Cement fixing material and application thereof in fixing radioactive solid waste

Abstract

The invention belongs to the technical field of nuclear waste treatment, and particularly relates to a cement fixing material and application thereof in fixing radioactive solid waste. The cement fixing material provided by the invention comprises the following components in parts by weight: 20-46 parts of a cementing material; 39 to 55 parts of fine aggregate; 5-25 parts of a mineral admixture; 0.2 to 0.7 part of a functional auxiliary agent; the cementing material comprises Portland cement and sulphoaluminate cement, the fine aggregate comprises sand, the mineral admixture comprises slag, metakaolin and fly ash, the functional auxiliary agent comprises a water reducing agent, a retarder, a thickening agent, a waterproof agent and a volume stabilizer, and the volume stabilizer comprises anion exchange resin powder and / or sulfamic acid. The cement fixing material provided by the invention not only meets the current national standard when being used for fixing radioactive wastes, but also has the characteristics of long service life, safety and reliability; and meanwhile, good operability performance is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear waste treatment, and particularly relates to a cement fixing material and its application in fixing radioactive solid waste. Background Art

[0002] Solid waste with low and medium radioactive levels (hereinafter referred to as medium and low-level radioactive solid waste) exists in the operation and decommissioning stages of nuclear facilities. This type of waste has a large output, high decontrol difficulty, and complex minimization processes. Currently, cement fixation is generally used for treatment. National standards GB41930-2022 "Characteristics Identification of Low-Level Radioactive Waste Packages - Cement Solidified Bodies" and national nuclear industry standard EJ1186-2005 "Characteristics Identification of Radioactive Waste Bodies and Waste Packages" have formulated relatively unified requirements for the mechanical properties and durability of the fixation media and fixed bodies for medium and low-level radioactive solid waste: the fluidity of cement mortar is not less than 310 mm, the 28-day compressive strength is not less than 60 MPa, and the 28-day chloride ion migration charge is not more than 2500 C.

[0003] With the improvement of radioactive waste management requirements, the above indicators can no longer meet the control of the comprehensive performance of the cement mortar fixation medium and the fixed body. The reasons are as follows: (1) Cement-based materials will shrink during hardening. Medium and low-level radioactive waste fixed bodies are produced in units of steel barrels or steel boxes. After the cement fixation medium is poured into the above containers, under the action of chemical shrinkage and drying shrinkage of the cement-based materials, phenomena such as the separation of the fixed body from the container wall and cracking of the fixed body along the edges and corners of the waste will occur. (2) The production of cement fixed bodies requires a long operation time. If the fluidity loss is too large during the operation, the pouring work of the cement fixed body will be limited, and at the same time, the cement fixation medium will not be able to fill and fix the radioactive waste; (3) For cement fixation media with high fluidity requirements, from the end of mixing to the hardening period, there is often a problem of lagging bleeding of water and light substances. After the lagging bleeding phenomenon occurs, the radioactive nuclide ions attached to the radioactive waste will migrate to the surface of the fixed body along the bleeding channels. (4) For some metal wastes that are easily corroded, conventional radioactive solid waste fixation materials cannot provide an effective anti-corrosion environment for the corrosion of metal wastes during the subsequent disposal of the fixed body. After the metal corrodes, its volume will increase significantly, and the expansion stress generated by the volume increase will cause the cement fixed body to crack.

[0004] In summary, currently, it is no longer possible to safely, reliably, and permanently fix radioactive solid waste only by meeting the three indicators of initial fluidity, 28-day compressive strength, and 28-day chloride ion permeability resistance. Summary of the Invention

[0005] The object of the present invention is to provide a cement fixing material and its application in fixing radioactive solid waste. The cement fixing material provided by the present invention solves the technical problem that it is impossible to safely, reliably and permanently fix radioactive solid waste during the fixing treatment of radioactive solid waste. When using the cement fixing material provided by the present invention to fix radioactive waste, it not only meets the current national standards, but also has the characteristics of long service life, safety and reliability; at the same time, it also has good operability.

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

[0007] The present invention provides a cement fixing material, which comprises the following raw materials in parts by mass for preparation: 20-46 parts of a gelling material; 39-55 parts of fine aggregate; 5-25 parts of mineral admixture; 0.2-0.7 parts of functional additives; the gelling material comprises portland cement and sulfoaluminate cement, the fine aggregate comprises sand, the mineral admixture comprises slag, metakaolin and fly ash, the functional additives comprise a water reducing agent, a setting retarder, a thickening agent, a waterproof agent and a volume stabilizer, and the volume stabilizer comprises an anion exchange resin powder and / or sulfamic acid.

[0008] Preferably, the gelling material of the cement fixing material comprises the following raw materials in parts by mass for preparation:

[0009] 20-40 parts of portland cement and 2-6 parts of sulfoaluminate cement.

