JPH11118990A - Method for treating radioactive liquid waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dissolve a large amount of boron by an evaporation condensation process, suppress the deposition of boric acid salt, and at the same time achieve a high- magnification condensation by increasing the pH of liquid waste in an alkali addition process larger than 12. SOLUTION: After a boric acid liquid waste is supplied to a pH adjustment tank 4, a valve 6 is opened and sodium hydroxide in an alkali storage tank 5 is supplied to the tank 4. In the meantime, an agitator 7 is driven, thus agitating the boric acid liquid waste and NaOH and making uniform the composition. Then, a solution where pH is adjusted to at least 13 is supplied into a total amount condenser 10 by opening a valve 9. After that, the solution is heated at 100 deg.C under the atmosphere by a heater 10a and is subjected to evaporation condensation treatment, thus setting a boron concentration to approximately 150 g/L. More specifically, the amount of the solution is condensed from 3,000 L to approximately 100 L, which is approximately 30 times larger. After the condensed liquid is supplied to a kneading machine 12, a specific amount of ordinary portland cement in a curing material tank 13 is supplied to the kneading machine 12. By setting pH to 13 or more before curing, the curing reaction of cement can be promoted preferentially due to the precipitation reaction caused by boric acid ion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a radioactive liquid waste, and more particularly to a method for treating a radioactive liquid waste suitable for reducing and solidifying a radioactive liquid waste containing boron.

[0002]

2. Description of the Related Art Nuclear power plants generate radioactive waste liquid containing boron mainly in the form of boric acid (hereinafter referred to as boric acid waste liquid as appropriate). For example, for example, PWR
In a (pressurized water reactor), when regenerating an ion exchange resin for purifying reactor water, there is a washing waste liquid after washing with borate ions.

[0003] Such treatment of boric acid waste liquid is usually performed by a cement solidification method using cement as a solidifying material. At this time, it is important to improve the volume reduction by increasing the boron concentration in the boric acid waste liquid in order to reduce the number of solidified bodies as much as possible from the viewpoint of reducing the burden of disposal after solidification. However, when the boron concentration in boric acid waste liquid is increased,
Due to the disturbing action of borate ions, the setting of the cement is delayed during the solidification of the cement, and it has been difficult to obtain a sound cement solid.

Therefore, as a method for solving this problem,
A method has been proposed in which a soluble calcium compound is added to boric acid waste liquid to convert boron into insoluble calcium borate harmless to the hardening reaction of cement. Examples of such known techniques include, for example, JP-B-63-51519 and JP-B-63-51519.
There are JP-A-63-51520 and JP-B-6-31842.

In Japanese Patent Publication No. Sho 63-51519, first, NaOH is added to boric acid waste liquid to adjust the pH to neutral or alkaline (alkali addition step). Thereafter, a soluble calcium compound is added at a predetermined ratio to the boric acid waste liquid whose pH has been adjusted, and the mixture is stirred at a predetermined temperature to generate and precipitate calcium borate to form a paste (calcium addition step). Then, the paste is cooled and held for several hours to form a slurry that can be easily separated (ripening step). Thereafter, the slurry and the other slurry are separated from each other (separation step), and the slurry is evaporated and concentrated to a predetermined concentration at a predetermined pressure to obtain a paste again (evaporation and concentration step). Then, cement is added to the paste to perform a cement solidification process (solidification step).

Japanese Patent Publication No. Sho 63-51520 discloses a method of performing dry powdering by using a centrifugal thin film evaporator or the like in the evaporation and concentration step when performing the same treatment as described above.

[0007] In Japanese Patent Publication No. 6-31842, the amount of NaOH added in the alkali addition step is adjusted to a predetermined amount so that the same alkali addition step and calcium addition step as described above are performed, followed by aging and separation. Without performing the process, the waste liquid containing calcium borate is dried and powdered as it is (powdering step). Then, cement is added to the powder to perform a cement solidification treatment (solidification step).

[0008]

However, the processing method according to the above-mentioned known technique has the following problems.
That is, as a pretreatment for solidifying the waste liquid, a calcium addition step of adding a calcium compound to the waste liquid is indispensable, and the number of steps increases accordingly. In particular,
In JP-A-51519 and JP-B-63-51520, a precipitation step, an aging step, and a separation step are required even after the calcium addition step, and the number of steps is further increased.

