Absorbent material dryness determination method

Abstract

To provide an absorbent material dryness determination method that carries out a determination of a drying end of an absorption tower serving as a determined object efficiently and accurately, and can shorten time to determine the dryness end.SOLUTION: An absorbent material dryness determination method has the steps of: preliminarily preparing a correlation curve from a graph on a relationship between an inclination of a container outer wall temperature indicative of a temperature change per time of an outer wall temperature of an absorption container at a dryness end, and a temperature difference ΔT subtracting an evaporation temperature indicative of a saturation temperature of water in response to pressure of the absorption container from a heater temperature arranged in an outer periphery of the absorption container or the outer wall temperature; calculating, upon drying the absorption tower serving as the determined object, a temperature difference ΔT at the dryness subtracting the evaporation temperature of the water in response to the pressure of the absorption tower from the heater temperature of the heater or the outer wall temperature; and carrying out a determination of the dryness end in comparison of the relationship between the calculated temperature difference ΔT at the dryness and an inclination of the outer wall temperature at the dryness with the correlation curve.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for determining the dryness of an adsorbent that adsorbs radioactive materials contained in contaminated water, which is waste material from decommissioning work, when the adsorbent is dried in an adsorption tower. [Background technology]

[0002] Conventionally, in decommissioning work of nuclear reactors installed in nuclear facilities, etc., contaminated water and decontamination waste liquid containing radioactive materials (hereinafter collectively referred to as contaminated water) are discharged as waste (primary waste). One treatment method for removing (reducing) the radioactive materials in contaminated water is to use an adsorption tower containing an adsorbent, as disclosed in Patent Document 1, for example.

[0003] The adsorption towers used to remove radioactive materials from contaminated water are treated as secondary waste. An outlet header, which functions as a drain, is installed at the bottom of the adsorption tower. Treated water is pushed downwards in the adsorption tower by means such as an air blower, and most of it is discharged from the adsorption tower through the outlet header. However, this method leaves the treated water below the outlet header remaining inside the adsorption tower. If treated water remains in this state for a long period of time, corrosion may occur in the adsorption tower, potentially leading to leakage of the remaining treated water. Therefore, a method is adopted to remove the treated water (residual water) remaining in the adsorption tower: drying an adsorbent material that adsorbs the radioactive materials contained in the contaminated water inside the adsorption tower. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5236835 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conventional method of drying the adsorbent in the adsorption tower has the following problems. In other words, if the temperature of the adsorbent or the pressure change in the adsorption tower is used as a criterion for determining the completion of the drying process, it is necessary to install a new device such as a temperature sensor inside the adsorption tower, which not only requires costly and time-consuming installation work, but also makes the work itself difficult due to the high radiation dose.

[0006] Furthermore, when the evaporation rate of the treated water in the adsorption tower is used as a criterion for determining the completion of the drying process, if the actual equipment being evaluated is dried until the amount of evaporated water stops, it takes a very long time to make the determination. Because the number of adsorption towers is very large compared to the number of dryers installed, there is a need to be able to more efficiently and accurately determine the completion of the drying process and to further shorten the time required to make the determination in order to shorten the work time required to dry the adsorbent in the adsorption towers using the dryers, and there is room for improvement in this regard.

[0007] The present invention aims to provide a method for determining the dryness of an adsorbent, which can efficiently and accurately determine the completion of drying in an adsorption tower to be determined, and can shorten the time required to determine the completion of drying. [Means for solving the problem]

[0008] One aspect of the present invention is a method for determining the dryness of an adsorbent that adsorbs radioactive materials contained in contaminated water when the adsorbent is dried in an adsorption tower, the method comprising the steps of: creating a correlation curve from a graph of the relationship between the slope of the vessel outer wall temperature, which indicates the temperature change per hour in the outer wall temperature of the adsorption vessel at the end of drying, and the temperature difference ΔT, which is obtained by subtracting the evaporation temperature, which indicates the saturation temperature of water that corresponds to the internal pressure of the adsorption vessel, from the heater temperature of a heater arranged on the periphery of the adsorption vessel or from the outer wall temperature; calculating, during drying of the adsorption tower to be determined, the temperature difference ΔT during drying, which is obtained by subtracting the evaporation temperature, which indicates the saturation temperature of water that corresponds to the internal pressure of the adsorption vessel, from the heater temperature of the heater or the outer wall temperature of the heater; and determining the completion of drying by comparing the calculated relationship between the temperature difference ΔT during drying and the slope of the vessel outer wall temperature with the correlation curve.

