JPS58165082A - Zircaloy coated 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 provides a Zircaloy tube 41 with a Zircaloy cladding tube for nuclear fuel which has excellent high-temperature water corrosion resistance.

Zircaloy cladding tubes for nuclear fuel (simply referred to as Zircaloy cladding tubes) have excellent corrosion resistance because their outer surfaces are in contact with high-temperature water or steam in the nuclear reactor. ! I# has a high temperature water corrosion resistance (hereinafter also simply referred to as corrosion resistance).

Its corrosion resistance is influenced by the precipitates 111 of intermetallic compounds formed by Zr, the main component of the zircaloy association, and 8neF@tCreNi, the additive component. is known to be made into china clay.

From this viewpoint, in order to ensure the corrosion resistance of Zircaloy cladding tubes in the prior art, the following method is generally adopted.

That is, in the state of the forged bar before extrusion billet cutting, 10
"β treatment" is performed by heating to a high temperature of 00℃ or higher and water quenching. With this, finely dispersed precipitation of polyintermetallic compounds is achieved.

After that, various processes such as forging, extrusion, tube rolling, and annealing are performed to obtain the loaded tube product, and the heating temperature at that time is usually 7.
600 or less to prevent agglomeration of the intermetallic compounds as much as possible. However, when heating during forging, extrusion, and cold working, K has a limit because it is impossible to reduce the temperature unnecessarily in order to ensure a predetermined softening.

Therefore.

During heating during processing, the temperature may exceed 760°C, and the above-mentioned compounds will coagulate, resulting in a slight decrease in corrosion resistance.

This is sufficient under the steady operating temperature of the nuclear reactor (below 400°C), but when operated under severe conditions F exceeding 500°C, corrosion conditions are even more severe. Unfortunately, the above measures are not enough, and we need to take a new approach.

(9) In the prior art, it has been proposed to subject the entire product to β-processing, or to subject the entire pre-product to β-processing, and then process and finish the product at a later date.

However, this does improve corrosion resistance.

It was found that the ductility of the pipe as a whole was insufficient and was not necessarily desirable as a transverse pipe product.
.

In this way, the Zircaloy cladding tube according to the prior art has a high temperature (
(near 600°C) corrosion resistance is insufficient, and the ductility of the entire pipe is decreased, so it is not necessarily satisfactory. Therefore, the inventors of the present invention In order to improve this point, as a result of intensive research, we found that high-temperature water radiation is a problem only on the outer surface of the tube in contact with the reactor cooling water, and inside the tube containing uranium oxide and pellets. Focusing on the fact that the surface and inner quality of the pipe are not targeted, we decided to limit the β treatment to improve corrosion resistance only to the surface layer, and the remaining portion, which corresponds to the entire surface layer, was not subjected to β treatment, and the pipe manufacturing process By keeping the fine crystal grains formed during machining intact, there are no nicks that impair the ductility of the entire Zircaloy cladding, and the outer surface that comes in contact with cooling water has excellent resistance to light corrosion. The present invention has been completed based on the discovery that extremely desirable properties can be obtained as a nuclear fuel cladding tube. 1 In other words, one F! 4 is pipe products! The pipe product is characterized in that a β-treated layer is provided only on the outer surface layer of the pipe product after pipe production. Zircaloy-clad tube with excellent high-temperature water corrosion resistance.

``Only in the outer surface layer of the pipe product'' means rapid surface heating of the pipe product. The "1β treated layer" is a fine and 1-1 dispersed layer of the above-mentioned intermetallic □ compound due to the l treatment applied to the outer-surface layer portion, which will be described later. The thickness of the tube is determined by the heating temperature, cooling rate, etc., but in the present invention, the thickness can be appropriately determined depending on the relationship between the required corrosion resistance and the required ductility of the tube body.Generally, from 20 ps to 80p is considered sufficient. However,
Its thickness does not exceed 200p.

In accordance with the sixth aspect of the present invention, the surface of the Zircaloy cladding tube as an FC+ finished product manufactured by the prior art is heated under conditions such that only the outer surface layer of the tube is heated, and then rapidly cooled as soon as possible. .

The β treatment layer is formed only on the outer surface of the cladding tube. Therefore, one main body portion is not affected by heating during the β treatment, and coarsening of crystal grains does not occur.

The fine crystal grains formed during pipe manufacturing are preserved as they are, so there is no decrease in the ductility of the pipe as a whole.

5. Various heating methods can be considered at this time, such as electron beams, lasers, electric furnaces, and rust induction heating. Further, in order to avoid oxidation and nitridation of the surface, it is preferable to heat K in a vacuum or in an inert gas atmosphere such as argon.

