JPH0675088A - Disassembling method for spent fuel rod - Google Patents

Abstract

PURPOSE:To obtain a simple disassembling method for a spent fuel rod which does not require cutting with a cutting blade being apt to cause malfunction of using device. CONSTITUTION:A spent fuel rod O1a is pinched with electrode plates 2 and the spent fuel rod O1a is heated with a current supplied from a power supplier 3 by way of a circuit cables 7. By supplying power in accordance with the electric resistance of the spent fuel rod O1a, it is heated over 1200 deg.C and below 1500 deg.C, held for more than 5 minutes and cooled. By this processing, the zirconium type material of the fuel clad is oxidized to be ceramic type zirconium oxide and is destructed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconium system which constitutes a spent fuel rod or a spent fuel assembly which is an assembly thereof (in the present invention, these are simply referred to as spent fuel rods). TECHNICAL FIELD The present invention relates to a disassembling method for taking out fuel pellets from a fuel cladding tube made of material.

[0002]

2. Description of the Related Art A conventional spent fuel assembly dismantling device (shearing device) will be described with reference to FIGS.

FIG. 8 showing a spent fuel rod and a fuel assembly.
In the figure, 01 is a spent fuel assembly, 01a is a plurality of fuel rods of the same fuel assembly 01, 01b is a spacer for keeping the distance between the fuel rods 01a, and 01c is a tie plate for fixing the bundle of the fuel rods 01a. Is.

FIG. 9 showing the structure of a single spent fuel rod 01a.
In FIG. 1, 100 is a fuel cladding tube, 101 is a fuel cladding tube 1
The cylindrical fuel pellet 102 built into the fuel cell No. 00 has a blind plug at the end to prevent it from dropping outside during use.
It is attached by welding to 0.

Further, in FIG. 10 showing a disassembling device (shearing device) for a spent fuel assembly, 200 is a shear rod fragment of a fuel rod,
Reference numeral 201 is a pressing blade, 202 is a hydraulic rod for moving the pressing blade 201, and 203 is a hydraulic device for moving the pressing blade. Reference numeral 211 is a cutting blade, 212 is a hydraulic rod for moving the cutting blade 211, and 213 is a hydraulic device for moving the cutting blade.

Reference numeral 221 denotes an extruding metal piece for moving the spent fuel assembly 01 for shearing, 222 denotes a hydraulic rod for moving the extruding metal piece 221, 223 for a fuel assembly extruding hydraulic device, and 224 for a spent fuel assembly. Fuel assembly 01
231 is a gutter for guiding the cut fuel shear fragments 200 to the melting tank, and 241 is a dismantling device (shearing device).
It is the gantry.

When the spent fuel assembly 01 is sheared by using these dismantling devices (shearing devices), one of the tie plates 01c is cut off and the spent fuel assembly 01 is cut off.
Is carried into the guide member 224 of the disassembling device (shearing device), the other tie plate 01c is applied to the push-out fitting 221, and then the fuel assembly pushing hydraulic device 223 is operated in the extending direction to thereby dispose of the spent fuel assembly. Push body 01 one pitch.

Then, the presser blade moving hydraulic device 203 is advanced in the extending direction to press near the tip of each fuel cladding tube 100, and then the cutting blade moving hydraulic device 213 is operated in the extending direction to cut the cutting blade 211. To advance each fuel rod cladding tube 10
The tip portion of 0 is cut, and the resulting cut piece 200 is guided to the melting tank through the gutter 231.

When the tip portion of the fuel rod cladding tube is cut by the above procedure, the holding blade moving hydraulic device 203 and the cutting blade moving hydraulic device 213 are operated in the contracting direction to move the holding blade 201.
And the cutting blade 211 is retracted so that the spent fuel assembly 0
1 is released from the pressing blade 201 and the cutting blade 211. Next, the fuel assembly pushing hydraulic device 223 is operated again in the extension direction to push the spent fuel assembly 01 by one pitch, and thereafter the above-described method is repeated to repeat the fuel rod cladding tube 10.
The pieces 0 are cut one after another, and the cut pieces 200 are sent to the melting tank through the gutter 231.

