JPH0762225B2 - Manufacturing method of highly corrosion resistant zirconium alloy products - Google Patents

Description

The present invention relates to a method for producing a high-corrosion resistant zirconium alloy product using a novel high-corrosion resistant zirconium-based alloy member, and in particular, no nodularity corrosion and white general corrosion occur. , A method for producing a nuclear reactor fuel assembly product having excellent corrosion resistance.

[Conventional technology]

The BWR fuel assembly is roughly divided into a large number of fuel rods (a fuel pellet 1, a fuel cladding tube 2 covering the same, and an end plug 3 as shown in the schematic sectional view of FIG. 3, the portion of FIG. 4). (See the sectional view), a spacer 4 for holding them at a predetermined distance from each other, and a square channel box 5 for accommodating them.
It is composed of. Reference numeral 6 denotes an upper tie plate, and 7 denotes a lower tie plate. Further, when manufacturing these fuel assemblies, a complicated manufacturing process is performed, and each structure is assembled by welding.

The fuel cladding tube is a strength member, and as shown in Fig. 4, the inside is in contact with the fuel pellet and the outside is in contact with the reactor water, so it is used in the corrosive gas generated during combustion and in the corrosive environment of high temperature and high pressure water and steam. To be done. In particular, it is important to prevent the corrosion of the outer surface contacting the reactor water. The welding point is the joining point between the upper and lower end plugs and the fuel cladding tube. Reference numeral 10 means a welded portion.

The spacer is a lattice-shaped frame body as shown in a plan view in FIG. 5, and the fuel rod is inserted into each spacer lattice. Such spacers are provided at seven locations along the longitudinal direction of the BWR fuel assembly, and keep a number of fuel rods at predetermined intervals and fix them to prevent lateral vibration of the fuel rods and bending in the longitudinal direction. ing. FIG. 5 is a plan view of the spacer, and the fuel cladding tube 2 is fixed by the spacer bar 9 and the lantern type leaf spring 8. The spacer is assembled at the welded portion 10. For this reason, the spacer is used under the condition that the stress from the fuel rod is applied. In addition, since this member comes into contact with reactor water, there is a concern that it may cause corrosion.

The channel box is a rectangular tubular body that houses the fuel rods bundled by the spacers inside. In FIG. 3, the fuel rods are fixed by the upper tie plate 6 and the lower tie plate 7, and the channel box 5 is placed so as to cover it. Is inserted. FIG. 6 shows an enlarged perspective view of the channel box, which has a rectangular tube shape in which plate-worked materials divided into two are joined at the welded portion 10. This member serves to forcibly guide the high temperature water and steam generated in the fuel rods to the upper part during plant operation, and is used for a long period of time in the state where the stress that spreads to the outside of the square tube is constantly applied. Since this member also comes into contact with reactor water, there is a concern that Nojiura corrosion may occur. Further, hydrogen is generated (Zr + 2H ₂ O → ZrO ₂ + 2H ₂ ) during the oxidation reaction of the zirconium-based alloy for this member, and there is a concern that this hydrogen will be embrittled by being taken into the material. .

As described above, the fuel cladding tube, the channel box, and the spacer material constituting the fuel structure are mainly required to have corrosion resistance and hydrogen embrittlement resistance. Conventionally, a fuel cladding tube as a member of a fuel assembly is a Zr-Sn-Fe-Cr-Ni alloy, Zircaloy-2 (1.5 wt% Sn, 0.1 wt% Fe, 0.
1 wt% Cr and 0.05 wt% Ni residual Zr) and Zircaloy-4 (1.5 wt% Sn, 0.2 wt% Fe and 0.1 wt% Cr residual Zr) excluding Ni are used for the channel box and spacer. These fulfill their functions under the current operating conditions of the reactor. However, in the future, from the viewpoint of improving the economical efficiency of the nuclear power plant, if the operating period is extended (or the burnup of the fuel rod is increased), it is expected that more severe usage conditions will be added.

