Method for treatment of spent radioactive ion exchange resins
10157691 ยท 2018-12-18
Assignee
Inventors
- Hee-Chul Yang (Daejeon, KR)
- Min-Hoon BAIK (Daejeon, KR)
- Hyung-Ju Kim (Daejeon, KR)
- Dong Yong Chung (Daejeon, KR)
- Jong-Won Choi (Daejeon, KR)
Cpc classification
C02F11/008
CHEMISTRY; METALLURGY
International classification
Abstract
[A] method and an apparatus for the treatment of waste ion exchange resins containing radionuclides, and further relating to a method for the treatment of waste ion exchange resins containing radionuclides by the stepwise heat treatment and an apparatus to accomplish the method.
Claims
1. A method for treating waste ion exchange resins containing radionuclides comprising the following steps: drying waste ion exchange resins containing radionuclides (step 1); separating an ion exchanger containing radionuclides from the dried waste ion exchange resin with maintaining sulfur dioxides in a reactor (step 2); converting a volatile compound containing radionuclides obtained from the ion exchanger separated above into non-volatile sulfur oxides containing radionuclides (step 3); converting the sulfur oxides containing radionuclides above into chlorides containing radionuclides (step 4); and separating and collecting radionuclides from the chlorides containing radionuclides above by volatilization and condensation (step 5), wherein the separation of ion exchanger in step 2 is performed at 150400 C.
2. The method for treating waste ion exchange resins containing radionuclides according to claim 1, wherein the method additionally includes a step of forming carbonized materials from the remaining organic material generated in the waste ion exchange resin whose ion exchanger was separated in step 2 above.
3. The method for treating waste ion exchange resins containing radionuclides according to claim 2, wherein the formation of carbonized materials is performed at 550700 C.
4. The method for treating waste ion exchange resins containing radionuclides according to claim 1, wherein the drying in step 1 is performed at 100150 C.
5. The method for treating waste ion exchange resins containing radionuclides according to claim 1, wherein the conversion into sulfur oxides containing radionuclides in step 3 is performed at 400550 C.
6. The method for treating waste ion exchange resins containing radionuclides according to claim 1, wherein the conversion into chlorides containing radionuclides in step 4 is performed at 800900 C.
7. The method for treating waste ion exchange resins containing radionuclides according to claim 1, wherein the volatilization of radionuclides in step 5 is performed at 14001500 C.
8. The method for treating waste ion exchange resins containing radionuclides according to claim 1, wherein the radionuclide is one or more compounds selected from the group consisting of Cs, Sr, Mn, Fe, Ba, Ni, and Co.
9. The method for treating waste ion exchange resins containing radionuclides according to claim 1, wherein the non-volatile sulfur oxide containing radionuclides in step 3 is one or more compounds selected from the group consisting of Cs.sub.2SO.sub.4, SrSO.sub.4, BaSO.sub.4, NiSO.sub.4, FeSO.sub.4, MnSO.sub.4, and CoSO.sub.4.
10. The method for treating waste ion exchange resins containing radionuclides according to claim 1, wherein the additional step of solidification of the radionuclides separated and recovered in step 5 is included.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The application of the preferred embodiments of the present invention is best understood with reference to the accompanying drawings, wherein:
(2)
(3)
(4)
(5)
(6)
(7)
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(8) Hereinafter, the present invention is described in detail.
(9) The present invention provides a method for treating waste ion exchange resins containing radionuclides comprising the following steps:
(10) drying waste ion exchange resins containing radionuclides (step 1);
(11) separating the ion exchanger containing radionuclides from the dried waste ion exchange resin (step 2);
(12) converting the volatile compound containing radionuclides obtained from the ion exchanger separated above into non-volatile sulfur oxides containing radionuclides (step 3);
(13) converting the sulfur oxides containing radionuclides above into chlorides containing radionuclides (step 4); and
(14) separating and collecting radionuclides from the chlorides containing radionuclides above by volatilization and condensation (step 5).
