JPH0636044B2 - Method for manufacturing nuclear fuel cladding tube with liner - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a nuclear fuel cladding tube with a liner, and more specifically, with a liner for improving the performance of preventing stress corrosion cracking due to fission products. The present invention relates to a method for manufacturing a nuclear fuel cladding tube.

[Prior Art and its Problems] Conventionally, a nuclear fuel clad tube with a liner having a zirconium metal or zirconium alloy coated on its inner surface is disclosed in Japanese Examined Patent Publication No. 55-3.
It is known from Japanese Patent No. 3037.

According to the above-mentioned publication, since the high-purity zirconium layer of the liner nuclear fuel clad contains only 1000 ppm of impurities at the maximum, it is effective for stress corrosion cracking of the liner-type nuclear fuel clad caused by fission products such as iodine. It can be prevented.

However, such a liner-equipped nuclear fuel cladding tube lined with a high-purity zirconium metal layer cannot completely prevent stress corrosion cracking.

That is, in a nuclear fuel cladding tube with a liner coated with a high-purity zirconium metal layer having an impurity content of 1000 ppm or less, due to its high purity, the grain size of the zirconium metal layer becomes coarse, and as a result, the coating The thickness of the layer varies, and it is impossible to secure the necessary coating layer thickness for preventing stress corrosion cracking.

On the other hand, JP-A-54-59600 discloses a nuclear fuel clad tube with a liner for coating a zirconium metal layer having an impurity content of 1000 to 5000 ppm. Due to the influence of, the crystal grain size of the coating layer portion becomes small, and the thickness of the coating layer can be made uniform, but there is a problem that hardening of the coating layer is recognized and stress corrosion resistance decreases. is there.

OBJECT OF THE INVENTION It is an object of the present invention to provide a method for producing a lined nuclear fuel cladding tube having a coating layer with improved resistance to stress corrosion caused by fission products such as iodine.

[Means for Achieving the Object] As a result of intensive studies by the present inventors in order to achieve the object, the intermetallic compound in zirconium that appeared in the step of producing a zirconium billet is a forging step and an annealing step. The present invention has been reached by finding that the coarsened intermetallic compound finally reduces the stress corrosion resistance.

That is, the gist of the present invention for achieving the above-mentioned object is a billet forming step of processing a zirconium briquette into an inner tube billet, a step of processing zircaloy into an outer tube billet, and inserting the inner tube billet into the outer tube billet. To produce a blank pipe, and rolling the blank pipe,
In the billet forming step in the method for producing a nuclear fuel clad tube with a liner, which comprises the step of manufacturing a nuclear fuel clad tube with a liner by annealing, obtain a zirconium ingot obtained by melting zirconium briquette, and then obtain an inner tube billet and an outer tube billet. Before the insertion into the zirconium ingot, the forged body obtained by forging this, or the inner tube billet obtained from the forged body is subjected to β-treatment, It is a manufacturing method.

The billet forming process for processing a zirconium briquette into an inner tube billet is roughly divided into, for example, a melting process for melting zirconium briquette, a process for converting molten zirconium into an ingot, a forging process for forging a zirconium ingot, and a forged body as a hollow cylinder. It consists of the billet processing process of forming into.

In practice, the melting process may include multiple melting operations such as primary melting and secondary melting. Also,
The billet working process also includes a re-billet working process.

In the present invention, the β-treatment is newly added during the step of producing the zirconium liner which is usually performed.

Since this β-treatment prevents coarsening of the intermetallic compound in zirconium, any one of, for example, a zirconium ingot, a forged body from the zirconium ingot, and a billet which is a hollow cylindrical body obtained from the forged body is used. .Beta.-processing can be performed on. However, considering the efficiency of the billet forming process,
β-processing may be performed.