[0009] According to the present invention, the outer wall temperature of the adsorption vessel at the end of drying is acquired in advance to determine the gradient of the vessel outer wall temperature, which indicates the temperature change per unit time. Then, a temperature difference ΔT is calculated by subtracting the evaporation temperature, which indicates the saturation temperature of water corresponding to the internal pressure of the adsorption vessel, from the heater temperature of a heater disposed around the adsorption vessel. A correlation curve can be created from a graph of the relationship between the gradient and the temperature difference ΔT. The created correlation curve can then be used as a criterion for determining the end of drying. Therefore, during drying in the adsorption tower to be determined, the temperature difference ΔT is calculated by subtracting the evaporation temperature, which indicates the saturation temperature of water corresponding to the internal pressure of the adsorption vessel, from the heater temperature or outer wall temperature of the heater. The previously created correlation curve can then be used to determine the end of drying by comparing the gradient of the vessel outer wall temperature in the adsorption tower during drying with the correlation curve. Thus, the method for determining the drying end of an adsorbent according to the present invention can more accurately determine the end of drying, even for an adsorption tower to be determined where the initial amount of water in the vessel is unknown. That is, the end of drying in the adsorption tower to be determined can be determined efficiently and accurately, thereby shortening the time required for determining the end of drying. Therefore, the drying operation can be completed efficiently for a large number of adsorption towers. Furthermore, according to the present invention, since the method measures the temperature of the outer wall of the adsorption tower, there is no need to install a new thermometer inside the adsorption tower, which has a high radiation dose, and the work can be carried out efficiently without any difficulty.

[0010] Furthermore, the present invention is characterized in that the criterion for determining the completion of drying is when, in the graph of the temperature difference ΔT and the gradient of the container outer wall temperature created in advance, a value specified by the temperature difference ΔT of the object to be determined and the gradient of the container outer wall temperature coincides with the correlation curve or is within a predetermined range including the vicinity of the correlation curve.

[0011] According to the present invention, the completion of drying can be determined when the temperature difference ΔT and the gradient of the container outer wall temperature during drying match a correlation curve created in advance or when they are within a predetermined range including the vicinity of the correlation curve. Therefore, the completion of drying can be determined easily and accurately by visual inspection.

[0012] In the present invention, the heater is preferably provided on the peripheral surface and the bottom surface of the adsorption tower.

[0013] According to the present invention, heaters are provided not only on the peripheral surface of the adsorption tower but also on the bottom surface thereof, so that the treated water that may remain at the bottom of the adsorption tower can be reliably heated.

[0014] Furthermore, in the present invention, it is preferable that the adsorption tower has an inner container filled with the adsorbent and an outer container arranged outside the inner container with an air layer interposed therebetween to shield radiation from reaching the outside, and that the temperature of the outer wall of the adsorption tower is measured by a thermometer installed on the outer surface of the inner container or the inner surface of the outer container.

