A radioactive waste classification method based on multi-robot collaboration

Abstract

The present invention relates to the field of robot technology, and provides a radioactive waste classification method based on multi-robot collaboration, including: setting a sorting robot waiting area and a handover operation area in the manual loading area; when detecting that the manual loading area has completed the loading of waste bags, the sorting robot transports the waste bags to the handover operation area, and while transporting to the handover operation area, breaks the bags to obtain radioactive waste from the waste bags, and splits and identifies the radioactive waste; starts an idle measuring robot to move to the corresponding handover operation area to pair with the sorting robot, and the sorting robot puts the radioactive waste into the temporary storage bin of the measuring robot; the measuring robot transports the radioactive waste to the barreling operation area; while transporting to the barreling operation area, measures the specific activity of the radioactive waste in the temporary storage bin, and puts the radioactive waste into different waste barrels according to the measured value of the specific activity in the temporary storage bin. The present invention has high sorting efficiency for radioactive waste and ensures the safety of workers.

Description

Technical Field

[0001] The invention relates to the technical field of robots, and in particular to a radioactive waste classification method based on multi-robot collaboration. Background Art

[0002] At present, most of the radioactive waste sorting work is done manually; the second is semi-automatic sorting, for example, the sorting facilities are equipped with lifting devices that can lift and move waste barrels, mobile imaging devices, sorting operation platforms, and measurement systems. In the semi-automatic sorting method, some sorting operation platforms and measurement platforms require manual participation. This will not only reduce the sorting efficiency, but also cannot guarantee the safety of the staff. Therefore, it is necessary to study the systematic and full-process form of automatic sorting of radioactive waste, reduce the problem of workers contacting radioactive waste during the sorting process, and improve the efficiency of automated sorting. Summary of the invention

[0003] The technical problem to be solved by the present invention is: in order to solve the technical problems of low sorting efficiency of radioactive waste and unguaranteed safety of workers, a radioactive waste classification method based on multi-robot collaboration is provided.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A radioactive waste classification method based on multi-robot collaboration, comprising:

[0006] Step S1, setting a sorting robot waiting area and a handover operation area in the manual loading area;

[0007] Step S2, when it is detected that the waste bag loading is completed in the manual loading area, the sorting robot transports the waste bag to the handover operation area, and while transporting it to the handover operation area, the waste bag is broken to obtain the radioactive waste, and the radioactive waste is separated and identified;

[0008] Step S3, start the idle measuring robot to move to the corresponding handover operation area to pair with the sorting robot, and the sorting robot puts the radioactive waste into the temporary storage bin of the measuring robot;

[0009] Step S4, the measuring robot transports the radioactive waste to the barreling operation area; while transporting the radioactive waste to the barreling operation area, the specific activity of the radioactive waste in the temporary storage bin is measured, and the radioactive waste is placed in different waste barrels according to the measured value of the specific activity in the temporary storage bin.

[0010] Furthermore, step S2 includes: identifying the disassembled radioactive waste; the identification process includes: step S21, marking the radioactive waste with a dose rate less than or equal to 20mSv / h with a first classification condition; selecting radioactive waste made of cotton and linen fabrics, rubber products, and plastic products to be marked with a second classification condition; step S22, sorting the radioactive waste marked with both the first classification condition and the second classification condition.

[0011] Further, step S3 includes:

[0012] Step S31, obtaining the position coordinates of the sorting robot in the handover operation area, calculating the position coordinates of the measuring robot in the handover operation area, and obtaining the intersection point of the sorting robot and the measuring robot in the handover operation area;

[0013] Step S32, the measuring robot moves to the junction point and pairs with the sorting robot;

[0014] Step S33, placing the radioactive waste that needs to be sorted identified in step S2 into a temporary storage bin of the measurement robot.

