JP6587973B2 - Apparatus and method for treating radioactive liquid waste - Google Patents

Description

  The present invention relates to a treatment apparatus and a treatment method for radioactive liquid waste.

  Among radioactive effluents containing radionuclides generated in nuclear facilities, certain radioactive effluents contain hardness components such as non-radioactive strontium, sodium, calcium, and magnesium in addition to radioactive strontium and radioactive cesium.

  Patent Document 1 discloses a method of bringing a titanium silicate compound such as crystallized silicotitanate (CST) into contact with an aqueous sodium hydroxide solution having a predetermined concentration in order to further improve the adsorption performance of cesium and strontium from such a radioactive liquid waste. It is disclosed.

  Moreover, the radioactive liquid waste containing the hardness component derived from seawater usually contains calcium and magnesium at a higher concentration than strontium, and these ions consume the adsorption sites. Patent document 2 discloses a treatment apparatus for radioactive strontium-containing wastewater having a two-stage configuration in which calcium and magnesium are removed at the front stage and strontium is removed at the rear stage.

  In addition, the target is not limited to radioactive waste liquid, but for wastewater containing hardness components, Patent Document 3 adds an alkaline agent to cause precipitation of alkaline earth metals such as calcium, magnesium, strontium, and the like. An apparatus and a processing method for removing high-hardness waste water to be removed are disclosed.

  Non-Patent Document 1 describes that the distribution coefficient of strontium for ion exchange decreases as the sodium chloride concentration increases, and the distribution coefficient of strontium that is a divalent ion increases in inverse proportion to the square of the sodium concentration. It is described.

Japanese Patent No. 5285183 JP 2014-145687 A JP 2015-112593 A

Teresia Moller et al .: "Ion exchange of 85Sr, 134Cs and 57Co in sodium titanosilicate and the effect of crystallinity on selectivity", Separation and Purification Technology 28 (2002) 13-23

  In the two-stage apparatus described in Patent Document 2, since calcium and magnesium adsorbed and removed in the previous stage contain strontium having the same ionic valence 2, they are improved in that radioactive waste increases. There is room.

  Moreover, in the method and apparatus described in Patent Document 3, precipitation containing strontium becomes radioactive waste, but this is sludge having a high water content and is difficult to handle.

  An object of the present invention is to reduce the amount of radioactive waste that is difficult to handle.

  The processing apparatus for radioactive liquid waste according to the present invention includes a first chemical addition unit for adding a precipitation generating agent to the radioactive liquid waste, an adsorption tower, and a chemical for dissolving the precipitate generated by adding the precipitation generating agent to the radioactive liquid waste. A second chemical addition unit to be added, and the adsorption tower has a configuration in which the supernatant liquid is first sent out of the precipitate and the supernatant liquid, and then the solution obtained by dissolving the precipitate is sent. .

  According to the present invention, it is possible to effectively use the adsorbent by preventing the consumption of adsorption sites by calcium and magnesium and increasing the adsorption of strontium.

  Further, according to the present invention, since radioactive strontium can be efficiently removed from the radioactive liquid waste, the obtained solution can be released to the natural world, and the amount of generated radioactive waste can be reduced. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram illustrating a radioactive waste liquid treatment apparatus of Example 1. It is a schematic block diagram which shows the processing apparatus of the radioactive waste liquid of Example 2. FIG. It is a flowchart which shows the processing method of the radioactive waste liquid of this invention.

  The present invention relates to a processing apparatus and processing method for radioactive waste liquid, and more particularly to a processing apparatus and processing method suitable for adsorbing and removing radioactive strontium from a radioactive waste liquid containing radioactive strontium.

  In the present invention, most of the divalent ions containing strontium are precipitated at the front stage of the adsorption tower, the supernatant liquid containing sodium ions and low-concentration strontium is separated from the precipitate, and the supernatant liquid is passed through the adsorption tower. After removing strontium by adsorption, the precipitate containing divalent ions is dissolved again, and this solution is passed through an adsorption tower to perform strontium adsorption treatment.