[0015] According to the present invention, a thermometer is provided on the outer surface of the inner vessel or the inner surface of the outer vessel of the adsorption tower, which allows for accurate measurement of the outer wall temperature of the adsorption tower. Moreover, the thermometer can be easily installed using the air space between the inner vessel and the outer vessel. [Effects of the Invention]

[0016] According to the method for determining dryness of an adsorbent according to the present invention, the completion of drying of the adsorption tower to be determined can be determined efficiently and accurately, and the time required for determining the completion of drying can be shortened. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a vertical cross-sectional view showing an adsorption tower to which a method for determining dryness of an adsorbent according to an embodiment of the present invention is applied. [Figure 2] FIG. 1 is a flow diagram of a test method. [Figure 3] 10A and 10B are diagrams showing an example of changes over time in the temperature of the outer wall of the container and the amount of residual water in the test, where (a) shows the second test and (b) shows the third test. [Figure 4] 10A and 10B are diagrams showing an example of changes over time in the temperature of the outer wall of the container and the amount of residual water in the tests, where (a) shows the fourth test and (b) shows the fifth test. [Figure 5] FIG. 10 is a diagram showing the relationship between the gradient of the container outer wall temperature, which indicates the temperature change per unit time of the outer wall temperature of the adsorption container, and the temperature difference ΔT. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a method for determining dryness of an adsorbent according to an embodiment of the present invention will be described with reference to the drawings. The dimensions, materials, and other specific values shown in the embodiment are merely examples for facilitating understanding of the invention and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same function and configuration are assigned the same reference numerals to avoid redundant explanation, and elements not directly related to the present invention are not shown.

[0019] Fig. 1 is a vertical cross-sectional view showing an adsorption tower 10 to which an adsorbent dryness determination method (hereinafter simply referred to as the dryness determination method) according to an embodiment is applied. As shown in Fig. 1, the adsorption tower 10 is filled with an adsorbent 5 that adsorbs radioactive materials such as cesium up to a filling height H1. As the adsorbent 5, for example, zeolite or silicate titanate can be suitably used.

[0020] An inlet header 101 that functions as a water supply port is provided at the top of the adsorption tower 10. A water supply pipe (not shown) is connected to the inlet header 101. An outlet header 102 that functions as a drain port is provided at the bottom of the adsorption tower 10. A drain pipe 103 is connected to the outlet header 102.

[0021] Contaminated water is supplied to the adsorption tower 10 from the water supply pipe via the inlet header 101. The supplied contaminated water passes through the inside of the adsorbent 5, whereby radioactive materials are adsorbed by the adsorbent 5, and the water becomes treated water from which radioactive materials have been removed (or reduced). The treated water is discharged to the outside from the outlet header 102 through a drain pipe 103. When the adsorption tower 10 reaches the end of its performance life and is replaced, compressed air is supplied from the water supply pipe to air-blow and discharge the treated water, and the treated water remaining in the adsorbent 5 is pushed down and discharged from the outlet header 102 through the drain pipe 103.

[0022] At this time, the water below the outlet header 102 cannot be pushed out, and therefore treated water (residual water) at a residual water height H2 remains inside the adsorption tower 10. In addition, the adsorbent 5 at a predetermined height H3 above the outlet header 102 is wet with water, i.e., contains a large amount of water.

[0023] The adsorption tower 10 is provided with a hydrogen vent pipe (not shown) to prevent hydrogen generated by the radioactivity adsorbed on the adsorbent 5 radiolytically decomposing the treated water from remaining inside the tower, and a hydrogen vent valve (not shown) is provided at the end of the pipe.

[0024] The adsorption tower 10 has a cylindrical, bottomed inner container 11 filled with an adsorbent 5, and an outer container 12 arranged outside the inner container 11 with an air layer 13 interposed therebetween to shield radiation from reaching the outside. The adsorption tower 10 is supported from below by a base frame 14. The upper opening of the inner container 11 is sealed by an upper lid 110.

[0025] The outer container 12 has a side wall 121 and a bottom wall 122. The side wall 121 and the bottom wall 122 are both arranged with a gap (air layer 13) between them and the inner container 11. A heater 20 (side heater 21) is provided on an outer surface 121a of the side wall 121 of the outer container 12. A heat insulating material 15 is provided on the outer surface 121a of the side wall 121 so as to cover the side heater 21 from the outside. For example, a half-split band heater is used as the side heater 21, and the pair of band heaters are arranged to sandwich the outer container 12, thereby covering the entire circumference of the outer container 12.

