JP3058952B2 - Method of treating boric acid-containing liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nuclear power plant (PW).
R) and a method for treating a boric acid-containing liquid such as spent fuel pit water.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional technique for treating a boric acid-containing liquid using a reverse osmosis membrane (R / O membrane). In this method, a boric acid-containing liquid is supplied to a reverse osmosis membrane module (hereinafter referred to as an R / O membrane module) (15)
Before the treatment, the solid content in the boric acid-containing liquid is removed by performing a pretreatment with a filter in order to prevent clogging of the membrane of the R / O membrane module. This pretreatment removes large solids in the boric acid-containing liquid by the cartridge filter (11), and then by the ultrafiltration filter liquid supply pump (12).
At a pressure of several kg / cm ² , water is passed through an ultrafiltration filter module (hereinafter, referred to as a UF module) (13), and small solids are removed by filtration with the UF module (13). The primary side of the UF module (13) becomes a concentrated waste liquid containing a large amount of solids, and flows to the radioactive waste treatment system.

[0003] The boric acid-containing solution is pressurized to several tens of kg / cm ² by a reverse osmosis membrane module feed pump (14).
Reverse osmosis is applied to the primary side of the R / O membrane of the / O membrane module (15). Due to the pressure on the primary side of the R / O membrane of the R / O membrane module (15), the water in the boric acid-containing liquid has an effect of reverse osmotic pressure, and permeates through the R / O membrane and moves to the secondary side. silica,
Impurities such as chloride ions and organic substances do not penetrate much due to their large molecular size, remain on the primary side, and proceed to the radioactive waste treatment system. The boric acid content in the boric acid-containing liquid has a characteristic of transmitting to the secondary side by appropriately setting the type of the R / O film and the operating conditions of the R / O film module (15). Therefore, the permeate that has passed through the membrane of the R / O membrane module (15) becomes an aqueous solution containing boric acid from which impurities have been removed to some extent. That is, boric acid in the boric acid-containing liquid supplied to the R / O film module (15) permeates to the secondary side of the R / O film,
Collected as boric acid solution. On the other hand, the R / O membrane module (1
The liquid remaining on the primary side of the R / O film in 5) has a high impurity concentration such as silica and chloride ions, and flows into the radioactive waste treatment system as a high impurity concentration waste liquid.

[0004]

SUMMARY OF THE INVENTION In the present invention, a boric acid-containing solution is treated using an R / O film. When performing processing of a boric acid-containing liquid, the problem to establish a system that takes into consideration the solidification device is that while increasing the recovery rate of boric acid in the boric acid-containing liquid, the removal rate of impurities represented by silica is reduced. It is to improve it and to reduce the volume of waste liquid.

The method shown in FIG. 3 is a processing method using one stage of an R / O membrane module.
Determined by the performance of the R / O membrane used in the membrane module, the silica concentration cannot be reduced below the reference value for reactor water reuse in the current situation. In addition, the volume of waste liquid cannot be reduced.

Accordingly, an object of the present invention is to provide a nuclear power plant
Reduce the impurity content of liquid waste and liquid containing boric acid such as spent fuel pit water in the PWR to below the standard value for reactor water reuse by simple treatment, and reduce the volume of waste. It is to plan.

[0007]

FIG. 1 shows a method of the present invention in which a plurality of RO modules are used in combination to continuously process a boric acid-containing liquid. The first-stage R / O membrane module (4), the second-stage R / O membrane module (5), and the third-stage R / O membrane module (4) having different separation rates for components in the boric acid-containing liquid, for example, boric acid, silica, and chlorine. The R / O membrane module (6) is connected in a cascade and collected as a permeate to the secondary side of the first-stage R / O membrane module (4), and the second-stage R / O membrane module is recovered. The permeate to the secondary side of (5) and the permeate of the third stage R / O membrane module (6) are recycled to the untreated boric acid-containing solution, and the third stage R / O membrane module (6) is recycled. By recovering the liquid remaining on the primary side as a concentrated waste liquid, silica and boric acid containing a small amount of chlorine are recovered as a permeated recovery liquid, and the volume of the concentrated waste liquid is reduced.

