JPH048758B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel spacer and a fuel assembly, and particularly to a fuel spacer and a fuel assembly suitable for application to a boiling water nuclear reactor.

[Conventional technology]

Traditionally, fuel spacers in fuel assemblies contain tin 1.20
~1.70 wt%, iron 0.18-0.24 wt%, chromium 0.07
A zirconium-based alloy (Zircaloy-4) containing ~0.13% by weight has been used.

[Problem that the invention seeks to solve]

In recent years, in response to the need to improve the economic efficiency of nuclear power generation, the need for high burnup fuel assemblies has increased in order to reduce fuel cycle costs, that is, to support long cycles. When increasing the burnup of a fuel assembly, in addition to ensuring the stability of the core, improving the performance of the fuel assembly components, especially the performance of fuel spacer materials, is an important issue.

As a result of examining the characteristics of current zirconium-based alloys in response to the above requirements, the inventors clarified the problems when applying fuel spacers made of current zirconium-based alloys to high burnup fuel assemblies. I made it.

That is, Zircaloy-4 exhibits excellent corrosion resistance and hydrogen absorption resistance under the conditions of use in a nuclear reactor.
However, it has been found that Zircaloy-4 reacts with reactor water during use in a nuclear reactor, and as the period of use increases, oxides are generated on the surface and the thickness of the base metal progresses. On the other hand, it was also found that the base material of Zircaloy-4 takes in hydrogen generated by oxidation, so hydrogen embrittlement progresses as the period of use increases. The usage limits of fuel spacers are determined by the strength reduction due to corrosion and the reduction in ductility and strength due to hydrogen embrittlement, but property deterioration due to hydrogen embrittlement is particularly problematic.

Therefore, when increasing the burnup of a fuel assembly,
It is necessary to use a material with better corrosion resistance and hydrogen absorption resistance for the fuel spacer. Also, the fuel spacer is made of Zircaloy-4 with a thickness of about 0.5 to 1 mm.
Zircaloy is produced by applying high-density plastic processing and dimple forming processing to plates, etc.
The structure consists of four plates assembled by welding. Therefore, the zirconium-based alloy constituting the fuel spacer needs to have good plastic workability in addition to the above-mentioned properties.

Typical examples of zirconium-based alloys include Zircaloy-2 (tin 1.20
~1.70 wt%, iron 0.07-0.20 wt%, chromium 0.05
Zirconium-based alloys containing ~0.15% by weight and 0.03-0.08% by weight of nickel are known. Zircaloy-2 is used for fuel rod cladding tubes, end plugs, etc., and although it exhibits excellent corrosion resistance similar to Zircaloy-4, its hydrogen absorption resistance is slightly inferior to that of Zircaloy-4.

As a method for improving the corrosion resistance of zirconium-based alloys, quenching treatment from the α+β phase temperature region is disclosed in Japanese Patent Application Laid-open No. 53
It is known from the publication No.-73408. Japanese Unexamined Patent Publication 1973-
Publication No. 73408 improves corrosion resistance by subjecting the zirconium-based alloy to quenching at the final product stage, and after quenching, no processing such as cold rolling for the purpose of reducing wall thickness is applied. If hard plastic working is applied to a material that has been quenched in the final product stage, microscopic cracks may occur in the material, which may even lead to breakage. This is not preferred as a method for improving corrosion resistance.
Further, since the spacer plate material is a thin plate of about 0.5 to 1 mm, the product will be deformed if it is hardened after dimple processing or other processing. As described above, JP-A-53-73480 cannot be applied to improving the corrosion resistance of spacer materials.

The fuel spacer needs to have a thickness and structure that have sufficient strength against repeated loads that the fuel assembly receives during earthquakes and handling. In addition, since the fuel spacer is constantly in contact with reactor water, it must be made of a material that has sufficient performance in terms of resistance to reactor water. On the other hand, Zircaloy-4, which has corrosion resistance equivalent to Zircaloy-2 and has better hydrogen absorption resistance than Zircaloy-2, is used for fuel spacer components, but the design life of the fuel assembly Currently, the service life limit (years) is determined by the material's embrittlement due to corrosion thinning and hydrogen absorption.
Therefore, in order to achieve a high burnup, it is necessary to reduce the amount of corrosion thinning of the fuel spacer constituent members, that is, to improve the corrosion resistance, and to suppress hydrogen embrittlement, that is, to reduce the amount of hydrogen absorption. In order to meet this requirement, which is essential for achieving high burnup, designers conducted research on manufacturing methods that improve corrosion resistance while ensuring the plastic workability of Zircaloy-4, which has a low hydrogen absorption rate, and reviewed the spacer structure. Although progress is being made, the current situation is that a solution has not been found.

