JPS6317917B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to, for example, a method for plating the inner surface of a Zircaloy tube for nuclear fuel coating. As nuclear fuel cladding tubes, metal steel protection tubes that can completely seal and protect the fuel are used, and these tubes are required to be heat resistant, non-reactive, and non-corrosive, and currently the main materials used are aluminum alloys and stainless steel. Tubes made of , zirconium alloy (Zircaloy), etc. are used. Among these, Zircaloy tubes are particularly strong at temperatures below 600°C, have a smaller neutron absorption cross section than stainless steel, and are more expensive, but because they can use low-enriched uranium fuel, they are almost always used in light water-cooled power reactors. ing. Electroplating is sometimes performed to form a barrier layer on the inner surface of such Zircaloy tubes, but in this case, the inner surface of the tube is cleaned as a pretreatment, and then the surface is cleaned with various hydrofluoric acid-based pickling solutions. Activation is performed. However, in this method, since the pickling solution is circulated by a pump or the like, the flow is disturbed at the inlet and outlet of the pipe, making it impossible to uniformly activate the entire inner surface of the pipe. Additionally, this method has the disadvantage that the etching rate at the inlet and outlet portions is higher than that at the inside of the tube, resulting in dimensional errors. In addition, the above-mentioned pickling solution has the problem of being affected by gas generated by the reaction during pickling. Therefore, when electroplating the inner surface of a tube that has been activated using this method, the adhesion of the plating at the inlet and outlet portions of the tube is inferior to that of the inside of the tube, resulting in defects such as blistering after heating. may occur. The present invention has been made in view of the above points, and an object of the present invention is to provide a method for plating the inner surface of a Zircaloy tube, which can uniformly activate and uniformly plate the inner surface of the tube. The gist of the present invention is that in pickling activation treatment, which is a pretreatment when plating the inner surface of a Zircaloy tube,
Using at least one type of pickling liquid selected from acidic ammonium fluoride, hydrosilicic acid, neutral ammonium fluoride, fluoric acid, and boronic acid, and subjecting both ends of the tube to a similar melting reaction as in the tube. The pickling activation process is performed by connecting a dummy tube of the same quality and diameter as shown in FIG. That is. The present invention does not suppress the turbulence generated at the inlet and outlet of the pickling solution circulating inside the Zircaloy tube to be plated, but connects another tube, also called a dummy tube, of the same quality as the aforementioned tube. It thereby absorbs such turbulence and also equalizes the influence of the gas line over the pipe, which is caused by the reaction during pickling. Therefore, as another tube, a tube made of plastic or the like is insufficient, and the influence of the gas cannot be equalized over the entire tube. In order to minimize the influence of gas etc., a metal tube of the same quality as a Zircaloy tube is suitable. This is because a metal tube of the same quality as a Zircaloy tube exhibits the same dissolution reaction as a Zircaloy tube. In this sense, as the homogeneous metal tube, a tube made of zirconium, titanium, an alloy thereof, or an iron-based metal such as stainless steel is used. In addition, the pickling solution mentioned above is unique to Zircaloy, and is usually used for the acidic ammonium fluoride mentioned above,
A mixed acid mainly consisting of hydrosilicic acid, neutral ammonium fluoride, hydrofluoric acid, or boronic acid is used and exhibits an excellent activation reaction. Next, an embodiment of the method for plating the inner surface of a Zircaloy tube according to the present invention will be described with reference to the accompanying drawings. In the figure, 1 is a Zircaloy (formally Zircaloy-2) tube with a plated inner surface, and 2 is another metal tube called a dummy tube made of the same type of Zircaloy tube as the tube 1, which is connected to both ends of the Zircaloy tube 1. be done. 3 is plastic pipe, 4 is circulation pump, 5
is a container containing pickling solution. As an example, after cleaning the inner surface of a Zircaloy tube 1 with an inner diameter of 10 mmφ and a length of 200 cm with a degreasing liquid, metal tubes 2 of the same type were connected to both ends of the tube and set as shown in the figure. The inner surface of the Zircaloy tube 1 is activated by circulating 8 ml of hydrofluoric acid and the remaining pickling solution of distilled water using the pump 4. After that, the liquid temperature was 55±5℃, 1A/copper cyanide plating bath containing 55g/copper cyanide, 67g/sodium cyanide, and 10g/sodium hydroxide.
At a current density of dm ² , the inner surface of Zircaloy tube 1 is approximately 10μ
A Zircaloy tube with a predetermined inner surface plating was obtained by thick copper plating. The Zircaloy tube obtained in this way and the Zircaloy obtained by plating by the conventional method, that is, the same method as above, but by pickling and activation treatment without connecting another metal tube to both ends of the tube to be plated. The table shows the comparative test results of the plating adhesion of each tube. For the test, each Zircaloy tube was plated and then immersed in boiling water.
2 minutes in a heat treatment oven at 200°C.
This figure shows the occurrence of blisters on the plated surface when heated under vacuum for hours. As a result, in the case of the conventional method, blisters occurred at approximately 10 cm at both ends of the tube. However, in the case of the example, although it is not shown in the table, 400℃,
No blistering was observed even after 2 hours of heat treatment.

[Table] As is clear from the above table, according to the method of the present invention, the presence of another metal tube 2 causes disturbance of the pickling solution and the influence of gas generated by the reaction between the pickling solution and the Zircaloy tube. The non-uniform phenomenon of activation treatment based on As a whole, it is possible to obtain a Zircaloy tube coated with internal plating with excellent adhesion and high precision. The present invention can be immediately applied, for example, to the manufacture of Zircaloy tubes for cladding nuclear fuel, and its industrial value is extremely large.

[Brief explanation of the drawing]

The figure is an explanatory diagram of an embodiment of the method for plating the inner surface of a Zircaloy tube according to the present invention. 1: Zircaloy tube, 2: Metal tube, 3: Plastic tube, 4: Circulation pump, 5: Container.

Claims (1)

[Claims] 1 In the pickling activation treatment, which is a pretreatment when plating the inner surface of the Zircaloy tube, acidic ammonium fluoride, hydrosilicic acid, neutral ammonium fluoride,
A pickling solution of at least one type selected from hydrofluoric acid and borofusic acid is used, and dummy tubes of the same quality and diameter that exhibit the same dissolution reaction as the tube are connected to both ends of the tube. A method for plating the inner surface of a Zircaloy tube, characterized in that a pickling activation treatment is performed by circulating a pickling liquid filled in the tube as part of a passage.