JPH11183677A - Method for manufacturing nuclear fuel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a nuclear fuel by laminating at least one type of a thermally decomposed carbon, boron, and nitrogen and an element which forms a compound with it, and the compound by either method of the chemical vapor deposition, sputtering, or gas penetration into a plurality of layers and then performing baking. SOLUTION: In a first stage, an element or a compound that reacts with at least one type of a thermally decomposed carbon, boron and nitrogen and becomes carbide, boride, nitride, or the like and at least one type of the thermally decomposed carbon, boron, and the nitrogen are selected, which is successively or in reverse order laminated or penetrated into a plurality of layers by at least one type of the chemical vapor deposition method, the sputtering method, and the gas penetration method. At a second stage, laser beams, arc, microwave, and the like are applied to the nuclear fuel surface where a compound is applied for a short time, thus causing a high-temperature combustion synthesis reaction. The time, temperature, and atmospheric pressure are set to approximately 1-2 seconds, 1, 700-4,000 deg.C, and 10<-3> -10<-2> atmospheric pressure, respectively, thus obtaining a nuclear fuel sintered body that can be used not only in a high- temperature gas oven but also in a pressurized light-water reactor and a heavy-water reactor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a nuclear fuel coated with at least one selected from carbides, borides and nitrides. Compounds decomposed by carbon by heat (py
rolitic carbon (hereinafter abbreviated as "pyrolytic carbon"), boron and nitrogen to react with at least one selected from the group consisting of carbides,
An element or compound capable of forming at least one selected from borides and nitrides; and ii) pyrolytic carbon, boron or nitrogen selected from chemical vapor deposition, sputtering and gas infiltration. One or more of one or more selected from carbides, borides and nitrides obtained by laminating or impregnating two or more layers sequentially or in reverse order, and then burning and synthesizing the layers at high temperature and pressure. The present invention relates to a method for producing a nuclear fuel in which these composites are applied in a stacked manner.

[0002]

2. Description of the Related Art Nuclear power generation is divided into a high temperature gas reactor type, a pressurized light water reactor type and a heavy water reactor type according to the type of reactor used, and the type of nuclear fuel used differs according to each type. That is, the high temperature gas reactor type uses a particle type nuclear fuel, and the pressurized light water reactor type and the heavy water reactor type, which are currently adopted for nuclear power generation in Korea, use a nuclear fuel sintered body.

[0003] Existing high-temperature gas-cooled reactor nuclear fuel is obtained by coating a graphite layer and a carbide layer on the surface of the nuclear fuel in order to increase its stability, and burning fission products from nuclear fuel particles or a sintered body when burning in a furnace. Is suppressed from being released. In this existing method, a coated nuclear fuel was used in which silicon carbide and other carbides were directly applied to spherical nuclear fuel particles having a diameter of several hundred microns (μm) by a chemical vapor deposition method. That is, a spherical nuclear fuel (UCO, ThO ₂ ) having a diameter of about 400 μm was produced by applying a methylchlorosilane gas and an ethylene gas by a fluidized chemical vapor deposition method. Work must be performed at a high temperature of about 1200 ° C. or higher, and at a high temperature of about 1600 ° C. to apply the silicon carbide layer, so that defects in the microstructure of the coating layer increase, and chlorine is added to the silane compound. Since at least one compound selected from the group consisting of methylchlorosilane, dimethylchlorosilane, triethylchlorosilane and the like containing an element is used, the silane compound is decomposed in the process and toxic hydrogen chloride and chlorine gas are generated.

On the other hand, in pressurized light water reactors and heavy water reactors, there are dish-shaped grooves at the upper and lower stages of the cylindrical shape, and the diameter and height are about 9.9.
Nuclear fuel (UO ₂ ) of a relatively large sintered body of × 10 mm
However, the existing method of fluidized chemical vapor deposition, which is an asymmetric method, cannot be directly applied to a large nuclear fuel sintered body that is asymmetric and relatively heavy compared to nuclear fuel particles,
The technique of applying a carbide to such a nuclear fuel sintered body has not yet been used.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide one kind of carbide, boride and nitride which does not have the disadvantages of the above-mentioned conventional method and which can be applied to a nuclear fuel sintered body. The object of the present invention is to provide a method for producing a coated nuclear fuel.

