JP2014228288A - Decontamination method for contaminated solid and decontamination apparatus for contaminated solid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination method and a decontamination apparatus enabling radioactive cesium to be easily removed with a high decontamination rate from a contaminated solid such as a soil and a sludge contaminated by the radioactive cesium.SOLUTION: The decontamination method is provided for decontaminating a contaminated solid such as a soil and a sludge contaminated by a radioactive cesium by removing the radioactive cesium from the contaminated solid, and the decontamination method includes: a contaminated solid charging step of charging a contaminated solid into a decontamination machine; an oxalic acid solution charging step of charging an oxalic acid solution into a vessel; a hydrothermal reaction condition setting step of sealing the vessel and setting an interior of the vessel under a hydrothermal reaction condition; an elution step of eluting the radioactive cesium into the oxalic acid solution under the hydrothermal reaction condition; and an oxalic acid solution discharge step of discharging the oxalic acid solution from the vessel, performed in this order. Thereby, the radioactive cesium is removed from the solid, and after that, a neutralizer charging step of charging a neutralizer into the vessel and a neutralizer discharging step of discharging the neutralizer from the vessel are performed, and finally, the solid decontaminated and remained in the vessel is recycled as the soil.

Description

  The present invention relates to a method for recovering and decontaminating cesium from contaminated solids such as soil and sludge contaminated with radioactive cesium, and an apparatus for recovering and decontaminating cesium from contaminated solids.

  A large amount of radioactive material may be released due to an accident at a nuclear power plant, etc., and there may be soil contamination caused by the radioactive material. Examples of radioactive substances that cause soil contamination include iodine 131, cesium 134, and cesium 137. Among these, cesium 134 and cesium 137 are particularly problematic as causes of soil contamination. Cesium 134 has a half-life of about 2 years, and cesium 137 has a half-life of about 30 years, which is longer than that of iodine 131, which is about 8 days. In addition, cesium 134 and cesium 137 (hereinafter, cesium 134 and cesium 137 are collectively referred to as radioactive cesium) belong to the alkali metal of the periodic table and have the same chemical properties, so they are very soluble in water. There is also a risk of being taken up by vegetables and root vegetables grown in soil contaminated with radioactive cesium. Therefore, as a decontamination method for contaminated soil and sludge, a method for decontamination by removing radioactive cesium is required.

  Various proposals have been made regarding methods for removing radioactive cesium adsorbed on equipment such as metals used in nuclear power plants and decontaminating them. However, radioactive cesium has a positive monovalent cation and has a characteristic of being strongly adsorbed to clay minerals contained in soil and sludge. Therefore, even if the method for removing radioactive cesium used in nuclear power plants is applied to soil and sludge as it is, the expected effect may not be obtained.

  As a decontamination method for soil or sludge contaminated with radioactive substances, for example, in Patent Document 1, a magnetic substance is supported on an adsorbent having an adsorptivity to radioactive cesium, and a solid contaminated with radioactive cesium. Adding the adsorbent to the adsorbent, adsorbing the radioactive cesium in the solid to the adsorbent, and separating and removing the adsorbent carrying the magnetic material by magnetic force. A processing method has been proposed.

  In Patent Document 2, the contaminated soil is subjected to semi-autogenous / autogenous wet grinding with a grinder to obtain a ground slurry, and the ground soil slurry is continuously supplied to the hydrocyclone to obtain the contaminated soil slurry. While overflowing from the hydrocyclone, the decontaminated soil slurry is underflowed from the hydrocyclone and classified, and a flotation agent containing a collection agent is added to the contaminated soil slurry and continuously supplied to the flotation machine. Thus, a method has been proposed in which the levitated material enriched with radioactive cesium is levitated and recovered from the upper part of the flotation machine, while the underflow water is recovered from the lower part.

JP 2013-24812 A JP2013-64690A

  As described above, some proposals have been made on methods for removing radioactive substances from contaminated solids such as contaminated soil and sludge, but the number is very small. This is because, in the technical field of nuclear energy, development is proceeding so that radioactive materials do not leak from nuclear power plants, and therefore it is not assumed that radioactive materials leak into soil or sludge.

  Although the proposals in Patent Document 1 and Patent Document 2 can also reduce the radiation level of soil and sludge, there is a need for a decontamination method and apparatus that can be simplified and have a higher decontamination rate.

