JPS5825466A - Manufacture of zirconium base alloy-clad pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a zirconium-based alloy cladding tube for a nuclear reactor fuel rod.

Thin-walled zirconium-based tubes known as silica are commonly used as clad tubes for fuel rods in nuclear reactors. These alloys include alloying materials such as tin, iron, nickel, etc. In the case of Zircaloy, the α phase is stable at temperatures below 790°C and the β phase is stable at temperatures above 950°C, whereas the two-phase region, that is, the α plus β phase region
Occurs between 0'O and 950°C. In the α phase, zirconium atoms are arranged in a hexagonal canned lattice, and in the β phase, they are arranged in a body-centered cubic lattice. The so-called β of Zircaloy to obtain desired properties such as improved corrosion properties, etc.
During rapid cooling, the material is heated to a temperature in the β phase region and rapidly cooled to a temperature in the α phase region.

Conventionally, in the production of Zircaloy clad tubes, β-quenching is performed after forging them into in-bod Y rods. After producing the extruded billet of the rod, the billet is extruded to the α-phase state at a temperature below 680°C, and then this extruded material undergoes several stages of cold rolling, which allows subsequent cold rolling between successive cold rolling steps. Annealed at 625'-700℃ for smoothing.
Perform intermediate annealing. Cooling of the extrudate after each intermediate annealing takes place relatively slowly at a rate of up to 6° C. per minute in a temperature range just below the annealing temperature and without the use of any coolant. After the final cold rolling step, a final annealing imparts the desired properties to the material. Tubes made from silicalloy under this final annealing conditions conventionally employed have proven to have sufficient resistance to corrosion at the operating conditions commonly applied in nuclear reactors. However, the evolving situation is one of ever-increasing use of fuel, which means that the operating time of fuel assemblies is becoming longer and longer. Therefore, the cladding material is exposed to corrosive water for a longer period of time than before, increasing the risk of corrosion damage. It would therefore be desirable to obtain better corrosion properties from the alloys used without undesirable changes in mechanical properties.

In particular, it is already known from U.S. Pat. I can do it. U.S. Patent No. 3,865,635
As is clear from the above, Zircaloy tubes with good mechanical properties can be obtained by subjecting the extruded material to β-quenching before subjecting it to the final cold rolling process.

The exact reason why β-quenching achieves improved resistance to accelerated nodular corrosion has not yet been fully determined. However, the improvements appear to be related to the size of the intermetallic compounds as well as their distribution in the material.

The intermetallic compound, the so-called second phase, is composed of a compound mainly containing chain components of iron, chromium, and nickel in addition to zirconium, and has a granular form. The dissolution and precipitation achieved by β quenching results in a reduction in grain size and a redistribution from uniformly distributed grains to grains constituting an arrangement at the grain boundaries of the α grains formed during the β phase change.

β-quenching of the finished cladding tube reduces the ductility of the tube, which causes drawbacks in the manufacturing method. Beta-quenching the extrusion to its final dimensions before cold rolling reduces deterioration of the mechanical properties of the finished tube. However, β-quenching, whether performed on the finished tube or before the final cold rolling process, increases the amount of scrap and also forms an oxide layer on the tube surface that must be removed. When the output decreases, it becomes K. Furthermore, β-quenching is itself a process that complicates the manufacture of clad tubes.

The present invention provides a nuclear reactor fuel rod having resistance to nodular corrosion and mechanical properties at least as good as the best cladding pipes known to date without the use of post-extrusion beta quenching. It has been demonstrated that it is possible to manufacture clad pipes.

The present invention is a method for manufacturing a cladding tube of a silicone-based alloy for a fuel rod of a nuclear reactor, in which the silicone-based alloy is extruded at a temperature of 680°C or less, and the extruded product is subjected to cold rolling, annealing, cold rolling and straight arcing. In the method, the intermediate annealing is performed at a temperature exceeding 650 ° C. in at least one intermediate annealing tα phase region, and the final annealing is performed after the final cold rolling,
650°C in the alpha phase region before the extrudate undergoes the next cold rolling.
After each intermediate annealing at a temperature WIL greater than Annealing after intermediate annealing is up to 600
It relates to a manufacturing method characterized in that it is carried out at a temperature of °C. Intermediate annealing at temperatures above 650°C in the alpha phase region is preferably carried out at temperatures in the range 675-725°C. Cooling is preferably carried out in a furnace filled with helium, which has good thermal conductivity. Cooling is performed at any rate greater than 5° C. per minute. The annealing time at temperature 1 above 650° C. in the α phase region is 0.5 to 10 hours.

After the final cold rolling, the extrudate is subjected to a final annealing at a temperature of 400-600°C, preferably 525-575°C.

