阅读说明：本技术 一种基于流延成型的fcm燃料芯块制备方法 (Preparation method of FCM fuel pellet based on tape casting ) 是由 刘荣正 刘超华 黄荣厦 刘马林 刘兵 于 2021-07-29 设计创作，主要内容包括：本发明公开了一种基于流延成型的FCM燃料芯块制备方法,包括配制SiC流延浆料,往SiC流延浆料加入TRISO燃料颗粒,制得单层FCM燃料生带,将单层FCM燃料生带叠层,裁切制得芯块生坯,对芯块生坯进行冷等静压和排胶,制得定型的半制品芯块,对半制品芯块烧结,制得FCM燃料芯块。本发明实现了生产成本低、周期短的FCM燃料芯块的制备,避免FCM燃料芯块工作时因为温度分布不均匀对燃料芯块完整性有害,提高了FCM燃料的经济性,提高了核反应堆的安全性,有利于实现产业化。(The invention discloses a preparation method of FCM fuel pellets based on tape casting, which comprises the steps of preparing SiC tape casting slurry, adding TRISO fuel particles into the SiC tape casting slurry to prepare a single-layer FCM fuel green tape, laminating the single-layer FCM fuel green tape, cutting to prepare pellet green blanks, carrying out cold isostatic pressing and glue discharging on the pellet green blanks to prepare shaped semi-finished pellets, and sintering the semi-finished pellets to prepare the FCM fuel pellets. The invention realizes the preparation of the FCM fuel pellet with low production cost and short period, avoids the harm to the integrity of the FCM fuel pellet due to uneven temperature distribution when the FCM fuel pellet works, improves the economy of the FCM fuel, improves the safety of a nuclear reactor, and is beneficial to realizing industrialization.)

1. A preparation method of FCM fuel pellets based on tape casting is characterized by comprising the following steps:

step 1, preparing SiC tape casting slurry;

step 2, adding TRISO fuel particles into the SiC tape-casting slurry to prepare a single-layer FCM fuel green tape;

step 3, laminating the single-layer FCM fuel green belt, and cutting to obtain a pellet green body;

step 4, carrying out cold isostatic pressing and glue discharging on the pellet green body to prepare a shaped semi-finished pellet;

and 5, sintering the semi-finished product pellets to obtain the FCM fuel pellets.

2. A method for preparing FCM fuel pellets based on tape casting according to claim 1, wherein the substep of preparing SiC tape casting slurry in step 1 is:

step 1.1, mixing SiC powder, a sintering aid, a dispersing agent and absolute ethyl alcohol, and performing ball milling on the mixture for 24 hours to prepare slurry A, wherein the proportion of the sintering aid is 10 wt% -15 wt%, the sintering aid is alumina and yttrium oxide, and the mass ratio is (4-7): (6-9), the dispersant is castor oil, the proportion of the dispersant is 0.4 wt% -0.5 wt%, and the proportion of the absolute ethyl alcohol is 45 wt% -55 wt%;

step 1.2, adding 5-9 wt% of adhesive and 4-7 wt% of plasticizer into the slurry A, and performing second ball milling for 24 hours to obtain slurry B, wherein the adhesive is polyvinyl butyral (PVB), the plasticizer is o-phthalic dimethyl dibutyl ester (DBP) and polyethylene glycol (PEG), and the volume ratio is 5: 1;

and step 1.3, defoaming the slurry B under the condition that the vacuum degree is 0.1Pa to obtain SiC tape-casting slurry.

3. A method for preparing FCM fuel pellets based on tape casting according to claim 1, wherein the sub-step of adding the TRISO fuel particles to the SiC tape casting slurry in step 2 to prepare single-layer FCM fuel green tape is:

step 2.1, uniformly distributing TRISO fuel particles and uniformly fixing the TRISO fuel particles on a casting film at intervals, wherein the distribution of the TRISO fuel particles is in a regular triangle shape, and the intervals are 0.05 mm-0.20 mm;

step 2.2, covering the casting film with the TRISO fuel particles with the SiC casting slurry in the step 1 to obtain a TRISO/SiC slurry mixture;

and 2.3, carrying out tape casting on the TRISO/SiC slurry mixture obtained in the step 2.2 to prepare a single-layer FCM fuel green tape, wherein the tape casting conditions are that the tape casting speed is 10-40 mm/min and the drying temperature is 30-60 ℃.

4. A method for preparing FCM fuel pellets based on tape casting according to claim 1, wherein in step 3, the sub-steps of laminating single-layer FCM fuel green tapes and cutting to obtain green pellets are as follows:

step 3.1, cutting the single-layer FCM fuel green tape obtained in the step 2 into equal lengths to obtain equal-length FCM fuel green tapes;

3.2, laminating the FCM fuel green belts with equal length in a mold, wherein the interval of TRISO fuel particles between adjacent laminations is 0.10-0.20 mm;

and 3.3, cutting the laminated FCM fuel green belt with equal length along the edge of the TRISO fuel particles to obtain a pellet green body, wherein the content of the TRISO fuel particles is 40-50 vol%.