  As described in Non-Patent Document 1, the distribution coefficient of strontium, which is a divalent ion, is inversely proportional to the square of the sodium concentration, which is a monovalent ion, and inversely proportional to the square of the divalent ion concentration. When strontium is adsorbed in the presence of sodium and divalent ions (calcium, magnesium, etc.), both sodium and divalent ions become adsorption-interfering ions, reducing the efficiency of strontium adsorption.

  Therefore, sodium and divalent ions are separated by precipitation, and the sodium ion rich solution and the divalent ion rich solution are treated separately to reduce the strontium adsorption hindrance.

  In particular, when the adsorbent added with sodium disclosed in Patent Document 1 is used, it is desirable to treat the divalent ion-rich solution after treating the sodium ion-rich solution first. This is because the composition of the adsorbent to which sodium is added is generally maintained.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing a radioactive waste liquid treatment apparatus of the present invention.

  In this figure, the radioactive waste liquid treatment apparatus 100 includes a waste liquid tank 1, storage tanks 2, 3, and 4, an adsorption tower 5, an alkali supply unit 6 (first chemical addition unit), and an acid supply unit 7 ( 2nd chemical | medical agent addition part) and the piping 11, 12, and 13 are provided.

  The waste liquid tank 1 is connected to the storage tank 2 through a pipe. An alkali supply unit 6 and an acid supply unit 7 are connected to the storage tank 2 by pipes. The alkali supply unit 6 includes an alkali solution tank, a valve, and a pump. The acid supply unit 7 includes an acid solution tank, a valve, and a pump. Further, the storage tank 2 is connected to a pipe 11 and a pipe 12, which are connected to the storage tanks 3 and 4, respectively. The storage tank 3 and the storage tank 4 are connected to a pipe 13, and the pipe 13 is connected to the adsorption tower 5.

  The radioactive waste liquid stored in the waste liquid tank 1 contains ions such as strontium, calcium, magnesium, and sodium. A certain amount of this radioactive waste liquid is supplied to the storage tank 2 through a pipe connected to the waste liquid tank 1 and the storage tank 2. An alkaline solution is supplied from the alkali supply unit 6 to the radioactive waste liquid supplied to the storage tank 2. As the supplied alkaline solution, for example, an aqueous solution in which a metal hydroxide such as a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is dissolved, or an aqueous solution in which a metal carbonate such as a sodium carbonate aqueous solution or a sodium hydrogen carbonate aqueous solution is dissolved is used. Here, instead of the alkali solution, a powder such as a metal hydroxide or a metal carbonate which is a solute of the alkali solution may be supplied to the radioactive liquid waste. Therefore, the chemical | medical agent supplied to a radioactive waste liquid here can be named generically with an alkaline agent.

  The amount of the alkaline solution supplied to the storage tank 2 may be determined by measuring the pH of the radioactive liquid waste with a pH measuring device (not shown) installed in the storage tank 2, or the composition of the radioactive liquid waste may be determined in advance. The supply amount according to the composition may be determined by checking. Here, pH is a hydrogen ion index.

  When the alkaline solution is supplied to the storage tank 2, the pH of the radioactive liquid waste in the storage tank 2 changes to alkaline, and calcium, magnesium, strontium carbonate and hydroxide are generated according to the pH, and precipitation occurs. . As a result of precipitation, the concentration of divalent ions such as calcium in the radioactive liquid waste is reduced, and the radioactive liquid waste in the storage tank 2 has a sodium ion rich composition. The radioactive waste liquid (supernatant liquid) that has become rich in sodium ions is transferred to the storage tank 3 through the pipe 11. Between the piping 11 and the storage tank 2, you may install the filter (not shown) for suppressing the entrainment of a deposit.

  After the sodium ion-rich radioactive waste liquid (supernatant liquid) is transferred, the acid solution is supplied to the storage tank 2 from the acid supply unit 7. As the acid solution to be supplied, for example, an aqueous solution in which hydrochloric acid, sulfuric acid, nitric acid or the like is diluted is used. The amount of acid supplied to the storage tank 2 is set so that the precipitate in the storage tank 2 is sufficiently dissolved, and the pH of the solution of the precipitate becomes a pH suitable for the subsequent adsorption treatment.