[0006]

Means for Solving the Problems Here, the present inventors,
In the course of continuing research to solve the above problems, on the surface of the nuclear fuel, i) reacting with one or more selected from pyrolytic carbon, boron and nitrogen to form carbides, borides and nitrides. Ii) one or more elements selected from pyrolytic carbon, boron and nitrogen selected from a chemical vapor deposition method, a sputtering method, and a gas infiltration method. After laminating or infiltrating two or more layers sequentially or in reverse order by one or more kinds, the layers are burned and synthesized at high temperature and high pressure, and one or more kinds selected from carbide, boride and nitride are formed. The present invention has been completed by developing a method for producing a nuclear fuel in which these and their composites are applied in a stack.

That is, the method for producing a nuclear fuel according to the present invention is characterized in that the surface of the nuclear fuel reacts with at least one selected from the group consisting of pyrolytic carbon, boron, and nitrogen to form carbide, boride, and nitride. Ii) one or more elements selected from pyrolytic carbon, boron and nitrogen, and one or more elements selected from a chemical vapor deposition method, a sputtering method, and a gas infiltration method. As described above, after laminating or infiltrating two or more layers sequentially or in reverse order, the layers are subjected to combustion synthesis at high temperature and high pressure.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention relates to a step of applying or penetrating a compound layer to nuclear fuel (first step) and a step of performing high-temperature combustion synthesis of the compound layer applied or penetrated on the surface of nuclear fuel in the first step. (Second stage) will be described in detail. First, in the first step, i) reacting with one or more selected from pyrolytic carbon, boron and nitrogen to form one or more selected from carbides, borides and nitrides on the surface of the nuclear fuel. Two or more layers of the element or compound and ii) one or more selected from pyrolytic carbon, boron or nitrogen by one or more selected from a chemical vapor deposition method, a sputtering method, and a gas permeation method in order or in reverse order Laminate or infiltrate.

At this time, as a carbon source of the pyrolytic carbon,
Methane (CH ₄ ), acetylene (C ₂ H ₂ ), ethylene (C
₂ H _4), propane (C ₃ H ₈₎ can be used hydrocarbons such as boron as boron source for boron (B), boron oxide (B ₂ O ₃₎ and metal - boron compound (MoB, MoB ₂ , ZrB ₂ etc.)
And at least one selected from the group consisting of nitrogen and nitrogen can be used as a nitrogen source.

Elements or compounds which can react with one or more selected from the above pyrolytic carbon, boron and nitrogen to form one or more selected from carbides, borides and nitrides include: , Silicon, silicon compounds, zirconium (Z
r), zirconium compounds and boron compounds. At this time, silane (SiH ₄ ),
There are compounds that can be decomposed at low temperatures (200 to 300 ° C) such as tetramethylsilane ((CH ₃ ) ₄ Si) and hexamethyldisilane (C ₆ H ₁₈ Si ₂ ), and zirconium oxide (ZrO ₂ ) Or zirconium chloride (ZrC
l ₄ ), and examples of the boron compound include boron carbide (B ₄ C) and boron nitride (BN).

The compound is characterized in that it is applied or penetrated on the surface of the nuclear fuel at a relatively low temperature as compared with the temperature of the existing method, but at a temperature of 500 to 1200 ° C. and an atmospheric pressure of 10 ^-5 to 1. The pressure is adjusted to apply or permeate the compound on the surface of the nuclear fuel. When applying or penetrating the compound on the surface of the nuclear fuel using a chemical vapor deposition apparatus, as the vapor deposition apparatus for applying the compound to the surface of the nuclear fuel, it is preferable to use a fluidized chemical vapor deposition or a plasma enhanced chemical vapor deposition apparatus, It is particularly preferred to utilize a plasma enhanced chemical vapor deposition apparatus for the deposition of.

