Research method for magnesium-based fuel matrix irradiation damage behavior under simulated service condition

Abstract

The invention discloses a research method for simulating the irradiation damage behavior of a magnesium-based fuel matrix under a service condition. The method comprises the following steps: respectively calculating the incidence depths of Mg < + > and He < + > with different energies in a magnesium alloy by adopting SRIM software; preparing a target material with certain beam density Mg < + >; vacuum of the irradiation target chamber is extracted, neutron fluence required by an irradiation experiment is set according to an SRIM calculation result, and Mg < + > and He < + > ion beams are injected into the sample at the same time; a transmission electron microscope sample is prepared from the irradiated sample along the irradiation depth by using an FIB and is used for representing irradiation damage behaviors of neutron irradiation and fission gas to the magnesium-based fuel matrix; according to the method, a magnesium alloy sample is subjected to synergistic irradiation by adopting He + and Mg + double-beam ions, so that the irradiation damage behavior research of an Mg alloy fuel matrix material under a service condition can be effectively and conveniently realized, and meanwhile, the rapid screening of a heat-resistant Mg alloy system for a fuel matrix is realized.

Description

Technical Field

[0001] The invention relates to nuclear fuel cycle and radiation effect research, and in particular to a method for studying the radiation damage behavior of a magnesium-based fuel matrix under simulated service conditions. Background Art

[0002] After the U.S. Department of Energy launched the "De-enrichment Program", UMo / Al fuel is considered to be the mainstream development direction of fuel elements for research reactors worldwide due to its high uranium loading and good service performance. However, with the increase in service temperature and burnup, UMo / Al fuel still faces failure risks such as pillow deformation and blistering failure caused by irradiation swelling and reduced thermal conductivity, which seriously affects the safety of reactor operation.

[0003] To solve this problem, researchers tried to replace Al with a magnesium (Mg) matrix that does not react with U or Mo, thus forming UMo / Mg / Al fuel, which is recognized as the most promising solution. Although many off-pile research results have shown that UMo / Mg / Al fuel exhibits good mechanical and thermal properties, it is not yet known whether UMo / Mg / Al fuel, especially the Mg alloy as the fuel matrix, can still maintain good high-temperature strength and plasticity after being damaged by high-dose fast neutron irradiation, and whether it will not significantly affect its neutron economy and thermal conductivity. Therefore, screening a nuclear heat-resistant Mg alloy system and mastering its service performance is the primary problem that needs to be solved in this field.

[0004] Under service conditions, the Mg alloy fuel matrix is ​​mainly affected by the superposition of neutron irradiation and fuel fission fragments (fission gas) recoil, which causes irradiation damage, thus affecting its thermal / mechanical properties. Since reactor neutron irradiation has the characteristics of high cost, long cycle, and many interference factors (wide neutron energy spectrum, uneven temperature distribution), it is not conducive to the screening of Mg alloy matrix materials and the study of their irradiation damage behavior.

[0005] Ion irradiation, because its initial process of producing atomic displacement is very similar to neutron irradiation, has many advantages such as single and stable energy, controllable temperature, low experimental cost, short cycle, and basically no radioactivity. Therefore, ion irradiation is widely used internationally to simulate the neutron irradiation damage behavior of materials. The difference is that conventional nuclear structural materials only need to consider the radiation damage caused by neutron irradiation, while magnesium alloys as fuel matrix materials need to consider the superposition effect of neutron irradiation and fission gas at the same time. However, there are currently no reports on the research methods for the irradiation damage behavior of magnesium-based fuel matrices under service conditions. In view of the above situation, it is necessary to propose an effective and convenient research method. Summary of the invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a research method for the radiation damage behavior of a magnesium-based fuel matrix under simulated service conditions, which is mainly used to effectively and conveniently realize the research on the radiation damage behavior of Mg alloy fuel matrix materials under service conditions, and at the same time realize the rapid screening of heat-resistant Mg alloy systems for fuel matrices.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows.

[0008] A method for studying the irradiation damage behavior of magnesium-based fuel matrix under simulated service conditions is proposed. + and Mg + Dual-beam ion coordinated irradiation simulates the radiation damage in the magnesium-based fuel matrix under service conditions. He gas is used to generate He + Ion irradiation simulates the radiation damage caused by the recoil of fuel fission gas; MgO is used as a target to generate self-ions (Mg + ) Irradiation simulation of radiation damage caused by neutron irradiation, including the following steps:

[0009] Step 1: SRIM simulation: SRIM software is used to calculate different energy Mg + and He + The injection depth in magnesium alloys is determined by the energy range of the ion accelerator and the micro-nano processing depth of the focused ion beam. + and He + The coordinated irradiation ensures that Mg + and He + There are common observable areas of damage from irradiation;

[0010] Step 2: Beam current adjustment: Prepare a beam current density that can be adjusted to a certain value. + The target material is selected and the beam centering and irradiation area are adjusted;

[0011] Step 3: Sample pretreatment before irradiation: mainly including sample cutting, mechanical grinding and polishing, electrolytic polishing, ultrasonic cleaning and metallographic inspection;

[0012] Step 4: Dual-beam ion coordinated irradiation experiment: Draw the vacuum of the irradiation target chamber, set the neutron injection required for the irradiation experiment according to the SRIM calculation results, and set the required irradiation temperature. + and He + The ion beam is simultaneously injected into the sample;

[0013] Step 5. Preparation and characterization of irradiation damaged samples: Referring to the results of the irradiation damage layer depth calculated by SRIM, the irradiated samples were micro-nano processed along the irradiation depth direction using a focused ion beam scanning electron microscope (FIB) to prepare transmission electron microscope samples for characterizing the irradiation damage behavior of neutron irradiation and fission gas on the magnesium-based fuel matrix.

