JPS5847290A - Liner cladding tube for nuclear fuel and its fabrication - 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 1. The present invention relates to a nuclear fuel element used in the core of a nuclear reactor, particularly a liner cladding tube for storing nuclear fuel therein, and a method for manufacturing the same. The object of the present invention is to provide a cladding tube whose thickness can be measured over its entire length by non-destructive testing.

Conventionally, the core of a nuclear fission reactor is in the form of pellets, as described in Japanese Patent Publication No. 55-33037.

Nuclear fuel in the form of rods is stored in a cladding tube, and the fuel is gathered and assembled at regular intervals using a support grid, and an appropriate number of them are combined to form a reactor core. The cladding tube, which houses the nuclear fuel, is non-reactive with respect to the coolant and moderator flowing outside, and is non-reactive with respect to the radioactive fission product, which is the gas inside, and does not leak to the outside. It has a function to prevent Therefore, the material of the cladding is usually made of special materials such as zirconium or its alloys, which can cope with chemical reactions during operation, but on the other hand, it can cause various mechanical problems during operation. It also causes In other words, brittle cracks in the cladding occur due to the interaction between nuclear fuel pellets and the cladding (pellet, cladding, injection, hereinafter referred to as PCI action), and the intersection between the cracks in the nuclear fuel pellet and the cladding caused by the heat during the nuclear fission reaction. There is a risk that stress will be concentrated at the end of the cladding tube or the end of the nuclear fuel pellet, resulting in damage to the cladding tube and the leakage of fission products.

Therefore, in order to deal with this problem, 1. In particular, the thickness of the entire inner diameter tube on the inner surface of the cladding tube is 10'. Kan Zenju (
Conventionally, there was no way to measure the thickness of the liner over the entire length of the pipe, and currently both ends of the pipe are cut and the thickness of the main pipe and part of the liner is measured using a metal and eye test. Currently, the pipe thickness and uneven wall thickness at the center of the pipe cannot be inspected, as the liner thickness is measured using the difference in structure, which relies on destructive testing.

That is, in the conventional cladding tube, as shown in FIG. , hot extrusion was carried out to form an assembly of both tubes, and this was manufactured as a cladding tube tc) of a predetermined diameter by processing such as rolling.
(See Publication No. 330375, Column 10, Lines 33-44) Therefore, even if it is unclear whether the pipe diameter, especially the thickness of the liner pipe, is uniform throughout the pipe number, the destructive test 1. However, if there is a part of the pipe with an unsuitable thickness, there is no choice but to use it only for inspecting the end of the pipe, and the local fracture caused by the PC1 action increases.

The present invention solves these conventional defects when manufacturing the cladding tube! In order to make it possible to non-destructively measure the thickness and wall thickness deviation of a part of the liner of the cladding tube after manufacturing by applying this devised processing, the inner tube, which will become the inner tube, is pre-processed in large numbers in the axial direction. After inserting this into the main tube that will become the outer tube, the two are metallurgically joined by hot extrusion, rolling, etc. to form a liner skin of the required diameter. The present invention is characterized by a method for obtaining a cladding tube and a nuclear fuel cladding tube provided with a slit liner inside obtained by kneading.

Hereinafter, specific embodiments of the present invention will be described.

FIG. 2 is a diagram showing an outline of the steps in the manufacturing method of the present invention, and shows, for example, a main tube (1
), for example, a liner tube made of zirconium (2
Using the two raw tubes of No. 1, the latter liner tube (2) is inserted into the mother tube as an outer tube and the latter liner tube (2) is inserted as an inner tube, and then the two tubes are hot extruded. The liner tube (2) is stretched in the direction through a known process such as rolling, and both are metallurgically connected to reduce the tube diameter to the required diameter. The process of manufacturing the liner pipe (4), which is 10% H IW with pipe thickness, is the same as before, but what is important here is that the liner pipe is As shown in FIG. 3, relatively short slit-shaped holes (3) with severe lfB are cut out at appropriate intervals in the axial direction.

In this case, when the product is manufactured by the above-mentioned manufacturing method, the defective part of the hole (3) is not manufactured into a product. (5), and if the decrease in wall thickness is about 10%, use ultrasonic wall thickness measurement to scan the entire length of the cladding tube in a spiral as shown in Figure 5 (a). It can be detected accurately and displayed on the recording paper as shown in Figure 5 (b), and the liner tube 1 (h, ) (h2) of each part
・Can be easily measured.

Note that although the defective portion of the hole (3) is shaped like a relatively short slit, it may be a recess without a liner, such as a circular hole, and the size of the defective portion may vary.

The spacing needs to be just enough to measure the wall thickness over the entire length of the manufactured cladding tube.

