阅读说明：本技术 一种处理中低放射性核废料的镁基水泥固化基材及方法 (Magnesium-based cement curing substrate and method for treating low-medium radioactive nuclear waste ) 是由 张婷婷 邹婧 王宝民 于 2020-04-28 设计创作，主要内容包括：本发明涉及一种处理中低放射性核废料的镁基水泥固化基材及方法,该固化基材是采用轻烧镁粉和高活性硅源为主要原材料,钠盐/钾盐作为改性外加剂,在常温条件下加水反应形成的水化硅酸镁胶凝体系。用该体系制备的水泥固化体具有良好的力学性能、抗浸出、抗冻融和抗浸泡性能,各项指标均满足国家规范要求,尤其对中低放射性核废料中危害最大的两种核素<Sup>137</Sup>Cs、<Sup>90</Sup>Sr表现出优异的抗浸出性能,第42d核素离子浸出率低至10<Sup>-4～5</Sup>cm/d,本发明为中低放射性核废料的处理处置提供了一种新型的水泥基固化材料,具有广阔的应用前景。(The invention relates to a magnesium-based cement curing base material for treating low-medium radioactive nuclear waste and a method thereof. The cement solidified body prepared by the system has good mechanical property, leaching resistance, freeze fusion resistance and soaking resistance, all indexes meet the national standard requirements, especiallyTwo nuclides with the greatest harm in low-level radioactive nuclear waste 137 Cs、 90 Sr shows excellent leaching resistance, and the leaching rate of 42d nuclear species ions is as low as 10 ‑4～5 cm/d, the invention provides a novel cement-based curing material for the treatment and disposal of medium-low radioactive nuclear waste, and has wide application prospect.)

1. A method for treating magnesium-based cement-cured substrates of low-to-medium radionuclide waste, characterized in that it comprises the following operative steps:

the method comprises the following steps: weighing main raw materials of the curing substrate, light-burned magnesium oxide and a high-activity silicon source powder material, weighing, mechanically mixing for 10-20 min, and keeping drying to obtain mixed powder;

step two: dissolving the admixture in water, adding the dissolved admixture, the radioactive waste material and the quartz sand into the mixed powder in the step one, and stirring the mixture into slurry with good working performance by using a cement mortar stirrer;

step three: and (3) putting the slurry obtained in the step two into a mold, putting the mold into a constant temperature and humidity box, curing for 1-2 d, then removing the mold, and continuously curing the cured body to the specified age, wherein the curing condition is that the temperature is 25 +/-2 ℃ and the humidity is more than or equal to 95%.

2. A method of treating a low radionuclide waste magnesium based cement cured substrate according to claim 1 characterized by: the light-burned magnesia MgO in the step one is prepared from magnesite MgCO₃Calcining at 750-800 deg.C to obtain the product, wherein the MgO content is above 90%, and the particle size of the powder is 10 μm.

3. A method of treating a low radionuclide waste magnesium based cement cured substrate according to claim 1 characterized by: the high-activity silicon source in the step one is prepared from homogeneous materials of granulated blast furnace slag, fly ash or silica fume, SiO₂The content of (B) is more than 95%, and the particle size is usually 100-300 nm.

4. A method of treating a low radionuclide waste magnesium based cement cured substrate according to claim 1 characterized by: and the additive in the second step is a sodium salt/potassium salt, so that the working performance of the system can be improved.

5. A method of treating a low radionuclide waste magnesium based cement cured substrate according to claim 1 characterized by: the quartz sand added in the second step is used for improving the dry shrinkage defect of the system, the particle size distribution range is 5-500 mu m, and D50 is 168.84 mu m.

6. A method of treating a low radionuclide waste magnesium based cement cured substrate according to claim 1 characterized by: based on the consideration of experimental safety, the nuclear waste required by the stirred solidified body in the third step is provided with non-radioactive nuclide ions Cs by chlorine salt and nitrate analytical pure reagent⁺、Sr²⁺Substitution of two most harmful representative nuclides in nuclear waste¹³⁷Cs、⁹⁰Sr。

7. A magnesium based cement cured substrate obtainable by any one of claims 1 to 5, wherein: the magnesium-based cement curing base material comprises the following components in percentage by mass: 20-40% of light-burned magnesia, 30-60% of silica fume, 1-2% of an additive and 0-3% of nitrate or chloride, and the water-cement ratio of the system is determined according to the water consumption of standard consistency.

Technical Field

The invention relates to the technical field of nuclear waste treatment methods, in particular to a magnesium-based cement curing substrate and a method for treating low-medium radioactive nuclear waste.

Background

In China, since the first nuclear power station, Zhejiang sea salt Qinshan nuclear power station, in 1991 and grid-connected power generation, the China nuclear power industry develops rapidly and accounts for the total power generation amount in ChinaBy 4%, the size of the transport and installation machine reaches the third level of the world, and the size of the construction machine reaches the first level of the world. As a clean energy source, nuclear energy will play an increasingly important role in the energy system. However, in the process of developing and utilizing nuclear energy, the problems caused by the nuclear waste with large quantity are not ignored. Investigations have shown that nuclear waste with high radioactivity accounts for only about 1%, the remaining 99% are mainly low and medium radioactive nuclear waste, and cesium and strontium are two nuclides with the greatest harm, namely fission nuclides generated during the operation of a nuclear reactor, and have a longer half-life period (¹³⁷The half-life of Cs is 30.2 years,⁹⁰sr half-life 28.8 years), the specific gravity of radioactivity accounting for the total radioactivity of the mixed fission product is large, the mixed fission product exists in the form of ions, the mixed fission product is easy to migrate in water environment, and the enrichment effect can cause the canceration of organism cells to generate irreversible influence. Therefore, proper disposal of low-to-medium level waste, especially cesium and strontium, presents a significant challenge to the development of the nuclear power industry.