  An object of the present invention is to provide a decontamination method and a decontamination apparatus that can easily remove radioactive cesium from contaminated solids such as soil and sludge contaminated with radioactive cesium at a high decontamination rate.

  The present invention is a method for decontaminating contaminated solids by removing radioactive cesium from contaminated solids such as soil and sludge contaminated with radioactive cesium, and introducing the contaminated solids into a container of a decontamination machine A charging step, a oxalic acid solution charging step for charging the oxalic acid solution into the container, a hydrothermal reaction condition setting step for sealing the container and setting the inside of the container under hydrothermal reaction conditions, and a hydrothermal reaction condition An elution step of eluting the radioactive cesium into the oxalic acid solution and a oxalic acid solution discharging step of discharging the oxalic acid solution from the container are sequentially performed.

  The present invention also relates to a decontamination apparatus for contaminated solids that removes radioactive cesium from decontaminated solids such as soil and sludge contaminated with radioactive cesium, and to which the contaminated solids and oxalic acid solution are introduced. A decontamination machine having a double-structure container having a shell and an inner shell, and a steam boiler for injecting steam between the outer shell and the inner shell of the container to set the interior of the container under hydrothermal reaction conditions The radioactive cesium is eluted in the oxalic acid solution under hydrothermal reaction conditions, and the contaminated solid is decontaminated by discharging the oxalic acid solution from the container.

  According to the present invention, it is possible to provide a decontamination method and a decontamination apparatus for contaminated solids that can achieve a high decontamination rate by reacting the contaminated solids with oxalic acid under hydrothermal reaction conditions.

It is a functional block diagram of the decontamination apparatus of the contaminated solid which concerns on embodiment of this invention. It is an external appearance schematic diagram of the decontamination machine of the said decontamination apparatus. It is the cross-sectional schematic diagram which fractured | ruptured a part of container of the decontamination machine of the said decontamination apparatus. It is a flowchart of the decontamination method of the contaminated solid which concerns on embodiment of this invention. It is explanatory drawing about hydrothermal reaction conditions. It is a graph which shows the relationship between the solid-liquid ratio (mass ratio) of a contaminated solid and an oxalic acid solution, and a decontamination rate. It is a graph which shows the relationship between the density | concentration of an oxalic acid solution, and a decontamination rate. It is a graph which shows the relationship between the temperature at the time of a decontamination process, and a decontamination rate. It is a graph which shows the relationship between the time of a decontamination process, and a decontamination rate. It is a graph which shows the relationship between the kind of contaminated solid, and a decontamination rate. It is a graph which shows the relationship between the frequency | count of a decontamination process, and a decontamination rate. It is a graph which shows the relationship between the eluent used for decontamination, and a decontamination rate.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a decontamination device 1 for contaminated solids according to the present embodiment, FIG. 2 is a schematic external view of a decontamination machine 2, and FIG. 3 shows a container 31 of the decontamination machine 2. It is the cross-sectional schematic diagram which fractured | ruptured one part. The present embodiment relates to a method and apparatus for decontaminating contaminated solids such as soil and sludge contaminated with radioactive cesium, mixing contaminated solids and oxalic acid (HOOC? COOH) under hydrothermal reaction conditions, It is characterized by removing radioactive cesium. Hereinafter, the decontamination method and the decontamination apparatus will be described in detail. Note that soil and sludge contaminated with radioactive cesium are referred to as contaminated solids, solids after decontamination are referred to as decontaminated solids, and only soil and sludge are referred to as solids.

  As shown in FIG. 1, the decontamination apparatus 1 in this embodiment includes a decontamination machine 2, a waste liquid treatment apparatus 4, a steam boiler 5, and a power supply device 6. Further, the decontamination apparatus 1 includes an oxalic acid tank 11, a neutralizer tank 12, a hydrogen peroxide tank 13, a kerosene tank 14, a recovered oxalic acid tank 21, a decontamination waste liquid tank 22, and a cesium-containing waste liquid tank 23.