I) an element or compound capable of reacting with one or more selected from pyrolytic carbon, boron and nitrogen to form one or more selected from carbides, borides and nitrides; , Ii) one or more kinds of application or infiltration sequence selected from pyrolytic carbon, boron and nitrogen may be applied i) and then applied or infiltrated (sequentially) ii) or from ii) After applying pyrolytic carbon or boron, i) may be applied (in reverse order).

In the second step, one of a heat source selected from a laser beam, an arc and a microwave is instantaneously applied within a few seconds to the surface of the nuclear fuel coated with the compound, i). A high-temperature combustion synthesis reaction is caused between one or more selected from silicon, a silicon compound, zirconium, a zirconium compound and a boron compound and ii) pyrolytic carbon, boron and nitrogen. At this time, one kind selected from a laser beam, an arc, and a microwave as a heat source is irradiated for 1 to 2 seconds to 1700 to 4000 ° C.
At a high temperature. At this time, the atmospheric pressure is 10 ^-3 to 1
Adjust to 0 ^-2 atm.

As a result of the high-temperature combustion synthesis reaction, a pyrolytic carbon layer or a boron layer and one or more layers selected from carbides, borides and nitrides are formed on the surface of the nuclear fuel. That is, one or more selected from silicon, silicon compound, zirconium, zirconium compound and boron compound on the surface diffuses and penetrates through the combustion reaction, and to the outside, one selected from carbide, boride and nitride. The above is generated, and a residual pyrolytic carbon layer or a boron layer exists inside. For example, when pyrolytic carbon is reacted with at least one selected from a silicon compound, a zirconium compound and a boron compound,
At least one selected from silicon carbide, zirconium carbide and boron carbide is generated outside the surface of the nuclear fuel, and pyrolytic carbon remains inside the surface of the nuclear fuel.

The thickness of the carbide layer, boride layer and nitride layer on the surface of the nuclear fuel is several microns (μm) according to the degree of the high-temperature combustion reaction.
m) can be adjusted from a few hundred microns or more. On the surface of the nuclear fuel, in addition to the process of applying a laser beam, arc or microwave to cause a high-temperature combustion synthesis reaction, pyrolytic carbon or boron and silicon, silicon compound, zirconium, zirconium compound through a chemical vapor deposition apparatus And a nuclear fuel on which at least one selected from the group consisting of boron compounds is deposited, by heat treatment at a high temperature in a high-temperature reduction furnace or a nitrogen atmosphere to form a pyrolytic carbon layer or a boron layer, a carbide layer, a boride layer and a nitride layer. And at least one selected from the following.

[0016]

The present invention will now be described in detail with reference to the following examples. The following examples illustrate the invention,
The content of the present invention is not limited by the examples. [Example 1] Using reagent-grade propane as a carbon source, using a fluidized chemical vapor deposition apparatus, at a temperature of 1200 ° C,
First, pyrolytic carbon was applied to the surface of the particulate nuclear fuel at a pressure of 1 atm. FIG. 1 shows a cross section of the particulate nuclear fuel coated with pyrolytic carbon, and a bright layer can be seen around the particles. FIG. 2 is an enlarged view showing a state seen from the surface of the pyrolytic carbon layer, and FIG. 3 is a cross-sectional view of the pyrolytic carbon layer. Thus, in the first half of the first stage, a pyrolytic carbon layer is clearly formed on the surface of the nuclear fuel particles.

Next, silane (SiH ₄ ) is used as a compound capable of forming a carbide by reacting with pyrolytic carbon, and is decomposed at a temperature of 500 ° C. and a pressure of 10 ⁻⁵ atm in a plasma enhanced chemical vapor deposition apparatus. The applied silicon was applied to the surface of the nuclear fuel. As can be seen from the X-ray diffraction diagrams of FIGS. 4 and 5, on the surface of the nuclear fuel after the completion of the first stage, a stack of a pyrolytic carbon layer at the lower part and a silicon layer at the upper part is formed. .