  Waste liquid (divalent ion solution) generated by dissolving the precipitate by supplying acid to the storage tank 2 is transferred to the storage tank 4 through the pipe 12. Between the pipe 12 and the storage tank 2, a filter (not shown) for suppressing entrainment of a residue that has not been dissolved by the acid may be installed.

  The radioactive waste liquid transferred to the storage tank 3 and the storage tank 4 is sent to the adsorption tower 5 through the pipe 13. The adsorption tower 5 is filled with an adsorbent having high adsorption selectivity with respect to strontium. As the adsorbent having high adsorption selectivity, crystallized silicotitanate (CST), titanic acid or titanate, artificial zeolite, or the like can be used.

  Here, the water flow to the adsorption tower 5 is carried out with the radioactive waste liquid rich in sodium ions in the storage tank 3 first, and after the radioactive liquid waste in the storage tank 3 has been passed, the divalent in the storage tank 4 Pass the radioactive waste liquid of the ionic solution. This is because the concentration of strontium contained in the radioactive liquid waste in the storage tank 3 is expected to be lower than the concentration of strontium contained in the radioactive liquid waste in the storage tank 4. By treating the radioactive waste liquid having a low strontium concentration while the adsorbent in the adsorption tower 5 is fresh, and then treating the radioactive waste liquid having a high strontium concentration, the removal rate of strontium can be increased.

  In addition, when using Na-type adsorbents, sodium loss in the adsorbent (substitution with other ions) is suppressed by first passing a sodium-rich radioactive waste liquid, and further sodium rich in high concentration. By passing the waste liquid, it is possible to increase the amount of Na adsorbed by the adsorbent and to improve the performance of the adsorbent.

  The radioactive liquid waste that has passed through the adsorption tower 5 is measured for radiation dose at the outlet (not shown), and is released if it is determined that the concentration is less than a predetermined radionuclide concentration. When a radionuclide having a concentration equal to or higher than a predetermined concentration is detected, the radioactive liquid waste that has passed through the adsorption tower 5 is stored in another tank, and additional processing is performed.

  As described above, according to the present embodiment, the radioactive liquid waste can be treated while effectively using the adsorbent, and the generation of secondary waste can be suppressed.

  Another embodiment of the present invention will be described with reference to FIG. The difference from the first embodiment is that a drug supply unit 8 (first drug addition unit) is connected to the storage tank 2 instead of the alkali supply unit 6 of the first embodiment.

  The medicine supply unit 8 includes a medicine tank, piping, a pump, and an on-off valve. The drug tank is filled with an organic drug that forms a complex by combining with a divalent ion such as strontium. Here, examples of the organic agent that forms a complex include oxalic acid, citric acid, tartaric acid, ethylenediamine, diethylenetriamine, iminodiacetic acid, ethylenediaminetetraacetic acid, and disodium rhodizonate.

  To the radioactive waste liquid transferred from the waste liquid tank 1 to the storage tank 2, the organic medicine is supplied from the medicine supply unit 8, and the radioactive waste liquid and the organic medicine are mixed in the storage tank 2. A divalent ion (calcium, magnesium, strontium, etc.) contained in the radioactive liquid waste and an organic agent form a complex.

  It is desirable that the complex formed here has a property insoluble in water. Therefore, as the organic drug supplied from the drug supply unit 8, one that forms an insoluble complex with divalent ions is selected.

  After the precipitation of the complex is caused by the supply of the organic chemical, the solution in the storage tank 2 is transferred to the storage tank 3 through the pipe 11. At this time, the radioactive liquid waste transferred to the storage tank 3 is a sodium ion rich solution containing a small amount of strontium.

  Here, the amount of the complex generated in the storage tank 2 can be adjusted by appropriately selecting the type of the organic drug supplied from the drug supply unit 8 and the pH in the storage tank 2. In addition, strontium and calcium and / or magnesium can be roughly separated by selecting organic agents that have different easiness of complex formation between strontium and calcium and / or magnesium.

