JP2000235099A - Incineration disposal of graphite waste containing radioactive nuclide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent dust explosion, and to reduce mandays for incineration, by not pulverizing a graphite waste into fine powder but leaving it as it is or only crushing it into a block form to carry out volume-reducing treatment by the incineration. SOLUTION: A graphite waste 11 used in a nuclear reactor to be waste- disposed is stored in a fusion furnace 16 as it is or after crushed into a block form. The waste 11 is heated by an induction heating coil 14 and an induction thermal plasma torch 13 to be burnt while supplying oxygen or air into the furnace 16. Fluorine gas or chlorine gas ionized and heated by the plasma torch 13 is emitted thereafter from the torch 13 toward an incineration ash of the graphite waste 11 generated by the burning, in a condition where the incineration ash of the graphite waste 11 generated in the burning remains in the fusion furnace 16, and a radioactive nuclide contained in the incineration ash is converted into a fluoride or a chloride to be vaporized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for incinerating waste graphite containing radionuclides, such as graphite moderator, which is discarded after being used in a nuclear reactor.

[0002]

2. Description of the Related Art Conventionally, this kind of graphite waste material has been pulverized into fine particles and then incinerated in a fluidized bed incinerator. This fluidized bed incinerator has a flow straightening plate such as a perforated plate in a container, and is configured such that heated oxygen or air is blown up from holes of the perforated plate. When the fine particles of graphite waste material are put into the container of the incinerator, the fine particles are suspended by the above-mentioned heated oxygen and the like, suspended and incinerated.

[0003]

However, in the above-mentioned conventional method of incinerating graphite waste material by incineration with a fluidized bed incinerator, when the graphite waste material is pulverized, fine particles containing radionuclides are diffused into the atmosphere. In order to prevent the crushing, the crushing must be performed in a closed container, and there is a problem that the crushing device becomes complicated. Further, the fine particles of graphite waste material are flammable substances. If the fine particles are suspended in the air, a dust explosion may occur. Therefore, there is also a problem that explosion prevention measures must be taken. SUMMARY OF THE INVENTION An object of the present invention is to reduce the volume of waste graphite by incineration or by simply crushing it into a block without breaking it down into fine particles, so that dust explosion can be prevented and the number of incineration man-hours can be reduced. An object of the present invention is to provide a method for incinerating waste graphite containing nuclides. Another object of the present invention is to relatively easily decontaminate radionuclides contained in incinerated ash remaining after incineration of graphite waste material,
An object of the present invention is to provide a method for incinerating waste graphite containing radionuclides, which can reduce exposure during maintenance work such as refractory replacement in a melting furnace.

[0004]

The invention according to claim 1 is
As shown in FIG. 1, a step of accommodating the graphite waste material 11 used in the nuclear reactor and discarded in a melting furnace 16 as it is or in a block shape, and supplying oxygen or air into the melting furnace 16. While the graphite waste material 11 is being
And a step of heating and burning by the induction thermal plasma torch 13, and a step of heating the induction thermal plasma torch 1 with the incinerated ash of the graphite waste material 11 generated by the combustion remaining in the melting furnace 16.
Converting the radionuclides in the incinerated ash to fluorides or chlorides and volatilizing them by discharging fluorine gas or chlorine gas heated by ionization from 3 toward the incinerated ash from the induction thermal plasma torch 13; This is a method for incineration of graphite waste materials containing.

In the method for incinerating waste graphite according to the first aspect, the waste graphite 11 can be incinerated and reduced in volume simply by crushing the waste graphite 11 as it is or without breaking it into fine particles. In addition, the number of incineration steps can be reduced, and the occurrence of dust explosion can be prevented. Further, since radionuclides contained in the incineration ash remaining after the incineration of the graphite waste material 11 can be converted into their fluorides or chlorides and volatilized,
Radionuclide contained in incineration ash can be decontaminated relatively easily,
Exposure can be reduced in maintenance work such as replacement of refractories in the melting furnace 16.

[0006]

Embodiments of the present invention will now be described with reference to the drawings. As shown in FIG. 1, the graphite waste material 11 is a graphite moderator which is discarded after being used in a nuclear reactor in this embodiment, and the graphite waste material 11 is incinerated by an incinerator 12. Further, when the entire shape of the used graphite waste material is small, it is directly introduced into the incineration apparatus 12 though not shown. When the graphite waste material is large, it is crushed into a small cylindrical graphite waste material 11 having a predetermined size as shown in the figure, and then is put into the incineration treatment device 12. In the incineration apparatus 12, an induction thermal plasma torch 13 and an induction heating coil 14 are used together as a heating source.
The incinerator 12 is a melting furnace 1 capable of storing the graphite waste material 11.
6, the induction heating coil 14 provided around the melting furnace 16, the induction thermal plasma torch 13 provided facing the graphite waste material in the melting furnace 16, and formed at the bottom of the melting furnace 16. A valve 17 for opening and closing the discharge port 16a.