(15) Hereinafter, the method of the invention for treating waste ion exchange resin containing radionuclides is described in detail step by step.
(16) In the method of the invention for treating waste ion exchange resin containing radionuclides, step 1 is to dry the waste ion exchange resin containing radionuclides.
(17) This step is to eliminate H.sub.2O and CO.sub.2 in the waste ion exchange resin through gasification by heating, wherein soluble solids and floating solids included in the waste ion exchange resin can be concentrated.
(18) The said waste ion exchange resin is resulted from a long used ion exchange resin which is used for the separation and purification in water treatment processes in various industrial fields including nuclear power industry. That is, the waste ion exchange resin used to be an ion exchange resin used in various fields such as production of pure water, waste water treatment, collection of high value products, medicinal field, and food purification, etc. In particular, it can be a waste ion exchange resin containing radionuclides which is resulted from the long term use of an ion exchange resin in the course of the purification of waste water containing radionuclides in a nuclear power plant.
(19) The waste ion exchange resin herein can be originated from an ion exchange resin containing a functional group that can be ionized by the chemical conjugation with a polymeric gas. More specifically, when ions included in the functional group of the ion exchange resin are replaced with radionuclides included in waste water, the ion exchange resin turns into the waste ion exchange resin. For example, the ion exchange resin can include a functional group containing sulfonic acid group (SO.sub.3H+) in styrene-divinylbenzene copolymer gas and the substitution of cations in the ion exchange resin with radionuclides included in waste water results in the waste ion exchange resin containing radionuclides.
(20) The ion exchange resin, for example, can contain cations such as hydrogen ions to eliminate radionuclides including Cs in nuclear power plant waste water, and at this time if there is a Cs ion having 2+ electric charge around in a surrounding solution, this ion can be substituted with two hydrogen ions having +1 electric charge each, resulting in the waste ion exchange resin.
(21) The step to dry the waste ion exchange resin above is to eliminate moisture included in the waste ion exchange resin. The drying process can be performed at 100150 C. If the temperature is lower than 100 C., moisture is not gasified. On the other hand, if the temperature is higher than 150 C., the ion exchanger is separated, so that not only moisture but also gas including SO.sub.2 are discharged, which is a problem.
(22) In the method of the invention for treating waste ion exchange resin containing radionuclides, step 2 is to separate the ion exchanger containing radionuclides from the dried waste ion exchange resin.
(23) The separation of the ion exchanger is to separate radionuclides from the waste ion exchange resin, and the radionuclides separated in step 2 can stay as a volatile oxide or hydroxide.
(24) Hereinafter, the process of the separation of ion exchanger in step 2 is described in
(25) As shown in
(26) The ion exchanger included in the waste ion exchange resin above can be separated by the process of step 2. After the separation, gas containing styrene-divinylbenzene copolymer, oxide containing radionuclides, and sulfur dioxide (SO.sub.2) can be generated.
(27) At this time, the separation of ion exchanger in step 2 can be performed at 150400 C.
(28) If the temperature is lower than 150 C., the separation of ion exchanger from the waste ion exchange resin is not completed properly. On the other hand, if the temperature is higher than 400 C., the generation of sulfur dioxide gas (SO.sub.2) is accelerated, which means the time for it to stay in the reactor is short so that the contact between sulfur dioxide gas (SO.sub.2) and radionuclides is not smoothly completed, in other words, non-reacted radionuclides and SO.sub.2 gas can be generated.
(29) It is important for the generated sulfur dioxide gas (SO.sub.2) to stay in the reactor long enough to be able to react with radionuclides in the waste ion exchange resin in order to be converted into sulfur oxides containing radionuclides. In step 2 above, an organic material is not decomposed and only a small volume of sulfur dioxide gas (SO.sub.2) that remains non-reacted with radionuclides is discharged. Therefore, unlike the conventional process for treating waste ion exchange resin such as incineration and vitrification, the method of the invention does not generate a large volume of exhaust gas containing SO.sub.2 and SO.sub.3, suggesting that the method of the invention does not need a large capacity exhaust gas treatment equipment.