In addition, in the step after the calcium addition step and before the solidification step, not the solution but the slurry or the powder is handled, so that a means for preventing clogging of the pipe is required separately. And the processing system becomes very complicated. In addition, in Japanese Patent Publication No. 6-31842, expensive powdering equipment is required, which increases the cost.

An object of the present invention is to provide a method for treating radioactive waste liquid which can perform high volume reduction and sound cement solidification with a simple processing system with a small number of steps for a radioactive waste liquid containing boron. is there.

[0011]

[Means for Solving the Problems]

(1) In order to achieve the above object, the present invention provides an alkali addition step of adding an alkali to a boron-containing radioactive waste liquid to adjust the pH to a predetermined range, and evaporating and concentrating the pH-adjusted waste liquid. In the method for treating a radioactive waste liquid having a step and a solidifying step of mixing the concentrated liquid with a cement-based solidifying material and solidifying, the pH is adjusted to be higher than 12 in the alkali adding step. The hardening reaction of the cement main component in the solidification step of the radioactive waste liquid containing boric acid is 2 (3Ca · SiO ₂ ) + 6H ₂ 0 → 3
Represented by _{CaO · 2SiO 2 · 3H 2 O} + 3Ca (OH) 2. Here, when the boron concentration in the waste liquid is increased, for example, Na ₂ B ₄ O ₇ + Ca ²⁺ → CaB ₄ O ₇ (precipitation) + 2Na ⁺
A precipitation reaction due to borate ions represented by the formula (1) occurs, and Ca to be consumed for cement hardening is consumed for precipitation of borate ions. Therefore, cement hardening is hindered and hardening is delayed. However, in the present invention, by setting the pH of the waste liquid to be higher than 12 in the alkali addition step before curing, the curing reaction of the cement main component can be accelerated in preference to the precipitation reaction by borate ions. Therefore, a sound cement solid can be formed without delay in hardening. The concentration of saturated boron in the waste liquid gradually increases in an alkaline region (pH> 7), but does not increase so much at pH 12 or lower. However, it tends to increase sharply as the pH becomes greater than 12. In the present invention, by setting the pH of the waste liquid to be higher than 12 in the alkali addition step as described above, more boron can be dissolved in the evaporative concentration step, so that high magnification while suppressing the precipitation of borate can be achieved. Can be concentrated. As described above, high volume reduction and sound cement solidification can be performed on the radioactive waste liquid containing boron.

(2) In the above (1), preferably,
As the alkali added in the alkali addition step, at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide is used. That is, calcium as alkali,
If a material containing magnesium, strontium, etc. is used, it becomes the same as the conventional method of adding calcium, and the slurry-like material or powder is handled in the step before the solidification step. Challenges arise. However, by using lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide instead of alkaline earth metals as alkalis, it is possible to eliminate such a possibility and to ensure a processing system. It can be simplified.

(3) In the above (2), more preferably, potassium hydroxide is used as the alkali to be added in the alkali step. Potassium marine products can achieve the largest volume reduction effect by having the highest saturated boron concentration.

(4) In the above (1), preferably, the pH is adjusted to 13 or more in the alkali addition step. The saturated boron concentration in the waste liquid is determined by the pH of the waste liquid.
Is 13 or more, 100 g / L or more than that of 12 or less. The curing time required for curing is 1/100 or less when the pH of the waste liquid is 13 or more than when it is 12 or less. With these, the pH becomes 1 in the alkali addition step.
By adjusting so as to be 3 or more, high volume reduction and sound cement solidification can be performed more reliably.

(5) In the above (4), more preferably, at least one of lithium hydroxide, sodium hydroxide, rubidium hydroxide and cesium hydroxide is used as the alkali added in the alkali adding step. In the evaporative concentration step, the waste liquid is evaporated and concentrated so that the concentration of boron in the concentrated liquid is 150 g / L or less. When using lithium hydroxide, sodium hydroxide, rubidium hydroxide, or cesium hydroxide as the alkali, the saturated boron concentration in the waste liquid becomes about 150 g / L when the pH of the waste liquid is 13, and increases as the pH becomes higher than 13. I do. Therefore, by performing the evaporative concentration of the waste liquid in the evaporative concentration step so that the boron concentration in the concentrated liquid is 150 g / L or less, the precipitation of the borate during the evaporative concentration can be almost surely prevented.

