CN108520790B - A kind of solidification method of fluorine-containing radioactive waste liquid - Google Patents

Abstract

The present invention provides a method for solidifying fluorine-containing radioactive waste liquid, comprising the following steps: S1, providing fluorine-containing radioactive waste liquid, the fluorine-containing radioactive waste liquid includes fluorine and radioactive waste liquid; S2, mixing cement ash with the fluorine-containing radioactive waste liquid The waste liquid is mixed to form a cement slurry, and the cement ash includes: KH ₂ PO ₄ , dead-burned MgO, additives and borax; S3, the cement slurry is solidified, initially set and finally set to form a first cement solidified body; S4, the The first cement solidified body is cured to form a second cement solidified body. The second cement solidified body has high compressive strength and can effectively encapsulate radioactive elements and fluoride ions to meet the requirements of final disposal.

Description

A kind of solidification method of fluorine-containing radioactive waste liquid

technical field

The present invention relates to a solidification method of radioactive waste liquid, and more particularly to a solidification method applied to fluorine-containing radioactive waste liquid.

Background technique

The molten salt reactor uses molten fluorine salt as the main coolant, and the fuel of the liquid molten salt reactor itself is dissolved in the high temperature molten salt of fluoride. The development and operation of molten salt reactors will generate radioactive wastes with fluorine salts as the main component. Various types of radioactive wastes will also be generated during the dry reprocessing of spent fuel, fuel salt analysis and testing, and the separation and recovery of fuel added salts. Radioactive waste must include fluorine-containing radioactive waste. In order to ensure the safety of the surrounding public and reduce the pollution of the waste liquid to the environment, it is necessary to reduce the volume and solidify the fluorine-containing radioactive waste liquid to make it meet the requirements of safe temporary storage.

When Portland cement solidifies the fluorine-containing radioactive waste liquid with high fluoride ion concentration, the initial setting time of the cement slurry will be greatly reduced. When the fluoride ion concentration is 8wt%, the initial setting time is only 2-3min; after adding retarder (borax) As a result, the compressive strength of the cement solidified body is greatly reduced, which cannot meet the requirements of the national standard.

Therefore, new cement formulations and methods are urgently needed for the solidification of fluorine-containing radioactive waste liquids to solve the problem of short initial setting time of cement slurry. At the same time, the cement solidified body has high compressive strength and can effectively encapsulate radioactive elements and fluoride ions to meet the requirements of final disposal.

SUMMARY OF THE INVENTION

In order to solve the above problems such as short solidification initial setting time of fluorine-containing radioactive waste liquid cement, the present invention provides a solidification method for fluorine-containing radioactive waste liquid.

The present invention provides a method for solidifying fluorine-containing radioactive waste liquid, comprising the following steps: S1, providing fluorine-containing radioactive waste liquid, the fluorine-containing radioactive waste liquid includes fluorine and radioactive waste liquid; S2, mixing cement ash with the fluorine-containing radioactive waste liquid The waste liquid is mixed to form a cement slurry, and the cement ash includes KH ₂ PO ₄ , burnt MgO, additives and borax; S3, the cement slurry is solidified, initially set and finally set to form a first cement solidified body; S4, the first cement solidified body is formed; A cement solidified body is cured to form a second cement solidified body.

Wherein, step S3 specifically includes curing the first cement solidified body in air to form a second cement solidified body.

Preferably, step S3 specifically includes curing the first cement solidified body in the air for 28 days to form the second cement solidified body. Wherein, step S2 includes: S21 , mixing cement ash with fluorine-containing radioactive waste liquid; S22 , first stirring slowly for 20s-40s, and then rapidly stirring for 80-100s to obtain a uniform cement slurry.

Preferably, in step S21, the weight ratio of the cement ash to the fluorine-containing radioactive waste liquid is 1:0.18-0.19.

Preferably, the initial setting time of the cement is 20-30 minutes, and the final setting time is 1-2 minutes.

Preferably, the weight ratio of KH ₂ PO ₄ , dead-burned MgO, additives and borax is 0.25:1:0-0.1:0.1-0.15. The use of phosphate instead of silicate prolongs the initial setting time of the cement slurry, enhances the compressive strength of the second cement solidified body, and has better encapsulation properties for fluoride ions. The use of dead-fired MgO increases the reactivity of the cement ash. The use of borax prolongs the initial setting time of the cement slurry. The use of additives improves the compressive strength of the second cement solidified body.

Preferably, the additive includes at least one of quartz sand, zeolite, silica fume and fly ash.

Preferably, the weight percentage of fluorine in the fluorine-containing radioactive waste liquid is 0.01-12%.

