JPS5888698A - Moldings for sealing spent nuclear fuel rod and its manufacture - 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 The present invention relates to a cylindrical or polygonal molded body made of graphite and nickel sulfide that safely encapsulates spent nuclear fuel rods in their single or molded form for a long period of time; Concerning a method for manufacturing a molded object.

Spent fuel elements from a nuclear reactor are processed for a period of time by either 1) reprocessing the fuel element to return the fuel material to the fuel element manufacturing process and separating the fission products and final storage (highly active waste); or 2) Direct final storage of spent fuel elements has been attempted. In either case, a highly active waste is produced which must be safely buried in a suitable geological formation for 1000 years or more.

In order to safely contain spent fuel elements of this type for long periods of time, a number of types of containers have been proposed which satisfactorily satisfy the desired conditions, such as sealing at possible pressures and temperatures or corrosion resistance against salt solutions. . As container materials, metals and non-metallic materials are mostly used.

Since graphite has excellent corrosion resistance, it has been proposed to provide a container with an anticorrosion layer made of graphite (Western German Patent Application No. 2942092). However, since graphite compacts with the necessary dimensions for accommodating the fuel elements cannot be manufactured air-tight or liquid-tight, they are subsequently coated with ξ irocarbon or silicon carbide. .

The coated container must be sealed air-tight and liquid-tight with the coated lid after filling with the fuel element. in this case,
Graphite or a suitable adhesive should be used. A significant disadvantage of this type of container design is the prohibitive technical outlay required for manufacturing and coating containers with large dimensions. Moreover, such large moldings cannot be coated with the desired quality requirements.

Furthermore, by pressing graphite powder together with a binder, a carbon matrix for encapsulating radioactive and toxic wastes can be created.
It is also known to produce molded bodies made of J-Lux.

In this case, nickel sulfide is preferably used as a binder (DE-A-2917437). The molded bodies are very dense and have good corrosion and leaching stability, especially towards salt solutions.

DE 28 18 781 A1 discloses an environmentally friendly storage method for used nuclear fuel rods, which involves bending the nuclear fuel rods and placing the resulting nuclear fuel rods in a protective container. Consists of putting inside. In this case, the nuclear fuel rod is preferably formed into a U-shape or into a wound roll. This method has the disadvantage of requiring a container and of relatively poor heat extraction to the outside of the nuclear fuel rod.

It is also known to press isobarically preformed nuclear fuel rods together with alumina and a thin steel jacket into blocks that can be stored permanently [1.
113 (1980), pp. 753-766].

However, in this case too the problem of heat extraction is not optimally solved. Furthermore, mechanical integrity is also not sufficient for all conceivable storage situations.

It is therefore an object of the present invention to safely extend spent nuclear fuel rods in raw or shaped form, which guarantees good heat extraction, has good corrosion and leaching stability and has high mechanical integrity. The object of the present invention is to provide a cylindrical or polygonal molded body made of graphite and nickel sulfide that can be encapsulated for a period of time.

This object is solved according to the invention by having an anchor plate in the spatula 1 region and the leg area and a metal rod fastened to the anchor plate parallel to the main axis of the shaped body inside the nuclear fuel rod-free zone. .

For the anchor plate and the metal rod any customary material can be used, but it is advantageous to use steel.

In order to improve the mechanical bond between the graphite/nickel sulphide matrix and the rod, it is advantageous to use a metal rod with a macroscopically grainy surface.

It has also proven advantageous for the shaped body to contain nickel sulfide, primarily in the form Nj,3S21, which further increases the corrosion and leaching stability. The shaped bodies generally contain as matrix materials 75 parts by weight of graphite and 25 to 90 parts by weight of nickel sulphide, preferably at least 80 parts of which are in the form of Ni, 3S2.

The shaped bodies according to the invention have a particularly high mechanical integrity and therefore fully meet the requirements imposed for permanent storage.