[0015] Furthermore, in step S32, when the measuring robot and the sorting robot are paired, a plurality of heterogeneous robot topology combinations are formed; the heterogeneous robot topology combinations include: a first heterogeneous robot topology combination and a second heterogeneous robot topology combination; wherein the first heterogeneous robot topology combination includes a plurality of point-to-point heterogeneous robot topology structures, each point-to-point heterogeneous robot topology structure includes a measuring robot and a sorting robot that match each other; the second heterogeneous robot topology combination includes a plurality of star-shaped heterogeneous robot topology structures, each star-shaped heterogeneous robot topology structure includes a sorting robot / measuring robot located in the center and measuring robots / sorting robots located around and matching each other.

[0016] Furthermore, step S33 includes the following processes: step S331, dividing the top temporary storage layer of the measuring robot into multiple temporary storage bins, each of which is set with a product material and a dose rate range to be stored; step S332, when the measuring robot receives radioactive waste, it analyzes the dose rate and product material type of the current radioactive waste, and places the radioactive waste into a temporary storage bin corresponding to the dose rate range and product material.

[0017] Furthermore, step S4 includes the following processes: step S41, when a waste bag is sorted, the radioactive waste in a single temporary storage bin is dropped from the bottom into the lower detection layer in turn; step S42, specific activity detection is performed on the radioactive waste in the single temporary storage bin in the detection layer to obtain the specific activity measurement value; step S43, according to the specific activity measurement value, the radioactive waste is transported to the top of the waste barrel corresponding to the specific activity range for unloading; step S45, repeating steps S42-S43 until the radioactive waste in all temporary storage bins is detected and unloaded.

[0018] Furthermore, step S42 includes: step S421, constructing a specific activity detection device, and calibrating the detection efficiency of the specific activity detection device with respect to gamma rays; step S422, measuring whether the weight of the radioactive waste on the specific activity detection device is less than a set threshold value, if it is less than the set threshold value, turning on the background measurement mode, performing background smoothing to obtain the background energy spectrum; if it is not less than the set threshold value, turning on the waste measurement mode, measuring the time t to obtain the radioactive waste energy spectrum; step S423, comparing the background energy spectrum with the radioactive waste energy spectrum, and performing background removal; step S424, using the efficiency curve method to analyze the activity of the sample nuclides, measuring the sample weight, and calculating the specific activity of the corresponding nuclides.

[0019] Furthermore, in step S422, during the local smoothing process, the calculation method of the current smoothed background value is:

[0020] ;

[0021] In the formula, B is the current smoothed background value; is the previous smoothed background value; is the background value of the current measurement; W is the background smoothing factor, which ranges from 0 to 99.

[0022] Furthermore, in step S424, when the efficiency curve method is used to analyze the activity of the sample nuclide, the calculation method is as follows:

[0023] ;

[0024] In the formula, is the activity of a nuclide in the sample to be tested on the specific activity detection device, is the gamma-ray count rate of the nuclide to be analyzed in the gamma energy spectrum of the sample to be tested, is the detection efficiency of the specific activity detection device for the gamma rays to be analyzed, t is the measurement time, and k is the calibration factor.

[0025] Further, step S43 includes: step S431, preparing waste barrels with different color information, setting the specific activity range corresponding to each waste barrel, and marking the position coordinates of each waste barrel; step S432, comparing the specific activity measurement value with the preset specific activity range, and matching the currently detected radioactive waste with the corresponding waste barrel; step S433, if the target waste barrel is matched, obtaining the target position coordinates and target color information of the target waste barrel; step S434, moving the unloading port of the detection layer to the top of the target waste barrel according to the target position coordinates; step S435, photographing the color information of the target waste barrel above the target waste barrel, matching the photographed color information with the target color information, and unloading if the match is successful;

[0026] In step S433, if the target waste bin cannot be matched, a standby waste bin with a different color from the existing waste bins is added, the position coordinates of the standby waste bin are marked, the specific activity range of the standby waste bin is set to meet the specific activity measurement value, and the discharge port of the detection layer is moved to the top of the standby waste bin according to the position coordinates of the standby waste bin and the material is discharged.

[0027] Compared with the prior art, the present invention has the following beneficial effects: the present invention is scientifically and reasonably designed, easy to use, and realizes automatic identification and unmanned barreling of radioactive waste to be sorted based on a sorting robot and a measuring robot. The present invention can perform unmanned measurement of the dose of radioactive waste and sort based on the dose, or perform unmanned measurement of the material of radioactive waste and sort based on the material, thereby achieving efficient operation and reducing personnel injury or result errors caused by manual sorting. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a flowchart of a method for classifying radioactive waste based on multi-robot collaboration.