[0010] Preferably, the portland cement comprises one or more of ordinary portland cement, pure portland cement, slag portland cement, pozzolanic portland cement and fly ash portland cement;

[0011] The sulfoaluminate cement comprises one or more of crack-resistant double-quick sulfoaluminate cement, high belite sulfoaluminate cement and low-alkali sulfoaluminate cement.

[0012] Preferably, the mineral admixture of the cement fixing material comprises the following raw materials in parts by mass for preparation:

[0013] 4-6 parts of slag, 11-14 parts of fly ash, 1-3 parts of metakaolin.

[0014] Preferably, the slag is S95-S105 grade slag; the fly ash is grade I-III fly ash; the metakaolin is calcined from kaolin at 600-800 °C.

[0015] Preferably, the sand is artificial sand and / or natural sand;

[0016] The sand has a continuous grading of 10-220.

[0017] Preferably, the functional additives of the cement fixing material include the following raw materials in parts by mass for preparation:

[0018] Water reducing agent: 0.14 - 0.5 parts, setting retarder: 0.02 - 0.05 parts, thickening agent: 0.02 - 0.04 parts, waterproof agent: 0.015 - 0.04 parts, volume stabilizer: 0.015 - 0.05 parts.

[0019] Preferably, the water reducing agent is a polycarboxylate water reducing agent; the setting retarder includes one or more of citric acid, tartaric acid and boric acid; the thickening agent is a cellulose ether; the waterproof agent is silicone and / or diatomaceous earth.

[0020] The present invention provides an application of the cement fixing material described in the above technical solution in fixing radioactive solid waste.

[0021] Preferably, the application includes the following steps:

[0022] Mix the cement fixing material described in the above technical solution with water to obtain a cement fixing medium;

[0023] Inject the cement fixing medium into a container containing radioactive solid waste to be fixed, and then carry out curing and disposal in sequence.

[0024] The present invention provides a cement fixing material, which includes the following raw materials in parts by mass for preparation: 20 - 46 parts of cementitious material; 39 - 55 parts of fine aggregate; 5 - 25 parts of mineral admixture; 0.2 - 0.7 parts of functional additive; the cementitious material includes portland cement and sulfoaluminate cement, the fine aggregate includes sand, the mineral admixture includes slag, metakaolin and fly ash, the functional additive includes water reducing agent, setting retarder, thickening agent, waterproof agent and volume stabilizer, and the volume stabilizer includes anion exchange resin powder and / or sulfamic acid. The cement fixing material provided by the present invention has the following beneficial technical effects:

[0025] In terms of the cementitious material, the present invention uses a compound of portland cement and sulfoaluminate cement. Cement solid bodies generally have radioactivity, and shrinkage stress and temperature stress cannot be reduced by measures such as watering curing or laying electric blankets for cooling / heat preservation. Shrinkage and cracking are extremely serious quality problems of cement solid bodies and are irreversible. This is because once cracks appear in the cement solid body due to shrinkage, its chloride ion permeability resistance will decrease severely, leading to an increased probability of the radionuclides attached to the radioactive waste migrating into the environment. And for the cement solid bodies produced by using portland cement alone, the occurrence frequency of shrinkage and cracking problems is very high. Therefore, the present invention uses a compound of portland cement and sulfoaluminate cement as the cementitious material. Among them, portland cement can provide the early and medium-term compressive strength of the cement, which is beneficial to the development of the mechanical properties of the cement solid body. At the same time, sulfoaluminate cement is used in combination. This cement has an expansion property and can compensate for the shrinkage phenomenon during the hardening of portland cement, making the volume of the cement solid body more stable.

[0026] In terms of mineral admixtures, the present invention uses a compound of slag, fly ash, and metakaolin. Slag can participate in cement hydration to generate hydration products such as calcium silicoaluminate, and at the same time can reduce the calcium-silicon ratio of calcium silicate hydrate, the hydration product of cement, increase the chain length of calcium silicate hydrate, and improve the stability of the hydration products; fly ash can significantly reduce the maximum temperature rise of the cement fixing material and further undergo a secondary hydration reaction with calcium hydroxide, the hydration product of cement, to generate calcium silicate hydrate to fill the microstructure; metakaolin can participate in the hydration reaction to generate denser calcium silicoaluminate and calcium silicate hydrate, greatly improving the density and chloride ion permeability resistance of the cement solid body. The present invention realizes the technical effects of adjusting the hydration products, reducing the maximum temperature rise, and strengthening the chloride ion permeability resistance through the ternary compound of the above materials.

[0027] In terms of functional additives, the present invention uses a water reducer, a retarder, a thickening agent, a waterproof agent, and a volume stabilizer. The volume stabilizer includes anion exchange resin powder and / or aminosulfonic acid. The present invention uses anion exchange resin powder and / or aminosulfonic acid as the volume stabilizer in the plastic stage of the cement fixing medium formed by the cement fixing material, and at the same time combines the above other functional additives, which can effectively improve the fluidity, fluidity retention ability, workability, stability, and micro-expansion property of the solid body.

