JP6813320B2 - Contaminated water treatment system and contaminated water treatment method - Google Patents

Description

An embodiment of the present invention relates to a contaminated water treatment system and a contaminated water treatment method for removing radionuclides from contaminated water containing components derived from seawater, groundwater, etc. and radionuclides.

In recent years, many proposals have been made for methods, systems and adsorbents for removing radionuclides from contaminated water containing radionuclides.
As a method of removing radionuclides from contaminated water containing radionuclides, a adsorption tower filled with an adsorbent that selectively adsorbs the radionuclides to be removed is used, and the contaminated water is passed through to make the radionuclides radioactive. A fixed layer adsorption method for removing nuclides is common.

In this fixed layer adsorption method, the radionuclide in the contaminated water is adsorbed from the inlet side of the adsorption tower, and the concentration of the radionuclide in the contaminated water decreases toward the outlet. Therefore, the adsorbent on the inlet side of the adsorption tower has a higher adsorption amount of radionuclides. Therefore, when the radionuclide concentration on the inlet side of the adsorption tower reaches the specified value, the adsorption tower is replaced with a new one even before the radionuclide concentration on the outlet side of the adsorption tower reaches the specified value. In addition, the surface dose rate of the adsorption tower and a part of the radiation emitted upward from the upper part of the adsorption tower are scattered by the air and fall again near the ground, which is called a skyshine line. Even if the amount of radiation emitted upward from the top of the adsorption tower increases and the Skyshine dose exceeds the permissible range, the adsorption tower will be replaced with a new one even before the radionuclide concentration on the outlet side reaches the specified value. Will be exchanged for.

Here, the amount of adsorbed radionuclides differs depending on the type of adsorbent and the properties of contaminated water, and is often expressed by the nuclide partition coefficient for each radionuclide determined by these factors. In the fixed layer adsorption method, the nuclide distribution coefficient is expressed by the formula (1) by the amount of radionuclide adsorbed at the outlet radionuclide concentration / inlet radionuclide concentration = 1 (denoted as the maximum radionuclide adsorption amount) and the inlet radionuclide concentration. ..

Nuclide distribution coefficient (L / Kg) = maximum radionuclide adsorption amount (Bq [nuclide] / Kg [adsorbent weight]) / inlet radionuclide concentration (Bq [nuclide] / L [contaminated water passage amount]) ... 1)
In the formula (1), Bq (becquerel) is a unit representing the amount of radioactivity.

Further, the outlet / inlet radionuclide concentration ratio represented by the formula (2) reached between 0.05 and 0.95, preferably 0.05 to 0.10. Based on the outlet radionuclide concentration and the inlet radionuclide concentration. By the way, it is common to replace the adsorption tower.

Outlet / inlet radionuclide concentration ratio = outlet radionuclide concentration (Bq [nuclide] / L [contaminated water passage amount]) / inlet radionuclide concentration (Bq [nuclides] / L [contaminated water passage amount]) ... (2 )

Japanese Unexamined Patent Publication No. 2015-64251 Japanese Unexamined Patent Publication No. 2011-20856 Japanese Unexamined Patent Publication No. 4-86599

In the conventional contaminated water treatment system, even if the adsorbent still has the adsorption performance, the adsorption tower must be replaced when the surface dose rate or the skyshine dose exceeds the upper limit, so the utilization efficiency of the adsorption tower There was a problem that the

An embodiment of the present invention has been made to solve the above problems, and an object of the present invention is to provide a contaminated water treatment system and a contaminated water treatment method in which the utilization efficiency of the adsorption tower is improved.

In order to solve the above problems, the contaminated water treatment system according to the embodiment of the present invention is an adsorption in a contaminated water treatment system for removing the radionuclides by passing contaminated water containing a radionuclide through an adsorption tower. The tower is filled with an adsorbent that adsorbs the radionuclide and a non-adsorbent made of granular lead that hardly adsorbs the radionuclide, and the non-adsorbent is placed on the outlet side of the adsorption tower in the same adsorption tower. It is placed more on the entrance side than on the entrance side .

In addition, the contaminated water treatment method according to the embodiment of the present invention removes radionuclides contained in the contaminated water by using the contaminated water treatment system according to the embodiment of the present invention.

According to the contaminated water treatment system and the contaminated water treatment method according to the embodiment of the present invention, the utilization efficiency of the adsorption tower can be improved.

(A) is a block diagram of the contaminated water treatment system according to the first embodiment, and (b) is a sectional view taken along line AA of (a). The block diagram of the contaminated water treatment system which concerns on 2nd Embodiment.

Hereinafter, embodiments of the contaminated water treatment system and the contaminated water treatment method of the present invention will be described with reference to the drawings.

