JPS6148873B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for manufacturing nuclear fuel cladding and nuclear fuel elements.

At present, nuclear fuel cladding tubes that house nuclear fuel in nuclear reactors are used in nuclear reactors, so they (1) have excellent corrosion resistance, (2) are non-reactive and have good thermal conductivity. 3) High toughness and ductility; (4) Small neutron absorption cross section.

Zirconium alloys are widely used as nuclear fuel cladding tubes because they have a small neutral absorption cross section, high toughness and ductility, and excellent corrosion resistance against demineralized water used as a coolant in nuclear reactors.

Nuclear fuel cladding tubes are susceptible to stress corrosion cracking due to corrosion caused by fission products such as iodine gas released from the nuclear fuel and stress caused by the expansion of nuclear fuel pellets, especially when the reactor load fluctuations are large. Occur.

As a method of preventing stress corrosion cracking, various metal barriers are provided between the nuclear fuel and the cladding. When using a zirconium alloy for the cladding, a composite cladding lined with high-purity zirconium is used as a metal barrier (Japanese Patent Application Laid-open No. 59600/1983). The thickness of the zirconium barrier is the same as that of the entire cladding. It is about 5-30% of the thickness. Compared to zirconium alloys, zirconium maintains its softness during neutron irradiation, reduces local strain generated in zirconium alloy cladding tubes, and has the effect of preventing stress corrosion cracking.

According to experiments conducted by the inventors, it has been found that if the thickness of the zirconium barrier is approximately 75 μm or more, the stress on the inner circumferential surface of the zirconium alloy cladding tube is rapidly alleviated.

Therefore, when manufacturing nuclear fuel cladding tubes, it is necessary to measure and control the thickness of the zirconium barrier. Since the zirconium alloy cladding tube and the zirconium barrier are made of almost the same material, measurement using eddy current or ultrasonic waves is not possible. It is possible to measure However, nuclear fuel cladding tubes are manufactured from large-diameter billets to narrow and thin-walled ones by hot extrusion and cold rolling.
Even if the overall thickness of the cladding tube can be controlled to a desired thickness, it is not guaranteed that the thickness of the ultra-thin zirconium barrier will be uniform along the length of the tube. Furthermore, because nuclear fuel cladding tubes undergo many processing steps before reaching the final product, the thickness of the zirconium barrier of each individual cladding tube varies.

Since it is not possible to measure the thickness of the zirconium barrier through destructive inspection of all nuclear fuel cladding tubes,
Considering the reliability of the cladding tubes used for nuclear fuel in nuclear reactors, it is necessary to sample the manufactured nuclear fuel cladding tubes and measure the thickness of the zirconium barrier through destructive inspection. It is essential.

An object of the present invention is to provide a method for manufacturing a nuclear fuel cladding tube that allows the thickness of a zirconium barrier to be measured non-destructively.

Another object of the invention is to enable the thickness of the zirconium barrier layer to be measured by non-destructive testing. The present invention provides a method for manufacturing a nuclear fuel element in which a nuclear fuel material body is loaded into a nuclear fuel cladding tube.

The present invention provides a method for forming a zirconium barrier layer on the inner circumferential surface of a cladding tube made of a zirconium-based alloy, comprising: forming grooves on the inner circumferential surface of the cladding tube base tube;
Inserting the raw tube forming the zirconium barrier layer into the raw tube filled with non-metallic powder in the groove, expanding the barrier layer raw tube, and then hot extrusion followed by cold plastic working and annealing, The thickness of the non-metallic powder layer is 1 to 10% of the thickness of the barrier layer, and after the final cold plastic working, the barrier layer is partially measured over the entire length of the cladding tube by an ultrasonic reflection method. A method of manufacturing a nuclear fuel cladding tube is characterized by the following.

