KR20140124636A - Ceramic-metal hybrid tube and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a ceramic-metal hybrid cladding tube capable of obtaining the advantages of metal and ceramic by combining the metal and the ceramic which are heterogeneous materials. The ceramic-metal hybrid cladding tube includes a ceramic tube which receives a nuclear fuel of a nuclear reactor and prevents the loss of the mechanical strength of the cladding tube due to heat generated in the nuclear reactor, and a metal tube which surrounds the ceramic tube to prevent the corrosion of the ceramic tube and is boned to a fitting plug to seal the nuclear fuel. The metal-ceramic hybrid cladding tube suggested in the present invention secures safety in not only the normal operation of the reactor but also an accident of the reactor.

Description

TECHNICAL FIELD [0001] The present invention relates to a ceramic-metal hybrid cladding,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear fuel cladding tube of a nuclear reactor, and more particularly, to a hybrid cladding tube which merely takes advantage of a conventional metal cladding tube and a ceramic cladding tube.

Prior to commercial use, zirconium metal was used as a cladding material for nuclear fuel cladding, but the development of cladding materials with improved hot and mechanical integrity was accelerated in response to the Fukushima nuclear accident. Prior to the Fukushima nuclear plant accident, if the purpose of technology development was to improve the economic efficiency of nuclear fuel under normal operating conditions, the accident safety enhancement of the nuclear fuel cladding in preparation for major accidents is given priority after the accident.

Cladding of metal materials including zirconium (Zr) may lose mechanical strength or melt at high temperatures. Since this phenomenon is a characteristic of metal, it is impossible to overcome the breakthrough by using metal cladding.

Therefore, academia and researchers are paying attention to ceramic-based fuel cladding which has been studied for the purpose of improving power output and safety. The main candidate material for ceramic-based cladding is silicon carbide (SiC) composites. SiC composite cladding has a neutron absorption cross-sectional area that is 20% smaller than that of a zirconium alloy. It has excellent high-temperature strength, creep resistance, oxidation resistance and abrasion resistance and is a substitute for conventional zirconium alloy cladding. .

However, the basic strength, toughness, and radiation stability of the nuclear fuel cladding have been overcome by the above-described manufacturing method, but the disadvantage of being weak to impact and fragile can not be completely solved due to the inherent characteristics of the ceramic material. Furthermore, it is reported that the SiC material melts in the light water reactor driving environment. This is a factor that affects not only the cladding but also the integrity.

Further background of the invention refers to the following prior art documents.

(Non-Patent Document 1) F. Rodriguez-Rojas, A.L. 30, 2010). In this paper, we propose a high-temperature sintering process for the sintering of austenitic sintered SiC ceramics. 119-128.

(Non-Patent Document 2) R.B. Matthews, Irradiation damage in reaction-bonded silicon carbide, Journal of Nuclear Materials, 51 (1974) 203-208.

It is an object of the present invention to provide a ceramic-metal hybrid cladding tube which has the advantages of a metal cladding tube and a ceramic cladding tube and which greatly improves safety against accidents over conventional cladding tubes.

Another object of the present invention is to propose a ceramic-metal hybrid cladding tube having improved nuclear material protection capability and mechanical toughness by complementing the disadvantages of the metal cladding tube and the disadvantage of the ceramic cladding tube.

Another object of the present invention is to disclose a method of manufacturing a ceramic-metal hybrid cladding tube in which different kinds of materials are mechanically combined.

In order to accomplish the object of the present invention, a ceramic-metal hybrid cladding tube according to an embodiment of the present invention is formed to accommodate nuclear fuel of a nuclear reactor and prevent the mechanical strength of the cladding tube from being lost due to heat generated in the reactor A ceramic tube, and a metal tube that surrounds the ceramic tube to prevent corrosion of the ceramic tube by the cooling water and is joined to the sealing cap to seal the fuel.

According to an example of the present invention, the ceramic tube forms an oxide film on the surface to protect the fuel from oxidation when an accident occurs in which the metal tube is oxidized.

According to another embodiment of the present invention, the ceramic tube is characterized in that the SiC particles are surrounded by at least one matrix phase selected from the group consisting of Si, MoSi ₂ , Mo ₅ Si ₃ C, TiSi ₂ and Ti ₃ SiC ₂ , Bonded composite.

According to another embodiment of the present invention, the metal tube is formed of a zirconium alloy.

In order to achieve the above-mentioned object, the present invention also discloses a method for manufacturing a ceramic-metal hybrid cladding tube. A method of manufacturing a ceramic-metal hybrid clad tube according to an embodiment of the present invention includes the steps of: preparing a ceramic tube by reaction sintering; attaching a metal tube to be wrapped around the ceramic tube when the ceramic tube is coupled with the ceramic tube, And bonding the ceramic tube and the metal tube having a size that can be in close contact with each other at room temperature using a difference in thermal expansion coefficient at a predetermined temperature.

According to another embodiment of the present invention, the step of manufacturing the ceramic tube comprises the steps of: forming a molded body having a shape of a ceramic tube to be manufactured from at least one selected from the group consisting of carbon, graphite, SiC and TiC; Injecting at least one melt selected from the group consisting of Si, Mo, and TiC into the melt and sintering at a temperature at which the melt injected into the melt can exist in a melt state to induce the reaction with the carbon or silicon carbide .

By the reaction, the SiC particles can be surrounded by at least one gaseous phase selected from the group consisting of Si, MoSi ₂ , Mo ₅ Si ₃ C, TiSi ₂ , and Ti ₃ SiC ₂ to form a composite material bonded with the matrix.

The step of injecting may include adding a SiC powder as a non-reactive filler to control the SiC fraction of the ceramic tube while generating a ceramic tube having a size capable of closely contacting the metal tube in the step of inducing the reaction.

According to another embodiment of the present invention, the step of fabricating the metal tube in a size capable of closely contacting the ceramic tube includes the steps of: dissolving a zirconium sponge to produce an ingot; hot working and extruding the ingot to produce an intermediate material And cold filing the intermediate material to produce a zirconium tube having a size that can be brought into close contact with the ceramic tube.

According to another embodiment of the present invention, the coupling step includes the steps of: thermally expanding the ceramic tube and the metal tube, which are of a size that can be in close contact with each other at room temperature, to a predetermined temperature, Inserting the ceramic tube into the larger metal tube; and cooling the ceramic tube and the metal tube to room temperature so that they are in close contact with each other.

The predetermined temperature of the thermally expanding step may be 600 to 750 ° C so that the detailed ceramic tube can be inserted into the metal tube and the metal tube is not deteriorated.

According to the present invention having the above-described structure, the metal tube disposed outside the cladding provides a solution to the sealing of the plug for fuel sealing, which is the biggest obstacle of the ceramic-based cladding, Can be performed.

Further, the present invention can increase the mechanical strength of the cladding tube by the ceramic composite material and protect the nuclear fuel from excessive oxidation even in the accident occurrence of the reactor.

Further, according to the present invention, the metal tube and the ceramic composite material complement each other to improve the safety of the reactor.

1 is a conceptual view of a ceramic-metal hybrid cladding tube according to an embodiment of the present invention;
FIG. 2 is a cross-sectional view of the ceramic-metal hybrid cladding of FIG. 1 taken along line AA. FIG.
3 is a photograph showing the microstructure of a SiC ceramic tube produced by reaction sintering.
Fig. 4 is a microstructure photograph showing that a crack occurred in a SiC ceramic tube in a neutron irradiation environment. Fig.
5 is a flow chart illustrating a method of fabricating a ceramic-metal hybrid cladding tube in accordance with an embodiment of the present invention.
Fig. 6 is a conceptual view showing a step of manufacturing a metal tube in the manufacturing method of Fig. 5;
FIG. 7 is a conceptual view showing a bonding process of combining the ceramic tube and the metal tube in the manufacturing method of FIG. 5;

Hereinafter, a ceramic-metal hybrid cladding tube according to the present invention will be described in detail with reference to the drawings. In the present specification, the same or similar reference numerals are given to different embodiments in the same or similar configurations. As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

The present invention combines the advantages of metal alloys and ceramic composites and provides a ceramic-metal hybrid cladding which is formed to complement each other.

FIG. 1 is a conceptual view of a ceramic-metal hybrid cladding 100 according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line A-A of the ceramic-metal hybrid cladding 100 of FIG.

The ceramic tube 110 is disposed in the innermost portion of the ceramic-metal hybrid cladding 100 and is formed to receive nuclear fuel of the reactor. Nuclear fuel is embedded in the ceramic tube 110, and the ceramic tube 110 serves as a primary protection function of the fuel. Since the ceramic tube 110 has a high neutron absorption cross-sectional area as compared with a zirconium alloy, it has high temperature strength, creep resistance and fretting wear resistance, so that the mechanical strength of the ceramic-metal hybrid cladding tube 100 is lost due to heat when a reactor accident occurs .

The ceramic tube 110 may be formed of a SiC composite material. The SiC composite material is a composite material in which the SiC particles are surrounded by at least one matrix phase selected from the group consisting of Si, MoSi ₂ , Mo ₅ Si ₃ C, TiSi ₂ , and Ti ₃ SiC ₂ and combined with the matrix. As can be seen from the photograph shown in FIG. 2, the SiC composite material can improve the heat resistance of the cladding because the mechanical integrity is not lost at a temperature of 1400 ° C or more.

In particular, in the present invention, the matrix phase of the SiC composite material includes not only Si but also MoSi ₂ , Mo ₅ Si ₃ C, TiSi ₂ , and Ti ₃ SiC ₂ . The SiC composite material including the Si matrix only has a flexural strength of about 300 MPa and a heat resistance of about 1450 캜. On the other hand, when the matrix is made of Mo, the bending strength is about 500 MPa, and the heat resistance of the MoSi ₂ matrix is about 1800 ° C. and the Mo ₅ Si ₃ C matrix is about 2000 ° C.

In addition, when the base of the ceramic tube 110 is Si, the ceramic tube 110 may be exposed to high-temperature, high-pressure cooling water to dissolve Si. The matrix may be MoSi ₂ , Mo ₅ Si ₃ C, TiSi ₂ , and Ti ₃ SiC ₂ , this phenomenon can be prevented.

The metal tube 120 surrounds the ceramic tube 110 to prevent the ceramic tube 110 from being corroded by the cooling water. The metal tube 120 is mechanically coupled to the ceramic tube 110 and surrounds the ceramic tube 110 having low corrosion resistance against cooling water from the outside. Corrosion of the tube 110 can be prevented.

The metal tube 120 provides a sealed end plug bonding method that is insufficient with the ceramic tube 110 alone. The metal tube 120 may be formed of a zirconium alloy and may be bonded to the sealing cap to seal the fuel to protect the fuel from external impact and prevent leakage of the fuel.

If an accident such as a simple coolant accident (LOCA) occurs in the reactor, the metal tube 120 is not oxidized, so that the metal tube 120 can still protect the ceramic tube 110 and the nuclear fuel in the event of an accident. However, when a serious accident occurs in which the accident size of the reactor exceeds the loss of the coolant, the metal tube 120 may lose its mechanical integrity or be lost by oxidation. Even if the metal tube 120 loses its mechanical integrity, the ceramic tube 110 forms an oxide film on its surface and maintains resistance to oxidation, thereby protecting the fuel.

For example, when a metal tube 120 such as zirconium is lost due to a serious accident, a ceramic tube 110 such as a SiC composite is formed by allowing Si to react with oxygen in the air, ₂ , so that resistance to oxidation can be maintained. As such, the ceramic-metal hybrid cladding tube 100 protects the internal fuel by the secondary protective film, thereby enhancing the safety of the nuclear-metal hybrid cladding tube 100 when an accident occurs.

Accordingly, during normal operation of the reactor, the ceramic tube 110 performs a primary protective function of the nuclear fuel, maintains the mechanical strength of the ceramic-metal hybrid cladding tube 100, and the metal tube 120 is sealed Thereby protecting the nuclear fuel and corrosion of the ceramic tube 110 from the cooling water.

Even if the mechanical integrity of the metal tube 120 is lost when an accident occurs in the reactor, the ceramic tube 110 forms an oxide film on the surface of the tube and maintains oxidation resistance, thereby protecting the fuel.

FIG. 3 is a photograph showing the microstructure of a SiC ceramic tube produced by reaction sintering, and FIG. 4 is a photograph of a microstructure showing a crack in a SiC ceramic tube in a neutron irradiation environment (Non-Patent Document 2).

The SiC ceramic tube has a neutron absorption cross-sectional area of about 20% smaller than that of a zirconium alloy, and thus exhibits excellent performance in a neutron irradiation environment. However, a volume expansion of SiC may occur in a neutron irradiation environment and cracks may occur. FIGS. 3 and 4 show the case where the base of the ceramic tube is Si. Comparing FIGS. 3 and 4, it can be seen that cracks are generated in the microstructure of the SiC ceramic tube by neutron irradiation.

The problem of cracking in the SiC ceramic tube in the neutron irradiation environment can be solved by replacing the base of the ceramic tube with MoSi ₂ , Mo ₅ Si ₃ C, TiSi ₂ , and Ti ₃ SiC ₂ instead of Si. MoSi ₂ , Mo ₅ Si ₃ C, TiSi ₂ , and Ti ₃ SiC ₂ have a larger flexural strength than Si, so that even when expansion occurs due to neutron irradiation, cracking of the ceramic tube can be limited.

The ceramic-metal hybrid cladding can be combined with a simple combination of a ceramic and a metal, and the ceramic tube and the metal tube can be combined with each other to improve the mechanical integrity of the cladding tube and safety in case of an accident.

Hereinafter, a manufacturing method for manufacturing a ceramic-metal hybrid cladding tube will be described. Since the ceramic-metal hybrid cladding has to be combined to show the advantages of each other, it can not be manufactured by a simple combination of ceramic and metal heterogeneous materials.

5 is a flow chart illustrating a method of fabricating a ceramic-metal hybrid cladding tube according to an embodiment of the present invention.

The manufacturing method of the ceramic-metal hybrid cladding tube includes a step (S100) of manufacturing a ceramic tube, a step (S200) of manufacturing a metal tube, and a step (S300) of combining a ceramic tube and a metal tube.

In the step S100 of manufacturing the ceramic tube, a ceramic tube is manufactured by reaction sintering and a step S110 of forming a ceramic tube-shaped molded body, a step S120 of injecting a melt into the molding body, and a step of reacting and sintering S130 ).

In step S110 of forming a ceramic tube-shaped molded body, a final ceramic tube-shaped body / structure is formed. In step S120 of injecting a melt into the molded body, a raw material to be formed into a matrix is injected into the formed body.

The raw material of the molded body may be carbon / graphite or SiC, and the molten material to be injected may be Si. When SiC is used as the raw material of the molded body, Si added with Mo or Si added with TiC can be used as the melt in addition to Si. It is also possible to use SiC and TiC as a raw material for the molding, and in this case, Si can be used as the melt. Table 1 shows the combination of raw materials of the molded body and raw materials on the base.

Molding material raw material Base material Carbon / graphite Si SiC Si, Si added with Mo, and Si added with TiC Mix SiC and TiC Si

In the step of injecting the melt (S120), the molten material is infiltrated into the inside of the molded body by a technique such as penetration by capillary force. In the step of injecting the melt, SiC powder, which is a non-reactive filler, may be added to precisely match the dimensions of the finally produced ceramic tube and the metal tube and adjust the fraction of SiC. The dimensions of the ceramic tube and the metal tube can be precisely adjusted so that the two tubes can be made to have a size that allows them to adhere to each other. In addition to adding SiC powder as a non-reactive filler, the density can be increased by centrifugal force.

In the step of reacting and sintering (S130), the molded article into which the melt is infused is sintered at a temperature at which the melt can exist as a melt at about 1400 ° C to induce the reaction between the molded article and the melt. When the molded body and the melt are reacted and sintered, the melt penetrates into the molded body to form a matrix. The matrix phase formed by reaction sintering may be at least one selected from the group consisting of Si, MoSi ₂ , Mo ₅ Si ₃ C, TiSi ₂ and Ti ₃ SiC ₂ , and the SiC particles are in the form of a composite .

After manufacturing the ceramic tube, a metal tube is manufactured (S200). Since the ceramic tube and the metal tube are separately manufactured, the metal tube is not necessarily manufactured after the ceramic tube is manufactured, but the metal tube may be manufactured first and then the ceramic tube may be manufactured. The step of manufacturing the metal tube will be described with reference to Fig.

FIG. 6 is a conceptual diagram showing a step (S200) of manufacturing a metal tube in the manufacturing method of FIG.

Referring to FIGS. 5 and 6, a metal tube may be made of a zirconium material, and a zirconium sponge is dissolved in a small amount of an alloy element to produce an ingot (S210). The produced ingot is hot-kneaded and quenched to form a shape capable of accommodating the nuclear fuel therein, and extruded to produce an intermediate material called TREX (S220). The intermediate material is subjected to cold peeling to produce a metal tube having a standard for a cover tube (S230). Cold fillering can be repeated several times as shown in FIG.

Referring again to FIG. 5, after the metal tube is manufactured, the ceramic tube and the metal tube are combined (S300). The step S300 of joining the ceramic tube and the metal tube includes a step S310 of heating and thermally expanding the ceramic tube and the metal tube S310, a step S320 of inserting the ceramic tube into the metal tube S320, And cooling (S330), which will be described with reference to Fig.

FIG. 7 is a conceptual diagram showing a coupling process of coupling the ceramic tube 210 and the metal tube 220 (S300) in the manufacturing method of FIG.

The ceramic tube 210 and the metal tube 220 are formed to have a size capable of being in close contact with each other at room temperature. The ceramic tube 210 is disposed inside the metal tube 220 so that the ceramic tube 210 and the metal tube 220 are in close contact with each other so that the outer diameter of the ceramic tube 210 is smaller than that of the metal tube 220. [ (220). The diameters of the metal tubes 220 produced by the step S200 of manufacturing the ceramic tube 210 and the ceramic tube 210 produced by the step S100 of manufacturing the ceramic tube in FIG. 7 were compared, 210 are made to coincide with the inner diameter of the metal tube 220.

Since the ceramic tube 210 and the metal tube 220 are formed to have a size that allows them to be in close contact with each other at room temperature, it is theoretically possible to insert the ceramic tube 210 into the metal tube 220 at room temperature, The ceramic tube 210 and the metal tube 220 can not be damaged by an external force.

In the thermal expansion step (S310), the ceramic tube (210) and the metal tube (220) are heated to a predetermined temperature to induce thermal expansion. Since the thermal expansion coefficient of the metal tube, zirconium alloy, is about 1.7 times larger than that of the ceramic tube, the zirconium alloy tube expands more than the SiC ceramic tube even when heated to the same temperature. Therefore, the gap between the outer diameter of the SiC ceramic tube and the inner diameter of the zirconium alloy tube is generated by the thermal expansion, and the ceramic tube 210 is inserted into the metal tube 220 in a state where theoretically, It becomes possible.

The temperature for thermally expanding the ceramic tube 210 and the metal tube 220 is preferably 600 to 750 占 폚. When the temperature is lower than 600 ° C, it is difficult to form a sufficient gap between the ceramic tube 210 and the metal tube 220, and when the temperature is higher than 750 ° C, the metal tube 220 may be deteriorated.

Table 2 compares the sizes of SiC ceramic tube and zirconium alloy tube before and after thermal expansion. As can be seen from Table 2, when heated to 600 ° C., a gap (Δ = 0.037-0.022 = 0.015) between the SiC ceramic tube and the zirconium alloy occurs, allowing the SiC ceramic tube to be inserted into the zirconium alloy tube.

Material Coefficient of thermal expansion Size at room temperature (mm) Size change after heating at 600 ° C (mm) SiC ceramics 43 탆 / mK Outer diameter 8.96 (thickness 0.3) +0.022 zircalloy 71 탆 / mK Inner diameter 8.96 (thickness 0.27) +0.037

The inner diameter of the metal tube 220 is set to be smaller than the outer diameter of the ceramic tube 210 in order to more firmly contact the ceramic tube 210 and the metal tube 220. The creep- May be used.

In the inserting step S320, the ceramic tube 210 is inserted into the metal tube 220 using the gap between the ceramic tube 210 and the metal tube 220. The ceramic tube 210 and the metal tube 220 are cooled to room temperature to induce heat shrinkage in the step of cooling the ceramic tube 210 and the metal tube 220 to the room temperature, To produce a ceramic-metal hybrid cladding tube.

The ceramic-metal hybrid cladding tube can be manufactured by the manufacturing method disclosed in the present invention, and the ceramic-metal hybrid cladding tube manufactured by the above-described manufacturing method is not merely a simple bonding of different materials but compliments the disadvantages as a heterogeneous material It is formed so as to take advantage only. This can greatly contribute to the improvement of reactor stability.

The above-described ceramic-metal hybrid cladding tube is not limited to the configuration and the method of the above-described embodiments, but the embodiments may be configured such that all or some of the embodiments are selectively combined so that various modifications can be made. have.

100: ceramic-metal hybrid cladding
110: Ceramic tube
120: metal tube

Claims (11)

A ceramic tube which is formed to receive nuclear fuel of the reactor and prevents the mechanical strength of the cladding tube from being lost by heat generated in the reactor; And
And a metal tube that surrounds the ceramic tube to prevent corrosion of the ceramic tube by cooling water and is joined to a sealing cap to seal the fuel. The method according to claim 1,
Wherein the ceramic tube forms an oxide film on the surface to protect the fuel from oxidation when an accident occurs in which the metal tube is oxidized. The method according to claim 1,
Wherein the ceramic tube is a composite material in which the SiC particles are surrounded by at least one gaseous phase selected from the group consisting of Si, MoSi ₂ , Mo ₅ Si ₃ C, TiSi ₂ , and Ti ₃ SiC ₂ and combined with the matrix. Metal hybrid cladding. The method according to claim 1,
Wherein the metal tube is formed of a zirconium alloy. Preparing a ceramic tube by reaction sintering;
Preparing a metal tube to be wrapped around the ceramic tube when the ceramic tube is coupled with the ceramic tube so that the metal tube can be in close contact with the ceramic tube; And
And joining the ceramic tube and the metal tube having a size that can be in close contact with each other at room temperature using a difference in thermal expansion coefficient at a predetermined temperature. 6. The method of claim 5,
Wherein the step of fabricating the ceramic tube comprises:
Forming a shaped body having a shape of a ceramic tube to be manufactured from at least one selected from the group consisting of carbon, graphite, SiC and TiC;
Injecting at least one melt selected from the group consisting of Si, Mo, and TiC into the formed body; And
And sintering at a temperature at which the molten material injected into the formed body can exist in a molten state to induce a reaction with the carbon or silicon carbide. The method according to claim 6,
Wherein the SiC particles are surrounded by at least one gaseous phase selected from the group consisting of Si, MoSi ₂ , Mo ₅ Si ₃ C, TiSi ₂ , and Ti ₃ SiC ₂ to form a composite material bonded with the matrix, Method of making ceramic - metal hybrid cladding. The method according to claim 6,
Wherein the step of injecting comprises adding a SiC powder, which is a non-reactive filler, to the ceramic tube to produce a ceramic tube of a size that can closely contact the metal tube, and to control the SiC fraction of the ceramic tube. Method of manufacturing a metal hybrid cladding tube. 6. The method of claim 5,
Wherein the step of fabricating the metal tube comprises:
Dissolving a zirconium sponge to produce an ingot;
Hot working and extruding the ingot to produce an intermediate material; And
And a step of cold-peeling the intermediate material to produce a zirconium tube having a size capable of closely contacting the ceramic tube. 6. The method of claim 5,
Wherein the combining comprises:
Heating the ceramic tube and the metal tube to a predetermined temperature to thermally expand the ceramic tube and the ceramic tube,
Inserting the ceramic tube into the metal tube having a relatively greater degree of thermal expansion due to a difference in thermal expansion coefficient; And
And cooling the ceramic tube and the metal tube to room temperature so that the ceramic tube and the metal tube are in close contact with each other. 11. The method of claim 10,
Wherein the predetermined temperature of the thermally expanding step is 600 to 750 DEG C so that the detailed ceramic tube can be inserted into the metal tube and the metal tube is not deteriorated.

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