For this purpose, a zirconium-based alloy having high strength and excellent corrosion resistance as compared with conventional materials is desired for the member.

That is, in a structural member of a BWR fuel assembly using zircaloy, spot-like gray-white corrosion products called nodular corrosion may occur on the surface, and this nodular corrosion causes further corrosion by long-term use. If accelerated, there is a risk that it will eventually peel and cause a decrease in wall thickness. It is not preferable that the activated release oxide film is mixed in the reactor water. In order to achieve a low pressure loss structure in the spacer,
It is necessary to thin the member. In this case, it is necessary to have high strength as well as corrosion resistance. Further, in the channel box, stricter conditions than those of conventional members for high burnup are added, such as excellent strength, particularly creep strength, after long-term use.

Conventional Zircaloy is not always sufficient as a material having high strength and high corrosion resistance that satisfies this condition. As one of high strength materials, Zr-2.5Nb alloy, Zr-3Nb-1Sn alloy and Excel (E
xcel) alloy (Zr-3Sn-0.8Nb-0.8Mo) and other Zr-Nb alloys. Among them, Zr-2.5 wt% Nb alloy is used in pressure pipes of Canadian plants. However, Zr-3Nb
-1Sn alloy and Zr-2.5Nb alloy are Proceedings of the International Symposium on Envelopemental Degradation of Materials In-Nuclear Power Systems 19
August 1983 [Proceedings of the International Symposi
um on Environmental Degradation of Metarials in Nu
clear Power Systems Water Reactors Mytle Beach.Sou
th Corolina August 22-25 (1983)] pp. 274-294, it is known that white general corrosion occurs in the weld and its heat affected zone under BWR environment. It is known that the alloy has a significantly higher oxide film growth rate than Zircairo.

Since this structural member has a complicated shape as shown in the previous drawings (FIGS. 4 to 6), welding work cannot be avoided. Therefore, although these high-strength Zr-Nb alloys have high strength,
It can be seen that no consideration is given to the corrosion resistance of the welded part.

In addition, conventional materials such as Skanook alloy (Japanese Patent Application No. 50-148213,
Japanese Examined Japanese Patent Publication No. 54-7494), Ozhennite 0.5
Alloys (0.1 wt% Nb-0.2 wt% Sn-0.1 wt% Fe-0.1 wt% Ni) and Zr-1.0 wt% Nb-1.0 wt% Sn-0.5 wt% Fe alloys. However, with these low Nb-containing Zr alloys, although white corrosion of welds is unlikely to occur, high strength cannot be obtained.

Thus, the materials that have been conventionally developed as fuel assembly materials have not been considered for long-term use. Therefore, it is important not only that the characteristics of the member that can be operated for a long period of time include characteristics such as strength, workability, and weldability, but especially that the corrosion resistance does not deteriorate due to welding.

[Problems to be solved by the invention]

From the viewpoint of improving the economical efficiency of the plant, the above-mentioned conventional technology has a problem of thinning of components due to corrosion of nodule and deterioration of hydrogen absorption due to hydrogen absorption during use from the viewpoint of improving the economic efficiency of the plant. There was a problem such as possible corrosion.

An object of the present invention is to provide a zirconium alloy member which has high strength and whose corrosion resistance does not decrease due to welding.

[Means for solving problems]

Briefly describing the present invention, the first invention of the present invention relates to a method for producing a corrosion-resistant zirconium alloy product, comprising 1.0 to less than 1.5% niobium, 0.5 to 2.2% tin, 0.2 to 1.0% molybdenum, And, in the method for producing a product using a zirconium alloy member in which the balance except unavoidable impurities is zirconium, after the final hot plastic working, cold rolling and annealing are repeatedly performed, and then solution treatment, The cold working and the welding are sequentially performed, and the heat treatment is performed at 450 to 700 ° C. before the welding after the cold working or after the welding.