Next, it was heated for 1 to 2 seconds at a temperature of 1700 ° C. at a pressure of 10 ⁻³ atm and then cooled. As a result, on the surface of the nuclear fuel, as shown in FIGS. 6 and 7, the surface of the silicon coating layer in a rough state before the high-temperature treatment becomes a dense silicon carbide composite layer by the high-temperature treatment. As can be seen from the X-ray diffraction diagram of FIG. 8, this dense surface layer is a layer containing silicon carbide as a main component and containing very little silicon.

On the other hand, the white particles on the left side of FIG. 9 show the simulated nuclear fuel particles before the carbide is applied.
The black particles on the right show the final simulated nuclear fuel particles after the carbide has been applied. The scanning electron micrograph described above and X
From the line diffraction diagram, it can be seen that a laminated structure in which the inner layer is a pyrolytic carbon layer and the outer layer is a silicon carbide layer is formed on the surface of the particle-type simulated nuclear fuel after the treatment according to the present invention.

The generated silicon carbide layer is made of β-silicon carbide (β
-SiC) has a composition of 99% or more, and α-
0.5% or less of silicon carbide (α-SiC) and silicon oxide (Si
O ₂ ) contained 0.3% or less and silicon (Si) contained 0.2% or less. In addition, the generated silicon carbide layer is used for Vickers (Vickers).
) Hardness test and water immersi
on) and measure the hardness and density respectively.
The hardness of the measurement result is 30 GPa or more and the density is 2.6 g / c.
m ³ or more and dense. [Example 2] A layer containing pyrolytic carbon and silicon was sequentially formed using the same raw materials and equipment as in Example 1 except that industrial propane was used instead of reagent grade propane. It was applied to the surface of a model simulated nuclear fuel, then heated for 1 hour in a high-temperature reducing furnace at a temperature of 1500 ° C. at a pressure of 10 ⁻³ atm or less, and then cooled to room temperature.

Also in this case, the surface coating layer of the particle type simulated nuclear fuel had a pyrocarbon structure in the inner structure and a silicon carbide layer in the outer structure. This silicon carbide layer has a composition of 99% or more of β silicon carbide (β-SiC), 0.5% or less of α-silicon carbide (α-SiC) and 0% of silicon oxide (SiO ₂ ) as impurities. 3% or less, and silicon (Si) contained 0.2% or less. The hardness and density of the silicon carbide layer measured by the same method as in Example 1 were 30 GPa or more, and the density was 2.6 g / cm ³ or more. [Example 3] A layer containing pyrolytic carbon and silicon was sequentially formed using the same raw materials and equipment as in Example 1, except that a simulated nuclear fuel was used instead of the particulate nuclear fuel. Is applied to the surface of a sintered-type simulated nuclear fuel, and then heated for 1 hour in a high-temperature reducing furnace at a temperature of 1500 ° C. at a pressure of 10 ⁻³ atm or less, and then cooled to room temperature. Produced a sequentially coated nuclear fuel.

The white circle on the left side of FIG. 10 shows the simulated nuclear fuel sintered body before the carbide is applied, and the black circles on the center and the right side show the circle after the carbide is applied. 1 shows a simulated nuclear fuel sintered body. FIG. 11 shows that the actual UO ₂ sintered body was coated with pyrolytic carbon and silicon, and then burned and synthesized by a temperature arc of 1700 ° C. or more at 10 ⁻³ atm and cooled for 1 to 2 seconds. 2 shows a cross section of a layer in which carbon was applied under the same conditions and method as in Example 1.

Also in this case, the coating layer on the surface of each sample had a pyrocarbon structure in the inner structure and a silicon carbide layer in the outer structure. In this silicon carbide layer, β-silicon carbide (β-SiC) has a composition of 99% or more, α-silicon carbide (α-SiC) is 0.5% or less as impurities, and silicon oxide (SiO ₂ ) is 0.3% or less, and silicon (Si) contained 0.2% or less. The hardness and density were measured by the same method as in Example 1. The silicon carbide layer formed as a result had a hardness of 30 GPa or more and a dense density of 2.6 g / cm ³ or more.

The raw materials, treatments and physical properties of the coating layers used in Examples 1 to 3 are summarized in Table 1 below.