The above-mentioned conventional technology only explains a method for improving corrosion resistance, and does not consider reducing the amount of hydrogen absorption, and has problems in application to spacer materials for high burnup fuel.

An object of the present invention is to provide a fuel spacer with excellent corrosion resistance, low hydrogen absorption, and excellent plastic workability.

[Means for solving problems]

The above purpose is that the fuel spacer is subjected to quenching treatment from the α+β phase or β phase temperature range after the final hot rolling, and is further subjected to multiple cold rolling treatments and multiple times of annealing treatment after the quenching treatment. This is accomplished by constructing the coated Zircaloy-2.

[Effect]

Conventionally, it was thought that the corrosion resistance of zirconium-based alloys could be improved by quenching, but the present invention
This is based on the new idea that when cold rolling is performed multiple times and annealing is performed multiple times after quenching, the effect of improving corrosion resistance deteriorates significantly depending on the difference in alloy composition.

FIG. 8 shows a comparison of the hydrogen absorption rates of Zircaloy-2 and Zircaloy-4. This data was obtained by exposing samples with the same manufacturing history to a corrosive environment and measuring the hydrogen content of the samples that exhibited the same degree of corrosion increase (mg/dm ² ) using the inert gas fusion thermal conductivity method. This is a comparison of the proportion of hydrogen in the total amount of hydrogen. As is clear from Figure 8, the ratio of the amount of hydrogen absorbed in the base material to the total amount of hydrogen generated by oxidation, that is, the hydrogen yield, is smaller in Zircaloy-4 than in Zircaloy-2, and the relative value is is 1, whereas Zircaloy-2 is 1.7. This property is why Zircaloy-4 has been used conventionally as a fuel spacer material. Therefore, materials that have been quenched, then cold-rolled multiple times and annealed multiple times were considered to be the most promising candidates for fuel spacer plates and tube materials for high-burnup fuel assemblies. .

FIG. 9 shows the corrosion test results of Zircaloy test materials (plate materials) with different manufacturing histories. Figure 10 shows the manufacturing history of various test materials. Zircaloy test material A
is hot rolled at 700℃ after quenching from the β phase temperature region, then annealed at 700℃,
Furthermore, it was manufactured by repeatedly cold rolling with a working degree of 40% and annealing at 600°C. Zircaloy test material B was produced by hot rolling and then α+β quenching, and Zircaloy test material C was produced by subjecting the final annealed material to α+β quenching. The quenching treatment was performed by maintaining the target quenching temperature for about 5 seconds and then cooling with water. The cooling rate was 100°C/sec or more.

In the case of manufacturing process C, both Zircaloy-2 and Zircaloy-4 were heated at 410° x 8 hours, followed by 510°C x 16
It exhibited excellent corrosion resistance under corrosion conditions of 500 mL, and its corrosion weight increase was approximately 50 mg/dm ² . Since the increase in corrosion weight, that is, the amount of hydrogen generated, is the same, Zircaloy-2, which has a higher hydrogen absorption rate as shown in FIG. 8, absorbs a larger amount of hydrogen, and therefore embrittlement progresses faster.
If the plastic workability is good, Zircaloy-4 manufactured by the above production process C is optimal as a plate material for spacers, but the plate material manufactured by this process has deteriorated plastic workability and cannot be used as a plate material for spacers. There are problems in using it.

From the viewpoint of plastic workability, the plate material manufactured in manufacturing process A or C satisfies the desired characteristics. However, new knowledge has been obtained that in the case of Zircaloy-4, the effect of improving corrosion resistance is significantly reduced by processes such as hot rolling, cold rolling, and annealing after quenching treatment, compared to Zircaloy-2. In the case of Zircaloy-4, the plate material in manufacturing process A has a corrosion increase of 1000 mg/dm ² or more,
The board material of B is ^about 200mg/dm2, and the material of C is 50mg/dm2.
It is about ^dm2 . On the other hand, for Zircaloy-2, the plate material in manufacturing process A is about 100mg/ ^dm2 , the manufacturing process B is about 50mg/ ^dm2 , and the manufacturing process C is 50mg/dm2.
It is about ² m2. In particular, manufacturing process B and manufacturing process C are almost equivalent. The present invention is achieved by the above-mentioned novel findings and the hydrogen absorption characteristics shown in FIG. That is, when compared in manufacturing process B, the ratio of the hydrogen absorption amounts of Zircaloy-4 and Zircaloy-2 is equal to the ratio of the product of their respective corrosion weight increases and hydrogen absorption rates, and Zircaloy-4:Zircaloy-2=
200mg×:50mg×1.7≒2:1 (Figure 11).
Therefore, results can be obtained that Zircaloy-2 has a smaller amount of corrosion thinning and a smaller amount of hydrogen absorption (lower degree of hydrogen embrittlement) than Zircaloy-4. This effect is not limited to plate materials but also applies to pipe materials. From the above, Zircaloy with improved corrosion resistance
It is clear that the material No. 2 exhibits excellent performance as a spacer component even under conditions of use in a furnace.