A second invention of the present invention relates to another method for producing a high corrosion resistant zirconium alloy product, wherein the alloy member used in the first invention is replaced by weight of niobium.
A zirconium alloy member comprising 1.0 to less than 1.5%, tin 0.5 to 2.2%, iron 0.04 to 1.0%, molybdenum 0.2 to 1.0%, and zirconium as the balance excluding inevitable impurities is used.

The present inventors have found that by improving the alloy composition of the Zircaloy and Zr—Nb system, the corrosion resistance of the alloy weld is improved.

Zr-Nb system ingot with Sn, Fe and Mo added individually or in combination, processed into a sample through the steps of casting, hot plastic working, annealing, solution treatment, cold plastic working, annealing and welding. Then, a characteristic test was conducted. As a result, as shown in Fig. 1, Zr-Nb alloys with two kinds of composite addition of Sn + Mo and Sn + Mo + Fe do not cause white corrosion if the Nb content is less than about 1.5% by weight, and white corrosion resistance does not occur. It was found that the sex is remarkably improved. On the other hand, in the tensile properties of the member
It was found that as the Nb content increases, the strength increases, but the ductility decreases. That is, FIG. 1 is a graph showing the relationship between the corrosion increase amount (mg / dm ² , vertical axis) and elongation (%, horizontal axis), and Nb amount (weight%, horizontal axis).

It has been found that the white corrosion of the welded portion can be sufficiently prevented by incorporating a post heat treatment at 450 to 700 ° C. in the step after welding the members.

The chemical composition of the member is defined for the following reasons. The addition of Sn suppresses the decrease in corrosion resistance of the zirconium-based alloy due to nitrogen, and the addition of Sn stabilizes the Zr-α phase in the weld structure and increases the solid solution of Nb in the α-Zr phase. It is a function of maintaining corrosion resistance. That is, Zr−Nb
The equilibrium phase of room temperature alloys (Nb <20% by weight) is 0.6
Α-Zr phase with solid solution of Nb of less than 1.5% by weight and Z of less than 1.5% by weight
It is a β-Nb phase in which r is solid-solved.
At 10 ° C. or higher, the α-Zr phase and β-Zr phase of pro-eutectoid are separated, and when further cooled, the β-Nb phase is precipitated from the β-Zr phase.

When the structure is observed, the rounded α-Zr phase and the precipitate are β
It can be distinguished from the Nb-rich phase in which the -Nb phase is finely precipitated.
Zr-1.0 wt% Nb-1.0 wt% Sn alloy α-Zr phase part is Sn
It is higher than that of the binary alloy of Zr-1.0 wt% Nb without addition. This is because the addition of Sn, which is an α-stabilizing element, expanded the α-Zr phase region in the equilibrium diagram. In Zr-Nb alloy welds, the part that is rapidly cooled from a high temperature due to the thermal cycle during welding tends to become a non-equilibrium phase of α-Zr phase or residual β-Zr phase due to supersaturation of solid solution of Nb. , Β-Zr phase by addition of Sn, β-Nb phase and α-
It becomes easy to decompose into Zr phase. It was clarified that the expansion of the α-Zr phase region, that is, the stabilization of the α phase where corrosion is unlikely to occur, contributes to the improvement of corrosion resistance.

The addition amount of Sn is preferably in the range of 0.7 to 2.0% by weight, and when it is less than 0.5% by weight, the effect is not obtained. If added in excess of 2.2% by weight, corrosion resistance will not be a problem, but ductility and workability of the member will deteriorate and it cannot be applied as a thin plate structural member.

Mo has the effect of remarkably improving the strength by adding a trace amount. Furthermore, by adding a compound with Sn or Sn + Fe, there is also an effect of improving the corrosion resistance. The increase in strength due to the addition of Mo is due to the fine precipitation of the intermetallic compound phase of Mo ₂ Zr.