5. A method for preparing FCM fuel pellets based on tape casting according to claim 1, wherein in step 3, the sub-step of laminating single-layer FCM fuel green tapes and cutting them into green pellets further comprises:

step 3.1, cutting the single-layer FCM fuel green tape into equal lengths to obtain equal-length FCM fuel green tapes;

step 3.2.1, setting a variable i with an initial value of 1; setting N as the lamination times; taking a 1 st FCM fuel green belt with equal length as a 1 st green belt layer;

step 3.2.2, laying TRISO fuel particles above the ith green belt layer to serve as the ith fuel layer; wherein the interval of the TRISO fuel particles is 0.10 mm-0.20 mm;

step 3.2.3, acquiring an infrared thermal imaging image of the ith fuel layer, and graying the infrared thermal imaging image to obtain a gray scale image;

step 3.2.4, extracting edge lines in the gray values through edge detection operators, wherein each edge line divides the gray values into a plurality of temperature control areas; calculating the arithmetic mean value of the gray values of all pixels in all temperature control areas;

step 3.2.5, setting the temperature control area with the maximum arithmetic mean value of the gray value of each pixel in each temperature control area as A; each temperature control area adjacent to A in each temperature control area is formed into a set B;

setting the temperature control area with the minimum arithmetic mean value of the gray values of all pixels in the set B as Bmin; setting a first temperature control threshold value as the maximum gray value of the pixel in Bmin;

setting the temperature control area with the maximum arithmetic mean value of the gray values of all pixels in the set B as Bmax; setting a second temperature control threshold value as the maximum gray value of the pixel in Bmax;

step 3.2.6, when the arithmetic mean value of the gray value of each pixel in the temperature control area with the maximum arithmetic mean value of the gray value of each pixel in each temperature control area exceeds a first temperature control threshold, recording that a first condition is met, otherwise, recording that the first condition is not met and a second condition is not met, wherein the first condition and the second condition are not met at the beginning;

when the first condition is met, further judging whether the gray value of a pixel point with the maximum gray value in each pixel in the temperature control area exceeds a second temperature control threshold value, if so, recording that the second condition is met, otherwise, recording that the second condition is not met;

step 3.2.7, when the first condition is satisfied and the second condition is satisfied, re-executing step 3.2.3 to step 3.2.6 at intervals T until going to step 3.2.9 when the first condition is satisfied and the second condition is not satisfied;

step 3.2.8, when the first condition is satisfied and the second condition is not satisfied, re-executing step 3.2.3 to step 3.2.6 at interval T until going to step 3.2.9 when the first condition is not satisfied and the second condition is not satisfied;

step 3.2.9, laying the (i + 1) th FCM fuel green tape with equal length as an (i + 1) th green tape layer above the (i) th fuel layer;

step 3.2.10, when i is less than or equal to N, increasing the value of i by 1 and transferring to step 3.2.2; when i > N, then a stack of equal length FCM fuel green tapes is obtained and transferred to step 3.2.11;

and 3.2.11, cutting the laminated FCM fuel green tape with equal length along the edge of the TRISO fuel particles to obtain the pellet green body, wherein the content of the TRISO fuel particles is 40-50 vol%.

6. A FCM fuel pellet preparation method based on tape casting according to claim 1, characterized in that the cold isostatic pressure in step 4 is 100MPa to 200MPa, the dwell time is 300 s; the glue discharging adopts a secondary glue discharging process, the highest temperature is 300-450 ℃, the heating rate of the glue discharging is 0.3-3 ℃/min, and the heat preservation is carried out for 0.5-1 h at the highest temperature of the glue discharging.

7. A method for preparing FCM fuel pellets based on tape casting according to claim 1, wherein the sintering mode in step 5 is spark plasma sintering, and the sintering conditions are as follows: the sintering temperature is 1700-1900 ℃, the sintering pressure is 10-50 MPa, the heating rate is 50-150 ℃/min, the heat preservation time is 0.1-0.5 h, and the sintering atmosphere is N₂Or Ar or vacuum.

8. A method of manufacturing FCM fuel pellets based on tape casting according to claim 3, characterized in that the fixed TRISO fuel particles in step 2.1 are controlled on the tape casting by negative pressure suction means, the sub-steps are:

step 2.1.1, casting a SiC raw belt without TRISO fuel particles on a casting film by using a casting scraper, wherein the height of the casting scraper is 0.6-0.7 mm;

step 2.1.2, moving the negative pressure suction device to the position above the TRISO fuel particles, providing negative pressure by using a vacuum pump, and adsorbing the TRISO fuel particles on needles which are uniformly distributed and have consistent intervals;

and 2.1.3, moving the negative pressure suction device to the position above the SiC green tape without the TRISO fuel particles, and switching the vacuum pump to positive pressure to provide blowing force so that the TRISO fuel particles are sunk into the SiC green tape to be fixed.

9. A tape-casting based FCM fuel pellet preparation method according to claim 3, wherein the fixed TRISO fuel particles in step 2.1 are controlled by a dispenser on the cast film, the sub-steps being:

step 2.1.1, uniformly dispensing glue on the casting film by a movable glue dispenser at consistent intervals;

step 2.1.2, spraying TRISO fuel particles on the cast film subjected to adhesive dispensing, and dispersing and fixing the TRISO fuel particles on the position of the adhesive by using a soft brush;

step 2.1.3, the TRISO fuel particles which are not fixed are sucked away by a vacuum machine.

10. A tape-casting based FCM fuel pellet preparation method according to claim 8 wherein the movement of the negative pressure suction means or the glue dispenser is controlled by a rail slide means or a robotic arm.

Technical Field

The invention relates to the technical field of nuclear fuel preparation, in particular to a preparation method of FCM fuel pellets based on tape casting.