[0010]

In the conventional disassembling apparatus (shearing device) for a spent fuel assembly shown in FIG. 10, each fuel cladding tube 100 of the spent fuel assembly 01 is pushed by the cutting blade 211, so that the cutting is performed. There is a high possibility that troubles or troubles will occur in the equipment around the blade 211. Repair of the equipment around the cutting blade 211 is a work in a high radiation environment.

For this reason, it is necessary to use a remote control device such as a manipulator, and in addition to the fact that repair takes a lot of time, there are many problems such as an increase in repair costs. In order to solve the above problems, the present invention aims to provide a method for disassembling a spent fuel rod, which is easy to operate and does not need to push each fuel cladding tube of the spent fuel assembly by a cutting blade. I am trying.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a fuel rod composed of a zirconium-based fuel cladding tube containing a spent fuel by a direct energization method.
A method is used in which the cladding tube is destroyed by heating it to a temperature of 0 ° C. or more and less than 1500 ° C., holding it for 5 minutes or more, and then cooling it.

Further, according to the present invention, a fuel rod composed of a zirconium-based fuel cladding tube containing a spent fuel is heated to a temperature of 1200 ° C. or higher but lower than 1500 ° C. by a high frequency heating method, and is held for 5 minutes or more and then cooled. The method of destroying the same cladding tube is also adopted.

Furthermore, the present invention also employs a method of heating the fuel rod in an oxygen-enriched atmosphere to shorten the heating / oxidation time of the fuel cladding tube.

[0015]

When the zirconium-based material of the fuel cladding tube is heated to a high temperature, it is oxidized and the ceramic-based zirconium oxide (Zr
O _2), and therefore, the above-mentioned manner 1200 ° C. or more by a direct current method or high-frequency heating method, after heating and held for 5 minutes or more to a temperature below 1500 ° C., and performs blocking to cool the heating power cooled During the process, the fuel clad tube made into ceramic is cracked and broken finely.

Incidentally, by using forced air cooling or water cooling in the cooling process, it is possible to accelerate the cooling time and the destruction of the fuel cladding tube. Further, according to the present invention, when the method of heating the fuel cladding tube to make the atmosphere around the fuel cladding tube an oxygen-enriched atmosphere, the time until the completion of oxidation can be shortened.

[0017]

Embodiments of the method according to the present invention will be specifically described below with reference to the drawings. First, an embodiment of a method for disassembling a spent fuel rod using a direct current method according to the present invention will be described with reference to FIGS. In FIG. 1, reference numeral 01 denotes a spent fuel assembly, which is specifically the same structure as that shown in FIG. 8, and the description thereof is omitted. 2 is an electrode plate for energizing the fuel rod 01a, 3 is a power supply device for energizing and heating the spent fuel rod 01a, and 4 is a power supply terminal.

5 is a voltmeter showing the potential difference applied to the spent fuel rod 01a, 6 is a circuit ammeter for heating the spent fuel rod 01a, 7 is a circuit wire of the dismantling device, and 7a is a circuit protection safety. A device (for example, a quick blow fuse) is shown. In the system shown in FIG. 1, the power corresponding to the electric resistance of the spent fuel rod 01a is adjusted via the power supply device 3,
When electricity is directly supplied to the spent fuel rod 01a, the spent fuel rod 01a is heated by resistance heating.

On the other hand, the zirconium-based material of the fuel cladding tube 100, which is the object of the present invention, is oxidized to a ceramic-based zirconium oxide (ZrO ₂ ) when heated to a high temperature, so after finding suitable heating conditions and heating. It is expected that the fuel cladding tube 100 will be finely broken by applying a slight external force naturally or by applying a slight external force by quenching. The present invention utilizes this principle to provide an effective and simple dismantling method of spent fuel rods, which is an alternative to the conventional disassembling method using a cutting blade.