The β-treatment consists of a heat treatment and a quenching treatment, and the heat treatment usually involves heating an object such as an ingot, a forged body or a billet to at least 900 ° C., preferably 1000 to 1100 ° C. At least a portion of the phase is phase transformed to the β phase and then the object is maintained at this temperature until the phase transformation begins, after which the object is heated to, for example, 650
Rapidly cool to below ℃, preferably below 600 ℃. The time for maintaining the object at the heating temperature is sufficient for the heated object not to absorb gas.

The cooling rate is usually 100 ° C./min, and the effect is small when heated at a temperature lower than 900 ° C.

Further, if the object is heat treated after the β-treatment, it is preferable to perform the treatment at a temperature of 650 ° C. or lower. If the heat treatment is performed at such a temperature, coarse intermetallic compounds are contained in the zirconium liner. The generation of compounds can be prevented.

The zirconium billet obtained by such β-treatment is used as an inner tube billet, and the inner tube billet is inserted into the outer tube billet together with the outer tube billet obtained in the step of processing zircaloy into the outer tube billet. And the step of producing the liner-attached nuclear fuel cladding tube by rolling and annealing the raw tube, and the liner-attached nuclear fuel cladding tube is produced.

The step of processing the zircaloy into the outer tube billet, the step of inserting the inner tube billet into the outer tube billet to produce a raw tube, and the step of rolling and annealing the raw tube to produce a nuclear fuel clad tube with a liner, It can be implemented by adopting a conventionally known technique.

Explaining the outline of each step, the step of processing zircaloy into an outer tube billet, for zircaloy, for example, zircaloy-2, briquette is, for example, primary melted, secondary melted and tertiary melted to produce a zircaloy ingot, and this zircaloy is manufactured. It consists of forging an ingot and processing it into a billet, β-processing this billet and then re-billing to produce the outer tube billet. The same applies to the production of Zircaloy-4 billet and Zircaloy-2.5% Nb billet.

The β-treatment in this step has almost the same contents as the β-treatment in the step of producing the zirconium liner, but this is to prevent corrosion due to water and steam.

The process of manufacturing the raw tube by inserting the inner tube billet into the outer tube billet is performed by inserting the inner tube billet into the outer tube billet, for example, electron beam welding, 500 to 700.
It passes through a die at a temperature of ° C and is annealed to produce a blank tube.

The steps of rolling and annealing the element tube to produce a nuclear fuel clad tube with a liner include, for example, first rolling, vacuum annealing, and second rolling.
The process includes rolling, vacuum annealing, third rolling, inner surface pickling, final annealing, roll straightening, inner surface sandblasting, outer surface mechanical polishing and the like.

[Effect of the Invention] According to the present invention, since β-treatment is performed in the step of producing a zirconium liner, even if the zirconium liner contains impurities at a content of 1000 ppm to 5000 ppm, the content of 1000 ppm or less. It is possible to provide a method for producing each fuel cladding tube with a liner having a stress corrosion resistance equivalent to that of a zirconium liner containing impurities.

Since the nuclear fuel clad tube with a liner produced by the method of the present invention has excellent stress corrosion resistance as described above, it can be made to have a large strength and a long life.

In addition, the content of impurities in the zirconium liner is especially 10
Even if it is not adjusted to less than 00ppm, the impurity content is 1000p
A nuclear fuel clad with a liner having a stress corrosion resistance equal to or higher than that of a zirconium liner of pm or less can be manufactured.

Moreover, performing the β-treatment in the step of producing a zirconium liner does not significantly change the conventional step, and therefore, a nuclear fuel clad tube with a liner having excellent characteristics can be produced at low cost. it can.

[Examples] (Example 1 and Comparative Example 1) Zirconium briquettes having impurities of the contents shown in Table 1 were first melted and secondarily melted to produce a zirconium ingot, and the zirconium ingot was forged to have a cylindrical shape. A forged body was manufactured.

This cylindrical forged body was billet processed and extruded to produce a crude zirconium billet, and then re-billet processing was performed to obtain a zirconium billet.

The zirconium billet is then heated to 1050 ° C,
Hold at this temperature for 5 minutes, then quench with water. The cooling rate at that time was 200 ° C./min.

