KR20140132267A - The volume reduction processing method of radioactive waste using the powder metallurgy technology - Google Patents

Abstract

The present invention provides a method for reducing the volume of radioactive waste by using a powder metallurgy technology, which solidifies flammable or nonflammable radioactive waste generated in nuclear facilities into a fixed size through compression molding and therefore can convert the radioactive waste into a non-dispersive material that has a high volume-reduction ratio and is stable both physically and chemically. According to the present invention, the method for reducing the volume of radioactive waste by using compression molding comprises: a pre-processing step that fabricates slugs for smooth compression molding by pre-compacting radioactive waste through a pre-compacting machine; a green pellet fabrication step that fabricates green pellets having a fixed size and density by compression-molding the slugs, which are fabricated in the pre-processing step, under a fixed temperature and pressure condition; and a step of fabricating sintered pellets by sintering the green pellets under a fixed temperature and pressure condition.

Description

Technical Field [0001] The present invention relates to a method for processing radioactive waste using powder metallurgy,

The present invention can increase the rejection rate of radioactive waste by solidifying the flammable or nonflammable radioactive waste generated in a nuclear facility into pellets of a certain size by using powder metallurgy technology, The present invention relates to a radioactive waste decontamination method capable of producing an acidic radioactive waste.

Generally, radioactive wastes occur in large quantities when operating nuclear facilities or in dismantling facilities. The radioactive waste generated in such a way is not likely to meet the requirements for the receipt of the radioactive waste repository, as well as the enormous disposal cost of disposing the radioactive waste directly at the disposal site without reducing or stabilizing it.

Solid radioactive wastes generated during decommissioning of nuclear facilities can be classified into non-combustible radioactive waste and combustible radioactive waste. Non-combustible radioactive wastes include metals and the like, and these metal wastes are mainly treated by methods such as melting. The combustible radioactive waste is treated by a method such as incineration.

Among them, when incineration of combustible radioactive waste is carried out, the volume reduction ratio of the waste is about 50 to 80%, and after the incineration, the reactivity, which can be called secondary waste, is ash .

However, such incineration ash has a large dispersibility and is inconvenient to handle, and since harmful heavy metals or radionuclides are concentrated due to the persimmon extract's unique sweetening effect, it is necessarily accompanied by solidification treatment or stabilization treatment in a form suitable for disposal.

Conventional stabilization treatment methods related to combustible solid radioactive waste such as incineration ash have been limited to techniques for adding and mixing cement, polymer, and the like to incineration ash. That is, as shown in FIG. 1, the incineration material processing technology, which is a conventional combustible solid radioactive waste, is a method of mixing combustible radioactive waste incineration powder together with additives such as cement or polymer, Solidified product.

However, the conventional method of solidifying radioactive waste as described above can contribute to stabilization of radioactive waste disposal, but since a separate solidifying agent such as cement or polymer is mixed with the ash that is concentrated radioactive material, And the effect of reducing radioactive waste is reduced.

In addition, since the conventional method for solidifying radioactive waste as described above requires expensive non-radioactive material such as cement or polymer to be added to the ash, which is a radioactive waste, the disposal cost of the waste is increased and the economical efficiency is lowered. It is necessary to use a liquid such as water in order to cause secondary radioactive contamination.

[0004] In order to increase the radioactive waste disposal cost, there has been considered a method of charging the incineration as a radioactive waste into a storage container having high integrity and then filling the waste into the storage container. However, There is a problem in that the cost of the high-integrity storage container to be charged is so high that the economic burden due to the increase in disposal cost is increased.

Korean Patent Laid-Open Publication No. 1986-0000671, Patent Publication No. 2013-0022064

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method and apparatus for separating flammable or non-combustible radioactive waste generated in a nuclear power facility into a pellet And solidifying the pellets into a safe form that does not cause cracking and expansion so as to increase the rejection rate of the radioactive waste and to provide physically and chemically stable non-dispersible wastes The present invention also provides a method of deporting radioactive waste using powder metallurgy technology which can maintain its integrity even after storage for a long period of time.