(30) If sulfur dioxide (SO.sub.2) remains in gas, even though it is a small amount, radionuclides can be converted into sulfur oxides. So, the volatile radionuclides can be converted into sulfur oxides containing non-volatile radionuclides by keeping the sulfur dioxide (SO.sub.2) generated in step 2 instead of discharging it.
(31) As an example,
(32) In the method of the invention for treating waste ion exchange resin containing radionuclides, step 3 is to convert the compound containing volatile radionuclides generated in the ion exchanger separated above into sulfur oxides containing non-volatile radionuclides.
(33) At this time, the conversion of sulfur oxides in step 3 is performed at the temperature between 400550 C.
(34) If the temperature for the conversion into sulfur oxides in step 3 is lower than 400 C., the conversion of the compound containing radionuclides into sulfur oxides will be too slow so that radionuclides might not be completely converted into sulfur oxides. On the other hand, if the temperature for the conversion into sulfur oxides in step 3 is higher than 550 C., the compound containing radionuclides can be gasified and discharged even before being converted into sulfur oxides.
(35) For example, cesium turns into gas in the forms of Cs.sub.2O, CsOH, and Cs.sub.2O.sub.2H.sub.2 at the temperature of 550 C. and higher.
(36) The radionuclide replaced in the waste ion exchange resin above can be one or more compounds selected from the group consisting of Cs, Sr, Mn, Fe, Ba, Ni, and Co. The sulfur oxide containing the converted radionuclides can be one or more compounds selected from the group consisting of Cs.sub.2SO.sub.4, SrSO.sub.4, BaSO.sub.4, NiSO.sub.4, FeSO.sub.4, MnSO.sub.4, and CoSO.sub.4. At this time, the sulfur oxide containing the said radionuclides is non-volatile, so that the radionuclide therein is not gasified at the temperature of 700 C. or under.
(37) In the meantime, the method of the invention can additionally include a step of forming carbonized materials from the remaining organic material generated in the waste ion exchange resin whose ion exchanger was separated in step 2 above. At this time, the carbonization of the remaining organic material is preferably performed at 550700 C., but not always limited thereto.
(38) The remaining organic material above can include carbon, oxygen, hydrogen, and nitrogen. The remaining organic material containing oxygen, hydrogen, and nitrogen can be gasified at 550700 C. and the remaining carbon component can be converted into carbonized materials.
(39) In step 3 and the additional step of forming carbonized materials, the volatile compound containing radionuclides can be converted into non-volatile sulfur oxides containing radionuclides. A small amount of each hydrogen, nitrogen, and oxygen included in the remaining organic component in the waste ion exchange resin gas such as divinylbenzene copolymer can be gasified, and the carbon component therein can be carbonized. At this time, the component that would be gasified includes neither radionuclides nor sulfur dioxide (SO.sub.2) gas. Therefore, the problems caused by the conventional method such as the deposition of volatile radionuclides, the discharge of radionuclides together with exhaust gas in the air, and the generation of exhaust gas containing sulfur dioxide (SO.sub.2) gas can be prevented.
(40) In the method of the invention for treating waste ion exchange resin containing radionuclides, step 4 is to convert the sulfur oxides containing radionuclides into chlorides containing radionuclides.
(41) At this time, the conversion into chlorides containing radionuclides is performed preferably at 800900 C.
(42) If the temperature for the conversion into chlorides in step 4 is lower than 800 C., the chlorination process would be too slow. If the temperature for the conversion into chlorides in step 4 is higher than 900 C., the chlorination equipment can be corroded.
(43) The sulfur oxide containing radionuclides is a stable material at high temperature, but it can be converted into a chloride in the presence of chlorine gas via the reaction with the chlorine gas.
(44) As an example,
(45) As shown in
(46) In step 4, the carbon component does not chlorinated or gasified by Cl.sub.2. Therefore, the carbon component does not volatilized by the high temperature treatment at 1400 C. or up in step 5 and instead remains as carbonized material.