[First Embodiment]
The contaminated water treatment system and the contaminated water treatment method according to the first embodiment will be described with reference to FIGS. 1 (a) and 1 (b).
In the following description, an example in which the radionuclide to be treated is cesium will be described, but it goes without saying that it can be applied to other radionuclides such as strontium.

(Constitution)
As shown in FIGS. 1A and 1B, the contaminated water treatment system 10 according to the first embodiment selectively adsorbs the adsorption tower 2 and the radioactive cesium filled in the adsorption tower 2. Supply of material 1, substance 3 that does not easily adsorb radioactive cesium (hereinafter referred to as “non-adsorbent”), and contaminated water 4 that is connected to the upper part of the adsorption tower 2 and contains ionic radioactive cesium. It is composed of a pipe 6 and a discharge pipe 7 connected to the lower part of the suction tower 2 and discharging the treated water 5 treated in the suction tower 2.

The adsorption tower 2 is made of a cylinder having a thickness and a material capable of shielding radiation from radioactive cesium, but the thickness of the cylinder may be reduced and a radiation shielding material may be provided around the cylinder. Further, the shape of the suction tower 2 is not limited to the cylindrical body, and various shapes such as an elliptical cylinder body and a square cylinder body can be used.

Further, in the present embodiment, the cylindrical adsorption tower 2 is vertically arranged, the upper portion is the inlet side of the contaminated water and the lower portion is the outlet side. However, the contaminated water 4 is supplied from the lower portion of the adsorption tower 2 and the treated water 5 is provided. May be discharged from the upper part, or the suction tower 2 may be placed horizontally.

As the adsorbent for radioactive cesium, silicate, clinoptilolite, chavasite, mordenite, ferrocyanide, Prussian blue type metal complex, and the like are used.

Further, as the non-adsorbent 3, lead, sand, cement, etc. are used, but the present invention is not limited to this, and any other substance may be used as long as it has a function of hardly adsorbing radioactive cesium, or the adsorbent 1 of radioactive cesium. A substance having a smaller adsorption performance of radioactive cesium than the above may be used.

In the first embodiment, granular lead balls are used as the non-adsorbent material 3, and the lead balls are dispersed and arranged substantially evenly inside the adsorption tower 2.
Further, in the first embodiment, the ratio (occupancy rate) of the total volume of the non-adsorbent 3 to the internal volume of the adsorption tower 2 is about 50%, and this occupancy is the material of the non-adsorbent 3. It can be changed as appropriate depending on the required adsorption performance, allowable radiation amount, and the like.

For example, if the occupancy rate of the non-adsorbent 3 is 20%, the filling amount of the adsorbent 1 is reduced by 20%, so that the maximum adsorbed amount of radioactive cesium is also reduced by 20%.
As the shape of the granular non-adsorbent material 3, various shapes such as a spherical shape, an elliptical spherical shape, a rectangular shape, and a lump shape are used.
Further, the size (shape), weight and number of the non-adsorbent 3 loaded in the adsorption tower 2 can be appropriately changed depending on the internal volume of the adsorption tower 2, the required adsorption performance, the allowable radiation amount and the like.

The size and / or weight of the adsorbent 1 and the non-adsorbent 3 are different so that the adsorbent 1 and the non-adsorbent 3 can be easily separated and recovered when the used adsorption tower 2 is processed. It is desirable to.

Further, when a material having a radiation shielding function such as lead is used as the non-adsorbing material 3, it also has a function of shielding radiation from the adsorbed radioactive cesium, so that the surface dose rate and skyshine dose of the adsorption tower 2 are reduced. It also has an effect of causing radiation.

Further, a radiation monitor (radiation detector) for measuring the concentration of radioactive cesium is installed at the inlet and outlet of the adsorption tower 2 (not shown). Further, a radiation monitor for measuring the surface dose rate and the skyshine dose of the adsorption tower 2 is appropriately installed around the adsorption tower 2 (not shown).
These radiation monitors are also used to grasp the adsorption status and the adsorption amount in the adsorption tower 2.

Further, when radioactive cesium is adsorbed on the adsorbent 1, the temperature of the treated water 5 rises due to the heat generated by the adsorbed radioactive cesium. Therefore, a thermometer is installed at the outlet of the adsorption tower 2 and the temperature of the treated water. The amount of radioactive cesium adsorbed may be predicted by monitoring.

(Action)
In the contaminated water treatment system 10 configured as described above, when the contaminated water 4 containing radioactive cesium in the ion form is introduced into the adsorption tower 2 from the supply pipe 6, the radioactive cesium is released from the upper part of the adsorption tower 2 to the adsorbent 1. Will be adsorbed to.

