JP2015225026A - Method for solidifying boric acid containing waste liquid with cement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for solidifying a boric acid containing waste liquid with cement, capable of forming the boric acid containing waste liquid into a stable solidified body having high volume reduction.SOLUTION: The method for solidifying a boric acid containing waste liquid with cement comprises: the preparation step of adding an alkali metal compound having an amount satisfying an alkali metal/boron molar ratio of 0.15-0.35 to a boric acid included in a radioactive boric acid containing waste liquid to the radioactive boric acid containing waste liquid; the drying step of supplying the boric acid containing waste liquid having the alkali metal compound added at the preparation step to a drier to prepare a dried powder; and the mixing step of mixing the dried powder, mixing water and a hydraulic inorganic solidification material while controlling a temperature to 0-45°C to prepare a mixture.

Description

  The present invention relates to a cement solidification method for boric acid-containing waste liquid.

  In a pressurized water nuclear power plant, a lot of boric acid-containing waste liquid used for adjusting the output of a nuclear reactor is generated. Moreover, in a boiling water nuclear power plant, boric acid water that is urgently injected into a nuclear reactor is stored, and boric acid-containing waste liquid is generated.

  The boric acid-containing waste liquid is neutralized with sodium hydroxide or the like and then solidified with cement or asphalt.

  In cement solidification, boric acid interferes with the setting reaction of the cement, which may cause a significant delay in setting and a decrease in strength of the solidified body. Therefore, various proposals such as adding calcium hydroxide as a pretreatment agent to the kneaded mixture of boric acid containing waste liquid and cement from the viewpoint of solidifying the boric acid containing waste liquid while increasing volume reduction have been proposed. Has been made.

  In addition, in order to avoid delay in hardening due to borate and hydrate formation of sodium borate, after adding calcium hydroxide to radioactive boric acid-containing waste liquid to dry powder, compression solidification, solidification with resin, A method of performing cement solidification or the like has been proposed (for example, see Patent Document 1). This method is useful for processing after stabilizing the borate, but it is possible that insoluble waste liquid components may adhere to the inside of pipes and dryers, and these attached waste liquid components are washed. There were inconveniences such as difficulty.

  Also, as a method of solidifying cement after drying radioactive boric acid containing waste liquid into dry powder, boric acid containing waste liquid is dried without pretreatment such as poor solubilization, and sodium aluminate is solidified as a cement solidification accelerator. A method has been proposed in which lithium hydroxide is added to a solidification material as an auxiliary material and cemented by cementation (for example, see Patent Document 2). In this method, the amount of sodium aluminate and lithium hydroxide added increases to about 35% by weight in the solidified material. And since these solidification promotion materials etc. are expensive, there also existed the subject that cost increased.

  In addition, in the conventional method for solidifying a boric acid-containing waste liquid, deterioration of kneadability and false setting may occur during kneading.

JP-A-2-208600 JP 2001-97757 A

  As described above, in the conventional cement solidification treatment method for boric acid-containing waste liquid, there is a demand for improving the work stability, producing a higher volume reduction, and producing a more stable solidified body.

  The present invention has been made in order to solve the above-described problems, and improves the stability of the work, reduces the volume of the boric acid-containing waste liquid, and can produce a stable solidified body. An object of the present invention is to provide a method for solidifying cement.

  One aspect of the method for solidifying a boric acid-containing waste liquid according to the present invention is a method of solidifying a radioactive boric acid-containing waste liquid in a solidification container, the boric acid-containing waste liquid being included in the boric acid-containing waste liquid. Adjustment step of adding an alkali metal compound in an amount such that the alkali metal / boron molar ratio is 0.15 to 0.35 with respect to the boric acid to be added, and the boric acid containing alkali metal compound added in the adjustment step A kneaded product is prepared by supplying a waste liquid to a dryer to prepare a dry powder, and kneading the dry powder, kneaded water, and a hydraulic inorganic solidified material while controlling the temperature at 0 to 45 ° C. And a kneading step.

