KR20150056677A - Method for Cylindrical Neutron Absorber containing Rare Earth oxides from Spent Nuclear Fuel and the apparatus thereof - Google Patents
Method for Cylindrical Neutron Absorber containing Rare Earth oxides from Spent Nuclear Fuel and the apparatus thereof Download PDFInfo
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- KR20150056677A KR20150056677A KR1020130138590A KR20130138590A KR20150056677A KR 20150056677 A KR20150056677 A KR 20150056677A KR 1020130138590 A KR1020130138590 A KR 1020130138590A KR 20130138590 A KR20130138590 A KR 20130138590A KR 20150056677 A KR20150056677 A KR 20150056677A
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Abstract
The present invention relates to a method for producing a cylindrical neutron absorber using rare earths present in spent nuclear fuel and an apparatus for use in the method, and more particularly to a method for manufacturing a cylindrical neutron absorber using SiO 2 , Al 2 O 3 , and B 2 O 3 , and a method for producing a rare-earth oxide-containing sintered body as a cylindrical neutron absorber. The method for producing a sintered body according to the present invention is characterized in that a sintered body containing a rare earth oxide in an amount of 50 wt% or more can be produced by a simple method. The sintered body containing the rare earth oxide of the present invention has an advantage that it exhibits remarkably high density, improved thermal stability, and has remarkably low leakage rate of the radioactive material.
Description
The present invention relates to a method of manufacturing a cylindrical neutron absorber using rare earths present in spent nuclear fuel and to an apparatus used in the method.
At present, the power generated by nuclear power accounts for about 40% of domestic power generation, and the spent fuel resulting from nuclear power generation is known to reach 850 tons per year. Pyro-processing (dry refining technology process, pyroprocessing) is emerging as a way to recycle such spent fuel. Pyro processing is a technology for recovering uranium (U) and nuclear fuel materials such as ultra uranium (TRU) elements from spent nuclear fuel using an electrochemical method in a high temperature (500 to 650 ° C) molten salt medium. In the pyrolysis process, a waste molten salt containing a radioactive rare earth chloride or the like is generated. There is a need for a new technique for precipitating and recovering radioactive rare earth chloride present in such waste molten salt as an oxide.
On the other hand, a vitrification method is being carried out for the treatment of radioactive waste molten salt. When vitrification method is used, the radionuclides are physically and chemically solidified in a glass structure to solidify them into glassy solid, which is advantageous in that it is flexible in composition and process parameters and has high resistance to radiation, but has a disadvantage of low resistance. In addition, when a glass solidified material is used as a gamma-ray irradiation apparatus, it is difficult to efficiently use gamma-ray irradiation in a practical industry because it has low specific activity (Ci / g) (International Atomic Energy Agency, Feasibility of Separation and Utilization of Caesium and Strontium from High Level Liquid Waste, Technical Report Series No. 356, IAEA, Vienna (1993)).
In this connection, in Korean Patent Nos. 0192128 and 1090344, it is disclosed that 40 to 65 wt% of fly ash and silica, 15 to 30 wt% of alumina, 5 to 15 wt% of iron oxide, 1 to 15 wt% of molybdenum oxide, 1 to 10% by weight of oxides, and 1 to 10% by weight of vanadium oxides. The above-mentioned prior patent discloses a cesium (Cs-137) high thermal and high radioactive nuclide having a half-life of about 30%, which is expected to be 99% or more volatile in a high-temperature heat treatment process using an aluminosilicate ceramic filter, (CsAlSi 2 O 6 ), CsAlSiO 4 , and CsAlSi 5 O 12 ) to reduce the radiation and heat of the spent nuclear fuel and ultimately to reduce the area required for disposal It is suggested that
On the other hand, among the rare earth elements, Eu, Gd, Sm and other elements are considered to be effective as a critical control material in storing spent fuel because the thermal neutron absorption cross-sectional area is higher than that of commercially used boron alloy steel. In the spent fuel processing process, rare earth oxides containing these rare earth elements are generated as radioactive waste. It is very effective in terms of radioactive waste management to use the sintered body as a critical control material in homogeneous and stable form, Economic benefits can be achieved through recycling and replacement of expensive critical control materials.
Studies on the preparation of solid state rare earth oxides generated in the spent fuel processing process have been carried out in a great deal of time, and there have been many studies on simple solidification of glass using commercial glass medium or solidification in ceramic form considering long half- Has come. In the case of a simple type of glass solidification, a high temperature of 1,500 ° C or more is required to have a waste content of 20 wt% or more, and in the case of ceramic solidification, a severe condition such as high temperature compression is required. In addition, the above methods also have a disadvantage in that it is not easy to produce a homogeneous solid or sintered body by phase separation.