[0014] Based on the technical solution provided by the present invention, further improvements are made.

[0015] Different energies of Mg calculated according to SRIM + Ions and He + The depth of the damaged layer of ions in the Mg alloy and the maximum beam density that can be obtained under different irradiation energies are used to determine the Mg + The ion irradiation energy is 1.5 MeV, He + The ion irradiation energy is 100 keV.

[0016] Further optimization of the above technical solution: the higher the electronegativity of the element, the easier it is to combine electrons to form negative ions. Since Mg has negative electron affinity, it is not easy to form metastable negative ions, so it is difficult to obtain strong Mg + As for the ion beam current, only the beam current drawn out by MgO can reach above 10nA after reaching the target chamber, which meets the experimental requirements. Therefore, the target material is MgO.

[0017] Further optimization and improvement, the irradiated sample size is 1mm×3mm×5mm.

[0018] Preferably, considering Mg + and He + Comparative analysis of radiation damage between single / co-irradiated samples, the He + The ion irradiation area is 10mm×10mm, Mg + The ion irradiation area is 10mm×6mm, He + Ions and Mg + The ion cooperative irradiation area is 10 mm × 3 mm.

[0019] Further optimization and improvement to ensure Mg + and He + The ion beam has a sufficiently large cooperative irradiation area and independent irradiation area. + and He + The incident angle of the ion beam and the sample normal are both 22.5°, Mg + and He + The angle between the ion beams is 45°.

[0020] Preferably, the irradiation temperature is 200°C;

[0021] With further optimization and improvement, the effective depth range of the FIB micro-nano processed sample is 500nm-1000nm.

[0022] Compared with the prior art, the technical effect achieved by the present invention is: providing a research method for irradiation damage behavior of magnesium-based fuel matrix under simulated service conditions, by using He + and Mg + Dual-beam ion coordinated irradiation of magnesium alloy samples can effectively and conveniently realize the study of radiation damage behavior of Mg alloy fuel matrix materials under service conditions, and at the same time realize the rapid screening of heat-resistant Mg alloy systems for fuel matrices. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1.5MeV Mg + SRIM simulation results of ion-irradiated Mg alloy.

[0024] Figure 2 100keV He + SRIM simulation results of ion-irradiated Mg alloy.

[0025] Figure 3 For He + and Mg + Dual-beam ion individual / cooperative irradiation region and area.

[0026] Figure 4 For He + and Mg + Incident beam angle distribution of dual-beam ion cooperative irradiation. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] like Figure 1-Figure 4 As shown, a research method for irradiation damage behavior of a magnesium-based fuel matrix under simulated service conditions includes the following steps:

[0029] Step 1: Use the “Ion Dissociation and Quick Calculation of Damage” function of the Stopping and Range of Ions in Matter (SRIM) software to calculate the Mg content of different energies (10 keV-10 MeV). + and He + The incident depth in magnesium alloy, combined with the acceleration energy of the ion accelerator itself and the micro-nano processing depth of FIB in magnesium alloy, are Mg+ and He + The ion beam selects the appropriate implantation energy to obtain the data of the irradiation defect (vacancy) concentration distribution with depth, and then uses the calculation formula between the dislocation damage rate (D isl ocat ion PerAtom, dpa) and the irradiation defect concentration to obtain the Mg at a specific energy. + / He + Ion beam irradiation damage (dpa)-irradiation depth-ion concentration relationship curve for Mg + and He + The coordinated irradiation ensures that Mg + and He + There is a common irradiation damage area within a certain depth of the magnesium alloy caused by the ion beam;

[0030] Step 2: The ion irradiation experiment requires that the sample surface is flat and has no stress damage layer. Therefore, before the ion irradiation experiment, the sample needs to be pre-treated, mainly including sample cutting, mechanical grinding and polishing, electrolytic polishing, ultrasonic cleaning and metallographic inspection; the sample is preliminarily processed using equipment such as a wire cutting machine to ensure that the sample can be placed in the irradiation target chamber; the cut sample surface is ground and polished in turn using sandpaper of different particle sizes (400#, 600#, 800#, 1000#, 1500#, 2000#, 5000#) until the sample surface reaches a mirror effect; electrolytic polishing is used to remove fine scratches and stress layers after mechanical grinding and polishing, and the electrolyte is 10% perchloric acid + 90% alcohol solution, and the temperature is between -30℃ and -25℃; after polishing, it is immediately rinsed with alcohol, and the sample surface is observed with a metallographic microscope to confirm that there are no scratches and distortions on the surface;

