JP6180748B2 - Sedimentation separation apparatus and sedimentation separation method for radioactive liquid waste - Google Patents

Description

  The present invention relates to a sedimentation separation apparatus and sedimentation separation method for radioactive liquid waste containing solid particles such as nuclear fuel materials.

  In the event of a core melting accident at a nuclear power plant during a major disaster, the molten core is currently cooled by water injection. At that time, some of the nuclear fuel materials such as uranium (U) and plutonium (Pu) eluted from the fuel rods. Becomes solid particles and precipitates in the cooling water. When a nuclear reactor in which such a core melting accident has occurred is to be decommissioned, it is necessary to treat solid particles containing nuclear fuel material in the radioactive liquid waste stored in the building or containment vessel. Since these solid particles are present in the radioactive liquid waste, from the viewpoint of volume reduction and safety management, for example, solid-liquid separation processing is performed by sedimentation separation means, and then transferred to a storage container or the like and stored for a long time. Since this precipitation separation method is a simple solid-liquid separation system that uses gravity sedimentation of solid particles due to the density difference between the solid particles and the liquid, it is widely used in various fields (Patent Document 1).

  However, when the nuclear waste material in the form of solid particles is contained in the radioactive liquid waste, there is a risk of becoming a critical state during processing depending on the solid particle concentration. Accordingly, in a nuclear fuel reprocessing facility that uses spent nuclear fuel material as a processing target, strict criticality prevention management is required to prevent the processing target from becoming a critical state in the processing step. Therefore, measures such as forming a recovery tank for depositing and recovering nuclear fuel in a flat plate shape having a non-critical interval and providing a multi-stage sedimentation tank have been taken (Patent Documents 2 and 3).

Japanese Examined Patent Publication No. 63-35959 Japanese Patent Application Laid-Open No. 6-265589 JP-A-9-178888

  As described above, in the nuclear fuel reprocessing facilities shown in Patent Documents 2 and 3, a plurality of recovery tanks for depositing and recovering nuclear fuel are formed in a flat plate shape having a non-critical interval, or a multistage sedimentation tank is provided. Although measures have been taken, strict criticality prevention measures are required even in the treatment process of radioactive liquid waste when the radioactive liquid waste contains solid particulate nuclear fuel material.

  Therefore, it is conceivable to use the criticality prevention means in these nuclear fuel reprocessing facilities for the treatment of radioactive liquid waste at the time of decommissioning, but these collection tanks (sedimentation tanks) are small in volume, so that a large amount of radioactive liquid waste can be shortened. It is difficult to process in time, and there is a problem that the processing facility is enlarged and the processing time is prolonged because the collection tanks (sedimentation tanks) are arranged in multiple stages.

  Furthermore, when these recovery tanks (precipitation tanks) are used as precipitation separation tanks, the bottom surface is flat, so there is a possibility that solid particles in the radioactive waste liquid will deposit and deposit unevenly at the bottom of the recovery tank (precipitation tank). There was a problem that criticality management became difficult.

  The present invention has been made to solve the above-mentioned problems, and is capable of processing a large volume of radioactive waste liquid in a short time and can reliably prevent the occurrence of criticality in the processing step, and a sedimentation apparatus and sedimentation apparatus for radioactive waste liquid. An object is to provide a separation method.

In order to achieve the above object, a radioactive waste liquid sedimentation separation apparatus according to the present invention is disposed at a top of the precipitation separation tank, a precipitation separation tank in which the lower part is inclined in an inverted conical shape and into which radioactive waste liquid is injected. A plurality of granular critical deterrent members into the sedimentation tank, and the sedimentation rate of the granular critical deterrent members is equivalent to the sedimentation rate of the nuclear fuel material contained in the radioactive liquid waste It is characterized by being.
Moreover, the sedimentation method for radioactive liquid waste according to the present invention is characterized in that the radioactive liquid waste is separated by precipitation using the radioactive liquid waste sedimentation apparatus according to the present invention.

  According to the present invention, it becomes possible to process a large volume of radioactive liquid waste containing nuclear fuel materials that require critical control such as uranium and plutonium in a short time, and reliably prevent the occurrence of criticality in the processing process. Can do.

(A) is sectional drawing of the sedimentation-separation apparatus which concerns on 1st Embodiment, (b) is the AA arrow directional view of (a). (A) is sectional drawing of the sedimentation-separation apparatus which concerns on the modification of 1st Embodiment, (b) is the top view. (A) is sectional drawing of the sedimentation-separation apparatus which concerns on the other modification of 1st Embodiment, (b) is the top view. (A) is sectional drawing of the sedimentation-separation apparatus which concerns on the other modification of 1st Embodiment, (b) is a schematic diagram of the drive mechanism in which the criticality suppression member was installed. (A), (b) is sectional drawing of the sedimentation-separation apparatus which concerns on 2nd Embodiment, (c) is the BB arrow directional view of (b). Sectional drawing of the sedimentation-separation apparatus which concerns on 3rd Embodiment. Sectional drawing of the sedimentation-separation apparatus which concerns on the modification of 3rd Embodiment. The whole block diagram of the sedimentation-separation apparatus which concerns on 3rd Embodiment. The figure which shows the relationship between the particle size of a criticality suppression member in 3rd Embodiment, and a sedimentation distance.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a radioactive waste liquid sedimentation separation apparatus and sedimentation separation method according to the present invention will be described with reference to the drawings.

[First Embodiment]
The sedimentation separator according to the first embodiment will be described with reference to FIG.
(Constitution)
The sedimentation separation apparatus according to this embodiment is basically composed of an inverted conical sedimentation separation tank and a critical suppression member made of a neutron absorber provided at the bottom thereof.

  The sedimentation separation tank 1 has an inverted conical shape having, for example, an inverted conical shape whose bottom portion is inclined toward the lower end portion 1b, and an inclination angle of the inclined surface 1a is a sludge 3 in the radioactive waste liquid 2 to be injected. It is set to an angle equal to or greater than the angle of repose so as to form a stable deposited portion without being unevenly distributed at the bottom of one.

  As shown in FIGS. 1A and 1B, a plurality of criticality inhibiting members 5 are provided at the center position of the bottom of the sedimentation separation tank 1 and its concentric position. The number, installation interval, and height of the rod-like and cylindrical criticality-inhibiting members 5 are appropriately determined from the viewpoint of preventing criticality according to the capacity of the sedimentation separation tank 1, the amount of radioactive waste liquid 2, the content of nuclear fuel material, and the like. The setting can be changed.

  The critical deterrent member 5 is an element having a large thermal neutron absorption cross section, such as lithium (Li), boron (B), rhodium (Rh), cadmium (Cd), indium (In), samarium (Sm), europium (Eu). , Gadolinium (Gd), dysprosium (Dy), erbium (Er), thulium (Tm), hafnium (Hf), mercury (Hg), etc. and compounds of these elements, or at least one of these elements and their compounds The containing material is used.

  A radioactive waste liquid 2 containing a solid content (sludge) such as a metal oxide, hydroxide or carbonate containing nuclides such as uranium and plutonium that requires critical control is injected into the precipitation separation tank 1 from a supply pipe 20. However, water, alcohol, TBP (tributyl phosphate) and the like are appropriately added to the radioactive waste liquid 2 as a liquid medium. The radioactive waste liquid 2 injected into the sedimentation separation tank 1 through the supply pipe 20 accumulates sludge 3 at the bottom by sedimentation separation, and stores the supernatant 4 at the top.

In addition, in order to measure neutrons and radiation dose generated from the radioactive liquid waste 2, a criticality monitor 12 and a radiation dosimeter 13 for criticality management are installed outside the precipitation separation tank 1.
In addition, you may make the structural material which comprises the sedimentation-separation tank 1 contain the neutron absorber with a large thermal neutron absorption cross-section mentioned above.

(Function)
In the sedimentation separator configured as described above, the radioactive waste liquid 2 injected into the sedimentation separation tank 1 through the supply pipe 20 is separated from the sludge in the radioactive waste liquid 2 as time passes, so that the bottom of the precipitation separation tank 1 is obtained. Is deposited as sludge 3. At that time, since the lower inclination angle of the sedimentation separation tank 1 is larger than the repose angle, the sludge 3 is deposited almost uniformly on the bottom of the sedimentation separation tank 1 without being unevenly distributed. Neutrons are emitted from uranium and plutonium contained in these sludges 3, but the criticality is suppressed because the neutrons are absorbed by the criticality suppressing members 5 arranged concentrically.

  In addition, a criticality monitor 12 and a radiation dose rate meter 13 are installed outside the sedimentation separation tank 1, and the generation of criticality is ensured by monitoring the amount of neutrons and radiation generated from the liquid 2 and sludge 3 to be treated. Can be prevented. Furthermore, if an abnormality occurs in the sludge 3 deposition process or the discharge operation due to some trouble, these abnormalities can be detected quickly from the measurement results of the critical monitor 12 and the radiation dose rate meter 13, so that it is safer. The radioactive waste liquid 2 can be treated.

The sludge 3 that has settled and separated is transferred from the discharge pipe 21 to a storage container or the like and is safely managed so that no criticality occurs.
One of the coastal monitor 12 and the radiation dose rate meter 13 can be deleted as necessary.

(Modification)
2 to 4 show modified examples of the criticality restraining member.
FIGS. 2A and 2B are examples in which lattice-like critical deterring members 6 are arranged in a plurality of numbers at the bottom of the precipitation separation tank 1.

  FIGS. 3A and 3B are examples in which a plurality of rod-like criticality restraining members 7 are arranged at the bottom of the precipitation separation tank 1. In addition, the rod-like criticality suppression member 7 can be used in various shapes such as a circular shape and a polygonal cross section.

FIGS. 4A and 4B show an example in which a plurality of cylindrical guide tubes 10 are installed at the bottom of the sedimentation separation tank 1 and a rod-like critical deterrent member 8 made of a neutron absorber is inserted therein. The plurality of rod-like criticality suppression members 8 are attached to the drive mechanism 11 and inserted into the guide tube 10 from the lower part of the sedimentation separation tank 1 by the drive mechanism 11 (not shown) during the treatment of the radioactive waste liquid 2. Since the criticality suppression member 8 is movable, damage inspection, replacement, shape change, etc. of the criticality suppression member 8 can be appropriately performed.
Further, the guide tube 10 may be formed in a lattice shape or a concentric shape, and a lattice shape or a concentric critical suppression member may be used in accordance with the shape.

  In any of the modifications shown in FIGS. 2 to 4, the number, arrangement, height, etc. of the criticality restraining members depend on the capacity of the sedimentation separation tank 1, the components of the radioactive liquid waste 2, etc., as in the first embodiment. The design can be changed as appropriate.

(effect)
According to the first embodiment of the present invention, the sedimentation / separation tank 1 is shaped like an inverted spindle, and the inclination angle of the bottom of the sedimentation / separation tank 1 is made larger than the repose angle of the sludge 3 in the radioactive waste liquid 2. The sludge 3 in the radioactive waste liquid 2 can be quickly lowered toward the bottom, and the sludge 3 can be deposited substantially uniformly without uneven distribution. The sludge 3 deposited on the bottom of the sedimentation separation tank 1 can be reliably prevented from reaching criticality by the criticality suppression members 5 to 8 arranged at the bottom of the sedimentation separation tank 1. Thereby, since the large-capacity radioactive liquid waste 2 can be processed safely and reliably, the processing capacity and the processing period of the radioactive liquid waste can be greatly improved.

[Second Embodiment]
A radioactive waste liquid sedimentation separation apparatus and sedimentation separation method according to a second embodiment will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the same part as each part of the apparatus which concerns on 1st Embodiment, and duplication description is abbreviate | omitted about the same structure.

(Constitution)
In the second embodiment, deposits such as sludge 3 are prevented from adhering to the inner wall surface of the sedimentation separation tank 1 and the outer peripheral surfaces of the critical deterring members 5 to 8 and the guide tube 10, and the adhered deposits are removed. It is characterized by having a sludge cleaning section 15 for this purpose.

  The sludge cleaning unit 15 includes a small circulation pump 15a that circulates the supernatant 4 accumulated in the upper part of the sedimentation separation tank 1 during the treatment of the radioactive waste liquid 2, and the inner wall surface and criticality of the sedimentation separation tank 1 after the sludge 3 is discharged. It comprises spraying nozzles 15b for spray cleaning the outer peripheral surfaces of the restraining members 5 to 8 and the guide tube 10, and a plurality of them are installed on the inner peripheral surface of the settling separation tank 1 as shown in FIG. Power is supplied from the outside to the circulation pump 15a via the power cable 17, and the supernatant 4 or water stored outside is supplied to the spray nozzle 15b through the pipe 18.

  In addition, the number and arrangement | positioning of the circulation pump 15a and the injection nozzle 15b can be suitably changed according to the capacity | capacitance or shape of the sedimentation tank 1, the arrangement | positioning of the critical suppression members 5-8, etc. For example, the circulation pump 15a and the injection nozzle 15b may be arranged not only on the inner peripheral surface of the sedimentation separation tank 1 but also in the internal space of the sedimentation separation tank 1 by a support member (not shown). Moreover, you may comprise the sludge washing | cleaning part 15 only with the circulation pump 15a or the injection nozzle 15b.

(Function)
In the second embodiment configured as described above, the circulation pump 15a is operated during the treatment of the radioactive waste liquid 2, and the supernatant 4 stored in the upper part of the sedimentation tank 1 is circulated. As a result, a circulating flow of the supernatant 4 is generated in the sedimentation / separation tank 1, and sludge 3 and the like are prevented from adhering to the inner peripheral surface of the sedimentation / separation tank 1, the critical deterring members 5 to 8 and the outer periphery of the guide tube 10. To do. The water flow generated by the circulation pump 15a is adjusted to a water flow that does not disturb or raise the sludge 3 accumulated at the bottom of the sedimentation separation tank 1.

  Next, after the precipitation separation process of the radioactive liquid waste 2 is completed and the sludge 3 is discharged from the precipitation separation tank 1, the supernatant 4 and water separately stored from the nozzle 15b are injected into the precipitation separation tank 1, Deposits adhering to the inner peripheral surface of the settling tank 1 and the outer peripheral surfaces of the critical inhibition members 5 to 8 and the guide tube 10 are removed.

(effect)
According to the second embodiment, by providing the sludge cleaning unit 15 including the circulation pump 15a and the injection nozzle 15b on the inner circumferential surface of the sedimentation separation tank 1, the inner circumferential surface of the sedimentation separation tank 1 and the criticality suppressing member. Since it is possible to efficiently suppress the adhesion of sludge and the like to the outer peripheral surface of 5 to 8 and the guide tube 10 and remove the deposits, it is possible to keep the sedimentation separation ability of the sedimentation separation apparatus good.

[Third Embodiment]
A radioactive waste liquid sedimentation separation apparatus and sedimentation separation method according to a third embodiment will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the same part as each part of the apparatus which concerns on 1st and 2nd embodiment, and duplication description is abbreviate | omitted about the same structure.

(Constitution)
The third embodiment is characterized in that a granular neutron absorbing material (borosilicate glass or boron carbide) is used as a critical suppression member.

First, the principle of this embodiment will be described with reference to FIG.
FIG. 9 shows the sedimentation distance in water (m; v) after 30 minutes of metal oxides of uranium and plutonium, which are typical elements of nuclear fuel materials, and borosilicate glass and boron carbide, which are generally used as neutron absorbers. It is a figure which shows the relationship with the particle size d with respect to x0.5h) . Particle size for sedimentation distance in water d is calculated by equation (1).

Here, d is the particle diameter (m), η is the viscosity count of water at 20 ° C. (Pa · s), v is the sedimentation velocity (m / s), ρ _S is the particle density (kg / m ³ ), ρ _w is the density of water (kg / m ³ ), and g is the acceleration of gravity (m / s ² ).

  From FIG. 9, when the particle size of the granular critical restraining member 9 introduced into the radioactive liquid waste 2 is about three times the particle size of the nuclear fuel material (uranium and plutonium metal oxides: uranium oxide and plutonium oxide), sedimentation occurs. It can be seen that the distances are almost the same. That is, in FIG. 9, the critical restraining member 9 (borosilicate glass, boron carbide) has a settling distance in the range of about 0.01 m to 10 m, and the particle size of the metal oxide (uranium oxide and plutonium oxide) is about 3 times. It is shown that it is doubled. This is because the density of the metal oxides (uranium oxide and plutonium oxide) of the nuclear fuel material is larger than the density of the critical suppression member 9.

  Therefore, the particle size of the granular critical restraining member 9 (borosilicate glass, boron carbide) is about three times that of the sludge made of metal oxide (uranium oxide and plutonium oxide). It becomes possible to mix the critical suppression member 9 substantially uniformly.

FIG. 6 is a schematic view of the sedimentation separation tank 1 according to the third embodiment, in which a charging portion 16 for a granular criticality suppression member 9 is provided in the upper part of the precipitation separation tank 1.
The charging section 16 is filled with a critical deterrent member 9 having a particle size approximately three times as large as the most frequent particle size of uranium oxide and plutonium oxide contained in the radioactive liquid waste 2. Sequentially charged into the tank 1.
In addition, it is desirable to grasp in advance the particle size distribution and particle size frequency of uranium oxide and plutonium oxide contained in the radioactive liquid waste 2 by sampling or the like.

(Function)
In the present embodiment configured as described above, when the radioactive liquid waste 2 is filled in the sedimentation separation tank 1, the granular critical suppression member 9 is sequentially charged from the charging unit 16, but the granular critical suppression member 9 By making the particle size about three times that of uranium oxide and / or plutonium oxide, the criticality suppression member 9 is sludge at the bottom of the precipitation separation tank 1 at a settling rate approximately the same as that of uranium oxide and plutonium oxide in the radioactive waste liquid 2. 3 together. At this time, the granular criticality restraining member 9 is not unevenly distributed above or below the sludge 3, but is deposited in a substantially uniform manner in the sludge 3. Thereby, it is possible to reliably prevent the occurrence of criticality during the precipitation separation process.

  Further, as shown in FIG. 8, the sludge 3 after the precipitation treatment is appropriately discharged into the storage container 22, but also in this case, the granular critical suppression members 9 are mixed in the storage container 22 almost uniformly. The criticality does not occur even in the storage container 22.

(Modification)
In the above embodiment, the granular critical deterrence member 9 having a constant particle size is used as the substantially deterrence member 9, but the particle size distribution of the uranium oxide and the plutonium oxide is 2 or 3 or more depending on the particle size frequency. Different criticality restraining members may be used. For example, if the sludge composed of uranium oxide and plutonium oxide in the radioactive liquid waste 2 has two peaks, as shown in FIG. 7, two types of critical deterrence members 9a and 9b having different particle sizes are provided. The particle size is set to approximately three times the particle size of the corresponding uranium oxide and plutonium oxide.

  If the sludge having a small particle diameter is 3a and the sludge having a large particle diameter is 3b, the sludge 3b having a large particle diameter is deposited below the sludge 3a as shown in FIG. The sludge 3a is mixed with a critical deterrent member 9a having a small particle size of about 3 times the particle size of the sludge 3a, and the sludge 3b has a large particle size of about 3 times the particle size of the sludge 3b. The suppression member 9b is mixed substantially uniformly.

(effect)
According to the third embodiment, when the radioactive liquid waste 2 containing the nuclear fuel material is filled in the sedimentation separation tank 1, the granular criticality suppression member 9 having a predetermined particle diameter is charged from the charging unit 16; The criticality suppression member 9 can be mixed substantially evenly in the sludge 3 deposited on the bottom of the sedimentation separation tank 1. Thereby, since it can prevent reliably that a criticality generate | occur | produces during the process of the radioactive waste liquid 2, the sedimentation-separation process of the radioactive waste liquid 2 can be implemented safely.

  If the particle sizes of uranium oxide and plutonium oxide in the radioactive liquid waste 2 have a plurality of peaks, a plurality of types of critical deterrence members 9a, 9b,. By using-, it is possible to more reliably prevent the occurrence of criticality during the treatment of the radioactive liquid waste 2.

  Further, even when the sludge 3 after the precipitation separation is transferred to the storage container 22, since the granular criticality suppression member 8 is mixed in the sludge 3 almost uniformly, it is ensured that the criticality is generated even at the storage destination. Can be prevented.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. For example, the shape and size of the sedimentation tank 1 and the size, shape and material of the rod-like or granular criticality suppressing member can be appropriately changed according to the volume of the liquid 3 to be treated, the components and the type of the liquid medium. It is. Moreover, you may use together a rod-shaped etc. and granular criticality suppression member.

  These novel embodiments can be implemented in various other forms, and various omissions, combinations, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Sedimentation separation tank, 2 ... Radioactive waste liquid, 3 ... Sludge, 4 ... Supernatant, 5-8 ... Critical suppression member, 9 ... Critical suppression member (granular), 10 ... Guide pipe, 11 ... Drive mechanism, 12 ... Criticality monitor, 13 ... Radiation dose meter, 13 ... Sludge cleaning section, 15a ... Circulation pump, 15b ... Injection nozzle, 16 ... Injection section, 17 ... Power cable, 18 ... Pipe, 20 ... Supply pipe, 21 ... Discharge pipe, 22: Storage container.

Claims (12)

A precipitation separation tank whose lower part is inclined in an inverted conical shape and into which radioactive waste liquid is injected; and a charging unit disposed in the upper part of the precipitation separation tank and charged with a plurality of granular critical suppression members into the precipitation separation tank; Have
The radioactive waste liquid sedimentation apparatus according to claim 1, wherein a sedimentation speed of the granular critical restraining member is equal to a sedimentation speed of a nuclear fuel material contained in the radioactive waste liquid. Precipitation separator for radioactive liquid waste according to claim 1, characterized in that the particle size of critical countering element of the particulate is set according to the particle size distribution of the nuclear fuel substance contained in the radioactive liquid waste.   3. The radioactive waste liquid precipitation separator according to claim 1, wherein a particle size of the granular critical suppression member is approximately three times a particle size of the nuclear fuel material.   The radioactive waste liquid precipitation separator according to any one of claims 1 to 3, wherein the granular critical deterrent member comprises a plurality of types of critical deterrent members having different particle diameters.   The sedimentation separation of radioactive liquid waste according to any one of claims 1 to 4, wherein the sludge accumulated at the bottom of the sedimentation separation tank is transferred to a storage container in a state where the granular criticality suppression members are evenly dispersed. apparatus.   The radioactive waste liquid precipitation separator according to any one of claims 1 to 5, wherein the critical suppression member is made of a neutron absorber.   The radioactive waste liquid precipitation separation apparatus according to any one of claims 1 to 6, wherein the structural material constituting the precipitation separation tank contains a neutron absorbing material.   The radioactive waste liquid precipitation separator according to any one of claims 1 to 7, wherein an inclination angle below the precipitation separation tank is larger than an angle of repose of sludge contained in the radioactive waste liquid.   The radioactive waste liquid precipitation separator according to any one of claims 1 to 8, wherein a plurality of sludge cleaning sections are provided on an inner peripheral surface of the precipitation separation tank.   The apparatus for separating and separating radioactive waste liquid according to claim 9, wherein the sludge washing unit comprises a circulation pump and / or a spray nozzle.   The radioactive waste liquid precipitation separation apparatus according to any one of claims 1 to 10, wherein a criticality monitor and / or a radiation dosimeter is disposed outside the bottom of the precipitation separation tank.   A radioactive waste liquid precipitation separation method, wherein the radioactive waste liquid is precipitated and separated using the radioactive waste liquid precipitation separation apparatus according to claim 1.

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