The molded body of the present invention is produced by pressing a mixture of graphite, nickel and sulfur in which nuclear fuel rods are embedded in a matrix at a temperature higher than 100°C by the method of the present invention.
In a method for manufacturing a cylindrical or polygonal molded body made of graphite and nickel sulfide that safely encapsulates spent nuclear fuel rods in their original or molded shape for a long time, graphite, nickel, and sulfur are first added to a matrix. Then add the anchor plate with the metal rods fixed thereon, then add the nuclear fuel rods together with the IJ sock powder, add another anchor plate with the metal rods fixed on it, and then add the matrix powder again. At that time, the matrix powder in the area where the nuclear fuel rods are embedded is pre-compressed, and metal rods are attached only to the area of the anchor plate where there are no nuclear fuel rods in the matrix above or below. can do. In this case, the press is 40
It is advantageous to carry out at temperatures of 0-500°C.

In this case, the anchor plate is pressed in in such a way that the metal rod is compressed in the central and peripheral areas where the nuclear fuel rods are absent and is fixed in the hardened matrix. This significantly increases the integrity of the compact, especially under tensile and bending loads, so that it is possible to encapsulate the nuclear fuel rods in any desired shape (e.g. rolled, folded or straight)1, advantageously. transforms a nuclear fuel rod into a disc-shaped spiral body,
In this case, the central region preferably has a diameter of ≧80 mm.

When manufacturing this fuel rod spiral body, the pitch should be ≦6.
It has proven advantageous to keep it in the column.

The compression ratios of the matrices of the nuclear fuel-containing range and the nuclear fuel-free range are matched to each other such that the residual deformability within both ranges is of the same magnitude. This makes it possible to achieve a uniform overall density over the entire length of the compact.

With the method according to the invention, in addition to a large number of nuclear fuel rods, it is also possible to advantageously encapsulate individual fuel rod coils in a graphite/nickel sulphide matrix.

Such disks can be stacked in suitable containers for permanent storage and can be easily removed or stored permanently if desired. To facilitate removal, the disc may also have a central gripping hole.

In addition to untouched nuclear fuel rods, contaminated nuclear fuel rod sleeves can also be enclosed in this way.

The invention will now be described in detail with reference to the illustrated embodiments.

The molded body has one anchor plate in each of the spatula 12 region 2 and the leg region 3, on which the metal rod 4 is attached, so to speak, when pressing the molded body, the anchor plate 1 in which the nuclear fuel rods 5 are absent. Fixed only in range. Therefore, nuclear fuel rod 5
is preferably shaped as a disc-shaped spiral body with a central part 7 devoid of fuel rods, so that the metal rods can be arranged not only in the outer regions of the molded body but also in the central part.

Next, the molded article of the present invention and the method of the present invention will be explained in detail with reference to Examples.

Example 1 7) As a starting powder for IJ socks, a mixture consisting of 437 parts by weight of pulverized natural graphite, 15 parts by weight of finely ground sulfur and 41.3 parts by weight of nickel metal powder was prepared by dry mixing. The nuclear fuel rod had an internal diameter of 8 (turn) and was coated with a sintered UO2 pellet with a density of 10.49/c, rd. The individual nuclear fuel rods were inserted into a suitable steel tube and the reading tube was sealed on both sides. One end of the taut nuclear fuel rod was wrapped using suitable equipment into a swirler having an outer maximum pitch ≦6rMI and a diameter of about 260 mm.

In order to encapsulate the spiral body, a steel master mold with a diameter of 300 wm is filled with a layer of matrix powder, which is cold pre-pressed and on which an anchor plate with five metal rods (on the outer periphery) is placed. 3 bottles, 2 bottles inside). Another 10 mm thick layer of matrix powder was applied onto the anchor plate.

A nuclear fuel rod spiral was placed thereon, and then 7 trisox powder was filled to a height approximately corresponding to the layer thickness of the nuclear fuel rod spiral. In the central and peripheral areas of the spiral body, the matrix powder content is reduced by additional precompacting to approximately 30
% increased. In order to construct a molded body, 39 swirl bodies were further stacked and arranged in layers based on the above process. After installation, a second anchor plate having metal rods arranged in a staggered manner was inserted into the upper end surface of the whirlpool body. On top of this anchor plate was filled another matrix powder in the same amount as was filled below at the beginning of the process. After heating to 130℃,
Finish pressing was performed at a pressing pressure of 50 MN/-. To react the sulfur/nickel mixture to Ni, 3S2, the temperature was increased to 450° C. while maintaining pressure.