The melting furnace 16 has a bowl-shaped lower furnace body 18 formed so as to be able to accommodate the graphite waste material 11, and the lower furnace body 18.
And an upper furnace body 19 shaped like a bowl. The lower furnace body 18 and the upper furnace body 19 are formed of a magnesia-based or alumina-based refractory having heat resistance, and the like.
The outer surfaces of the lower furnace body 18 and the upper furnace body 19 are
1 and the upper heat insulating wall 22 respectively. One end of a gas discharge pipe 23 is connected to the outer peripheral surface of the upper furnace body 19, and the other end of the gas discharge pipe 23 is connected to a blower (not shown) via an exhaust gas purification device (not shown).

Although not shown, the exhaust gas treatment apparatus includes a secondary combustor for burning unburned carbon, carbon monoxide, hydrogen, etc., a cooling tower for cooling the exhaust gas from the secondary combustor with water spray, dust and dust. Ceramic or bag filter that removes dioxins in a form, and HEPA (High Efficiency Part) that removes almost all radionuclides.
an air filter), an alkaline scrubber for neutralizing hydrogen chloride and sulfur oxides caused by burning vinyl chloride and rubber, and a denitration tower for removing nitrogen oxides caused by plasma combustion in the melting furnace 16. A charging cylinder 24 into which the graphite waste material 11 can be charged is connected to the upper surface of the upper furnace body 19,
The charging port at the upper end of the charging cylinder 24 is openably closed by a lid 24a. The outer peripheral surface of the charging cylinder 24 is a cylindrical heat insulating wall 24b.
Coated. Reference numeral 26 in FIG. 1 is a viewing window provided in the upper furnace body 19 for monitoring the incineration status of the graphite waste material 12 in the melting furnace 16.

The induction heating coil 14 is buried in the lower heat insulating wall 21 so as to surround the outer peripheral surface of the lower furnace body 18, and is electrically connected to a high-frequency power source (not shown). Further, the induction thermal plasma torch 13 is attached to the outer peripheral surface of the upper heat insulating wall 22 toward the inside of the lower furnace body 18, and only one is shown in FIG. Preferably, it is attached. As shown in detail in FIG. 2, the plasma torch 11 includes a base plate 27 attached to the outer peripheral surface of the upper heat insulating wall 22, a small-diameter ceramic tube 28 erected on the base plate 27, and a small-diameter ceramic tube 28
A large-diameter ceramic tube 29 which is loosely fitted to the small-diameter ceramic tube 28 and which is fitted into the large-diameter ceramic tube 29 and whose lower end is attached to the base plate 27.
9, a central holder 33 for holding the central part of the tube 9, an upper holder 34 fitted to the upper part of the large-diameter ceramic tube 29 and a lower end attached to the upper surface of the central holder 33, and a lower end to the upper end of the small-diameter ceramic tube 28. Gas inlet pipes 36a and 36b are inserted through the upper holder 34 so as to face and introduce a predetermined gas into the small-diameter ceramic pipe 28.

The upper insulating wall 22 and the base plate 27 have tapered discharge holes 22a and communication holes 27 having the same hole center.
a is formed, and a large-diameter hole 19 a facing the discharge hole 22 a and the communication hole 27 a is formed in the upper furnace body 19. The predetermined gas introduced into the small-diameter ceramic tube 28 from the gas introduction pipes 36a and 36b is oxygen or air when the graphite waste material 11 is burned, and the radionuclide contained in the incinerated ash remaining after the combustion of the graphite waste material 11 is performed. At the time of removal, it is fluorine gas or chlorine gas. A torch induction coil 37 is wound below the large diameter ceramic tube 29, and the coil 37 is electrically connected to a high frequency power supply 38. A supply passage 27b is formed in the base plate 27 to communicate with a lower end of a cooling water passage 39 formed between the small-diameter ceramic tube 28 and the large-diameter ceramic tube 29. A discharge passage 34a communicating with the upper end is formed.

The cooling water in a cooling water tank (not shown) is supplied to the supply passage 27b by a pump (not shown), and the cooling water passing through the cooling water passage 39 and the discharge passage 34a is cooled by a cooler (not shown). ) To return to the cooling water tank. This cooling water is circulated at a pressure lower than the atmospheric pressure in order to prevent water leakage when the small-diameter ceramic tube 28 or the large-diameter ceramic tube 29 is broken. Gas inlet pipes 36a, 3
The base end of 6b is connected to a first tank (not shown) for storing the oxygen or air and a second tank for storing the fluorine gas or chlorine gas. Alternatively, it is configured to be switchable so that either the chlorine gas is introduced into the small-diameter ceramic tube 28. Reference numeral 41 in FIG. 2 denotes an electromagnetic shield member that covers the plasma torch 13.