Then, when the adsorption by the adsorbent 1 proceeds throughout the adsorption tower 2 and the outlet / inlet radionuclide concentration ratio reaches a predetermined value, or the surface dose rate or skyshine dose of the adsorption tower 2 exceeds the upper limit value, The treatment of contaminated water is stopped and the adsorption tower 2 is replaced with a new one.
The used adsorption tower 2 is moved to a treatment facility where the adsorbent 1 and the non-adsorbent 3 are separated, and the non-adsorbent 3 is reused.

(Example 1)
As shown in FIG. 1, the adsorbent 1 consisting Keichitan salts with radioactive cesium ion adsorption performance in a cylindrical adsorption column 2 of every vertical longitudinal as well as 10 3 ^Kg filling, to the internal volume of the adsorption column 2, The non-adsorbent 3 composed of a large number of lead balls was substantially uniformly dispersed and arranged so that the occupancy rate was about 50%.

Contaminated water 4 having a concentration of radioactive cesium-137 of 5 × 10 ⁷ Bq / L, which is entirely present in the ionic form, is passed through the adsorption tower 2 through the supply pipe 6 from the upper part of the adsorption tower 2 and through the discharge pipe 7 from the lower part. It was discharged as treated water 5.

Properties of cesium distribution coefficient of the adsorbent 1 contaminated water, when may vary depending on the type of Keichitan salt, assumed as ¹⁰ 5 L / Kg, maximum adsorption concentration of 137Cs in accordance with Equation (1) is, 5 × ¹⁰ 12 Bq / It becomes Kg (= 5 × 10 ⁷ Bq / L × 10 ⁵ L / Kg).

When the concentration of radioactive cesium-137 on the inlet side and the concentration of radioactive cesium-137 on the outlet side are equal, the amount of radioactive cesium-137 adsorbed becomes maximum and becomes 5 × 1015 Bq (= 5 × 1012 Bq / Kg × 103 kg).

In this embodiment, when the outlet / inlet radionuclide concentration ratio reaches 0.05 to 0.10., The injection of contaminated water is stopped and the adsorption tower 2 is replaced. Further, in the used adsorption tower 2, the adsorbent 1 and the non-adsorbent 3 were separated and recovered at the treatment facility, and the non-adsorbent 3 was reused.

Since the adsorption tower 2 adsorbs radioactive cesium from the adsorbent 1 located upstream, the surface dose rate and skyshine dose of the adsorption tower 2 increase as the adsorption of radioactive cesium progresses, but non-adsorption. Since the material 3 is dispersedly arranged in the adsorption tower 2, the surface dose rate and the skyshine dose do not exceed the upper limit values, but if the surface dose rate and the skyshine dose exceed the permissible values, At that point, the injection of the contaminated water 4 is stopped.

(effect)
According to this embodiment, the non-adsorbent 3 that can be reused is used, and the amount (occupancy) of the non-adsorbent 3 loaded in the adsorption tower 2 is appropriately adjusted to be adsorbed on the adsorbent 1. The amount of radioactive cesium produced can be adjusted to a desired value, and the surface dose rate or skyshine dose of the adsorption tower 2 can also be adjusted so as not to exceed the permissible value.
As a result, the safety and operating efficiency of the contaminated water treatment system 10 can be improved, and the radiation exposure and environmental radioactivity of the workers can be reduced.

Further, according to the configuration of the present embodiment, it is not necessary to use a heavy shielding material for reducing the skyshine dose, and the adsorption tower 2 can be miniaturized and simplified. Therefore, it is possible to prevent the heat generated during the adsorption of radioactive cesium from staying in the adsorption tower 2. Further, the manufacturing cost can be reduced by saving the space of the contaminated water treatment system 10.

Further, since the non-adsorbent 3 having a weight, size, etc. different from that of the adsorbent 1 is used, the non-adsorbent 3 can be easily separated and recovered from the adsorbent 1, and the non-adsorbent 3 can be easily reused. This simplifies the processing of the used adsorption tower 2 and makes effective use of resources.

[Second Embodiment]
The contaminated water treatment system and the contaminated water treatment method according to the second embodiment will be described with reference to FIG. In the second embodiment, similarly to the first embodiment, an example in which the cylindrical adsorption tower 2 is vertically arranged, the upper part is the inlet side of the contaminated water, and the lower part is the outlet side will be described.

As described above, the amount of radioactive cesium-137 adsorbed on the adsorption tower 2 is the upper limit of the amount of radiation (surface dose rate) emitted from the entire adsorption tower 2 or mainly in the upper region of the adsorption tower 2. It is limited by the upper limit of the site boundary dose (skyshine dose) emitted from the adsorbed radioactive cesium.

Therefore, if the surface dose rate or skyshine dose of the adsorption tower 2 exceeds the upper limit before the outlet / inlet radionuclide concentration ratio reaches the specified value, the injection of the contaminated water 4 is stopped and the adsorption tower 2 is replaced. Must.

