JP2015064221A - Radioactive nuclide removal system and radioactive nuclide removal method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radioactive nuclide removal system and a method capable of efficiently utilizing filled adsorbent for removing radioactive nuclide from radioactive contaminated water which contains absorption inhibitory substances such as sea water components.SOLUTION: A radioactive nuclide removal system 10 includes: piping 12 for delivering radioactive contaminated water from a storing tank 11; plural absorption units 13 (13a, 13b, 13c) each of which is filled with an adsorbent having a different absorbing characteristics of the radioactive nuclide with respect to radioactive contaminated water 25 which contains absorption inhibitory substances; a switch part 14 that switches to allow the radioactive contaminated water 25 to pass through any one of the plural absorption units 13 (13a, 13b, 13c) according to the measured concentration value of the absorption inhibitory substance in the tank 11. The radioactive nuclide removal system 10 switches the absorption unit according to the concentration of the absorption inhibitory substances.

Description

  The present invention relates to a technique for removing radionuclides from radioactively contaminated water.

Water used in nuclear facilities is treated by filtration with a filter or ion exchange with a resin to remove impurities such as radionuclides.
For example, condensate of primary cooling water in a boiling water reactor (BWR) is purified by a condensate purification facility comprising a condensate filter such as a hollow fiber and a condensate demineralizer such as an ion exchange resin.
The reactor water is purified by a reactor water purification facility comprising a pre-coated powder ion exchange resin and a mixed bed type desalting tower (Patent Document 1).

The waste liquid generated by washing other than the reactor coolant, for example, is purified and reused by a concentrator or a desalinating apparatus (Patent Document 2).
In this way, the water used in the nuclear power plant during normal operation can always maintain a sufficiently low radioactivity level.

Japanese Examined Patent Publication No. 7-69460 JP 2012-71263 A

By the way, when a severe accident occurs in a nuclear power plant and fuel is damaged, radioactive polluted water containing radionuclides such as cesium, iodine, and strontium, which are uranium fission products, is generated.
In addition, when seawater is used for cooling after an accident, this radioactively contaminated water contains chlorine, sodium, calcium, etc. derived from seawater.

As a method of removing the radionuclide, there is a method of using an appropriate adsorbent according to the type and form of the element, for example, a neutral substance, a cation, or an anion.
By filling the adsorption tower with such an appropriate adsorbent and passing water to be treated, radionuclides in the water can be removed.
In this adsorption tower, when the nuclide cannot be sufficiently removed or the dose rate on the surface becomes high, the adsorbent is refilled or the adsorption tower is replaced.

However, it is known that zeolite, which is an effective cesium adsorbent, has reduced adsorption performance under conditions where the salt concentration is high.
Further, it is known that silver, which is an effective adsorbent for iodine, also has a decrease in adsorption performance under high salt concentration conditions because the chemical properties of iodine and chlorine are similar.
Similarly, the adsorption performance of the adsorbent for strontium is also affected by the calcium concentration, and performance degradation under high concentration conditions is inevitable.

Therefore, when contaminated water having a high salinity concentration or calcium concentration is treated, the saturation point of the adsorbent with respect to the radionuclide is lowered. As a result, there is a problem that the adsorption tower loses its removal capability within a short time while the adsorption amount of the radionuclide is small (see FIG. 2A).
On the other hand, when contaminated water having a low salinity concentration or calcium concentration is treated, a large amount of radionuclide is adsorbed at the upper part of the adsorption tower. As a result, before the adsorbent at the end of the adsorption tower begins to adsorb the radionuclide, the dose rate on the adsorption tower surface exceeds the limit value (see FIG. 2B), and the adsorbent exchange or adsorption tower exchange is performed. There are issues that need to be addressed.

  The present invention has been made in consideration of such circumstances, and in removing radionuclides from radioactively contaminated water containing seawater components etc., radionuclide removal that can efficiently operate the packed adsorbent The purpose is to provide technology.