Background

In a commercial pressurized water reactor nuclear power plant, the nuclear fuel used by the nuclear power plant usually uses zirconium alloy as a cladding material, the comprehensive performance of the zirconium alloy is enough to meet the use requirement in normal operation, but once an accident occurs and the environmental temperature is too high, the performance of the zirconium alloy can be seriously degraded, and the zirconium water can react to generate hydrogen, so that explosion can occur, and a catastrophic result can be caused.

After the fukushima accident happens, in order to improve the safety and reliability of the nuclear power station and reduce the operation cost, a new generation of fuel concept accident fault-tolerant fuel (ATF) is produced, the fuel obviously improves the bearing capacity of the accident, the probability of hydrogen explosion under the accident working condition can be effectively reduced, meanwhile, the good performance is kept during normal operation, and the full ceramic micro-packaging Fuel (FCM) is one of the fuels.

The FCM fuel mainly comprises TRISO fuel particles and SiC-based ceramic, and the SiC matrix has good thermal conductivity, radiation damage resistance, environmental stability and diffusion resistance. Furthermore, the encapsulation of the TRISO particles in a dense SiC matrix provides multiple obstacles to the release of fission products.

Current FCM fuels are primarily hot pressed from particles of TRISO fuel dispersed in a SiC matrix. In order to more efficiently produce FCM fuels, researchers have investigated a variety of production methods.

Such as the document "Ang C, Singh G, Snead L, et al, preferably study of study zero-depth Filled Ceramic Microencapsulated (FCM) fuel [ J]In International Journal of Applied Ceramic Technology, 2019, the authors employed SiC with Al₂O₃、Y₂O₃PEI, drying and de-agglomerating to form a round green body with dents, filling the dents with TRISO particles, and stacking and sintering the green body to prepare the FCM pellet. The FCM pellet prepared by the method has high density, and prevents TRISO particles from cracking. However, the preparation method has complicated steps and is difficult to realize industrialization.

Also, for example, the documents "Kim H M, Kim Y W, Lim K Y. pressure strained silicon carbide matrix with a new qualitative addition for full microbial encapsulated fuels [ J]In the Journal of the European Ceramic Society, 2019, 39(14), the authors add SiC to AlN, Y₂O₃、Sc₂O₃And mixing MgO, performing ball milling, drying and sieving to obtain matrix powder, and then respectively pressing the shell without the TRISO particles and the core mixed by the coated TRISO particles and the matrix powder by using the matrix powder. Assembling the shell and the core together, and preparing the FCM core block by pressureless sintering. The volume fraction of TRISO particles of the FCM pellets is low, the distribution of the TRISO particles is uneven, and more residual air holes are formed in the SiC matrix, which may affect the working performance of the FCM pellets.

Also, as disclosed in patent specification CN107578837A, a method for integrally molding a plate-like all-ceramic-coated fuel pellet includes the steps of: (1) respectively preparing SiC/TRISO composite green tapes and single SiC green tapes; (2) preparing a green body having an upper layer structure, a middle layer structure and a lower layer structure; wherein, the upper layer structure and the lower layer structure are both more than one layer of single SiC green tape, and the middle layer structure is more than one layer of SiC/TRISO composite green tape; (3) carrying out cold isostatic pressing and glue discharging treatment on the green body to prepare a semi-finished product; (4) and sintering the semi-finished product to obtain a finished product. The distribution of TRISO fuel particles in the SiC/TRISO composite green tape is not uniform, the distance cannot be controlled, and the volume fraction of the TRISO fuel particles of the FCM pellet is low, so that the economy of the FCM fuel is damaged; meanwhile, the process flow is relatively complicated and is not suitable for industrialization.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a preparation method of FCM fuel pellets based on casting molding.

In order to achieve the technical purpose, the technical scheme of the invention is as follows:

a tape casting based FCM fuel pellet preparation method comprising the steps of:

step 1, preparing SiC tape casting slurry;

step 2, adding TRISO fuel particles into the SiC tape-casting slurry to prepare a single-layer FCM fuel green tape;

step 3, laminating the single-layer FCM fuel green belt, and cutting to obtain a pellet green body;

step 4, carrying out cold isostatic pressing and glue discharging on the pellet green body to prepare a shaped semi-finished pellet;

and 5, sintering the semi-finished product pellets to obtain the FCM fuel pellets.

Further, the substep of preparing the SiC casting slurry in step 1 is:

step 1.1, mixing SiC powder, a sintering aid, a dispersing agent and absolute ethyl alcohol, and performing ball milling on the mixture for 24 hours to prepare slurry A, wherein the proportion of the sintering aid is 10 wt% -15 wt%, the sintering aid is alumina and yttrium oxide, and the mass ratio is (4-7): (6-9), the dispersant is castor oil, the proportion of the dispersant is 0.4 wt% -0.5 wt%, and the proportion of the absolute ethyl alcohol is 45 wt% -55 wt%;

step 1.2, adding 5-9 wt% of adhesive and 4-7 wt% of plasticizer into the slurry A, and performing second ball milling for 24 hours to obtain slurry B, wherein the adhesive is polyvinyl butyral (PVB), the plasticizer is o-phthalic dimethyl dibutyl ester (DBP) and polyethylene glycol (PEG), and the volume ratio is 5: 1;

and step 1.3, defoaming the slurry B under the condition that the vacuum degree is 0.1Pa to obtain SiC tape-casting slurry.

