JPS6013477B2 - Method for manufacturing fuel cladding for nuclear reactors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides mechanical interaction with fuel pellets.
et/CladInteraction, hereinafter “PCI
The present invention relates to a method for manufacturing a fuel cladding tube for a nuclear reactor that can alleviate the effects (abbreviated as J).

Conventionally, uranium dioxide (U02) aggregates have been used as nuclear fuel in light water reactors, and zirconium alloys (such as zircaloy), which have excellent corrosion resistance, neutron absorption cross-section, and high-temperature strength, have been used to coat the aggregates. -2 or -4
) thin-walled tubes are used, but the gap between the fuel and the cladding tube is extremely small, several hundred mm, in order to improve heat conduction (related to the thermal efficiency of the entire reactor).

For this reason, for example, when a nuclear reactor is operated rapidly, thermal expansion of the fuel pellets tends to cause PCI effects, and as a result, failure of the zirconium alloy cladding is predicted, so measures to improve this are desirable. It was rare. In addition, when nuclear fission gases such as iodine and cadmium Cd generated as the fuel burns accumulate in the fuel rays and cause PCI effects, the cladding tube is subject to erosion by iodine and PCI.
There is a risk that stress corrosion cracking may occur due to the stress caused by the I action. As a measure to improve the above disadvantages, P
In order to alleviate the CI effect, to avoid direct contact of gases such as iodine and cadmium to the cladding tube, and to prevent stress corrosion cracking of the cladding tube, a layer of soft metal such as pure steel or pure zirconium is coated with zirconium. There is a barrier tube formed on the inner surface of an alloy tube.

However, in the case of steel barrier pipes, copper and zirconium alloy are 7
At high temperatures of 00°C or higher, it is relatively easy to diffuse. "Various intermetallic compounds mainly composed of copper-zirconium binary alloy are formed at the interface between the copper barrier tube and the zirconium alloy and form arms, which alleviates the PCI effect phenomenon. The problem is predicted that the effectiveness will be reduced.The present invention prevents the diffusion phenomenon of the copper barrier tube at high temperature, does not become an arm by itself, and prevents the PCI action phenomenon due to chemical reaction with nuclear fuel or mechanical action. The object of the present invention is to provide a method for manufacturing a zirconium alloy cladding tube that can be permanently relaxed.

That is, the method for manufacturing a nuclear reactor cladding tube of the present invention includes the steps of: forming a steel layer on the inner surface of a zirconium alloy tube; and oxidizing the zirconium alloy at the interface between the zirconium alloy and the bowl layer. forming an oxide layer;
It is characterized by consisting of.

A fuel rod using a fuel cladding tube manufactured by the method of the present invention will be explained with reference to FIG.

The upper and lower ends of the fuel cladding tube 1 are hermetically sealed with end plugs 2 and 3, and a fuel pellet 4 is loaded inside. The space 5 and the gap between the pellet and the cladding tube are filled with gas such as argon, and the fuel pellet is fixed by a plenum spring 6. As is clear from FIG. 2, which is an enlarged view of a part 7 of the fuel cladding tube 1, an oxide layer 22 is formed on the inner surface of the zirconium alloy tube 21, and a copper layer is further formed on the oxide layer 22. A layer 23 is formed. The method for manufacturing a fuel cladding tube of the present invention includes forming a copper layer on the inner surface of a zirconium alloy tube, and then oxidizing the zirconium alloy at the interface between the zirconium alloy and the steel layer.
This is a method of forming an oxide layer.

At this time, as conditions for forming the oxide layer, it is preferable to perform heat treatment at a dissociated oxygen partial pressure of oxidized steel. Under such conditions, the steel layer is not oxidized, and the zirconium alloy surface can be selectively oxidized at the copper-zirconium alloy interface. In this method, the inner surface of a zirconium alloy tube is transformed into an oxide layer that does not react with the copper layer in order to prevent diffusion phenomena at high temperatures in steel barrier clad tubes.