[0028] In summary, the cement fixing material provided by the present invention, through the compounding of the above-mentioned preparation raw materials, has the characteristics of ideal fluidity retention, high stability, good durability, and excellent strength and durability. The cement fixing material provided by the present invention is tested according to GB41930 "Characteristics Identification of Low-Level Radioactive Waste Packages - Cement Solidified Bodies", EJ1186 "Characteristics Identification of Radioactive Waste Bodies and Waste Packages", GB8076 "Concrete Admixtures", GB / T50448 "Technical Specification for Application of Cementitious Grouting Materials", GB / T2419 "Test Method for Fluidity of Cement Mortar", GB / T17671 "Test Method for Strength of Cement Mortar (ISO Method)", GB / T50082 "Standard for Test Methods of Long-Term Performance and Durability of Concrete", GB / T 50080 "Standard for Test Methods of Properties of Ordinary Concrete Mixtures", and EJ914 "Concrete Containers for Low- and Medium-Level Radioactive Solid Wastes". Among them: the fluidity of the cement fixing material is between 340 and 370 mm, and the fluidity at 30 min is between 310 and 370 mm; there is no bleeding in the fixed medium; the vertical expansion rate at 3 h is between 0.10 and 0.50, and the difference between the expansion values at 24 h and 3 h is between 0.02 and 0.30; the compressive strength at 1 d is between 30 and 55 MPa, the compressive strength at 3 d is between 45 and 70 MPa, and the compressive strength at 28 days is between 80 and 100 MPa; the chloride ion permeability at 28 d is less than 1000 C; it has no rusting effect on metals such as steel bars, steel drums, and steel boxes. The above performances not only meet the requirements of GB41930 "Characteristics Identification of Low-Level Radioactive Waste Packages - Cement Solidified Bodies" and EJ1186-2005 "Characteristics Identification of Radioactive Waste Bodies and Waste Packages", but also have good operability and long-term durability. Specific Embodiments

[0029] The present invention provides a cement fixing material, which comprises the following preparation raw materials in parts by mass: 20 - 46 parts of a cementitious material; 39 - 55 parts of fine aggregate; 5 - 25 parts of mineral admixture; 0.2 - 0.7 parts of functional additives; the fine aggregate includes sand, the mineral admixture includes slag, metakaolin, and fly ash, the functional additives include a water reducer, a retarder, a thickening agent, a waterproof agent, and a volume stabilizer, and the volume stabilizer includes an anion exchange resin powder and / or sulfamic acid.

[0030] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well-known to those skilled in the art.

[0031] In terms of parts by mass, the raw materials for preparing the cement fixing material provided by the present invention include 20 to 46 parts of a cementitious material. In the present invention, the cementitious material includes portland cement and sulfoaluminate cement. The portland cement preferably includes one or more of ordinary portland cement, pure portland cement, slag portland cement, pozzolanic portland cement, and fly ash portland cement, and can be ordinary portland cement (P·O42.5) in the examples. The sulfoaluminate cement preferably includes one or more of crack-resistant double-fast sulfoaluminate cement, high belite sulfoaluminate cement, and low-alkali sulfoaluminate cement, and is preferably crack-resistant double-fast sulfoaluminate cement. The sulfoaluminate cement used in the examples can be sulfoaluminate cement (42.5).

[0032] In the present invention, the cementitious material of the cement fixing material preferably includes the following raw materials in parts by mass: 20 to 40 parts of portland cement and 2 to 6 parts of sulfoaluminate cement; preferably 25 to 35 parts of portland cement and 3 to 5 parts of sulfoaluminate cement; in the examples, the mass part of the portland cement can be 33 parts, and the mass part of the sulfoaluminate cement can be 4 parts.

[0033] Based on the mass parts of the gel material, the raw materials for preparing the cement fixing material provided by the present invention include 39 to 55 parts of fine aggregate, preferably 40 to 52 parts, and more preferably 45 to 50 parts. It can be 50 parts in the examples. In the present invention, the fine aggregate includes sand. The sand is preferably artificial sand and / or natural sand, and can be artificial sand in the examples. The artificial sand is preferably obtained by successively crushing, water screening, first drying, water quenching, heavy hammer crushing, jaw crushing, iron removal, reverse flotation, pickling, water washing, second drying, secondary iron removal, and screening of the original stone. The sand is preferably in a continuous gradation of 10 to 220.

[0034] Based on the mass parts of the gel material, the raw materials for preparing the cement fixing material provided by the present invention include 5 to 25 parts of mineral admixture. In the present invention, the mineral admixture includes slag, metakaolin, and fly ash. The slag is preferably slag of grades S95 to S105, and more preferably S95 grade granulated blast furnace slag. The fly ash is preferably fly ash of grades I to III, and more preferably dry-discharged fly ash with an activity index ≥ 85%. The metakaolin is preferably calcined from kaolin at 600 to 800 °C, and more preferably metakaolin with an activity index ≥ 105%.