〔Example〕

An embodiment of the present invention will be described below.

Figure 1 shows a fuel assembly applied to a boiling water reactor. The fuel assembly includes fuel rods 2 and water rods 4 bound together by fuel spacers 3A. The fuel spacer 3A has a spacer band provided with a plurality of spacer dimples 3B. As mentioned above, the reason why the material of the fuel spacer 3A is required to have good plastic working is because of the necessity of working (pressing) the spacer dimple 3B.

The fuel spacer 3B only needs to have the function of bundling the fuel rods 2 and water rods 4, and its structure may be a lattice structure made of a combination of plate materials as shown in FIG.
Various types of structures are possible, such as a round cell structure as shown in the figure and an octagonal cell structure as shown in FIG. The fuel assembly according to the embodiment of the present invention may use any of the above fuel spacers.

Example 1 The lattice-type fuel spacer 3A shown in FIG.
A spacer bar 8 arranged perpendicular to the X and Y directions, a spacer band 6 to which both ends of the spacer bar 8 are attached surrounding the spacer bar 8 assembled in a lattice pattern, and an S-shape provided on the spacer bar 8 shaped spacer divider 7 and spacer bar 8
The lantern spring 9 is provided at the intersection of the lantern springs 9 and 9. FIG. 3 shows the lantern spring 9. Spacer bar 8, spacer band 6
The spacer divider 7 constitutes a spacer member. Lantern spring 9 is attached to the spacer member. The thin plate materials of the spacer bar 8 having the spacer divider 7 and the spacer band 6 used in this example were manufactured using Zircaloy-2 through the manufacturing steps A, B, and C shown in FIG. 10. However, since forging was performed immediately after vacuum arc melting, only this point is shown in manufacturing process A shown in Figure 10.
It is different from B and C. In order to compare the characteristics of the fuel spacer, a spacer member using Zircaloy-4 instead of the above-mentioned Zircaloy-2 was also constructed. Zircaloy-4 thin plates were also produced in the same manner as the Zircaloy-2 thin plates described above, using the manufacturing processes A, B, and C shown in FIG. Therefore, there are six types of thin plate materials because there are three types of manufacturing processes and two types of materials. Manufacturing process C, that is, the fuel spacer plate material manufactured by subjecting the final rolled thin plate material (plate thickness approximately 1 mm) to quenching treatment from the α+β phase temperature range, cracks occur during plastic processing (dimple processing) regardless of the material. Ta. The spacer plates (approximately 1 mm in thickness) produced in manufacturing processes A and B both had good plastic workability (dimple processing) and caused no problems in producing fuel spacers. (For A, the plate thickness was approximately 20 mm and the quenching process was performed from the β phase temperature range. For B, the plate thickness was approximately 10 mm and the quenching process was performed from the α+β phase temperature range.) Above There are four types of fuel spacers: a spacer made of Zircaloy-2 thin plate material manufactured in manufacturing process A (hereinafter referred to as A・Zry-2), and a fuel spacer made of Zircaloy-4 made in the same process (hereinafter referred to as A・Zry-4). ), a fuel spacer made of Zircaloy-2 thin plate material manufactured in manufacturing process B (hereinafter referred to as B・Zry-2), and a fuel spacer made of Zircaloy-4 made in the same process (hereinafter referred to as B・Zry-4). A test specimen was cut out and subjected to the corrosion test described above, and the hydrogen absorption amount and corrosion increase were measured. The corrosion weight gain was determined in units of mg/dm ² by dividing the difference in weight of the test piece before and after the corrosion test by the test piece surface area.
The amount of hydrogen absorbed was determined by the inert gas fusion thermal conductivity method. In this test, results equivalent to those shown in FIGS. 9 and 11 were obtained. That is, A.
Zry-2, B・Zry-2 is better than A・Zry-4, B・
A.
Zry-2 or B.Zry-2 is preferred. In addition,
The lantern spring is made of Inconel.