According to another aspect of the present invention, there is provided a method of processing radioactive waste using powder metallurgy, comprising the steps of: (a) preparing a radioactive waste through a preliminary molding machine to produce a preform for smooth compression / Wow; (b) compressing and molding the preformed body manufactured through the pretreatment under a predetermined temperature and pressure condition to produce a molded body having a predetermined size and density; (c) sintering the molded body under a constant temperature and pressure condition to produce a sintered body.

Here, the radioactive waste in step (a) may be a powdery ash generated during the incineration of the combustible radioactive waste, a dry powder of the boric acid waste liquid generated during operation in the nuclear power generating facility, a metal waste as the non-combustible radioactive waste It can be a slag.

In the step (a), the ash powder is charged into the vessel and mixed with the bottom ash generated in the incineration treatment of the combustible radioactive waste, the fly ash ash, and the fly ash filter fly ash, A container handling step of mixing the mixed material for a predetermined period of time, re-mounting the mixed container to an adapter, rotating the container, and loading the container into a hopper of the preformer; A preliminary molding step of molding the ash through the hopper into a slug having a predetermined size through a preforming machine; And an assembling step of passing the slug formed through the preformer to the granulator again to form particles of a granule shape having a predetermined size.

Meanwhile, in the step (b), the forming pressure for forming the formed body may be set within a range of 100 to 500 MPa.

In the step (c), the sintering temperature for forming the sintered body may be set within a range of 800 to 1200 ° C.

In the vessel handling step, the mixed vessel may be mounted on an adapter, and the vessel may be inverted upside down and vibrated through a vibrator to load the ash powder into the hopper.

According to the method for treating radioactive waste using the powder metallurgy technique of the present invention having the above-described structure, combustible or non-combustible radioactive waste generated in a nuclear power facility is compressed and molded under a certain pressure condition to produce a pellet- The sintering treatment of the formed body is carried out within a predetermined temperature range to greatly increase the radioactive waste disposal rate and can be manufactured as physically and chemically stable non-dispersible waste, thereby maintaining its stability and soundness during long-term storage .

In addition, the amount of waste to be charged to the storage container can be greatly increased due to the increase in the radioactive waste disposal rate, so that the amount of expensive storage containers can be minimized, and the disposal cost of radioactive waste (including transportation costs) It is possible to greatly reduce the cost of use and greatly reduce the economic burden due to waste treatment.

Further, in the process of producing a pellet-shaped molded body by compression / molding, a preforming process for producing slug or granule-shaped particles is additionally carried out to improve the fluidity of the powder such as the ash and the like, It is possible to efficiently produce the formed body and improve the quality of the formed body.

In addition, by setting the molding pressure at a pressure in the range of 100 to 500 MPa at the time of compression and molding of the radioactive waste by a press machine or the like, the density of the molded body is excessively lowered to overcome the problem of difficulty in handling, It is possible to overcome the problem that the density becomes excessively high and cracks are generated in the formed body.

Further, if the sintering temperature is set to a temperature within the range of 800 to 1200 DEG C during the sintering of the compact, it is possible to prevent the sintering phenomenon which may occur when the sintering temperature becomes excessively high, It is possible to overcome the difficult problem of handling the sintered body which may occur when the temperature is lowered.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram schematically showing a conventional combustible radioactive waste treatment process. FIG.
BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to a radioactive waste disposal system,
FIG. 3 is a process chart sequentially showing a process of reducing radioactive waste using the powder metallurgy method according to the present invention. FIG.
FIG. 4 is a graph showing the relationship between the apparent density and the reducing ratio according to the pre-forming pressure of the granules in which the preform slug prepared according to the first embodiment of the present invention is assembled.
5 is a graph showing the relationship between the molding density and the reducing ratio according to the molding pressure of a green pellet manufactured according to the second embodiment of the present invention
6 is a graph showing the relationship between the sintering temperature and the reducing ratio of the sintered body manufactured according to the third embodiment of the present invention, according to the molding pressure.
FIG. 7 is a graph showing fracture strength of a sintered body manufactured according to the fourth embodiment of the present invention measured at a sintering temperature according to molding pressure. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a schematic view illustrating a system for processing a radioactive waste using powder metallurgy according to an embodiment of the present invention. FIG. 3 is a flowchart illustrating a process for reducing radioactive waste using a powder metallurgy method according to the present invention, .