Furthermore, the present invention forms a zirconium barrier layer on the inner peripheral surface of the cladding tube made of a zirconium-based alloy,
Next, in the method of loading nuclear fuel pellets having an outer diameter smaller than the inner diameter of the barrier layer into the cladding tube,
A groove is formed on the inner circumferential surface of the cladding tube blank, and the blank tube forming the zirconium barrier layer is inserted into the blank tube in which the groove is filled with nonmetal powder, and the gap between the barrier layer blanks is expanded. , then after hot extrusion, cold plastic working and annealing, the thickness of the non-metallic powder layer is 1 to 10% of the thickness of the barrier layer, and after the final cold plastic working, the thickness of the barrier layer is A method for manufacturing a nuclear fuel element, characterized in that the nuclear fuel pellets are loaded into the cladding tube after partially measuring the entire length of the cladding tube by an ultrasonic reflection method.

As mentioned above, the cladding tube made of zirconium alloy has excellent corrosion resistance against the atmosphere inside the nuclear reactor.

In particular, Sn1~2% and Fe0.05~0.2% by weight.
A Zr alloy containing 0.05-0.15% Cr and 0.03-0.1% Ni is preferred.

The zirconium barrier is provided on the entire inner circumferential surface of the zirconium alloy cladding tube to shield the cladding tube from trapped nuclear fuel material and protect the cladding tube from fission product gases. Its thickness is preferably 1 to 30% of the thickness of the cladding tube. especially,
5-15% is preferred. The zirconium barrier remains soft during irradiation, minimizing localized strain within the nuclear fuel element, thus preventing stress corrosion cracking. In particular, zirconium has a small neutron absorption cross section and is provided in close contact with the inner peripheral surface of the zirconium alloy cladding tube. Zirconium is of appropriate purity, preferably containing impurities of 5000 ppm or less. Among impurities, oxygen 200-1200ppm, Al 75ppm or less,
B0.4ppm or less, Cd0.4ppm or less, C270ppm or less,
Cr200ppm or less, Co20ppm or less, Cu50ppm or less, Hf100ppm or less, Fe1500ppm or less,
Mg 20ppm or less, Mn 50ppm or less, Mo 50ppm or less, Ni 70ppm or less, Nb 100ppm or less, N 80ppm or less, Si 120ppm or less, Sn 50ppm or less, W 100ppm
Below, Ti is preferably 50 ppm or less and U is 3.5 ppm or less.

The non-metallic powder layer allows the thickness of the zirconium barrier to be measured from either the inner or outer surface of the nuclear fuel cladding without destroying the nuclear fuel cladding. This area is
The existence of objects or spaces that are physically different from the materials of the zirconium alloy cladding tube and the zirconium barrier, which can be identified by ultrasonic reflection. Providing an area that can be identified by ultrasound reflection facilitates accurate measurement of the zirconium barrier thickness.

As a region that can be identified by ultrasonic reflection, a nonmetallic powder layer different from the materials of the cladding tube and the barrier is interposed at the boundary between the zirconium alloy cladding tube and the zirconium barrier. The presence of this region causes the ultrasonic waves to be reflected at each boundary, so that the thickness of the zirconium barrier can be measured non-destructively on either the inner or outer surfaces of the nuclear fuel cladding.

Solid nonmetallic powders include solid lubricants or metal oxides. In particular, solid lubricants have the advantage that they can also be used as lubricants during hot drawing of nuclear fuel cladding tubes. Graphite, molybdenum disulfide, etc. are used as solid lubricants, and alumina, zirconia, etc. are used as oxides.
Titania etc. can be used.

An area capable of non-destructive testing is provided at the interface between the cladding and the barrier. The thickness of this region is preferably between 1 and 10% of the thickness of the zirconium barrier, especially between 1 and 5%.
% is preferred.

According to the present invention, a nuclear fuel cladding tube made of a zirconium alloy and having a zirconium barrier on its inner circumferential surface is loaded with nuclear fuel material, and a gap is provided between the inner circumferential surface of the nuclear fuel cladding tube and the nuclear fuel material body. A region capable of non-destructive inspection is provided at the boundary between the zirconium alloy cladding and the zirconium barrier, and the zirconium barrier has a nuclear fuel cladding having a desired thickness measured by non-destructive inspection. can be provided.