(6) In the above (4), preferably, as the alkali added in the alkali addition step,
Evaporation and concentration of the waste liquid is performed using potassium hydroxide and in the evaporation and concentration step, such that the boron concentration in the concentrated liquid is 200 g / L or less. When potassium hydroxide is used as the alkali, the saturated boron concentration in the waste liquid becomes about 200 g / L when the pH of the waste liquid is 13, and increases as the pH becomes higher than 13. Therefore, by performing the evaporative concentration of the waste liquid in the evaporative concentration step so that the boron concentration in the concentrated liquid is 200 g / L or less, it is possible to almost certainly prevent borate precipitation during the evaporative concentration.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG.

FIG. 1 shows a flow of a processing system for executing the processing method according to the present embodiment. The treatment system shown in FIG. 1 is for treating boric acid waste liquid generated from a radioactive substance handling facility such as a nuclear power plant, and a waste liquid storage tank 1 for storing boric acid waste liquid, and a boron concentration in the waste liquid. , A sampling device 2 for sampling a part of the waste liquid to obtain a pH value, a valve 3 provided at an outlet pipe from the waste liquid storage tank 1, and an aqueous solution containing sodium hydroxide (NaOH) sufficiently concentrated as an alkali for pH adjustment. And a valve 6 provided at the outlet pipe of the alkali storage tank 5, and a boric acid waste liquid from the waste liquid waste storage tank 1 and an alkali from the alkali storage tank 5 , 6 and the pH adjusting tank 4 supplied through the
A pH monitor 8 for detecting the pH value in the inside, a valve 9 provided at an outlet pipe of the pH adjustment tank 4, and a solution in the pH adjustment tank 4 are guided through the valve 9, and heated by a heater 10a to evaporate and concentrate. Concentrator 10 to be performed and this concentrator 1
0, a solidified material tank 13 for storing ordinary Portland cement as solidified material, and a desired amount of cement in the tank 13 provided in the solidified material tank 13 outlet pipe. A kneading machine 12 in which the condensate in the concentrator 10 is guided through the valve 11 and the cement from the solidified material tank 13 is guided through the knitting machine 14;
Stirrer 15 provided inside to stir the concentrate and the cement
And a valve 16 provided at an outlet pipe of the kneader 12.

The treatment method according to the present embodiment is carried out in a system having the above-described configuration. The procedure is roughly described as shown in FIG. An alkali addition step 101 for adjusting the pH to 13 or more; an evaporative concentration step 102 for evaporating and concentrating the waste liquid whose pH has been adjusted; and a solidification step 103 for mixing the concentrated liquid with a cement-based solidifying material for solidification treatment. have. Hereinafter, these steps will be described in detail.

(1) Alkali Addition Step In this step, first, a part of the boric acid waste liquid stored in the waste liquid storage tank 1 is extracted by the sampling device 2 and analyzed to determine the boron concentration and the pH. Then, the amount of boric acid waste liquid to be supplied to the pH adjustment tank 4 is determined according to the obtained boron concentration. The determination at this time is determined based on the relationship between the concentration of saturated boron that can be dissolved in the boric acid waste liquid and the pH value of the boric acid waste liquid as shown in FIG. FIG. 3 shows that the inventors of the present invention have previously made potassium hydroxide (K
OH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), cesium hydroxide (CsOH) and rubidium hydroxide (RbOH) were used, and the relationship between the saturated boron concentration and the pH value of the boric acid waste liquid was examined. It is a figure showing the experiment result. As shown in FIG. 3, the saturated boron concentration gradually increases in the alkaline region (pH> 7), but does not increase so much at pH 12 or lower. But pH
Exceeds 12, the saturated boron concentration sharply increases,
Is 13 or more, each alkali becomes 100 g / L or more larger than the case where the pH is 12 or less. That is, when sodium hydroxide (NaOH), lithium hydroxide (LiOH), cesium hydroxide (CsOH), or rubidium hydroxide (RbOH) is used as the alkali, the saturated boron concentration at a pH of 13 is about 150 g / L. And, in particular,
When potassium hydroxide (KOH) is used as the alkali, the saturated boron concentration at a pH of 13 is about 200 g.
/ L or more. Here, in this embodiment, NaOH is used as the alkali, and the concentration is performed until the pH becomes 13 as described later. However, since the saturated boron concentration at pH = 13 is about 150 g / L from FIG. Concentrate to this value. That is, when the boron concentration in the boric acid waste liquid in the tank 1 is, for example, 5 g / L, about 1 g
It will be concentrated about 30 times until it becomes 50 g / L. Therefore, in this case, assuming that the concentrated liquid to be finally mixed with the cement in the kneader 12 is 100 L, the amount of waste liquid to be supplied from the waste liquid storage tank 1 to the pH adjustment tank 4 is 100 L × 30 = 3000 L. , And manually operate the valve 3 to remove 3000 L of waste liquid into the PH adjustment tank 4.
To supply. Note that p detected by the sampling device 2
The H value is used for reference during manual operation of the valve 6 during alkali supply described later.

