CN109727696B - MOX pellet recycling method - Google Patents

Abstract

A MOX pellet recycling method comprises the following steps: the method comprises the following steps: selecting MOX fuel pellets, and analyzing and detecting appearance, size, uranium plutonium content, impurity content, O/M and density data of the MOX fuel pellets; step two: recycling the unqualified O/M core blocks; step three: recycling the core blocks with unqualified density; step four: recycling the core blocks with unqualified outer diameters; step five: and recycling a plurality of unqualified pellets.

Description

MOX Pellet Recovery and Reuse Method

technical field

The invention belongs to the field of recovery and reuse, and in particular relates to a method for recovery and reuse of MOX pellets.

Background technique

During the MOX green body pressing and pellet sintering process, a certain amount of unqualified pellets are produced due to unsatisfactory parameters such as material fluidity, material physical and chemical properties, and sintering process. In order to improve the product qualification rate, unqualified pellets need to be processed Recycle.

At present, in the field of traditional nuclear fuel manufacturing, unqualified products are mainly processed by container storage. There are three shortcomings. First, the storage of unqualified pellets leads to low utilization of uranium and plutonium materials; The manufacturing cost of pellets is high; the third is that the accumulated pellets will cause radiation damage to equipment and personnel. In order to solve these problems, this patent designs a method of recycling MOX pellets. By sorting out the reasons for unqualified pellets and adopting targeted treatment methods, the problems of low utilization rate of uranium and plutonium materials and large accumulation of pellets are solved. , Realize the reasonable utilization of unqualified pellets, and improve the qualified rate of products.

Contents of the invention

The purpose of the present invention is to provide a method for recycling and reusing MOX pellets, which solves the problem of a single processing method for unqualified pellets and realizes rational utilization of unqualified pellets.

Technical scheme of the present invention is as follows: a kind of MOX pellet recycling method comprises the following steps:

Step 1: Select MOX fuel pellets, analyze and test their appearance, size, uranium and plutonium content, impurity content, O/M, and density data;

Step 2: Pellets whose O/M is not between 1.90 and 1.99 are regarded as unqualified pellets. Put the pellets into the quartz sintering boat, and then put the sintering boat into the sintering furnace; pump the air pressure in the furnace To 0.01-5.00Pa, pass Ar+% _H2 at a speed of 0.1-15.0L/min, select a mixed gas with a content of 0.1-10.0%H2, keep the air pressure between 8-18KPa, and do this reciprocatingly for 1-10 times , the oxygen potential is -800～-150KJ/mol, the dew point is -50～0℃, the H ₂ O content is 10～1000ppm; the temperature in the sintering furnace is raised at a rate of 0.1～10℃/min, and the Keep warm for 0.5-48 hours, keep the air pressure between 1-14KPa, control the gas flow rate at 0.1-35L/min, oxygen potential -700-250KJ/mo, dew point -5-60°C, H ₂ O content of 10 ~1000ppm;

Step 3: For pellets with a density value less than 91% TD, put the pellets into a quartz sintering boat, and then put the sintering boat into the sintering furnace; pump the air pressure in the furnace to between 0.05 and 2.00 Pa. 10L/min speed feeds Ar+%H ₂ , the content of H ₂ is 1-15%, the air pressure is kept between 5-16KPa, and this reciprocating operation is performed 1-10 times, the oxygen potential is -600--150KJ/mol, and the dew point is - 30～0℃, H ₂ O content is 50～700ppm; the temperature in the sintering furnace is raised at a rate of 0.1～3℃/min, and kept at 1200～1800℃ for 0.5～12h, and the air pressure is kept between 2～22KPa. The gas flow control speed is 0.5~10L/min, the oxygen potential is -600~-100KJ/mo, the dew point is -10~-40℃, and the H ₂ O content is 200~1200ppm;

Step 4: Send the pellets with an outer diameter exceeding 8.8mm into the grinding machine at a speed of 5-20cm/min, and grind the pellets at a speed of 30-800rpm;