Preferably, the weight percentage of fluorine in the fluorine-containing radioactive waste liquid is 2%.

Preferably, the weight percentage of fluorine in the fluorine-containing radioactive waste liquid is 12%.

Preferably, the fluorine-containing radioactive waste liquid contains at least one of Cs ⁺ , Sr ²⁺ and Co ²⁺ .

Preferably, the radioactive waste liquid contains radioactive element Cs with a mass content of 0-4.412 g/L.

Preferably, the radioactive waste liquid contains radioactive element Sr with a mass content of 0-4.601 g/L.

Preferably, the radioactive waste liquid contains the radioactive element Co with a mass content of 0-4.305 g/L.

The invention provides a solidification method for fluorine-containing radioactive waste liquid, which solves the problem of short initial setting time of cement slurry. At the same time, the cement solidified body has high compressive strength and can effectively encapsulate radioactive elements and fluoride ions to meet the requirements of final disposal.

Description of drawings

Fig. 1 is the variation diagram of the leaching rate of radioactive elements 0-42d in the second cement solidified body corresponding to Example 1;

Fig. 2 is the cumulative leaching rate variation diagram of radioactive elements 0-42d in the second cement solidified body corresponding to Example 1;

Fig. 3 is the average leaching concentration variation diagram of F ^- 0-42d in the corresponding second cement solidified body of Example 1;

Figure 4 is a graph showing the change in the leaching rate and cumulative leaching ratio of F ^- 0-42d in the second cement solidified body corresponding to Example 1.

Detailed ways

The technical solutions of the present invention will be described in detail below in conjunction with the specific embodiments of the present invention, but the following examples are only for understanding the present invention, but not for limiting the present invention, the examples in the present invention and the features in the examples Combinable with each other, the invention can be implemented in many different ways as defined and covered by the claims.

Example 1

A method for solidifying a fluorine-containing radioactive waste liquid provided according to the present invention includes step S1, and a fluorine-containing radioactive waste liquid is provided, wherein the fluorine-containing radioactive waste liquid includes fluorine and radioactive waste liquid.

The radioactive waste liquid is prepared by mixing CsNO ₃ , Sr(NO ₃ ) ₂ and Co(NO ₃ ) ₂ solutions, and the fluorine is provided by NaF added to the radioactive waste liquid. In this way, the fluorine-containing radioactive waste liquid was prepared by using CsNO ₃ , Sr(NO ₃ ) ₂ , Co(NO ₃ ) ₂ and NaF solution to form a simulated radioactive waste liquid, wherein the contents of radioactive elements Sr, Cs and Co were 4.412g/g/ L, 4.601g/L, 4.305g/L.

A method for solidifying fluorine-containing radioactive waste liquid provided by the present invention includes step S2, adding cement ash and 44.4 mL of fluorine-containing radioactive waste liquid into a cement slurry mixer, the weight ratio of the two being 1:0.185, and stirring slowly first 30s, then quickly stir for 90s to get a uniform grout.

According to the solidification method of fluorine-containing radioactive waste liquid provided by the present invention, the solidification method includes step S3: injecting the obtained cement slurry into a plastic mold of Φ50× ^50mm3 for solidification, obtaining a first solidified cement body through initial setting and final setting, and curing it The second cement solidified body was obtained after 28 days.

Cement ash includes KH ₂ PO ₄ , dead burned MgO, additives and borax, wherein the additives include quartz sand, zeolite, silica fume and fly ash. In this example, according to the formula in Table 1, a cement slurry mixer was used to mix the above-mentioned cement ash components and 2.12 g of NaF solid uniformly. And in this embodiment, the type of dead-fired MgO is 200 mesh, thereby increasing the reactivity of cement ash; the type of quartz sand is 800 mesh, so as to reduce the porosity of the first and second cement solidified bodies formed.

The cement slurry, the first cement solidified body and the second cement solidified body were characterized by the following methods.

(1) Characterization of cement slurry: Observe the fluidity of cement slurry and whether there is delamination. Record the initial setting time and final setting time of cement.

Specifically, in this embodiment, the fluidity of the cement slurry is moderate, and there is no delamination phenomenon. The initial setting time of the cement slurry is about 30 minutes, and the initial setting time is longer, and the final setting is 1-2 minutes after the initial setting.

(2) Characterization of the first cement solidified body: The appearance of the first cement solidified body was observed.

Specifically, in this embodiment, the first cement solidified body has a complete appearance, no cracks, and no free liquid on the surface.

(3) The leaching test of the second cement solidified body: the leaching performance test is carried out according to the requirements of GBT 7023-2011.