The effect of adding Mo is shown in FIG. That is, FIG. 2 shows the oxide film thickness (μm, vertical axis) and Mo addition amount (weight%, horizontal axis).
It is a graph which shows the relationship with. 0.2 as shown in FIG.
Addition of less than wt% is small. On the other hand, the reason why the upper limit value is set is that the hardness increases, the workability decreases, and the ductility of the member decreases. At the same time, a large amount and addition of Mo are not good for nuclear properties. In other words, these elements have a significantly larger thermal neutron absorption cross-section than Zr, which adversely affects the neutron economic efficiency.

The addition of Fe has the effect of modifying the oxide film in the corrosion of zirconium-based alloys. These elements are precipitated as an intermetallic compound phase, and improve the corrosion resistance by stabilizing the α phase. In other words, the addition of Sn stabilizes the α-Zr phase and promotes the precipitation of β-Nb, and Fe that cannot form a solid solution in the α-Zr phase becomes Fe.
This is because it precipitates as an intermetallic compound phase of -Nb or Fe-Zr and reduces the amount of Nb solid solution in the nonequilibrium phase. A non-equilibrium phase is observed even with the addition of Fe, but the amount of solid solution of Nb is considerably lower than that of the alloy without addition. Fe is contained as an impurity in Zr in an amount of about 0.03% by weight, but these effects cannot be obtained unless Fe is added in an amount of at least 0.04% by weight.
The precipitation of the intermetallic compound phase due to the addition of Fe also contributes to the improvement of strength. However, addition of a large amount of Fe exceeding 0.1% by weight adversely affects the ductility and nuclear properties of the alloy.

Nb is a basic chemical composition of Zr-Nb system, and β-Nb is precipitated by the aging treatment to improve the strength. The above-mentioned FIG. 1 shows the relationship between the corrosion increase amount of the alloy weld (as welded) and the Nb content. The Zr-Nb binary alloy is remarkably highly susceptible to white corrosion. Addition of 0.1% by weight already causes white corrosion, and further addition of Nb further promotes corrosion.

On the other hand, the Zr-Nb-Sn-Mo quaternary alloy of the present invention and Zr-Nb-
In the Sn-Fe-Mo quinary alloy, white corrosion does not occur with less than 1.5% by weight of Nb, but with the addition of a large amount of Nb exceeding that, white corrosion occurs as in the binary alloy. The reason why corrosion tends to occur as the Nb content increases is that the structure is α-Zr in the non-equilibrium phase.
Alternatively, it is because the β-Zr phase is easily formed, and a large amount of Nb is formed as a solid solution. This is remarkable in the Zr-Nb binary alloy. On the other hand, the quaternary alloy or the quinary alloy of Sn, Fe and Mo of the present invention promotes β-Nb precipitation by adding Sn and precipitates intermetallic compounds such as Fe-Nb, Fe-Zr and Mo-Nb. Therefore, since the amount of Nb solid solution in the non-equilibrium phase has decreased, the corrosion resistance and strength are high. However, when the Nb content exceeds 1.8% by weight, the effect of the addition is lost. However, the improvement of corrosion resistance due to the precipitation of β-Nb is normal aging treatment (about 500 ℃, 24 hours).
The white corrosion does not occur even with a high Nb content (about 3% by weight).

On the other hand, high Nb content increases the strength, but decreases ductility.
Considering the manufacturing process of the fuel assembly, the workability of the member is important because it is thin. Therefore, the upper limit of Nb content is 1.5% by weight for product parts that emphasize workability.
It is preferable that the elongation is less than 20% and the elongation is about 20%. Also, with respect to the lower limit value (1.0% by weight), Nb content less than 1.0% by weight causes insufficient strength and further increases susceptibility to Noduleura corrosion. The balance of the alloy consists of Zr and inevitable impurities.

Conventional fuel cladding tubes, spacers, and channel boxes are difficult to change the manufacturing process due to the complexity of their shapes, and welding is inevitable.