(47) In the method of the invention for treating waste ion exchange resin containing radionuclides, step 5 is to separate and collect radionuclides from the chlorides containing radionuclides by volatilization and condensation.
(48) In step 5, radionuclides can be volatilized and then condensed, followed by fixation. The carbon component can be separated as carbonized materials in this step. Thus, the method of the invention can give the maximum volume reduction effect in the course of discarding radionuclides and is advantageous in reducing CO.sub.2 generation, so that this method is a pro-environmental and efficient method for treating waste ion exchange resin.
(49) At this time, the volatilization of radionuclides in step 5 is induced at 14001500 C. under the reduced pressure up to 1 Torr. This condition is suitable for volatilizing the chlorinated radionuclide. If the temperature for the volatilization of radionuclides in step 5 is under 1400 C., the volatilization of radionuclide chlorides is not completed quickly, suggesting that the treatment period is longer. If the temperature is higher than 1500 C., energy waste is expected.
(50) In the meantime, the separated radionuclides by volatilization can be condensed and fixed. A carbonized material is not volatilized in step 5. Therefore, the carbonized material would stay even after the radionuclides are volatilized. The remaining carbonized material does not contain radioactive materials, so that it can be recycled or treated as a general waste.
(51) The present invention also provides an apparatus for the treatment of waste ion exchange resins containing radionuclides, which is composed of:
(52) a dryer (100) to dry the waste ion exchange resin containing radionuclides;
(53) a screw conveyor reactor (400) to heat-treat the dried waste ion exchange resin discharged from the dryer above, stepwise; and
(54) an inorganic chlorination reactor (600) to convert the reactant discharged from the screw conveyor reactor above into a chloride.
(55) Hereinafter, the apparatus for the treatment of waste ion exchange resins containing radionuclides of the present invention is described in more detail with the figures.
(56) As shown in the process drawing of
(57) The dryer (100) of the invention is a device for the elimination of moisture included in the waste ion exchange resin, which can be operated at 100150 C.
(58) To dry the waste ion exchange resin in the dryer above, the dryer can include tritium (H-3) and radioactive carbon (C-14) in addition to water vapor (H.sub.2O) and carbon dioxide (CO.sub.2) separated by gasification. To discharge the separated gas after cleaning, the dryer can be additionally equipped with a moisture condenser (200) and a CO.sub.2 absorption/recovery equipment (300). To help vapor and carbon dioxide separated by gasification be discharged from the dryer (100) through the moisture condenser (200) and the CO.sub.2 absorption/recovery equipment (300), N.sub.2 or Ar, the inactive gas, can be supplied into the gas tunnel.
(59) The screw conveyor reactor (400) of the invention is a device to heat-treat the waste ion exchange resin passed on from the dryer (100) phase-dependently, which includes two different regions having different temperatures each other. That is, the screw conveyor reactor (400) has two different regions, which are the ion exchanger separation region (401) and the sulfur oxide conversion region (402). The carbonized material generation region (403) can be additionally included in this device.
(60) The ion exchanger separation region (401) in the screw conveyor rector (400) can be operated at 150400 C. The heat-treatment in this region is to separate the ion exchanger including sulfonic acid group (SO.sub.3H.sup.+) and SO.sub.3M.sup.+ in the waste ion exchange resin. Oxides or hydroxides can be formed or sulfur dioxide (SO.sub.2) can be generated after the separation of the ion exchanger including sulfonic acid group (SO.sub.3H.sup.+) and SO.sub.3M.sup.+.
(61) The sulfur oxide conversion region (402) in the screw conveyor rector (400) is connected to the ion exchanger separation region (401), and can be operated at 400550 C. The heat-treatment in the sulfur oxide conversion region (402) is performed to form a sulfur oxide containing radionuclides. In this region, the volatile radionuclides separated in the ion exchanger separation region above are converted into non-volatile radionuclides and thus discharge of sulfur dioxide gas can be prevented.