[0031] Step 3: First, according to Mg + Ion beam characteristics, screening from pure Mg and various Mg-containing compounds to produce high beam density Mg + Ion beam target; secondly, combined with the energy range of the accelerator, adjust and test Mg at different energies + The beam current density of the ion beam is determined by screening the optimal injection energy based on the obtained beam current intensity; and the appropriate He is adjusted using the same method + The injection energy of the ion beam is adjusted by adjusting the shape of the magnetic confinement coil and the deflection electrode to control the Mg + and He + Ion beam centering and irradiation area;

[0032] Step 4: Start the mechanical pump and molecular pump in sequence to reduce the vacuum degree of the irradiation target chamber to 1×10 -4Pa, the sample is heated by heating the accelerating resistance wire behind the irradiation sample stage, and the temperature of the sample is controlled by a temperature measuring thermocouple; then, according to the relationship between the ion beam irradiation damage (dpa) and the ion injection obtained by SRIM calculation, the Mg + and He + The ion beam fluence counter and Mg + and He + The ion beam is injected into the sample at the same time, and the irradiation experiment is completed when the counter stops counting;

[0033] Step 5: Refer to the specific energy Mg obtained by SRIM calculation + and He + The depth of the irradiation damage layer of the ion beam is determined, and the irradiated sample is micro-nano processed along the irradiation depth direction using a focused ion beam scanning electron microscope (FIB). The area of ​​the processed sample is controlled by adjusting the beam size, micro-nano processing time, and processing area size. When a sample of sufficient area is obtained, the sample is welded to the nanomanipulator using an ion beam, and the ion beam current is adjusted again to thin the sample step by step until the electron beam can easily penetrate the sample, completing the preparation of the transmission electron microscope sample. The different imaging modes of the transmission electron microscope can be used to observe the number, size, type, density and distribution of irradiation defects in the sample, thereby realizing the characterization and analysis of the irradiation damage behavior of the magnesium-based fuel matrix.

[0034] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several modifications and improvements can be made without departing from the principles and core ideas of the patent of the present invention. These modifications and improvements are also considered to be within the scope of protection of the patent of the present invention.

Claims

1. A method for studying the irradiation damage behavior of a magnesium-based fuel matrix under simulated service conditions, comprising the following steps: Step 1: SRIM simulation: SRIM software is used to calculate different energy Mg + and He + The injection depth in magnesium alloys is determined by the energy range of the ion accelerator and the micro-nano processing depth of the focused ion beam. + and He + The coordinated irradiation ensures that Mg + and He + There are common observable areas of damage from irradiation; Step 2: Beam current adjustment: Prepare a beam current density that can be adjusted to a certain value. + The target material is selected and the beam centering and irradiation area are adjusted; Step 3: Pre-treat the sample before irradiation to ensure that the sample surface is flat and has no stress damage layer; Step 4: Dual-beam ion coordinated irradiation experiment: Draw the vacuum of the irradiation target chamber, set the neutron injection required for the irradiation experiment according to the SRIM calculation results, and set the required irradiation temperature. + and He + The ion beam is simultaneously injected into the sample; Step 5. Preparation and characterization of irradiation damaged samples: Referring to the results of the irradiation damage layer depth calculated by SRIM, the irradiated samples are micro-nano processed along the irradiation depth direction using a focused ion beam scanning electron microscope (FIB) to prepare transmission electron microscope samples for characterizing the irradiation damage behavior of neutron irradiation and fission gas on the magnesium-based fuel matrix.

2. The method according to claim 1, characterized in that Different energies of Mg calculated according to SRIM + Ions and He + The depth of the damaged layer of ions in the Mg alloy and the maximum beam density that can be obtained under different irradiation energies are used to determine the Mg + The ion irradiation energy is 1.5 MeV, He + The ion irradiation energy is 100 keV.

3. The method according to claim 2, characterized in that The method according to claim 1 is characterized in that the sample pretreatment before irradiation includes sample cutting, mechanical grinding and polishing, electrolytic polishing, ultrasonic cleaning and metallographic inspection.

4. The method according to claim 3, characterized in that The target material is MgO.

5. The method according to claim 4, characterized in that The irradiated sample has a size of 1 mm×3 mm×5 mm.

6. The method according to claim 1, characterized in that Consider Mg + and He + Comparative analysis of radiation damage between single / co-irradiated samples, the He + The ion irradiation area is 10mm×10mm, Mg + The ion irradiation area is 10mm×6mm, He + Ions and Mg + The ion cooperative irradiation area is 10 mm × 3 mm.

7. The method according to claim 1, characterized in that To ensure Mg + and He + The ion beam has a sufficiently large cooperative irradiation area and independent irradiation area. + and He + The incident angle of the ion beam and the sample normal are both 22.5°, Mg + and He + The angle between the ion beams is 45°.

8. The method according to claim 1, characterized in that The irradiation temperature is 200°C.

9. The method according to claim 1, characterized in that The effective depth range of the FIB micro-nano processing sample is 600 μm-1000 μm.

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