JPS6026650A - Fuel cladding pipe for nuclear reactor - Google Patents

Abstract

PURPOSE:To obtain a cladding pipe with superior resistance to corrosion and stress corrosion cracking by hot extruding a Zr alloy to form a pipe, hardening the whole pipe, lining the hardened pipe with a Zr liner layer, and subjecting it to repeated cold rolling and annealing. CONSTITUTION:A Zr alloy is hot extruded to form a pipe, and the whole pipe is hardened. The hardened pipe is lined with a Zr liner layer, and it is subjected to repeated cold rolling and annealing. The hardening is required only to be carried out before the lining and after the hot extrusion. The mechanical characteristics of the hardened layer are comparable to those of a hardened layer formed in a conventional stage, and a cladding pipe with superior corrosion resistance can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a cladding tube for nuclear reactor fuel and a method for manufacturing the same, and in particular to a zirconium-based alloy with improved corrosion resistance and SCC resistance, and an atomic cladding tube made of a zirconium liner layer. Regarding cladding tubes for reactor fuel.

[Background of the invention]

Zirconium alloys have excellent corrosion resistance and a small neutron absorption cross section, so they are used for fuel rod cladding tubes, fuel assembly channel boxes, etc., which are structural members in nuclear reactors. The zirconium alloy used in the above application is Zircaloy-2 (zirconium with about 1.5 SnH).
'LCr: approx. 0.1 h, Fe: approx. 0.1%, Nl: approx. 0
．． 05%) and Zircaloy-4 (zirconium with Sn: about i, s*, Fe: about 0.2%, Cr:
There are two types: one with about 0.1- added. but,
Even when a zirconium alloy with excellent corrosion resistance is exposed to high-temperature, high-pressure water or steam in a furnace for a long period of time, the heat transfer coefficient decreases due to the thick oxide film, resulting in local overheating. However, in some cases, it may interfere with the operation of the nuclear reactor. In order to prevent such accidents, methods of improving corrosion resistance by heat treatment are conventionally known.

Pure zirconium forms a dense hexagonal crystal (α
At higher temperatures, it has a body-centered cubic (β phase) crystal structure. In zirconium alloys, generally Sn is an α-phase stabilizing element and Fe is a β-phase stabilizing element.

Since Cr, Ni, or Nb is added, there is a temperature range in which the α phase and β phase coexist (hereinafter referred to as the [α+β] phase temperature range). In Zircaloy-2 or Zircaloy-4, the [α and β] phase temperature range is approximately 8
It is 30C to 960C.

At about 960 C or higher, the temperature becomes a β phase unit (hereinafter referred to as β phase temperature range). Zirconium alloys rapidly cooled from the [α10β] phase temperature range or β phase temperature range have a martensitic structure, and some or most of the alloying elements are supersaturated solid solutions in the zirconium matrix. .

However, if the cooling rate is slow, Fe and Cr mainly precipitate as intermetallic compounds with zirconium during the cooling process and become coarse.

Utilizing the properties of such zirconium alloy, conventional
] A heat treatment for improving the υ corrosion resistance of a zirconium alloy member by rapidly cooling it from the phase temperature range or β phase temperature range is known. The former is [α+β
] quench, the latter is called β quench.

On the other hand, the inner surface of the tube is lined with a zirconium liner layer,
Methods for improving SCC resistance are also known. A known method for improving the corrosion resistance of liner tubes is to harden only the surface layer of the lychee tube using high frequency or laser so that the inner liner layer is not affected by heat. , cold rolling, pickling, etc., the thickness of the outer surface layer of the hardened liner tube gradually becomes thinner, resulting in a decrease in reliability regarding corrosion resistance.

[Purpose of the invention]

The object of the present invention is to eliminate the above-mentioned drawbacks and to provide an SCC resistant material made of a zirconium-based alloy and a zirconium liner layer.
An object of the present invention is to improve the corrosion resistance of a cladding tube with excellent properties, and to provide a fuel cladding tube for a nuclear reactor that is excellent in both corrosion resistance and SCC resistance, and a complete method for manufacturing the same.

[Summary of the invention]

The present invention relates to a method for manufacturing a nuclear reactor fuel cladding tube made of a zirconium-based alloy by hot-extruding the zirconium-based alloy and then cold-rolling the zirconium-based alloy. The present invention provides a complete summary of a nuclear reactor fuel cladding tube and its manufacturing method, characterized in that the inner surface of the entry tube is lined with a zirconium liner layer and subjected to repeated cold rolling and annealing.

[Embodiments of the invention]

The present invention will be explained in detail below.

The method for producing a cladding tube for nuclear reactor fuel according to the present invention includes hot extrusion, quenching the entire body, then lining the inner surface of the quenched tube with a zirconium liner layer, and cold rolling at 650C or less, preferably at 6'00C or less. It is characterized by performing annealing, and other than the above, it is carried out in the same manner as a normal manufacturing method.

The entire quenching can be done before the zirconium liner layer lining process and after hot extrusion, and then cold rolling and annealing are performed several times, so that the mechanical properties of the quenched layer can be maintained in the normal manufacturing process. It is possible to produce a cladding tube that is equivalent to that produced by conventional methods and has excellent corrosion resistance.

The overall quenching temperature may be at least 870C, preferably at least 930C, and the annealing temperature after cold rolling may be at most 650C, preferably at most 600C. This is 87
Zirconium heated to a temperature of 0C or higher has a part of its structure transformed into a β phase, and this β phase contains l, an alloying element.
'e, Cr.

