JPS60195497A - Pellet solidifying method of radioactive waste and device thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method and apparatus for solidifying radioactive waste into pellets, which comprises drying and powdering radioactive waste and then press-molding the powder into pellets. It is particularly suitable for slurry-like radioactive waste that is pulverized using a centrifugal thin film dryer and then solidified into pellets.

[Background of the invention]

Conventionally, radioactive waste generated from equipment handling radioactive materials such as nuclear power plants has been classified and treated or stored according to its characteristics. For example, radioactive liquid waste in the form of a solution, such as ion-exchange resin recycled waste liquid (main component is sulfuric acid: Na2SO4), which is generated in large quantities at boiling water nuclear power plants, is solidified with cement or asphalt in drums. has been done. In addition, used ion exchange resins, filter aids, etc. are stored in the tank in the form of slurry. For this reason, there was a drawback that the storage space for these radioactive wastes became large. Therefore, after drying and powdering the radioactive waste mentioned above using a dryer such as a centrifugal thin film dryer,
Attempts have been made to significantly reduce the volume of radioactive waste by pelletizing it using a granulator such as a briquetting machine. However, the radioactive waste to be treated contains various impurities in addition to the main components such as sulfuric acid and IJium, and its composition changes day by day, making it difficult to obtain pellet gold with high strength and stable physical properties. There wasn't.

[Purpose of the invention]

An object of the present invention is to provide a method and apparatus for solidifying pellets of radioactive waste that can always obtain pellets with high strength and stable physical properties even if the composition of the radioactive waste to be treated changes. .

[Summary of the invention]

The main feature of the present invention is that it uses a system that includes a drying process and a solidification process, and in a system that pulverizes radioactive waste and then turns it into pellets, a part of the slurry to be treated is sampled and its physical properties are evaluated. The drying process is determined according to the physical property values [Embodiment of the invention] The drying machine and granulator, which are the main equipment for solidifying radioactive waste into pellets, depend on the composition of the waste to be processed! The optimum operating conditions differ, and depending on the composition, it may be necessary to add a binder before granulation. The composition of waste generated from nuclear power plants includes various impurities in addition to the main components, and its composition changes daily. Therefore, it is necessary to always maintain the operating conditions of the assimilation device at optimum values. Therefore,
In the example described below, a part or all of the waste slurry is sampled to automatically measure the relationship between concentration and viscosity coefficient, the concentration of insoluble components in the slurry, and the elastic modulus of the waste. Using this result, the powdering process of the centrifugal thin film dryer and the granulation process of the briquetting machine are simulated by computer to determine the operating conditions for the equipment. This calculation result is used to optimally control the entire system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be specifically described with reference to the drawings, taking as an example a case in which the first embodiment of the present invention is applied to a radioactive waste processing apparatus generated from a nuclear power plant. FIG. 1 is a conceptual diagram of a pellet solidification device. In FIG. 1, l is a waste liquid storage tank, 2 is a used resin storage tank, 3 is an adjustment tank, 4 is a metering pump, 5 is a centrifugal thin film dryer, 6 is a powder produced by the dryer 5, and 7 is a binder. A mixer mixes the binder from the hopper 8 and the powder 6, 9 a granulator that turns the powder from the mixer 7 into pellets, 10 pellets, 11 a drum into which the pellets 11 are placed, 12 the slurry in the tank 3 70 is a control computer, 71 is a display using a color CRT (cathode ray tube), 72 is a data input device, and 73 is a typewriter.

The processing method of this embodiment will be explained in detail below.

Waste liquid generated at a nuclear power plant is concentrated and then stored in a waste liquid storage tank 1. The main component of this waste liquid is Na2SO4, which is generated as a result of the regeneration of granular ion exchange resin in boiling water nuclear power plants, and NazB, which is generated by adjusting the concentration of boric acid in the primary cooling water, in pressurized water nuclear power plants.
It is iOy.

In addition, concentrated wastewater contains sand and seawater components as impurities. - Granular and powdered ion exchange resin used for purifying secondary cooling water is stored in the used resin storage tank 2.
is stored in. This resin contains iron rust caused by corrosion of the pipes. Waste from each storage tank is
After being transported to an adjustment tank 3 and stirred uniformly, it is supplied to a centrifugal thin film dryer 5 using a metering pump 4. The produced dry powder 6 falls by gravity into a mixer 7, where the binder stored in the binder hopper 8 is added to the powder as needed, and then the powder and binder are mixed uniformly.

This mixture is passed through a granulator 9 and molded into almond-shaped pellets 10 under pressure. The generated beret 10 is 200
Fill the drum 11 of t. A stable solidified product can be formed by injecting asphalt, plastic, inorganic cement, or water glass into the drum 11 and filling the gaps between the pellets. A physical property measuring device 12, which measures the physical property values necessary to determine the operating conditions of the centrifugal thin film dryer 5 and granulator 9 of this system, is attached to the adjustment tank 3 and automatically removes a portion of the waste. Sampling and measuring physical property values. This value is input to the control computer 70 (70a...
-Storage device, 70b... Arithmetic control device, 70c...
CRTitllJ diagonal device, 70d...process input/output device) and store the device specifications in the storage device;
By combining the processing conditions input through the data input device 72, the dry powdering process and the granulation process are simulated.
Calculate the required operating conditions.

