A method for treating radioactive waste ion exchange resin

Abstract

The present invention provides a method for treating radioactive waste ion exchange resin, and relates to the field of environmental protection technology. The present invention does not add non-radioactive contaminated resin powder, and the adhesive only occupies the gaps between the radioactive waste ion exchange resin particles, so the volume reduction ratio is high; the present invention uses an adhesive to bond the non-radioactive resin powder, and the resin block obtained after thermal overpressure has high strength, and the compressive strength is greater than 30 MPa, which is much higher than the compressive strength requirement of 7 MPa for cement solidified bodies. Even if an accident occurs and the resin block is soaked in water, the resin block will not be scattered, and in the case of damage to the outer packaging, the resin will not leak radioactivity due to pulverization; and, since the resin block will not be pulverized, the inner barrel can be omitted, and the block can be directly placed in a steel barrel outer packaging of a suitable size, reducing the operation process and cost.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection, and in particular to a method for treating radioactive waste ion exchange resin. Background Art

[0002] Ion exchange resin is a commonly used wastewater treatment agent in nuclear power plants, and is generally used in the treatment of low-level radioactive wastewater. There are two main ways to dispose of spent ion exchange resins in nuclear power plants: cement solidification and thermal overpressure.

[0003] Cement blocks are water-resistant and can remain stable over a wide temperature range, so cement solidification is a recognized method for fixing radionuclides in the industry. However, an obvious disadvantage of cement solidification is that the volume of solid waste increases significantly, which is obviously incompatible with the requirement of solid waste reduction in nuclear power plants. Therefore, only a few nuclear power plants around the world still use it.

[0004] At present, newly built nuclear power plants at home and abroad generally use thermal overpressure to treat spent ion exchange resins. There are two types of thermal overpressure processes: (1) Add a certain amount of resin powder to the spent ion exchange resin, dry it at 160°C, put it into a 160-liter special steel container, and then press it into a thin pancake at 130°C and a pressure of about 3000-4000 kN. This thermal overpressure method has two disadvantages: first, the addition of non-radioactive contaminated resin powder in the hot pressing process not only increases the cost, but also reduces the volume reduction ratio of the radioactive spent ion exchange resin because the volume of the resin powder itself exceeds the total volume of the voids between the resin particles; second, the pressed resin pancake has no mechanical strength (no mechanical strength with or without resin powder). If there is no metal shell, it will be completely powdered within three hours. If the metal shell is damaged, the radioactive waste in it is very easy to leak. (2) The spent ion exchange resin is ball-milled into powder, dried at 160°C, and then placed in a 160-liter special steel container. It is then pressed into a thin pancake at 130°C and a pressure of about 3,000 to 4,000 kN. Since no additional resin powder is added and the void volume between the original larger resin particles is reduced, this process can achieve a relatively large volume reduction ratio. However, the disadvantage of this process is that the introduction of ball milling not only increases the number of steps, but also easily causes pollution to the working environment. In order to improve the ball milling efficiency, a certain amount of water needs to be added during the ball milling process, further increasing the amount of radioactive wastewater generated. Summary of the invention

[0005] The object of the present invention is to provide a method for treating radioactive spent ion exchange resin, which has a high volume reduction ratio. Even if the outer packaging is damaged, the resin will not leak radioactivity due to powdering. The process is simple, will not cause pollution to the working environment, and does not require additional water addition.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The invention provides a method for treating radioactive waste ion exchange resin, comprising the following steps: mixing the radioactive waste ion exchange resin and an adhesive, and subjecting the obtained mixture to thermal overpressure; the adhesive is polyurethane, epoxy resin or polyvinyl acetate emulsion; and no non-radioactive contaminated resin powder is added during the mixing.

[0008] Preferably, based on the dry weight of the spent radioactive ion exchange resin, the mass of the adhesive is more than 5% of the mass of the spent radioactive ion exchange resin; when the adhesive is polyvinyl acetate emulsion, the mass of the adhesive is based on the solid content of the polyvinyl acetate emulsion.

[0009] Preferably, the mass of the adhesive is 5-20% of the dry mass of the radioactive spent ion exchange resin.

[0010] Preferably, when the adhesive is polyurethane or epoxy resin, a curing agent is also added during the mixing.

[0011] Preferably, when the adhesive is polyurethane, the curing agent includes glycol, polyol, triethanolamine or MOCA.

[0012] Preferably, when the adhesive is epoxy resin, the curing agent includes an amine curing agent.

[0013] Preferably, before the mixing, the waste radioactive ion exchange resin is dried.

[0014] Preferably, the temperature of the thermal overpressure is 130-180°C.