In manufacturing the clad tube of the present invention, it is important to note that the size of the second phase particles in the finished tube is considerably smaller than the size in the conventional clad tube manufacturing without β quenching after extrusion, such as when β quenching is used. I understand. however,
Contrary to the case after β-quenching, in KI the phase particles are evenly distributed in the material. It may be the small size of the second phase particles as well as their uniform distribution achieved by the present invention that provides a favorable combination of good resistance to corrosion and good mechanical properties.

The siliconium-based alloy is preferably a siliconium-tin alloy, such as the alloys known under the trade names Silicalloy 2 and Silicalloy 4, in which the amount of tin T1
．． 2-1.7%, iron"t' 0.07-0.2416,
0.05-0.15- for chrome, o-o for nickel,
o'so-, the remainder being siliconium and the usual existing impurities, the weight of which is stated in units by weight as with the other -s mentioned in the text. Silicaloy 2
is 1.2-1.7% tin, 0.07-0.20% iron, 0.05-0.15% chromium and 0.03-o
, contains 1% oa of nickel. Silicaloy 4 contains 1.2-1.7% tin, 0.18-0.24% iron,
Contains 0.07-0.13% chromium and is nickel-free.

The siliconium-based alloy is preferably beta-quenched, ie heated to a temperature in the beta phase region and rapidly cooled to a temperature in the alpha phase region, prior to extrusion. However, silicon-based alloy β
It is possible to use it without quenching. Beta quenching prior to extrusion is carried out by heating the alloy to a temperature suitably 950 DEG-1250 DEG C., preferably 1000 DEG-1150 DEG C., and rapidly cooling it to a temperature in the alpha phase region. Next, cooling from the operating temperature of the β phase region to a temperature of 750°C is carried out at a rate of 1-50°G per second, and cooling from 790°C to a temperature of 500°C or less is greater than 5°C per minute. This is preferably done in proportion.

Next, the present invention will be described in detail by giving examples thereof.

Forge 9 inks of Zircaloy 2 into a rod with a diameter of 150-200 mm. The rod piece is subjected to a β-quenching treatment by heating it at a temperature of 1050°C for 15 minutes and cooling it to room temperature at a rate of 5-10°C per second. Extruded billets are made from rods. These billets are extruded without prior heating. The extrudate is then subjected to a 6-stage rolling process, which results in a final outer diameter of 12.3 sm. 1st and 2nd
The extrudate is annealed to a temperature of 1565° C. between the rolling steps and the final rolling. After the final cold rolling, the tube is finally annealed to a temperature of 565°C. Both the intermediate annealing as well as the final annealing are carried out in a vacuum furnace. In the finished pipe, the second phase particles are 0.05-0.4
with a mean particle size of about 0.15 μm. For clad tubes made by conventional methods and not subjected to beta quenching early in the finished or extruded state, the second phase particles have a size between approximately 0.1-0.6 μm and an average particle size of about 0.5 μm. It has size. 700
Instead of carrying out an intermediate annealing between WJ2 and the last cold rolling at a temperature of 575 °C, this intermediate annealing is
It can be carried out at temperatures of °C. During corrosion tests, which have been shown to closely simulate nuclear reactor operating conditions, clad tubes made according to the present invention are only a fraction of those obtained with conventional manufacturing without post-extrusion beta quenching, and It shows a weight dein of the same size as that of the product manufactured by β quenching process. The mechanical properties of the clad tube made according to the present invention are as follows: 1. is the same, and is considerably better than the case of a pipe subjected to β-quenching treatment in the finished state.

The corrosion test described above is carried out in an autoclave with water vapor at a pressure of 9.8 MPa and l1lj of 500°C. Weight gain is a measure of the degree of corrosion the tube has undergone.

Agent Asamura Hao 4 other people

Claims (4)

[Claims] (1) j [A method for producing a silicone-based alloy clad tube for a fuel rod in a child reactor, in which the silicone-based alloy is extruded at a temperature below 680°C, and the extrudate is subjected to cold rolling and annealing, and At least one intermediate annealing is performed at 650°C in the α phase region.
In a process carried out from the last cold rolling to the final annealing at a temperature exceeding 650 °C, the annealing temperature From Jf, 1 to 650°C, it is cooled at a rate of at least 5°C per minute, and at 650°C in the α phase region.
Annealed after the last intermediate annealing at temperatures exceeding 6
A manufacturing method characterized in that it is carried out at a temperature of 00°C. (2) A method according to claim 1, characterized in that at least one intermediate annealing is carried out at a temperature of 675'-725°C. (3) Scope of claims! Item 1 or W! , according to the method according to Section 2, the silicone 9 five-base alloy has a weight of 1.2-1
．． 7 - amount of iron and weight ratio 0.07 - 0.24 -,
0.05-0.15- of chromium per weight and 0.05-0.15- of chromium per weight
- 0.08 - of nickel, the remainder being silicon; nium and any existing impurities of the usual type. (4) Claims ii! 8. A manufacturing method according to any one of Items 1 to 3, in which the siliconium-based alloy used during extrusion is β-quenched by t%.