The present invention will be explained below with reference to the drawings.

Figure 1 shows a cladding tube 1 made of zirconium alloy.
and a zirconium barrier 2 lined on its inner peripheral surface.
FIG. 2 is a cross-sectional view of a nuclear fuel cladding tube obtained by the manufacturing method of the present invention, which has a region 3 that can be partially non-destructively inspected at the boundary between the nuclear fuel cladding tube and the nuclear fuel cladding tube.

Figure 2 shows a region 3 that can be partially non-destructively inspected at the boundary between a zirconium alloy cladding tube 1 and a zirconium barrier 2 lined on its inner peripheral surface, and the thickness of the zirconium barrier is non-destructively inspected. FIG. 2 is a cross-sectional view of a nuclear fuel element of the present invention obtained by loading a nuclear fuel material body 4 into a nuclear fuel cladding tube as measured by. The nuclear fuel material is loaded with a slight gap between the inner peripheral surface of the nuclear fuel cladding tube and the nuclear fuel material body. The nuclear fuel material body 4 is made of a material selected from uranium, thorium, plutonium, or a mixture thereof, and is made of pellets divided into a plurality of pieces.

FIG. 3 is a sectional view taken along the line AA' in FIG. FIG. 4 is a sectional view of another nuclear fuel cladding tube of the present invention in which a nonmetallic powder layer 3 is interposed at the boundary between the zirconium alloy cladding tube 1 and the zirconium barrier 2.

Graphite powder is used as the powder.

FIG. 5 is a cross-sectional view of a nuclear fuel cladding tube in which grooves formed in the same manner as in FIG. 4 are filled with a metal oxide such as alumina, zirconia, titania, or the like.

Example Zirconium alloy with an outer diameter of 140.5 mm, an inner diameter of 70 mm, and a length of 350 mm (by weight, Sn1.42%, Cr0.10%, Fe0.14
%, Ni 0.05%, balance Zr), four vertical grooves with a width of 10 mm and a depth of 0.5 mm were formed along the entire length at 90 degree intervals on the inner circumferential surface of the hollow tube, and graphite powder was viscous into the grooves. It was applied with a binder and dried. A pure zirconium hollow tube is fitted into this hollow tube, and the rubber tube expansion method (patent application 1986-
No. 50748), the two hollow tubes were fixed and integrated, and after hot extrusion into a desired shape, cold rolling and annealing were repeated to produce a nuclear fuel cladding tube in the desired shape.

This nuclear fuel cladding tube has an outer diameter of 12.52 mm and an inner diameter of 10.80 mm.
mm, wall thickness 0.86 mm, and length 4 m. This nuclear fuel cladding tube was inspected from the outer periphery using water immersion ultrasonic pulse reflection method. Ultrasonic waves were emitted from the outer circumference of the tube, and the reflected echoes were displayed on a cathode ray tube, and the output signals were recorded on a recorder. The results are shown in FIG. FIG. 6a is a diagram showing an ultrasonic reflection waveform in a portion where graphite powder is not present, and FIG. 6b is a diagram showing an ultrasonic reflection waveform in a portion where graphite powder is present. In the figure, A and A' are echoes reflected from the outer circumferential surface of the zirconium alloy clad tube, and B and B' are echoes reflected from the inner circumferential surface of the zirconium barrier. C and C' are echoes reflected from the inner peripheral surface of the zirconium alloy cladding tube and echoes reflected from the outer peripheral surface of the zirconium barrier, but because the graphite powder layer is very thin, they are recorded at almost the same location. . In this way, if there is a region that is physically different from the zirconium alloy cladding tube and the zirconium barrier,
Since reflected echoes can be detected on each of those surfaces,
The thickness of the zirconium barrier could be measured non-destructively and accurately by the spacing of the echoes.