After the boric acid waste liquid is supplied to the pH adjusting tank 4 in this manner, the valve 6 is gradually opened manually to gradually supply sodium hydroxide in the alkaline storage tank 5 to the pH adjusting tank 4. During this time, the stirrer 7 is driven to stir the boric acid waste liquid and NaOH so that the composition in the solution in the tank 4 becomes uniform. Also, at this time, the pH of the solution
Is constantly measured by the pH monitor 8, and the valve 6 is opened to continuously supply NaOH until the pH becomes 13 or more. When the pH reaches a predetermined value of 13 or more, the valve 6 is closed and the NaOH is supplied.
Stop supplying.

(2) Evaporation and Concentration Step In this step, first, the solution whose pH has been adjusted to 13 or more in the above (1) is supplied into the concentrator 10 by opening the valve 9. Then, at atmospheric pressure, 1
The mixture is heated to 00 ° C. and subjected to an evaporative concentration treatment to adjust the boron concentration to about 150 g / L. In the previous example, the amount of solution was 30
Concentrate about 30-fold from 00L to about 100L.

(3) Solidification Step In this step, first, in the above (2), when the boron concentration is about 15
The solution concentrated to 0 g / L is supplied into the kneader 12 by manually opening the valve 11. At this time,
The concentrated solution may be supplied after cooling to room temperature, or may be in a high temperature state after concentration. This is because the higher the temperature, the more the solubility of the borate increases, so that precipitation hardly occurs and the hardening reaction of the cement is accelerated. However, in the case where the concentrated solution is boiling, the cement may be quickly set up on the contrary. Therefore, in this sense, the temperature is preferably at least 80 ° C. or less.

After supplying the concentrated solution to the kneader 12, a predetermined amount (for example, 180 kg) of the ordinary Portland cement in the solidifying material tank 13 is supplied to the kneader 12 via the quantitative transfer device 14. At this time, kneading water for replenishment may be supplied into the kneader 12 as needed. Then, the concentrated solution and the cement supplied into the kneader 12 are mixed with the stirrer 15.
After mixing to prepare a good paste, the mixture is filled into a solidification container 17 via a valve 16.

Next, the operation of the processing method according to the present embodiment represented by the steps (1) to (3) will be described below. (A) Prevention action of curing delay It is known that the curing reaction of the main component of cement in the solidification step of the radioactive waste liquid containing boric acid is represented by the following formula.

2 (3Ca · SiO ₂ ) + 6H ₂ 0 → 3CaO · 2SiO ₂ · 3H ₂ O + 3Ca (OH) ₂ (Equation 1) Here, when the boron concentration in the waste liquid is increased, for example, Na ₂ B ₄ O ₇ + Ca ²⁺ → CaB ₄ O ₇ (precipitated) + 2Na ⁺ ... (2) A precipitation reaction occurs due to borate ions, and Ca to be consumed for cement hardening is consumed for borate ion precipitation. Therefore, the hardening of the cement is hindered and the hardening is delayed. Here, in the present embodiment, a sound cement solidified body can be formed without such a hardening delay. This will be described with reference to FIG. FIG.
Fig. 3 shows the results of a hardening experiment performed by the present inventors in order to examine the relationship between the pH of boric acid waste liquid and the hardening time of cement. As shown in FIG. 4, the pH of the boric acid waste liquid is
Is not more than 12 and not less than 13, there is a remarkable difference in the time until curing. More specifically, the curing time in the latter case is 1/100 or less of the curing time in the former case, and the cement reaction represented by the formula 1 is more effective than the precipitation reaction by borate ion represented by the formula 2. It can be seen that the curing reaction of the component is preferentially accelerated. Also, regarding the hardness after curing, when the pH of the boric acid waste liquid is set to 12 or less, it hardens only to the extent that free water disappears even if left for a long time, whereas when the pH is set to 13 or more. For example, it was found that a strength of 150 kg / cm ² or more can be obtained after one day. In the present embodiment, the pH of the waste liquid is set to 1 in the alkali addition step before curing.
By setting the ratio to 3 or more, the hardening reaction of the cement main component can be promoted preferentially over the precipitation reaction by borate ions, so that a sound cement solid can be formed without delay of hardening. . (B) High Volume Reduction Action, etc. As described above with reference to FIG. 3, the saturated boron concentration in the boric acid waste liquid becomes 100 g / L or more when the pH is 13 or more than when the pH is 12 or less. . In the present embodiment, the pH of the waste liquid is increased to more than 13 by adding NaOH in the alkali addition step, and the saturated element concentration is reduced to about 15
The concentration is increased to 0 g / L, and boron is dissolved in the evaporative concentration step up to the saturated element concentration of about 150 g / L.
This makes it possible to concentrate at a high magnification while almost certainly preventing the precipitation of borate, so that the volume at a high magnification can be reduced. In addition, since the concentrated solution does not include precipitates such as slurry and does not cause precipitation of solids such as borate and the like, it is possible to greatly reduce the occurrence of problems such as scale adhesion to the concentrator 10 in the evaporative concentration step. In addition, during the kneading in the solidification step, the kneading load is small and mixing can be performed quickly and uniformly.