  In the radionuclide removal system of the present invention, a pipe for delivering radioactively contaminated water accommodated in a tank and an adsorbent having different radionuclide adsorption capacities with respect to the radioactively contaminated water in which an adsorption inhibitor is dissolved are separately provided. A plurality of adsorption units filled in the tank, and a switching unit that allows the radioactively contaminated water to pass through any one of the plurality of adsorption units according to a measured value of the concentration of the adsorption inhibitor in the tank. It is characterized by that.

  It is an object of the present invention to provide a radionuclide removal technique that can efficiently operate a filled adsorbent when removing radionuclides from radioactively contaminated water containing seawater components and the like.

Schematic which shows 1st Embodiment of the radionuclide removal system which concerns on this invention. (A), (B), and (C) are characteristic diagrams showing the adsorption concentration of the radionuclide in the adsorption unit with respect to the salinity concentration in the contaminated water. Schematic which shows 2nd Embodiment of the radionuclide removal system which concerns on this invention. Schematic which shows 3rd Embodiment of the radionuclide removal system which concerns on this invention. Schematic which shows 4th Embodiment of the radionuclide removal system which concerns on this invention.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the radionuclide removal system 10 according to the first embodiment includes a pipe 12 that delivers radioactive contaminated water 25 accommodated in a tank 11, and the radioactive contaminated water in which an adsorption inhibitor is dissolved. A plurality of adsorption units 13 (13a, 13b, 13c) separately packed with adsorbents having different radionuclide adsorption capacities with respect to 25, and a plurality of adsorption units according to the measured value of the concentration of the adsorption inhibitor in the tank 11. 13 (13a, 13b, 13c) is provided with a switching unit 14 that allows the radioactively contaminated water 25 to pass therethrough.

The tank 11 temporarily stores the radioactive contaminated water 25, and the radioactive contaminated water 25 can be delivered to the outside through the connected pipe 12.
This radioactively contaminated water 25 contains radionuclides such as cesium, iodine and strontium which are uranium fission products, and also contains components such as chlorine, sodium and calcium derived from seawater used for cooling. Yes.

Note that there are actually a plurality of tanks 11, in which only one tank 11 is shown in the drawing. And the density | concentration of the radionuclide and the seawater origin component of the radioactive contamination water 25 accommodated is different in each of the some tank 11. FIG.
Therefore, a part of the radioactively contaminated water 25 is collected as the sample 27 from the tank 11 and qualitative and quantitative analysis is performed in the analysis chamber 28 at a distance to recognize the concentrations of the radionuclide and seawater-derived components in each tank 11.

  Here, the adsorption units 13a, 13b, and 13c shown in FIG. 1 have a high adsorption ability of radionuclides in the contaminated water under the conditions in which the adsorption inhibitor (seawater-derived component) is dissolved in this order for explanation. It is assumed that three kinds of adsorbents of lower and lower levels are filled with each.

Based on FIG. 2, the distribution of the adsorption concentration of the radionuclide in the adsorption unit with respect to the salinity concentration in the contaminated water will be described using the adsorption unit 13b having a medium radionuclide adsorption ability as an example.
As shown in FIG. 2A, when the radioactively contaminated water 25 having a high salinity concentration is passed through the adsorption unit 13b having a medium adsorption capacity, the adsorbent gradually moves from the inlet toward the outlet at a low saturation point. Adsorption saturation is reached. And in a short time (the amount of treatment of the contaminated water 25 is small), the treated water 26 in which the removal of the radionuclide is insufficient is output from the outlet.

  As shown in FIG. 2B, when the radioactively contaminated water 25 having a low salinity concentration is passed through the adsorption unit 13b having a medium adsorption capacity, the adsorbent gradually becomes saturated with adsorption at the high saturation point. Reach. And before this saturation point reaches the exit of the adsorption unit 13b, the surface dose rate exceeds the limit value, and the adsorption unit 13b needs to be replaced while leaving a large amount of unused adsorbent. .