DISCLOSURE Technical Problem The present invention has been made in order to solve the problems of the prior art as described above and also to provide a method of recycling radioactive waste. The present inventors have found that the rare earth oxide generated during the high- , It was found that the use of a glass medium composed of SiO 2 -Al 2 O 3 -B 2 O 3 to produce a neutron absorber with a high rare earth oxide content and a physically stable sintered body The present invention has been accomplished on the basis of these findings.
That is, an object of the present invention is to provide a method for manufacturing a sintered body, that is, a cylindrical neutron absorber having a high rare earth oxide content and a physically stable content by adding SiO 2 , Al 2 O 3 , and B 2 O 3 as a glass medium composition to a rare earth oxide And the like.
However, the technical problem to be solved by the present invention is not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.
In order to achieve the above object, the present invention provides a process for producing a sintered body containing a rare earth oxide, comprising the steps of:
(a) 15.0 to 35.2% by weight of silicon dioxide (SiO 2 ), 6.0 to 26.0% by weight of aluminum oxide (Al 2 O 3 ) and 0.2 to 26.0% by weight of boron oxide (B 2 O 3 ) 20.0% by weight of a glass material;
b) charging the mixed oxide into a sintering vessel; And
c) sintering the sintering vessel in a sintering furnace.
The present invention also relates to a glass-ceramics composition for use in the production of a sintered body containing rare earth oxides, wherein the composition comprises 15.0-35.2 wt.% SiO 2 , 6.0-26.0 wt.% Al 2 O 3 , And 0.2 to 20% by weight of B 2 O 3, based on the total weight of the glass composition.
SiO 2 that the present invention is to produce a thermally and chemically stable sintered body when the rare earth oxide content (50 wt%) is high, and retain a homogeneous form from 1,500 ℃ or less temperature condition, considering the environment is used as the threshold-controlling material -Al 2 O 3 -B 2 O 3 , and a method of manufacturing an effective and economical form of a sintered body (neutron absorber) applicable to storing spent fuel.
Further, the present invention is a simple process which can obtain a homogeneous sintered body at a relatively low temperature, has high usability, and is easy to scale-up.
As described above, when the spent fuel is stored through the manufacturing method of the present invention, it is possible to replace the expensive commercial critical control material, which is advantageous in terms of radioactive waste management and economical cost reduction. The economic effect to be obtained can be greatly improved.
In addition, by using a sintered container composed of a cap, a container and a bottom cover in the present manufacturing method, it is possible to minimize the generation of additional waste that may be generated in the manufacturing process of the sintered body and to reuse the cap as a container, It can contribute to economic efficiency.
1 is a view showing a form of a sintered vessel used for producing a sintered body containing a rare earth oxide and a method for recycling a cap after sintering to a vessel.
FIG. 2 is a view showing a sintering furnace used for producing a sintered body containing a rare earth oxide by using the sintering vessel shown in the present invention.
3 is a photograph showing the shape and structure of the sintered body produced in the present invention.
4 is a view showing the distribution of the surface and constituent elements of the rare-earth oxide-containing sintered body according to the present invention.
As a result, the present inventors have found that, in order to study a method of producing a stable sintered body of radioactive waste containing rare earth oxides generated during the high temperature heat treatment process of spent nuclear fuel, silicon dioxide (SiO 2 ) A sintered body containing at least 50 wt% of a rare earth oxide was prepared using aluminum oxide (Al 2 O 3 ) and boron trioxide (B 2 O 3 ).
As a result, it has been confirmed that the sintered body produced according to the above method has excellent thermal and chemical stability, high density, good resistance to spallation, high non-radioactivity, and can be utilized for neutron absorption. .
Accordingly, the present invention is characterized by providing a method for producing a sintered body containing a rare earth oxide, which comprises the steps of:
(a) 15.0 to 35.2% by weight of silicon dioxide (SiO 2 ), 6.0 to 26.0% by weight of aluminum oxide (Al 2 O 3 ) and 0.2 to 26.0% by weight of boron oxide (B 2 O 3 ) 20.0% by weight of a glass material;
b) charging the mixed oxide into a sintering vessel; And
c) sintering the sintering vessel in a sintering furnace.
In one embodiment of the present invention, the size of the rare earth oxide and the glass medium may be 200 [mu] m to 300 [mu] m. In the production of the sintered body, the rare earth oxide and the glass medium can be uniformly mixed when having the above range.
The
In another embodiment of the present invention, the
In another embodiment of the present invention, the step c) includes the steps of: c-1) sealing the sintering furnace and reducing the pressure to 150 to 250 Torr; c-2) supplying argon gas to the sintering furnace; And (c-3) sintering the sintering furnace at a temperature of 1,000 ° C to 2,000 ° C. . ≪ / RTI >
In addition, the present invention is a glass medium composition used for the sintered body of producing a rare-earth oxide, wherein the composition comprises, based on 100% by weight of the total composition, SiO 2 15.0 ~ 35.2% by weight, Al 2 O 3 6.0 ~ 26.0 % by weight, and B 2 0.2 to 20% by weight of O 3 .