[0025]

[Table 1]

[0026]

As described above, the production method of the present invention is a conventional method, that is, it is expensive, is thermally decomposed at a relatively high temperature of 1570 ° C. or more, and removes harmful hydrochloric acid and chlorine gas after the reaction. Compared to the production method using methylenechlorosilane (CH ₃ SiCl ₃ ), dimethylchlorosilane ((CH ₃ ) ₂ SiCl ₂ ) and trimethylchlorosilane ((CH ₃ ) ₃ SiCl ₃ ) compounds, the price is lower and the plasma Lower temperature (20
Silane (SiH ₄ ), tetramethylsilane ((CH ₃ ) ₄ Si) and hexamethyldisilane (C ₆ H), which are thermally decomposed at 0 to 300 ° C. and do not generate harmful chlorine and hydrochloric acid gas even after the reaction. _{Since 18} Si ₂ ) is used, the characteristics of the nuclear fuel are not affected during the coating process, and the silicon carbide layer can be coated more economically in a shorter time. Further, in the production method of the present invention, in the step of burning and synthesizing the applied pyrolytic carbon and silicon at a high temperature, one kind selected from a laser beam, an arc and a microwave is added instantaneously in a short time. As compared with the conventional manufacturing method in which the nuclear fuel is left for a long time, a fine crystal structure can be maintained and adjusted without accompanying a phase change of the nuclear fuel. Moreover, it is an excellent production method applicable not only to nuclear fuel particles used in a high-temperature gas reactor type but also to a nuclear fuel sintered body used in a pressurized light water reactor and a heavy water reactor.

In the present invention, instead of silicon or a silicon compound, one selected from zirconium, a zirconium compound and a boron compound can be reacted with pyrolytic carbon to produce boron carbide or zirconium carbide; It is also a useful method that is applied to a high-temperature combustion synthesis reaction of silicon, a silicon compound, zirconium, a zirconium compound, and a boron compound with boron or nitrogen instead of pyrolytic carbon to form a boride or a nitride thereof.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph of a cross section of nuclear fuel particles coated with pyrolytic carbon.

FIG. 2 is a scanning electron micrograph of a pyrolytic carbon layer which is an outer surface layer of nuclear fuel particles.

FIG. 3 is a high magnification scanning electron micrograph of a cross section of a pyrolytic carbon layer which is an outer surface layer of nuclear fuel particles.

FIG. 4 is an X-ray diffraction diagram of a lower pyrolytic carbon layer before combustion synthesis.

FIG. 5 is an X-ray diffraction diagram of the upper silicon layer before combustion synthesis.

FIG. 6 is a scanning micrograph of a nuclear fuel surface before pyrolytic carbon and silicon are applied and are subjected to combustion synthesis.

FIG. 7 is a scanning electron micrograph of a nuclear fuel surface after pyrolytic carbon and silicon are applied and synthesized by combustion.

FIG. 8 is an X-ray diffraction diagram of a silicon carbide layer after combustion synthesis.

FIG. 9 is a photograph of a nuclear fuel particle before and after application of carbide.

FIGS. 10A and 10B are photographs before and after application of carbide in a nuclear fuel sintered body.

FIG. 11 is a cross-sectional photograph of a UO ₂ sintered body coated with pyrolytic carbon, silicon carbide, and pyrolytic carbon.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Youw-woo Lee, Korea, Taejong-Shi 305-350, U-Sung-Ku, Kayong-Dong K. # 12-105 (72) Inventor Bang-gu Kim, Republic of Korea, Taejong-si 302-150, Theok, Manun-Dong Cambyn AP. # 108-1503 (72) Inventor Yun-Won Lee Republic of Korea, Taejong-Shi 305-340, Yusong-ku, Doryeong-dong 393-5 (72) Inventor Sanhona South Korea, Taejong-Shi 305-333, Yusong- H, Owen-Don Hanbit AP. # 110-103 (72) Inventor Donsun Seung-South Korea, Taejong-Shi 305-340, Yusong-ku, Doryeong-Dong Research-Center Hyundai Apt. # 102-701 (72) Inventor Yong Choi Taejong, South Korea -Shi 305-390, Yusong-k, Chungmin-Don Expo E.P. # 301-501

