JP2006028553A - Zirconium alloy and channel box utilizing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zirconium alloy whose growth by irradiation is suppressed, and which has high corrosion resistance and is utilizable for a channel box or the like. <P>SOLUTION: The zirconium alloy has a composition comprising, by weight, 1.20 to 1.70% tin, 0.18 to 0.24% iron, 0.07 to 0.13% chromium and 0.28 to 0.37% iron+chromium, also comprising at least one kind of element selected from niobium, tantalum and vanadium by ≤0.6% in total, and the balance zirconium with inevitable impurity elements. Alternatively, the other zirconium alloy has a composition comprising 1.20 to 1.70% tin, 0.24 to 0.55% iron, 0.07 to 0.13% chromium, 0.31 to 0.68% iron+chromium, and the balance zirconium with inevitable impurity elements. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zirconium alloy, particularly a zirconium alloy having improved deformation characteristics by increasing corrosion resistance or suppressing irradiation growth, and a channel box using this zirconium alloy.

In current normal boiling water reactors, Zircaloy-4 (trademark) is used as a material for a channel box that surrounds the fuel assembly and forms a coolant flow path. Zircaloy-4 is a zirconium alloy adopted in consideration of neutron economy, corrosion resistance, and the like, and its composition is 1.20 to 1.70% tin and 0.18 to 0.80 iron in terms of weight ratio. It contains 24%, chromium 0.07 to 0.13%, iron + chromium 0.28 to 0.37%, and the balance consists of zirconium and inevitable impurity elements (see Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 10-73690 JP-A-6-317687 Zirconium in the nuclear industry: Eleventh Symposium (1995)

  Recently, in order to improve operation efficiency, use of a channel box for long-term operation using a high burnup and refueling cycle has been studied. However, it is known that when such operation is performed, the conventional channel box is bent due to irradiation growth or the like, and recently, there is a concern about bending due to local corrosion.

  Accordingly, the present invention provides a zirconium alloy that can be used for a channel box and the like and that is made of this zirconium alloy, which has improved deformation characteristics by suppressing irradiation growth and suppressing hydrogen absorption by enhancing corrosion resistance. The purpose is to do.

  In order to achieve the above object, a zirconium alloy according to one embodiment of the present invention has a weight ratio of 1.20 to 1.70% tin, 0.18 to 0.24% iron, and 0.07 to 0 chromium. .13%, containing iron + chromium 0.28 to 0.37%, and containing at least one element of niobium, tantalum, vanadium in total of 0.6% or less, with the balance being zirconium and inevitable It consists of an impurity element.

  Here, the contents of tin, iron, chromium, and iron + chromium are all equivalent to those of the conventional zircaloy-4. Tin is added in order to improve mechanical properties and to suppress the adverse effect of nitrogen contained in sponge zirconium as a raw material on corrosion resistance. Iron and chromium are alloying elements added mainly to improve corrosion resistance.

  Here, the reason why at least one element of niobium, tantalum, and vanadium is added is that irradiation growth is thereby suppressed. For example, FIG. 2 shows an example of the effect of suppressing irradiation growth when niobium is added. FIG. 2 is a graph disclosed in Non-Patent Document 1, in which the vertical axis represents irradiation growth rate (IIG) (%) and the horizontal axis represents neutron irradiation amount. White circle (○), white triangle (△), and black triangle are general zircaloy materials without niobium addition, and white star (☆) is a 1.2Sn-0.35Fe-1Nb alloy in a 330-350 ° C environment. Represents a characteristic. From this figure, it can be seen that irradiation growth is suppressed by the addition of niobium.