Returning to FIG. 1, the discharge port 16a is provided with the waste graphite material 1.
The valve 17 is provided for supplying oxygen or air into the melting furnace 16 at the time of combustion of 1 and for discharging the incinerated ash remaining in the melting furnace 16, and a valve 17 is attached to the lower surface of the melting furnace 16. The valve 17 is a slide valve. This valve 1
Reference numeral 7 denotes a base hole 43a attached to the lower surface of the melting furnace 16 and communicating with the discharge port 16a, as shown in detail in FIGS.
A base plate 43 having a discharge port 16a and a base hole 4
3a, an insert nozzle 44 having a nozzle hole 44a, a bottom plate 46 and a seal plate 47 attached to the lower surface of the base plate 43, and a slide plate slidably inserted between the bottom plate 46 and the seal plate 47. And a hydraulic cylinder 49 attached to the base plate 43 and driving the slide plate 48. Holes 46a and 47a communicating with the nozzle holes 44a are formed in the bottom plate 46 and the seal plate 47, respectively. The slide plate 48 has the holes 46a,
A communication hole 48a that can communicate with 47a and a number of small holes (not shown) that can blow oxygen or air toward the nozzle hole 44a are formed near the communication hole 48a. These small holes are formed in blowing passages 48 formed in the slide plate 48.
b, it is connected to an oxygen tank or an air tank (not shown). The slide plate 48 is connected to a piston 49a of a hydraulic cylinder 49 via a connector 50. When the piston 49a of the hydraulic cylinder 49 is projected, the discharge port 16a is closed by the slide plate 48 and the small hole faces the discharge port 16a. When the piston 49a is retracted, the discharge port 16a communicates with the communication hole 48a of the slide plate 48. It is configured to be open. Reference numeral 51 in FIGS. 3 and 4 denotes a chute nozzle having a chute hole 51a.

In this embodiment, graphite moderator has been described as graphite waste material. However, graphite refractories of waste incinerators or melting furnaces, or nuclear fusion materials, may be used for graphite parts containing radionuclides. A heat-resistant wall of a furnace may be used. It is preferable that these waste graphite materials are crushed into square blocks and then charged into an incineration treatment device. Further, in this embodiment, the valve that closes the communication hole with the three plates of the bottom plate, the slide plate, and the seal plate has been described, but a valve that closes the communication hole with the two plates of the bottom plate and the seal plate may be used. Further, in this embodiment, the valve is driven by a hydraulic cylinder, but may be driven by an air cylinder or another actuator.

A method of incinerating waste graphite using the incineration apparatus configured as described above will be described. First, with the valve 17 closed (FIG. 3), the discharge port 16 is filled with sand 52, and oxygen or air is introduced into the melting furnace 16 through small holes (not shown) through the blowing passage 48b of the slide plate 48. Blow continuously. Next, the lid 24b (FIG. 1) is opened and the graphite waste material 11 is charged into the melting furnace 16, and then the lid 24b is closed. When a high-frequency voltage is applied to the induction heating coil 14 in this state, an induction current flows through the graphite waste material 11 in the melting furnace 16 by electromagnetic induction, and the Joule heat generated at this time burns the graphite waste material 11.

On the other hand, cooling water flows through the supply passage 27b, the cooling water passage 39, and the discharge passage 34a of the induction thermal plasma torch 13, and oxygen or air flows through the gas introduction pipes 36a and 36b into the small diameter ceramic pipe 28. When a high frequency voltage is applied to the induction thermal plasma torch 13 to ionize the oxygen or air, and the ionized oxygen or air is induction heated by the torch induction coil 37, a high-temperature plasma gas 13a of about 10,000 ° C. is generated, This gas 13a is connected to the communication hole 27.
a through the discharge hole 22a and the large-diameter hole 19a.
6 is released. This plasma gas 11a is supplied to the melting furnace 1
When released to 6, the temperature becomes about 3000 ° C., but the heat of the high-temperature plasma gas 13a causes the graphite waste material 11 to burn more quickly, that is, the combustion of the graphite waste material 11 is promoted. The gas generated during the combustion of the graphite waste material 11 is guided to an exhaust gas treatment device (not shown) through a gas discharge pipe 23, purified, and then exhausted by a blower (not shown).