The upper limit of the surface dose rate and the skyshine dose differs depending on each facility and environment, but the upper limit of the skyshine dose may be set more strictly.
In the second embodiment, paying particular attention to the case where the upper limit of the skyshine dose is strictly set, the adsorption tower 2 is provided so that the contaminated water treatment system 10 does not stop operating early due to the skyshine dose. It is characterized by being configured.

(Constitution)
In the adsorption tower 2 according to the second embodiment, as shown in FIG. 2, the number of non-adsorption materials 3 to be filled in the upper part (inlet side) of the adsorption tower 2 is increased, and the lower part (outlet side) of the adsorption tower 2 is increased. ), The number of non-adsorbents 3 is gradually reduced. That is, more non-adsorbents 3 are arranged on the inlet side than on the outlet side in the adsorption tower 2.

(Action)
In the adsorption tower 2 configured as described above, since the upper part of the adsorption tower 2 is filled with a large amount of non-adsorbent 3 that does not adsorb radioactive cesium, the skyshine dose radiated from the upper part of the adsorption tower 2 is reduced. Can be transformed into. Further, in the lower part of the adsorption tower 2, since the filling amount of the non-adsorbent 3 is gradually reduced, the adsorption amount of radioactive cesium is gradually increased.
As a result, the amount of radioactive cesium adsorbed can be set to a desired value, and an increase in the skyshine dose can be suppressed.

(Example 2)
In Example 2, when the upper limit of the skyshine dose is set to be stricter than the surface dose rate, for example, when the upper limit of the skyshine dose is 2.0 × 10 ¹⁴ (2.0E + 14) Bq. explain.

As shown in FIG. 2, the adsorbent 1 consisting Keichitan acid salt in a cylindrical adsorption column 2 of vertical with radioactive cesium ion adsorption performance was 10 3 ^Kg filling. Further, from the upper side to the lower side of the adsorption tower 2, a non-adsorbent material 3 composed of a large number of lead balls was filled in each region so as to have the occupancy ratio shown in Table 1.

The occupancy rate of the entire non-adsorbent 3 with respect to the internal volume of the adsorption tower 2 is about 50% as in Example 1, but is not limited to this, and the required adsorption amount and the upper limit of the skyshine dose are upper limit. It may be increased or decreased as appropriate according to the value or the like.

Table 2 shows the amount of radioactive cesium adsorbed in each region of the adsorption tower 2 configured as shown in Table 1.

Taking Table 2 into consideration, the amount of radioactive cesium adsorbed from the upper part of the adsorption tower to 1/10 is 2.0 × 10 ¹⁴ (2.0E + 14) Bq, which is the approximate upper limit of the skyshine dose, and the adsorption tower 2 as a whole The amount of radioactive cesium adsorbed is 2.5 × 10 ¹⁵ Bq, and it can be seen that radioactive cesium is efficiently adsorbed over the entire adsorption tower 2.
In the second embodiment, the replacement timing of the adsorption tower 2 is determined based on the outlet / inlet radionuclide concentration ratio, the skyshine dose, the surface dose rate, and the like.

(effect)
According to the second embodiment, in addition to the effect of the first embodiment, radioactive cesium can be efficiently adsorbed while suppressing an increase in the skyshine dose, so that the contaminated water treatment system 10 It is possible to improve the safety and operating efficiency of.

Further, by appropriately adjusting the distribution of the non-adsorbent 3 in the adsorption tower 2, the contaminated water treatment system 10 can be configured so as not to exceed the upper limit of the skyshine dose and the surface dose rate, which differ depending on the facility environment. It will be possible.

Although some embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Adsorbent, 2 ... Adsorption tower, 3 ... Non-adsorbent, 4 ... Contaminated water, 5 ... Treated water, 6 ... Supply pipe, 7 ... Discharge pipe, 10 ... Contaminated water treatment system

Claims (5)

In a contaminated water treatment system that removes radionuclides by passing contaminated water containing radionuclides through an adsorption tower.
The adsorption tower is filled with an adsorbent that adsorbs the radionuclide and a non-adsorbent made of granular lead that hardly adsorbs the radionuclide.
A contaminated water treatment system in which more of the non-adsorbent is arranged on the inlet side than on the outlet side in the adsorption tower in the same adsorption tower . The contaminated water treatment system according to claim 1, wherein the adsorbent and the non-adsorbent have different shapes and / or weights. The contaminated water treatment system according to claim 1 or 2, wherein the radionuclide is radioactive cesium or radiostrontium. The contaminated water treatment system according to any one of claims 1 to 3, wherein the non-adsorbent is separated and recovered from the adsorbent and reused. A method for treating contaminated water by using the contaminated water treatment system according to any one of claims 1 to 4 to remove radionuclides contained in the contaminated water.

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