Claims (10)

[Claims] 1. An element which reacts with one or more selected from pyrolytic carbon, boron and nitrogen to form one or more selected from carbides, borides and nitrides on the surface of a nuclear fuel or The compound and ii) one or more selected from pyrolytic carbon, boron and nitrogen are sequentially or reversely subjected to one or more selected from a chemical vapor deposition method, a sputtering method and a gas permeation method. A carbide or boride comprising a step of laminating or penetrating more than one layer (first step) and a step of burning and synthesizing the compound layer formed in the first step at high temperature and high pressure in a short time (second step) 1 selected from and nitride
A method for producing a nuclear fuel in which at least one or more of these compounds and their composites are applied in a laminated manner. 2. The method according to claim 1, wherein the first step is performed at a temperature of 500 to 1200 ° C. while adjusting the atmospheric pressure to 10 ^-5 to 1 atm, and at least one selected from carbides, borides and nitrides. The method for producing a nuclear fuel according to claim 1, wherein the composite of (1) is applied by lamination. 3. The second step is to ^{reduce the} atmospheric pressure to 10 ^-3 to 10 ^-2.
At least one selected from carbides, borides and nitrides and a composite thereof are applied in a layered manner by heating to a temperature of 1700 to 4000 ° C. for 1 to 2 seconds by adjusting to an atmospheric pressure. Item 3. The method for producing a nuclear fuel according to Item 1 or 2. 4. The carbon source of pyrolytic carbon is at least one selected from methane, acetylene, ethylene and propane, and the boron source is at least one selected from boron, boron oxide and a metal-boron compound. , The nitrogen source is nitrogen gas,
The method for producing a nuclear fuel according to any one of claims 1 to 3, wherein at least one selected from carbides, borides, and nitrides and a composite thereof are applied in a stack. 5. An element or compound which reacts with one or more selected from pyrolytic carbon, boron and nitrogen to form one or more selected from carbide, nitride and boride is silicon, silicon or silicon. A compound, zirconium, at least one selected from a zirconium compound and a boron compound, at least one selected from carbides, borides and nitrides, and a composite thereof, which is applied in a laminated manner. 4. The method for producing a nuclear fuel according to any one of 4 to 4. 6. The silicon compound is at least one selected from silane, tetramethylsilane and hexamethyldisilane, the zirconium compound is zirconium oxide or zirconium chloride, and the boron compound is boron carbide or boron nitride. 6. The method for producing a nuclear fuel according to claim 5, wherein at least one selected from carbides, borides and nitrides and a composite thereof are applied in a laminated manner. 7. At least one selected from pyrolytic carbon, nitrogen and boron on the surface of the first stage nuclear fuel and at least one selected from carbides, nitrides and borides by reacting with them. In the process of applying an element or compound that forms, one selected from carbides, borides and nitrides is applied using at least one selected from chemical vapor deposition, sputtering and gas infiltration. The method for producing a nuclear fuel according to any one of claims 1 to 6, wherein at least one species and a composite thereof are applied by lamination. 8. The heat source during the high-temperature combustion synthesis in the second stage is at least one selected from a laser beam, an arc and a microwave, and at least one selected from a carbide, a boride and a nitride. The method for producing a nuclear fuel according to any one of claims 1 to 7, wherein these composites are applied in a stack. 9. A nuclear fuel is a particle type or a sintered body.
The method for producing a nuclear fuel according to any one of claims 1 to 7, wherein at least one selected from carbides, borides, and nitrides and a composite thereof are applied in a stack. 10. When a silicon carbide layer is formed as a carbide on the surface of a nuclear fuel, the composition of the silicon carbide layer contains 99% or more of β-silicon carbide (β-SiC) and contains carbide, boride and nitride. The method for producing a nuclear fuel according to any one of claims 1 to 7, wherein at least one compound selected from the above and a composite thereof are applied in a laminated manner.