  As shown in FIG. 2 (C), when the radioactively contaminated water 25 having a medium salinity concentration is passed through the adsorption unit 13b having a medium adsorption capacity, the adsorbent enters the inlet at an appropriate height saturation point. Adsorption saturation is reached from the outlet to the outlet. Thereby, the adsorption unit 13b can process a large amount of radioactively contaminated water 25 without the surface dose rate exceeding the limit value.

The switching unit 14 passes the radioactively contaminated water 25 of the tank 11 having a high measured value of the adsorption inhibitory substance to the adsorption unit 13a having a high radionuclide adsorbing capacity, and the radioactively contaminated tank 11 having a low measured value. The water 25 is passed through the adsorption unit 13c having a low adsorption capacity, and the radioactively contaminated water 25 of the tank 11 having the intermediate measured value is passed through the adsorption unit 13b having a medium adsorption capacity.
A check valve 16 (16a, 16b, 16c) is provided at the end of the adsorption unit 13 (13a, 13b, 13c), and the treated water 26 that has passed through any one of the adsorption units 13 is adsorbed to other adsorption valves. The unit 13 is configured not to flow backward.

As a result, the radioactively contaminated water 25 passes through an appropriate adsorption unit 13 according to the concentration of the adsorption inhibitor, and these adsorption units 13 are moderately saturated from the inlet to the outlet as shown in FIG. At this point, adsorption saturation was reached, and it was used efficiently.
The radioactively contaminated water 25 passing through the adsorption unit 13 is accumulated in the pool 15 as detoxified treated water 26.

(Second Embodiment)
Next, a second embodiment of the present invention will be described based on FIG.
As shown in FIG. 3, in the radionuclide removal system 10 according to the second embodiment, each adsorption unit 13 (13a, 13b, 13c) is separately filled with adsorbents having different adsorption capacities depending on the radionuclide. The plurality of adsorption towers 17 (17 _{a1 to} 17 _a4 , 17 _{b1 to} 17 _b4 , and 17 _{c1 to} 17 _c4 ) are respectively connected in series.
3, parts having the same configuration or function as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

The adsorbent has adsorbability superiority or inferiority depending on the type of radionuclide (for example, Cs, Sr, Co, etc.), and the type of adsorbent also determines which radionuclide adsorbability is superior. Dependent.
For this reason, for example, adsorption towers 17 _{a1 to} 17 _c1 filled with an adsorbent that is superior in Cs adsorption capacity are arranged in the first stage, and adsorbent that is superior in Sr adsorption capacity is arranged in the second stage. The adsorbing towers 17 _{a2 to} 17 _c2 are arranged, the third stage is arranged with the adsorbing towers 17 _{a3 to} 17 _c3 filled with the adsorbent having superior Co adsorption ability, and the fourth stage is the other radionuclide. Adsorption towers 17 _{a4 to} 17 _c4 packed with an adsorbent that is superior in adsorbing capacity are arranged.
As a result, many types of radionuclides contained in the radioactively contaminated water 25 can be removed without unevenness.

(Third embodiment)
Next, a third embodiment of the present invention will be described based on FIG.
As shown in FIG. 4, the radionuclide removal system 10 according to the third embodiment includes an adsorption tower 17 (17 _{a1 to} 17 _c1 , 17 _{a2 to} 17 _c2 , 17 _{a3 to} 17 _c3 , 17 _{a4 to} 17 _c4 ), They are connected in series via the switching unit 14 (14 ₁ , 14 ₂ , 14 ₃ , 14 ₄ ).
4, parts having the same configuration or function as those in FIG. 3 are denoted by the same reference numerals, and redundant description is omitted.
Thereby, the adsorption tower 17 can be appropriately connected in series according to the concentrations of the various types of radionuclides contained in the radioactively contaminated water 25, and the path of the adsorption unit 13 that can remove these radionuclides with high efficiency. Can be formed.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described based on FIG.
As shown in FIG. 5, the radionuclide removal system 10 according to the fourth embodiment is provided with an adsorption inhibitor removal means 20 on the upstream side of the adsorption unit 13 (13a, 13b, 13c).
The adsorption inhibiting substance removing means 20 includes a precipitation tank 21 and a filtration tank 22.