2 and 3, a method of treating radioactive waste according to the present invention is a powder metallurgy process in which powdery radioactive waste is pressurized and molded under a predetermined pressure, and then heated and sintered .

Examples of the radioactive waste treated by the powder metallurgy process of the present invention include powdery ash generated during the incineration of the flammable radioactive waste, dry powder of the boric acid waste liquid generated during operation of the nuclear power plant, It may be a slag generated during melting of metal waste which is a non-combustible radioactive waste.

In the embodiment of the present invention to be described below, the case of the powder ash generated in the incineration process of the combustible radioactive waste will be described as an embodiment.

A method for depressurizing radioactive waste according to the present invention will be described with reference to FIGS. 2 and 3. FIG.

First, a container 110 containing a radioactive waste ash powder is mounted on a tumbler 112 as shown in FIG. 2, and the powder is mixed with the ash powder for a predetermined period of time. The incineration ash powder stored in the vessel 110 may be classified into a bottom ash, a fly ash, a fly ash filter, and a fly ash depending on the generation process. (110). After the mixing of the ash powder is completed, the mixed vessel 110 is mounted on the adapter 114, and the ash powder mixed in the vessel 110 is pre-compacted by a pre-compacting machine 116 via a hopper 117 (S201).

A cylindrical drum having a capacity of 200 liters may be used as the container 110 for storing and mixing the incineration ash. When the incinerator is introduced into the preformer 116, The incinerator mixed powder is charged into the hopper 117 of the preformer 116 when the vessel 110 mounted on the vessel 110 is turned upside down and vibrated by a vibrator 115. Subsequently, the ash material charged into the preformer 116 is compressed and stirred through the internal screw in the course of passing through the preformer 116, and is finely cut at the downstream end to obtain a slug slug 120. (S102)

The slug 120 manufactured through the preformer 116 is conveyed through a conveyer and then introduced into a granuling machine 124. The slug 120 passes through the inside of the granulator 124, (granules) 130 in the form of small granules (S103)

Here, granulation of the slag 120 made through the preformer 116 is referred to as granulation. Generally, since the powdery ash is easily dispersed, the fluidity of the powder of the ash can be improved. A preforming process is required in which the ash powder is formed into slag 120 and granules 130 as described above.

The granular ash produced by the preformer 116 and the granulator 124 is introduced into the hopper 136 of the press machine 134 and then pressurized in the presser 134 by a predetermined pressure And is formed into a green pellet 140 in the form of a cylindrical pellet having a predetermined size and density (S201).

At this time, the forming pressure for forming the formed body 140 in the press machine 134 may be set within the range of 100 to 500 MPa, preferably 300 MPa. The reason for setting this range is that when the molding pressure is applied at a pressure of 100 MPa or less, the molded body 140 is low in density and weak, which is difficult to handle, and when applied at a pressure higher than 500 MPa , There is a possibility that cracking may occur in the sintering process of the formed body 140.

Meanwhile, since the compact 140 formed by pressurizing and molding in the press 134 is in a state of being physically bonded through the compression and molding processes, the bonding force is loosened after a certain period of time, So that cracks may be generated, which may cause the molded body 140 to break or stretch. Therefore, when the molded body 140 is stored in the container 110, stress is applied to the container 110 due to the expansion force of the molded body 140, which may cause the container 110 to be damaged during storage for a long period of time .

Due to such a problem, there is a need for a heat treatment process in order to not only remove the internal stress of the press-molded formed body 140 in the press machine 134 but also to increase the detergency ratio. That is, the formed body 140 after the compression / molding process is sintered in a furnace 144 under a predetermined temperature condition to produce a final sintered pellet 150 (S301).