[0029] Figure 2 It is a structural schematic diagram of the specific activity detection device of the present invention.

[0030] Figure 3 It is a schematic diagram of the detection efficiency of gamma rays (662keV) of the specific activity detection device under different material densities and crystal thicknesses in the embodiment.

[0031] Figure 4 The specific activity detection device (50 mm crystal thickness) in the embodiment is 60 Schematic diagram of the detection efficiency of Co at different densities. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be noted that the terms “first” and “second” are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0034] like Figure 1 As shown, a radioactive waste classification method based on multi-robot collaboration includes: step S1, setting a sorting robot waiting area and a handover operation area in the manual loading area; step S2, when it is detected that the manual loading area completes the loading of waste bags, the sorting robot transports the waste bags to the handover operation area, and while transporting them to the handover operation area, breaks the bags to obtain radioactive waste, and splits and identifies the radioactive waste; step S3, starting an idle measuring robot to move to the corresponding handover operation area to pair with the sorting robot, and the sorting robot puts the radioactive waste into the temporary storage bin of the measuring robot; step S4, the measuring robot transports the radioactive waste to the barreling operation area; while transporting to the barreling operation area, the specific activity of the radioactive waste in the temporary storage bin is measured, and the radioactive waste is put into different waste barrels according to the measured value of the specific activity in the temporary storage bin. The present invention sets up a manual loading area, a sorting robot waiting area, a handover operation area and a barreling operation area. The sorting robot waiting area can be set in the manual loading area; multiple sorting robots can work simultaneously in the sorting robot waiting area, and a measuring robot waiting area can also be set up. The idle measuring robots wait for the working signal of the sorting robots to start, and the measuring robots receive the radioactive waste identified by the sorting robots in the handover operation area; the radioactive waste is tested for specific activity in the measuring robots, and then loaded into different waste barrels in the barreling operation area according to the test results. The present invention can avoid manual participation throughout the process, and safety is guaranteed. In addition, the sorting robots and measuring robots can also do sorting and measuring work while moving, and the sorting and measuring work are closely connected, which improves work efficiency.

[0035] Preferably, step S2 includes: identifying the disassembled radioactive waste; the identification process includes: step S21, marking the first classification condition for radioactive waste with a dose rate less than or equal to 20mSv / h; selecting radioactive waste made of cotton, linen, rubber products, and plastic products and marking the second classification condition; step S22, sorting the radioactive waste marked with both the first classification condition and the second classification condition. Radioactive waste with a dose rate greater than 20mSv / h can be directly collected by a sorting robot. Cotton, linen, rubber products, and plastic products are all combustible materials.

[0036] Preferably, step S3 includes: step S31, obtaining the position coordinates of the sorting robot in the handover operation area, calculating the position coordinates of the measuring robot in the handover operation area, and obtaining the intersection point of the sorting robot and the measuring robot in the handover operation area; step S32, the measuring robot moves to the intersection point and pairs with the sorting robot; step S33, placing the radioactive waste that needs to be sorted identified in step S2 into the temporary storage bin of the measuring robot.

[0037] Preferably, in step S32, when the measuring robot and the sorting robot are paired, a plurality of heterogeneous robot topology combinations are formed; the heterogeneous robot topology combinations include: a first heterogeneous robot topology combination and a second heterogeneous robot topology combination; wherein the first heterogeneous robot topology combination includes a plurality of point-to-point heterogeneous robot topology structures, each point-to-point heterogeneous robot topology structure includes a measuring robot and a sorting robot that match each other; the second heterogeneous robot topology combination includes a plurality of star-shaped heterogeneous robot topology structures, each star-shaped heterogeneous robot topology structure includes a sorting robot located in the center and measuring robots located around and matching each other, or each star-shaped heterogeneous robot topology structure includes a measuring robot located in the center and sorting robots located around and matching each other.