[0008]

The boric acid-containing liquid I is first stored in the R / O membrane circulating liquid tank (1) as shown in FIG.
Membrane module (5) and third stage R / O membrane module (6)
And then pressurized by the R / O membrane high pressure supply pump (2), then the UF module
It is sent to (3), where the solid content in the processing waste liquid is removed.

Next, the processing solution is sent to the first stage R / O membrane module (4), and the permeated recovery solution II that has permeated the R / O membrane to the secondary side and the first stage R / O membrane module (4). The concentrated waste liquid remaining on the primary side of the membrane module is separated, and the concentrated waste liquid
It is sent to the O membrane module (5).

The concentrated waste liquid concentrated in the first stage R / O membrane module is combined with the permeate reprocessing solution permeated to the secondary side by the second stage R / O membrane module (5). Separated into concentrated waste liquid remaining on the primary side of the R / O membrane module,
The permeate reprocessing liquid is recycled to the R / O membrane circulating liquid tank (1), and the concentrated waste liquid of the second-stage R / O membrane module is recycled to the third
It is sent to the R / O membrane module (6) of the stage.

The concentrated waste liquid of the second-stage R / O membrane module (5) is removed by the third-stage R / O membrane module (6).
The permeated reprocessing liquid and the concentrated waste liquid that have permeated to the secondary side are separated, the permeated reprocessing liquid is recycled to the R / O membrane circulating liquid tank (1), and the concentrated waste liquid is sent to the solidification device as the concentrated waste liquid III.

The third stage R / O film module (6)
A pressure regulating valve is provided on the concentrated waste liquid side of R / O.
The pressure on the primary side of the R / O membrane module at each stage can be set to about 15 to 60 kg / cm ² by the membrane high-pressure supply pump (2). Further, the pressure loss at the time of R / O membrane module (5) passing water, on the order of about 1 kg / cm ^2, much smaller than the hydraulic force 15~60kg / cm ² approximately by the high-pressure pump, the first stage, respectively R / O membrane module
(4), second stage R / O membrane module (5), third stage R
The primary pressure of the R / O membrane of the / O membrane module (6) hardly decreases, the same reverse osmosis pressure can be secured, and the performance does not decrease.

In the method of the present invention, the operation of the R / O membrane module is performed by setting the supply liquid flow rate / concentration flow rate ratio to about 1 to 6.
Oxygen is easily transmitted through the O film module, and the performance of removing impurities is deteriorated. Therefore, the first stage R / O membrane module
The ratio of the supply flow rate / concentration flow rate in (4) is made relatively small, and impurities, ie, silica, chloride ions, etc., are removed with high efficiency in the first stage R / O membrane module (4). Next, a second stage R / O membrane module (5) and a third stage R / O membrane module (6) are provided, and impurities are supplied to the secondary side at a relatively high supply flow rate / concentration flow rate ratio. By performing a concentration operation for selectively permeating water and boric acid without permeating, the final concentrated waste liquid amount can be reduced.

For example, the first stage R / O film module
The feed liquid flow rate / concentration flow rate ratio of (4) is about 1 to 2, and the feed liquid flow rate / concentration flow rate of the second stage R / O membrane module (5) is 5 to 5.
If the ratio of the supply flow rate / concentration flow rate of the third stage R / O membrane module (6) is about 5 to about 6, the first stage R / O
Assuming that the amount of waste liquid supplied to the membrane module (1) is about 100,
First stage R / O membrane module (4), second stage R / O
The membrane module (5), the third stage R / O membrane module (6), the concentrated waste liquid side liquid amount after the water passing treatment is about 1 to 4,
The R / O membrane module (5) in the third stage and the R / O membrane module (6) in the third stage have a small amount of permeate, about 1/100
The volume of waste is reduced by about 1/25.