The simulation status is displayed on the CRT display device 71 to notify the operator. The requested operating conditions are also recorded on a typewriter 73. Based on the calculation results, the centrifugal thin film dryer 5 and granulator 9 are controlled via the process input/output device to adjust the amount of binder added.

Next, a simulation model for the dry powderization and granulation process that is incorporated into the control computer 70 will be described. The structure of the centrifugal thin film dryer used for powdering is shown in FIGS. 2 and 3. The centrifugal thin film dryer 5 has a rotating shaft 15 in a body 13 to which a blade 14 is attached. In the upper part of the fuselage 13 a steam outlet 16 and a waste port 17 are provided. Inside it, there is a mist separator 1
8 and a distributor 19 are arranged to form a steam chamber 20. A steam jacket 21 is provided around the fuselage 13, and a steam port 22 and a steam outlet 23 are attached to the steam jacket 21. The blade 14 is rotatably attached via a pin to a support ring 25 that is fixed to the rotating shaft 15 by a support arm 24. This rotating shaft 15 is rotated by a driving motor 26 via a mechanical stepless reducer 74. A non-contact type tachometer 75 is attached to the rotating shaft 15, and while measuring the rotational speed of the rotating shaft 15, the reduction ratio of the stepless reducer 74 is adjusted by remote control. The waste slurry supplied from the adjustment tank is supplied into the body 13 from the waste population 17, is uniformly distributed in the circumferential direction by a distributor 19, and flows down the inner surface of the body 13 by gravity. I will do it.

This slurry is pressed against the inner surface of the body 13 by centrifugal force as the blade 16, which is attached to the rotation axis, rotates in the direction of arrow 27. In this way, the body 13
A thin film of slurry is formed inside. The slurry that has formed a thin film is heated and concentrated by saturated steam 170c flowing outside the body 13 and inside the steam jacket 21.

As the concentration progresses and the liquid film exceeds the saturation concentration, crystals precipitate within the thin film (9). Then, dry powder is generated by the action of the blade 14 and is discharged from the powder outlet 28.

When the performance of this centrifugal thin film evaporator was determined through experiments, it was found that dry powder was produced in the region shown in FIG. The limits of this region are determined by two solid lines: a solid line A, which has little dependence on the rotation speed, and an actual line MB, which varies greatly depending on the rotation speed.

The solid line A is determined by the amount of heat transferred from the steam jacket through the body to the liquid film. Therefore, if the processing flow rate is increased beyond the solid line A, the evaporation of water does not end even at the lower end of the body, and highly concentrated slurry flows out from the powder outlet. Realize the processing flow rate in the low rotation speed area! B
When the amount was increased above, a mass with a high moisture content flowed out from the powder outlet. In order to clarify the cause of this, we observed the flow state inside the centrifugal thin film evaporator using a visual experiment device. The results are shown in FIG. An isolated liquid film 30 exists on the front surface of the blade 29 which is rotating while contacting the body due to centrifugal force, and a part of the isolated liquid film 30 flows out from the gap between the rotating blade (10) root 29 and the body. It is then dried and the powder 31 flows out. FIG. 6 shows the results of measuring the relationship between the concentration of this liquid film and the kinematic viscosity coefficient. Solid component is Na2SO
In the case of 4, Na2SO4 crystals begin to precipitate in the liquid when the temperature exceeds the saturation a degree, and since the crystals are adhesive to each other, the kinematic viscosity coefficient increases rapidly with the concentration, and the concentration is 70W1%.
Above this, fluidity of the liquid is lost. In addition, the solid component Na
When the ratio of 2SO4 to spent resin is 1:1, low iJ
[Since the used resin exists as a suspension in the liquid,
It has a higher kinematic viscosity coefficient than an aqueous solution of Na2S04.

Even with this composition, when crystal precipitation of Na2SO4 begins, the kinematic viscosity increases rapidly, and fluidity is lost at a concentration of more than sowt%. From this result and the observation of the flow state shown in FIG. 5, it can be seen that the concentration of the isolated liquid film 30 existing on the front surface of the blade 29 increases due to heat transfer from the body. Before this liquid film layer rises until it loses its fluidity, the liquid film must pass through the gap between the body and the blade 29 and turn into powder. The faster the powder production rate is, the earlier the powderization is completed while the concentration of the isolated liquid film is low (11). To speed up powder production,
The number of rotations of the blade 29 may be increased.