[0038] Preferably, step S33 includes the following process: step S331, dividing the top temporary storage layer of the measuring robot into multiple temporary storage bins, each temporary storage bin sets the product material and dose rate range to be stored; the temporary storage bins are dynamically divided according to the process requirements of each classification task (artificially set default values ​​or dynamically set ranges each time). Division method 1: fixedly dividing the number of temporary storage bins according to the set dose rate range; division method 2: fixedly dividing the number of temporary storage bins according to the set material type; division method 3: fixedly dividing the temporary storage bins according to the classification process requirements combined with the material type and the radioactivity range; division method 4: dynamic division. Based on the classification process requirements (according to the dose rate, according to the product material, according to the dose rate and the material combination), the classification process range and conditions are given, and after the camera product material recognition and the dose rate of the overall material are initially screened, the system automatically estimates the amount of waste in each range and dynamically allocates the number of temporary storage bins. Step S332, when the measuring robot receives the radioactive waste, it analyzes the dose rate and product material type of the current radioactive waste, and puts the radioactive waste into the temporary storage bin corresponding to the dose rate range and product material. According to the preset fixed temporary storage bin or the system preset temporary storage bin, each sub-temporary storage bin has a fixed position space on the measuring robot. When the sorting robot completes the material identification and dose rate measurement of a single object, it is matched with the sub-temporary storage bin of the corresponding classification range.

[0039] Preferably, step S4 includes the following processes: step S41, when a waste bag is sorted, the radioactive waste in a single temporary storage bin is sequentially dropped from the bottom into the detection layer below; step S42, specific activity detection is performed on the radioactive waste in the single temporary storage bin in the detection layer to obtain a specific activity measurement value; step S43, according to the specific activity measurement value, the radioactive waste is transported to the top of the waste barrel corresponding to the specific activity range for unloading; step S45, repeating steps S42-S43 until the radioactive waste in all temporary storage bins is detected and unloaded.

[0040] Preferably, step S42 comprises: step S421, constructing a specific activity detection device, and calibrating the detection efficiency of the specific activity detection device with respect to gamma rays; Figure 2 The figure shows a schematic diagram of the structure of a specific activity detection device 30, which includes a square detection cavity formed by four large-area plastic scintillator detectors 31 and a weight sensor 32 located at the bottom of the measuring layer 3. Each large-area plastic scintillator detector 31 is seamlessly spliced, and there is no detection dead zone. The weight sensor 32 is installed on the bottom of the square detection cavity, that is, below the bottom detector, and can weigh the weight of the radioactive waste to be tested. Lead plates 33 are installed on the front, back, left, right and bottom of the square detection cavity.

[0041] Figure 3The detection efficiency of the specific activity detection device for 137Cs (662keV) gamma rays at different material densities and crystal thicknesses; Figure 4 For the specific activity detection device, the crystal thickness is fixed (50mm) 60 The detection efficiency of gamma rays (1173keV, 1332keV) emitted by Co at different densities. It can be seen that when the thickness of the detection crystal is constant, the higher the degree of compression (body source density), the greater the degree of absorption and scattering of gamma rays by the material, which reduces the detection efficiency. For radionuclides that emit higher energy gamma rays (such as 60 Co), the radiation penetration ability is stronger, but the influence of the source density cannot be ignored.

[0042] Step S422, measure whether the weight of the radioactive waste on the specific activity detection device is less than the set threshold value. If it is less than the set threshold value, turn on the background measurement mode, perform background smoothing to obtain the background energy spectrum; if it is not less than the set threshold value, turn on the waste measurement mode, measure the time t to obtain the radioactive waste energy spectrum; step S423, compare the background energy spectrum and the radioactive waste energy spectrum, and perform background removal; step S424, use the efficiency curve method to analyze the activity of the sample nuclide, measure the sample weight, and calculate the specific activity of the corresponding nuclide.

[0043] Furthermore, in step S422, during the local smoothing process, the calculation method of the current smoothed background value is:

[0044] ;

[0045] In the formula, B is the current smoothed background value; is the previous smoothed background value; is the background value of the current measurement; W is the background smoothing factor, which ranges from 0 to 99.