Further, the substep of adding TRISO fuel particles into the SiC tape-casting slurry in the step 2 to prepare the single-layer FCM fuel green tape comprises the following steps:

step 2.1, uniformly distributing TRISO fuel particles and uniformly fixing the TRISO fuel particles on a casting film at intervals, wherein the distribution of the TRISO fuel particles is in a regular triangle shape, and the intervals are 0.05 mm-0.20 mm;

step 2.2, covering the casting film with the TRISO fuel particles with the SiC casting slurry in the step 1 to obtain a TRISO/SiC slurry mixture;

and 2.3, carrying out tape casting on the TRISO/SiC slurry mixture obtained in the step 2.2 to prepare the single-layer FCM fuel green tape, wherein the tape casting conditions are that the tape casting speed is 10-40 mm/min, the drying temperature is 30-60 ℃, and the height of a tape casting scraper 1 is 1.5-2.5 mm.

Further, the substep of uniformly distributing and uniformly fixing the particles of the TRISO fuel on the casting film in the step 2.1 is as follows:

step 2.1.1, casting a SiC raw belt without TRISO fuel particles on a casting film by using a casting scraper 2, wherein the height of the casting scraper 2 is 0.6-0.7 mm;

step 2.1.2, moving the negative pressure suction device to the position above the TRISO fuel particles, providing negative pressure by using a vacuum pump, and adsorbing the TRISO fuel particles on needles which are uniformly distributed and have consistent intervals;

step 2.1.3, moving the negative pressure suction device to the position above the SiC green tape without the TRISO fuel particles, and switching a vacuum pump to provide blowing force for positive pressure to enable the TRISO fuel particles to be sunk into the SiC green tape to be fixed;

preferably, in step 2.1, the sub-step of fixing the TRISO fuel particles on the casting film with uniform distribution and uniform spacing can also be:

step 2.1.1, uniformly dispensing glue on the casting film by a movable glue dispenser at consistent intervals;

step 2.1.2, spraying TRISO fuel particles on the cast film subjected to adhesive dispensing, and dispersing and fixing the TRISO fuel particles on the position of the adhesive by using a soft brush;

step 2.1.3, the TRISO fuel particles which are not fixed are sucked away by a vacuum machine.

Further, the movement of the negative pressure suction device or the dispenser is controlled by a guide rail sliding block device or a mechanical arm.

Further, in step 3, the sub-steps of laminating the single-layer FCM fuel green belts and cutting the laminated single-layer FCM fuel green belts into green pellets are as follows:

step 3.1, cutting the single-layer FCM fuel green tape obtained in the step 2 into equal lengths to obtain equal-length FCM fuel green tapes;

3.2, laminating the FCM fuel green belts with equal length in a mold, so that the interval of TRISO fuel particles between adjacent laminations (namely between each lamination) is 0.10-0.20 mm;

and 3.3, cutting the laminated FCM fuel green belt with equal length along the edge of the TRISO fuel particles to obtain a pellet green body, wherein the content of the TRISO fuel particles is 40-50 vol%.

Preferably, the pellet green body or pellet may be in the shape of a column or a plate.

Preferably, in step 3, the sub-step of laminating the single-layer FCM fuel green tape and cutting the green pellet may further comprise:

step 3.1, cutting the single-layer FCM fuel green tape into equal lengths to obtain equal-length FCM fuel green tapes;

step 3.2.1, setting a variable i with an initial value of 1; setting N as the lamination times (N generally takes 10-50 times); then i takes a value range [1, N +1 ]; taking a 1 st FCM fuel green belt with equal length as a 1 st green belt layer;

step 3.2.2, laying TRISO fuel particles above the ith green belt layer to serve as the ith fuel layer; the method is characterized in that TRISO fuel particles are uniformly distributed and uniformly fixed on a green belt layer at intervals, and the TRISO fuel particles are superposed on the original fuel particles of the green belt layer, so that the prepared pellet green compact has the advantages of improved heat conductivity, uniform combustion temperature distribution and better combustion effect due to the fact that the fuel layers are paved twice under the condition of different temperatures, wherein the interval of the TRISO fuel particles is 0.10-0.20 mm;

step 3.2.3, acquiring an infrared thermal imaging image of the ith fuel layer, and graying the infrared thermal imaging image to obtain a gray scale image; (the gray scale value in the gray scale map at this time corresponds to the fuel bed temperature;

step 3.2.4, extracting edge lines in the gray values through edge detection operators, wherein each edge line divides the gray values into a plurality of temperature control areas; calculating the arithmetic mean value of the gray values of all pixels in all temperature control areas;

step 3.2.5, setting the temperature control area with the maximum arithmetic mean value of the gray value of each pixel in each temperature control area as A; each temperature control area adjacent to A in each temperature control area is formed into a set B;

setting the temperature control area with the minimum arithmetic mean value of the gray values of all pixels in the set B as Bmin; setting a first temperature control threshold value as the maximum gray value of the pixel in Bmin;

setting the temperature control area with the maximum arithmetic mean value of the gray values of all pixels in the set B as Bmax; setting a second temperature control threshold value as the maximum gray value of the pixel in Bmax;

step 3.2.6, when the arithmetic mean value of the gray value of each pixel in the temperature control area with the maximum arithmetic mean value of the gray value of each pixel in each temperature control area exceeds a first temperature control threshold, recording that a first condition is met, otherwise, recording that the first condition is not met and a second condition is not met, wherein the first condition and the second condition are not met at the beginning;