The above is an example of the manufacturing method of the present invention, but the point is that in the present invention, the liner pipe (2) is pre-processed with a large number of short slit holes in the axial direction. It is important that defects such as
) The means for inserting the liner pipe (2), metallurgically bonding the two, and reducing the pipe diameter to a predetermined diameter is limited to methods such as hot extrusion and rolling. All known methods can be used and are encompassed by the present invention.

In addition, when using the method of the present invention, the defective portion of the liner tube provided in advance before processing remains even after processing, so the improvement effect of the PCI action of a portion of the liner, which is the original purpose of the present invention, does not appear at first glance. Although some doubts remain, the PCI effect is negligible since the defective portion of the liner is only a localized defect in the inner surface of the cladding tube.

This is the thickness of a general banko liner calculated by design strength"-1
This is because it is normally not included, and the liner defect can be made sufficiently small compared to the size of the pellet-shaped nuclear fuel stored in the cladding tube. That is, the size of the liner defective portion is sufficiently small compared to the daily length t of the pellet, and the size of the liner defective portion is formed to be thinner than the same length in the axial direction.
The effects can be avoided. This is because, as mentioned above, brittle cracks in the cladding tube are caused by splits, eyes, or edges of the pellet.
Although it is not known that the liner is concentrated at the intersection with the coated surface, the missing part of the liner is relatively small and the percentage of the pellet is 7%.
- The groove or end of the liner does not necessarily intersect directly with the liner defect in the cladding. In addition, in the axial direction, the reason why the defect is made into a long and thin slit shape as described above is to improve the accuracy of liner thickness measurement, and the cracks in the pellet occur along the pipe wall in the cross-sectional direction. This is because the thermal gradient is small compared to the one where it occurs, so it does not break into as many small pieces. (See Figure 6) Furthermore, as another measure to avoid the PCI effect, a so-called ribbed cladding tube in which a narrow groove is carved in the longitudinal direction on the inner surface of the cladding tube has been proposed. It is also effective to rub a shape similar to that of the cladding tube. This is because by appropriately changing the shape of the ribbed cladding, it is possible to prevent stress concentration and static friction cracking before failure (when the yield point is reached and the cladding undergoes plastic deformation). However, the liner defects are known to be rain proof against damage, indicating that the liner defects of the present invention are free from the adverse effects of PCI action.

As described above in detail, the cladding tube of the present invention is characterized in that the liner 8 has a number of short slit-like holes of the same number axially formed in advance before processing, and even after processing, By ensuring that the defect portion remains, it is possible to measure the tube thickness over the entire length without destroying the cladding tube as in the conventional method by ultrasonic wall thickness measurement. It is possible to sufficiently avoid PCI effects and provide a more symmetrical and safer nuclear fuel element.
This production is extremely effective and is highly suitable for producing good products.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the manufacturing process of a conventional liner cladding tube for nuclear fuel, and FIG. 2 is a schematic diagram of the manufacturing process of a temporary liner cladding tube of the present invention.
Figures 3 (a) and (b) are front views and A-A' sectional views showing part of the liner tube before processing, and Figures 4 (a) and (b) show the thickness of the cladding tube after processing. The axial and cross-sectional views, FIGS. 5(A) and 5(B) are explanatory views of the scanning situation and the recording situation showing the ultrasonic tube thickness measurement method, and FIG. 6 is an explanatory view of the cracking situation of the pellet nuclear fuel. (1)・・・Mother tube. 9- (2)...Liner pipe. (3)...Slit-like hole. (41......Claying tube. (5)... Locally reduced portion. Patent issuer Nuclear Fuel Industry Co., Ltd. = 10- ¥3 (a) LA Koto 3 Trouble (mouth) ¥4 old) $4 distance ν) / Hana 6 picture (a) $f Uguchi) -Suyamaba mukokin old

Claims (1)

[Scope of Claims] 1. A liner-clad tube having an inner inner liner tube consisting of a mother tube, wherein the liner tube has an axial liner tube formed at appropriate intervals in the axial direction. Non-destructive testing revealed that the liner has defects such as a large number of short slit-like holes that extend over the entire length of the cladding tube, resulting in the presence of localized areas of reduced tube thickness in the axial direction of the cladding tube. A liner cladding tube for nuclear fuel that allows the thickness of the tube to be measured. 9. When manufacturing a cladding tube that stores nuclear fuel inside, a large number of short slit-shaped holes or other defects are formed in the axial direction in the liner tube, which will become the inner tube, in advance, and then inside the main tube, which will become the outer tube. A method for producing a liner cladding tube for nuclear fuel, which comprises: inserting the liner tube, then metallurgically bonding the liner tubes together by hot extrusion, rolling, etc., and forming them into a required tube diameter.