Specifically, in this embodiment, the compressive strength of the second cement solidified body is greater than 50 MPa, which is far greater than the requirement of the national standard of 7 MPa. After soaking in deionized water for 42 days, the appearance of the second cement solidified body has no obvious cracks or cracks, and the compressive strength loss is 12.8%, which meets the national standard of the second cement solidified body after soaking. The loss of compressive strength does not exceed 25%. Requirements, high compressive strength.

Referring to Figures 1 and 2, in this example, the 42d leaching rate of Sr ²⁺ in the second cement solidified body is 1.96×10 ^-5 cm/d, and the cumulative leaching rate is 6.10×10 ^-4 cm; the 42d leaching rate of Cs ⁺ The leaching rate was 6.46×10 ^-4 cm/d, and the cumulative leaching rate was 5.80×10 ^-2 cm; the 42-day leaching rate of Co ²⁺ was 8.29×10 ^-8 cm/d, and the cumulative leaching rate was 5.57×10 ^-5 cm , the result meets the limit value of GB14569.1-2011, forming an effective package for radioactive elements.

Referring to FIG. 3 , in this example, the highest average leaching concentration of fluoride ions in the second cement solidified body is 35 mg/L, which is far lower than the limit of 100 mg/L in GB 5085.3-2007.

Referring to FIG. 4 , the 42d leaching rate of fluoride ions in the second cement solidified body in this example is 1.74×10 ⁻³ cm/d, which is lower than the 42d leaching rate of Portland cement solidified in the prior art, which is 4.59× 10 ^-3 cm/d. The 42d leaching amount of fluoride ions accounted for 10.68% of the total fluoride ions in the cement solidified sample, and the remaining 89.32% of the fluoride ions were encapsulated in the second cement solidified body, which effectively encapsulated fluoride ions.

Example 2 - Example 12

The experimental process is basically the same as that of Example 1, except that the amount of each component used in each example is different, as shown in Table 1 below.

In Example 2-Example 12, the fluidity of each cement slurry is moderate, and there is no delamination phenomenon. The initial setting time of each cement slurry is between 20min and 30min, and the final setting is within 1 to 2 minutes after the initial setting, and the initial setting time is longer.

Each first cement solidified body has a complete appearance and no cracks.

The compressive strength of each second cement solidified body is greater than 50MPa, which conforms to the limit value of the national standard GB14569.1-2011, and the compressive strength is relatively high. The 42d leaching rate of Co ²⁺ of each second cement solidified body is lower than 1.54×10 ^-7 cm/d, the 42d leaching rate of Sr ²⁺ is lower than 2.63×10 ^-5 cm/d, and the 42d leaching rate of Cs ⁺ The rate is lower than 6.92×10 ^-4 cm/d, which conforms to the limit value of GB 14569.1-2011, which improves the encapsulation ability of radioactive elements. The leaching concentration of fluoride ions in each second cement solidified body is lower than 100mg/L, which conforms to the limit value of GB5085.3-2007, and forms an effective encapsulation for fluoride ions.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Various changes can be made to the above-mentioned embodiments of the present invention. Even not according to the method provided by the present invention. All simple and equivalent changes and modifications made according to the claims and descriptions of the present application shall fall within the protection scope of the claims of the present invention. What is not described in detail in the present invention is conventional technical content.

Claims (2)

1. a solidification method of fluorine-containing radioactive waste liquid, is characterized in that, described solidification method comprises the following steps: S1, providing fluorine-containing radioactive waste liquid, the fluorine-containing radioactive waste liquid includes fluorine and radioactive waste liquid, the weight percentage of fluorine in the fluorine-containing radioactive waste liquid is 0.01-12%, and the radioactive waste liquid contains Cs ⁺ , Sr ²⁺ and Co ²⁺ ; the contents of the Sr ²⁺ , Cs ⁺ and Co ²⁺ are 4.412g/L, 4.601g/L, 4.305g/L respectively; S2, mix cement ash with a weight ratio of 1:0.18-0.19 and the fluorine-containing radioactive waste liquid, first slowly stir for 20s-40s, and then rapidly stir for 80-100s to form a uniform cement slurry, the cement ash includes KH ₂ PO ₄ , dead-burned MgO and borax, the weight ratio of the KH ₂ PO ₄ , dead-burned MgO and borax being 0.25:1:0.1-0.15; S3, the cement slurry is formed into a first cement solidified body through solidification, initial setting and final setting, and the initial setting time is 20-30min, and the final setting time is 1-5min; S4, curing the first cement solidified body to form a second cement solidified body. 2 . The curing method according to claim 1 , wherein the fluorine-containing radioactive waste liquid is a simulated radioactive waste liquid. 3 .

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