  As shown in FIG. 2, the decontamination machine 2 includes a container 31 and a holding unit 41 that holds the container 31 in a rotatable manner. The container 31 has a cylindrical shape whose upper and lower portions are sealed, that is, a hollow cylindrical shape, and has a structure excellent in heat resistance, pressure resistance, and corrosion resistance that can withstand the conditions of the hydrothermal reaction. As shown in FIG. 3, the structure of the container 31 is a double structure comprising an outer shell 32 and an inner shell 33. A predetermined space is formed between the outer shell 32 and the inner shell 33, and a steam boiler is formed in this space. Steam is injected from 5. As shown in FIG. 2, the container 31 has a solid inlet 35 for introducing contaminated solids, a pipe connection port as a liquid inlet 37 for introducing an oxalic acid solution, water, a neutralizing agent, and the like, and an outer shell. Between the pipe 32 and the inner shell 33, there are provided a pipe connection port as a steam inlet 38 for injecting steam, a discharge port (not shown) for discharging the solution, and the like. The steam inlet 38 communicates between the outer shell 32 and the inner shell 33. The container 31 has a diameter of about 1700 mm, a height of about 2700 mm, a solid inlet 35 having a diameter of about 600 mm, and a liquid inlet 37 having a diameter of about 25 mm and connected to a pipe. Note that the present invention is not limited to this value.

  The holding portion 41 includes a pedestal 45 positioned below and a pair of leg portions 46 and 46 that rise upward from the pedestal 45. The pair of legs 46 and 46 and the container 31 are rotatably connected by shaft rods 48 and 48.

  The waste liquid treatment apparatus 4 shown in FIG. 1 concentrates the waste liquid in which cesium has dissolved, and discharges the concentrated waste liquid containing cesium to the cesium-containing waste liquid tank 23. The steam boiler 5 generates steam using kerosene as a raw material, and sends high-temperature steam between the outer shell and the inner shell of the container 31. The inside of the container 31 is brought into a high-temperature and high-pressure state when steam is sent between the outer shell 32 and the inner shell 33 from the steam boiler 5 and is subjected to hydrothermal reaction conditions described later. The power supply device 6 supplies power to the decontamination machine 2, the waste liquid treatment device 4, and the steam boiler 5.

  The decontamination apparatus 1 includes a first unit including a decontamination machine 2, a waste liquid treatment apparatus 4, a steam boiler 5, and a power supply apparatus 6, an oxalic acid tank 11, a neutralizing agent tank 12, a hydrogen peroxide water tank 13, The second unit includes a kerosene tank 14, a recovered oxalic acid tank 21, a decontamination waste liquid tank 22, and a cesium-containing waste liquid tank 23. And the decontamination apparatus 1 is set as the structure which can move by arrange | positioning a 1st unit and a 2nd unit to two vehicles, respectively. The combination of the apparatus and tank which comprise a 1st unit and a 2nd unit is not limited to these. Moreover, it is good also as a structure which mounts a 1st unit and a 2nd unit on one vehicle.

Next, the decontamination method will be described using the flowchart of FIG.
First, after measuring the radiation level of the contaminated solid, the contaminated solid is charged into the container 31 of the decontamination machine 2 (step 101: contaminated solid charging step), and oxalic acid as an eluent (decontamination agent) for radioactive cesium. An oxalic acid solution is charged into the container 31 from the tank 11 (step 103: oxalic acid solution charging step).

  Next, the steam inlet 38 of the container 31 and the steam boiler 5 are connected with a tube having high heat resistance, high temperature steam is injected into the space between the outer shell 32 and the inner shell 33, and the inside of the sealed container 31 is filled. It sets to hydrothermal reaction conditions (step 105: hydrothermal reaction condition setting process). As shown in FIG. 5, the hydrothermal reaction is a state in which liquid and gas are mixed at high temperature (about 100 ° C. to about 250 ° C.) and high pressure (about 1 atm to 20 atm (1 atm = 101.325 kPa)). Yes, it means a state in which the hydrolytic ability increases, the reaction rate due to temperature and pressure increases, and the physical properties of water as a solvent change.

  After the hydrothermal reaction condition setting step (step 105), the hydrothermal reaction condition is maintained for a predetermined time, and radioactive cesium is eluted in the oxalic acid solution (step 107: elution step). In this elution step (step 107), the container 31 may be rotated so that the contaminated solid and the oxalic acid solution are sufficiently mixed. Then, after the elution step (step 107), the inside of the container 31 is allowed to cool to about 40 ° C., and the oxalic acid solution from which radioactive cesium has been eluted is discharged from the outlet into the recovered oxalic acid tank 21 (step 109: oxalic acid solution) Discharge process). Note that the oxalic acid solution charging process (step 103) to the oxalic acid solution discharging process (step 109) are decontamination processes.