Therefore, the solid line B defining the powderization limit in Fig. 4 indicates that due to the insufficient rotation speed, the concentration of the isolated liquid film becomes cylindrical before the powderization of the liquid film is completed, and the fluidity of the liquid film increases. This corresponds to the case where the In the FA4 diagram, Na2SO4
The reason why the mixed composition of used resin and used resin requires less rotational speed for powdering is that the mixed composition has better fluidity in the high concentration range, as seen from the measurement results of the kinematic viscosity coefficient shown in Figure 6. It depends on whether it can be maintained or not. From these results, it can be seen that the main factor that determines the powdering performance of the centrifugal thin film dryer is the change in viscosity of the slurry. FIG. 7 shows the calculation process when this model is simulated by a computer. The calculations shown in Figure 7 are performed for each mesh that vertically divides the torso. First, using the flow rate and kinematic viscosity coefficient of the liquid film flowing down each mesh, calculate the length t-5 of the isolated liquid film using equation (1) from the balance between the gravity acting on the isolated liquid film and the viscous force with the body. do.

(12) Here, C: Kinematic viscosity coefficient of liquid film ■＝Downstream flow rate n: Number of blades for each stage g: gravitational acceleration Angle between θni blade and body It is.

Next, using the length t of the isolated liquid film, the heat flux transmitted from the body to the liquid film is calculated using equation qe (2).

Here, ΔT is the temperature difference between the heated steam and the liquid film, t is the heat transfer coefficient between the heated steam and the heat transfer surface, t is the thickness of the heat transfer surface, and is the thermal conductivity of the heat transfer surface. It is the heat transfer coefficient between the hot surface and the liquid film.

The powder production rate P generated through the gap between the blade and the body is calculated using equation (3).

(13) Here, e: experimental constant ρ1: Liquid film density C: Solid content concentration in liquid film δGap height between blade and body U Niblade circumferential speed It is.

From equation (2), the amount of heat transferred to the isolated liquid film is 1, which has the effect of increasing the concentration of the isolated liquid film, and powder generation suppresses the increase in concentration. From these two values, the change in concentration and downstream flow rate 'k for each mesh is calculated using equations (4) and (5).

V(Z+dZ)=V(Z)-qtn/l-1-pn=
−=(4)C(Z+dZ)=(V(Z)C(Z)
-pn)/V (Z+dZ) (5) where %H: latent heat of vaporization 2: distance from waste inlet.

The simulation of this powdering process is stopped under any of the following 3 (14) conditions. 1) Even at the lower end of the fuselage,
If there is a downstream flow rate of the liquid film, this is the waste slug I
This corresponds to a case where J fj is too large and drying is not completed, and the processing flow value is greater than the solid line A in FIG. 4. 2) When the concentration of the isolated liquid film existing in front of the rotary blade becomes sieved and loses its fluidity, an undried lump is formed.
This corresponds to the case where the processing flow rate is increased beyond the solid line B in the figure. 3) In cases where none of the former cases apply, all of the waste slurry supplied to the centrifugal thin film dryer is in a dry powder state, which is the powder defined by solid lines A and B in Figure 3. Corresponds to the conversion generation area. If there is a good correspondence between the calculated results and the experimental results, and if the kinematic viscosity coefficient of the waste slurry and the specifications of the equipment are known, then the powdering performance of the centrifugal thin film dryer can be fully evaluated.

Next, we will discuss the results of the study on the granulation process.

The main structure of the granulator is shown in Figure 8. A pair of disc-shaped rolls 31Vi has a pocket carved into its end face in the same shape as a pellet cut in half. This roll 31 rotates at a constant speed while a force is applied by hydraulic pressure in the direction (15) in which the gap between the rolls becomes narrower.

The dry powder produced by the centrifugal thin film dryer is added with a binder and then stored in the hopper 32 of the granulator. This mixed powder is preliminarily compressed by the rotation of the screw feeder 33, forced into the gap between the rolls 31, and formed into an almond-shaped pellet 34 by the compression force of the rolls.

The pressure of the hydraulic cylinder 36 that pressurizes the roll is released by the relief valve 3.
If the valve 8 is closed and the boost pump 39 is driven, the pressure will rise, and if the relief valve 38 is opened, the pressure will fall. Therefore, by operating the relief valve 38 and the boost pump while observing the value of the pressure gauge 37, the pressurizing force of the roll can be adjusted remotely. If the roll pressing force is too small, the strength of the pellet to be formed will decrease, and if it is too large, wear wrinkles on the roll 31, its bearings, etc. will become excessive. Since it has been empirically known that this pressing force depends on the physical properties of the powder, the results of examining the relationship between the powder composition and the optimum pressing force will be described below.

NazSOi powder was granulated by varying the pressure (1
6) Figure 9 shows the change in pellet compressive strength over time.