  According to the cement solidification treatment method of the present invention, it is possible to improve the work stability and reduce the volume of the boric acid-containing waste liquid to produce a stable solidified body.

The flowchart which shows the process of the cement solidification processing method of the boric acid containing waste liquid which concerns on one Embodiment of this invention. The block diagram which shows roughly the cement solidification processing apparatus of the boric acid containing waste liquid used for the cement solidification processing method of the boric acid containing waste liquid which concerns on one Embodiment of this invention. The graph which shows the relationship between the temperature of the kneaded material and a viscosity in an Example and a comparative example.

  FIG. 1 is a flowchart showing the steps of a cement solidification treatment method for boric acid-containing waste liquid according to an embodiment of the present invention, and FIG. 2 shows a cement of boric acid-containing waste liquid used in the cement solidification treatment method of the present embodiment. It is a schematic block diagram which shows a solidification processing apparatus. Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 is a flow chart showing a method for solidifying cement of boric acid-containing waste liquid according to this embodiment. In the cement solidification processing method of the boric acid-containing waste liquid according to the present embodiment, the adjustment step S100 in which the alkali metal compound 2 is added to the boric acid-containing waste liquid 1 in such an amount that the alkali metal / boron molar ratio is 0.15 to 0.35. And drying step S200 for preparing the dry powder 3 by drying the boric acid-containing waste liquid 1 to which the alkali metal compound 2 is added, and kneading the water 4 and the hydraulic inorganic solidified material 5 into the dry powder 3. It has a kneading step S300 for preparing the kneaded product 6.

  FIG. 2 is a block diagram schematically showing the cement solidification treatment apparatus 20 used in the cement solidification treatment method of the present embodiment. The cement solidification processing device 20 includes a boric acid-containing waste liquid tank 21 that contains the boric acid-containing waste liquid 1, and an alkali metal compound supply device 22 that supplies the alkali metal compound 2 to the boric acid-containing waste liquid 1 in the boric acid-containing waste liquid tank 21. And. The alkali metal compound supply device 22 measures the alkali metal compound 2 and supplies it to the boric acid-containing waste liquid tank 21. The cement solidification processing apparatus 20 includes a dryer 23 that prepares the dry powder 3 by drying the boric acid-containing waste liquid 1 to which the alkali metal compound 2 is added, and a kneader 24 connected to the dryer 23. I have. The dry powder 3 prepared by the dryer 23 is supplied to the kneader 24. Further, a kneading water supply device 25 that supplies the kneading water 4 to the kneading machine 24 and a hydraulic inorganic solidifying material supply device 26 that supplies the hydraulic inorganic solidifying material 5 are connected to the kneading machine 24. Reference numeral 27 denotes a solidification container in which the kneaded material 6 is housed and solidified.

(Adjustment step S100)
The object of cement solidification in this embodiment is a radioactive waste liquid containing boric acid (boric acid-containing waste liquid 1). The adjustment step S100 is a step of adding the alkali metal compound 2 to the boric acid-containing waste liquid 1. As a result, the alkali metal compound 2 reacts with boron in the boric acid-containing waste liquid 1 to produce an alkali metal borate salt. As the alkali metal compound 2, for example, an alkali metal hydroxide can be used. Moreover, a sodium compound can be used. Specifically, sodium hydroxide is preferably used as the alkali metal compound 2.

  In the adjustment step S100, the alkali metal compound 2 is added in such an amount that the alkali metal / boron molar ratio is 0.15 to 0.35, preferably 0.2 to 0.3. Thereby, the solubility with respect to the water of an alkali metal borate compound salt can be improved, and washing | cleaning properties, such as piping and a dryer, can be improved.

(Drying step S200)
The drying step S200 of the present embodiment is a step of drying and reducing the volume of the boric acid-containing waste liquid 1 to which the alkali metal compound 2 has been added in order to solidify the boric acid-containing waste liquid 1 in a large volume with a high volume reduction. In the drying step S200, the boric acid-containing waste liquid 1 to which the alkali metal compound 2 has been added is supplied to a dryer, where a drying process is performed to obtain a dry powder 3.