[0046] Furthermore, in step S424, when the efficiency curve method is used to analyze the activity of the sample nuclide, the calculation method is as follows:

[0047] ;

[0048] In the formula, is the activity of a nuclide in the sample to be tested on the specific activity detection device, is the gamma-ray count rate of the nuclide to be analyzed in the gamma energy spectrum of the sample to be tested, is the detection efficiency of the specific activity detection device for the gamma rays to be analyzed, t is the measurement time, and k is the calibration factor.

[0049] Preferably, step S43 includes: step S431, preparing waste barrels with different color information, setting the specific activity range corresponding to each waste barrel, and marking the position coordinates of each waste barrel; step S432, comparing the specific activity measurement value with the preset specific activity range, and matching the currently detected radioactive waste with the corresponding waste barrel; step S433, if the target waste barrel is matched, obtaining the target position coordinates and target color information of the target waste barrel; step S434, moving the unloading port of the detection layer to the top of the target waste barrel according to the target position coordinates; step S435, photographing the color information of the waste barrel above the target waste barrel, matching the photographed color information with the target color information, and unloading if the match is successful. Preferably, in step S433, if the target waste barrel cannot be matched, adding a standby waste barrel with a different color from the existing waste barrel, marking the position coordinates of the standby waste barrel, setting the specific activity range of the standby waste barrel to meet the specific activity measurement value, and moving the unloading port of the detection layer to the top of the standby waste barrel according to the position coordinates of the standby waste barrel and unloading. The present invention can also replace the color information with other symbolic identifications. In this way, the radioactive waste loaded into each waste barrel is within its specified specific activity range, which is convenient for subsequent treatment of the radioactive waste.

[0050] Finally, it should be noted that the above embodiments are only preferred embodiments of the present invention to illustrate the technical solutions of the present invention, rather than limiting them, and certainly not limiting the patent scope of the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. In other words, any changes or modifications made to the main design concept and spirit of the present invention that have no substantive significance, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention in other related technical fields is also included in the patent protection scope of the present invention.

Claims

1. A radioactive waste classification method based on multi-robot collaboration, characterized in that: include: Step S1, setting a sorting robot waiting area and a handover operation area in the manual loading area; Step S2, when it is detected that the waste bag loading is completed in the manual loading area, the sorting robot transports the waste bag to the handover operation area, and while transporting it to the handover operation area, the waste bag is broken to obtain the radioactive waste, and the radioactive waste is separated and identified; Step S3, start the idle measuring robot to move to the corresponding handover operation area to pair with the sorting robot, and the sorting robot puts the radioactive waste into the temporary storage bin of the measuring robot; Step S3 includes: step S31, obtaining the position coordinates of the sorting robot in the handover operation area, calculating the position coordinates of the measuring robot in the handover operation area, and obtaining the intersection point of the sorting robot and the measuring robot in the handover operation area; step S32, the measuring robot moves to the intersection point and pairs with the sorting robot; step S33, placing the radioactive waste that needs to be sorted identified in step S2 into the temporary storage bin of the measuring robot; Step S33 includes the following processes: Step S331, dividing the top temporary storage layer of the measuring robot into a plurality of temporary storage bins, each of which is set to store product materials and dose rate ranges; Step S332, when the measuring robot receives radioactive waste, it analyzes the dose rate and product material type of the current radioactive waste, and puts the radioactive waste into a temporary storage bin corresponding to the dose rate range and product material; Step S4, the measuring robot transports the radioactive waste to the barreling operation area; while transporting the radioactive waste to the barreling operation area, the specific activity of the radioactive waste in the temporary storage bin is measured, and the radioactive waste is placed in different waste barrels according to the measured value of the specific activity in the temporary storage bin; Step S4 includes the following processes: Step S41, when a waste bag is sorted, the radioactive waste in a single temporary storage bin is sequentially dropped from the bottom into the detection layer below; Step S42, specific activity detection is performed on the radioactive waste in the single temporary storage bin in the detection layer to obtain the specific activity measurement value; Step S43, according to the specific activity measurement value, the radioactive waste is transported to the top of the waste barrel corresponding to the specific activity range for unloading; Step S45, Step S42-Step S43 are repeated until the radioactive waste in all temporary storage bins is detected and unloaded.