As a result, it was found that the pellet compressive strength initially increases in direct proportion to the pressing force, but after a while, the pellet compressive strength reaches a constant value. Therefore, the pressurizing force when the pellet strength becomes constant is defined as the critical pressure (point PA in the figure), but it is desirable to operate the briquetting machine at the critical pressure PA in order to completely reduce wear on the equipment. . Effect of powder composition on critical pressure 7! In order to investigate this, the compaction process of the powder was observed using an electron microscope, and the results are shown in FIG. At a stage where the pressing force is low (initial state a), the arrangement of the powder changes and the powder becomes densely packed, thereby reducing the overall volume. As the pressing force is further increased, the powder undergoes plastic deformation and the contact area between the powders increases, resulting in an increase in adhesion (powder alignment state b), and when the pressing force reaches a critical pressure. , the powders are almost completely combined with each other, and there are no gaps between the powders (deformation state C of the powder). Therefore, even if the pressing force is increased beyond the critical pressure, the contact surface between the powders (
17) Since the product does not increase, the compressive strength of the pellet does not depend on the applied force above the critical pressure. Usually, N a2
Ionic crystals such as S04, NaNOs, and Na2B401 have low ductility, so they are crushed into small pieces when compressed along the -axis. However, as in the case of powder compression, it becomes difficult to break when pressure is applied from the surroundings, so even ionic crystals undergo plastic changes like metals, and the powder shape changes in the direction of increasing the overall density. Change. Furthermore, when considering the relationship between the physical properties of the powder and the critical pressure, it was found that there is a strong correlation between the elastic modulus and the critical pressure as shown in FIG. It was found that the factor that contributes most to the granulation properties is the elastic modulus of the powder.

Next, FIG. 12 shows the results of measuring the effect of the insoluble substance on the compressive strength of the pellet. The used ion exchange resin powder has a large elastic modulus, so when the pressure is reduced after pressure granulation, the used ion exchange resin powder tends to expand inside the pellet compared to the surrounding area. Therefore, internal stress remains in the pellet. Therefore, when a compression test is performed on the pellets produced (18), the more used ion exchange resin there is, the lower the compression force will cause the pellets to break. FIG. 13 shows the measurement results of pellet compressive strength when peso3 was included as an impurity. Fezes
The more that is included, the more the pellet strength decreases due to the internal stress caused by the difference in the elastic modulus. Compared to used ion exchange resin, Fe20s is less effective in reducing pellet strength than spe! OS is better!
Small difference in elastic modulus from S O4 and % Pe20
This is due to two effects: since B has a lower density, the space occupied by impurities within one pellet decreases.

If the amount of insoluble components in the powder component increases and it is not possible to form it into a pellet simply by applying pressure, it is necessary to add a binder to the dry powder. The relationship between the amount of binder added and pellet strength is shown in FIG. As the binder, various types of plastics can be considered, but in the example shown in Fig. 14, finely cut cellulose fibers, which are vegetable fibers, are used. The reason for using cellulose fiber is
Cell (19) Loin fiber is used as a filter aid in nuclear power plants, and pellets containing this cellulose fiber binder are
This is because it can be dissolved in water and returned to a solution and cellulose fiber.

Based on the above modeling of the powdering process in the centrifugal thin film dryer and the study results of the powder compression process in the granulator, we will describe the operation for determining pellet solidification. Details of the physical property measuring device shown in FIG. 1 are shown in FIG. 15.

After starting the circulation pump 41 attached to the adjustment tank 3 and stirring the composition inside the tank 3 uniformly, the valve 42
is opened, the metering pump 43 is started, and the slurry is supplied to the physical property measuring device 12. An overflow line 46 is provided in the horizontally installed sampling container 45, and the sampling amount is defined as 1 t. After stopping the metering pump 43, the valves 42 and 47 are closed. Inside this sampling container 45, there is provided a stirring blade 48 in which a 2 kW heater is fully incorporated. This stirring wing 4
A torque meter 51 is provided on the shaft 50 of the motor 49 that rotates the motor 8. Further, on the shaft 50 (20) there is a slip ring 44 for supplying power to the heater.

The sample liquid is heated by the heater while rotating the stirring blade 48 at 10 revolutions per minute. The generated steam is conveyed to the cooler 53 through the steam outlet 52, condensed, and then returned to the adjustment tank 3 by gravity.

Two sensors, a thermocouple 54 and an ultrasonic velocity meter 55, are attached to the sampling container 45.

After starting heating with the heater, the temperature of the liquid in the sampling container 45, the torque of the stirring blade 48, and the speed of sound in the solution are measured, and the results are input into the microcomputer 56. At this time, the signals transmitted to the microcomputer 56 are as shown in FIG. The temperature TL inside the sampling container 45 increases rapidly over time, but when the latent heat due to water evaporation is used, the temperature becomes a constant value #'tFR'. As soon as the evaporation of water ends, the liquid temperature starts to rise rapidly. The point where this water evaporation starts is defined as A, and the point where it ends is defined as B. If the temperature difference between this person and B is small, it is easy to powderize the slurry, and if the temperature difference is high, powderization is difficult. The reason for this principle (21) is NazSO4, NaN0*, Na2B40
In the case of a salt such as t, the boiling point rise is less than 5c, whereas in order to completely evaporate the water in an aqueous solution of H2SO4 or NaOH, it is necessary to heat it to nearly 300r.