  From the viewpoint of reducing deposits on the piping, etc., the temperature of the boric acid-containing waste liquid 1 after addition of the alkali metal compound 2 is, for example, higher than the precipitation temperature of sodium borate salt when sodium hydroxide is used as the alkali metal compound 2 The boric acid-containing waste liquid 1 is supplied to the dryer 23, preferably adjusted to 60 ° C. or higher, more preferably about 80 ° C. to 90 ° C. or higher. In the dryer 23, the boric acid-containing waste liquid 1 is preferably heated to about 80 ° C. or more, more preferably about 120 to 180 ° C., and particularly preferably about 160 ° C. to perform a drying treatment.

  Although it does not specifically limit as the dryer 23, It is preferable to use a centrifugal thin film dryer. Centrifugal thin film dryers have features such as high thermal efficiency, which can reduce the size of the device, reduce the amount of powder transferred to the gas phase during the drying process, and stabilize the particle size of the resulting sodium borate powder. It is for having.

  Note that, when the volume of the boric acid-containing waste liquid 1 is reduced, a concentration process or a sedimentation process may be performed instead of performing the above-described drying step S200. Thereby, a concentrated waste liquid can be obtained. In the concentration treatment, for example, the boric acid-containing waste liquid 1 is concentrated by heating, and the water content in the boric acid-containing waste liquid 1 is adjusted to about 30% or less by weight. In the sedimentation process, sodium borate is precipitated by adding an additive to the boric acid-containing waste liquid 1. A concentrated waste liquid can be obtained by separating the precipitated sodium borate salt. In this embodiment, the same effect can be obtained regardless of which processing is performed.

(Kneading process S300)
In the kneading step S300, the dry powder 3, the kneaded water 4, and the hydraulic inorganic solidified material 5 are kneaded to obtain the kneaded product 6. At this time, since heat is generated during kneading, the temperature of the kneaded product 6 is controlled to 0 to 45 ° C, preferably 0 to 40 ° C. Moreover, in kneading | mixing process S300, an alkaline aggregate and a high performance water reducing agent are further knead | mixed as needed.

  When the dry powder 3 and the kneaded water 4 are kneaded, a hydrated salt is generated by a hydration reaction. When a hydrate salt is produced, the viscosity of the kneaded product 6 is extremely increased and the kneadability may be deteriorated. Moreover, heat may be generated due to a hydration reaction between the dry powder 3 and the kneaded water 4, and false condensation may occur. According to this embodiment, in kneading | mixing process S300, the production | generation of a hydrate salt and the heat_generation | fever by this can be suppressed by knead | mixing, controlling the temperature of the kneaded material 6 to 45 degrees C or less. Therefore, deterioration of kneadability and false condensation can be suppressed.

  In the kneading step S300, as a method of controlling the temperature of the kneaded product 6, for example, at the laboratory level, the kneading time is adjusted to 45 ° C. or lower by adjusting the kneading time and taking, for example, 10 to 60 minutes or more. A method of kneading while heating can be employed. Moreover, since the calorific value increases in the scale of an actual apparatus, the kneaded material 6 may be cooled to the above temperature or lower by cooling the kneader 24 using a cooling device or the like. This method is industrially advantageous when a large amount of dry powder 3 is subjected to cement solidification treatment. Further, the material kneaded in the kneading step S300, that is, the dry powder 3, the kneaded water 4, the hydraulic inorganic solidified material 5 and the like may be cooled in advance so that the temperature of the kneaded product 6 is 45 ° C. or lower. . In this case, the temperature of the kneaded product 6 can be controlled to 45 ° C. or lower by cooling in advance to −20 ° C. or higher and 20 ° C. or lower, for example. When the kneaded water 4 is cooled in advance, the temperature of the kneaded water 4 is cooled to a temperature at which the kneaded water 4 does not freeze, usually 0 degrees or more.