[0035] In the present invention, the mineral admixture of the cement fixing material preferably includes the following raw materials in parts by mass: 4 to 6 parts of slag, 11 to 14 parts of fly ash, and 1 to 3 parts of metakaolin; preferably 4 to 5 parts of slag, 10 to 12 parts of fly ash, and 1 to 2 parts of metakaolin; in the examples, the mass part of the slag can be 4 parts, the mass part of the fly ash can be 8 parts, and the mass part of the metakaolin can be 1 part.

[0036] Based on the mass parts of the gel material, the raw materials for preparing the cement fixing material provided by the present invention include 0.2 - 0.7 parts of a functional additive, preferably 0.2 - 0.5 parts, more preferably 0.2 - 0.4 parts, and it can be 0.287 parts in the examples. In the present invention, the functional additive includes a water reducing agent, a retarder, a thickening agent, a waterproofing agent, and a volume stabilizer. The water reducing rate of the water reducing agent is preferably ≥20%. The water reducing agent is preferably a polycarboxylate water reducing agent, more preferably a polycarboxylate-based high-performance water reducing agent, and the water reducing rate of the polycarboxylate-based high-performance water reducing agent is preferably ≥20%. By using a water reducing agent with a water reducing rate ≥20% in the present invention, the water demand during the mixing of the cement fixing material can be significantly reduced, and at the same time, the mixed cement fixing medium and the hardened cement fixing body have good fluidity and strength. The retarder preferably includes one or more of citric acid, tartaric acid, and boric acid. The tartaric acid is preferably L-tartaric acid. The retarder is more preferably citric acid and tartaric acid, and the mass ratio of citric acid to tartaric acid is preferably (1 - 5):(5 - 1), and it can be 7:3 in the examples. The retarder is more preferably citric acid and tartaric acid. Among them, citric acid has a good effect on regulating the setting time of sulfoaluminate cement, and tartaric acid can stabilize the setting time of the Portland cement - sulfoaluminate cement composite system, playing a stabilizing role in the setting time regulation effect of citric acid. At the same time, citric acid and tartaric acid have a rust inhibition effect, which can assist in improving the rust prevention ability of the radioactive cement fixing material. The thickening agent is preferably a cellulose ether, more preferably a hydroxypropyl cellulose ether, and the viscosity of the hydroxypropyl cellulose ether is 400 - 2000 Pa·s, and it can be 600 Pa·s in the examples. The hydroxypropyl cellulose ether with a viscosity of 400 - 2000 Pa·s has a low air content and a moderate viscosity. It can not only ensure the stable distribution of cement, mineral admixtures, and sand in the system, but also retain free water, improving the stability of the cement fixing material and reducing the bleeding problem of the cement fixing material. The waterproofing agent is preferably silicone and / or diatomaceous earth, more preferably silicone. The waterproof effect of silicone is stable, which can improve the hydrophobicity of the cement fixing matrix, further improve the impermeability of the cement fixing body obtained from the cement fixing material, and is beneficial to the exertion of the effect of mineral admixtures. The volume stabilizer includes an anion exchange resin powder and / or aminosulfonic acid. The anion exchange resin powder is preferably a strongly basic macroporous anion exchange resin powder. The fineness of the anion exchange resin powder is preferably ≥200 mesh. The anion exchange resin powder used in the examples was purchased from Dow Chemical, and the product model is IRN78. The volume stabilizer has the characteristic of gradually releasing gas under alkaline conditions. As the hydration reaction occurs, the gas generated by the reaction of the volume stabilizer with the cement hydration products will play a role in filling the volume of the cement fixing medium in the plastic stage, further reducing the plastic shrinkage degree of the cement fixing medium.

[0037] In the present invention, the functional aids of the cement fixing material preferably include the following raw materials for preparation in parts by mass: water reducing agent 0.14 - 0.5 parts, setting retarder 0.02 - 0.05 parts, thickening agent 0.02 - 0.04 parts, waterproof agent 0.015 - 0.04 parts, volume stabilizer 0.015 - 0.05 parts; preferably, the water reducing agent is 0.14 - 0.3 parts, the setting retarder is 0.03 - 0.04 parts, the thickening agent is 0.03 - 0.04 parts, the waterproof agent is 0.02 - 0.035 parts, and the volume stabilizer is 0.02 - 0.04 parts; more preferably, the water reducing agent is 0.14 - 0.2 parts, the setting retarder is 0.03 - 0.04 parts, the thickening agent is 0.03 - 0.04 parts, the waterproof agent is 0.02 - 0.03 parts, and the volume stabilizer is 0.03 - 0.04 parts; in the examples, the mass fraction of the water reducing agent can be 0.14 parts, the mass fraction of the setting retarder can be 0.037 parts, the mass fraction of the thickening agent can be 0.04 parts, the mass fraction of the waterproof agent can be 0.03 parts, and the mass fraction of the volume stabilizer can be 0.04 parts.