Step 5: For a density value higher than 97.3% TD, a pellet height of less than 7.3mm, an outer diameter of less than 3.5mm, a _UO2 content of less than 56.4%, a _PuO2 content of less than 3.3%, and an impurity content of more than 6550 μg/g (U +Pu) pellets, put them into the crusher according to the filling rate of 10-80%, and carry out the crushing treatment at the crushing speed of 10-1000rpm under the pressure of 10-500N for 10-2000min; when the crushed particle size distribution In the 2-200μm distribution area, the specific surface area is 0.1-10m ² /g, after that, according to the filling rate of 20-400%, add _ZrO2 grinding balls with a diameter of 1-10mm in the ratio of 1:1 to Feed in N ₂ at a speed of 0.5-10L/h, pre-mix the materials uniformly at a speed of 1-30r/min for 1-90min; then feed N ₂ at a speed of 2-20L/h, Gradually increase the speed of ball milling, and stir at a speed of 10-1000rpm for 20-500min. After the treatment, gradually reduce the stirring speed at a speed of 3-60r/min until it stops;

Step 6: Analyze the uranium and plutonium content, particle size, specific surface, and impurity content of the mixed powder obtained by ball milling. If the strength of the mixed powder is between 0.3 and 1.2 μm, the specific surface area is 7.2 to 36.4㎡/g, and the uniformity Between 98.3 and 99.9, if the impurity content is less than 1730μg/g, it is a qualified powder.

In the second step, after the heat preservation is completed, the temperature is lowered to 35-70°C at a rate of 2-40°C/min, and the pellets are transported out of the sintering furnace, and stored for later use after O/M detection.

In the third step, after the heat preservation is completed, the temperature is lowered to room temperature at a rate of 0.1-10.0°C/min, and the pellets are transported out of the sintering furnace, and stored for later use after the density is detected.

In the fifth step, the crushing medium is WC hard alloy, the medium is spherical, and the diameter is 1-30 mm.

In the step 6, if each parameter is unqualified, return to the corresponding step for processing until the analysis result is qualified, and then mix with UO ₂ and PuO ₂ raw material powder according to the ratio of 5-40%wt, and carry out the subsequent processing of MOX pellet preparation .

Detailed ways

A method for recycling MOX pellets, comprising the following steps:

Step 1: Select MOX fuel pellets, analyze and test their appearance, size, uranium and plutonium content, impurity content, O/M, and density data.

Step 2: Pellets whose O/M is not between 1.90 and 1.99 are regarded as unqualified pellets. Put the pellets into the quartz sintering boat, and then put the sintering boat into the sintering furnace; pump the air pressure in the furnace To 0.01-5.00Pa, pass Ar+% _H2 at a speed of 0.1-15.0L/min, select a mixed gas with a content of 0.1-10.0%H2, keep the air pressure between 8-18KPa, and do this reciprocatingly for 1-10 times , the oxygen potential is -800～-150KJ/mol, the dew point is -50～0℃, the H ₂ O content is 10～1000ppm; the temperature in the sintering furnace is raised at a rate of 0.1～10℃/min, and the Keep warm for 0.5-48 hours, keep the air pressure between 1-14KPa, control the gas flow rate at 0.1-35L/min, oxygen potential -700-250KJ/mo, dew point -5-60°C, H ₂ O content of 10 ~1000ppm; after the heat preservation is over, cool down to 35-70°C at a rate of 2-40°C/min, transfer the pellets out of the sintering furnace, and store them for later use after detecting O/M;

Step 3: For pellets with a density value less than 91% TD, put the pellets into a quartz sintering boat, and then put the sintering boat into a sintering furnace. Pump the air pressure in the furnace to 0.05-2.00Pa, feed Ar+% _H2 at a speed of 1-10L/min, the _H2 content is 1-15%, and the air pressure is kept between 5-16KPa, and the reciprocating operation is 1-10KPa. 10 times, the oxygen potential is -600～-150KJ/mol, the dew point is -30～0℃, the H ₂ O content is 50～700ppm; the temperature in the sintering furnace is raised at a rate of 0.1～3℃/min, and the Insulate at 1800°C for 0.5 to 12 hours, keep the air pressure between 2 and 22KPa, control the gas flow rate at 0.5 to 10L/min, oxygen potential at -600 to -100KJ/mo, dew point at -10 to -40°C, H ₂ O content 200-1200ppm. After the heat preservation is over, cool down to room temperature at a rate of 0.1-10.0°C/min, transfer the pellets out of the sintering furnace, check the density and store them for later use.

Step 4: Send the pellets with an outer diameter exceeding 8.8 mm into the grinding machine at a speed of 5-20 cm/min, and grind the pellets at a rotational speed of 30-800 rpm.

Step 5: For a density value higher than 97.3% TD, a pellet height of less than 7.3mm, an outer diameter of less than 3.5mm, a _UO2 content of less than 56.4%, a _PuO2 content of less than 3.3%, and an impurity content of more than 6550 μg/g (U +Pu) pellets are added to the crusher at a filling rate of 10-80%, crushed at a crushing speed of 10-1000rpm, under a pressure of 10-500N for 10-2000min, and the crushing medium is WC cemented carbide. The medium is spherical, with a diameter of 1-30mm; when the particle size distribution of the crushed particles is in the distribution range of 2-200μm, and the specific surface area is 0.1-10m ² /g, then they are added to the ball mill tank according to the filling rate of 20-400%. Add ZrO ₂ grinding balls with a diameter of 1-10mm at a ratio of 1:1, feed N ₂ at a speed of 0.5-10L/h, and pre-mix the materials uniformly at a speed of 1-30r/min for 1-90min; Feed N ₂ at a speed of ~20L/h, gradually increase the ball milling speed at a speed of 1~25r/min, stir at a speed of 10~1000rpm for 20~500min, after the treatment is completed, gradually decrease at a speed of 3~60r/min stirring speed until it stops;

Step 6: Analyze the uranium and plutonium content, particle size, specific surface, and impurity content of the mixed powder obtained by ball milling. If the strength of the mixed powder is between 0.3 and 1.2 μm, the specific surface area is 7.2 to 36.4㎡/g, and the uniformity Between 98.3 and 99.9, if the impurity content is less than 1730μg/g, it is a qualified powder; if the parameters are unqualified, return to the corresponding steps for processing until the analysis result is qualified, and then mix with UO ₂ , PuO ₂ raw material powders were mixed for subsequent processing of MOX pellet preparation.

Claims (5)

1. A MOX pellet recycling method is characterized by comprising the following steps: the method comprises the following steps:

the method comprises the following steps: selecting MOX fuel pellets, and analyzing and detecting appearance, size, uranium plutonium content, impurity content, O/M and density data of the MOX fuel pellets;

step two: O/M is not between 1.90 and 1.The pellets between 99, which are considered to be unqualified pellets, are loaded into a quartz sintering boat, and then the sintering boat is loaded into a sintering furnace; pumping the pressure in the furnace to 0.01-5.00 Pa, and introducing Ar and H at the speed of 0.1-15.0L/min ₂ Selecting mixed gas with content of H2 of 0.1-10.0%, maintaining gas pressure at 8-18 KPa, repeating the above steps for 1-10 times, oxygen potential at-800 to-150 KJ/mol, dew point at-50-0 deg.C, and H ₂ The content of O is 10-1000 ppm; the temperature in the sintering furnace is increased at the speed of 0.1-10 ℃/min, the temperature is kept at 600-1500 ℃ for 0.5-48H, the air pressure is kept between 1-14 KPa, the gas flow control speed is 0.1-35L/min, the oxygen potential is-700 to-250 KJ/mol, the dew point is-5 to-60 ℃, and the H temperature is ₂ The content of O is 10-1000 ppm;

step three: for pellets with a density value of less than 91% td, the pellets are loaded into a quartz sintering boat, which is then loaded into a sintering furnace; pumping the air pressure in the furnace to 0.05-2.00 Pa, and introducing Ar +% H at the speed of 1-10L/min ₂ ，H ₂ The content is 1 to 15 percent, the air pressure is kept between 5 and 16KPa, the operation is repeated for 1 to 10 times, the oxygen potential is between-600 and-150 KJ/mol, the dew point is between-30 and 0 ℃, and the temperature is H ₂ The O content is 50-700 ppm; the temperature in the sintering furnace is increased at the speed of 0.1-3 ℃/min, the temperature is kept at 1200-1800 ℃ for 0.5-12H, the air pressure is kept between 2-22 KPa, the gas flow control speed is 0.5-10L/min, the oxygen potential is-600 to-100 KJ/mol, the dew point is-10 to-40 ℃, and the H temperature is high ₂ The O content is 200-1200 ppm;

step four: conveying the pellets with the outer diameter of more than 8.8mm into a grinding machine at the speed of 5-20 cm/min, and grinding the pellets at the rotating speed of 30-800 rpm;

step five: TD content of density higher than 97.3%, pellet height of 7.3mm or less, outer diameter of less than 3.5mm, and UO content ₂ Content of PuO is less than 56.4% ₂ Adding pellets containing less than 3.3% of uranium plutonium and more than 6550 [ mu ] g/g of uranium plutonium as impurities into a crusher at a loading rate of 10-80%, and crushing at a crushing speed of 10-1000 rpm under a pressure of 10-500N for 10-2000 min; when the particle size of the crushed particles is distributed in a cloth range of 2-200 mu m, the specific surface area is 0.1-10 m ² After/g, according to 20Adding ZrO with the diameter of 1-10 mm into a ball milling tank according to the proportion of 1 ₂ Grinding ball, N is introduced at the speed of 0.5-10L/h ₂ The materials are mixed uniformly in advance for 1 to 90 minutes at the speed of 1 to 30 r/min; then N is introduced at the speed of 2-20L/h ₂ Gradually increasing the ball milling speed according to the speed of 1-25 r/min, stirring at the rotating speed of 10-1000 rpm for 20-500 min, and gradually reducing the stirring speed at the speed of 3-60 r/min until the treatment is stopped;

step six: and analyzing the uranium plutonium content, the particle size, the specific surface and the impurity content of the mixed powder obtained by ball milling and thinning, wherein if the particle size of the mixed powder is between 0.3 and 1.2 mu m, the specific surface area is 7.2 to 36.4 square meters per gram, the uniformity is between 98.3 and 99.9, and the impurity content is less than 1730 mu g/g, the mixed powder is qualified powder.

2. The MOX pellet recycling method according to claim 1, wherein the MOX pellet recycling method comprises the following steps: in the second step, after the heat preservation is finished, the temperature is reduced to 35-70 ℃ at the speed of 2-40 ℃/min, the pellets are transported out of the sintering furnace, and the pellets are stored for later use after O/M detection.

3. The MOX pellet recycling method according to claim 1, wherein the MOX pellet recycling method comprises the following steps: in the third step, after the heat preservation is finished, the temperature is reduced to the room temperature at the speed of 0.1-10.0 ℃/min, the pellets are transported out of the sintering furnace, and the pellets are stored for later use after the density is detected.

4. The MOX pellet recycling method according to claim 1, wherein: in the fifth step, the crushing medium is WC hard alloy, the medium is spherical, and the diameter of the medium is 1-30 mm.

5. The MOX pellet recycling method according to claim 1, wherein: in the sixth step, if each parameter is unqualified, returning to the corresponding step for processing until the analysis result is qualified, and then according to the proportion of 5-40% w.t and UO% ₂ 、PuO ₂ Mixing the raw material powders, and performing MOX pellet preparationAnd (6) processing.