Therefore, the pressure on the primary side of the R / O membrane module is increased by the pressure regulating valve (8) to 27-30
This can be achieved by setting the pressure to about kg / cm ² (the secondary system is at atmospheric pressure or a back pressure of several kg / cm ² ). Also,
The flow rate of each R / O membrane module (4), (5), (6) is
The processing flow rate per unit area (R / O
Since the membrane permeation flow rate / concentration flow rate) is clear, each R
It depends on the area of the / O film.

In the method of the present invention, the second stage R / O
Membrane module (5) Permeate, third stage R / O membrane module (6) First stage R / O membrane module (4) by returning permeate to circulating fluid tank and recirculating Since the impurity concentration in the supply liquid is lower than the concentration of the processing waste liquid, the impurity concentration in the first-stage R / O membrane module (4) permeation recovery liquid can be further reduced.

Further, the second stage R / O film module (5)
The permeated liquid, the third-stage R / O membrane module (6) The permeated liquid is returned to the circulating liquid tank, and is recycled so that boric acid in the supply liquid of the first-stage R / O membrane module (4) can be obtained. Since the concentration is higher than the concentration of the processing waste liquid, the concentration of boric acid in the permeation / recovery liquid of the first-stage R / O membrane module (4) can be further increased.

The first-stage R / O film module (4), the second-stage R / O film module (5), and the third-stage R / O film module (6) as described above. In the method of the present invention using an apparatus in which cascades are connected, the first-stage R / O membrane module (4) has a supply flow rate / concentration flow rate ratio of 1 to 2 and, for example, chloride ion, silica or the like. It is preferable to use an R / O film made of a material having a high impurity removal rate. Further, as the material of the R / O films of the second-stage R / O film module (5) and the third-stage R / O film module (6), impurities do not permeate to the secondary side. It is preferable to use a material having a high supply flow rate / concentration flow rate ratio.

[0019]

FIG. 2 shows an embodiment of the present invention. In the present embodiment, the R / O film of the first stage R / O film module (4) has a supply flow rate / concentration flow rate ratio of 1 to 2 and a high impurity removal rate obtained by SC-Toray. 8100 and the second
For the R / O membrane of the R / O membrane module (5) of the third stage and the R / O membrane module (6) of the third stage, Toray SC-1100 which can obtain a high supply flow rate / concentration flow rate ratio is used. did. The liquid pressure was set to about 30 kg / cm ² by controlling the R / O membrane high-pressure supply pump (2) and the pressure regulating valve (8). Assuming that the ratio of the respective film areas is 1 for the first stage R / O film, the second stage R / O film is 0.6, and the third stage R / O film is 0.1.
It was about to be.

In the present embodiment, the waste liquid boric acid I was supplied at a supply flow rate of 2.1 m ³ / hour, a boron concentration of 600 ppm, and silica of 6 pp.
m, 3 ppm of chloride ion, that is, the amount of boron in the treated waste liquid is 1.26 kg / hour, the amount of silica is 12.6 g / hour, and the amount of chloride ion is 6.3 g / hour.

The permeate recovery liquid II is supplied at a supply flow rate of 2.0 m ³ / hour,
Since the boron concentration is 481 ppm, silica is 0.33 ppm, and chloride ion is 0.15 ppm, the amount of boron in the permeated liquid is 0.962 kg / h, the amount of silica is 0.66 g / h, and the amount of chloride ion is 0.3 g / h. Time.

Therefore, under these conditions, the recovery rate of boron in the method of the present invention is (0.962 kg / hour) / (1.26 kg / hour) × 100 = 76% (at a boron separation rate of 0.2%).
3). The separation rate of silica in the method of the present invention is (12.6)
g / hr-0.66 g / hr) / (12.6 g / hr) = 0.
95, which is better than the performance of the R / O membrane module alone of 0.89.

The chloride ion separation rate of the performance of the method of the present invention is (6.3 g / hour-0.3 g / hour) / (6.3 g / hour).
Time) = 0.95, and the performance of the method of the present invention is better than the performance of the R / O membrane module alone of 0.90.