Meanwhile, Zircaloy-2 is melted, forged, billet processed, β-
Zircaloy tubes containing impurities shown in Table 1 were manufactured by processing and billeting again.

The zirconium billet was inserted into the zircaloy tube, and electron-beam welding, extrusion, and annealing were performed to form a raw tube.

By repeating the rolling and annealing of this raw tube, acid cleaning, polishing, roll straightening, etc., a nuclear fuel clad tube with a liner was manufactured.

The outer diameter of this nuclear fuel clad tube with liner was 12.3 mm, the inner diameter was 10.5 mm, the wall thickness was 0.9 mm, and the zirconium liner portion had a wall thickness of 0.075 mm.

Further, a zirconium liner was produced in the same manner as in the production of the zirconium liner of Example 1 except that β-treatment was not performed in the production of the zirconium liner, and a nuclear fuel clad tube with a liner was produced in the same manner as in Example 1. did.

A short length of a liner nuclear fuel clad tube with iodine enclosed at a concentration of 10 mg / cm ² was loaded into a stress corrosion cracking (SCC) test device (high temperature diameter measuring device), and the load at which stress corrosion cracking occurred was measured.

The SCC test apparatus is composed of a sample chamber, a heating device for heating the sample chamber, a load device for expanding the nuclear fuel clad tube by applying a load to the nuclear fuel clad tube for sample arranged in the sample chamber in the axial direction. The loading device was loaded with a six-part hollow pellet in a nuclear fuel cladding tube, a core was inserted and arranged in the central axis portion of the pellet, and push rod connectors were attached to the upper and lower ends of this core via spacers. The pressure of the push rod connecting member causes the radial pressure by the six-part hollow pellets to be generated, thereby expanding the diameter of the nuclear fuel cladding tube.

The SCC test of a nuclear fuel cladding with a liner is carried out by expanding the nuclear fuel cladding by applying an axial load to the six-part split hollow pellets in the test cladding placed in a sample chamber heated to 350 ° C. by a heating device. It was carried out by causing a crack in the nuclear fuel cladding tube.

Whether or not a crack has occurred in the nuclear fuel clad pipe is determined in the load-displacement recording in a load device that applies a load to the push rod connector, a sudden decrease in load caused when a crack occurs, and a crack occurs. When released, iodine released from the damaged portion was trapped with a potassium iodide solution, and the discoloration of the potassium iodide solution to yellowish brown was observed to make a comprehensive judgment.

FIG. 1 shows the SCC test results for Example 1 and Comparative Example 1.

[Brief description of drawings]

FIG. 1 is a graph showing SCC test results in Example 1 and Comparative Example 1.

Claims (4)

[Claims] 1. A billet forming step of processing a zirconium briquette into an inner tube billet, a step of processing zircaloy into an outer tube billet, and a step of inserting an inner tube billet into an outer tube billet to produce a raw tube, and In the billet forming step in the method for producing a nuclear fuel clad tube with a liner, which comprises a step of rolling and annealing a raw tube to produce a nuclear fuel clad tube with a liner, until the inner tube billet is inserted into the outer tube billet, Zirconium ingot obtained by melting a zirconium briquette, a forged body obtained by forging this, or an inner tube billet obtained from the forged body is subjected to β-treatment, and a method for producing a nuclear fuel clad tube with a liner . 2. The β-treatment comprises the zirconium ingot obtained by melting a zirconium briquette, a forged body obtained by forging the same, or an inner tube billet obtained from the forged body in which the α phase is at least partially. The method for producing a nuclear fuel clad tube with a liner according to claim 1, which is a treatment of heating to a temperature for converting to a β phase and then rapidly cooling. 3. The method for producing a nuclear fuel clad tube with a liner according to claim 2, wherein the temperature at which the α phase is at least partially converted to the β phase is at least 900 ° C. 4. The method for producing a nuclear fuel clad tube with a liner according to claim 2, wherein the temperature for performing the rapid cooling is 650 ° C. or lower.