Example 2 When the fuel spacer 3C shown in FIG. 4 was manufactured using the same manufacturing parameters as in Example 1, the same results as in Example 1 were obtained regardless of the plate and tube materials.
The fuel spacer 3C is formed by interconnecting a plurality of round cells 10 and surrounding the outside with a spacer band 6. The round cell 10 is provided with a spring 11 as shown in FIG. Fuel rod 2 is round cell 1
Inserted within 0. The spacer band 6 and the round cells 10 constitute a spacer member. The spring 11 is
It can also be said that it is attached to the spacer member. Note that the round cell 10 was manufactured as follows.

How to manufacture a round cell in manufacturing process A in Figure 10: The outer diameter of the cell is approximately 150 mm, and the inner diameter is approximately 50 mm, which is called a billet.
A thick-walled Zircaloy-2 cylinder with a length of about 500 mm was subjected to β-quenching treatment, and then hot extruded at a temperature of 600°C to 750°C to produce a Zircaloy-2 blank tube with an outer diameter of about 64 mm. Next, the raw pipe is cold rolled three times to have an outer diameter of approximately 10 mm.
A thin-walled tube with a wall thickness of about 1 mm was made, and this was cut and plastically worked to produce a round cell. A Pilger rolling mill was used for cold rolling.

Round cell manufacturing method in manufacturing process B in Figure 10: The entire Zircaloy-2 raw tube is subjected to α+β quenching treatment, and then cold-rolled three times to form a thin-walled tube with an outer diameter of approximately 10 mm and a wall thickness of approximately 1 mm. This was cut and subjected to plastic working to produce round cells. A Pilger rolling mill was used for cold rolling.

In the fuel spacer of this embodiment, the spacer member including the round cells 10 is constructed using Zircaloy-2 manufactured in either manufacturing process A or B in FIG. Spring 11 is made of Inconel.

Example 3 When the fuel spacer 30 shown in FIG. 6 was manufactured using the same parameters as in Example 1, the same results as in Example 1 were obtained. The octagonal cell 12, like the round cell 10 of Example 2, was manufactured by bending a final rolled sheet material of Zircaloy-2 (manufactured in manufacturing process A or B). The spring 11 provided in the octagonal cell 12 is made of Inconel.

〔Effect of the invention〕

According to the present invention, since the characteristics of the fuel spacer are improved, it is possible to obtain a fuel spacer that can withstand high burn-up and has little corrosion.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of a fuel assembly according to an embodiment of the present invention, FIG. 2 is a plan view of the fuel spacer of FIG. 1,
Figure 3 is a structural diagram of the lantern spring in Figure 2.
4 and 6 are plan views of other embodiments of the fuel spacer, FIGS. 5 and 7 are spring structure diagrams used in the fuel spacer of FIGS. 4 and 6, and FIG. 8 is a Zircaloy FIG. 9 is an explanatory diagram showing a comparison of the corrosion test results of various corrosion resistance improving materials. FIG. 10 is a flowchart explaining the manufacturing process of the test material. FIG. 11 is an explanatory diagram showing a comparison of the hydrogen absorption amounts of Zircaloy-2 and Zircaloy-4, which ensure plastic workability and improve corrosion resistance. 1... Upper tie plate, 2... Fuel rod, 3
A, 3C, 3D...Spacer, 3B...Spacer dimple, 4...Water rod, 5...Lower tie plate, 6...Spate band, 7...Spacer divider, 8...Spacer bar, 9...Lantern spring , 10...round cell, 11...spring, 12...octagonal cell.

Claims (1)

[Scope of Claims] 1. A fuel spacer comprising a spacer member that defines a plurality of compartments into which fuel rods are inserted, and a spring member that is attached to the spacer member and presses the fuel rods inserted into the compartments. In,
The spacer member is (α+
The zirconium-based alloy is made of a zirconium-based alloy that has been subjected to a quenching treatment from the β) phase or the β-phase temperature range, and has been cold-rolled and annealed after the quenching treatment, and the zirconium-based alloy contains at least nickel. A fuel spacer characterized by: 2. The fuel rod has a plurality of fuel rods, an upper tie plate and a lower tie plate that hold both ends of each of the fuel rods, and a fuel spacer that maintains a predetermined distance between each of the fuel rods, A fuel assembly in which the spacer includes a spacer member that defines a plurality of compartments into which fuel rods are inserted, and a spring member that is attached to the spacer member and presses the fuel rod inserted into the compartments. In the spacer member, after the final hot rolling, (α
The zirconium-based alloy is made of a zirconium-based alloy that has been quenched from the +β) phase or β-phase temperature range and that has been cold-rolled and annealed after the quenching treatment, and the zirconium-based alloy contains at least nickel. A fuel assembly characterized by: