CN112331367A

CN112331367A - Novel reactor fuel rod cladding and preparation method thereof

Info

Publication number: CN112331367A
Application number: CN202011120927.0A
Authority: CN
Inventors: 周涛; 张家磊; 丁锡嘉; 陈宁; 冯祥; 陈娟
Original assignee: Southeast University; North China Electric Power University
Current assignee: Southeast University; North China Electric Power University
Priority date: 2020-10-19
Filing date: 2020-10-19
Publication date: 2021-02-05
Anticipated expiration: 2040-10-19
Also published as: CN112331367B

Abstract

The invention discloses a nuclear reactor fuel rod cladding, which comprises a core body (1) and an outer core body protection layer (4); the core body (1) is composed of pure molybdenum or molybdenum alloy, and the outer protective layer (4) of the core body is a metal coating. Wherein the metal coating is selected from Fe-Cr-Si coating, stainless steel coating or Si-Mo coating. The invention provides a novel cladding material for a nuclear reactor fuel rod, and effectively improves the impact resistance and fatigue resistance of a fuel assembly cladding, and the safety and operating efficiency of a nuclear reactor.

Description

Novel reactor fuel rod cladding and preparation method thereof

Technical Field

The invention belongs to the field of energy sources including the field of nuclear power and the field of mechanical manufacturing, and particularly relates to a cladding applicable to a rod bundle assembly including a fuel rod, a control rod guide tube and the like.

Background

After some nuclear accidents occur, nuclear power safety becomes the focus of general attention of the international people again, and how to further improve the nuclear power safety, particularly the safety threshold of a nuclear reactor for resisting over-design-standard nuclear accidents, becomes an important issue of sustainable development of nuclear energy. The zirconium alloy cladding has good radiation resistance and corrosion resistance as a material approved by a nuclear power plant, and has been applied in nuclear reactors for over 50 years.

However, in severe accident situations, particularly in the event of loss of coolant without safe injection, the zirconium alloy cladding rapidly oxidizes or corrodes under high pressure steam conditions, releasing large amounts of heat and hydrogen. Under accident conditions, when the temperature is higher than 800 ℃, the tensile strength and creep strength of the zirconium alloy cladding can be further reduced, deformation and even bursting of the fuel rods are caused, and the coolability of the reactor core is affected.

To overcome the deficiencies of zirconium alloys, researchers have found that molybdenum has a melting point as high as 2623 ℃ (4753 ° f) while maintaining high strength at high temperatures and pressures. And the molybdenum has a large unit elastic modulus, so that the molybdenum has positive application in the aspects of high strength and low weight, and can be used as a cladding material of a nuclear reactor fuel rod.

Patent application US2015/0063522 discloses a nuclear fuel rod cladding consisting of molybdenum or a molybdenum-based alloy. An outer protective layer consisting of a zirconium based alloy or of aluminium comprising stainless steel on the outer surface of the cladding. The molybdenum cladding can show the advantages of high thermal conductivity, low expansion coefficient and the like at high temperature and high pressure, but the zirconium-based alloy or the aluminum containing stainless steel is adopted as the outer protective layer, so that the corrosion resistance of the whole cladding is reduced, and the chemical property of zirconium at high temperature and high pressure has potential safety hazard on the safe operation of a reactor.

French dominic hutz et al devised a fuel rod cladding for a light water reactor comprising a substrate composed of pure molybdenum or of a molybdenum-based alloy and at least one chromium-based coating layer composed of pure chromium or of a chromium-based alloy. The chemical property of the chromium is inactive, the chromium is stable to oxygen and water vapor at normal temperature, the chromium starts to react with the oxygen at the temperature higher than 600 ℃, the reaction is slow after an oxide film is generated on the surface, and the oxide film is damaged and the reaction is fast again when the temperature is heated to 1200 ℃. At high temperature, chromium reacts with nitrogen, carbon and sulfur and is dissolved in hydrochloric acid and sulfuric acid. To a certain extent, the molybdenum clad and the rod bundle assembly within the clad cannot be effectively protected.

In summary, although the existing research has made a certain progress, the existing nuclear fuel rod cladding made of molybdenum or molybdenum-based alloy still has the potential safety hazard of being easily corroded and damaged due to the defect of the outer protective layer of the molybdenum cladding, and cannot meet the requirement of nuclear power safety.

Disclosure of Invention

In order to overcome the above problems, the present inventors have conducted intensive studies to design a novel nuclear reactor cladding and a method for manufacturing the same, wherein the cladding material is a core composed of pure molybdenum or a molybdenum alloy and an outer protective layer composed of a Si — Mo coating layer having a gradient structure. The cladding still keeps good radiation resistance and corrosion resistance under high temperature and high pressure, and effectively ensures the safety of the rod bundle assembly in the reactor, thereby completing the invention.

Specifically, the present invention aims to provide the following:

the invention provides a novel nuclear reactor cladding which comprises a core body 1 and an outer core protection layer 4; the core body 1 is made of pure molybdenum or molybdenum alloy, and the outer protective layer 4 of the core body is a metal coating.

In another aspect, the invention provides a method of preparing a nuclear reactor cladding according to the first aspect of the invention, the method comprising the steps of:

step 1, pretreating a core body 1;

step 2, spraying the core body 1;

and step 3, carrying out heat treatment on the core body 1.

The nuclear reactor fuel rod cladding provided by the invention can achieve the following technical effects:

(1) the nuclear reactor fuel rod cladding provided by the invention has good irradiation resistance and corrosion resistance under high temperature and high pressure, and effectively improves the impact resistance and fatigue resistance of the fuel rod cladding.

(2) The method for preparing the nuclear reactor fuel rod cladding provided by the invention adopts plasma spraying, the process is simple, the obtained coating has high quality, the distribution is uniform, and the bonding capability between the coating and the core body is strong.

Drawings

FIG. 1 illustrates a cross-sectional view of a nuclear reactor fuel rod cladding in accordance with a preferred embodiment of the present invention;

FIG. 2 illustrates a top view of a nuclear reactor fuel rod cladding in accordance with a preferred embodiment of the present invention;

fig. 3 shows a photomicrograph of a transition layer and an out-diffusion layer in accordance with a preferred embodiment of the present invention.

The reference numbers illustrate:

1-a core body;

2-a transition layer;

3-an outer diffusion layer;

4-core outer protective layer;

5-fuel assembly.

Detailed Description

The invention is explained in more detail below with reference to the figures and examples. The features and advantages of the present invention will become more apparent from the description.

The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

A first aspect of the invention provides a nuclear reactor fuel rod cladding comprising a core 1 and an outer core protective layer 4, as shown in figures 1 and 2.

Wherein the core body 1 consists of pure molybdenum or a molybdenum alloy. Preferably, the mass fraction of molybdenum in the pure molybdenum is greater than or equal to 99%, preferably greater than or equal to 99.5%, and more preferably greater than or equal to 99.9%.

The existence of impurities in the metal can form a galvanic cell under certain conditions, and the corrosion speed of the metal is accelerated. Thus, the higher the purity of pure molybdenum, the greater the corrosion resistance of the cladding when it is made.

Preferably, the mass of molybdenum in the molybdenum alloy accounts for 45-70%, more preferably 50-65%, and even more preferably 55-60% of the total mass.

Compared with pure molybdenum, the molybdenum alloy is added with other atoms with larger or smaller size, so that the regular layered arrangement of metal atoms is changed, and the relative sliding among atomic layers is difficult, therefore, the molybdenum alloy has high strength, large hardness and good corrosion resistance. The nuclear reactor fuel rod cladding prepared by the molybdenum alloy is not easy to deform or burst under accident conditions.

The molybdenum alloy is selected from molybdenum-titanium alloy, molybdenum-zirconium alloy, molybdenum-hafnium alloy or molybdenum-tungsten alloy, more preferably molybdenum-titanium alloy or molybdenum-hafnium alloy, and more preferably molybdenum-tungsten alloy. The molybdenum-tungsten alloy can improve the room temperature brittleness and high temperature anti-sagging capability of molybdenum, and has the characteristics of corrosion resistance, good high temperature strength, hardness and the like; the uniaxial tensile strength can reach 600-1200MPa, the yield stress can reach 7800-1200MPa, and the hardness can reach 200-300 HBS.

The uniaxial tensile strength of the tungsten-molybdenum alloy is preferably 600MPa to 1200MPa, more preferably 700MPa to 1100MPa, and even more preferably 800MPa to 1000 MPa.

The yield stress of the tungsten-molybdenum alloy is preferably 7800MPa to 1200MPa, more preferably 800MPa to 1100MPa, and even more preferably 900MPa to 1000 MPa.

The hardness of the tungsten-molybdenum alloy is preferably 200HBS to 300HBS, more preferably 220HBS to 280HBS, and even more preferably 240HBS to 260 HBS.

Preferably, the thickness of the core 1 is 100 μm to 600. mu.m, preferably 200 μm to 550. mu.m, more preferably 250-500. mu.m.

Preferably, the core outer protective layer 4 is a metal coating, wherein the metal coating is selected from the group consisting of an Fe-Cr-Si coating, a stainless steel coating or a Si-Mo coating, preferably a stainless steel coating and a Si-Mo coating, more preferably a Si-Mo coating. The Si-Mo coating comprises molybdenum disilicide (MoSi)₂) Said molybdenum disilicide (MoSi)₂) Has higher melting point (2030 ℃), moderate density (6.24g/cm3) and excellent high-temperature oxidation resistance. In high-temperature aerobic environment at more than 1000 ℃, MoSi₂The surface can form a layer of continuous and compact SiO₂And the protective layer prevents the inward diffusion of oxygen and shows excellent high-temperature oxidation resistance.

In the Si — Mo coating layer, the mass of molybdenum is 65 to 90%, more preferably 68 to 88%, and still more preferably 70 to 85% of the total mass.

The core outer protective layer 4 has a gradient structure therein, the gradient structure comprises a transition layer 2 and an outer diffusion layer 3, and the transition layer 2 is located between the core 1 and the outer diffusion layer 3.

Wherein, when the core body 1 is pure molybdenum and the metal coating is a Si-Mo coating, the transition layer 2 is made of MoSi₂The thickness of the transition layer 2 is 5 μm to 50 μm, preferably 10 μm to 30 μm, more preferably 15 to 25 μm.

The outer diffusion layer 3 is made of 2Mo₅Si₂-Mo₃Si, the thickness of the outer diffusion layer 3 is 10 μm to 120. mu.m, preferably 20 μm to 100. mu.m, and more preferably 40 to 60 μm.

In a second aspect, the invention provides a method of preparing a nuclear reactor fuel rod cladding, the method comprising the steps of:

step 1, pretreating a core body 1;

wherein the pretreatment comprises surface sand blasting, ultrasonic cleaning and drying treatment.

Preferably, the blasting strength of the surface blasting is 0.1 to 0.5MPa, more preferably 0.2 to 0.4MPa, and still more preferably 0.3 MPa.

The sand blasting refers to the process of forming a high-speed spraying beam by using compressed air as power to spray a spraying material (such as copper ore sand, quartz sand, carborundum, iron sand, sea sand and the like) to the surface of a core body to be treated at a high speed, and due to the impact and cutting action of the spraying material on the surface of the core body, the surface of the core body can obtain certain cleanliness and different roughness after the sand blasting, so that the mechanical property of the surface of the core body is improved, the fatigue resistance of the core body can be improved, and the adhesive force between the core body and a metal coating is increased.

Among them, the strength of blasting determines the magnitude of the impact and cutting action to which the core surface is subjected, and the inventors have found through a large number of experiments that the mechanical properties of the core surface after blasting are optimal when the blasting strength is controlled to be between 0.1 and 0.5 MPa.

Wherein the ultrasonic cleaning is carried out in distilled water, absolute ethyl alcohol or an aqueous solution of ethyl alcohol, preferably in absolute ethyl alcohol.

The ultrasonic cleaning time is 3-15min, preferably 5-10min, and more preferably 8 min.

Wherein the drying treatment is carried out at 60-150 ℃ for 0.5-4h, preferably at 80-120 ℃ for 1-2h, and more preferably at 100 ℃ for 1.5 h.

Step 2, spraying the core body (1);

wherein the spraying is selected from flame spraying, electric arc spraying or plasma spraying, preferably plasma spraying.

The quality of the coating is determined by the process conditions of plasma spraying, and the process parameters in the plasma spraying technology mainly comprise gas flow, spraying distance, spraying power and powder feeding rate.