  In addition, it is preferable that the fluidity (viscosity characteristic) of the kneaded material 6 is obtained over about 1 hour or more from the viewpoint of ensuring the kneading time and the washing time of the kneading machine 24 after kneading with a margin. .

  Although it does not specifically limit as the hydraulic inorganic solidification material 5, It is preferable to use Portland cement. When the boric acid-containing waste liquid 1 is cemented, the calcium in the cement tends to decrease due to the binding of calcium in the cement with boric acid. Therefore, Portland cement having a large amount of calcium in the hydraulic inorganic solidified material 5 can be suitably used. Further, as the hydraulic inorganic solidifying material 5, a mixture of Portland cement and blast furnace slag, a mixture of Portland cement and fly ash, or the like may be used.

  As alkaline aggregate, what grind | pulverized cement hardened | cured material, granular slaked lime, etc. can be used, for example. The particle size of the alkaline aggregate is preferably about 2.5 mm or less, like the fine aggregate used for general cement solidification. From the viewpoint of disposal of radioactive waste in Japan, the leachate of the cement solidified body 8 is preferably alkaline, but by adding alkaline aggregate, the leachate of the cement solidified body 8 is made alkaline, preferably the pH is 12 or more. Can be adjusted.

  The kneading step S300 in the present embodiment preferably includes a primary kneading step S301 and a secondary kneading step S302.

  In this case, in the primary kneading step S301, the dry powder 3 is kneaded in the kneaded water 4 to obtain the primary kneaded product 7. When the dry powder 3 is kneaded into a kneaded mixture of cement and kneaded water as in a normal cement kneading procedure, a hydrated salt is generated, and the kneadability is likely to deteriorate. In this aspect, in the primary kneading step, the dry powder 3 and the kneaded water 4 are kneaded first, so that a hydrated salt can be generated in advance during this time. In the primary kneading step S301, it is preferable to knead the dry powder 3 and the kneaded water 4 for, for example, 10 minutes or longer in consideration of the generation time of the hydrated salt.

  In the secondary kneading step S302, the hydraulic inorganic solidified material 5 is kneaded with the primary kneaded material 7 obtained in the primary kneading step S301 to obtain the kneaded material 6. The alkaline aggregate and the high-performance water reducing agent used as necessary are preferably kneaded in the secondary kneading step S302.

  Note that the order of the primary kneading step S301 and the secondary kneading step S302 is not limited to the above, and the secondary kneading step S302 may be performed first, and then the primary kneading step S301 may be performed. In this case, first, the hydraulic inorganic solidified material 5 is kneaded with the kneaded water 4 in the secondary kneading step S302, and then the dry powder 3 is kneaded in the primary kneading step S301.

  The kneaded material 6 thus obtained is excellent in viscosity characteristics. The kneaded product 6 is charged into the solidification container 27 from the kneader 23 and solidified in the solidification container 27, whereby a cement solidified body 8 having excellent solidification characteristics can be obtained (outdrum mixing method).

  Moreover, you may perform the cement solidification processing method of this embodiment by the in-drum mixing method. That is, the dry powder 3, the kneaded water 4, the hydraulic inorganic solidifying material 5, the alkaline aggregate used as needed, and the high-performance water reducing agent are all kneaded in the solidifying container 27, and the resulting kneaded material 6 is solidified. The container 27 may be solidified as it is. In this case, as a method for cooling the kneaded product 6, a method of cooling the kneaded product 6 by cooling the solidification container 27 can also be adopted. The in-drum mixing method can further reduce equipment costs and operation costs.

  As mentioned above, since the cement solidification processing method of this embodiment can suppress the viscosity increase of the kneaded material 6 and can obtain the kneaded material 6 having a good viscosity characteristic, it is excellent in workability. Furthermore, since calcium is not used, there is no problem of adhesion of waste liquid components to piping or the like.