FIG. 2 shows an experimental result for finding out an appropriate heating condition in the spent fuel rod dismantling method by the direct current heating method. The figure shows the temperature and heating conditions of the fuel cladding tube when heating in air. According to this, the fuel cladding tube 10
When the temperature of 0 is raised to about 1300 ° C., the rate of decrease of current and the rate of increase of voltage increase in the state where the output set value of the power regulator is constant (basically constant current control is performed). This tendency becomes more remarkable when the temperature of the fuel cladding tube 100 reaches about 1400 ° C.

This phenomenon indicates that the fuel cladding tube 100 is oxidized and rapidly becomes a ceramic type zirconium oxide (ZrO ₂ ) having a high electric resistivity. The fuel clad tube 100 is kept at about 1300 ° C. or more and about 1400 ° C. or less and left for about 10 minutes, and then the heating power is cut off to cool the fuel clad tube by natural cooling in the ambient temperature atmosphere. Cracks and breaks throughout and is finely broken.

The electric power heating condition based on the above knowledge becomes the basis of the optimum heating condition when the direct energization method is applied to the disassembly of the spent fuel rod. On the other hand, the temperature of the fuel cladding tube 100 is 1
Even when the temperature is maintained at about 000 ° C. to 1100 ° C., the oxidation of the fuel cladding tube 100 gradually progresses and becomes a ceramic, but the whole is not uniformly oxidized and uneven oxidation occurs.

Once such a state occurs, the resistance of the fuel cladding tube 100 locally increases, and heat generation at that portion increases. As a result, before the temperature of the fuel cladding tube 100 locally rises and the whole becomes ceramic and becomes fragile, it breaks from this portion and heating cannot be continued, and the disassembly of the fuel cladding tube is complete. Not done to.

Further, the temperature of the fuel cladding tube 100 is set to 1500 ° C.
If it is set too high, the fuel cladding tube may be rapidly oxidized and burned, which may cause a danger and may cause problems such as thermal influence on the fuel pellets contained therein.

As described above, when the spent fuel rod and the fuel cladding tube are heated by the direct energization method, the heating power is adjusted so that the heating temperature of the fuel cladding tube is maintained at 1200 ° C. or more and less than 1500 ° C. The tube is uniformly oxidized during heating without causing troubles such as local breakage, and ceramizes (zirconium oxide ZrO ₂ ).

After the heating is finished, if the heating power is immediately cut off and cooling is carried out by spontaneous cooling, the fuel cladding tube is cracked and broken during the cooling process and finely broken. It is possible to shorten the cooling time and accelerate the destruction of the fuel cladding tube by using forced air cooling or water cooling in the cooling process.
Further, by setting the atmosphere in which the spent fuel rods are placed in the above-mentioned heating step to be an oxygen-enriched atmosphere, it is possible to shorten the time until the completion of oxidation.

The judgment of the completion of oxidation of the spent fuel rods and the fuel cladding tubes is basically made by supplying the heating power by the power regulator which performs the constant current control operation, and the change rate of the potential difference between the heating electrodes is 2 volt / min or more. As a standard, hold for 5 minutes or more in this state. Of course, when the spent fuel rods and the fuel cladding tubes are placed in an oxygen-enriched atmosphere during heating, this heating holding time is shortened.

FIG. 3 shows an example of the first embodiment when the direct current method according to the present invention is used. FIG. 3 shows a method of electrically heating the spent fuel assembly 01 as a whole.
Since the spent fuel assembly 01 has been described above, its description is omitted.

In FIG. 3, 8 is an insulator and a supporting rod for supporting the heating circuit electric wire 7, 9 is a braided electric wire connecting the electric wire 7 and the current-carrying terminal 2, 20 and 21 are insulating materials, 22 is insulating materials 20, 21 Spent fuel assembly tie rate through
1 c is a hydraulic device for pressing the electrode plate 2, 23 is an insulating plate on which the spent fuel assembly 01 is placed, and 24 is an insulating material 21.
Is a support member, and 25 is a mount. This method is suitable when there is a high-power heating power source.