[0026] The base stand 14 has a horizontal plate 141 that faces the bottom wall 122 of the outer container 12 from below. A heater 20 (bottom heater 22) is provided on the lower surface 141a of the horizontal plate 141. The bottom heater 22 is also covered from below with a heat insulating material (not shown).

[0027] When water evaporates in the adsorption tower 10, the water temperature drops due to latent heat, making evaporation difficult. Therefore, by supplying heat to the adsorption tower 10 using the heater 20, the latent heat is compensated for and the drop in water temperature is prevented. This makes it possible to suppress a decrease in the evaporation rate and increase the evaporation efficiency of the treated water. Furthermore, by covering the heater 20 with a heat insulating material 15, the heat of the heater 20 can be efficiently supplied to the adsorption tower 10.

[0028] A plurality of thermocouples 30 (thermometers) for measuring the outer wall temperature t1 of the inner container 11 are attached at intervals in the vertical direction to the outer surface 11a of the inner container 11. That is, the thermocouples 30 are arranged in the region (air layer 13) between the inner container 11 and the outer container 12. In this embodiment, five cross sections (cross sections R1 to R5) are set in the inner container 11, and an appropriate number of thermocouples 30 are arranged at intervals in the circumferential direction at each of the cross sections R1 to R5. Note that there may be only one thermocouple 30 at each of the cross sections R1 to R5. In this way, the outer wall temperature t1 of the adsorption tower 10 is measured by the thermocouple 30 installed on the outer surface 11a of the inner vessel 11. The thermocouple 30 is not limited to being installed on the outer surface 11a of the inner vessel 11, and can also be installed on the inner surface 12a of the outer vessel 12, for example.

[0029] The dryness determination method of this embodiment is carried out using the heater 20 (21, 22), thermocouple 30, and a vacuum pump (not shown) that is part of the drying device. The vacuum pump is located downstream of the adsorption tower 10. The vacuum pump sucks air containing water vapor from inside the adsorption tower 10, which is supplied from the hydrogen vent pipe, through a pipe, thereby reducing the pressure inside the adsorption tower 10. The vacuum pump is connected to a cooling trap (not shown) through an air pipe. The air sucked by the vacuum pump is sent to the cooling trap through the air pipe. The cooling trap cools the air sucked from the adsorption tower 10 to condense the moisture.

[0030] Furthermore, a pressure gauge (not shown) is connected to the air pipe between the vacuum pump and the adsorption tower 10. This allows the pressure in the adsorption tower 10 to be detected.

[0031] In addition, this embodiment includes a control unit (not shown) for implementing the dryness determination method. The control unit acquires the outer wall temperature t1 measured by the thermocouple 30, the heater temperature t2 of the heater 20, the pressure P of the adsorption tower 10, and the saturation temperature of water (evaporation temperature t3) corresponding to the pressure P. As a feature of the dryness determination method of this embodiment, the control unit creates in advance a correlation curve Q (see FIG. 5) from a graph of the relationship between the gradient of the container outer wall temperature, which indicates the temperature change per hour of the outer wall temperature t1 of the adsorption tower 10, and the temperature difference ΔT, which is the value (t2-t3) obtained by subtracting the evaporation temperature t3, which indicates the saturation temperature of water corresponding to the pressure P, from the heater temperature t2, and performs control to determine that drying is complete when the gradient of the container outer wall temperature in the adsorption tower 10 undergoing drying, which is the subject of determination, reaches the correlation curve Q. Specifically, the criterion for determining whether drying is complete in the adsorption tower 10 undergoing drying is when, in the graph shown in Figure 5, which was created in advance, the value determined by the temperature difference ΔT of the object to be determined and the gradient of the container outer wall temperature coincides with the correlation curve Q or is within a predetermined range including the vicinity of the correlation curve Q.

[0032] In this manner, in this embodiment, a dryness determination method is implemented for determining completion of drying of the adsorbent 5 when the adsorbent 5 that adsorbs radioactive materials contained in contaminated water is dried in the adsorption tower 10.

[0033] Next, an example of a method for creating the correlation curve Q shown in FIG. 5, which is used in the dryness determination method of this embodiment, will be described in detail. The correlation curve Q can be determined by testing, for example, using a test device simulating the adsorption tower 10 or an actual adsorption vessel 10A (see FIG. 1) before use. Here, FIG. 1 shows the adsorption tower 10, but the adsorption vessel 10A used as the test device also has a similar configuration to the adsorption tower 10, so the adsorption tower 10 and the adsorption vessel 10A will be described using the same FIG. 1. Therefore, the same symbols will be used for the various parts and components of the adsorption vessel 10A.

[0034] First, the test conditions will be described. As shown in FIG. 1, the adsorption vessel 10A, which is the test equipment, used an inner vessel 11 made of stainless steel (SUS304). The inner vessel 11 had an inner diameter of 900 mm, a height of 1,775 mm, an operating pressure of 5 kPa to 0.3 MPa, and a maximum operating temperature of the outer wall surface of 230°C. A sampling hole for the adsorbent 5 was provided in the top cover 110. A drainage torus pipe was installed at the bottom. The outer vessel 12 had an inner diameter of 980 mm and a height of 2,000 mm. Similar to the adsorption tower 10, the adsorption vessel 10A had an outer vessel 12 installed outside the inner vessel 11 with an air gap 13 of approximately 30 mm between them, and a heat insulating material 15 installed on the outer surface 121a of the outer vessel 12.

[0035] The side heaters 211 are installed on the outer surface 121a of the outer vessel 12 in four sections in the tube axis direction, with a total electric capacity of 9.6 kW and a maximum operating temperature of 250° C. A bottom heater 22 is installed on the horizontal plate 141 of the base frame 14 that supports the outer vessel 12.

[0036] A plurality of thermocouples 30 were installed on the outer surface 11a of the inner vessel 11 of the adsorption vessel 10A. These thermocouples 30 were provided at each of five cross sections R1 to R5 of the adsorption vessel 10A. The first cross section R1 is a horizontal cross section at the height of the center of the adsorption vessel 10A in the tube axis direction. The second cross section R2 is a horizontal cross section at the height of an intermediate portion between the first cross section R1 and the vessel top surface 11b. The third cross section R3 is a horizontal cross section at the height of an intermediate portion between the first cross section R1 and the vessel bottom surface 11c. The fourth cross section R4 is a horizontal cross section at the height near the vessel top surface 11b. The fifth cross section R5 is a horizontal cross section at the height near the vessel bottom surface 11c. A total of ten thermocouples 30 were provided at each of the cross sections R1 to R5, one on the outer surface 11a of the inner vessel 11 and one on the inner surface 12a of the outer vessel 12.

[0037] 2, the test method begins with step S1, in which the adsorbent 5 inside the adsorption vessel 10A is dried, and then pure water is filled into the adsorption vessel 10A from the bottom. Then, when it is confirmed that the pure water filled from the top of the adsorption vessel 10A has overflowed, the filling of the pure water is stopped (step S2). After that, air is blown from the top of the adsorption vessel 10A (step S3), drainage begins (step S4), and after visually confirming that no water has come out of the drain hose, drainage is stopped (step S5).

[0038] Next, the vacuum pump is turned on (step S6), and the pressure inside the container is reduced to the test conditions described below, and then the heater 20 is turned on to start the test (step S7). This allows data on the outer wall temperature t1 to be acquired, and the data is organized, and the heater is turned off (test end) (step S8). Thereafter, the adsorbent 5 is sampled (step S9), and the moisture content is measured (step S10).

[0039] Next, 12 tests (Test Nos. 1 to 12) were conducted to create the correlation curve Q. Table 1 shows the test conditions for Tests 1 to 12, namely, the heater temperature (°C) of the side heater 21, the heater temperature (°C) of the ribbon heater (bottom heater 22), the pressure inside the vessel (kPa), the reference temperature (temperature difference) ΔT (°C) of the outer wall of the adsorption vessel 10A, and the gradient of the vessel outer wall temperature.

[0040] [Table 1]

[0041] The outer wall temperature reference ΔT of the adsorption vessel 10A is the temperature difference obtained by subtracting the evaporation temperature t3, which indicates the saturation temperature of water according to the pressure of the adsorption vessel 10A, from the heater temperature t2 of the heater 20 arranged on the outer periphery of the adsorption vessel 10A.

[0042] Examples of the changes over time in the container outer wall temperature t1 and the residual water volume in the tests are shown in Figures 3(a), (b) and 4(a), (b). Figure 3(a) is a diagram showing the second test. Figure 3(b) is a diagram showing the third test. Figure 4(a) is a diagram showing the fourth test. Figure 4(b) is a diagram showing the fifth test. In Figures 3(a), (b) and 4(a), (b), the horizontal axis represents elapsed time (h) and the vertical axis represents the container outer wall temperature (°C) and pressure (kPa). Figures 3(a), (b) and 4(a), (b) show the results of the changes over time at the first cross section R1 to the fifth cross section R5 described above, as well as the results of the changes over time in the vacuum pressure. The three dotted lines shown in FIGS. 3(a) and 3(b) and 4(a) and 4(b) indicate pore volume 1, pore volume 2 / 3, and pore volume 1 / 2.

[0043] Here, we explain the pore volume, which is the criterion for determining the completion of drying. The adsorption vessel 10A consists of the adsorbent (solid), the pores of the adsorbent, and the spaces between the adsorbent particles. When water is filled into the adsorption vessel 10A, the pores of the adsorbent and the spaces between the adsorbent particles are filled with water. At this time, the water in the pores of the adsorbent is called adsorbed water, and the water between the adsorbent particles is called free water. Next, when the water is drained using gravity or compressed air, the water is discharged from the free water, but not all of it is discharged due to surface tension. Similarly, the adsorbed water is almost not discharged due to surface tension. After that, when drying begins, the free water near the inner wall of the vessel evaporates first, followed by the adsorbed water. However, once the free water has evaporated, it is unlikely that water will drip. Therefore, when the amount of remaining water is equal to the amount of adsorbed water (pore volume), drying is considered to be near completion. However, considering the unevenness of the moisture distribution, the criterion for determining the completion of drying was set to when the residual water volume reaches 2 / 3 of the pore volume.

[0044] As shown in Figures 3(a) and 3(b) and Figures 4(a) and 4(b), from the relationship between the container outer wall temperature and the amount of residual water, it was confirmed that for all cross sections R1 to R5, the rate of temperature rise decreases after a certain time has passed from the initial stage of drying (after the heater is turned on). Furthermore, when the amount of residual water reaches 2 / 3 of the pore volume, the rate of temperature rise remains at a reduced level, suggesting that drying has ended.

[0045] Fig. 5 is a graph showing the relationship between the gradient of the outer wall temperature of the adsorption vessel 10A, which indicates the temperature change per unit time at the outer wall, and the temperature difference ΔT. In Fig. 5, the horizontal axis represents the temperature difference ΔT, and the vertical axis represents the gradient of the outer wall temperature of the adsorption vessel 10A, and the gradient of the outer wall temperature of the adsorption vessel 10A and the temperature difference ΔT when the residual water volume reached two-thirds of the pore volume in the first to twelfth tests described above are plotted.

[0046] As shown in Figure 5, the slope tends to increase as the temperature difference ΔT increases, and a correlation can be found between the slope of the container outer wall temperature and the temperature difference ΔT. Therefore, a correlation curve Q can be created from the relationship between the slope of the container outer wall temperature and the temperature difference ΔT, which are the data from Tests 1 to 12. Then, when the slope of the container outer wall temperature in the actual adsorption tower 10 reaches the preset correlation curve Q, it can be determined that drying of the adsorption container 10A has been completed. In other words, after a certain amount of time has passed since the start of drying, the slope of the container outer wall temperature decreases, eventually reaching the correlation curve Q, and it can be determined that drying has been completed.

[0047] As described above, in the method for determining dryness of this embodiment, by creating a correlation curve Q at the end of drying in advance, the end of drying in the adsorption tower 10 to be determined can be suitably determined using this correlation curve Q. That is, during drying in the adsorption tower 10 to be determined, the outer wall temperature t1 of the adsorption tower 10 and the temperature difference ΔT obtained by subtracting the evaporation temperature indicating the saturation temperature of water according to the pressure of the adsorption tower 10 from the heater temperature of the heater 20 are calculated, and the drying can be determined to be completed when the relationship between the gradient (gradient of the container outer wall temperature) in the adsorption tower 10 during drying and the gradient reaches the previously created correlation curve Q.

[0048] Next, the operation of the method for determining whether an adsorbent is dry will be described in detail with reference to FIG. In the method for determining the dryness of the adsorbent 5 according to this embodiment, the outer wall temperature of the adsorption vessel 10A at the end of drying is acquired in advance to determine the gradient of the vessel outer wall temperature, which indicates the temperature change per unit time. Then, a temperature difference ΔT is calculated by subtracting the evaporation temperature, which indicates the saturation temperature of water corresponding to the internal pressure of the adsorption vessel 10A, from the heater temperature of the heater 20 disposed on the outer periphery of the adsorption vessel 10A. A correlation curve Q (see FIG. 5 ) can be created from a graph of the relationship between the gradient and the temperature difference ΔT. The created correlation curve Q can then be used as a criterion for determining the end of drying. Therefore, during drying in the adsorption tower 10 to be determined, the temperature difference ΔT during drying is calculated by subtracting the evaporation temperature, which indicates the saturation temperature of water corresponding to the pressure in the adsorption tower, from the heater temperature of the heater 20. The previously created correlation curve Q can then be used to determine the end of drying by comparing the gradient of the vessel outer wall temperature in the adsorption tower 10 during drying with the correlation curve Q.

[0049] As described above, the method for determining the dryness of the adsorbent 5 according to the present embodiment allows for a more accurate determination of the completion of drying, even for an adsorption tower 10 to be determined, for example, where the amount of water in the initial container is unknown. That is, the completion of drying of the adsorption tower 10 to be determined can be determined efficiently and accurately, and the time required for the determination can be shortened. Therefore, the drying process can be completed efficiently for a large number of adsorption towers 10.

[0050] Furthermore, according to the method for determining the dryness of an adsorbent according to this embodiment, the temperature of the outer wall of the adsorption tower 10 is measured, so there is no need to install a new thermometer inside the adsorption tower 10, which has a high radiation dose, and the work can be carried out efficiently without any difficulty.

[0051] Furthermore, in this embodiment, the judgment criterion can be when the temperature difference ΔT and the gradient of the container outer wall temperature during drying match a correlation curve Q created in advance, or when they are within a predetermined range including the vicinity of the correlation curve Q. Therefore, the completion of drying can be easily and accurately determined by visual inspection.

[0052] In this embodiment, the heater 20 is provided on the peripheral surface and the bottom surface of the adsorption tower 10. Therefore, since the heater 20 is provided not only on the peripheral surface but also on the bottom surface of the adsorption tower 10, the treated water that may remain at the bottom of the adsorption tower 10 can be reliably heated.

[0053] In this embodiment, the adsorption tower 10 includes an inner container 11 filled with the adsorbent 5, and an outer container 12 disposed outside the inner container 11 with an air layer 13 interposed therebetween to shield radiation from reaching the outside. The temperature of the outer wall of the adsorption tower 10 is measured by a thermocouple 30 (thermometer) installed on the outer surface 11a of the inner container 11 or the inner surface 12a of the outer container 12. This allows the temperature of the outer wall of the adsorption tower 10 to be measured with high accuracy. Moreover, the thermocouple 30 can be easily installed using the air layer 13 between the inner container 11 and the outer container 12.

[0054] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

[0055] For example, the configurations such as the installation position and installation area of the heater 20, the number and installation positions of the thermocouples 30, etc. are not limited to those in the above-described embodiment, and can be changed as appropriate.

[0056] Furthermore, in this embodiment, the method for creating the correlation curve Q is a method of performing a test using the adsorption vessel 10A, which is a test specimen simulating the adsorption tower 10, to create the correlation curve Q. However, as described above, the object for determining the correlation curve Q is not limited to the test specimen adsorption vessel 10A, and it is of course possible to create the correlation curve Q using an actual adsorption tower 10.

[0057] In the above-described embodiment, an adsorption vessel is used in the step of creating a correlation curve, and the correlation curve is created from the relationship between the slope of the vessel outer wall temperature, which indicates the temperature change per unit time in the adsorption vessel outer wall temperature at the end of drying, and the temperature difference ΔT, which is the heater temperature of a heater disposed around the adsorption vessel minus the evaporation temperature, which indicates the saturation temperature of water corresponding to the pressure inside the adsorption vessel. However, the temperature difference ΔT is not limited to the heater temperature, and may be the outer wall temperature. In other words, the temperature difference ΔT may be the temperature difference, which is the outer wall temperature of the adsorption vessel minus the evaporation temperature, which indicates the saturation temperature of water corresponding to the pressure inside the adsorption vessel. [Explanation of symbols]

[0058] 5 adsorbent, 10 adsorption tower, 10A adsorption vessel, 11 inner vessel, 11a outer surface, 12 outer vessel, 12a inner surface, 13 air layer, 20 heater, 21 side heater, 22 bottom heater, 30 thermocouple (thermometer), Q correlation curve

Claims

1. A method for determining dryness of an adsorbent that adsorbs radioactive materials contained in contaminated water when the adsorbent is dried in an adsorption tower, comprising: creating a correlation curve from a graph showing the relationship between the gradient of the adsorption vessel outer wall temperature, which indicates the temperature change per unit time of the adsorption vessel outer wall temperature at the end of drying, and the temperature difference ΔT, which is obtained by subtracting the evaporation temperature, which indicates the saturation temperature of water corresponding to the pressure of the adsorption vessel, from the heater temperature of a heater disposed around the adsorption vessel or from the outer wall temperature; calculating a temperature difference ΔT during drying of the adsorption tower to be determined by subtracting an evaporation temperature indicating a saturation temperature of water corresponding to a pressure in the adsorption tower from a heater temperature of the heater or an outer wall temperature of the adsorption tower; a step of comparing the calculated relationship between the temperature difference ΔT during drying and the gradient of the container outer wall temperature during drying with the correlation curve to determine whether drying has been completed; A method for determining dryness of an adsorbent, comprising:

2. 2. The method for determining dryness of an adsorbent according to claim 1, wherein the criterion for determining the completion of drying is when a value specified by the temperature difference ΔT of the object to be determined and the slope of the outer wall temperature of the container in the graph of the temperature difference ΔT and the slope of the outer wall temperature of the container, created in advance, matches the correlation curve or is within a predetermined range including the vicinity of the correlation curve.

3. The method for determining dryness of an adsorbent according to claim 1 , wherein the heater is provided on a peripheral surface and a bottom surface of the adsorption tower.

4. the adsorption tower includes an inner container filled with the adsorbent, and an outer container disposed outside the inner container with an air layer interposed therebetween to shield radiation from reaching the outside, The method for determining dryness of an adsorbent according to claim 1 , wherein the temperature of the outer wall of the adsorption tower is measured by a thermometer installed on the outer surface of the inner container or the inner surface of the outer container.

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