As described above, according to the present embodiment, high volume and sound solidification of the boric acid waste liquid can be performed. In order to confirm this effect, the inventors of the present application concentrated a boric acid waste liquid having a pH of 8 and a boron concentration of 5 g / L from 3000 L to 100 L by 30 times, kneaded it with 180 kg of Portland cement, and solidified. No precipitate is formed in the waste liquid even at the time of concentration and cooling to room temperature, and the solidified substance is 150 kg / c after one day.
It was confirmed that a sufficient strength of m ² was obtained. Further, according to the present embodiment, at this time, the conventional calcium addition step is not required, so that the number of steps can be reduced. Further, at this time, since the slurry-like material and the powder are not handled as in the related art, and all of them can be kept in a solution state before the solidification step, the processing system can be simplified.

In the first embodiment, the pH of the boric acid waste liquid is adjusted to be 13 or more in the alkali addition step, but may be adjusted to be at least larger than 12. This is for the following two reasons. In FIG. 4, as described above, when the pH of the boric acid waste liquid is set to 12 or less, a curing time 100 times or more is required as compared with the case where the pH is set to 13 or more.
As shown in the figure, when the pH exceeds 12, the curing time is sharply shortened. For example, when the pH is 12.5, the curing time is about 1/10 as compared with the case where the pH is 12. On the other hand, when the pH is 12 or less, the curing time does not change much. For example, the difference in curing time between the case where the pH is 11.5 and the case where the pH is 12 is 1.2 times or less. Therefore, if the pH is at least higher than 12, the pH becomes 1
The curing time can be greatly reduced as compared with the case of 2 or less, and a sound solidified body can be produced. In FIG. 3, as described above, when the pH of the boric acid waste liquid is 13 or more, the saturated boron concentration becomes 100 g / L or more as compared with the case where the pH is 12 or less. As described above, when the pH exceeds 12, the saturated boron concentration increases sharply, for example, when the pH is 12.
At 5 the saturated boron concentration is 50 compared to when the pH is 12.
g / L or more. On the other hand, when the pH is 12 or less, the saturated boron concentration does not change so much. For example, the difference in the saturated boron concentration between the case where the pH is 7 and the case where the pH is 12 is about 20 g / L, and the largest KOH But 60
g / L. Therefore, at least pH 12
If it is larger, the concentration of saturated boron can be increased more than when the pH is 12 or less, and precipitation during solidification can be suppressed.

In the first embodiment, in the alkali addition step, the waste liquid in the waste liquid storage tank 1 is sampled by the sampling device 2 to detect the boron concentration and the pH in the waste liquid. The present invention is not limited to this. For example, the waste liquid may be sampled in the pH adjustment tank 4. Further, NaOH as an alkali is stored in the form of an aqueous solution in the alkali storage tank 5, but may be added in the form of a tablet, powder, slurry or the like. Further, at this time, NaOH was gradually added while measuring the pH of the waste liquid with the pH monitor 8, but the present invention is not limited to this. A predetermined amount may be added. The alkali to be added is not limited to sodium hydroxide, but may be lithium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, or a mixture of two or more thereof. In these cases, a similar effect is obtained (for the case where potassium hydroxide is used, see the second embodiment described later). In this case, even with the same alkaline earth metal, if an alkali containing calcium, magnesium, strontium, or the like is used, it becomes the same as the conventional method of adding calcium, and the slurry or powder is handled in the step before the solidification step. Therefore, a similar problem that the processing system becomes complicated occurs. Therefore,
By using lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide instead of them, such a possibility can be eliminated and the treatment system can be reliably simplified.

