main part of the spacer of FIG. 1;
FIG. 3 is a sectional view taken along the line III-III in FIG. 2;
[Explanation of symbols]
1 ... spacer,
2 ... cell,
3 short circular tubes,
4 ... stopper part,
5 ... spring member,
7 ... Fuel rod.

Claims (3)

In a nuclear reactor spacer having a plurality of cells in the form of a short tube and having a stopper formed by pressing a predetermined portion of the outer peripheral surface inward by press working,
A fuel spacer for a nuclear reactor, wherein each of the cells is made of a zirconium alloy, and all the cells including the stop part have a recrystallized structure in which the (0001) plane is gathered in parallel with the surface . In a method of manufacturing a reactor spacer having a plurality of cells formed by pressing a predetermined portion of an outer peripheral surface of a short tube made of a zirconium alloy and forming a stopper portion by being depressed inward,
A fuel for a nuclear reactor, characterized in that a recrystallization annealing is performed after the cells are subjected to press working so that all the cells including the stopper portions have a recrystallized structure in which (0001) planes are gathered parallel to the surface. Manufacturing method of spacer. A fuel assembly comprising: the fuel spacer for a nuclear reactor according to claim 1; and a fuel rod held in each cell of the spacer.

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