Ni and Sn are sufficiently dissolved in solid solution and then rapidly cooled to form an α phase with supersaturated solid solution of alloying elements, improving corrosion resistance, and the annealing temperature after cold working is lowered to 65%.
By setting the temperature to 0C or less, precipitation of all combined elements can be suppressed as much as possible, and the effect of the quenching treatment remains even after repeated processing and annealing.

[Embodiments of the invention]

The present invention will be explained in more detail with reference to examples below.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 The zirconium-based alloy used is Zircaloy-2 alloy. Its main components are 1.5wt%Sn%0.15w
t%Fe, 0.1wt9! +Cr, 0.05Wt Chi Ni
and the remaining Zr. The extruded raw tube made of the above components was hardened by high frequency, then cold rolled with a low degree of deformation, and further annealed for 600tZ'X2hr.
Dimensional accuracy, particularly in the inner diameter, was achieved by oxidation using a mixed solution of and HF. A zirconium tube separately produced by cold rolling was inserted into the above-mentioned quenched tube. During insertion, the quenching treatment was heated to 500 C^ to improve insertability. The double tube manufactured by the above method was evacuated, both end faces of the double tube were electron beam welded in vacuum, and the quenched tube and zirconium tube were brought into close contact with each other by hydraulic tube expansion.

It is confirmed that the metal structure of the raw tube that has undergone the quenching treatment has an acicular structure that is characteristic of a quenched structure.

FIG. 1 shows a method of manufacturing a nuclear reactor fuel cladding tube according to the present invention. The outer and inner diameters and inner thickness of the composite pipe produced by the method described above were successively reduced by cold rolling three times and annealing three times to produce a product pipe.

As shown in the figure, the annealing temperature after intermediate cold rolling is 600t:
' (590±10C). Other manufacturing processes are
The process is the same as that for conventional fuel cladding tubes.

FIG. 2 shows the zircaloy layer and zirconium liner layer of the nuclear reactor fuel cladding tube according to the present invention.

Both layers were sufficiently recrystallized, and no acicular structure peculiar to the hardened structure was observed. In addition, Zircaloy-zN has the alloying element 8n+Fe+C'+N& sufficiently dissolved in the matrix, and the precipitates are finer and less dense than cladding tubes manufactured by normal processes. The amount of precipitation was small.

As mentioned above, the product of the present invention has a metal structure similar to that produced by a conventional process except for the precipitation of intermetallic compounds, and its mechanical properties are equivalent to those produced by a conventional process.

FIG. 3 shows the results of a corrosion test in high-temperature, high-pressure steam of the nuclear reactor fuel cladding tube of the present invention and a normal cladding tube. The test piece used in the corrosion test was a short cladding tube with a length of 50 mm.

However, the zirconium liner layer, which has low corrosion resistance, was removed by machining using a lathe, and then the mechanical layer was removed by pickling with a mixed solution of HNO3 and HF. According to the corrosion test results, the corrosion weight increase of standard cladding pipe is 1000 m.
g/dm2, the corrosion weight gain of the cladding tube of the present invention is 100 mg/dm2.
In addition, the surface of the product of the present invention has a black, glossy appearance, and no nodular corrosion has occurred.
It was found to have excellent nodular corrosion resistance.

On the other hand, a lot of nodular corrosion occurs on the surface of the cladding tube, and the nodular corrosion resistance is low.

As described above, the cladding tube of the present invention has excellent corrosion resistance. Further, it is clear from the manufacturing method of the product of the present invention that the above-mentioned excellent corrosion resistance is a property exhibited by the entire Zircaloy-2 part.

〔Effect of the invention〕

According to the present invention, it is possible to uniformly and reliably improve the corrosion resistance of the entire Zircaloy 2 layer of a reactor fuel cladding tube with a double tube structure made of Zircaloy 2 and zirconium, so that the zirconium liner layer on the inner surface can be improved uniformly and reliably. In combination with this, it is possible to manufacture a highly reliable cladding tube with high SCC resistance and high corrosion resistance.

Moreover, the above effect allows the usage period of the cladding tube to be extended, resulting in effects such as improved efficiency and economical efficiency.

[Brief explanation of the drawing]

Fig. 1 is a process diagram after hot extrusion of the conventional method and the method of the present invention in manufacturing cladding tubes for reactor fuel, Fig. 2 is a structural diagram of the cladding tube for reactor fuel of the present invention, and Fig. 3 is a diagram of the present invention. This figure shows the corrosion characteristics of the reactor fuel cladding tube and the normal cladding tube. No. 1521 $Z mouth

Claims (1)

[Scope of Claims] 1. By hot-extruding a zirconium-based alloy and then cold-rolling it, the entire cladding tube for nuclear fuel made of a zirconium-based alloy is quenched after hot extrusion. A cladding tube for nuclear fuel, characterized in that the inner surface of the quenched tube is then lined with a zirconium liner layer, and cold rolling and annealing are repeatedly performed. 2. After quenching, the tube is cold-rolled with a low degree of processing to achieve accuracy in both the inner and outer diameters, especially the inner diameter, and a zirconium tube separately produced by cold rolling is shrink-fitted to this tube. A nuclear reactor fuel cladding tube according to claim 1. 3. The reactor fuel cladding tube according to claims 1 and 2, characterized in that the overall quenching temperature is 870 t:' or more, and the annealing temperature is 600 C or less. 4. The reactor fuel cladding tube according to claims 1 and 2, characterized in that the entire hardening is performed by high-frequency heating.