Therefore, if the I)H of the waste slurry deviates significantly from neutrality, NaOH will remain in a liquid state during the dry powdering process, and this liquid will bind the powders together and inhibit the powdering process. do.

(In Fig. 16, the curve TV indicates the speed of sound, and TF indicates the kinematic viscosity coefficient.) From the measurement results in Fig. 16, the physical property values necessary for the microcomputer are evaluated. The time difference from point A to point Bt is tl
Then, the amount of water W in the sampling container can be determined by equation (6).

Here, Q is the input from the heater, and H is the latent heat of water.

Knowing the amount of water, it is possible to calculate the amount of solids present in the sampling container before heating with the heater begins. Through this calculation, the time on the horizontal axis (22) in FIG. 16 can be recalculated into concentration as shown in FIG. 17. From the curve in Figure 17, the relationship between the amount of insoluble components in the solution, the proportion of used resin, the concentration and the kinematic viscosity coefficient,
The average elastic modulus of solid components can be completely evaluated. ′First, the kinematic viscosity coefficient ν of the slurry containing no insoluble solid components is (
7) It is generally known that it is expressed by the formula Jl.

shi=shio(1+2.5φ+7.3φ2)・・・・・・
...(7) Here, ν0 is the kinematic viscosity coefficient of the liquid, and φ is the volume fraction of the solid component. Therefore, by substituting the value of the kinematic viscosity coefficient before heating with the heater (calculated from A in Figure 17) into equation ('7), the volume fraction φ of the solid component that can be deposited in the waste can be calculated. . Next, the speed of sound when a solid substance exists in a liquid is estimated as follows by Jrick. (Urlck R, J.

:J, ApI), Phys, 18.983 (1947
)A 5ound Velocity Method
for Determining the Comprehension
ssib 1ty ofIi”1nely 1)ivi
ded 5ubstances) (23) where %VI is the sound velocity in the suspension, vo is the sound velocity in the liquid, and φ
is the volume fraction of the solid matter, τ is the elastic modulus of the solid matter and the liquid, respectively -p, and *, then (9) formula % formula % (9) In addition, U is expressed by the formula (10). , ■ as a function of solid particle size are illustrated in the Urick report supra.

U-(ρ--ρ, 1/ρ number ・・・・・・・・・(10
) where ρ1 is the density of the liquid and ρ is the density of the solid. By measuring before starting heating with the heater, from equation (7), the solid needle φ in the sampling liquid is closed, and this value 'l
The average elastic modulus of the solid material can be calculated by substituting it into equation i-(8). Since the main non-soluble components in waste materials are used resin and pelo3, the elastic modulus when both are mixed is (1
1) Can be evaluated using formula.

(24) K,=to α1 to 1 (1−α) ・・・・・・・
(11) Here, K and U are the elastic modulus of resin, K+ is the elastic modulus of pesos, and α is the resin fraction in the non-soluble component. By combining equations (11) and (7), the ratio of used resin and Fe2O3 in waste can be completely evaluated.

Next, the sound velocity at high concentration of B in Figure 17 was measured, and (8
) Calculate the average elastic modulus of the solid material from the equation.

The evaluation process by the control computer 12 in FIG.
The input values from the physical property measuring device shown in the figure are the following four points.

(1) Relationship between slurry concentration and viscosity (2) Temperature at the start and end of water evaporation (3) Fe!
rs concentration (4) Resin concentration (5) Elastic modulus of crystal First, whether or not it can be powdered is evaluated based on the temperature at the start and end of water evaporation. If the difference between the two is more than 10 C-L, it is considered difficult to powderize and the operator is instructed to investigate the cause.
Shown on cRT display. If pulverization is possible, the pulverization process is simulated by incorporating the specifications of the device (25) held in the storage device and the processing conditions input by the operator. Here, the device specification data stored in advance in the storage device are the following items.

(1) Body diameter (2) Body length 3) Body thickness (4) Thermal conductivity of the fuselage (5) Number of blades for each stage The items to be input by the operator are as follows.

Based on (1) the temperature of the heated steam, (2) the internal pressure, and the relationship between the concentration and viscosity coefficient determined by the physical property measuring device, we simulated the inside of the centrifugal thin film dryer according to the flow shown in Figure 7. Let's do it.