It was found that the plastic workability and weldability did not change significantly as compared with the conventional material within the chemical composition range of the present invention. As for the corrosion resistance, it is possible to improve the corrosion resistance and white corrosion resistance in the case of manufacturing in a normal manufacturing process (welding is possible). In order to impart more sufficient corrosion resistance, 450-700 ℃ after welding, 3-30
This can be done by performing a post heat treatment for about an hour. The reason for setting the post heat treatment after welding is to sufficiently precipitate Nb dissolved in the matrix of the alloy. When the temperature is lower than 450 ° C, the precipitation is not sufficiently obtained, and when it exceeds 700 ° C, Nb is not obtained.
Due to the re-dissolution of, and the reduction of its effect. The alloy of the present invention is also effective as a fuel rod end plug material and has excellent corrosion resistance without heat treatment after welding.

In addition, for members that require higher strength, it is preferable to re-quence from the β or α + β temperature near the final process of the product, and then perform post heat treatment at 450 to 700 ° C for about 3 to 30 hours. is there.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to these examples.

Example 1 Industrial pure zirconium was used as the material, and the zirconium alloys shown in Table 1 were melted. An arc melting furnace was used for melting. Each sample was solution treated at 1000 ° C and then
Hot plastic working at 750 ° C, cold rolling and annealing (650 ° C) were repeated to make a 2 mmt thin plate. Next, solution treatment was performed at 880 ° C. for 1 hour, further 10% cold working was performed, then welding was performed, and finally post heat treatment (500 ° C., 24 hours) was performed.

Corrosion test pieces were sampled from the welded joint material and subjected to high temperature steam test to evaluate Nojiura corrosion susceptibility and high temperature water corrosion test to evaluate white corrosion susceptibility, respectively. The corrosion test in high temperature steam was held at 510 ° C. and 105 kg / cm ² superheated steam for 20 hours. The high temperature water corrosion test was performed at 288 ℃ and 85kg / cm ^{2 in} high temperature water to about 300
Held for hours. The corrosion resistance was evaluated by visually observing the appearance after the test, measuring the amount of corrosion, and measuring the thickness of the oxide film.

As a result of the corrosion test, it can be seen that as shown in Table 1, the material of the present invention does not cause nodular corrosion or white corrosion and has excellent corrosion resistance.

The material of the present invention has a tensile property of about 80 kg / mm ² and an elongation of 30%, and has high strength and high ductility. Further, the ductility reduction phenomenon due to hydrogen absorption was not observed in the alloy of the present invention.

Next, in the above-mentioned welding process, heat treatment was performed at 500 ° C. for 24 hours before welding, and the same corrosion resistance evaluation was performed on the samples that were not subjected to heat treatment after welding. As a result, the corrosion resistance of the material without post-weld heat treatment caused significant white corrosion with the conventional Zr-2.5 wt% Nb, but in the present invention, a black dense uniform oxide film is exhibited, and white corrosion does not occur and corrosion resistance is excellent. I understand that.

Example 2 An example of applying the present invention member to a spacer will be described. FIG. 7 shows the shape of the spacer (FIG. 7-1 is a plan view, and FIG. 7-2 is a side view seen from the Y direction in FIG. 7-1).
FIG. 8 is a process drawing showing the spacer manufacturing process. The structure of the spacer is composed of a spacer band 11, a spacer bar 9, a spacer divider 12, and a lantern type leaf spring 8, and the lattice points and the spacer bar 9 and the spacer band 11 are spot-welded.

As the member, the ingot of the present invention material 2 melted in Example 1 was divided and used. Repeated hot rolling at about 750 ℃ twice, thickness 3mm
Plate, and by further repeating cold rolling and annealing (650 ° C), a plate having a thickness of about 0.7 mm was obtained. Next, as in Example 1, solution treatment was performed, and further cold working was performed. A plate for a spacer band and a spacer bar was processed by punching with this plate. Furthermore, the spacer band was subjected to dimple 13 processing and bending processing. Then, the lantern type leaf spring 8 was assembled and processed, and TIG welding 10 was performed at a predetermined position to assemble the spacer.
While subjecting this spacer to a corrosion test,
Fabricate a spacer that has been heat treated at 500 ° C for 20 hours,
The same corrosion test as in Example 1 was performed.