  The inventors have independently confirmed that niobium suppresses irradiation growth and that precipitates containing it as a main component are not easily dissolved by neutron irradiation. It is known that the deformation of the channel box is mainly caused by the difference in irradiation growth due to the difference in the irradiation amount of the channel box facing each other. Irradiation growth is closely related to the C component dislocations generated by irradiation, and in order to suppress the movement and increase in density, niobium-based precipitates that are stable to irradiation are formed and the movement of the dislocations is prevented. , Aimed at curbing growth itself. Therefore, even if iron, which is a conventional precipitate constituent element, is dissolved by neutron irradiation, the precipitate can be maintained by the presence of niobium. As a result, irradiation growth can be suppressed.

  Alternatives to niobium can be tantalum and vanadium. Here, the total content of these elements is 0.6% or less by weight because it is a solid solubility limit in zirconium. If it is added more than this, it is not preferable because the current manufacturing process of Zircaloy must be changed.

  In addition, the zirconium alloy according to another aspect of the present invention has a weight ratio of 1.20 to 1.70% tin, 0.24 to 0.55% iron, 0.07 to 0.13% chromium, iron + It contains 0.31 to 0.68% of chromium, and the balance is composed of zirconium and inevitable impurity elements.

  The proponent believes that the deformation of the channel box can be suppressed by improving the corrosion resistance in addition to the suppression of irradiation growth. In general, corrosion and hydrogen absorption are in a reverse relationship. Oxygen constituting the water that is the cause of corrosion is used for corrosion (oxidation), and the remaining hydrogen is dissolved in zirconium known as a hydrogen solute metal. That is, when the corrosion amount is large, the hydrogen solid solution amount is also increased. As described above, the iron-based precipitate before irradiation gradually dissolves by irradiation, and the C component dislocation generated by irradiation moves freely. At the same time, the amount of hydrogen solid solution gradually increases. The channel box is rolled to increase dimensional accuracy during manufacturing, and contains a small amount of local distortion during the dimensional correction process, and free-movable C component dislocations gradually gather at such locations. . When the dislocation moves, the hydrogen is swept away, creating a place where the hydrogen concentration is locally high. That is, hydrogen and C component rearrangement tend to gather at the same place. Since the C component dislocation promotes irradiation growth, local irradiation growth occurs in a place where the hydrogen concentration is locally high. If the irradiation growth is different at the opposite sides of the quadrangle, bending occurs locally at that portion.

Therefore, the iron component in the zirconium alloy is increased for the purpose of improving the corrosion resistance for the purpose of suppressing the solid solution (absorption) amount of hydrogen and suppressing the movement of the C component dislocation for a long period of time. Here, the content of tin is equivalent to that of the conventional Zircaloy-4, and the effect is the same as that of the conventional one. The reason why iron is 0.24% or more by weight is that, as shown in FIG. 3, the corrosion rate is remarkably reduced by making iron 0.24% or more. Here, FIG. 3 is a diagram showing the relationship between the amount of iron in the zircaloy after irradiation and the corrosion rate at 400 ° C. FIG. The vertical axis represents the corrosion rate after irradiation (mg / dm ² · d), and the horizontal axis represents the iron content (%). From this figure, it can be seen that when the iron content is higher than the conventional iron content corresponding to Zircaloy-4, the corrosion rate is significantly reduced.

  The zirconium alloy preferably has an average size of precipitates containing tin, iron and chromium of 0.05 to 0.35 μm.

  In general, as shown in FIG. 4, the larger the size of the zircaloy-4 precipitate, the higher the corrosion rate, which is not preferable. Here, FIG. 4 is experimental data showing the relationship between the size of the precipitate of Zircaloy-4 and the corrosion rate, the vertical axis is the corrosion rate calculated from the maximum oxide film (μm / GWD / T), and the horizontal axis is the precipitation. The average size (μm). As described above, increasing the content of iron or the like tends to increase the size of the precipitate, but by setting the average dimension to 0.05 to 0.35 μm, the corrosion rate is suppressed.