  After the transfer to the storage tank 3 is completed, an acid solution is supplied to the storage tank 2 from the acid supply unit 7 (second chemical addition unit), and the precipitate in the storage tank 2 is dissolved. Thereafter, this solution is transferred to the storage tank 4 through the pipe 12. This solution contains a large amount of divalent ions contained in the precipitate formed as a complex among the ions contained in the original radioactive liquid waste.

  In this embodiment, the ratio of strontium to calcium and / or magnesium can be adjusted by selecting an organic agent to be added to form a precipitate, and the strontium removal efficiency can be improved.

  FIG. 3 shows a summary of the radioactive waste liquid treatment method in Examples 1 and 2.

  As shown in the figure, first, precipitation separation (S101) of divalent ions contained in the radioactive liquid waste is performed. Here, the chemical | medical agent added to radioactive waste liquid in order to produce precipitation is an organic chemical | medical agent which forms a complex with an alkaline solution or a part or all of a bivalent ion. Here, the alkaline solution and the organic agent are referred to as “precipitation product”.

  Next, a supernatant liquid adsorption process (S102) is performed. Since divalent ions are separated in S101, the supernatant liquid is a solution containing a large amount of monovalent ions.

  Next, the precipitate is dissolved to produce a solution having a low concentration of monovalent ions and a high concentration of divalent ions (S103).

  Then, the adsorption process (S104) of the solution produced | generated by S103 is performed.

  The steps S101 to S104 can be repeated until the adsorbent used in the adsorption processes S102 and S104 approaches saturation and it becomes difficult to adsorb divalent ions.

  As the adsorbent used in S102 and S104, an adsorbent having high adsorption selectivity with respect to strontium is desirable.

  1: waste liquid tank, 2, 3, 4: storage tank, 5: adsorption tower, 6: alkali supply unit, 7: acid supply unit, 8: chemical supply unit, 11, 12, 13: piping, 100: radioactive liquid waste Processing equipment.

Claims (9)

A first drug addition unit for adding a precipitation-generating agent to the radioactive liquid waste;
An adsorption tower;
A second drug addition unit for adding a drug that dissolves the precipitate generated by adding the precipitation product to the radioactive liquid waste,
A treatment apparatus for radioactive waste liquid, having a configuration in which the supernatant of the precipitate and the supernatant is sent to the adsorption tower first, and then the solution obtained by dissolving the precipitate is sent.   The radioactive waste liquid treatment apparatus according to claim 1, wherein the precipitation generator is an alkaline agent or an organic chemical that forms a complex with some or all of the divalent ions contained in the radioactive liquid waste.   The radioactive waste liquid treatment apparatus according to claim 2, wherein the alkaline agent is a metal hydroxide or a metal carbonate.   The processing apparatus for radioactive liquid waste according to claim 2, wherein the organic agent is oxalic acid, citric acid, tartaric acid, ethylenediamine, diethylenetriamine, iminodiacetic acid, ethylenediaminetetraacetic acid, or disodium rhodizonate.   The radioactive waste liquid treatment apparatus according to claim 1, wherein the chemical in the second chemical addition unit is an acid.   The apparatus for treating a radioactive liquid waste according to claim 5, wherein the acid is hydrochloric acid, nitric acid or sulfuric acid.   The treatment apparatus for radioactive liquid waste according to claim 1, wherein the adsorbent incorporated in the adsorption tower is crystallized silicotitanate, titanic acid, titanate or artificial zeolite. A first step of adding a precipitation generator to the radioactive liquid waste;
A second step of adsorbing the supernatant liquid obtained in the first step;
A third step of adding an agent that dissolves the precipitate produced in the first step;
A fourth step of adsorbing the solution obtained by dissolving the precipitate in the third step,
The second step is a method for treating a radioactive liquid waste, which is performed before the fourth step.   The method for treating a radioactive liquid waste according to claim 8, wherein the steps from the first step to the fourth step are repeated.

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