The β treatment temperature, that is, the I quenching temperature, is generally V1000.
℃1000℃ or more, it varies somewhat depending on the semi-temperature.

The cooling method depends on the heating conditions), and it is not necessarily necessary to perform forced cooling; for example, air cooling may be used; however, when forced cooling is performed, it is generally preferable to cool as quickly as possible. The necessary rapid cooling process may be performed by supplying cooling water to the inner surface of the cladding tube or by using a chiller.

As mentioned above, the β-treated layer formed in the present invention is preferably subjected to surface engraving after pipe manufacturing.
Although it is provided only on the outer surface layer of the iI horizontal pipe, its thickness is not limited to % and can be adjusted as appropriate by changing the heating temperature and cooling rate. Generally 20μ~8
0μ is considered to be sufficient. It's 9, and it never exceeds 200p.

As described above, it is sufficient that the β-treated layer in the present invention is provided on the finished forged product, and there is no need to perform the β-treated layer at every step from pipe manufacturing to provide the β-treated layer. Also about the composition of the Zircaloy cladding tube itself! The present invention is not limited to this, and any Zircaloy cladding tube that can be used as a nuclear fuel cladding tube may be used. In addition,
If an oxide film etc. is formed on the surface of the all-F, belt polishing,
Alternatively, it can be removed by mechanical polishing such as grindstone polishing. Alternatively, chemical polishing may be performed by pickling and etching with nitric acid.

Next, the rjAft of the present invention will be further explained with reference to examples.

Example In this example, a Zircaloy-2 (trade name) cladding product, which had not been subjected to β treatment at the billet stage, was used as a test material.

The processing properties during pipe manufacturing are 98% area reduction rate, the structure is sufficiently refined, and the ductility is 8696 or more in tensile elongation at room temperature.

The above cladding tube product (outer diameter 1m52s+X wall thickness u86+m)
was heated from the outer surface with an electron beam in a 10-'Totr. The electron beam does not soften sharply,
Apply to the cow in a slightly sloppy state. In the magnetic beam test, a Zircaloy cladding tube as a test material with an accelerating voltage of SON, an electron beam current of 08 mA%, and a beam diameter of about 2 mm is driven so as to advance while rotating. The beam was made to hit the entire outer surface evenly. In this case, the number of rotations is 800
rprn, feed J) 1m/rotation was adopted. <5J! Unable to measure] Although forced cooling was not particularly performed in this example, a β-treated layer with a thickness of 80 μm was formed on the outer surface.

Although the test was carried out in a vacuum, an extremely thin oxide film was formed on the surface and the color was slightly discolored, so nitric acid 60Vo196. Pickling was carried out for about 1 minute in a nitric acid solution consisting of 5V 1% hydrofluoric acid and remaining water. After pickling, water washing, neutralization, water washing, pure water washing, and drying were performed in sequence.Next, in order to evaluate the high temperature water corrosion resistance of the Zircaloy cladding tube according to the present invention, the above cladding tube was subjected to a corrosion test. carried out.

At this time, in order to perform a corrosion test on only the outer surface of the tube, Zircaloy-2 end plugs were welded to both ends of the cladding tube to prepare a test piece.

The specimen thus obtained was subjected to a high-temperature steam test in an autoclave. The temperature of Qin is [500℃
, the pressure was 60Kr/c++1, and the test time was 12 hours.

For comparison, a test piece was prepared using the same procedure for Zircaloy-2 cladding 411f, which is made of the same material without surface heating as described above. An autoclave corrosion test was conducted. The results are shown in Table IKt, and it can be seen that the cladding tube according to No. 11, which was subjected to surface heating and a β treatment layer, exhibited excellent high-temperature water corrosion resistance.

The comparative example showed an increase in corrosion weight of about 81% compared to the inventive example.

Next, to confirm its ductility, a tensile test was carried out at room temperature.The tensile test was conducted in a tubular state under the condition 0, and the tensile rate was (16% 7 minutes). The distance between them was 60cm.In this case, for comparison, a similar test was also carried out on a normal Zircaloy-2 clad tube.The results are shown in Table 2Kt. No deterioration is observed at all.

Note that the Zircaloy 2 pipe for concrete breakage described above was subjected to β treatment at the billet stage in order to improve its corrosion resistance during its manufacturing process. It can be seen that the β process can be omitted.

Table 1 Table 2

Claims (1)

[Claims] Only on the outer surface of the pipe crystal! It is characterized by having a processing layer. Silkakui cladding with excellent high-temperature water corrosion resistance.