  After the oxalic acid solution discharging step (step 109), the radiation level of the decontaminated solid is measured (step 111: radiation level measuring step), and it is determined whether the decontamination rate or the radiation level exceeds a reference value. (Step 113: radiation level determination step). The radiation level is the solid radioactive concentration and is expressed in Bq / kg. The decontamination rate is a numerical value represented by (B−A) / B × 100, where A is the radiation level after decontamination and B is the radiation level before decontamination. As a reference value in the radiation level determination step (step 113), a high decontamination rate of 80% or 90%, or a national or local radiation level reference can be used as the reference value. For example, the clearance level of radiation cesium that can be released into the general environment is 100 Bq / kg, and this value can be used as a reference value for the radiation level determination process (step 113). Note that the present invention is not limited to these numerical values.

  In the case where the radiation level determination process (step 113) satisfies the standard and is sufficiently decontaminated, a basic aqueous solution is charged into the container 31 as a neutralizing agent (step 114: neutralizing agent charging process). The solid in 31 is washed and neutralized (step 115: neutralization step). After the neutralization step (step 115), the aqueous solution is discharged from the discharge port of the container 31 to the decontamination waste liquid tank 22 (step 117: neutralizing agent discharge step). In addition, as a neutralizing agent, a sodium hydroxide solution is mentioned, for example. Finally, the decontaminated solid remaining in the container 31 is discharged and reused as soil (step 119: solid recycling step).

  When the radiation level determination process (step 113) does not satisfy the standard and is not sufficiently decontaminated, the decontamination process (from the oxalic acid solution charging process (step 103) to the oxalic acid solution discharging process (step 109)) is a standard. Repeat until

  The oxalic acid solution discharged to the recovered oxalic acid tank 21 in the oxalic acid solution discharging step (step 109) is reused as the oxalic acid solution in the oxalic acid solution charging step (step 103) (step 121: oxalic acid solution reuse) Process). Note that the amount of radioactive cesium eluted in the oxalic acid solution is very small relative to the amount of the oxalic acid solution, so that it has a sufficient effect as an eluent even if it is reused as it is.

  The oxalic acid solution after sufficiently used as an eluent is decomposed into water and carbon dioxide by mixing hydrogen peroxide water, carbon dioxide is released into the atmosphere as it is, and water in which radioactive cesium is dissolved is treated as a waste liquid. After concentrating with the apparatus 4, it is stored. Note that the oxalic acid solution discharged to the recovered oxalic acid tank 21 in the oxalic acid solution discharging step (step 109) may be solid-liquid separated by a centrifugal separator and only the oxalic acid solution after separation may be reused.

  In the waste liquid processing apparatus 4, waste liquid processing is executed (step 131: waste liquid processing step). In the waste liquid treatment step (step 131), an operation for concentrating the waste liquid is performed. Store the solution containing the concentrated radioactive cesium. The method for concentrating the waste liquid is not limited to this, but it is also possible to put the waste liquid into the container 31 to bring the container 31 into a high-temperature and high-pressure state, and to heat and concentrate the waste liquid.

  As described above, in the decontamination method of the present embodiment, by mixing the contaminated solid and the oxalic acid solution under the hydrothermal reaction conditions, the elution rate of radiation cesium is higher than that in the normal reaction state (see FIG. 5). Therefore, a high decontamination effect can be obtained.

  FIG. 6 shows that the mass ratio of the contaminated solid to the oxalic acid solution is 1: 2, when the oxalic acid concentration is 2.0 mol / L, the treatment temperature is 140 ° C., the pressure is 353 kPa, and the treatment time is 0.5 hours. It is a figure which shows the decontamination rate in 1: 3 and 1: 5. As shown in FIG. 6, it can be seen that there is no significant change in the decontamination rate when the mass ratio of the contaminated solid and the oxalic acid solution is 1: 2 and 1: 3. It can also be seen that the decontamination rate of 1: 5 is high when the mass ratio of the contaminated solid to the oxalic acid solution is 1: 3 and 1: 5. Therefore, it is conceivable to increase the amount of the oxalic acid solution in order to increase the decontamination rate. However, when the amount of the oxalic acid solution is increased, problems such as an increase in cost and an increase in the size of the container 31 occur. Therefore, the mass ratio (solid-liquid ratio) of the contaminated solid and the oxalic acid solution in the contaminated solid charging process (step 101) and the oxalic acid solution charging process (step 103) is preferably 1: 2. Note that the present invention is not limited to this value.