[0015] Preferably, the thermal overpressure has a pressure of 130 to 300 Bar.

[0016] Preferably, the heat preservation and pressure holding time of the thermal overpressure is 120 to 400 minutes.

[0017] The invention provides a method for treating radioactive waste ion exchange resin, comprising the following steps: mixing the radioactive waste ion exchange resin and an adhesive, and subjecting the obtained mixture to thermal overpressure; the adhesive is polyurethane, epoxy resin or polyvinyl acetate emulsion; and no non-radioactive contaminated resin powder is added during the mixing.

[0018] The present invention does not add non-radioactive contaminated resin powder, and the adhesive only occupies the gaps between the radioactive waste ion exchange resin particles, so the volume reduction ratio is high; the present invention uses the adhesive to bond the non-radioactive resin powder, and the resin block obtained after thermal overpressure has high strength and a compressive strength greater than 30 MPa, which is much higher than the compressive strength requirement of 7 MPa for cement solidified bodies; even if an accident occurs and the resin block is soaked in water, the resin block will not be damaged; in the case of damage to the outer packaging, the resin will not leak radioactivity due to pulverization; and because the resin block will not be pulverized, the inner barrel can be omitted, and the block can be directly placed in a steel barrel outer packaging of a suitable size, thereby reducing the operation process and cost.

[0019] Due to the particularity of radioactive waste ion exchange resin, the adhesive is required to meet the following conditions:

[0020] (1) Strong bonding ability. The ion exchange resin used in nuclear power plants is a mixed bed resin. It has both hydrogen-type cation exchange resin and hydroxide-type anion exchange resin, but it does not have functional groups that can react with adhesives, so the adhesive has high bonding ability requirements.

[0021] (2) Radiation resistance. The radioactivity of spent ion exchange resins may be relatively high, so the adhesive must have strong radiation resistance to prevent it from being decomposed by radiation in a short period of time, resulting in bonding failure.

[0022] (3) High temperature resistance: Because thermal overpressure is carried out at 130°C or even higher, it is necessary to ensure that the adhesive will not decompose at the operating temperature.

[0023] (4) Water resistance: It can prevent radioactive leakage in accident conditions.

[0024] In summary, the present invention selects polyurethane, epoxy resin or polyvinyl acetate emulsion as the adhesive. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a photo of the resin block of Example 4 after being placed in the air for 10 days;

[0026] Figure 2 This is a photo of the resin block in Example 4 after being immersed in water for 54 days;

[0027] Figure 3 This is a photograph of the resin block of Comparative Example 2 after being left in the air for 3 hours. DETAILED DESCRIPTION

[0028] The invention provides a method for treating radioactive waste ion exchange resin, comprising the following steps: mixing the radioactive waste ion exchange resin and an adhesive, and subjecting the obtained mixture to thermal overpressure; the adhesive is polyurethane, epoxy resin or polyvinyl acetate emulsion; and no non-radioactive contaminated resin powder is added during the mixing.

[0029] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known in the art.

[0030] The invention mixes radioactive waste ion exchange resin and adhesive to obtain a mixed material.

[0031] The present invention has no special requirements for the radioactive waste ion exchange resin, and any waste ion exchange resin produced by nuclear power plants known in the art can be used. In the present invention, the polyurethane is preferably a polyurethane trimer. The present invention has no special requirements for the specific models of the epoxy resin and polyvinyl acetate emulsion, and any epoxy resin and polyvinyl acetate emulsion used for adhesives known in the art can be used. In an embodiment of the present invention, the epoxy resin is epoxy resin E51; the solid content of the polyvinyl acetate emulsion is 50%.

[0032] Before the mixing, the present invention preferably dries the spent radioactive ion exchange resin and then cools it to room temperature. In the present invention, the drying temperature is preferably 160° C. The present invention has no special requirements for the drying time, and it only needs to be dried to a constant weight. The present invention dries the spent radioactive ion exchange resin to prevent affecting the bonding effect of the adhesive.

[0033] In the present invention, based on the dry weight of the spent radioactive ion exchange resin, the mass of the binder is preferably 5% or more of the mass of the spent radioactive ion exchange resin, more preferably 5-20%, and most preferably 10%. When the binder is a polyvinyl acetate emulsion, the mass of the binder is based on the solid content of the polyvinyl acetate emulsion.

[0034] In the present invention, the mixing is preferably performed at room temperature.

[0035] In the present invention, when the adhesive is polyurethane or epoxy resin, a curing agent is preferably added during the mixing. When a curing agent is also included, the mixing preferably includes:

[0036] First, the adhesive and the curing agent are mixed under stirring conditions, and then the radioactive non-ion exchange resin is added. The present invention has no special requirements on the stirring rate during the mixing process, as long as the various substances can be mixed evenly.