(62) In the meantime, the screw conveyor reactor (400) can additionally contain the carbonized material formation region (403) next to the sulfur oxide conversion region (402). The carbonized material formation region (403) can be operated at 550700 C. The heat-treatment in the carbonized material formation region (403) is performed to discharge oxygen, hydrogen, and nitrogen included in the remaining organic compound and to carbonize the carbon component therein, by which gasification of carbon compound can be prevented when the radionuclides are separated via volatilization.
(63) The screw conveyor rector (400) can additionally contain a heat-generator that is equipped outside of the reactor in the form of a heater. Most reaction induced in the screw conveyor reactor (400) is endothermic reaction. So, the temperature of the inside of each reactor can be properly maintained by the heat-generator containing a heater equipped outside of the reactor.
(64) The inorganic chlorination reactor (600) of the invention is a device to convert sulfur oxides among the reactants that had passed through the screw conveyor rector (400) into chlorides containing radionuclides. Chlorine and oxygen gas can be injected in the reactor. The reactor is operated at 800900 C.
(65) The chlorides containing radionuclides converted from sulfur oxides in the inorganic chlorination reactor (600) are heat-treated at 14001500 C., by which the radionuclide are volatilized and recovered. At this time, the wet scrubber (700) can be connected to the inorganic chlorination reactor. The wet scrubber (700) is to condense the radionuclides released from the inorganic chlorination reactor (600) by volatilization. The liquid waste, wherein radionuclides are concentrated, released from the wet scrubber (700) is dried and solidified, resulting in the separation and collection of the radionuclides.
(66) Practical and presently preferred embodiments of the present invention are illustrative as shown in the following Examples.
(67) However, it will be appreciated that those skilled in the art, on consideration of this disclosure, may make modifications and improvements within the spirit and scope of the present invention.
Example 1
(68) Step 1: The waste ion exchange resin wherein Cs radionuclide was substituted in the ion exchange resin containing sulfonic acid group (SO.sub.3H.sup.+) in styrenedivinylbenzene copolymer gas was used. The waste ion exchange resin was placed in the dryer (100) and dried at 150 C. for 2.5 hours.
(69) Step 2: The waste ion exchange resin dried in step 1 was put in the ion exchanger separation region (401) of the screw conveyor reactor (400), which was heated at 350 C. The temperature at inlet was maintained at about 150 C. and the temperature of the high temperature region in this region was up to 400 C. The sulfur dioxide gas generated at this time was slowly discharged through the sulfur oxide conversion region.
(70) Step 3: The reactants obtained in step 2 were heat-treated in the sulfur oxide conversion region (402) of the screw conveyor reactor (400) at about 550 C. for 30 minutes.
(71) Step 4: The reactants obtained in step 3 were heat-treated in the carbonized material formation region (403) of the screw conveyor reactor (400) at about 700 C. for 2 hours, followed by discharge.
(72) Step 5: The reactants resulted from step 4 were put in the inorganic chlorination reactor (600), followed by heat-treatment in the presence of chlorine gas 100 ppm, oxygen gas 100 ppm, and nitrogen gas 1 atm, at 800 C. for 90 minutes.
(73) Step 6: The reactants resulted from step 5 were heat-treated at about 1400 C. in vacuum condition, by which the vaporized volatilized radionuclide was separated. The separated radionuclide was condensed in the wet scrubber.
BRIEF DESCRIPTION OF THE MARK OF DRAWINGS
(74) 100: dryer 200: moisture condenser 300: CO.sub.2 recovery equipment 400: screw conveyor reactor 401: ion exchanger separation region 402: sulfur oxide conversion region 403: carbonized material generation region 500: SO.sub.2 adsorption/absorber 600: chlorination reactor 700: wet scrubber 800: HEPA (high efficiency particulate air filter) filter system
(75) Those skilled in the art will appreciate that the conceptions and specific embodiments disclosed in the foregoing description may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present invention. Those skilled in the art will also appreciate that such equivalent embodiments do not depart from the spirit and scope of the invention as set forth in the appended Claims.