Next, FIG. 4 shows an example of the second embodiment of the present invention.
Shown in. FIG. 4 shows a method for individually heating the fuel cladding tubes 01a by energization. Description of the symbols already described will be omitted. In FIG. 4, 10 is a clamp type electrode plate for sandwiching the fuel cladding tube. Reference numeral 30 is an insulating plate on which the fuel cladding tube 01a is placed. This method is suitable when the capacity of the heating power source is small.

FIGS. 3 and 4 show examples of heating methods for the spent fuel assembly 01 and the fuel cladding tube 01a. By these methods, the spent fuel under the proper heating conditions described above is used. After heating and cooling the rod and the fuel cladding tube 01a, the rod and the fuel cladding tube 01a are dropped into a melting tank provided in the lower part of the heating device, and the impact causes the fuel rod and the fuel cladding tube 0a.
1a is finely broken.

FIG. 5 shows the combination of the heating device and the melting tank for the spent fuel assembly 01, and the state of destruction of the spent fuel assembly 01 in the melting tank. When disassembling the fuel cladding tube 100, the same procedure as in FIG. 5 is performed.
In the example of FIGS. 3 to 5, the atmosphere outside the spent fuel assembly 01 and the fuel cladding tube 01a is not shown, but if it is carried out in the atmosphere or in an oxygen-rich atmosphere in order to promote oxidation. The processing time can be shortened.

In the example shown in FIG. 5, the spent fuel assembly 01 and the fuel cladding tube 01a after heating are directly melted in the melting tank 40.
Although the method of dropping the fuel clad tube 01a into the melting tank 40 has been described above, it is needless to say that the fuel clad tube 01a finely broken by heating and cooling may be transferred and dropped into the melting tank 40 by a known appropriate transfer method.

Next, the case where the spent fuel rod is heated and destroyed by the high frequency heating method will be described with reference to FIG. In FIG. 6, 01a is a fuel rod which is a constituent element of the spent fuel assembly 01 described above. Reference numeral 52 is a heating coil for high frequency induction heating having an internal cooling function, and 53 is an electrode plate for supplying power to the heating coil 52.

54 is a high frequency power source, 55 is a power source terminal, 56
Indicates a circuit wire. Reference numeral 57 denotes a boss for mounting the cooling water supply pipe of the heating coil 52, and 58 denotes a cooling water supply pipe. Reference numeral 59 indicates a boss for mounting the cooling water delivery pipe of the heating coil 52, and 50 indicates a cooling water delivery pipe.

In FIG. 1, when a high frequency current is passed from the high frequency power source 54 to the heating coil 52 via the circuit wire 56 and the electrode plate 53, an eddy current is generated in the fuel rod 01a placed in the magnetic field created by the heating coil. It is generated and heated. In high frequency induction heating, the eddy current flowing in the object to be heated does not flow uniformly in the object to be heated but concentrates on the surface. Therefore, it is more effective to select a frequency corresponding to the outer diameter and thickness of the fuel cladding tube 100. Can be heated.

Since the coil 52 generates heat by its own resistance when energized, and is heated by radiant heat from the fuel cladding tube which is heated to a high temperature, it is usually made of a copper circular tube, and cooling water is made to flow inside it. Make sure the temperature does not exceed safe limits. As described above, the zirconium-based material of the fuel cladding tube 100, which is the subject of the present invention, is oxidized to high temperature ceramic zirconium oxide (ZrO ₂ ).

Therefore, the appropriate heating conditions (1200
After heating at ℃ or more, less than 1500 ℃ and holding for 5 minutes or more), if the heating power source is immediately turned off and cooling is performed by natural cooling, the fuel clad tube made into ceramic is cracked and broken finely during the cooling process. . Further, by forcibly using the air cooling method or the water cooling method in the cooling process, the cooling time of the fuel cladding tube can be shortened and the destruction thereof can be promoted. When the fuel cladding tube 100 is heated, the atmosphere around the fuel cladding tube is made into an oxygen-enriched atmosphere so that the time until the completion of oxidation can be shortened.

FIG. 7 shows a fuel cladding tube 10 which is a component of the fuel rod 01a destroyed by rapid cooling after high frequency induction heating.
0, the end blind plug 101, and the fuel pellet 102 are dropped into the separately provided melting tank 40. A known method such as a belt conveyor is used to introduce the fuel rod fragments destroyed by the rapid cooling after the high frequency induction heating into the melting tank.