[0037] In the present invention, when the adhesive is polyurethane, the curing agent preferably includes one or more of diol, polyol, triethanolamine and MOCA; the present invention has no special restrictions on the specific type of the diol, and any diol known in the art for curing agents can be used, such as triethylene glycol and 1,6-hexanediol; the present invention has no special restrictions on the specific type of the polyol, and can be polycaprolactone and polypropylene glycol. When the adhesive is epoxy resin, the curing agent preferably includes an amine curing agent; the present invention has no special requirements on the specific type of the amine curing agent, and any amine curing agent known in the art for epoxy resin curing can be used, such as polyamide, polyethylene imine, and tetraethylene pentamine. In an embodiment of the present invention, when the adhesive is a polyurethane trimer, the curing agent is triethylene glycol, 1,6-hexanediol, polycaprolactone and triethanolamine, or PPG2000 (polypropylene glycol) and triethanolamine; when the adhesive is epoxy resin, the curing agent is polyethylene imine.

[0038] The present invention has no special requirements on the amount of the curing agent, which is determined according to the isocyanate group content of the polyurethane and the epoxy value of the epoxy resin. This is common knowledge in the art and will not be elaborated here.

[0039] In the present invention, when the adhesive is polyvinyl acetate emulsion (EVA emulsion), the mixing preferably includes: mixing the radioactive waste ion exchange resin and the EVA emulsion under stirring conditions, and then drying the obtained mixed wet material. The present invention preferably transfers the mixed wet material to a mold used for thermal overpressure and dries it at 160°C, then cools it to the temperature of thermal overpressure and performs thermal overpressure. The purpose of drying the mixed wet material in the present invention is to remove the moisture carried by the EVA emulsion to prevent adverse effects on thermal overpressure.

[0040] After obtaining the mixed material, the present invention performs thermal overpressure on the mixed material.

[0041] The present invention preferably places the mixed material in a mold for thermal overpressure. The present invention has no special requirements on the size of the mold, and the size well known in the art can be used. In an embodiment of the present invention, the diameter of the mold is 53 mm.

[0042] In the present invention, the temperature of the thermal overpressure is preferably 130-180°C, more preferably 130-150°C, the pressure is preferably 130-300 Bar, more preferably 130-200 Bar, and the heat and pressure holding time is preferably 120-400 minutes, more preferably 150 minutes.

[0043] In the thermal overpressure process of the present invention, the mixed material is solidified to obtain a resin block (also called a resin pancake).

[0044] The method for treating the radioactive spent ion exchange resin provided by the present invention is described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] Weigh 5 grams of polyurethane (MDI trimer), add 1.5 grams of triethylene glycol at room temperature and stir quickly, then add 100 grams of radioactive spent ion exchange resin dried to constant weight at 160°C and cooled to room temperature, stir evenly and transfer to a mold (mold diameter 53 mm), press at 130°C and 130 Bar pressure for 150 minutes. Take out the resin block, and measure the geometric dimensions of the resin block to be 45 mm in height, 53.4 mm in diameter, 3.69 in volume reduction ratio, and 32 MPa in compressive strength.

[0047] In the present invention, the volume reduction ratio is equal to the solid volume of the radioactive waste ion exchange resin before treatment divided by the volume of the resin block obtained after treatment. The compressive strength is tested according to the method specified in the standard GB 14569.1-2011 "Performance requirements for low and medium level radioactive waste solidification bodies - cement solidification bodies".

[0048] Example 2

[0049] Weigh 10 grams of polyurethane (MDI trimer), add 1.15 grams of 1,6-hexanediol at room temperature, quickly mix well, then add 110 grams of radioactive spent ion exchange resin dried to constant weight at 160°C and cooled to room temperature, stir well and transfer to a mold (mold diameter 53mm), press at 130°C and 130Bar pressure for 150 minutes. Take out the resin block, and measure the geometric dimensions of the resin block to be 50mm high, 53.4mm in diameter, 3.65 in volume reduction ratio, and 31.7 MPa in compressive strength.

[0050] Example 3

[0051] Weigh 5 grams of epoxy resin E51, add 1.8 grams of polyethyleneimine, stir evenly, pour in 100 grams of radioactive spent ion exchange resin dried to constant weight at 160°C and cooled to room temperature, stir evenly, then transfer the resin-binder mixture to a mold (mold diameter 53 mm), and then press at 130°C and 130 Bar pressure for 150 minutes. Take out the resin block, and measure the geometric dimensions of the resin block to be 48.7 mm in height, 53.0 mm in diameter, 3.63 in volume reduction ratio, and 34.5 MPa in compressive strength.