[0038] The cement fixing material provided by the present invention has the characteristics of good fluidity, high volume stability, good durability, and coordinated development of strength and durability through the compounding of the above-mentioned raw materials for preparation. Using the cement fixing material provided by the present invention can achieve efficient fixation of radioactive solid waste, improve the stability and compactness of the cement solid obtained from the cement fixing material, and extend the durability of the cement solid.

[0039] The present invention provides a preparation method of the cement fixing material as described in the above technical solution, including the following steps:

[0040] Mix the raw materials for preparing the cement fixing material to obtain the cement fixing material.

[0041] The present invention has no special requirements for the mixing, and it is only necessary to mix the raw materials for preparing the cement fixing material evenly.

[0042] The present invention provides an application of the cement fixing material as described in the above technical solution in fixing radioactive solid waste.

[0043] In the present invention, the radioactive solid waste is preferably low- and medium-level radioactive solid waste. The low- and medium-level radioactive solid waste is generated during the operation and decommissioning of nuclear facilities.

[0044] In the present invention, the application preferably includes the following steps:

[0045] Mix the cement fixing material as described in the above technical solution with water to obtain a cement fixing medium;

[0046] Inject the cement fixing medium into the container containing the radioactive solid waste to be fixed, and then carry out curing and disposal in sequence according to the on-site construction requirements.

[0047] In the present invention, the cement fixing material described in the above technical solution is mixed with water to obtain a cement fixing medium. In the present invention, the water can be washing water. The mass ratio of the water to the cement fixing material is preferably 0.09 - 0.18:1, more preferably 0.1 - 0.15:1, and can be 0.12:1 in the examples.

[0048] After obtaining the cement fixing medium, in the present invention, the cement fixing medium is injected into the container containing the radioactive solid waste to be fixed, and then curing and disposal are carried out in sequence according to the on-site construction requirements.

[0049] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in combination with examples, but they cannot be understood as limiting the protection scope of the present invention.

[0050] In the following examples and comparative examples: The slag is S95 grade granulated blast furnace slag, the fly ash is dry-discharged fly ash with an activity index ≥ 85%, the metakaolin is metakaolin with an activity index ≥ 105%. The quartz sand has a continuous gradation of 10 - 220 mesh. The fineness of the anion exchange resin powder (Dow Chemical, IRN78) is ≥ 200 mesh. The waterproof agent is silicone.

[0051] Example 1

[0052] This example provides a nuclear waste fixing material. According to the component formulation shown in Table 1, it contains the following preparation raw materials in parts by mass:

[0053] 33 parts of Portland cement (P·O42.5); 4 parts of sulfoaluminate cement (42.5); 4 parts of slag; 8 parts of fly ash; 1 part of metakaolin; 50 parts of quartz sand; 0.14 part of polycarboxylate water reducer (water reduction rate ≥ 20%); 0.037 part of retarder (mass ratio of citric acid: tartaric acid = 7:3); 0.04 part of hydroxypropyl methylcellulose ether (viscosity: 600 Pa·s); 0.03 part of waterproof agent; 0.04 part of sulfamic acid.

[0054] The preparation method of the above nuclear waste fixing material includes the following steps: Weigh each component by mass, and mix them evenly to obtain the nuclear waste fixing material.

[0055] The usage method of the above nuclear waste fixing material includes the following steps:

[0056] Take 100 parts by mass of the nuclear waste fixing material prepared above, mix it thoroughly with 12 parts by mass of water at a rotation speed of 180 r / min for 2 min, pour in the required medium- and low-level radioactive waste, and conduct performance sampling tests simultaneously.

[0057] Example 2

[0058] This example provides a nuclear waste solidification material. According to the component formula shown in Table 1, it contains the following preparation raw materials in parts by mass:

[0059] 33 parts of Portland cement (P·O 42.5); 4 parts of sulfoaluminate cement (42.5); 4 parts of slag; 8 parts of fly ash; 1 part of metakaolin; 50 parts of quartz sand; 0.14 part of polycarboxylate water reducer (water reduction rate ≥ 20%); 0.037 part of retarder (citric acid: tartaric acid = 7:3); 0.04 part of hydroxypropyl methylcellulose ether (viscosity: 600 Pa·s); 0.03 part of waterproof agent; 0.04 part of anion exchange resin powder.

[0060] The preparation method of the above nuclear waste fixing material includes the following steps: Weigh each component in parts by mass and mix them evenly to obtain the nuclear waste fixing material.

[0061] The usage method of the above nuclear waste fixing material includes the following steps:

[0062] Take 100 parts by mass of the nuclear waste fixing material prepared above, mix it thoroughly with 12 parts by mass of water at a rotation speed of 180 r / min for 2 min, pour in the required medium- and low-level radioactive waste, and conduct performance sampling tests simultaneously.