[0040]

As described above in detail, in the method for disassembling a spent fuel rod according to the present invention, a fuel rod made of a zirconium-based fuel cladding tube containing a spent fuel is directly subjected to a direct current method or a high frequency heating method. 1200 ℃ or more 1500 ℃
The cladding tube is destroyed by heating to a temperature of less than 5 minutes and holding it for 5 minutes or more, and then cooling the cladding tube, and it is possible to provide a disassembling method of a new principle which replaces the conventional physical disassembling apparatus with a cutting blade.

According to the dismantling method of the present invention, it is possible to provide a fuel dismantling method which is much simpler and has less trouble in the apparatus used as compared with the conventional fuel dismantling apparatus. Further, according to the present invention, if the spent fuel rods are disassembled by heating the fuel rods in an oxygen-rich atmosphere, the disassembly time can be shortened.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an embodiment of a spent fuel rod disassembling method using a direct energization method according to the present invention,

FIG. 2 is a graph showing the results of an experiment conducted to find an appropriate heating condition in the spent fuel rod disassembling method according to the present invention,

3A and 3B are drawings showing an example of a first embodiment of a disassembling method using a direct energization method according to the present invention, in which FIG. 3A is a front view and FIG.
Is a side view,

4 (a) is a front view, FIG. 4 (b) is a side view, and FIG. 4 (a) is a drawing similar to FIG. 3 showing an example of a second embodiment of a disassembling method using a direct current application method according to the present invention.

5A and 5B are drawings showing a state in which a fuel rod disassembled by the direct current method according to the present invention is broken using a melting tank, FIG. 5A is a front view, and FIG. 5B is a side view.

FIG. 6 is a drawing showing an example of an embodiment of a disassembling method using a high-frequency heating method according to the present invention, in which (a) is a front view and (b) is a side view.

FIG. 7 is a cross-sectional view showing a state in which a fuel rod disassembled by the method of the present invention is destroyed in a melting tank,

FIG. 8 is a drawing showing a spent fuel assembly, in which (a) is a front view and (b) is a side view.

FIG. 9 is a front view showing a fuel rod taken out of the fuel assembly, with one portion cut away;

FIG. 10 is a sectional view showing a conventional spent fuel rod disassembling apparatus.

[Explanation of symbols]

 01 Spent fuel assembly 01a Fuel rod 2 Electrode plate 3 Power supply device 4 Power supply terminal 7 Circuit wire 8 Insulator 9 Braided wire 10 Electrode plate 40 Melting tank 52 High frequency induction heating coil 53 Electrode plate 54 High frequency power supply 56 Circuit wire 57 Boss for mounting cooling water supply pipe 59 Boss for mounting cooling water delivery pipe 100 Fuel cladding pipe 102 Fuel pellets

Front Page Continuation (72) Inventor Hiroshige Yasuyuki 5-717-1, Fukahori-cho, Nagasaki City, Nagasaki Research Institute, Mitsubishi Heavy Industries, Ltd. (72) Inventor Yotsumi Otsuka 1-1, Atsunoura-machi, Nagasaki City Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard

Claims (3)

[Claims] 1. A fuel rod made of a zirconium-based fuel cladding tube containing a spent fuel is provided by direct energization method 1200.
A method for disassembling a spent fuel rod, comprising: heating at a temperature of not lower than 1500 ° C and lower than 1500 ° C, holding for 5 minutes or more, and then cooling to destroy the same cladding tube. 2. A fuel rod made of a zirconium-based fuel cladding tube containing a spent fuel is produced by a high frequency heating method to obtain 120
A method for disassembling a spent fuel rod, comprising heating the temperature to 0 ° C. or more and less than 1500 ° C., holding it for 5 minutes or more, and then cooling to destroy the same cladding tube. 3. The method for disassembling a spent fuel rod according to claim 1, wherein the heating of the fuel rod is performed in an oxygen-enriched atmosphere.