As a result, as shown in FIG. 19, the range that can be powdered is determined based on the relationship between the rotation speed and the processing flow (+1), and the image is displayed on the Crt and T indicators. Since the blade is constantly rotating while in contact with the body, the tip of the blade will cause damage. Since the amount of wear is proportional to the cube of the number of revolutions, (26) it is better to operate the device at the lowest possible number of revolutions. Here, the amount of wear is proportional to the cube of the number of rotations because the amount of wear is proportional to the product of the contact force between the blade and the body, which is proportional to the square of the number of rotations, and the circumferential speed, which is proportional to the number of rotations. It is. Therefore, it is optimal to operate at point C in Figure 19, but considering the safety margin, the processing flow rate at point C is reduced by 10%.
The operating condition is a point where the rotation speed is low and the rotation speed is 10% higher. This operating point is displayed on the ecRT screen, and the rotation speed and processing flow rate are recorded on a typewriter. Furthermore, since the product of the slurry concentration and the processing flow rate is the amount of powder produced in the centrifugal thin film dryer, this is used in calculations for the next granulation process.

Next, input the following granulator specifications and calculate the granulator operating conditions.

(1) Number of pockets on the roll surface (n) (2) Without changing the weight of the pellet, calculate the roll rotation speed ω using the following equation (12).

ω= 2 XF/ (n XV) −−−−−−−−
-(12)(27) Here, F is the amount of powder produced from the T centrifugal thin film dryer.

Equation (12) assumes that the pelletization is performed in the granulator at a speed higher than the amount of powder produced by the centrifugal thin film dryer, and the safety factor is set to 2.

In calculating the roll pressing force, from the measurement results of the crystal elastic modulus, using the graph in Figure 11, the critical pressure P+ffi
demand. Using this critical pressure Pl, the pressurizing force Pze of the roll is calculated from equation (13).

p, =P, xhxs .--(1, 3) where h: roll width S: pellet spacing.

Furthermore, addition of binder i: Xff1. The following equation (14) is used so that the strength of the generated pellet remains constant even if the composition varies.

Here, Y: Fe203 concentration (28) Z: Wa・1 fat concentration a: Slope in Figure 14 b: Slope in Figure 12 C: Gradient in Figure 13 It is.

The values of Y and Z used in equation (14) are input from a physical property measuring device.

The smaller the amount of binder added, the more desirable it is because the amount of waste generated can be reduced. Therefore, if the amount of binder added exceeds 30 wt% as a result of calculation using formula (14), granulation is determined to be impossible and the composition is adjusted. In this case, the waste liquid from the waste liquid storage tank 2 may be added to the adjustment tank 3 in FIG. 1 to reduce the resin concentration in the slurry, and then all physical property measurements of the side vehicle slurry may be performed again.

If the amount of binder added is 30 wt% or less, it is determined that granulation is possible, and the following operating conditions are transmitted to each device.

(1) Flow rate of waste slurry supplied to the centrifugal thin film dryer (2) Blade rotation speed of the centrifugal thin film dryer (3) Rotation speed of the granulator roll (4) Pressure force of the granulator roll (5) Binder Required addition amount The above items are set as follows.

(1) Adjust the rotation speed of the metering pump whose flow rate is directly proportional to the rotation speed.

(2) The blade rotation speed is controlled by the set value of the continuously variable transmission 74 shown in FIG.

(3) The rotation speed of the roll is controlled by changing the rotation speed of a variable motor that drives the roll.

(4) The pressurizing force of the roll is determined by the hydraulic cylinder 36 in Fig. 8.
The boost pump 39 and the relief valve 38 are operated so that the oil pressure of the pump reaches a predetermined value.

(5) To adjust the amount of binder added, first measure the amount of powder produced in the centrifugal thin film dryer using a weight scale attached to the mixer 7, then measure the weight while adding the binder, and when the predetermined amount is reached. , by the method of discontinuing the addition of binder.

According to this embodiment, by automatically sampling (30) a portion of the waste, it is possible to generate pellets with stable compressive strength even if the composition varies.

Next, a second embodiment of the present invention will be described.

This embodiment is suitable for cases where powdering performance varies depending on the composition ratio of halonic acid and sodium, such as sodium borate waste liquid generated from pressurized water nuclear power plants. Depending on the composition of sodium borate, when water is evaporated under operating conditions of 100C and 1 atm in a centrifugal thin film dryer, sodium borate containing crystallization water is precipitated in the waste liquid, unlike in the case of sodium sulfate. If the powder contains water of crystallization, during the process of pressure-molding the powder into pellets, a portion of the water of crystallization becomes liquid due to the rise in temperature of the powder, preventing the powders from coming into direct contact with each other. Therefore, it is difficult to pelletize just by applying pressure. Effluents generated from pressurized water nuclear power plants generally have an excess of oxalic acid compared to compositions suitable for powdering and pelletizing.