2. A radioactive waste classification method based on multi-robot collaboration according to claim 1, characterized in that: Step S2 includes: identifying the disassembled radioactive waste; the identification process includes: step S21, marking the first classification condition for radioactive waste with a dose rate less than or equal to 20mSv / h; selecting radioactive waste made of cotton and linen fabrics, rubber products, and plastic products to mark the second classification condition; step S22, sorting the radioactive waste marked with both the first classification condition and the second classification condition.

3. The method for radioactive waste classification based on multi-robot collaboration according to claim 1 is characterized in that: In step S32, when the measuring robot and the sorting robot are paired, a plurality of heterogeneous robot topology combinations are formed; the heterogeneous robot topology combinations include: a first heterogeneous robot topology combination and a second heterogeneous robot topology combination; wherein the first heterogeneous robot topology combination includes a plurality of point-to-point heterogeneous robot topology structures, each point-to-point heterogeneous robot topology structure includes a measuring robot and a sorting robot that match each other; the second heterogeneous robot topology combination includes a plurality of star-shaped heterogeneous robot topology structures, each star-shaped heterogeneous robot topology structure includes a sorting robot / measuring robot located in the center and matching measuring robots / sorting robots located around it.

4. The method for radioactive waste classification based on multi-robot collaboration according to claim 1 is characterized in that: Step S42 includes: step S421, constructing a specific activity detection device, and calibrating the detection efficiency of the specific activity detection device with respect to gamma rays; step S422, measuring whether the weight of the radioactive waste on the specific activity detection device is less than a set threshold value, if it is less than the set threshold value, starting the background measurement mode, performing background smoothing to obtain the background energy spectrum; if it is not less than the set threshold value, starting the waste measurement mode, measuring the time t to obtain the radioactive waste energy spectrum; step S423, comparing the background energy spectrum with the radioactive waste energy spectrum, and performing background removal; step S424, using the efficiency curve method to analyze the activity of the sample nuclides, measuring the sample weight, and calculating the specific activity of the corresponding nuclides.

5. The method for radioactive waste classification based on multi-robot collaboration according to claim 4 is characterized in that: In step S422, during the local smoothing process, the calculation method of the current smoothed background value is: ； In the formula, B is the current smoothed background value; is the previous smoothed background value; is the background value of the current measurement; W is the background smoothing factor, which ranges from 0 to 99.

6. The method for radioactive waste classification based on multi-robot collaboration according to claim 4 is characterized in that: In step S424, when the efficiency curve method is used to analyze the activity of the sample nuclide, the calculation method used is as follows: ； In the formula, is the activity of a nuclide in the sample to be tested on the specific activity detection device, is the gamma-ray count rate of the nuclide to be analyzed in the gamma energy spectrum of the sample to be tested, is the detection efficiency of the specific activity detection device for the gamma rays to be analyzed, t is the measurement time, and k is the calibration factor.

7. The method for radioactive waste classification based on multi-robot collaboration according to claim 1 is characterized in that: Step S43 includes: step S431, preparing waste barrels with different color information, setting the specific activity range corresponding to each waste barrel, and marking the position coordinates of each waste barrel; step S432, comparing the specific activity measurement value with the preset specific activity range, and matching the currently detected radioactive waste with the corresponding waste barrel; step S433, if the target waste barrel is matched, obtaining the target position coordinates and target color information of the target waste barrel; step S434, moving the unloading port of the detection layer to the top of the target waste barrel according to the target position coordinates; step S435, photographing the color information of the target waste barrel above the target waste barrel, matching the photographed color information with the target color information, and unloading if the match is successful; In step S433, if the target waste bin cannot be matched, a standby waste bin with a different color from the existing waste bins is added, the position coordinates of the standby waste bin are marked, the specific activity range of the standby waste bin is set to meet the specific activity measurement value, and the discharge port of the detection layer is moved to the top of the standby waste bin according to the position coordinates of the standby waste bin and the material is discharged.

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