  In general, when the neutron irradiation time is long, iron in the precipitate composed of iron and chromium is solid-dissolved, resulting in iron-depleted precipitate, and then chromium is also solid-dissolved, and the precipitate is miniaturized or disappears. End up. It can be seen that the corrosion resistance is maintained by precipitates having a size of about 0.05 μm or more, and decreases as the precipitate size increases. On the other hand, if this precipitate is dissolved, the corrosion resistance is lowered. The size of the precipitate is determined by the manufacturing process, particularly the heat treatment conditions. Therefore, it is effective to add a large amount of iron which is easily dissolved by irradiation from the beginning.

  Since the amount of iron in this range exceeds the solid solution limit, there is no basis for an upper limit due to solid solution. However, when the iron content increases, there is a concern that, in the same manufacturing process as the conventional one, the precipitate size becomes large, the corrosion resistance decreases, and the thermal neutron absorption cross section increases. Therefore, the upper limit of the iron content is set to 0.55% which is a good range obtained from the test results.

  The zirconium alloy preferably contains a total of 0.6% or less of at least one element selected from niobium, tantalum, and vanadium. The effect of adding niobium, tantalum, and vanadium is the same as that of the above-described aspect of the invention.

  The zirconium alloy preferably has an average size of precipitates containing tin, iron and chromium of 0.05 to 0.35 μm.

    In the present invention, an excellent channel box can be manufactured using the zirconium alloy.

  According to the present invention, it is possible to provide a zirconium alloy with high corrosion resistance and suppressed irradiation growth, and a channel box using this zirconium alloy.

  FIG. 1 is a longitudinal sectional view of a fuel assembly using an embodiment of a channel box according to the present invention. The shape of this fuel assembly is the same as that of a conventional boiling water nuclear reactor fuel assembly, and several tens of fuel rods 2 are arranged in a square lattice and are bound by an upper tie plate 3 and a lower tie plate 4. Has been. A handle 4 for fuel handling is formed on the upper portion of the upper tie plate 3. Fuel spacers 5 are disposed at a plurality of locations between the upper tie plate 3 and the lower tie plate 4 to maintain the mutual spacing between the fuel rods 2. The periphery of the fuel assembly is surrounded by a rectangular tubular channel box 10.

  In the nuclear reactor (not shown), the coolant flowing in from the lower tie plate 4 is heated and boiled while flowing upward around the fuel rod 2 inside the channel box 10 to form a gas-liquid two-phase flow. And flows out from the upper tie plate 3.

  Here, the zirconium alloy is used as the material of the channel box 10. Thereby, the irradiation growth of the channel box 10 can be suppressed, the bending of the channel box 10 can be suppressed, and the corrosion resistance can be improved. Further, this material can be used for the fuel spacer 5.

The longitudinal section of the fuel assembly using the embodiment of the channel box concerning the present invention. The graph which shows the relationship between irradiation amount and irradiation growth. The graph which shows the relationship between the quantity of iron in Zircaloy after combustion, and corrosion rate. The graph which shows the relationship between deposit size and corrosion.

Explanation of symbols

2 ... Fuel rod 3 ... Upper tie plate 4 ... Lower tie plate 5 ... Fuel spacer 10 ... Channel box

Claims (5)

Containing, by weight, 1.20 to 1.70% tin, 0.18 to 0.24% iron, 0.07 to 0.13% chromium, 0.28 to 0.37% iron + chromium, and A zirconium alloy comprising at least one element of at least one of niobium, tantalum, and vanadium in a total amount of 0.6% or less, the balance being zirconium and inevitable impurity elements. Contains, by weight, 1.20 to 1.70% tin, 0.24 to 0.55% iron, 0.07 to 0.13% chromium, 0.31 to 0.68% iron + chromium, and the balance Zirconium alloy characterized by comprising zirconium and inevitable impurity elements. The zirconium alloy according to claim 2, comprising at least one element of niobium, tantalum, and vanadium in a total amount of 0.6% or less. The zirconium alloy according to any one of claims 1 to 3, wherein the average size of the precipitate containing tin, iron and chromium is 0.05 to 0.35 µm. A channel box using the zirconium alloy according to claim 1.

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