As described above, the sintered body 140 produced by the pressure molding is sintered in the heating furnace 144, whereby the internal stress of the formed body 140 generated by the compression in the preceding step is released, So that the stability of the incineration materials can be maintained even if the incineration materials are stored in the container 110 for a long period of time. In addition, the amount of the incineration ash can be increased, so that a greater amount of the ash can be stored.

At this time, the sintering temperature for forming the sintered body 150 in the heating furnace 144 is preferably set to a temperature within the range of 800 to 1200 ° C because the sintering temperature of the formed body 140 is higher than 1200 ° C There is a possibility that the formed body 140 is melted, and when the sintering temperature is lower than 800 ° C, there may be difficulties in handling.

The sintered body 150 that has undergone the compression / molding process and the sintering process as described above is charged into the container 110, which is a radioactive waste treatment container, and is stored in the disposal paper in a tightly sealed state for a long period of time. )

Since the sintered body 150 subjected to the final sintering treatment has a volume reduced to about 1/8 of that of the raw powder of the incinerator initially charged, the amount of radioactive Waste can be charged. Therefore, since the amount of the container 110 for storing the radioactive waste can be reduced, the processing cost of the radioactive waste can be greatly reduced. In addition, the molded body 140 which has been pressure-molded through the press machine 134 is heat-treated and sintered in the heating furnace 144 to prevent cracking due to expansion of the molded body and to maintain a strong chemical bond, Stability and soundness can be maintained.

< Example  1> By assembly Sweetening effect

Step 1: Combustible wastes from the nuclear facility are incinerated through the incineration process and converted into the form of ash. These incinerators are classified into bottom ash, post-combustion ash, and fly ash filter fly ash depending on the location of the generation process. The composition of the ash is somewhat different according to the composition of combustible waste, but approximately 70 ~ 90% The weight ratio of the fly ash to the combustion furnace is 5 ~ 15%, and the weight of the fly ash filter is 5 ~ 20%. Here, in this embodiment, the ash is mixed with 70% of the bottom ash, 15% of the fly ash, 15% of the fly ash filter, and the ash is mixed for 1 hour.

The apparent density of the ash powders mixed through the mixing process was measured to be 0.29 (g / cm 3). A preform (slug) was then produced at a molding pressure of 100 MPa and 300 MPa using a press. The density of the prepared preform was approximately 10.1 mm in diameter, 3.7 to 4.0 mm in height, and 0.6 g in weight. The density was 1.86 (g / cm 3) when molded at 100 MPa and 2.09 g / cm &lt; 3 &gt;). The preform thus prepared was granulated using a granulator having a sieve having a diameter of 1 mm. The apparent density of the granulated granules after pressurization to 100 MPa was 0.89 (g / ㎤), which was 3.1 higher than that of the ash powder, and the apparent density of the granulated granules after pressurization to 300 MPa was 1.04 / ㎤), indicating that the weight ratio increased by 3.6. The graph of FIG. 4 is a graph showing the apparent density and the reduction ratio of the granules in which the preform (slug) produced according to the preforming pressure is assembled. Here, the sweetening ratio is a value obtained by dividing the apparent density of the granules by the apparent density of the powder.

Thus, in the conventional method of solidifying radioactive waste, when the incineration material granules are used in comparison with the incineration material powder, the weight ratio is increased by about 3 to 4 times according to the density of the granules.

< Example  2> Depending on molding pressure Sweetening effect

Step 1: Combustible wastes from the nuclear facility are incinerated through the incineration process and converted into the form of ash. These incinerators are classified into bottom ash, post-combustion ash, and fly ash filter fly ash depending on the location of the generation process. The composition of the ash is somewhat different according to the composition of combustible waste, but approximately 70 ~ 90% The weight ratio of fly ash and fly ash is 5 ~ 15% and 5 ~ 20%, respectively. Here, in this embodiment, the ash is mixed with 70% of the bottom ash, 15% of the fly ash, 15% of the fly ash filter, and the ash is mixed for 1 hour.