FIG. 7 is a diagram showing the relationship between the average thickness of the zirconium barrier at four locations in the circumferential direction and the length of the cladding tube, measured by the method described above. As shown in the figure, the thickness of the zirconium barrier was 86-98 μm.

Note that the area where graphite powder exists has a depth of approximately 5 μm.
m and width was 5 mm.

FIG. 8 is a block diagram of a nuclear fuel assembly constructed of nuclear fuel cladding tubes 10 manufactured by the above method and obtained by measuring the thickness of the zirconium barrier by non-destructive testing. Nuclear fuel cladding tube 10 of the present invention
One end is opened, and a space 11 is provided at the open end,
Furthermore, a gap was provided between the nuclear fuel pellets 4 and the inner peripheral surface of the nuclear fuel cladding tube, and the nuclear fuel pellets 4 were loaded. Further, a nuclear fuel pellet holding device 8 was inserted into the space 11. Next, the empty space 11 is filled with nuclear fuel pellets 4.
A closing member was provided at the open end while communicating with the opening end, and the joint portion was sealed.

As described above, according to the present invention, the thickness of the zirconium barrier can be measured for all nuclear fuel cladding tubes by non-destructive testing. As a result, a nuclear fuel element can be obtained using a nuclear fuel cladding tube having a desired thickness of zirconium barrier, and a highly reliable nuclear fuel assembly can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a nuclear fuel cladding tube obtained by the manufacturing method of the present invention, FIG. 2 is a cross-sectional view of a nuclear fuel element of the present invention, and FIG. 4 to 5 are cross-sectional views of other nuclear fuel cladding tubes obtained by the manufacturing method of the present invention, FIG. 6 is a line diagram showing ultrasonic reflection echoes of the nuclear fuel cladding tube, and FIG. 7 is a cross-sectional view of another nuclear fuel cladding tube obtained by the manufacturing method of the present invention. Diagram showing the thickness of the zirconium barrier in nuclear fuel cladding,
and FIG. 8 are configuration diagrams of a nuclear fuel assembly using the nuclear fuel element of the present invention. 1...A cladding tube made of a zirconium alloy, 2...
...Zirconium barrier, 3...Nonmetal powder layer, 4...
... Nuclear fuel material body, 5 ... Channel, 6 ... Lifting handle, 7 ... Nuclear fuel element, 8 ... Holding device, 9
...Stud, 10...Nuclear fuel cladding tube.

Claims (1)

[Claims] 1. A method for forming a zirconium barrier layer on the inner peripheral surface of a cladding tube made of a zirconium-based alloy, comprising:
A groove is formed on the inner circumferential surface of the cladding tube blank, the groove is filled with non-metallic powder, the blank tube forming the zirconium barrier layer is inserted into the blank tube, and the barrier layer blank tube is expanded. , then after hot extrusion, cold plastic working and annealing, the thickness of the non-metallic powder layer is 1 to 10% of the thickness of the barrier layer, and after the final cold plastic working, the thickness of the barrier layer is 1. A method for manufacturing a nuclear fuel cladding characterized by partially measuring the entire length of the cladding using an ultrasonic reflection method. 2. A method in which a zirconium barrier layer is formed on the inner peripheral surface of a cladding tube made of a zirconium-based alloy, and then nuclear fuel pellets having an outer diameter smaller than the inner diameter of the barrier layer are loaded into the cladding tube, the inner periphery of the cladding tube being The raw tube for forming the zirconium barrier layer is inserted into the raw tube in which a groove is formed on the surface and nonmetallic powder is filled in the groove, the barrier layer raw tube is expanded, and then hot extruded and then cold extruded. After plastic working and annealing,
The thickness of the non-metallic powder layer is 1 of the thickness of the barrier layer.
~10%, and after the final cold plastic working, the thickness of the barrier layer is partially measured over the entire length of the cladding tube by an ultrasonic reflection method, and then the nuclear fuel pellets are loaded into the cladding tube. Characteristic methods for producing nuclear fuel elements.