  FIG. 7 shows that the concentration of the oxalic acid solution is 1 mol / wt when the treatment temperature is 140 ° C., the treatment time is 1 hour, the solid-liquid ratio (mass ratio of the contaminated solid and the oxalic acid solution) is 1: 5, and the pressure is 353 kPa. It is a figure which shows the decontamination rate in L, 2 mol / L, and 3 mol / L. As shown in FIG. 7, when the concentration of the oxalic acid solution is 1 mol / L and 2 mol / L, the decontamination rate is higher in the 2 mol / L oxalic acid solution, and a large change appears in the decontamination rate. I understand that. On the other hand, it can be seen that between 2 mol / L and 3 mol / L, the decontamination rate was slightly higher at 3 mol / L, but no significant change was observed. Therefore, the concentration of the oxalic acid solution to be added in the oxalic acid solution charging step (step 103) is preferably 2 mol / L from the balance between the amount of oxalic acid used and the effect. Note that the present invention is not limited to this value.

  FIG. 8 shows the temperature in the container 31 when the oxalic acid concentration is 2.0 mol / L, the treatment time is 1 hour, the solid-liquid ratio is 1: 5, and the pressure is 353 kPa (saturated vapor pressure at each temperature). Is a figure which shows the decontamination rate in 90 degreeC, 120 degreeC, and 140 degreeC. As shown in FIG. 8, it can be seen that the decontamination rate is less than 90% at 90 ° C. and 120 ° C., but exceeds 90% at 140 ° C. Therefore, in the hydrothermal reaction condition setting step (step 105), it is preferable to set the temperature to 140 ° C. or higher. The pressure in the hydrothermal reaction condition setting step (step 105) is better as a reaction, but if the pressure is increased too much, the cost for increasing the pressure resistance of the container 31 increases, and the weight of the container 31 increases. Problems arise. Therefore, the pressure is preferably about 353 kPa (3.48 atm, about 3.5 atm). As a matter of course, the pressure may be further increased as long as there is a member that is light, has high pressure resistance, is low in cost, and can withstand hydrothermal reaction conditions, and is not limited to the above values.

  FIG. 9 shows the treatment time of 0.5 hour, 1 hour, 2 when the oxalic acid concentration is 2.0 mol / L, the treatment time temperature is 140 ° C., the pressure is 353 kPa, and the solid-liquid ratio is 1: 5. It is a figure which shows the decontamination rate in time. As shown in FIG. 9, it can be seen that there is no significant change in the decontamination rate at the treatment time of 0.5 hour and 1 hour, and it is slightly higher at 2 hours. Therefore, from the viewpoint of time efficiency, it is preferable that the time (treatment time) for maintaining the hydrothermal reaction condition in the elution step (step 107) is 0.5 hour. When time efficiency is not considered, it is a matter of course that the decontamination rate increases when the reaction is performed for a long time, and therefore, the present invention is not limited to the above values.

  Next, the effect of decontamination using the decontamination method in this embodiment will be described. FIG. 10 shows various types when the oxalic acid concentration is 2 mol / L, the processing temperature is 140 ° C., the pressure is 353 kPa, the processing time is 0.5 hours, the solid-liquid ratio is 1: 2, and the processing step is one time. It is a figure which shows the decontamination rate of soil. As shown in FIG. 10, the decontamination rates are 91.6% for schoolyard soil 1, 78.5% for schoolyard soil 2, 52.0% for schoolyard soil 3, 73.6% for farmland soil 1, and farmland soil. 2 is 55.7%, and farmland soil 3 is 64.7%. It can be seen that the decontamination rate varies greatly depending on the type of soil. On the other hand, it turns out that the effect that a decontamination rate exceeds 90% may be acquired by one processing process.

  FIG. 11 is a diagram showing the decontamination rate when the decontamination process is performed a plurality of times on the schoolyard soil 3 having the lowest decontamination rate in FIG. 10. As shown in FIG. 11, the decontamination rate was 51.7% for one processing step, 86.0% for two processing steps, and 99.7% for three processing steps. That is, even if the soil has the lowest decontamination rate, a very high decontamination effect can be obtained by repeating the treatment step three times.