According to the method of the present invention, silica which cannot be easily removed by a desalting tower or the like is recovered at a standard value of 0.5 ppm.
It can be removed below and other impurities can be removed with high performance.

[0025]

EFFECTS OF THE INVENTION In a liquid waste treatment system of a PWR nuclear power plant,
The cost can be reduced by incorporating the method for treating a boric acid-containing liquid of the present invention. That is, the current liquid waste treatment system of the PWR nuclear power plant is a system in which waste liquid boric acid is concentrated by a waste liquid evaporator and then solidified. However, there is a problem that the installation space is large and the cost is high. Further, there is also a problem that impurities such as silica cannot be completely removed, and silica is accumulated in a primary loop. On the other hand, by incorporating this R / O membrane system, the R / O membrane system itself becomes a conventional R / O membrane system.
Although the membrane area is slightly increased as compared with the O membrane system, the concentration and solidification treatment equipment in the liquid waste treatment system is not required,
Significant cost reduction. By combining a three-stage R / O membrane module to form a system having a circulation loop, equipment having excellent performance of removing impurities such as silica can be obtained. Further, the ratio of the supply liquid flow rate / concentrated liquid flow rate of each R / O membrane module can be reduced to 1 to 6, so that the flow rate can be easily adjusted, and the concentration of boric acid or silica on the concentrated liquid side can be improved. The likelihood of precipitation is also reduced. Because of the continuous processing method, the flow rate of the processing waste liquid can be increased, and the operation time can be reduced. In addition, about 10 hours after the start of the R / O membrane high-pressure supply pump, a permeated recovery liquid and a concentrated waste liquid having a constant concentration are obtained, and the treatment in the next stage is advantageous.

[Brief description of the drawings]

FIG. 1 is a schematic view of a boric acid-containing liquid treatment system according to the present invention.

FIG. 2 is a schematic view of a boric acid-containing liquid treatment system shown in an example.

FIG. 3 is a schematic diagram of a conventional boric acid regeneration system.

[Explanation of symbols]

 1 R / O membrane circulating liquid tank 2 R / O membrane high pressure supply pump 3 UF module 4 First stage R / O membrane module 5 Second stage R / O membrane module 6 Third stage R / O Membrane module 7 Solidifier 8 Pressure regulating valve 11 Cartridge filter 12 Ultrafiltration filter feed pump 13 UF module 14 Reverse osmosis membrane module feed pump 15 R / O membrane module I Boric acid-containing waste liquid II Permeate recovery liquid III Concentrated waste liquid

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Osamu Murakami 1-1-1, Wadazakicho, Hyogo-ku, Kobe-shi, Hyogo Prefecture Inside Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (56) References , A) JP-A-62-50697 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/44 B01D 61/58 G21F 9/06 511

Claims (1)

(57) [Claims] 1. A boric acid-containing solution is sent to a solid content removing means, and then processed by a reverse osmosis membrane module. The primary side of the reverse osmosis membrane module is recovered as a concentrated solution, and the secondary side is recovered as a permeate. In the method for treating boric acid-containing waste liquid, the reverse osmosis membrane module is installed in three stages, the first stage reverse osmosis membrane module, the second stage reverse osmosis membrane module, and the third stage The reverse osmosis membrane module is connected in a cascade and recovered as a permeate recovery liquid to the secondary side of the first stage reverse osmosis membrane module, and the permeate to the secondary side of the second stage reverse osmosis membrane module is recovered. And recycling the permeate of the third-stage reverse osmosis membrane module into an untreated boric acid-containing solution, and collecting the liquid remaining on the primary side of the third-stage reverse osmosis membrane module as a concentrated waste liquid, whereby silica and silica are recovered. Boric acid with low chlorine content is used as the permeate recovery solution. A method for treating a boric acid-containing liquid, wherein the volume of the concentrated waste liquid is reduced while collecting the concentrated waste liquid.