As a result, none of the spacers showed white corrosion and showed high corrosion resistance.

Example 3 The present invention is applicable not only to a BWR plant but also to a PWR plant and an AT.
It can also be applied as a fuel structural member for R plants and high conversion reactors. Also, not only fuel structural members but also high temperature and high pressure water come into contact with them,
It can be applied as a structural member used in an environment in which a fast neutron (E> 1 MeV) irradiation dose is 1 × 10 ¹⁹ n / cm ² or more.

〔The invention's effect〕

As described above, according to the present invention, a novel zirconium alloy member is provided, whereby a fuel cladding tube made of zirconium alloy having particularly excellent corrosion resistance and its end plug,
Since the spacer and the channel box can be manufactured, a highly economical fuel assembly can be manufactured and the reliability can be improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between corrosion increase and elongation and Nb amount, FIG. 2 is a graph showing the relationship between oxide film thickness and Mo addition amount, and FIG. 3 is a schematic cross-sectional view of a fuel assembly. The figure is a schematic partial cross-sectional view of a fuel rod. FIG. 5 is a plan view of a spacer.
FIG. 7 is a perspective view of the channel box, FIG. 7-1 is a plan view showing the structure of the spacer, FIG. 7-2 is a side view seen from the Y direction, and FIG. 8 is a spacer manufacturing process drawing. 1: Fuel pellet, 2: Fuel cladding tube, 3: End plug, 4: Spacer,
5: Channel box, 6: Upper tie plate, 7: Lower tie plate, 8: Lantern type leaf spring, 9: Spacer bar, 1
0: Weld, 11: Spacer band, 12: Spacer divider, 13: Dimple

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jiro Kuniya 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitate Manufacturing Co., Ltd.Hitachi Laboratory Ltd. Hitachi Research Laboratory (72) Inventor Isao Masaoka 4026 Kuji-machi, Hitachi City, Ibaraki Prefecture Hiritsu Manufacturing Co., Ltd. Hitachi Research Laboratory (72) Inventor Tetsuro Yasuda 3-1-1 Sachimachi, Hitachi City, Ibaraki Hitachi Ltd. Hitachi factory (56) Reference JP-A-61-170552 (JP, A) JP-B-45-13226 (JP, B1)

Claims (4)

[Claims] 1. Niobium 1.0 to less than 1.5% by weight, tin 0.5.
~ 2.2%, molybdenum 0.2 ~ 1.0%, and a method of manufacturing a product using a zirconium alloy member consisting of zirconium as the balance excluding unavoidable impurities, in the final hot plastic working, after cold rolling and annealing. Is repeatedly applied, and then solution treatment, cold working, and welding are sequentially performed, before welding after the cold working, or after the welding,
A method for producing a highly corrosion resistant zirconium alloy product, characterized by performing heat treatment at 450 to 700 ° C. 2. A method for producing a highly corrosion resistant zirconium alloy product according to claim 1, wherein the product is a fuel spacer for a fuel assembly, a channel box for a fuel assembly, or a fuel cladding tube for a fuel assembly. . 3. By weight, niobium 1.0 to less than 1.5%, tin 0.5.
~ 2.2%, iron 0.04 ~ 1.0%, molybdenum 0.2 ~ 1.0%, and a method of manufacturing a product using a zirconium alloy member consisting of zirconium for the balance excluding unavoidable impurities. Rolling and annealing are repeatedly performed, and then solution treatment, cold working, and welding are sequentially performed, and heat treatment is performed at 450 to 700 ° C. before welding after the cold working or after the welding. A method for producing a high corrosion resistant zirconium alloy product, which is characterized by being applied. 4. The method for producing a high corrosion resistant zirconium alloy product according to claim 3, wherein the product is a fuel spacer for a fuel assembly, a channel box for a fuel assembly, or a fuel cladding tube for a fuel assembly. .