[0052] Example 4

[0053] Weigh 100 grams of radioactive waste ion exchange resin that has been dried to constant weight at 160°C and cooled to room temperature, add 10 grams of EVA emulsion (solid content 50%), stir evenly, transfer to a mold, dry again at 160°C to remove the moisture in the EVA emulsion, then naturally cool to 130°C, and press at 130°C and 130 Bar pressure for 150 minutes. Take out the resin block, and measure the geometric dimensions of the resin block to be 46.6 mm in height, 53.2 mm in diameter, 3.59 in volume reduction ratio, and 31.2 MPa in compressive strength. After the resin block has been placed in the air for 10 days, the pressed block is still intact, as shown in the figure. Figure 1 As shown; after 54 days of immersion in water, the briquettes are still intact and do not fall apart. Figure 2 shown.

[0054] Example 5

[0055] Weigh 18 grams of polycaprolactone, add 10 grams of polyurethane (MDI trimer), melt at 80°C and stir evenly. Continue to stir the mixture at 80°C for 2 hours to allow the polycaprolactone and polyurethane to fully react. Then add 100 grams of resin that has been dried to constant weight and cooled to room temperature, stir evenly, then add 1 gram of triethanolamine and continue to stir evenly. Transfer the mixture to a mold and press at 130°C and 130Bar pressure for 150 minutes. Take out the resin block and measure the geometric dimensions to be 52 mm high, 53.4 mm in diameter, 3.1 in volume reduction ratio, and 29.3 MPa in compressive strength.

[0056] Example 6

[0057] Weigh 15 grams of PPG2000 (polypropylene glycol), add 6 grams of polyurethane (MDI trimer), stir at 80°C for 2 hours to allow PPG2000 and polyurethane to fully react. Then add 100 grams of resin that has been dried to constant weight and cooled to room temperature, stir evenly, then add 1 gram of triethanolamine, continue to stir evenly, transfer the mixture to a mold, and press at 130°C and 130 Bar pressure for 150 minutes. Take out the resin block, and measure the geometric dimensions to be 48 mm in height, 53.4 mm in diameter, 3.46 in volume reduction ratio, and 30.3 MPa in compressive strength.

[0058] Comparative Example 1

[0059] Weigh 100g of radioactive spent ion exchange resin dried to constant weight at 160℃ and cooled to room temperature, add 10g of dolphin 1352 emulsion as a binder, stir evenly, transfer to a mold, and press at 130℃ and 130Bar pressure for 200 minutes. After taking out, it is found that dolphin 1352 does not solidify under the pressing conditions, and no formed resin block can be obtained.

[0060] Comparative Example 2

[0061] Weigh 280g of radioactive waste ion exchange resin, add 80g of resin powder (the ratio currently used in nuclear power plants), dry at 160℃ to constant weight, and then press at 130℃ and 130Bar pressure for 400 minutes. Take out the pressed block, because there is no adhesive, the pressed block is very fragile. After leaving the pressed block in the air for 3 hours, the pressed block is completely powdered (such as Figure 3 shown).

[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for treating spent radioactive ion exchange resin, characterized in that: The method comprises the following steps: mixing radioactive waste ion exchange resin and adhesive, and subjecting the obtained mixture to thermal overpressure; the adhesive is polyurethane, epoxy resin or polyvinyl acetate emulsion; and no non-radioactive contaminated resin powder is added during the mixing; Before the mixing, the spent radioactive ion exchange resin is dried; The mass of the adhesive is more than 5% of the mass of the radioactive spent ion exchange resin, based on the dry weight of the radioactive spent ion exchange resin; when the adhesive is a polyvinyl acetate emulsion, the mass of the adhesive is based on the solid content of the polyvinyl acetate emulsion; When the adhesive is polyurethane or epoxy resin, a curing agent is also added during the mixing; The thermal overpressure has a pressure of 130 to 300 Bar.

2. The processing method according to claim 1, characterized in that: The mass of the adhesive is 5-20% of the dry mass of the radioactive waste ion exchange resin.

3. The processing method according to claim 1, characterized in that: When the adhesive is polyurethane, the curing agent includes one or more of diol, polyol, triethanolamine and MOCA.

4. The processing method according to claim 1, characterized in that: When the adhesive is epoxy resin, the curing agent includes an amine curing agent.

5. The processing method according to claim 1, characterized in that: The temperature of the thermal overpressure is 130-180°C.

6. The processing method according to claim 1, characterized in that: The heat preservation and pressure holding time of the thermal overpressure is 120 to 400 minutes.

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