JPS636631B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a surface treatment method for a zirconium alloy tube, and more particularly to a surface treatment method suitable for finishing the inner surface of the tube to a roughness suitable for plating work. For nuclear fuel cladding, zirconium or zirconium alloys have a smaller thermal neutron absorption cross section than aluminum alloys or stainless steel, and are superior in non-reactivity and non-corrosion. Zirconium tubes or zirconium alloy tubes are mostly used in light water-cooled nuclear reactors because they have excellent mechanical properties at high temperatures. However, analysis of the behavior of fuel rods has shown that when nuclear fuel burns, fissile material that is corrosive to zirconium is generated, and in the presence of this fissile material, the mechanical A phenomenon in which the cladding tube is damaged due to the interaction is observed. This phenomenon is not a problem with conventional zirconium tubes under normal usage conditions, but when trying to improve the load variation ability during combustion, the mechanical stress due to thermal expansion of the nuclear fuel pellets and cladding increases.
Damage is encouraged. By the way, it has been recognized that it is effective to preliminarily interpose a substance on the inner surface of the cladding tube, which quickly chemically binds corrosive fissile material and eliminates its corrosive action. For this reason, for example, in JP-A-51-69793 and JP-A-54-45495, the inner surface of a zirconium alloy tube is covered with a copper coating, and a chromium or zirconium oxide layer is formed between the copper coating and the zirconium substrate. proposed the use of fuel rods with diffusion barriers. This is intended to reduce metal embrittlement and stress corrosion cracking caused by the interaction between nuclear fuel pellets and cladding tubes by coating them with copper.
Chemical plating or electroplating methods are used to coat copper, but conventional plating pretreatments do not provide a good quality plating, resulting in peeling or blistering. In particular, these plating defects occur frequently near both ends of the pipe. Therefore, a solution to this problem is strongly desired. The present invention has been made in view of the above, and its purpose is to provide a surface treatment method for a zirconium alloy tube that can form a uniform metal coating with good adhesion on the inner surface of the tube. There is a particular thing. In the present invention, when a metal coating layer is formed on the inner surface of a zirconium alloy tube by plating or the like, peeling of the coating layer or blistering occurs due to
This was done after experimentally confirming that appropriate surface roughening and uniformity are required, greatly influenced by pre-treatment etching, and ammonium fluoride-based Adding acid such as fluoric acid, nitric acid or sulfuric acid to the solution increases the etching rate of zirconium alloy from 4 to 4.
Using an etching solution adjusted to 10 μ/10 minutes, dummy tubes made of the same type of material with a length of at least 5 cm are connected to both ends of the zirconium alloy tube, and the entire tube is tilted by 5 to 60 degrees for a predetermined period of time. It is characterized by being finished by etching. First, various experimental examples and their evaluation results will be explained. [Experiment Example 1] After degreasing two Zircaloy tubes with an inner diameter of 10.8 mm, a wall thickness of 0.86 mm, and a length of 4 m and washing them with water, two Zircaloy tubes with a length of approximately 30 cm were connected to both ends of the tube as dummy tubes, and acid was added. As a washing solution, add sulfuric acid (H ₂ SO ₄ ) to 15 g of acidic ammonium fluoride (NH ₄ F・HF) solution.
Using a solution in which the etching speed of the two Zircaloy tubes was adjusted to 7 μ/10 minutes by adding 1 g/1 g/ml of Zircaloy, the two Zircaloy tubes tilted at an angle of about 10 degrees were placed in the solution and etched for about 2 minutes to form the Zircaloy two tubes. Roughen the internal surface. Immediately afterward, rinse with water and perform ultrasonic cleaning under running water to remove any residue remaining on the surface. after that,
After oxidation treatment with water vapor and activation treatment, copper plating is performed to a thickness of approximately 5 μm using a chemical copper plating solution. Furthermore, after washing with water, it is dried to leave the copper plating surface in a clean state. Next, the two inner-copper-plated zircaloy tubes made in this way were heated to 200°C in a vacuum, treated to improve adhesion, and divided in half to determine whether or not blisters were generated during this heat treatment. The plating adhesion was investigated by a bending test. As a result, Zircaloy 2 which underwent the above pretreatment
In the tube, no blisters were generated and the plating adhesion was good. [Experimental example 2] Ammonium fluoride (NH ₄ F) 14 as pickling solution
Add sulfuric acid (H ₂ SO ₄ ) in the range of 0 to 5 g/ to a solution of 2 g/fluoric acid (HF) to adjust the etching rate to 2, 4, 6, 8, 10, 12 μ/10 minutes. The same test as in Experimental Example 1 was carried out by applying chemical copper plating of about 5 μm to the inner surface of two Zircaloy tubes, except that each of the above solutions was used. [Experiment example 3] Stop connecting the dummy tubes to both ends of the Zircaloy 2 tubes, or make sure that the dummy tubes have little reaction with the pickling solution.
SUS 304 tubes were connected to both ends of the Zircaloy 2 tube and treated in exactly the same manner as in Experimental Example 1, and the internal surface of the Zircaloy 2 tube was chemically copper plated to a thickness of about 5μ.
A test similar to Experimental Example 1 was conducted. [Experimental Example 4] When roughening the internal surface of two Zircaloy tubes with a pickling solution, the treatment was carried out under exactly the same conditions as Experimental Example 1, except that the inclination angles of the tubes were set to 3 degrees and 30 degrees, Chemical copper plating of about 5 μm was applied to the inner surface of two Zircaloy tubes, and the same test as in Experimental Example 1 was conducted. Table 1 summarizes the occurrence of blisters during heat treatment and the plating adhesion test results of the two Zircaloy tubes in Experimental Examples 1 to 4, in which chemical copper plating of approximately 5 μm was applied to the internal surfaces.