In one embodiment of the present invention, the composition preferably includes 21.0 to 29.0 wt% of SiO 2 , 12.0 to 20.0 wt% of Al 2 O 3, and 6.0 to 12.0 wt% of B 2 O 3 .
As used herein, the term "sinter" means that powder is heated to solidify the powders firmly together.
As used herein, the term "glass medium" means a material that allows rare earth oxides to be sintered and solidified. The glass medium may also be used as glass solidifying agent, solidifying agent, solidifying medium and the like.
Hereinafter, the present invention will be described in detail by steps.
The step a) is a step of preparing a sample for producing a sintered body by mixing a rare earth oxide and a glass medium. Wherein the glassy medium composition is capable of solidifying the rare earth oxides through sintering and comprises 21.0 to 29.0% by weight of SiO 2 , 12.0 to 20.0% by weight of Al 2 O 3 and 12.0 to 20.0% by weight of B 2 O 3 To 12.0% by weight, preferably 21.0 to 29.0% by weight of SiO 2 , 12.0 to 20.0% by weight of Al 2 O 3 and 6.0 to 12.0% by weight of B 2 O 3 , As the embodiment of the present invention, the sintered body produced as the range of the glass medium may contain 25.0 wt% of SiO 2 , 16.7 wt% of Al 2 O 3 and 8.3 wt% of B 2 O 3 , Can contain rare earth oxides, and can achieve high density and thermal / chemical stability. By using the glass medium, the sintered body of the present invention has an advantage that it can contain at least 50 wt% of rare earth oxides.
The rare earth oxide and the glass medium preferably have a size of 200 mu m to 300 mu m and can be uniformly mixed when they have a size of 254 mu m or less.
Step b) is a step of charging an oxide mixed with the glass medium into the
When the sample is charged (filled) in the sintering vessel before the sintering, the sample is filled up to the upper cap portion on the vessel as shown in FIG. 1. After the sintering, the density is increased to fill spaces between the powders, The height of the sintered body decreases below the height of the container portion as shown in FIG. Based on these characteristics, the sintering vessel of the present invention is composed of three parts: the cap part, the container part and the bottom cover part, and the upper cap part 11 allows the container part 12 to be reused again, There is no need to cut the upper part of the container part, and the container part can be used efficiently and economically.
In the step b), when the rare earth oxide and the glass medium sample are charged into the vessel, the mixing form of the sample should not be changed. Therefore, when the sample is to be charged in step b), a certain amount of the sample should be loaded and taped so that the powder sample can be filled in the sintered container in order to produce a homogeneous sintered body without pores.
Step c) is a step of sintering the
In the step c), the sintering vessel is placed in the sintering furnace, the sintering furnace is closed, and the pressure is reduced to 200 Torr or less. After the pressure in the sintering furnace is reduced, Ar gas is purged to form an inert atmosphere, heated at a rate of 6 ° C / min to 1,000 to 2,000 ° C (internal temperature), and then sintered for a predetermined time according to the amount of the powder sample . The sintering temperature may preferably be 1,450 ° C. When the sintering is completed, the sintering vessel is cooled to room temperature, the pressure inside the sintering furnace is converted to normal pressure, and then the sintering vessel is taken out. In the removed sintered vessel, the upper cap portion is removed to easily separate the sintered body from the sintered vessel.
In the preferred embodiment, the sintered body according to the present invention is 3.8 ~ 4.0 g / cm and had a high density of 3, and a glass transition temperature of 780 ℃, the rare earth element and the leach rate of the glass medium constituent elements is 10 -5 10 -6 g / m 2 -day and 10 -3 g / m 2 -day, it was confirmed that the leaching rate was very low and could be used as a stable critical control material, ie, a neutron absorber (see Example 3).
Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited by the following examples.
Example 1. Preparation of sintered body
The recovered rare earth oxide was sampled using a simulated sample of salt waste generated by spent fuel pyro processing and pulverized to have a size of 254 탆 or less using a disk mill. The composition of the glass medium was such that 25.0 wt% of SiO 2 , 16.7 wt% of Al 2 O 3 and 8.3 wt% of B 2 O 3 were used for a mixture sample (total composition) of a glass medium and an oxide (a rare earth oxide : 50 wt%). At this time, the size of the glass medium used was also pulverized using a disk mill so as to have a size of 254 mu m or less.