[0063] Comparative Example 1

[0064] This comparative example provides a nuclear waste solidification material. According to the component formula shown in Table 1, it contains the following preparation raw materials in parts by mass:

[0065] 37 parts of Portland cement (P·O 42.5); 4 parts of slag; 8 parts of fly ash; 1 part of metakaolin; 50 parts of quartz sand; 0.14 part of polycarboxylate water reducer (water reduction rate ≥ 20%); 0.037 part of retarder (citric acid: tartaric acid = 7:3); 0.04 part of hydroxypropyl methylcellulose ether (viscosity: 600 Pa·s); 0.03 part of waterproof agent; 0.04 part of aminosulfonic acid.

[0066] The preparation method of the above nuclear waste fixing material includes the following steps: Weigh each component in parts by mass and mix them evenly to obtain the nuclear waste fixing material.

[0067] The usage method of the above nuclear waste fixing material includes the following steps:

[0068] Mix 100 parts by mass of the above-prepared nuclear waste immobilization material with 12 parts by mass of water at a rotation speed of 180 r / min for 2 min, pour in the required low- and medium-level radioactive waste, and simultaneously conduct performance sampling tests.

[0069] Comparative Example 2

[0070] This comparative example provides a nuclear waste solidification material. According to the component formulation shown in Table 1, it contains the following preparation raw materials in parts by mass:

[0071] 37 parts of Portland cement (P·O 42.5); 4 parts of sulfoaluminate cement; 8 parts of fly ash; 1 part of metakaolin; 50 parts of quartz sand; 0.14 part of polycarboxylate water reducer (water reduction rate ≥ 20%); 0.037 part of retarder (citric acid: tartaric acid = 7:3); 0.04 part of hydroxypropyl methylcellulose ether (viscosity: 600 Pa·s); 0.03 part of waterproofing agent; 0.04 part of aminosulfonic acid.

[0072] The preparation method of the above nuclear waste immobilization material includes the following steps: Weigh each component by mass and mix them evenly to obtain the nuclear waste immobilization material.

[0073] The usage method of the above nuclear waste immobilization material includes the following steps:

[0074] Mix 100 parts by mass of the above-prepared nuclear waste immobilization material with 12 parts by mass of water at a rotation speed of 180 r / min for 2 min, pour in the required low- and medium-level radioactive waste, and simultaneously conduct performance sampling tests.

[0075] Comparative Example 3

[0076] This comparative example provides a nuclear waste solidification material. According to the component formulation shown in Table 1, it contains the following preparation raw materials in parts by mass:

[0077] 41 parts of Portland cement (P·O 42.5); 4 parts of sulfoaluminate cement; 4 parts of slag; 1 part of metakaolin; 50 parts of quartz sand; 0.14 part of polycarboxylate water reducer (water reduction rate ≥ 20%); 0.037 part of retarder (citric acid: tartaric acid = 7:3); 0.04 part of hydroxypropyl methylcellulose ether (viscosity: 600 Pa·s); 0.03 part of waterproofing agent; 0.04 part of aminosulfonic acid.

[0078] The preparation method of the above nuclear waste immobilization material includes the following steps: Weigh each component by mass and mix them evenly to obtain the nuclear waste immobilization material.

[0079] The usage method of the above nuclear waste immobilization material includes the following steps:

[0080] Take 100 parts by mass of the nuclear waste immobilization material prepared above, mix it thoroughly with 12 parts by mass of water at a rotation speed of 180 r / min for 2 min, pour in the required low- and medium-level radioactive waste, and conduct performance sampling tests synchronously.

[0081] Comparative Example 4

[0082] This comparative example provides a nuclear waste solidification material. According to the component formula shown in Table 1, it contains the following preparation raw materials in parts by mass:

[0083] 34 parts of Portland cement (P·O 42.5); 4 parts of sulfoaluminate cement; 4 parts of slag; 8 parts of fly ash; 50 parts of quartz sand; 0.14 parts of polycarboxylate water reducer (water reduction rate ≥ 20%); 0.037 parts of retarder (citric acid: tartaric acid = 7:3); 0.04 parts of hydroxypropyl methylcellulose ether (viscosity: 600 Pa·s); 0.03 parts of waterproof agent; 0.04 parts of aminosulfonic acid.

[0084] The preparation method of the above nuclear waste immobilization material includes the following steps: Weigh each component by mass and mix them evenly to obtain the nuclear waste immobilization material.

[0085] The usage method of the above nuclear waste immobilization material includes the following steps:

[0086] Take 100 parts by mass of the nuclear waste immobilization material prepared above, mix it thoroughly with 12 parts by mass of water at a rotation speed of 180 r / min for 2 min, pour in the required low- and medium-level radioactive waste, and conduct performance sampling tests synchronously.