However, on the other hand, if the inner surface of the zirconium alloy tube is altered into an oxide layer before forming the steel layer, the bonding strength with the copper layer will be insufficient, so the manufacturing method described above is preferred. More specifically, in the first step, a copper plating layer is formed on the inner surface of the zirconium alloy tube. That is, the inner surface of the zirconium alloy is cleaned by degreasing and pickling, and then a steel plating layer is formed by a crab plating method or an electroless scale plating (chemical plating) method. The thickness of the steel plating layer is preferably about 2 to 20 meters from the viewpoint of neutron absorption cross section. Electrical steel plating methods include ordinary copper sulfate plating, pyrophosphate steel plating,
Any of the cyanide steel plating baths may be used.For electroless copper plating, ordinary Ihigaku copper plating solutions containing copper sulfate, Rossel's salt, sodium hydroxide, formalin, etc. may be used. Following the first step of steel plating, the following second step is performed.In the second step, the steel plating layer obtained in the first step is not oxidized, and the zirconium alloy surface is coated at the copper/zirconium alloy interface. This is a step of selectively oxidizing the oxidized steel. That is, it is a step of setting an oxygen partial pressure atmosphere in which such selective oxidation can be carried out and performing heat treatment. For this purpose, for example, the copper powder 5 foundation and oxidized steel (Cu0, Cu20, etc.) are heated. ) 50 parts of the powder is thoroughly mixed with powder, and then compressed into a size approximately the diameter of the fuel cladding tube at a pressure of 3 to 5 mm to form an oxidizing agent. 0.5 to 5 at a temperature of 150 to 600℃ sealed in a container with a gas atmosphere
Heat for a period of time to perform oxidation treatment. If the temperature is lower than 150°C, a sufficient oxide layer cannot be obtained, and if the temperature exceeds 600°C, the deposited layer will peel off, which is not preferable.

By this oxide treatment, the copper plating layer is not oxidized, and an oxide layer mainly composed of zirconium oxide can be formed by selective oxidation at the interface between the copper plating layer and the zirconium alloy. The thickness of the acid oxide layer is preferably 0.01 to 2 m. Through these first and second steps, the inner surface of the cladding tube becomes a steel layer, an oxidized metal layer, and a zirconium alloy from the surface, and the presence of the oxide layer prevents diffusion at high temperatures, and the presence of the steel layer prevents PCI. The effect phenomenon can also be alleviated. As described above, the present invention prevents diffusion at high temperatures and prevents the zirconium alloy tube from becoming arms, and the presence of the steel layer permanently alleviates the PCI effect, so the power reactor downtime is also reduced, and the economic effect is significant.

Example As a fuel cladding tube for a light water reactor, electrical steel plating was applied to the inner surface of a Zircaloy-2 alloy tube with an outer diameter of 12.5cm, a tube wall thickness of 0.8cm, and a length of 4075mm by the process shown in Table 1. Ta.

Electric steel plating is sulfuric acid steel 200 yen/so, sulfuric acid 50 tanok,
Electroplating was carried out for 25 minutes at a current density of approximately IA/d, using chloride ion at 50/day, thiourea at 0.01/day, and dextrin at 0.01 day/day, using a pure steel rod as the anode. Ta. Table 1: Through this electric steel plating, a uniform copper layer was obtained with a thickness of 5±1 m over the entire length of the 4075 skin.

This copper-plated Zircaloy-2 tube was cut into two lengths and used as samples. On the other hand, after thoroughly mixing 5 parts of copper powder with a grain size of -325 mesh and 5 parts of suboxide steel powder with a grain size of -250 mesh, the mixed powder 159 was weighed and the diameter IQ
The oxidizing agent was created by inserting it into a gunwale mold and compression molding it at 4 tons/base. Next, after inserting the compression-molded oxidizing agent into the steel plating sample, a 5
It was vacuum sealed at a vacuum degree of rr to form an oxidation capsule.

Furthermore, after selective oxidation treatment was performed under various conditions shown in Table 2, the thickness of the formed oxide film, the bonding strength with the copper plating layer, etc. were measured, and the results are shown in Table 2. From the results shown in Table 2, by employing the manufacturing method of the present invention, a steel barrier fuel cladding tube containing an oxide layer that prevents diffusion at high temperatures can be easily and inexpensively manufactured.

A similar test was conducted over the entire length of the 4075 side, and satisfactory results were obtained. Further, the samples prepared by the methods of Examples 1 to 5 were sealed in a quartz tube at a vacuum level of 2 x 10-5 tons, and heated at 750 qo for 1 field hour to test the diffusion state.

In the sample that was not subjected to the oxide layer forming treatment in the second step, the copper plating layer completely diffused into the Zircaloy 2 alloy and no steel layer was observed, but in the sample with the oxide layer of the present invention, No diffusion phenomenon was observed, and the inner surface of the cladding tube had a pure brocade color.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a fuel trough in which a cladding tube of the present invention is filled with fuel pellets, and FIG. 2 is a partially enlarged view thereof. 1... Fuel cladding tube, 2, 3... End plug,
4... Fuel pellet, 7... Enlarged portion according to Figure 2, 21... Zirconium alloy tube, 22... Oxide layer, 23... ·····steel. Figure 1 Figure 2

Claims (1)

[Claims] 1. Forming a copper layer on the inner surface of a zirconium alloy tube; and oxidizing the zirconium alloy to form an oxide layer at the interface between the zirconium alloy and the copper layer. A method for manufacturing a fuel cladding tube for a nuclear reactor, comprising the steps of: 2. The method according to claim 1, wherein the zirconium alloy oxide layer is formed by heat treatment of copper oxide under dissociated oxygen partial pressure.