Therefore, the physical property measuring device 12 is equipped with N as shown in FIG.
A0H (31) addition device (tank 57) is added to add the necessary NaOH.
The amount added is also evaluated. Components in the figure that are the same as those in FIG. 15 are designated by the same numbers. Waste Q14 is sampled, heated, concentrated, and the kinematic viscosity coefficient of the waste and the sound velocity in the liquid are continuously recorded. Due to the precipitation of sodium chlorate containing crystal water, the kinematic viscosity coefficient of the waste decreases to its original value of 1.
At the time of 00 times, addition of Na0)1 is started. From the Na011 tank 57, a gear pump 58 that can control the number of supplies in proportion to the rotational speed is used to weld 45° to the NBOIVk sampling melter 45.
The amount of water in the RI aqueous solution is selected so as to balance the amount of water evaporated by heating with the heater. As a result, the water content does not change even if Na0I] water liquor is added. In this state, the second
As shown in Figure 1, the relationship between the addition cap of Na01-1 and the kinematic viscosity coefficient shows that the kinematic viscosity coefficient decreases due to the change in composition due to the increase in NaOH and the dissolution of crystal water. At this time, the point D (FIG. 21) at which there is almost no further decrease in the kinematic viscosity coefficient is defined as the required amount of NaOH added. According to this embodiment, in addition to the operating conditions of the thin film dryer and granulator, the NaOH
The amount added can also be evaluated.

According to the first and second embodiments of the present invention described above, in a system that dry powders using a centrifugal thin film evaporator and pelletizes using a granulator, a part of target waste is sampled and its physical properties are By measuring the values, the operating conditions of the equipment are automatically determined, which has the effect of reducing the burden on the operator and making it possible to maintain a constant strength of the pellets produced. be.

A third embodiment of the invention is shown in FIG. The same or corresponding parts as in FIG. 1 are indicated by the same reference numerals.

The difference from FIG. 1 is that an extrusion granulator was used instead of a briquette rung machine as the granulator.

Therefore, the only physical property values to be measured are the relationships between concentration and viscosity. The operating procedure is shown below.

The average amount generated per day is transported from the waste liquid storage tank 1 and the used resin storage tank 2 to the adjustment tank 3, respectively.

After stirring the adjustment mixture 3 to make the composition in the resin uniform (33), the relationship between the degree of m and the viscosity is measured using the physical property measuring device 12. The signal of this measurement data is input to the arithmetic and control device 70, and the waste processing conditions are inputted from the data input device 72, and combined with the device specification data stored in the storage device 70a of the arithmetic and control device 70. , by the calculation procedure shown in Fig. 7, the 19th
Measure the area where powder can be produced as shown in the figure. The processing flow lid and blade rotation speed, which are the operating conditions of the centrifugal thin film dryer 5, are calculated by assuming a margin rate of about 10% for pulverization. Based on this result, the operation of the centrifugal thin film dryer 5 is controlled and the amount of powder produced is evaluated.

The granulation mechanism of the extruder 80 (extrusion granulator) is as follows. A screw 83 driven by a motor 82 is disposed inside the cylindrical container 81, and the cylindrical container 81 is heated by a heat medium 82 supplied from the outside. Thermoplastic powder 92 is supplied to this extruder 80 by a screw 85 driven by a motor 84 . This plastic powder 92 is placed inside the cylindrical container 81.
It is heated from the outside (34) and becomes fluidized, and is moved by the rotation of the screw 83. During this process, it mixes with the powder 86 produced by the centrifugal thin film dryer 5 and is extruded through the pores 87. At the exit of the pore 87, there is a chopper 89 which is rotated by a motor 88, and a cylindrical pellet 90 is produced in this portion. The pellets 90 are filled into a 200 t drum 11 by gravity.

Motor 9 that supplies generated powder 86 to extruder 80
The rotation speed 1 supplies the produced powder 86 at the same speed as the powder produced by the centrifugal thin film dryer 5 based on the relationship between the throughput and the rotation speed verified in advance. This is because when the extruder 80 is operated intermittently, the time during which the powder is heated is not uniform, and as a result, the strength of the pellets produced varies due to deterioration of the powder produced from the used resin. It's to wake up. Therefore, based on the amount of powder produced from the centrifugal thin film dryer 5 calculated by the control computer, the motor 91 for powder supply, the motor 84 for plastic powder supply, and the pellet production speed (35 degrees) are adjusted. Adjust the rotation speed of the motor 82 for use. At this time, the amount F2 of the plastic powder to be added is calculated using equation (15) so that the molten plastic occupies 50% of the volume of the pellet.

Here, %F1: Amount of powder produced by the centrifugal thin film dryer ρ1: Density of the powder produced ρ! is the niblastic density.

The reason why the proportion of plastic was set at 50% will be explained. Assuming that the generated powder is a uniform sphere and arranged in a cubic lattice, the space occupied by the generated powder is 52%. Therefore, the void between the powders is 1.48%.If the amount of plastic added is more than the amount that can fill this void, the powder is considered to have fluidity.On the other hand, if the amount of plastic added is large As the amount of plastic increases, the amount of waste generated also increases, so it is better to reduce the amount of plastic added as much as possible.
6) The proportion of plastic is 50%. According to this embodiment, even when an extruder (extrusion granulator) is used as the granulator, the same effects as in the 1.2 embodiment can be obtained.