Example 1
Hereinafter, the result of the cement solidification test of the boric acid-containing waste liquid based on the process shown in FIG. 1 will be described. In this example, dry powder, kneaded water, and ordinary Portland cement (hydraulic inorganic solidified material) kneaded in the following were used that were stored at room temperature (25 ° C.) before use.

  Sodium hydroxide was added to a 12% by weight aqueous solution of boric acid heated to about 60 ° C. to adjust the Na / B molar ratio to 0.25 to obtain an aqueous solution of sodium borate (adjustment step). This sodium borate aqueous solution was used as a simulated waste liquid and quantitatively supplied to a centrifugal thin film dryer set at a heating temperature of about 160 ° C. to obtain a dry powder of sodium borate (drying step).

  Next, 393 g of kneaded water and then 315 g of the dry powder of sodium borate prepared above were put into a 1 L polycup and kneaded for about 60 minutes with a table stirrer (primary kneading step). At this time, heat was generated due to the hydration reaction of the dry powder and the kneaded water, but the primary kneaded product was removed by spending the above time for kneading.

  Next, 750 g of ordinary Portland cement was mixed with the primary kneaded material and kneaded for about 10 minutes to obtain a kneaded material (secondary kneading step). At this time, the kneaded product was removed from heat by spending the above time for kneading. Further, although heat was generated during kneading, the amount of heat generated was less than in the primary kneading step, and the kneading property was good. The temperature of the kneaded product at the end of kneading was 29.8 ° C., and the viscosity was 8.5 dPa · s. Thereafter, the kneaded material was poured into a mold having an inner diameter of 50 mmφ × height of 100 mmH and solidified to obtain a solidified body having good solidification characteristics.

(Example 2)
In the same manner as in Example 1, a dry powder of sodium borate and kneaded water were kneaded for about 60 minutes. In the same manner as in Example 1, ordinary Portland cement was mixed and kneaded for about 10 minutes. The kneadability was good, and the temperature of the kneaded product at the end of kneading was 35.8 ° C. and the viscosity was 8 dPa · s. Thereafter, the kneaded product was solidified in the same manner as in Example 1 to obtain a solidified body having good solidification characteristics.

(Example 3)
In the same manner as in Example 1, a dry powder of sodium borate and kneaded water were kneaded for about 60 minutes. In the same manner as in Example 1, ordinary Portland cement was mixed and kneaded for about 10 minutes. The kneadability was good, and the temperature of the kneaded product at the end of kneading was 34.1 ° C. and the viscosity was 9 dPa · s. Thereafter, the kneaded product was solidified in the same manner as in Example 1 to obtain a solidified body having good solidification characteristics.

(Comparative Example 1)
In the same manner as in Example 1, a dry powder of sodium borate and kneaded water were kneaded for about 15 minutes. When ordinary Portland cement was mixed and kneaded for about 10 minutes in the same manner as in Example 1, the viscosity of the kneaded product increased and the kneadability deteriorated. The temperature of the kneaded product at this time was 49.5 ° C., and the viscosity was 80 dPa · s.

(Comparative Example 2)
In Example 1, it knead | mixed on the conditions similar to Example 1 except having used the dry powder of sodium borate which temperature was previously adjusted to 40 degreeC, and kneading | mixing water. When the dry powder of sodium borate and the kneaded water were kneaded for 60 minutes and then ordinary Portland cement was mixed, the viscosity of the kneaded product was increased, and false coagulation occurred, making it impossible to knead. The temperature of the kneaded material at this time was 67 ° C., and the viscosity increased to 150 dPa · s or more.

  Table 1 shows the temperature of the material (dry powder, kneaded water, ordinary Portland cement) before starting kneading, the temperature and viscosity at the end of kneading, and kneadability in the above Examples and Comparative Examples.

  Moreover, the relationship between the temperature at the end of kneading and the viscosity in Examples and Comparative Examples is shown in the graph of FIG. 3 with the temperature of the kneaded product as the horizontal axis and the viscosity as the vertical axis.