The pulverized glass medium and rare earth oxide are mixed to form a mixed state in the
Then, the sintering furnace was closed, the pressure was reduced to 200 Torr or less, and argon gas (Ar) was purged to form an inert atmosphere. The sintering furnace with an inert atmosphere was heated to 1450 ℃ at a rate of 6 ℃ / min and then sintered while holding the temperature for a certain period of time.
After the sintering was completed, the sintering vessel was cooled in a state where the sintering vessel was placed in the sintering furnace, and then the sintering vessel was taken out under a reduced pressure state at normal pressure.
The cap part (11) was separated from the sintering vessel to produce a sintered body of the type shown in Fig.
Example 2. Analysis of shape, structure and surface of sintered body
The shape and structure of the sintered body manufactured in Example 1 were observed and shown in Fig. As shown in Fig. 3, it was confirmed that the sintered body had a cylindrical structure (Fig. 3 (a)) and an amorphous structure (Fig. 3 (b)). In particular, the rare earth oxides were formed into a stable amorphous state by mixing the rare earth oxides with the glass medium in a favorable manner through the diffraction analysis apparatus (XRD) as shown in FIG. 3 (b).
From the above results, it was confirmed that the produced sintered body can produce a smooth cylindrical amorphous sintered body easy to apply as a neutron absorber.
Example 3. Density and Property Analysis of Sintered Body
As a result of measuring the density of the sintered body manufactured according to the present invention, the sintered body has a density of 3.8 to 4.0 g / cm 3 , so that the density of the conventional high-level solid waste is 2.5 to 3.0 g / cm 3 Respectively.
4 (a) shows the result of analyzing the surface morphology of the sintered body manufactured by the above method using SEM-mapping. FIG. 4 (b) shows the distribution pattern of the sintered body constituent elements produced by using SEM-EDX. It was found that the rare earth elements were uniformly distributed in the sintered body as well as existing in the sintered body.
As a result of analyzing the thermal properties of the sintered body using TG-DTA, it was found that the glass transition temperature was 780 ° C. and the leaching characteristics of the rare earth elements and the glass medium constituents were examined according to the PCT leaching method. As a result, (10 -4 to 10 -5 g / m 2 -day and 10 -2 g / m 2 -day), which are comparative bases, are used in the range of -5 to 10 -6 g / m 2 -day and 10 -3 g / / m 2 -day).
The results of Examples 2 and 3 indicate that the rare earth oxide-containing sintered body manufactured through the present technology is thermally and chemically stable and can be used stably in an environment used as a critical control material. Therefore, the sintered body produced by the present invention can be used as a neutron absorber.
It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above description is intended to be illustrative and not restrictive in all respects.
The sintering vessel (10)
The cap portion (11)
The container (12)
The bottom cover part (13)
In the
The cover part (101)
In the
The heat-
The argon
Refractory brick (105)
Claims (9)
(a) 15.0 to 35.2% by weight of silicon dioxide (SiO 2 ), 6.0 to 26.0% by weight of aluminum oxide (Al 2 O 3 ) and 0.2 to 26.0% by weight of boron oxide (B 2 O 3 ) 20.0% by weight of a glass material;
b) charging the mixed oxide into a sintering vessel; And
c) sintering the sintering vessel in a sintering furnace.
Characterized in that the sintered body is cylindrical.
Characterized in that the sintered body is used as a neutron absorber.
Characterized in that in step a) the rare earth oxide and the glass medium are milled to a size of 200 mu m to 300 mu m.
Characterized in that the sintering vessel (10) comprises a detachable cap part (11), a container part (12) in which the oxide and the glass medium are loaded, and a bottom cover part (13).
Characterized in that the sintering furnace (100) comprises a cover part (101) of a sintering furnace, a heat insulating part (102), a heating part (103), an argon gas supplying part (104) and a refractory brick (105).
The step c)
c-1) sealing the sintering furnace and reducing the pressure to 150 to 250 Torr;
c-2) supplying argon gas to the sintering furnace; And
c-3) sintering the sintering furnace at a temperature of 1,000 ° C to 2,000 ° C;
≪ / RTI >
Wherein the composition comprises 21.0 to 29.0 wt% of SiO 2 , 12.0 to 20.0 wt% of Al 2 O 3, and 6.0 to 12.0 wt% of B 2 O 3 , based on 100 wt% of the total composition.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20180126820A (en) * | 2017-05-18 | 2018-11-28 | 포항공과대학교 산학협력단 | Borate glass wasteform to immobilize rare-earth oxides from pyro-processing and manufacturing method thereof |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20180126820A (en) * | 2017-05-18 | 2018-11-28 | 포항공과대학교 산학협력단 | Borate glass wasteform to immobilize rare-earth oxides from pyro-processing and manufacturing method thereof |
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