〔Effect of the invention〕

According to the present invention, a part of the substance to be treated is sampled from radioactive waste, its physical property values are measured, and based on this, numerical calculations are performed by an arithmetic and control device, and a centrifugal thin film dryer or granulator is processed. Since the operating conditions are determined, the effect is that even if the composition of the radioactive waste to be treated changes, pellets with high strength and stable physical properties can always be obtained.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing a first embodiment of the radioactive waste pellet solidification apparatus of the present invention, FIG. 2 is a longitudinal cross-sectional view showing details of the centrifugal thin film dryer shown in FIG. 1, and FIG. Figure 2 is a horizontal sectional view of the centrifugal thin film dryer, Figure 4 is a characteristic diagram showing the operating range that can be dried and powdered by the centrifugal thin film dryer, and Figure 5 is the pulverization state of the centrifugal thin film dryer based on the results of visual experiments. (37) Figure 6 is a diagram showing the actual measured value of the relationship between the concentration and kinematic viscosity coefficient of waste treated with the radioactive waste pellet solidification device a of the present invention, and Figure 7 is a diagram showing the relationship between centrifugal thin film drying. The pulverization process of the machine was simulated [(7) Figure showing the flowchart, Figure 8 is a schematic diagram showing the structure of briquetting type granulation, Figure 9 shows the relationship between pressing force and pellet strength. Figure 10 is an explanatory diagram showing the compression process of powder observed using an electron microscope, Figure 11 is a diagram experimentally determined the relationship between the elastic modulus of powder and critical pressure, and Figure 12 is a diagram of NazSO.
Figure 13 is an experimental diagram of pellet compressive strength when resin is mixed in 1dNazso<F'e203
Figure 14 is a diagram of the relationship between the amount of cellulosic binder added and the increase in the pellet compressive strength measured in an experiment, and Figure 15 is a diagram of the relationship between the amount of cellulosic binder added and the increase in pellet compressive strength. FIG. 1 is a system diagram showing details of the physical property measuring device shown in FIG. 1; FIG. 16 is a diagram showing an example of changes over time in the physical property values of the waste slurry input from the physical property measuring device shown in FIG. 15 to the arithmetic and control device; Figure 17 shows the measurements shown in Figure 16 (38
) Diagram where the horizontal axis is the concentration of the calculated results, No. 18
The figure is a flowchart showing the calculation flow in the arithmetic control device, Figure 19 is a diagram showing the performance curve of a centrifugal thin film dryer on a CRT screen, and Figure 20 is a diagram showing the physical property measuring device in the second embodiment of the present invention. A detailed system diagram, Figure 21 is N
A characteristic diagram showing the change in the kinematic viscosity coefficient due to the addition of a0)i, and FIG. 22 is a system diagram showing the third embodiment of the pellet assimilation device for radioactive waste of the present invention. 1... Waste liquid storage tank, 2... Used resin storage tank, 3... Adjustment tank, 5... Centrifugal thin film IP2' dryer, 8... Binder bottling machine, 9... Granulator, 10・
...Berrett, 12...Physical property measuring device, 57...N
a0I-1 tank, 70... Arithmetic control unit, 71...
- Display device, 72... Data input device, 73... Typewriter, 80... Extruder (extrusion granulator). Agent Patent Attorney Akio Takahashi (39) Kukinbeichu Z6 Diagram θ 20 4-θ lθ 〃 んV Inru Ken Jshi <wt Kei no Kashi 7 Mouth 1 Figure 70) ζ Nol I21 1 2 3 4 Goki U゛1 age <x, g f'a-no; 5 chopsticks/J rotation 2θ figure 121 figure Sa oN tJn-9twt %/

Claims (1)

[Claims] 1. In a system that pulverizes radioactive waste and then pelletizes it using a system that includes a drying process and a solidification process, a part of the slurry to be treated is sampled and its physical property values are measured. , a pellet assimilation method for radioactive waste, which is characterized by determining the operating conditions of the drying process and solidification process according to the physical property values thereof. 2. A method for solidifying radioactive waste into pellets according to claim 1, characterized in that the physical property values to be measured are the viscosity of the slurry and the sonic velocity of the slurry. 3. Radioactive waste comprising a dryer that pulverizes radioactive waste, a granulator that granulates the waste powder, and a binder hopper that adds a binder to the powder before being granulated. In the material processing apparatus, a physical property measuring means for measuring the physical property value of the waste supplied to the dryer, a calculation control means, and a metal holder, the calculation control means having the specifications of the dryer and the granulator. Data is stored in memory, and the calculation control means inputs all the signals from the physical property measuring means and the treatment conditions of the waste, calculates the operating conditions of the dryer and granulator, and the amount of binder added, and calculates them. A pellet assimilation device for radioactive waste characterized by controlling 4. In claim 3, the arithmetic control means simulates the signal from the physical property measuring means and the data on the waste processing conditions, the powdering process of the dryer, and the granulation process of the granulator. A pellet solidification apparatus for radioactive waste, characterized in that data is inputted to calculate the operating conditions of a dryer and a granulator and the amount of binder added.