Among other things, gas flow directly affects the enthalpy and velocity of the plasma flame, which in turn affects the spray efficiency and coating porosity. When the spraying power is constant, too large or too small a gas flow rate leads to a decrease in the spraying efficiency and an increase in the porosity of the coating.

Preferably, in the present invention, the flow rate of the plasma gas Ar is in the range of 25 to 55slpm (standard liters per minute), more preferably 35 to 45slpm, for example 40 slpm.

Preferably, in the present invention, the plasma gas H₂The flow rate of (a) is 2 to 16slpm, more preferably 5 to 12slpm, for example 8 slpm.

Preferably, in the present invention, the flow rate of the powder carrier gas Ar is in the range of 1 to 8slpm, more preferably 3 to 5slpm, for example 4 slpm.

Wherein the spray distance is a linear distance from the end face of the nozzle to the core surface. If the spraying distance is too close, the powder heating time is short, and the impact deformation is insufficient, so that the coating is easy to fall off. If the spraying distance is too far, the powder heated to a molten state is cooled when it comes into contact with the core, and the flying speed begins to decrease, which may reduce the coating quality and the spraying efficiency.

Preferably, in the present invention, the spray distance is 100-200nm, preferably 120-180nm, for example 150 nm.

Wherein the powder feeding rate is matched with the spraying power. When the powder feeding rate is constant, if the spraying power parameter is too small, the powder is not melted well, cannot deform when impacting the core body, is easy to rebound, and has low deposition efficiency. When the powder feeding rate is constant, if the spray power parameter is too large, although the melting and impact deformation of the powder are good, the powder is heavily oxidized and ablated, the coating contains more soot, and the molten particles are heavily splashed, which may degrade the quality of the coating.

Preferably, in the present invention, the spraying power is 25kW to 65kW, preferably 35kW to 50kW, for example 40 kW. The powder feed rate is 10rpm to 40rpm, preferably 15rpm to 30rpm, for example 25 rpm.

Preferably, when the metal coating is a Si — Mo coating, silicon powder is sprayed on the surface of the core 1 by using a plasma spraying technique to obtain a silicon coating.

Wherein the particle size of the silicon powder is 15-100 μm, preferably 40-80 μm, and more preferably 50 μm.

The purity of the silicon powder is 90 wt% or more, preferably 95 wt% or more, and more preferably 96 wt% or more.

The silicon powder is dried for 0.5-3h at 60-150 ℃, preferably dried for 1-2h at 80-120 ℃, and more preferably dried for 0.8-1.5h at 90-110 ℃ before use.

Wherein the thickness of the silicon coating is 15-170 μm, preferably 30-130 μm, and more preferably 50-100 μm. The thickness of the silicon coating can be adapted to the size requirements of the bundle assembly such as a fuel rod.

And 3, carrying out heat treatment on the core body (1).

Wherein the heat treatment is performed in an inert gas, preferably the inert gas is selected from one or more of nitrogen, helium, argon, such as argon.

Wherein, the heat treatment is preferably carried out at 800-1800 ℃ for 3-15h, more preferably at 1000-1500 ℃ for 5-10h, and even more preferably at 1200-1300 ℃ for 7-8 h.

Wherein, when the metal coating is a Si-Mo coating, the silicon coating can generate a gradient structure after heat treatment to form a MoSi coating₂ A transition layer 2 consisting of Mo₅Si₂-Mo₃An outer diffusion layer 3 of Si, as shown in fig. 3.

The generation of the gradient structure enables the cladding to have good radiation resistance and corrosion resistance at high temperature and high pressure, and effectively improves the impact resistance and fatigue resistance of the cladding of the fuel rod.

EXAMPLE preparation of Nuclear electric reactor Fuel rod cladding

The core 1 in this example was selected to be pure molybdenum, with a silica fume particle size of 45 μm and a purity greater than 98 wt.%. The preparation method of the nuclear power reactor fuel rod cladding comprises the following steps:

1) and carrying out sand blasting treatment on the core body 1 under the sand blasting strength of 0.5MPa, after the sand blasting is finished, putting the core body 1 into absolute ethyl alcohol for ultrasonic cleaning for 2 times, each time for 7 minutes, and then drying the cleaned core body 1 at 100 ℃ for 2 hours.