Further, when the combustion of the graphite waste material 11 is completed, a small amount of the incinerated ash of the graphite waste material 11 remains in the melting furnace 16. This incinerated ash contains radionuclides such as cobalt 60. Therefore, the blowing passage 48 of the slide plate 48
b, the supply of oxygen or air from the gas introduction tubes 36a, 36b into the small-diameter ceramic tube 28 is stopped, and then the gas introduction tubes 36a, 36b After flowing fluorine gas or chlorine gas into the small-diameter ceramic tube 28, a high-frequency voltage is applied to the induction thermal plasma torch 11 to ionize the fluorine gas or chlorine gas, and the ionized fluorine gas or chlorine gas is used for the torch. Induction heating is performed by the induction coil 37.

At this time, a high-temperature plasma gas 11a of about 10,000 ° C. is generated and discharged into the melting furnace 16 through the communication hole 27a, the discharge hole 22a and the large-diameter hole 19a. When this plasma gas 11a is released into the melting furnace 16, about 3
Although the temperature becomes 000 ° C., the high-temperature plasma gas 11a reacts with the radionuclide to convert the radionuclide into its fluoride or chloride and volatilize it. The volatilized radionuclide fluoride or chloride is led to the exhaust gas treatment device through the gas discharge pipe 23 and purified, and then exhausted by the blower. As a result, the radionuclide contained in the incinerated ash is reduced, that is, the radioactivity level of the incinerated ash is reduced, so that it is possible to reduce the exposure in maintenance work such as refractory exchange in the melting furnace 16. When the amount of incinerated ash in the melting furnace 16 reaches a predetermined amount, the valve 17 is set to the hydraulic cylinder 49.
, And the communication hole 48a of the slide plate 48 communicates with the discharge port 16a (FIG. 4). At this time, first sand 52
Is discharged from the chute hole 51a of the chute nozzle 51, and subsequently, the incinerated ash whose radioactivity level has decreased is discharged.

[0018]

As described above, according to the present invention, graphite waste material is heated and burned by an induction heating coil and an induction heat plasma torch while supplying oxygen and the like into a melting furnace.
In the state where the incinerated ash of the graphite waste remains in the melting furnace, the radionuclide in the incinerated ash is discharged by discharging the fluorine gas or the chlorine gas heated by ionization with the induction thermal plasma torch toward the incinerated ash. Converted to chlorides or chlorides and volatilized, it must be crushed in a closed container to prevent fine particles containing radionuclides from being released into the atmosphere. Compared with the method of incineration, in the present invention, the graphite waste material is not atomized,
By crushing as it is or by simply crushing it into a block, incineration and volume reduction can be performed, and the number of incineration steps can be reduced.

Further, in comparison with the conventional method of making graphite waste fine and burning it, the present invention does not make the waste graphite fine because there is a possibility that a dust explosion may occur. No dust explosion occurs because it is only necessary to crush it as it is or in a block shape. Further, according to the present invention, since radionuclides contained in the incinerated ash remaining after the incineration of graphite waste can be converted into fluorides or chlorides and volatilized, the radionuclides contained in the incinerated ash can be relatively easily removed. I can dye it. As a result, it is possible to reduce the exposure in maintenance work such as refractory replacement in the melting furnace.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an apparatus for incinerating graphite waste according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a portion A in FIG.

FIG. 3 is an enlarged sectional view of a portion B in FIG. 1;

FIG. 4 is a sectional view corresponding to FIG. 3, showing a state in which a discharge plate of a melting furnace is opened by sliding a slide plate of a valve.

[Explanation of symbols]

 11 Waste Graphite 13 Induction Thermal Plasma Torch 14 Induction Heating Coil 16 Melting Furnace

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F23G 7/00 ZAB F23J 1/00 A F23J 1/00 G21F 9/02 501Z G21F 9/02 501 B09B 3 / 00 303J F-term (reference) 3K061 AA23 AB01 AC09 BA04 BA05 BA10 CA13 CA14 DA02 DB11 DB17 DB20 NA01 NA07 NA18 NA19 4D004 AA50 AB09 CA04 CA27 CA28 CB13 CB33 CB50

Claims (1)

[Claims] A step of crushing and storing a graphite waste material (11) used in a nuclear reactor and discarded in a melting furnace (16) as it is or in a block shape; Heating and burning the graphite waste material (11) with an induction heating coil (14) and an induction thermal plasma torch (13) while supplying oxygen or air; and incineration ash of the graphite waste material (11) generated by the combustion. Is left in the melting furnace (16), and the induction thermal plasma torch is
By releasing the fluorine gas or chlorine gas ionized and heated by (13) from the induction thermal plasma torch (13) toward the incineration ash, the radionuclide in the incineration ash is converted into its fluoride or chloride. Converting and volatilizing the waste.