when the first condition is met, further judging whether the gray value of a pixel point with the maximum gray value in each pixel in the temperature control area exceeds a second temperature control threshold value, if so, recording that the second condition is met, otherwise, recording that the second condition is not met; (i.e., calculate the area on the ith fuel bed that may cause local temperature imbalance);

step 3.2.7, when the first condition is satisfied and the second condition is satisfied, re-executing step 3.2.3 to step 3.2.6 at intervals T until going to step 3.2.9 when the first condition is satisfied and the second condition is not satisfied; (the fuel bed temperature is now equalized);

step 3.2.8, when the first condition is satisfied and the second condition is not satisfied, re-executing step 3.2.3 to step 3.2.6 at interval T until going to step 3.2.9 when the first condition is not satisfied and the second condition is not satisfied; (the temperature of the fuel layer is balanced, the heat conductivity of the green body is improved after the balance is achieved, and the temperature distribution of combustion is uniform);

step 3.2.9, laying the (i + 1) th FCM fuel green tape with equal length as an (i + 1) th green tape layer above the (i) th fuel layer;

step 3.2.10, when i is less than or equal to N, increasing the value of i by 1 and transferring to step 3.2.2; when i > N, then a stack of equal length FCM fuel green tapes is obtained and transferred to step 3.2.11;

and 3.2.11, cutting the laminated FCM fuel green tape with equal length along the edge of the TRISO fuel particles to obtain the pellet green body, wherein the content of the TRISO fuel particles is 40-50 vol%.

Further, the pressure of the cold isostatic pressing in the step 4 is 100 MPa-200 MPa, and the pressure maintaining time is 300 s; the glue discharging adopts a secondary glue discharging process, the highest temperature is 300-450 ℃, the heating rate of the glue discharging is 0.3-3 ℃/min, and the heat preservation is carried out for 0.5-1 h at the highest temperature of the glue discharging.

Further, in the step 5, the sintering mode is spark plasma sintering, and the sintering conditions are as follows: the sintering temperature is 1700-1900 ℃, the sintering pressure is 10-50 MPa, the heating rate is 50-150 ℃/min, the heat preservation time is 0.1-0.5 h, and the sintering atmosphere is N₂Or Ar or vacuum.

Compared with the prior art, the invention has the following beneficial technical effects:

1. the invention can simplify the preparation process flow, realize industrialization, and has low production cost and short period;

2. the invention realizes the preparation of the FCM pellets with uniform distribution of TRISO particles and uniform spacing, and avoids the harm to the integrity of the fuel pellets due to nonuniform temperature distribution during working;

3. the volume fraction of TRISO particles of the FCM pellet prepared by the invention is higher, and the neutron economy of FCM fuel is improved;

4. the FCM pellet prepared by the invention has the characteristics of high thermal conductivity, corrosion resistance and capability of sealing fission products and gases, and the safety of a nuclear reactor is further improved.

Drawings

The above and other features of the present invention will become more apparent by describing in detail embodiments thereof with reference to the attached drawings in which like reference numerals designate the same or similar elements, it being apparent that the drawings in the following description are merely exemplary of the present invention and other drawings can be obtained by those skilled in the art without inventive effort, wherein:

FIG. 1 is a schematic view of a casting machine equipped with a negative pressure suction device;

FIG. 2 is a partial schematic view of a casting machine with a dispenser mounted thereon;

FIG. 3 is a schematic diagram showing the arrangement of needles in a negative pressure suction device, in which the suction heads are arranged in a regular triangle and the distances between adjacent needles are consistent;

FIG. 4 is a polished surface of FCM fuel pellets, shown as polished TRISO fuel particles in a circle;

fig. 5 is a flow chart of a preparation method of FCM fuel pellets based on tape casting provided by the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are merely illustrative of the invention and are not intended to be limiting.

Fig. 5 is a flow chart of a FCM fuel pellet preparation method based on casting, and a FCM fuel pellet preparation method based on casting according to an embodiment of the present invention will be described with reference to fig. 5.

Fig. 1 is a schematic diagram of a casting machine equipped with a negative pressure suction device, wherein S1 is a film rolling machine, S2 is a roller, S3 is a drying box, S4 is a casting blade 1, S5 is a casting blade 2, S6 is a casting slurry tank 1, S7 is a hopper 1, S8 is a pneumatic tube, S9 is a vacuum pump, S10 is a guide rail slider device, S11 is a casting blade 3, S12 is a casting blade 4, S13 is a casting slurry tank 2, and S14 is a winding drum.

Fig. 2 is a partial schematic view of a casting machine equipped with a dispenser, wherein S15 is a suction port, S16 is a fur brush, S17 is a hopper 2, and S18 is a dispenser.

FIG. 3 is a schematic view showing the arrangement of needles in a negative pressure suction apparatus, in which the suction heads are arranged in a regular triangle and the distances between the adjacent needles are uniform.

FIG. 4 is a polished surface of FCM fuel pellets, shown as polished TRISO fuel particles in a circle.

The following exemplarily illustrates a preparation method of FCM fuel pellets based on tape casting provided by the present invention, comprising the following steps:

step 1, preparing SiC tape casting slurry;

step 2, adding TRISO fuel particles into the SiC tape-casting slurry to prepare a single-layer FCM fuel green tape;

step 3, laminating the single-layer FCM fuel green belt, and cutting to obtain a pellet green body;

step 4, carrying out cold isostatic pressing and glue discharging on the pellet green body to prepare a shaped semi-finished pellet;

and 5, sintering the semi-finished product pellets to obtain the FCM fuel pellets.

Further, the substep of preparing the SiC casting slurry in step 1 is:

step 1.1, mixing SiC powder, a sintering aid, a dispersing agent and absolute ethyl alcohol, and performing ball milling on the mixture for 24 hours to prepare slurry A, wherein the proportion of the sintering aid is 10 wt% -15 wt%, the sintering aid is alumina and yttrium oxide, and the mass ratio is (4-7): (6-9), the dispersant is castor oil, the proportion of the dispersant is 0.4 wt% -0.5 wt%, and the proportion of the absolute ethyl alcohol is 45 wt% -55 wt%;

step 1.2, adding 5-9 wt% of adhesive and 4-7 wt% of plasticizer into the slurry A, and performing second ball milling for 24 hours to obtain slurry B, wherein the adhesive is polyvinyl butyral (PVB), the plasticizer is o-phthalic dimethyl dibutyl ester (DBP) and polyethylene glycol (PEG), and the volume ratio is 5: 1;

and step 1.3, defoaming the slurry B under the condition that the vacuum degree is 0.1Pa to obtain SiC tape-casting slurry.

Further, the substep of adding TRISO fuel particles into the SiC tape-casting slurry in the step 2 to prepare the single-layer FCM fuel green tape comprises the following steps:

step 2.1, uniformly distributing TRISO fuel particles and uniformly fixing the TRISO fuel particles on a casting film at intervals, wherein the distribution of the TRISO fuel particles is in a regular triangle shape, and the intervals are 0.05 mm-0.20 mm;

step 2.2, covering the casting film with the TRISO fuel particles with the SiC casting slurry in the step 1 to obtain a TRISO/SiC slurry mixture;

and 2.3, carrying out tape casting on the TRISO/SiC slurry mixture obtained in the step 2.2 to prepare the single-layer FCM fuel green tape, wherein the tape casting conditions are that the tape casting speed is 10-40 mm/min, the drying temperature is 30-60 ℃, and the height of a tape casting scraper 1 is 1.5-2.5 mm.

Further, the substep of uniformly distributing and uniformly fixing the particles of the TRISO fuel on the casting film in the step 2.1 is as follows:

step 2.1.1, casting a SiC raw belt without TRISO fuel particles on a casting film by using a casting scraper 2, wherein the height of the casting scraper 2 is 0.6-0.7 mm;

step 2.1.2, moving the negative pressure suction device to the position above the TRISO fuel particles, providing negative pressure by using a vacuum pump, and adsorbing the TRISO fuel particles on needles which are uniformly distributed and have consistent intervals;

step 2.1.3, moving the negative pressure suction device to the position above the SiC green tape without the TRISO fuel particles, and switching a vacuum pump to provide blowing force for positive pressure to enable the TRISO fuel particles to be sunk into the SiC green tape to be fixed;

preferably, in step 2.1, the sub-step of fixing the TRISO fuel particles on the casting film with uniform distribution and uniform spacing can also be:

step 2.1.1, uniformly dispensing glue on the casting film by a movable glue dispenser at consistent intervals;

step 2.1.2, spraying TRISO fuel particles on the cast film subjected to adhesive dispensing, and dispersing and fixing the TRISO fuel particles on the position of the adhesive by using a soft brush;

step 2.1.3, the TRISO fuel particles which are not fixed are sucked away by a vacuum machine.

Further, the movement of the negative pressure suction device or the dispenser is controlled by a guide rail sliding block device or a mechanical arm.

Further, in step 3, the sub-steps of laminating the single-layer FCM fuel green belts and cutting the laminated single-layer FCM fuel green belts into green pellets are as follows:

step 3.1, cutting the single-layer FCM fuel green tape obtained in the step 2 into equal lengths to obtain equal-length FCM fuel green tapes;

3.2, laminating the FCM fuel green belts with equal length in a mold, so that the interval between the TRISO fuel particles between the adjacent laminated layers is 0.10-0.20 mm;

and 3.3, cutting the laminated FCM fuel green belt with equal length along the edge of the TRISO fuel particles to obtain a pellet green body, wherein the content of the TRISO fuel particles is 40-50 vol%.

Preferably, in step 3, the sub-step of laminating the single-layer FCM fuel green tape and cutting the green pellet may further comprise:

step 3.1, cutting the single-layer FCM fuel green tape into equal lengths to obtain equal-length FCM fuel green tapes;

step 3.2.1, setting a variable i with an initial value of 1; setting N as the lamination times (N generally takes 10-50 times); taking a 1 st FCM fuel green belt with equal length as a 1 st green belt layer;

step 3.2.2, laying TRISO fuel particles above the ith green belt layer to serve as the ith fuel layer; the method is characterized in that TRISO fuel particles are uniformly distributed and uniformly fixed on a green belt layer at intervals, and the TRISO fuel particles are superposed on the original fuel particles of the green belt layer, so that the prepared pellet green compact has the advantages of improved heat conductivity, uniform combustion temperature distribution and better combustion effect due to the fact that the fuel layers are paved twice under the condition of different temperatures, wherein the interval of the TRISO fuel particles is 0.10-0.20 mm;