2) Adopting plasma spraying technology, wherein the flow of plasma gas Ar is 35slpm, and the flow of plasma gas H is₂The flow rate of (2) is 10slpm, the flow rate of powder carrier gas Ar is 4slpm, the spraying distance is 150nm, the spraying power is 40kW, and the powder feeding speed is 20rpmUnder the conditions, silicon powder was sprayed on the surface of core body 1 to obtain a silicon coating having a thickness of 115 mm.

3) And (3) carrying out heat treatment on the sprayed core body 1 in argon at 1300 ℃ for 7h, and then cooling to room temperature to obtain the nuclear power reactor fuel rod cladding.

The present invention has been described above in connection with preferred embodiments, but these embodiments are merely exemplary and merely illustrative. On the basis of the above, the invention can be subjected to various substitutions and modifications, and the substitutions and the modifications are all within the protection scope of the invention.

Claims

1. A nuclear reactor fuel rod cladding, characterized by: the cladding comprises a core (1) and a core outer protective layer (4);

the core body (1) is composed of pure molybdenum or molybdenum alloy, and the outer protective layer (4) of the core body is a metal coating.

2. The enclosure of claim 1, wherein: the core body (1) is composed of pure molybdenum or molybdenum alloy;

wherein the mass fraction of molybdenum in the pure molybdenum is more than or equal to 99 percent;

the mass of molybdenum in the molybdenum alloy accounts for 45-70% of the total mass; the molybdenum alloy is selected from molybdenum-titanium alloy, molybdenum-zirconium alloy, molybdenum-hafnium alloy or molybdenum-tungsten alloy.

3. The enclosure of claim 2, wherein: the thickness of the core (1) is 100-600 μm, preferably 200-400 μm, more preferably 300 μm;

the uniaxial tensile strength of the tungsten-molybdenum alloy is 600MPa-1200MPa, the yield stress is 7800MPa-1200MPa, and the hardness is 200HBS-300 HBS.

4. The enclosure of claim 1, wherein: the core outer protective layer (4) is provided with a gradient structure, the gradient structure comprises a transition layer (2) and an outer diffusion layer (3), and the transition layer (2) is positioned between the core (1) and the outer diffusion layer (3).

5. The enclosure according to one of claims 1 to 4, wherein: the metal coating is selected from Fe-Cr-Si coating, stainless steel coating or Si-Mo coating,

the metal coating is preferably a stainless steel coating and a Si-Mo coating, more preferably a Si-Mo coating;

in the Si-Mo coating, the mass of molybdenum accounts for 65-90% of the total mass.

6. The enclosure of claim 4 or 5, wherein: when the core body (1) is pure molybdenum and the metal coating is a Si-Mo coating, the transition layer (2) is made of MoSi₂The thickness of the transition layer (2) is 5-50 μm;

the outer diffusion layer (3) is made of Mo₅Si₂-Mo₃Si, and the thickness of the outer diffusion layer (3) is 10-120 mu m.

7. A method of preparing a nuclear reactor fuel rod cladding, preferably a nuclear reactor fuel rod cladding as claimed in any one of claims 1 to 6, wherein: the method comprises the following steps:

step 1, pretreating a core body (1);

step 2, spraying the core body (1);

and 3, carrying out heat treatment on the core body (1).

8. The method of claim 7, wherein: in the step 1, the pretreatment comprises surface sand blasting, ultrasonic cleaning and drying treatment;

the sand blasting strength of the surface sand blasting is 0.1-0.5MPa, more preferably 0.2-0.4MPa, and more preferably 0.3 MPa;

the ultrasonic cleaning time is 3-15min, preferably 5-10min, and further preferably 8 min;

the drying treatment is carried out at 60-150 ℃ for 0.5-4h, preferably at 80-120 ℃ for 1-2h, and more preferably at 100 ℃ for 1.5 h.

9. The method of claim 7, wherein: in step 2, the spraying is selected from flame spraying, electric arc spraying or plasma spraying, and is preferably plasma spraying.

10. The method of claim 7, wherein: in step 3, the heat treatment is carried out in inert gas, and the inert gas is selected from one or more of nitrogen, helium and argon;

the heat treatment is carried out at 800-1800 ℃ for 3-15h, preferably at 1000-1500 ℃ for 5-10h, and more preferably at 1200-1300 ℃ for 7-8 h.