From Table 1, it can be seen that in Examples 1 to 3, the temperature of the kneaded product is controlled to 45 ° C. or lower, and thus the kneaded product at the end of kneading has a viscosity of 50 dPa · s or less and is excellent in viscosity characteristics. Furthermore, in Examples 1 to 3, the occurrence of false condensation has not been confirmed.
On the other hand, in Comparative Examples 1 and 2, it can be seen that in the kneading step (primary kneading step or secondary kneading step), the viscosity of the kneaded product was greatly increased and the kneadability deteriorated. Further, in Comparative Example 2, false condensation occurred.

  Further, FIG. 3 shows that in order to adjust the viscosity of the kneaded product to 50 dPa · s or lower, the concentration of the kneaded product may be cooled to about 43 ° C. or lower.

  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. These novel embodiments can be implemented in various other forms, and various omissions, 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.

  S100 ... Adjustment step, S200 ... Drying step, S300 ... Kneading step, S301 ... Primary kneading step, S302 ... Secondary kneading step, 1 ... Boric acid-containing waste liquid, 2 ... Alkali metal compound, 3 ... Dry powder, 4 ... Kneading Water, 5 ... Hydraulic inorganic solidified material, 6 ... Kneaded product, 7 ... Primary kneaded product, 8 ... Cement solidified body, 17 ... Solidified container, 20 ... Cement solidified treatment device, 21 ... Boric acid-containing waste liquid tank, 22 ... Alkali Metal compound supply device, 23 ... dryer, 24 ... kneading machine, 25 ... kneading water supply device, 26 ... hydraulic inorganic solidified material supply device.

Claims (10)

A method for solidifying radioactive boric acid-containing waste liquid in a solidification container,
An adjusting step of adding an alkali metal compound in an amount such that an alkali metal / boron molar ratio is 0.15 to 0.35 with respect to boric acid contained in the boric acid-containing waste liquid, to the boric acid-containing waste liquid;
A drying step of supplying the boric acid-containing waste liquid to which the alkali metal compound has been added in the adjustment step to a dryer to prepare a dry powder;
A cement solidification treatment of a boric acid-containing waste liquid, comprising: a kneading step of preparing a kneaded product by kneading the dry powder, kneaded water, and a hydraulic inorganic solidified material at a temperature of 0 to 45 ° C. Method. The kneading step includes
A primary kneading step of kneading the dry powder and the kneaded water to prepare a primary kneaded product;
A cement solidification treatment method for a boric acid-containing waste liquid according to claim 1, further comprising a secondary kneading step of kneading a hydraulic inorganic solidified material in the primary kneaded product.   3. The method for solidifying cement of boric acid-containing waste liquid according to claim 1 or 2, wherein the alkali metal compound is a sodium compound.   The method for solidifying a cement of boric acid-containing waste liquid according to any one of claims 1 to 3, wherein the alkali metal compound is an alkali metal hydroxide.   5. The method for solidifying a boric acid-containing waste liquid according to any one of claims 1 to 4, wherein the dryer is a centrifugal thin film dryer.   6. The method for solidifying a boric acid-containing waste liquid according to claim 1, wherein the hydraulic inorganic solidifying material is Portland cement.   The method for solidifying a cement containing boric acid-containing waste liquid according to any one of claims 1 to 6, wherein in the kneading step, the kneaded product is prepared in the solidification container and then solidified.   In the kneading step, the kneaded product is prepared using a kneader, and the kneaded product is charged into the solidification container from the kneader and then solidified. The cement solidification method of the boric acid containing waste liquid as described.   The temperature control of the kneaded material in the kneading step is performed by cooling the dry powder, the kneading water, and the hydraulic inorganic solidified material in advance before the kneading step. 9. The method for solidifying cement of boric acid-containing waste liquid according to any one of 8 above.   10. The cement solidification treatment of boric acid-containing waste liquid according to claim 9, wherein the dry powder, the kneaded water, and the hydraulic inorganic solidified material are cooled to −20 to 20 ° C. in advance before the kneading step. Method.

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