After cooling to 300°C, the molded body was extruded.

The finished pressed molded product had the following characteristics.

ψ=300 H=760 Matrix density 3.3 f/cr
ll density 97% of theoretical value Thermal conductivity 0.8 W/crn,
X-ray thermal expansion coefficient 9.2 stones/m
, K pressure resistance 107MN/m
Example 2 A matrix powder was produced in the same manner as in Example 1. The nuclear fuel rods filled in the capsule, about 5 m long, were bent 20 times, so the height was 450 m++ and the width was 250 mm.

The bent fuel rods were enclosed in a rectangular matrix. After filling the first matrix powder layer and inserting the anchor plate with two metal rods on the outside, six bent fuel rods were placed and the hollows were filled with matrix powder. After introducing the second anchor plate with staggered metal rods, the same amount of matrix powder as filled at the beginning of the method was laminated onto it. Pressing was carried out in the same manner as in Example 1.

The IJ sock properties of the finished pressed compacts corresponded to the properties of the compacts described in Example 1.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal sectional view of a molded body of the present invention, and FIG. 2 is a diagram showing a spiral-shaped nuclear fuel rod. 1... Anchor plate, 2... Head range, 3... Leg range, Cow... Metal rod, 5 - Nuclear fuel rod, 6... Spiral body, 7... Center range, first page Continued 0 Inventors Thomas Schmidt-Pansberg 50 Lindenring, Federal Republic of Germany 50 Lindenring 37 0 Inventors Pans Huschka 9 Grünaustrasse 7, Hanau, Federal Republic of Germany 543-

Claims (1)

[Scope of Claims] (1) A cylindrical or polygonal molded body made of graphite and nickel sulfide for safely enclosing used nuclear fuel rods in a raw or molded shape for a long period of time,
Anchor plate (1) on spatula 12 range (2) and leg range (3)
) and a metal rod (4) fixed to an anchor plate (1) parallel to the main axis of the molded body inside the nuclear fuel rod absent zone, the molded body enclosing a used nuclear fuel rod. . 2. The molded article according to claim 1, wherein the metal rod (4) has a macroscopically rough surface. 3 Molded body 3.4 according to claim 1 or 2 containing nickel sulfide in the form of Ni3S2, in which a nuclear fuel rod (5) is formed into a disc-shaped spiral body (6). , the spiral body has a central region (7) free of nuclear fuel material with a diameter ≧80 mm.
The molded article according to any one of Items 1 to 3. 5 The pitch of the disc-shaped spiral body (6) is ≦6.
The molded article according to any one of claims 1 to 4. 6. The molded article according to any one of claims 1 to 5, characterized only by the disc-shaped spiral body (6) of the nuclear fuel rod (5). 7. A mixture of graphite, nickel and sulfur in which nuclear fuel rods have been embedded is placed in a matrix. By pressing at a temperature higher than 0°C, a cylindrical or polygonal molded body made of graphite and nickel sulfide is produced that can safely encapsulate spent nuclear fuel rods in their original or molded shape for a long time. In the method, graphite is first added to the matrix,
A matrix powder consisting of nickel and sulfur is then added to the anchor plate to which the metal rods are fixed, followed by another anchor plate to which the metal rods are fixed together with the IJ sock powder, and then again to the anchor plate to which the metal rods are fixed. The matrix powder in the area where the nuclear fuel rods are embedded is pre-compressed, and the metal rods are placed only in the area of the anchor plate where there are no nuclear fuel rods in the matrix either above or below. A method for manufacturing a molded body for enclosing used nuclear fuel rods, characterized by attaching a. 86. The method according to claim 7, characterized by a temperature of 400 to 500° C. during finishing pressing.