  FIG. 12 shows various eluents of radioactive cesium when the treatment temperature is 140 ° C., the pressure is 353 kPa, the treatment time is 1 hour, the solid-liquid ratio is 1: 5, and the test soil (test solid) is school ground soil 1. It is a figure which shows the decontamination rate using an eluent. As shown in FIG. 12, the decontamination rate was 82.6% for oxalic acid 1.0 mol / L, 96.0% for oxalic acid 2.0 mol / L, and 95.2% for oxalic acid 3.0 mol / L. It can be seen that the value is very high. On the other hand, ammonium oxalate 0.1 mol / L is 9.8%, formic acid 1 mol / L is 2.2%, formic acid 2 mol / L is 3.2%, formic acid 3 mol / L is 4.1%, potassium nitrate 0.01 mol / L is 0.9%, potassium nitrate 0.1 mol / L is 6.2%, potassium nitrate 1.0 mol / L is 10.2%, ammonium nitrate 0.01 mol / L is 1.6%, ammonium nitrate 0.1 mol / L Of 6.1% and ammonium nitrate 1 mol / L of 10.3%, the decontamination rate was very low. Therefore, it is understood that oxalic acid is most suitable as an eluent for radioactive cesium.

  As described above, in the contaminated solid decontamination method of this embodiment, the contaminated solid and the oxalic acid solution are put into the container 31 of the decontamination machine 2 and reacted under hydrothermal reaction conditions, thereby achieving a high decontamination effect. It can be provided.

  In addition, after the decontamination treatment, the neutralized solid is added to the decontaminated solid in the container 31 to neutralize the solid, so that the solid can be prevented from being acidic and can be reused immediately after decontamination ( Soil).

  Furthermore, by repeating the decontamination process a plurality of times, a high decontamination effect can be provided even for contaminated solids that cannot be decontaminated by a single decontamination process.

  And by measuring the radiation level after the decontamination treatment and deciding whether to repeat the decontamination treatment according to the measured value or to shift to the neutralization treatment, the decontamination time can be shortened in the soil having a high decontamination effect. At the same time, a high decontamination effect can be obtained by repeating the decontamination process in the soil having a low decontamination effect.

  Further, by reusing the oxalic acid solution used in the decontamination method of the present embodiment, the amount of oxalic acid used can be reduced, so that the cost for decontamination can be reduced.

  Further, by using an oxalic acid solution having a concentration of 2 mol / L as the oxalic acid solution, a high decontamination effect can be obtained while suppressing the amount of oxalic acid used as shown in FIG.

  Further, in the hydrothermal reaction condition setting step (step 105), by setting the temperature to 140 ° C. and 353 kPa (3.6 kgf / cm 2), as shown in FIG. In addition to being obtained, the pressure resistance of the container 31 is improved even if the pressure resistance is low (to the extent that it can withstand the pressure), so that the weight of the container 31 can be kept low and the cost of the container 31 can be reduced.

  Further, by setting the amount of the oxalic acid solution charged into the container 31 in the oxalic acid solution charging step (step 103) to be twice the mass of the contaminated solid (solid-liquid ratio is 1: 2), FIG. As described above, the amount of oxalic acid used can be reduced while maintaining a high decontamination effect.

  Since the decontamination apparatus 1 includes at least the decontamination machine 2 provided with the container 31 and the steam boiler 5, the inside of the container 31 can be set under hydrothermal reaction conditions. The decontamination apparatus 1 which can obtain an effect can be provided.

  In addition, by making the decontamination apparatus 1 movable by a vehicle or the like, the contaminated solid can be collected, decontaminated, and reused after the decontamination can be performed at the place where the contaminated solid is collected. Therefore, it is possible to prevent further diffusion of radioactive cesium due to transportation of contaminated solids and to reduce transportation costs.

  In the above-described flow, the discharge of the oxalic acid solution and the neutralizing agent is only described as being discharged from the container 31. However, a separate centrifuge may be provided, and the solid-liquid may be separated by the centrifuge. Good. Using a centrifuge to separate the solid and oxalic acid solution or the solid and neutralizing agent can reduce the time required for these operations, and the amount of oxalic acid solution and neutralizing agent remaining in the solid. Can be reduced.

  In the above-described flow, the radiation level measurement process (step 111) and the radiation level determination process (step 113) are executed, and the decontamination work is repeated according to the radiation level, but as shown in FIG. Even in soil where the decontamination rate was the lowest in one decontamination operation, a very high decontamination rate was achieved in the three decontamination operations, so the number of decontamination operations may be set to 3 in advance. .

  Furthermore, although manual decontamination has been described in the conventional decontamination methods, all can be automated. That is, all the decontamination operations can be automated by adding a control device including a storage medium storing the decontamination operation program described in the above flow and an arithmetic device such as a CPU.

  And this invention is not limited to the above embodiment, All changes are possible unless the summary of invention is changed. In addition, the numerical values described so far are only the optimal numerical values in the experiment, and are not meant to be limited to the numerical values. The optimum numerical value may vary depending on the materials of various devices used for decontamination and the environment where decontamination work is performed.

DESCRIPTION OF SYMBOLS 1 Decontamination apparatus 2 Decontamination machine 4 Waste liquid processing apparatus 5 Steam boiler 6 Power supply apparatus 11 Oxalic acid tank 12 Neutralizing agent tank 13 Hydrogen peroxide water tank 14 Kerosene tank 21 Recovery oxalic acid tank 22 Decontamination waste liquid tank 23 Cesium containing waste liquid Tank 31 Container 32 Outer shell 33 Inner shell 35 Solid inlet 37 Liquid inlet 38 Steam inlet 41 Holding part 45 Base 46 Leg part 48 Shaft bar

Claims (10)

A decontamination method for contaminated solids by removing radioactive cesium from contaminated solids such as soil and sludge contaminated with radioactive cesium,
A contaminated solid charging process for charging the contaminated solid into a decontamination container;
An oxalic acid solution charging step of charging the oxalic acid solution into the container;
Hydrothermal reaction condition setting step of sealing the container and setting the inside of the container under hydrothermal reaction conditions;
An elution step of eluting the radioactive cesium into the oxalic acid solution under hydrothermal reaction conditions;
An oxalic acid solution discharging step of discharging the oxalic acid solution from the container;
A method for decontaminating contaminated solids characterized in that After the oxalic acid solution discharging step,
A neutralizing agent charging step of charging a neutralizing agent into the container;
A neutralizing agent discharging step of discharging the neutralizing agent from the container;
The method for decontaminating contaminated solid according to claim 1, wherein: Before the neutralizing agent charging step,
3. The removal of contaminated solid according to claim 2, wherein the oxalic acid solution charging step, the hydrothermal reaction condition setting step, the elution step, and the oxalic acid solution discharging step are performed a plurality of times. Dyeing method. After the oxalic acid solution discharging step,
Measuring the radiation level of the solid in the container, and performing a radiation level determination step to determine whether the radiation level is below a reference value;
When it is determined that the radiation level is determined to be below the reference value in the radiation level determination step, the neutralizing agent charging step is performed,
When it is determined that the radiation level determination step is not below the reference value, the oxalic acid solution charging step, the hydrothermal reaction condition setting step, the elution step, the oxalic acid solution discharging step, 4. The method for decontaminating contaminated solids according to claim 2 or claim 3, wherein:   The decontamination of contaminated solid according to any one of claims 1 to 4, wherein the oxalic acid solution discharged in the oxalic acid solution discharging step is reused in the oxalic acid solution charging step. Method.   6. The decontamination method for contaminated solid according to claim 1, wherein in the oxalic acid solution charging step, an oxalic acid solution having a concentration of 2 mol / L is charged into a container.   The decontamination method for contaminated solid according to any one of claims 1 to 6, wherein in the hydrothermal reaction condition setting step, the temperature is set to 140 ° C and 353 kPa.   The amount of the oxalic acid solution charged into the container in the oxalic acid solution charging step is twice the mass of the contaminated solid charged in the contaminated solid charging step. 8. The method for decontaminating contaminated solids according to any one of 7 above. A decontamination device for contaminated solids that removes radioactive cesium from decontaminated solids such as soil and sludge contaminated with radioactive cesium,
A decontamination machine comprising a container into which contaminated solids and an oxalic acid solution are charged;
A steam boiler that injects steam into the container and sets the inside of the container under hydrothermal reaction conditions,
A decontamination apparatus for contaminated solids, wherein the radioactive cesium is eluted in the oxalic acid solution under hydrothermal reaction conditions, and the contaminated solid is decontaminated by discharging the oxalic acid solution from the container. The decontamination apparatus for contaminated solids according to claim 9, wherein the apparatus is movable by a vehicle or the like.

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