JPH10239473A - Reactor fuel covered pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable reactor fuel covered pipe having hydrogen absorption resistance to the hydrogen generated within the covered pipe while keeping a hardness of the same degree as conventional pure zirconium. SOLUTION: A zirconium-made lining layer 5 metallurgically bonded to a zirconium alloy-made reactor fuel covered pipe 2 contains 0.5wt.% or more and 1wt.% or less in total in zirconium of a trace additive of either one or more of Fe, Ni, Co, Rh, and Pd, 1200ppm or less of oxygen, and 2000ppm in total of inevitable impurities. An oxide film layer 6 for preventing the covered pipe base material from absorbing the hydrogen generated from a fuel rod inner part is formed in the inner surface thin layer area of the lining layer 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cladding tube used for a fuel rod for a nuclear reactor, and more particularly to a zirconium lining layer of a cladding tube base material.

[0002]

2. Description of the Related Art A fuel cladding tube made of a zirconium alloy is usually used for a fuel rod for a light or heavy water cooled reactor. FIG. 2 shows an example of a general fuel rod.
(A) is a schematic cross-sectional view in the axial direction, and (b) is an enlarged schematic cross-sectional view in the orthogonal direction.

As shown in FIG. 2A, a lower end plug 4a is provided.
A large number of fuel pellets 1 inside the fuel cladding tube 2 sealed with
And the upper end plug 4b via the plenum spring 3.
A fuel rod is formed by sealing with.

[0004] In general, when a zirconium alloy cladding tube is irradiated with neutrons, irradiation embrittlement occurs and stress corrosion cracking is likely to occur. Therefore, in order to prevent stress corrosion cracking, it is known to provide a zirconium lining layer 5 which is softer and higher in purity than a zircaloy alloy, as shown in FIG. . This relatively soft lining layer 5 reduces local stress. For example, for a fuel cladding substrate having an outer diameter of 8 to 20 mm and a wall thickness of 0.4 to 1.5 mm, the lining layer has a thickness of 0.03 to 0.2 mm.

According to US Pat. No. 4,300,492,
As pure zirconium used for such a cladding tube lining layer, the total impurity content is 1000 ppm to 5000 ppm.
ppm, of which the oxygen content is 1200 ppm. Such zirconium is a so-called commercial reactor grade sponge zirconium.

[0006]

However, in the conventional fuel cladding tube as described above, if water enters the fuel rod (cladding tube) due to manufacturing defects of the cladding tube or fretting with foreign matter, High purity zirconium layer of lining and UO ₂
Will rapidly oxidize. The hydrogen released by this reaction moves inside the fuel rods and is absorbed by the cladding base material, and precipitates as zirconium hydride in the low temperature portion of the cladding, embrittle the cladding. This can cause a serious accident called so-called hydrogenation secondary failure.

On the other hand, when a high-purity zirconium alloy containing another alloy element is used as the lining layer, the corrosion resistance of the zirconium lining layer in high-temperature and high-pressure steam is improved, and hydrogen accompanying the corrosion of the lining layer is increased. The occurrence is suppressed. However, there is a possibility that hydrogen generated due to oxidation of the pellet may be absorbed.

The present invention has been made in view of the above-mentioned problems, and has the same degree of softness as conventional high-purity zirconium, but maintains hydrogen generated inside the cladding tube, while maintaining the suppression of rapid oxidation of the inner surface. An object of the present invention is to obtain a highly reliable fuel cladding tube for a nuclear reactor having hydrogen absorption resistance.

[0009]

In order to achieve the above object, a fuel cladding tube for a nuclear reactor according to the first aspect of the present invention comprises a zirconium alloy fuel cladding substrate for a nuclear reactor which contains nuclear fuel therein. And a zirconium lining layer metallurgically bonded to the cladding substrate, wherein the lining layer comprises a total of 0.0
5 wt% or more and 1 wt% or less of Fe, Ni, Co, Rh,
A minor additive of one or more of Pd;
ppm or less of oxygen and unavoidable impurities of 2000 ppm or less in total, and in an inner surface thin layer region of the lining layer,
An oxide film layer is formed to prevent the cladding tube base from absorbing hydrogen generated from inside the tube.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The high-purity zirconium used for the cladding lining layer of the present invention is commercially available sponge zirconium, generally not more than 1200 ppm of oxygen and a total of 20 ppm.
A substance containing unavoidable impurities of not more than 00 ppm and appropriately containing a trace amount of an additive. At this time, the composition was selected so as to exhibit excellent corrosion resistance without substantially affecting the plasticity required for the lining layer.

That is, the composition of the high-purity zirconium for the lining layer according to the present invention is such that a total of at least one of Fe, Ni, Co, Rh and Pd is 0.05 wt% or more and 1.0 wt% or less. It is included at the following contents.

Further, in the present invention, as shown in the sectional view of the cladding tube of FIG. 1, an oxide film layer 6 is further formed on the inner surface thin layer region of the lining layer 5, so that the oxide film layer 6 is formed. With sufficient thickness, it is possible to prevent the cladding tube base 2 from absorbing hydrogen from inside the cladding tube (fuel rod).