Further, in the first embodiment, in the evaporative concentration step, the evaporative concentration is performed by heating to 100 ° C. under the atmospheric pressure. However, the present invention is not limited to this, and may be performed under reduced pressure. In this case, it goes without saying that evaporation and concentration can be sufficiently performed even at a temperature lower than 100 ° C. (see a third embodiment described later).

Further, in the first embodiment,
In the solidification step, ordinary Portland cement was used as a solidification material, but is not limited to this. That is, blast furnace cement, silica cement, fly ash cement,
Any commonly used cement solidifying material such as alumina cement can be used, and in these cases, the same effect is obtained.

A second embodiment of the present invention will be described with reference to FIG. This embodiment combines the functions of the pH adjustment tank 4 and the condenser 10 in the processing system of the first embodiment shown in FIG. 1 and uses potassium hydroxide (KOH) as the alkali stored in the alkali storage tank 5. This is an embodiment in the case of using ()).

FIG. 5 is a flow chart of a processing system for executing the processing method according to the present embodiment. The same members as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In FIG.
In this processing system, the pH adjustment tank 4 and the condenser 10 in FIG. 1 are replaced with a condenser 210 having a pH adjustment function having both functions. That is, in the alkali addition step, after the boric acid waste liquid in the waste liquid storage tank 1 is supplied to the condenser 210 with a pH adjusting function via the valve 3, the potassium hydroxide in the alkali storage tank 5 is adjusted through the valve 6 to the pH adjusting function. To the condenser 210 until the pH becomes 13 or more. Other system configurations and operations are almost the same as those in FIG.

According to this embodiment, similarly to the first embodiment, a high-volume and sound cement solidification can be performed on boric acid waste liquid. Further, since potassium hydroxide having the highest saturated boron concentration (see FIG. 3) is used as the alkali, the greatest volume reduction effect can be obtained. In order to confirm these effects, the inventors of the present application prepared a boric acid waste solution having a pH of 8 and a boron concentration of 5 g / L from 4000 L to 1 L.
Concentrate 40 fold to 00L and mix this with Portland cement 1
When kneaded with 80 kg and solidified, it was confirmed that no precipitate was formed in the waste liquid even at the time of evaporative concentration and cooling to room temperature, and that the solidified body had a sufficient strength of 150 kg / cm ² after one day. did. Further, according to the present embodiment, one tank is used.
As a result, the system can be further simplified.

A third embodiment of the present invention will be described with reference to FIG. This embodiment is a case where, in the processing system of the second embodiment shown in FIG. 5, the functions of the condenser 210 with the pH adjustment function and the kneader 12 are combined and the evaporation and concentration are performed under reduced pressure lower than the atmospheric pressure. FIG.

FIG. 6 is a flow chart of a processing system for executing the processing method according to the present embodiment. 1 and 5 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 6, the processing system includes a condenser 210 having a pH adjustment function and a kneader 12 shown in FIG.
The kneading machine 312 with H adjustment / condensing function is replaced.
Note that sodium hydroxide is used as the alkali as in the first embodiment. That is, in the alkali addition step, after supplying the boric acid waste liquid in the waste liquid storage tank 1 through the valve 3 to the kneading machine 312 with the pH adjusting / condensing function, the sodium hydroxide in the alkali storage tank 5 is discharged through the valve 6. pH 1 in kneader 312 with pH adjustment / condensing function
Supply until 3 or more. In the evaporative concentration step, the pressure in the kneader 312 is reduced to a predetermined pressure lower than the atmospheric pressure by a pressure reducing means (not shown), and the kneader 31
Heating to a predetermined temperature lower than 100 ° C. (for example, 80 ° C.) by the heater 312a attached to the heating unit 2 to perform the evaporative concentration treatment, and the boron concentration is set to about 150 g / L. Thereafter, in the solidification step, a predetermined amount of the ordinary Portland cement in the solidified material tank 13 (for example, 1
(80 kg) into the kneader 312 and mixed by the stirrer 15. Other system configurations and operations are almost the same as those in FIG.