[0087] Comparative Example 5

[0088] This comparative example provides a nuclear waste solidification material. According to the component formula shown in Table 1, it contains the following preparation raw materials in parts by mass:

[0089] 33 parts of Portland cement (P·O 42.5); 4 parts of sulfoaluminate cement; 4 parts of slag; 8 parts of fly ash; 1 part of metakaolin; 50 parts of quartz sand; 0.14 parts of polycarboxylate water reducer (water reduction rate ≥ 20%); 0.04 parts of hydroxypropyl methylcellulose ether (viscosity: 600 Pa·s); 0.03 parts of waterproof agent; 0.04 parts of aminosulfonic acid.

[0090] The preparation method of the above nuclear waste immobilization material includes the following steps: Weigh each component by mass and mix them evenly to obtain the nuclear waste immobilization material.

[0091] The usage method of the above nuclear waste immobilization material includes the following steps:

[0092] Mix 100 parts by mass of the above-prepared nuclear waste immobilization material with 12 parts by mass of water at a rotation speed of 180 r / min for 2 min, pour in the required medium- and low-level radioactive waste, and simultaneously conduct performance sampling tests.

[0093] Comparative Example 6

[0094] This comparative example provides a nuclear waste solidification material. According to the component formula shown in Table 1, it contains the following preparation raw materials in parts by mass:

[0095] 33 parts of Portland cement (P·O 42.5); 4 parts of sulfoaluminate cement; 4 parts of slag; 8 parts of fly ash; 1 part of metakaolin; 50 parts of quartz sand; 0.14 part of polycarboxylate water reducer (water reduction rate ≥ 20%); 0.037 part of retarder (citric acid: tartaric acid = 7:3); 0.04 part of hydroxypropyl methylcellulose ether (viscosity: 600 Pa·s); 0.03 part of waterproofing agent.

[0096] The preparation method of the above nuclear waste immobilization material includes the following steps: Weigh each component by mass and mix them evenly to obtain the nuclear waste immobilization material.

[0097] The usage method of the above nuclear waste immobilization material includes the following steps:

[0098] Mix 100 parts by mass of the above-prepared nuclear waste immobilization material with 12 parts by mass of water at a rotation speed of 180 r / min for 2 min, pour in the required medium- and low-level radioactive waste, and simultaneously conduct performance sampling tests.

[0099] For the solidified bodies prepared from the nuclear waste immobilization materials in each example and comparative example, test the initial and 30-min fluidity, 1-day compressive strength, 3-day compressive strength, 28-day compressive strength, and 28-day chloride ion permeability (electric flux) according to EJ1186-2005 and GB / T17671-2021. Refer to GB / T50080-2016 to test whether there is bleeding in the solidified body. Refer to GB8076-2008 and JGJ / T192-2009 to test whether the solidified body corrodes the steel bars. Test the expansion rate according to GB / T50448-2015. The test results are shown in Table 2.

[0100] Table 1 Component formula of nuclear waste solidification materials in examples and comparative examples (in parts by mass)

[0101]

[0102]

[0103] Table 2 Performance test results of examples and comparative examples

[0104]

[0105] Examples 1-2 above illustrate the compliance of the performance indicators of the cement fixing material formula provided by the present invention and the balance among various indicators after introducing components such as sulfoaluminate cement, ternary compounding of mineral admixtures, and volume stabilizers. The current national standards and industry standards only impose basic constraints on the performance of nuclear waste fixing materials. However, for fixing materials that meet the requirements of fluidity, 28-day compressive strength, and 28-day chloride ion permeability resistance, serious problems may occur during application, such as the inability to fix radioactive waste due to excessive fluidity loss, detachment of the fixed body from the container wall due to shrinkage of the fixing material, and cracking of the fixed body. Once these problems occur, they cannot be restored, which will further lead to the stagnation of radioactive waste disposal and management. On the other hand, for the cement fixing material provided by the present invention, its initial fluidity, 28-day compressive strength, and 28-day chloride ion permeability resistance indicators not only far exceed the requirements of national standards and industry standards, but also the indicators such as 30-minute fluidity, early-age compressive strength, and expansion rate have been developed in a balanced manner. These indicators have practical significance for the production of radioactive waste fixed bodies: the maintenance of 30-minute fluidity is beneficial to avoiding problems such as the inability to smoothly discharge the fixed medium and the inability to completely fill radioactive waste due to extended stirring, replacement of containers, and hot weather; the rapid growth of early-age compressive strength is beneficial to the timely transfer of the fixed body and saves valuable space; the controllable expansion at the initial and hardened stages is beneficial to compensating for the chemical shrinkage in the plastic stage of the fixed body and reducing the cracking risk after the fixed body hardens; the elimination of bleeding phenomenon is beneficial to restricting the random migration of radioactive nuclide ions in the fixed body with the secretion of water and reducing the difficulty of radiation monitoring.

[0106] Comparing Example 1 with Comparative Example 1, it can be found that when sulfoaluminate cement is replaced by Portland cement, the volume of the fixed body shrinks after hardening, and at the same time, the 1-day compressive strength and chloride ion permeability resistance decrease. This shows that sulfoaluminate plays a positive correlation role in improving the stability, early mechanical properties, and durability of the fixed body.