There are various methods for forming an oxide film layer on the inner surface of the cladding lining layer, such as heating the lining layer surface to a high temperature or applying an oxidizing agent to form an oxide film. In order to form a uniform and dense oxide film,
For example, an anodic oxidation method is a suitable method. In this method, an oxide film can be formed by applying a voltage using the electrolyte solution filled in the cladding tube as a cathode, and by appropriately setting the applied voltage and time, control can be performed so that an arbitrary oxide film thickness can be obtained. That's the way you can. However, if the voltage is low, the surface is dissolved, so it is desirable that the applied voltage be at least 2 V or more.

[0014]

EXAMPLE A high-purity zirconium alloy for a cladding liner having various compositions determined on the basis of the conditions according to the present invention was obtained from a commercially available sponge zirconium (No. 24) containing no zircaloy-2 (No. 24). .25) as a comparative example, and sponge zirconium to which one or a combination of Fe, Ni, Co, Rh, and Pd was added at various contents were used as test pieces (Nos. 1 to 23). Each was evaluated for corrosion resistance by a corrosion test.

Specifically, each test piece was heated at 400 ° C., 105
After 24 hours under atmospheric conditions, the corrosion gain was measured.
Here, the corrosion increment is the rank ◎ those 20 mg / dm ² or ^{less, 20mg / dm 2 ~40mg / dm} 2 and the rank ○ the following ones, rank × those corrosion increment larger beyond 40 mg / dm ² Was evaluated. Table 1 shows the results. In this case, all the test pieces commonly contain 500 ppm of oxygen.

[0016]

[Table 1]

As can be seen from Table 1, in the case where each of the additives Fe, Ni, Co, Rh, and Pd is contained alone, any of the additives within the range of 0.05 to 1.0 wt% is used. In the cases (Nos. 1 to 15, 23), high corrosion resistance was also exhibited.

In addition, in the case of adding two of the trace additives (total 0.5 wt% or less) (Nos. 16 to 22), the evaluation was ranked ラ ン ク in all cases, indicating high corrosion resistance. In Table 1 above, only the case where one or two of the trace additives are added is shown, but even when three or more of the trace additives are added (total 0.5 wt% or less). Similarly, high corrosion resistance is obtained.

Next, high-purity zirconium (No. 5, 8, 11, 14, 16, 17, 17) having a composition exhibiting high corrosion resistance in the corrosion test described above.
8,19,23), the alloy liner cladding was manufactured by lining the inner surface of the cladding base material, and an oxide film was formed on the inner surface of the lining layer of each cladding by anodization.

That is, 1% K is contained in the cladding tube as an electrolyte solution.
An OH aqueous solution is charged, and this is
A volt voltage was applied for a few seconds to a few minutes. The resulting oxide film thickness is about 50 to 100 when 40 volts is applied for several seconds.
nm, about 800 n when 120 volts are applied for several minutes
m.

A hydrogen absorption resistance test was performed on each of the alloy liner cladding tubes on which the oxide films having the above thicknesses were formed. In this test, hydrogen gas was passed through each cladding tube at 350 ° C. for 12 hours, and then the cladding tube base material was subjected to hydrogen analysis. The results are shown in Table 2 below. At this time, as a comparative example, the same hydrogen absorption test was performed on each of the zircaloy alloys of Nos. 24 and 25 in Table 1 without oxidation treatment.

[0022]

[Table 2]

As can be seen from Table 2, the film thickness is 50 to 80.
In each of the cladding tubes on which an oxide film was formed over a range of 0 nm, the hydrogen absorption amount of all (Nos. 31 to 41) was 0.2 mg / mg.
A result of not more than dm ² was obtained. This is significantly less than the comparative example having no oxide film layer of 2 nm or less without oxidation treatment (Nos. 42 and 43), and it can be said that hydrogen absorption hardly occurred.

[0024]

According to the fuel cladding for a nuclear reactor of the present invention,
As described above, since the cladding tube lining layer has high corrosion resistance, there is an effect that generation of hydrogen due to oxidation of the cladding tube lining layer is suppressed. Furthermore, even when hydrogen is generated inside the cladding tube, the absorption of hydrogen into the cladding tube base is suppressed by the oxide film layer formed on the inner surface of the lining layer, so the reliability is much higher than before. High fuel cladding for reactors.

[Brief description of the drawings]

FIG. 1 is an enlarged schematic cross-sectional view in a direction perpendicular to an axis of a fuel cladding tube for a nuclear reactor according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing an example of a conventional general fuel rod for a nuclear reactor, where (a) is a schematic cross-sectional view in the axial direction;
(B) is an enlarged schematic cross-sectional view in the direction perpendicular to the axis.

[Explanation of symbols]

 1: fuel pellet 2: cladding tube 3: plenum spring 4a: lower end plug 4b: upper end plug 5: lining layer 6: oxide film layer

Claims (1)

[Claims] 1. A fuel cladding tube comprising: a zirconium alloy nuclear reactor cladding base material containing nuclear fuel therein; and a zirconium lining layer metallurgically bonded to the cladding base material. The layers are a total of 0.05 w in zirconium
Fe, Ni, Co, Rh, Pd of not less than t% and not more than 1 wt%
Any one or more of a trace additive and 1200 pp
m, and an oxide film layer for preventing the cladding base material from absorbing hydrogen generated from inside the pipe in the inner surface thin layer region of the lining layer, containing oxygen of 2000 m or less and unavoidable impurities of 2000 ppm or less in total. A fuel cladding tube for a nuclear reactor, characterized in that the cladding is formed.