[Table] The following can be seen from the results in Table 1. (1) If the etching rate of the pickling solution is less than 4μ/10 minutes, roughening will be insufficient and the adhesion of copper plating will decrease. On the other hand, if the etching rate is higher than 10μ/10 minutes, blisters will occur and the plating layer will become non-uniform. (2) By connecting two Zircaloy pipes as dummy pipes to both ends of the two Zircaloy pipes, blistering at the ends can be prevented. However, if the dummy tube is a metal tube that does not react with the pickling solution, such as a SUS 304 tube, it will not be effective in preventing blisters at the end. (3) During pickling, if the angle of inclination of the two Zircaloy tubes is 3 degrees, the etching will be uneven due to the gas generated by the reaction, causing blisters. As is clear from the above results, when performing chemical copper plating on the internal surface of a zirconium alloy tube, if the etching rate of the pickling solution is higher than 10μ/10 minutes, the control range of pickling time will be narrowed.
The uniformity of roughening in the longitudinal direction of the pipe is reduced, and blisters occur during chemical copper plating. On the other hand, if the etching rate is lower than 4μ/10 minutes, roughening will be insufficient and the adhesion of copper plating will decrease. Therefore, in the present invention, a pickling solution with an etching rate of 4 to 10 μ/10 minutes is used. Note that the etching rate was measured using a pickling solution of 100%
It was determined from the weight loss when a Zircaloy alloy tube with a surface area of 10 cm ² was immersed in ml for 10 minutes. Furthermore, if the internal surface of the zirconium alloy tube is roughened as is using a pickling solution, the adhesion of the copper plating at both ends of the tube will be reduced. However, if dummy tubes that react with the pickling solution are connected to both ends of the tube for etching, the formation of blisters at the ends of the tube can be prevented. However, although the explanation has been omitted, if the length of the dummy tube is shorter than 5 cm, it will not be very effective, so in the present invention, a dummy tube made of the same material and having a length of at least 5 cm is connected to both ends of the zirconium alloy tube. Then I started to do etching. Furthermore, when etching the internal surface of a zirconium alloy tube with a pickling solution, it is necessary to tilt the zirconium alloy tube to easily discharge the generated gas, but if the angle of inclination is less than 4 degrees, this effect will be lost. This is sufficient; however, if the temperature exceeds 60 degrees, workability deteriorates because zirconium alloy tubes are generally long tubes. Therefore, in the present invention, the inclination angle is set to 5 to 60 degrees. From the above, as can be seen from the results in Table 1,
Even at the end of the zirconium alloy tube, metal plating could be performed uniformly and with good adhesion without causing blisters. In the above example, the pickling solution is filled into the zirconium alloy tube and allowed to stand still to etch and roughen the inner surface of the tube, but the pickling solution may also be circulated using a pump with the same effect. be. As explained above, according to the present invention, the inner surface of a zirconium alloy tube can be uniformly roughened over the entire surface, and when metal plating is performed, a uniform coating with good adhesion can be formed. It has the effect of being able to

Claims (1)

[Claims] 1. When finishing the internal surface of a zirconium alloy tube, connect dummy tubes made of the same type of material with a length of at least 5 cm to both ends of the zirconium alloy tube, tilt the entire tube by 5 to 60 degrees, and use ammonium fluoride-based The zirconium alloy is etched for a predetermined period of time using an etching solution prepared by adding an acid such as hydrofluoric acid, nitric acid or sulfuric acid to the solution so that the etching rate of the zirconium alloy is 4 to 10μ/10 minutes. Surface treatment method for zirconium alloy tubes.