The apparent density of the ash powders mixed through the mixing process was measured to be 0.29 (g / cm 3). A preform (slug) was then produced at a molding pressure of 100 MPa using a hydraulic press. The dimensions of the preform thus produced were approximately 10.1 mm in diameter, 3.7 to 4.0 mm in height and 0.6 g in weight, and a density of 1.86 g / cm 3 was measured. The preform thus prepared was granulated using a granulator having a sieve with a diameter of 1 mm, wherein the apparent density of granules was measured to be 1.04 (g / cm 3).

 Step 2: A green pellet was produced by pressurizing the ash granules with a molding pressure of 100 to 500 MPa in a hydraulic press. The molding densities of the compacts were about 10.1 mm in diameter, 5.5 to 6.5 mm in height and 1.0 g in weight. The molding densities of the compacts molded at 100 MPa, 300 MPa and 500 MPa were 1.88 (g / ㎤) , 2.07 (g / cm3) and 2.19 (g / cm3), respectively. Based on the apparent density of the ash powder of 0.29 (g / cm 3), the reduction ratios according to the molding pressures of 100 MPa, 300 MPa and 500 MPa were calculated to be 6.48, 7.14 and 7.55, respectively. Fig. 5 shows the molding density and the weight ratio of the molded article according to the molding pressure.

< Example  3> Depending on sintering temperature Sweetening effect

Step 1: Combustible wastes from the nuclear facility are incinerated through the incineration process and converted into the form of ash. These incinerators are classified into bottom ash, post-combustion ash, and fly ash filter fly ash depending on the location of the generation process. The composition of the ash is somewhat different according to the composition of combustible waste, but approximately 70 ~ 90% The weight ratio of fly ash and fly ash is 5 ~ 15% and 5 ~ 20%, respectively. Here, in this embodiment, the ash is mixed with 70% of the bottom ash, 15% of the fly ash, 15% of the fly ash filter, and the ash is mixed for 1 hour.

The apparent density of the ash powders mixed through the mixing process was measured to be 0.29 (g / cm 3). A preform (slug) was then produced at a molding pressure of 100 MPa using a hydraulic press. The dimensions of the preform thus produced were approximately 10.1 mm in diameter, 3.7 to 4.0 mm in height and 0.6 g in weight, and a density of 1.86 g / cm 3 was measured. The preform thus prepared was granulated using a granulator having a sieve with a diameter of 1 mm, wherein the apparent density of granules was measured to be 1.04 (g / cm 3).

 Step 2: A green pellet was produced by pressurizing the ash granules with a molding pressure of 100 to 500 MPa in a hydraulic press. The molding densities of the compacts were about 10.1 mm in diameter, 5.5 to 6.5 mm in height and 1.0 g in weight. The molding densities of the compacts molded at 100 MPa, 300 MPa and 500 MPa were 1.88 (g / ㎤) , 2.07 (g / cm3), and 2.19 (g / cm3), respectively

Step 3: The compacts produced at a molding pressure of 100 to 500 MPa were sintered at 800 to 1200 ° C for 2 hours under air atmosphere conditions. At this time, both the temperature rise and the cooling of the molded body were set at 4 ° C per minute. FIG. 6 shows the sintering ratio of the sintered body according to the sintering temperature according to the molding pressure under the experimental conditions. Here, the sintering ratio of the sintered body is based on the apparent density of the ash powder of 0.29 (g / cm 3). As can be seen from FIG. 6, it can be seen that the reducing ratio decreases with increasing sintering temperature, but tends to increase. The reason for this is that it is expected that some of the ash residue will be densified as volatile residual pores are removed as the temperature increases, resulting in an increase in the salting ratio.

< Example  4> Compressive strength measurement

Preliminary molding Slugs preliminarily molded at 100 MPa were assembled through a granulator, and the granules were molded at molding pressures of 100 MPa, 300 MPa, and 500 MPa, respectively. Then, the sintered body was sintered at sintering temperatures of 800 ° C, 1000 ° C and 1200 ° C for 2 hours, respectively. As a result, the dimensions of the sintered body were approximately 10 mm in diameter and 8.5 mm in length, and the L / D ratio was 0.85. The fracture strength of the sintered body having the L / D ratio was measured by using a universal tester (Instron 5582). The results are shown in FIG.