step 3.2.3, acquiring an infrared thermal imaging image of the ith fuel layer, and graying the infrared thermal imaging image to obtain a gray scale image; (the gray scale value in the gray scale map at this time corresponds to the fuel bed temperature;

step 3.2.4, extracting edge lines in the gray values through edge detection operators, wherein each edge line divides the gray values into a plurality of temperature control areas; calculating the arithmetic mean value of the gray values of all pixels in all temperature control areas;

step 3.2.5, setting the temperature control area with the maximum arithmetic mean value of the gray value of each pixel in each temperature control area as A; each temperature control area adjacent to A in each temperature control area is formed into a set B;

setting the temperature control area with the minimum arithmetic mean value of the gray values of all pixels in the set B as Bmin; setting a first temperature control threshold value as the maximum gray value of the pixel in Bmin;

setting the temperature control area with the maximum arithmetic mean value of the gray values of all pixels in the set B as Bmax; setting a second temperature control threshold value as the maximum gray value of the pixel in Bmax;

step 3.2.6, when the arithmetic mean value of the gray value of each pixel in the temperature control area with the maximum arithmetic mean value of the gray value of each pixel in each temperature control area exceeds a first temperature control threshold, recording that a first condition is met, otherwise, recording that the first condition is not met and a second condition is not met, wherein the first condition and the second condition are not met at the beginning;

when the first condition is met, further judging whether the gray value of a pixel point with the maximum gray value in each pixel in the temperature control area exceeds a second temperature control threshold value, if so, recording that the second condition is met, otherwise, recording that the second condition is not met; (calculate the area on the ith fuel bed that may cause local temperature imbalance);

step 3.2.7, when the first condition is satisfied and the second condition is satisfied, re-executing step 3.2.3 to step 3.2.6 at intervals T until going to step 3.2.9 when the first condition is satisfied and the second condition is not satisfied; (the fuel bed temperature is now equalized);

step 3.2.8, when the first condition is satisfied and the second condition is not satisfied, re-executing step 3.2.3 to step 3.2.6 at interval T until going to step 3.2.9 when the first condition is not satisfied and the second condition is not satisfied; (the fuel bed temperature is now equalized);

step 3.2.9, laying the (i + 1) th FCM fuel green tape with equal length as an (i + 1) th green tape layer above the (i) th fuel layer;

step 3.2.10, when i is less than or equal to N, increasing the value of i by 1 and transferring to step 3.2.2; when i > N, then a stack of equal length FCM fuel green tapes is obtained and transferred to step 3.2.11;

and 3.2.11, cutting the laminated FCM fuel green tape with equal length along the edge of the TRISO fuel particles to obtain the pellet green body, wherein the content of the TRISO fuel particles is 40-50 vol%.

Further, the pressure of the cold isostatic pressing in the step 4 is 100 MPa-200 MPa, and the pressure maintaining time is 300 s; the glue discharging adopts a secondary glue discharging process, the highest temperature is 300-450 ℃, the heating rate of the glue discharging is 0.3-3 ℃/min, and the heat preservation is carried out for 0.5-1 h at the highest temperature of the glue discharging.

Further, in the step 5, the sintering mode is spark plasma sintering, and the sintering conditions are as follows: the sintering temperature is 1700-1900 ℃, the sintering pressure is 10-50 MPa, the heating rate is 50-150 ℃/miN, the heat preservation time is 0.1h to 0.5h, and the preferred sintering atmosphere is N₂Or Ar or vacuum.

The present invention will be described in further detail with reference to examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art in light of the foregoing description are intended to be included within the scope of the invention. The specific process parameters and the like of the following examples are also only one example within a suitable range, i.e., those skilled in the art can select the appropriate range through the description herein, and are not limited to the specific values exemplified below.

Example 1

Preparing SiC tape-casting slurry: weighing 35.58g of SiC powder and Al₂O₃4.9045g powder, Y₂O₃6.5172g of powder and 0.5ml of castor oil are put into a ball milling tank for mixing, 75ml of absolute ethyl alcohol is added for first ball milling, and the ball milling time is 24 hours, so that slurry A is prepared; adding 6g of PVB75, 5ml of DBP and 1ml of PEG organic matter into the slurry A, and carrying out secondary ball milling for 24 hours to obtain slurry B; defoaming the slurry B under the condition that the vacuum degree is 0.1Pa to obtain SiC tape-casting slurry;

preparing a single-layer FCM fuel green belt with uniform distribution and uniform spacing of TRISO fuel particles: the method comprises the following steps of (1) carrying out tape casting on a casting scraper 3 (the height is set to be 0.7mm, the height of the casting scraper 4 is set to be 0.6mm, and then carrying out tape casting on SiC tape casting slurry to obtain a SiC raw tape without TRISO fuel particles, wherein a negative pressure suction device is controlled by a guide rail slider to move above a hopper 1 filled with the TRISO fuel particles, a vacuum pump provides negative pressure to suck the TRISO fuel particles onto a needle head, the negative pressure suction device moves above the SiC raw tape without the TRISO fuel particles, the vacuum pump converts vacuumizing into blowing air, the TRISO fuel particles are sprayed onto the raw tape, fixed impact force is obtained by sinking into the raw tape, the SiC tape casting slurry is covered downwards from a material groove 1, then carrying out tape casting, the tape casting is carried out, the tape casting speed is set to be 20mm/min, the drying temperature is set to be 40 ℃, the height of the casting scraper 1 is set to be 2.3mm, the height of the casting scraper 2.5mm, and after drying, preparing a single-layer FCM fuel raw tape casting;

preparing a green pellet: segmenting the single-layer FCM fuel green belt, and cutting the single-layer FCM fuel green belt into equal lengths of 100 mm; laminating the single-layer FCM fuel green belts with the same length in a corresponding mould, wherein the TRISO fuel particles on the upper layer and the lower layer are staggered by 0.10 mm; the stacked single layer FCM fuel green tape was cut into green pellets along the edges of the TRISO fuel particles according to the desired size.