According to this embodiment, similarly to the first and second embodiments, high volume reduction and sound solidification of boric acid waste liquid can be performed. In order to confirm these effects, the inventors of the present invention set the pH at 8 and the boron concentration at 5%.
g / L boric acid waste liquid was heated to 80 ° C. and concentrated 30 times from 3000 L to 100 L, kneaded with 180 kg of Portland cement and solidified, and precipitated in the waste liquid during evaporation and concentration and cooling to room temperature. No product was produced, and it was confirmed that the solidified material had a sufficient strength of 150 kg / cm ² after one day. Further, according to the present embodiment, the number of tanks can be reduced by one more than in the second embodiment, so that the system can be further simplified. Furthermore, since evaporation and concentration are performed under reduced pressure, evaporation can be performed at a temperature lower than 100 ° C., and there is also an effect that less electric energy is required for heating.

In the first to third embodiments, all valves are manually operated. However, it goes without saying that at least a part of the valves may be operated by automatic control. For example, the opening degree of the valve 6 may be automatically controlled according to the detection result from the pH monitor 8 and the valve 6 may be closed just when the pH becomes 13. In such a case, a similar effect is obtained.

[0039]

According to the present invention, high volume and sound solidification of a radioactive waste liquid containing boron can be performed. Also, at this time, the number of steps can be reduced because the calcium addition step as in the related art becomes unnecessary. Further, since the slurry-like material and the powder are not handled and all of them can be kept in a solution state before the solidification step, the processing system can be simplified.

[Brief description of the drawings]

FIG. 1 is a flowchart of a processing system that executes a processing method according to a first embodiment of the present invention.

FIG. 2 is a diagram schematically showing a procedure for performing a processing method.

FIG. 3 is a diagram showing an experimental result of examining a relationship between a saturated boron concentration and a pH value of a boric acid waste liquid.

FIG. 4 is a diagram showing the results of a hardening experiment performed to examine the relationship between the pH of boric acid waste liquid and the hardening time of cement.

FIG. 5 is a flowchart of a processing system that executes a processing method according to a second embodiment of the present invention.

FIG. 6 is a flowchart of a processing system that performs a processing method according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Waste liquid storage tank 4 pH adjustment tank 5 Alkaline storage tank 8 pH monitor 9 Valve 10 Concentrator 12 Kneader 13 Solidification material tank 101 Alkali addition process 102 Evaporation concentration process 103 Solidification process 210 Condenser with pH adjustment function 312 pH adjustment / condensation Kneading machine with function

Continued on the front page (72) Inventor: Shoichi Matsuda 3-1-1, Sakaimachi, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Plant

Claims (6)

[Claims] 1. An alkali addition step of adding an alkali to a boron-containing radioactive waste liquid to adjust the pH to a predetermined range, an evaporative concentration step of evaporating and concentrating the pH-adjusted waste liquid,
A solidifying step of mixing the concentrated liquid with a cement-based solidifying material and performing a solidifying treatment, wherein the alkali adding step adjusts the pH to be greater than 12. How to treat radioactive liquid waste. 2. The method for treating a radioactive waste liquid according to claim 1, wherein the alkali added in the alkali addition step is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide. A method for treating a radioactive liquid waste, comprising using at least one of them. 3. The method for treating a radioactive waste liquid according to claim 2, wherein potassium hydroxide is used as an alkali to be added in said alkali step. 4. The method for treating a radioactive liquid waste according to claim 1, wherein the pH is adjusted to 13 or more in the alkali addition step. 5. The method for treating a radioactive waste liquid according to claim 4, wherein at least one of lithium hydroxide, sodium hydroxide, rubidium hydroxide, and cesium hydroxide is used as the alkali added in the alkali adding step. A method for treating radioactive waste liquid, wherein the waste liquid is evaporated and concentrated so that the concentration of boron in the concentrated liquid is 150 g / L or less in the evaporation and concentration step. 6. The method for treating a radioactive waste liquid according to claim 4, wherein potassium hydroxide is used as an alkali to be added in said alkali adding step, and a boron concentration in the concentrated liquid is 200 g / A method for treating a radioactive waste liquid, comprising evaporating and concentrating the waste liquid so as to be L or less.