As shown in FIG. 7, the fracture strength tends to increase with increasing sintering temperature, and the fracture strength tends to increase with increasing molding pressure even at the same sintering temperature.

Here, the compressive strength test of the solid waste is described in KS F2405. In case of hard solid, the compressive strength of the specimen should be 3.44 MPa or more (specimen diameter: 50-100 mm, height / diameter: 2 (rigid)). Considering this fact, the diameter of the specimen was 10mm and the height / diameter ratio (L / D ratio) was 0.85, but the fracture compressive strength was 60 ~ 180 MPa, which was much higher than the compressive strength of solid waste.

As described above, when the incineration as a combustible radioactive waste is compressed and formed at a certain pressure and then sintered in a heating furnace through a heat treatment process, the ratio of the final sintered body to the initially introduced incineration material powder is increased to several tens of times Can be increased. Therefore, when the final sintered body is charged into a 200 liter drum, which is a radioactive waste container, it is possible to store a large amount of waste in one drum, thereby minimizing the number of drums used for the radioactive waste treatment, Can be greatly reduced. In addition, since the compacted body formed by compression molding in a press machine is sintered in a heating furnace to maintain a chemically strong bonding force, cracks are not generated in the sintered body even after elapse of a long time and can be maintained in a stabilized state. And soundness can be maintained.

In addition, in addition to the incineration as a combustible waste, the method for treating radioactive waste using the powder metallurgy method as described above is also applicable to a slag of metal waste, which is a dry powder of boric acid waste liquid generated during operation in a nuclear power plant, And the metal waste slag having a sponge shape can be treated by the above-described depilatory treatment method, so that it is possible to improve the ratio of detergent to raw material, It is possible to reduce the disposal cost of the waste and improve the economical efficiency.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limited to the embodiments set forth herein. Will be possible.

110: drum 112: tumbler
114: adapter 115: vibrator
116: preformer 117, 136: hopper
120: Slug 124: Assembly machine
130: granule 134: press
140: Molded body 144:
150: sintered body

Claims (10)

(a) a pretreatment step of forming the radioactive waste into a preform for smooth compression and molding by molding through a preformer;
(b) compressing and molding the preformed body manufactured through the pretreatment under a predetermined temperature and pressure condition to produce a molded body having a predetermined size and density;
(c) sintering the molded body under a constant temperature and pressure condition to produce a sintered body;
A method for depressurizing radioactive waste using powder metallurgy technology
The method according to claim 1, wherein the radioactive waste in step (a) is a powdery ash generated in the incineration process of the combustible radioactive waste.
The method according to claim 1, wherein the radioactive waste in step (a) is dry powder of a boric acid waste solution generated during operation in a nuclear power generating facility.
The method according to claim 1, wherein the radioactive waste in step (a) is a slag of metal waste, which is a non-combustible radioactive waste.
[3] The method according to claim 2, wherein the incineration ash is obtained by mixing bottom ash, fly ash, and fly ash filter fly ash at a constant weight ratio.
The method of claim 1, wherein the step (a)
The ash powder mixed with the bottom ash generated in the incineration process of the flammable radioactive waste, the fly ash ash after combustion, and the fly ash filter is charged into a container and then mounted on a tumbler and mixed. A container handling step of mounting the dispenser on an adapter and rotating the dispenser into a hopper of the preformer;
A preliminary molding step of molding the ash through the hopper into a slug having a predetermined size through a preforming machine;
And a granulation step of passing the slug through a pelletizer to form particles of a granule shape having a predetermined size. 2. The method for purifying radioactive waste according to claim 1,
The method of claim 1, wherein the forming pressure for forming the molded body in step (b) is set within a range of 100 to 500 MPa.
The method according to claim 1, wherein the sintering temperature for forming the sintered body in step (c) is set in the range of 800 to 1200 ° C.
[7] The method of claim 6, wherein the mixed vessel is mounted on an adapter in the container handling step, and the powder is charged into the hopper by vibrating the vessel through a vibrator while being inverted upside down. Method of deporting waste
The radioactive waste sintered body produced by the method of treating the radioactive waste according to any one of claims 1 to 9

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