And (3) carrying out cold isostatic pressing and glue discharging on the pellet green body to prepare a shaped semi-finished pellet: the cold isostatic pressing comprises the following specific processes: and (3) carrying out cold isostatic pressing on the pellets, wherein the pressure is 200MPa, and the pressure maintaining time is 300 s.

And (3) carrying out glue discharging treatment on the green body subjected to cold isostatic pressing, wherein a secondary glue discharging process is adopted to prevent the removal of TRISO particle pyrolytic carbon. The method comprises the following specific steps: and (3) placing the pellets subjected to cold isostatic pressing into a glue discharging furnace, heating to 300 ℃ at a heating rate of 0.3 ℃/min, preserving heat for 30min, and then cooling to room temperature along with the furnace. Heating to 450 deg.C at a rate of 2 deg.C/min, maintaining for 30min, and cooling in furnace to obtain shaped semi-finished product core block.

Sintering the semi-finished pellets to obtain FCM fuel pellets with uniformly distributed TRISO particles inside: sintering by adopting a spark plasma sintering technology, putting the semi-finished pellets into a die, placing the die in a sintering furnace, sintering at 1800 ℃, Ar in a sintering atmosphere, 10MPa in a sintering pressure, 100 +/-50 ℃/min in a heating rate, and 10min in a sintering heat preservation time, and finally obtaining the FCM fuel pellets with uniform distribution of TRISO fuel particles and uniform intervals.

Example 2

Preparing SiC tape-casting slurry: weighing 35.58g of SiC powder and Al₂O₃4.9045g powder, Y₂O₃6.5172g of powder and 0.5ml of castor oil are put into a ball milling tank for mixing, 75ml of absolute ethyl alcohol is added for first ball milling, and the ball milling time is 24 hours, so that slurry A is prepared; adding 6g of PVB75, 5ml of DBP and 1ml of PEG organic matter into the slurry A, and carrying out secondary ball milling for 24 hours to obtain slurry B; defoaming the slurry B under the condition that the vacuum degree is 0.1Pa to obtain SiC tape-casting slurry;

preparing a single-layer FCM fuel green belt with uniform distribution of TRISO fuel particles and uniform spacing: the glue dispenser dispenses glue on the casting film uniformly and at consistent intervals; secondly, spraying TRISO fuel particles on the tape casting film subjected to adhesive dispensing, and dispersing and fixing the TRISO fuel particles on the position of the adhesive by using a soft brush; finally, the unsecured particles of TRISO fuel are vacuumed away. Covering the SiC casting slurry prepared in the step (1) from a trough 1 downwards, performing casting molding, setting the casting speed to be 20mm/min, the drying temperature to be 40 ℃, the height of a casting scraper 1 to be 2.3mm and the height of a casting scraper 2 to be 2.5mm, and drying to prepare a single-layer FCM fuel green tape;

preparing a green pellet: segmenting the single-layer FCM fuel green belt, and cutting the single-layer FCM fuel green belt into equal lengths of 100 mm; laminating the single-layer FCM fuel green belts with the same length in a corresponding mould, wherein the TRISO fuel particles on the upper layer and the lower layer are staggered by 0.10 mm; the stacked single layer FCM fuel green tape was cut into green pellets along the edges of the TRISO fuel particles according to the desired size.

And (3) carrying out cold isostatic pressing and glue discharging on the pellet green body to prepare a shaped semi-finished pellet: the cold isostatic pressing comprises the following specific processes: and (3) carrying out cold isostatic pressing on the pellets, wherein the pressure is 200MPa, and the pressure maintaining time is 300 s.

And (3) carrying out glue discharging treatment on the green body subjected to cold isostatic pressing, wherein a secondary glue discharging process is adopted to prevent the removal of TRISO particle pyrolytic carbon. The method comprises the following specific steps: and (3) placing the pellets subjected to cold isostatic pressing into a glue discharging furnace, heating to 300 ℃ at a heating rate of 0.3 ℃/min, preserving heat for 30min, and then cooling to room temperature along with the furnace. Heating to 450 deg.C at a rate of 2 deg.C/min, maintaining for 30min, and cooling in furnace to obtain shaped semi-finished product core block.

Sintering the semi-finished pellets to obtain FCM fuel pellets with uniformly distributed TRISO particles inside: sintering by adopting a spark plasma sintering technology, putting the semi-finished pellets into a die, placing the die in a sintering furnace, sintering at 1800 ℃, Ar in a sintering atmosphere, 10MPa in a sintering pressure, 100 +/-50 ℃/min in a heating rate, and 10min in a sintering heat preservation time, and finally obtaining the FCM fuel pellets with uniform distribution of TRISO fuel particles and uniform intervals.

The invention is not the best known technology.

Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and do not limit the protection scope of the present invention. It will be understood by those skilled in the art that various deductions and equivalents may be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention.