JP2007003270A - Radioactive waste liquid treatment apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance a separation efficiency in operation of separating a radionuclide by controlling the valency of iron in a radioactive waste liquid and then changing iron into iron oxide. <P>SOLUTION: A radioactive waste liquid treatment apparatus comprises a waste liquid tank 1 wherein the pH of the waste liquid is controlled by using a pH conditioner fed from a pH conditioner tank 3 and iron ions contained in the waste liquid are reduced by a reducing agent fed from a reducing agent tank 2 while the liquid is being heated, a conversion tank 5 provided with a temperature control facility 4 wherein the pH of the waste liquid is controlled by using the pH conditioner fed from the pH conditioner tank 3 and iron hydroxide in the reduced radioactive waste liquid fed from the waste liquid tank 1 is converted into iron oxide, a solid-liquid separator 6 for executing the solid-liquid separation of the radioactive waste liquid fed from the conversion tank 5 into a supernatant liquid and residue, a supernatant liquid accepting tank 7 for storing the supernatant liquid fed from the solid-liquid separator 6 and a sludge tank 8 for storing the residue fed from the solid-liquid separator 6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radioactive waste liquid treatment apparatus and a treatment method for treating a radioactive waste liquid.

  In order to recycle waste liquids generated from nuclear power plants, especially ion exchange resins used for the purification of reactor primary system coolant, inorganic acid waste liquids generated by elution operations contain large amounts of metal ions and radioactive materials. Contains nuclides. Among these, the main component contained as metal ions is iron contained as the main constituent element of piping materials, and as radionuclides, cobalt, chromium, nickel or fission products that dominate as corrosion products of piping There are strontium or technetium.

  Waste liquids containing these metal ions and radionuclides are adjusted to neutrality or alkalinity by neutralization, then reduced in volume by operations such as concentration, and stored for a long time. These waste liquids contain a large amount of radionuclide and are characterized by a very high radioactivity level. For this reason, there exists a fault that a shielding structure enlarges.

  For this, a method for rationalizing the shielding structure by separating the radionuclide with a high radioactivity level by performing pretreatment by chemical operation and reducing the dose rate of the separated waste liquid has been proposed. . Among these, as an example of an effective pretreatment method, there is a separation method (crystallization coprecipitation method) by adding iron as a pretreatment and generating a coprecipitate with iron (for example, patent document) 1).

  Here, when the radionuclide is separated by the precipitation of iron, the iron contained in the waste liquid is present as iron hydroxide after the separation. That is, it is considered that most of the iron (ions) contained in the inorganic acid waste liquid is present in a valence of III. In this state, when a normal neutralization treatment is performed, the iron (ion) is in the form of iron hydroxide (III). Since iron hydroxide has high viscosity (poor settling property), solid-liquid separability deteriorates if a certain amount or more of iron (III) hydroxide is present in the waste liquid. For this reason, the time required for the solid-liquid separation work of the waste liquid takes a long time, and the employee may be excessively exposed.

At present, no clear method is defined for the disposal of these waste liquids after long-term storage. However, there is a possibility that this waste liquid and cement are finally kneaded and disposed of in the form of a solidified cement. Also at this time, the iron contained in the waste liquid becomes iron hydroxide, which may cause problems in handling during solid-liquid separation operation or kneading operation.
Japanese Patent No. 3264940

  This invention is made | formed in order to solve the said subject which arises when iron contained in a radioactive waste liquid or these iron can take an iron hydroxide form.

  That is, most of the iron (ions) contained in the inorganic acid waste liquid which is a radioactive waste liquid exists in a valence of III. When this radioactive liquid waste is subjected to a normal neutralization treatment, the iron (ion) is in the form of iron (III) hydroxide. Since this iron hydroxide has a high viscosity (poor settling property), if a certain amount or more of iron (III) hydroxide is present in the waste liquid, the solid-liquid separation property is deteriorated. For this reason, there is a problem that the time required for the solid-liquid separation operation of the waste liquid takes a long time and the employee may be excessively exposed.

  The present invention was made in order to solve the above-mentioned problems. By controlling the valence of iron in the radioactive liquid waste and making it into an iron oxide form, the radioactive liquid waste can improve the separation efficiency during the separation operation. It is an object of the present invention to provide a processing apparatus and a processing method therefor.

  In order to achieve the above object, in the treatment apparatus for radioactive waste liquid of the present invention, a reducing agent tank for storing a reducing agent, a pH adjusting agent tank for storing a pH adjusting agent, and a pH supplied from the pH adjusting agent tank. The pH is adjusted with the adjusting agent, and the waste liquid tank that reduces iron ions contained in the radioactive liquid waste while heating with the reducing agent supplied from the reducing agent tank, and the pH with the pH adjusting agent supplied from the pH adjusting agent tank. A conversion tank that adjusts and converts the iron hydroxide form in the reduced radioactive waste liquid supplied from the waste liquid tank to an iron oxide form, and the converted radioactive waste liquid supplied from the conversion tank and the supernatant liquid A solid-liquid separation device for solid-liquid separation into residues, a supernatant liquid receiving tank for storing a supernatant liquid supplied from the solid-liquid separation device, and a residue supplied from the solid-liquid separation device. It is characterized in that it has a sludge tank for the.

    In order to achieve the above object, in the method for treating radioactive liquid waste according to the present invention, the stored radioactive liquid waste is adjusted with a pH adjuster, and the iron ions contained in the radioactive liquid waste are reduced with a reducing agent while heating. A reduction step, and a conversion step of adjusting the pH of the radioactive liquid waste reduced in the reduction step with a pH adjuster and converting the iron hydroxide form in the radioactive liquid waste to an oxide form, and the conversion step A solid-liquid separation step for solid-liquid separation of the radioactive liquid waste converted in step into a supernatant and a residue, a supernatant liquid storage step for storing the supernatant liquid separated in the solid-liquid separation step, and the solid-liquid separation step And a sludge storage step for storing the residue separated by solid-liquid.

  According to the radioactive waste liquid treatment apparatus and the treatment method of the present invention, the iron valence in the radioactive waste liquid is controlled, that is, after the reduction of the ferric iron to the ferric iron by chemical treatment, the iron oxide form is obtained. Thus, it is possible to improve the separation efficiency when the radionuclide is separated.

  In addition, by controlling the valence of iron in the radioactive liquid waste, it is possible to reduce the load of the cement solidification treatment relating to the radioactive liquid waste carried out after the separation operation by adopting the iron oxide form.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a radioactive liquid waste processing apparatus and a processing method therefor according to the present invention will be described below with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

  FIG. 1 is a configuration diagram showing an outline of a radioactive liquid waste treatment apparatus according to an embodiment of the present invention.

  As shown in the figure, the radioactive waste liquid in the waste liquid tank 1 is reduced to a predetermined amount by supplying chemicals such as a reducing agent and a pH adjusting agent from the reducing agent tank 2 or the pH adjusting agent tank 3, respectively. It is adjusted so that it may become agent concentration and pH.

  At the same time, the waste liquid tank 1 is heated to a predetermined temperature by a heating heater 4 equipped with a temperature controller (not shown) while measuring the temperature with a thermometer 4a. After a predetermined time has elapsed, the radioactive waste liquid in the waste liquid tank 1 is transferred to the conversion tank 5 via the transfer pipe 1a.

  The conversion tank 5 is heated to a predetermined temperature by a heating heater 9 having a temperature controller (not shown) while measuring the temperature with a thermometer 9a. At the same time, the pH is adjusted by introducing the pH adjusting agent from the pH adjusting agent tank 3. By this pH adjustment, iron hydroxide in the radioactive liquid waste is converted to iron oxide.

  The radioactive liquid waste containing iron oxide converted from iron hydroxide is transferred to the solid-liquid separator 6 via the transfer pipe 5a.

  In the solid-liquid separator 6, the radioactive liquid waste is separated into supernatant and sludge. As this solid-liquid separation operation, there is a treatment method by sedimentation, filtration, use of magnetism or the like. The solid-liquid separated supernatant is transferred to the supernatant water receiving tank 7 and stored.

  The sediment deposited in the lower part of the supernatant water receiving tank 7 is transferred to the cement solidifying system 7a and stored for a long time. Further, the sludge mainly composed of iron oxide is transferred to the sludge tank 8 and stored. The sludge stored in the sludge tank 8 is transferred to the cement solidification system 8a and stored for a long time.

  In this embodiment configured as described above, after the valence of iron in the radioactive liquid waste is reduced by chemical treatment to reduce the valence III to valence II or control the ratio of the valence III and valence iron. It can be in the form of iron oxide.

  According to the present embodiment, the iron ions in the radioactive liquid waste are in the form of iron oxide, thereby suppressing the generation of iron hydroxide (III) that adversely affects solid-liquid separation, and separating radionuclides. In this case, the separation efficiency can be improved. Furthermore, it is possible to reduce the load of the cement solidification treatment relating to the radioactive liquid waste performed after the solid-liquid separation operation.

  FIG. 2 is a flowchart showing a procedure of the radioactive liquid waste processing method according to the embodiment of the present invention.

As shown in the figure, the radioactive liquid waste 11 containing iron ions is gently heated 12. Most of the iron ions contained in the radioactive waste liquid 11 before the treatment are present in III valence.

The pH adjustment 13 of the radioactive liquid waste 11 containing iron ions is performed. Furthermore, a chemical agent 14 such as a reducing agent (at least one selected from II-valent iron, sodium thiosulfate, sodium dithionite and sodium sulfide) is added to reduce iron ions to form II-valent iron 15.

  The pH adjuster 16 is further added to the radioactive waste liquid 11 containing the divalent iron 15 after the reduction to make the liquid property neutral or alkaline. Thereafter, the heating process 18 is continued while the iron hydroxide 17 is generated. In this way, morphological conversion to iron oxide 19 is promoted. The produced iron oxide 19 is recovered as a residue 21 after solid-liquid separation. The solution from which iron oxide 19 has been removed is recovered as filtrate 20.

  In the present embodiment configured as described above, the iron valence in the radioactive liquid waste can be converted into iron oxide form after reducing the valence III to valence II by chemical treatment.

According to this embodiment, by making the iron ions in the radioactive liquid waste into the iron oxide form,
It is possible to suppress the generation of iron hydroxide (valence III) that adversely affects the solid-liquid separation and improve the separation efficiency when the radionuclide is separated.

  Here, examples relating to the above-described introduction of the reducing agent will be described below.

  FIG. 3 is a graph showing the iron (III) reduction test result by introducing the reducing agent in FIG.

As a simulation of radioactive liquid waste, 200 mL of an iron chloride (III) (FeCl ₃ ) solution adjusted to 1,000 ppm of Fe (III) and pH 2 was prepared. This was heated to 50 ° C., and sodium thiosulfate (final addition amount 0.045 mol) was added as a reducing agent, and then the change in iron valence over time was measured. As shown in this figure, it can be seen that almost the entire amount of iron is rapidly reduced from III to II.

  FIG. 4 is a table showing the influence of the pH and temperature conditions of FIG. 2 on the iron form in the simulated waste liquid.

The form of iron when pH adjustment (parameter; pH 8, 10, 12) and temperature adjustment (parameter; room temperature, 50 ° C.) were subsequently performed on the simulated waste liquid after the reduction treatment shown in FIG. 3 was confirmed. The form of iron was confirmed by collecting the residue and analyzing by X-ray diffraction. When heated to pH 12, 50 ° C., iron oxide Fe ₃ O ₄ form was confirmed. It has been found that iron ions can exist as iron oxide under the conditions of heating to pH 12 and 50 ° C. In FIG. 5, the residue of this simulated waste liquid was collected and analyzed by X-ray diffraction. As a result of this analysis, an X-ray diffraction peak due to iron oxide is generated, and the state of generation of iron oxide can be confirmed.

  FIG. 6 is a graph showing the influence of the residue in the simulated waste liquid of FIG. 4 on the sedimentation rate.

  100 mL of slurry-like simulated waste liquid was placed in a graduated cylinder, the interface between the sedimentation residue and the supernatant, that is, the scale indicating the height of the sediment was read over time, and the sedimentation rate was calculated therefrom. From this figure, it can be seen that the sedimentation rate obtained with the waste liquid after the chemical treatment is about 3.5 times as compared with the case where it is not performed. This increase in sedimentation rate means an improvement in solid-liquid separation during sedimentation or filtration. From this, it can be seen that the operability of the solution is greatly improved by the treatment with the reducing agent, and the effectiveness of the treatment can be confirmed.

  FIG. 7 is a flow chart showing a process at the time of crystallization coprecipitation by the radioactive liquid waste processing method of another embodiment of the present invention. In this figure, heating is added after adding an excessive amount of iron (II value) to the embodiment of FIG. 2 in advance, and the same or similar parts as in FIG. The duplicated explanation is omitted.

  As shown in the figure, an excess amount of iron (II) 22 is added in advance and then heated, and then a precipitate 21 is generated.

  The radioactive liquid waste treatment of the present embodiment is applied to crystallization coprecipitation treatment and the like. In this flow, iron ions are not hydroxides but black precipitates are generated as oxides. At the same time, other metals contained in the radioactive liquid waste, such as cobalt, chromium, nickel, strontium, technetium, etc., are precipitated accompanying the precipitation residue. The sedimentation property of the precipitate, that is, the filterability can be improved, and at the same time, the radionuclide that causes the high dose rate can be easily separated.

  Moreover, when processing radioactive waste liquid through the nuclide separation process by crystallization coprecipitation, the sludge transferred to the sludge tank 8 shown in FIG. 1 includes other radioactive materials that cause a high dose rate in addition to iron. Contains nuclides such as cobalt-60. For this reason, it is necessary to install shielding equipment in the sludge tank 8 or its pre-stage equipment.

  On the other hand, since the dose rate caused by the solution in the supernatant water receiving tank 7 is sufficiently low, a large shielding facility is unnecessary, and the facility can be rationalized.

  FIG. 8 is a longitudinal sectional view showing a radioactive liquid waste treatment apparatus provided with a shielding body.

  As shown in this figure, sludge tank 61 and cement solidifying device (for L1) 62 are arranged on the first floor as devices that are expected to have a high dose rate among the devices constituting this radioactive liquid waste treatment apparatus. . On the second floor, a filtered water receiving tank 63, an inorganic ion exchange tower 64, a filter 65, a crystallization coprecipitation tower 66, and the like are arranged. Shielding bodies 61a to 66a are provided around the equipment for which this high dose rate is expected. By providing the shielding bodies 61a to 66a, the dose rate around the device can be reduced, and as a result, the work can be made more efficient, such as being accessible by employees for a long time.

  Note that a cement solidifying device (for L2) 67 is arranged on the first floor as a device for which a low dose rate is expected. On the second floor, a treated water receiving tank (A) 68, a treated water receiving tank (B) 69, and the like are arranged. These devices do not require a shield because of the low dose rate.

  FIG. 9 is a flowchart showing a procedure for producing a cement solidified body in the method for treating radioactive liquid waste according to still another embodiment of the present invention. This figure shows a configuration for solidifying the filtrate 20 as the supernatant liquid and the residue 21 as the sludge separated by the treatment of the reducing agent 14 as the medicine in FIG. 2, and is the same as FIG. Alternatively, common parts are denoted by common reference numerals, and redundant description is omitted.

  As shown in this figure, the supernatant liquid (filtrate) 20 after solid-liquid separation is measured in a measuring tank 43. This weighed supernatant 20 is put into a mixer 42 together with cement 41 weighed in an appropriate amount in a powder weighing tank 40. As this cement 41, ordinary Portland cement or blast furnace cement or the like is used. When mixing with the mixer 42, a water reducing agent or the like is added as necessary. The amount of the supernatant liquid to be added is appropriately supplied while being adjusted by a pump (not shown).

  After mixing for a required time by the mixer 42, the metering 44 is performed again, and then the container 45 is transferred and filled. Thereafter, the cement solidified body 46 is formed after the mixture is cured for a predetermined period.

On the other hand, the residue or 21 which is sludge after solid-liquid separation is weighed in a measuring tank 47 after processing. The main component of the residue 21 is iron oxide Fe ₃ O ₄ . The weighed residue 21 is put into the cement mixer 48 together with the kneading water 52. The introduced residue 21 is mixed with kneaded water by a mixer 48 for a certain period of time, and an appropriate amount corresponding to the container is weighed 49 and filled into the container 50. After curing the kneaded material for a predetermined period, a cement solid body 51 is formed.

  In the present embodiment configured as described above, the valence of iron in the radioactive liquid waste can be changed to iron oxide form after reducing the valence III to valence II by chemical treatment.

  According to the present embodiment, the iron ions in the radioactive liquid waste are in the form of iron oxide, thereby suppressing the generation of iron hydroxide (III) that adversely affects the solid-liquid separation, and the solid-liquid separation operation. It is possible to reduce the load of cement solidification processing related to the radioactive waste liquid to be implemented later.

  Further, the present invention is not limited to the above-described embodiments, and the cement solidified body may be changed to a glass solidified body or a glass solidified body, within a range not departing from the gist of the present invention. Various modifications can be made.

The block diagram which shows the outline | summary of the radioactive liquid waste processing apparatus of embodiment of this invention. The flowchart which shows the procedure of the radioactive liquid waste processing method of embodiment of this invention. The graph which shows the iron (III value) reduction | restoration test result by reducing agent addition of FIG. The table | surface which shows the influence which pH of FIG. 2 and temperature conditions have on the iron form in a simulation waste liquid. The characteristic view which shows the result of having collect | recovered the residue of the simulation waste liquid of FIG. 4, and performing the analysis by X-ray diffraction. The graph which shows the influence on the sedimentation rate of the residue in the simulation waste liquid of FIG. The flowchart which shows the process at the time of the crystallization coprecipitation by the radioactive liquid waste processing method of other embodiment of this invention. The longitudinal cross-sectional view which shows the radioactive waste liquid processing apparatus which provided the shielding body. The flowchart which shows the procedure for the cement solidification body preparation of the radioactive waste liquid processing method of further another embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Waste liquid tank, 2 ... Reducing agent tank, 3 ... pH adjuster tank, 4 ... Heating heater, 5 ... Conversion tank, 6 ... Solid-liquid separator, 7 ... Supernatant water receiving tank, 8 ... Sludge tank.

Claims (8)

A reducing agent tank for storing the reducing agent;
a pH adjusting agent tank for storing the pH adjusting agent;
A waste liquid tank that adjusts the pH with a pH adjuster supplied from the pH adjuster tank, and reduces iron ions contained in the radioactive waste liquid with the reducing agent supplied from the reducing agent tank,
A conversion tank that adjusts the pH with a pH adjuster supplied from the pH adjuster tank and converts the iron hydroxide form in the radioactive waste liquid supplied from the waste liquid tank and reduced to an iron oxide form while heating,
A solid-liquid separation device for solid-liquid separation of the radioactive waste liquid supplied and converted from the conversion tank into a supernatant and a residue;
A supernatant receiving tank for storing the supernatant supplied from the solid-liquid separator;
A sludge tank for storing the residue supplied from the solid-liquid separator;
A processing apparatus for radioactive liquid waste, comprising:   2. The apparatus for treating a radioactive liquid waste according to claim 1, wherein the reducing agent is at least one selected from II-valent iron, sodium thiosulfate, sodium dithionite, and sodium sulfide.   2. The radioactive waste liquid treatment apparatus according to claim 1, wherein a shielding body is provided on an outer surface of at least one container selected from the waste liquid tank, the conversion tank, the solid-liquid separator, and the sludge tank.   2. The radioactive waste liquid treatment apparatus according to claim 1, wherein the residue stored in the sludge tank is kneaded with cement and poured into a disposal container to form a cement solidified body.   The processing apparatus for radioactive waste liquid according to claim 4, wherein the supernatant liquid stored in the supernatant liquid receiving tank is concentrated and reduced and used as the kneading water for the cement. A reduction step of adjusting the pH of the stored radioactive liquid waste with a pH adjusting agent, and reducing iron ions contained in the radioactive liquid waste with a reducing agent while heating,
A conversion step of adjusting the pH of the radioactive liquid waste reduced in this reduction step with a pH adjuster and converting the iron hydroxide form in the radioactive liquid waste into an oxide form, and
A solid-liquid separation step for solid-liquid separation of the radioactive liquid waste converted in this conversion step into a supernatant and a residue;
A supernatant liquid storage step for storing the supernatant liquid separated in the solid-liquid separation step;
A sludge storage step for storing the solid-liquid separated residue in the solid-liquid separation step;
A process for treating radioactive liquid waste, comprising:   The method for treating a radioactive liquid waste according to claim 6, wherein the reduction step reduces the iron ions contained in the radioactive liquid waste while controlling the temperature in the liquid waste tank.   The method for treating radioactive liquid waste according to claim 6, wherein the conversion step converts the form of iron hydroxide contained in the radioactive liquid waste into the oxide form while controlling the temperature in the conversion tank.

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