When radioactively contaminated water 25 contains a large amount of metal ion components (including radionuclides) that are adsorption inhibitors, an appropriate drug is administered to neutralize and precipitate the metal ion components, thereby inhibiting the adsorption. The concentration of can be reduced.
The sedimentation tank 21 separates the sediment and the supernatant water into two phases, and further allows the supernatant water to pass through the filtration tank 22 so that only the liquid component not containing the solid content can be guided to the adsorption unit 13.

For example, when calcium is present in the radioactively contaminated water 25, adsorption of strontium is inhibited in the adsorption unit 13. Therefore, by transferring the radioactively contaminated water 25 from the tank 11 to the settling tank 21 and adding sodium carbonate, calcium is precipitated as calcium carbonate and can be removed by filtration.
Thereby, efficient removal of strontium which is a radionuclide is realized in the adsorption unit 13. Whether or not the radioactively contaminated water 25 is allowed to pass through the adsorption inhibiting substance removing means 20 can be selected by switching the valve V according to the concentration of the adsorption inhibiting substance.

Further, the radionuclide removal system 10 according to the fourth embodiment is provided with a neutral substance removal means 23 on the downstream side of the adsorption unit 13.
Even after passing through the adsorption unit 13 and removing ionic radionuclides, neutral radionuclides may remain in the radioactively contaminated water 25.
The neutral substance removing means 23 removes the neutral radionuclide remaining in the radioactively contaminated water 25 as described above, and is realized by, for example, activated carbon, molecular sieve, or the like.

  According to the radionuclide removal system of at least one of the embodiments described above, radiation is radiated according to the measured value of the concentration of the adsorption inhibitor for a plurality of adsorption units separately packed with adsorbents having different radionuclide adsorption capacities. By switching the contaminated water to pass through, the detoxification treatment of the radioactively contaminated water containing seawater components and the like can be carried out efficiently.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

10 ... radionuclide removal system, 11 ... tank, 12 ... pipe, 13 (13a, 13b, 13c ) ... adsorption unit, 14 ... switch unit, 15 ... pool, 16 ... check valve, 17 (17 _a1 ~17 _a4, 17 _{b1 to} 17 _b4 , 17 _{c1 to} 17 _c4 )... Adsorption tower, 20... Removal means for adsorption inhibiting substances, 21... Precipitation tank, 22. , 26 ... treated water, 27 ... sample, 28 ... analysis room.

Claims (7)

Piping for delivering radioactively contaminated water contained in the tank;
A plurality of adsorption units separately packed with adsorbents having different radionuclide adsorption capacities for the radioactively contaminated water in which the adsorption inhibitor is dissolved;
A radionuclide removal system comprising: a switching unit that allows the radioactively contaminated water to pass through any one of the plurality of adsorption units according to a measured value of the concentration of the adsorption-inhibiting substance in the tank. .   2. The adsorption unit according to claim 1, wherein each of the adsorption units is a series of a plurality of adsorption towers that are separately packed with adsorbents having different adsorption capacities depending on the radionuclide. Radionuclide removal system.   The radionuclide removal system according to claim 2, wherein the adsorption towers are connected in series via a switching unit.   The radionuclide removal system according to any one of claims 1 to 3, wherein means for removing the adsorption-inhibiting substance is provided upstream of the adsorption unit.   The radionuclide removal system according to claim 4, wherein the adsorption inhibiting substance removing unit includes a precipitation tank and a filtration tank.   The radionuclide removal system according to any one of claims 1 to 5, wherein a neutral substance removal unit is provided downstream of the adsorption unit. A step of individually filling a plurality of adsorption units with adsorbents having different radionuclide adsorption capacities for radioactively contaminated water in which adsorption inhibitors are dissolved;
Measuring the concentration of the adsorption inhibitor in the radioactively contaminated water contained in the tank;
Passing the radioactively contaminated water through any one of the plurality of adsorption units according to the measured value of the concentration of the adsorption inhibitor.

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