[0107] Comparing Example 1 with Comparative Example 2, it can be found that when slag is replaced by Portland cement, the initial fluidity, 30-minute fluidity, and chloride ion permeability resistance all decrease. It can be explained that slag plays a positive correlation role in regulating the operability of the fixed body and increasing the durability of the fixed body.

[0108] Comparing Example 1 with Comparative Example 3, it can be found that when fly ash is replaced by Portland cement, the initial fluidity, 30-minute fluidity, and chloride ion permeability resistance of the fixed body decrease significantly. It can be explained that fly ash plays a positive correlation role in improving the operability and durability of the fixed body.

[0109] Comparing Example 1 with Comparative Example 4, it can be found that when metakaolin is replaced by portland cement, the compressive strength and chloride ion permeability resistance of the solidified body at each age are significantly decreased. It can be illustrated that metakaolin has a positive correlation with improving the density of the solidified body.

[0110] Comparing Example 1 with Comparative Example 5, it can be found that when the system does not contain a retarder, the initial fluidity of the solidified body is significantly reduced, the fluidity at 30 min is almost completely lost, and at the same time, the chloride ion permeability resistance performance also shows a decreasing trend. It can be illustrated that the retarder has a positive correlation with improving the workability and durability of the solidified body.

[0111] Comparing Examples 1 and 2 with Comparative Example 6, it can be found that when the system does not contain anion exchange resin powder / sulfamic acid, the 3-h expansibility of the solidified body disappears and the expansibility after hardening also becomes poor. It can be illustrated that the anion exchange resin powder / sulfamic acid has a positive correlation with improving the expansibility of the solidified body (especially the 3-h expansibility).

[0112] From the above examples, it can be known that when the cementitious fixing material provided by the present invention is used to fix low- and medium-level radioactive solid waste. The cementitious fixing material has the advantages of large fluidity, small fluidity loss over time, no bleeding, micro-expansion in the plastic stage and after hardening of the solidified body, high compressive strength at each age, good chloride ion permeability resistance, and no corrosion to metal containers or metal waste.

[0113] Although the above examples have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all the embodiments. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A cement fixing material, characterized in that: The invention comprises the following raw materials in parts by weight: 20 to 46 parts of cementitious materials; 39 to 55 parts of fine aggregates; 5 to 25 parts of mineral admixtures; and 0.2 to 0.7 parts of functional additives; the cementitious materials comprise silicate cement and sulphoaluminate cement, the fine aggregates comprise sand, the mineral admixtures comprise slag, metakaolin and fly ash, the functional additives comprise water reducing agents, retarders, thickening agents, waterproofing agents and volume stabilizers, and the volume stabilizers comprise anion exchange resin powder and / or aminosulfonic acid.

2. The cement fixing material according to claim 1, characterized in that: The cementitious material of the cement fixing material comprises the following raw materials in parts by weight: 20-40 parts of Portland cement and 2-6 parts of sulphoaluminate cement.

3. The cement fixing material according to claim 1 or 2, characterized in that: The silicate cement includes one or more of ordinary silicate cement, pure silicate cement, slag silicate cement, pozzolanic silicate cement and fly ash silicate cement; The sulphoaluminate cement includes one or more of the following: crack-resistant double-fast sulphoaluminate cement, high-belite sulphoaluminate cement and low-alkali sulphoaluminate cement.

4. The cement fixing material according to claim 1, characterized in that: The mineral admixture of the cement fixing material comprises the following raw materials in parts by weight: 4-6 parts of slag, 11-14 parts of fly ash, and 1-3 parts of metakaolin.

5. The cement fixing material according to claim 1 or 4, characterized in that: The slag is of grade S95-S105; the fly ash is of grade I-III; and the metakaolin is prepared by calcining kaolin at 600-800°C.

6. The cement fixing material according to claim 1, characterized in that: The sand is artificial sand and / or natural sand; The sand has a continuous grade of 10 to 220.

7. The cement fixing material according to claim 1, characterized in that: The functional additive of the cement fixing material includes the following raw materials in parts by weight: 0.14-0.5 parts of water reducing agent, 0.02-0.05 parts of retarder, 0.02-0.04 parts of thickening agent, 0.015-0.04 parts of waterproofing agent, and 0.015-0.05 parts of volume stabilizer.

8. The cement fixing material according to claim 1 or 7, characterized in that: The water reducer is a polycarboxylate water reducer; the retarder includes one or more of citric acid, tartaric acid and boric acid; the thickener is cellulose ether; and the waterproofing agent is organic silicon and / or diatomaceous earth.

9. Use of the cement fixing material according to any one of claims 1 to 8 in fixing radioactive solid waste.

10. The use according to claim 9, characterized in that: The application comprises the following steps: Mixing the cement fixing material according to any one of claims 1 to 8 with water to obtain a cement fixing medium; The cement fixing medium is injected into a container containing radioactive solid waste to be fixed, and then curing and disposal are carried out in sequence.

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