At present, the internationally generally accepted treatment mode of the medium-low nuclear waste is solidification treatment, wherein the waste is converted into solid, namely solidified body, by using materials such as ceramics, asphalt, cement and the like, the solidified body is packaged into a specified closed container, and the sealed body is sent to the underground for burying and storing through an automatic transportation system, so that the aim of permanently isolating the biosphere is achieved. The cement solidification is the earliest and most mature solidification method, has the advantages of simple equipment process, low cost and the like, but the wide application also exposes the defects of the traditional cement-based solidification material, and the coagulation and hardening of a common portland cement system are abnormal due to a large amount of salt introduced when the nuclide leaching rate is high, the tolerance is small, and the waste treatment capacity is too large. Therefore, the development of a novel cement-based curing material can improve the leaching resistance of curing and the stability of a system, and has great significance for the safe treatment of nuclear waste.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects of the prior art and provide a magnesium-based cement curing material for treating medium-low radioactive nuclear wastes and a preparation method thereof, wherein the magnesium-based cement curing material has stable comprehensive performance and low leaching rate of nuclide ions.

In order to solve the technical problems, the technical scheme provided by the invention is as follows: the magnesium-based cement curing material for treating medium and low radioactive nuclear wastes comprises, by mass ratio, 20-40% of light-burned magnesium oxide, 30-60% of silica fume, 1-2% of sodium salt/potassium salt additive and 0-3% of nitrate/chloride salt, and the water-cement ratio of the system is established according to a water consumption experiment of standard consistency.

A method for treating a magnesium-based cement-cured substrate of low to medium radioactive nuclear waste, said method comprising the following operative steps:

the method comprises the following steps: weighing main raw materials of the curing substrate, light-burned magnesium oxide and a high-activity silicon source powder material, weighing, mechanically mixing for 10-20 min, and keeping drying to obtain mixed powder;

step two: dissolving the admixture in water, adding the dissolved admixture, the radioactive waste material and the quartz sand into the mixed powder in the step one, and stirring the mixture into slurry with good working performance by using a cement mortar stirrer;

step three: and (3) putting the slurry obtained in the step two into a mold, putting the mold into a constant temperature and humidity box, curing for 1-2 d, then removing the mold, and continuously curing the cured body to the specified age, wherein the curing condition is that the temperature is 25 +/-2 ℃ and the humidity is more than or equal to 95%.

Further, the light-burned magnesia MgO in the step one is prepared from magnesite MgCO₃Calcining at 750-800 deg.C to obtain the product, wherein the MgO content is above 90%, and the particle size of the powder is 10 μm.

Further, the high-activity silicon source in the step one is prepared from the homogeneous material of granulated blast furnace slag, fly ash or silica fume, SiO₂The content of (B) is more than 95%, and the particle size is usually 100-300 nm.

Furthermore, the additive in the second step is a sodium salt/potassium salt, so that the working performance of the system can be improved.

Furthermore, the quartz sand added in the second step is used for improving the dry shrinkage defect of the system, the particle size distribution range is 5-500 μm, and D50 is 168.84 μm.

Further, the cured body prepared by stirring in the third step is taken into consideration of experimental safetyThe nuclear waste provides non-radioactive nuclide ions Cs by using chlorine salt and nitrate analysis pure reagents⁺、Sr²⁺Substitution of two most harmful representative nuclides in nuclear waste¹³⁷Cs、⁹⁰Sr。

Firstly, weighing a plurality of parts of the components according to the mass ratio for later use, and uniformly mixing light-burned magnesium oxide and silica fume powder by using a stirrer for 10-20 min; secondly, preparing a modified additive aqueous solution; then adding the uniformly mixed magnesium oxide and silica fume powder into the aqueous solution for 2-3 times, and stirring the mixture into slurry with good fluidity by using a cement stirrer at an accelerated speed; and finally, filling the stirred slurry into a mold, putting the mold into a constant temperature and humidity box, curing for 1d, then removing the mold, and continuing curing to a specified age for performance test, wherein the curing conditions are as follows: the temperature is 25 +/-2 ℃, and the humidity is more than or equal to 95 percent.

The invention relates to a low radioactive nuclear waste solidified material in magnesium-based cement, which utilizes light-burned MgO and active SiO₂Reacting at normal temperature to finally generate a hydrated magnesium silicate gel system (MgO-SiO) of hydrated magnesium silicate gel (M-S-H)₂-H₂O). The pore solution environment of the system has a low pH value, and hardly reacts with aluminum-containing waste to generate H₂The nuclear waste containing active metals such as aluminum and the like can be effectively packaged. In addition, the hydrated magnesium silicate gel system has a porous structure and a specific surface area of 200m²/g^-1And the composite material has excellent adsorption performance, and can exert great advantages in the aspect of curing treatment of nuclear waste.

The invention has the beneficial effects that: the magnesium-based cement curing base material for treating the low-medium radioactive nuclear waste has excellent leaching resistance. The detection of relevant indexes of the solidified body made of the solidified base material is carried out according to the requirements of the national standard specification ' Standard leaching experiment method of Low and Medium horizontal radioactive waste solidified body ' (GB/T7023-2011) and the performance requirement of Low and Medium horizontal radioactive waste solidified body, namely the cement solidified body ' (GB 14569.1-2011), and the result shows that the compressive strength of the magnesium-based cement solidified body cured for 28d under the standard curing condition is between 23 and 36MPa (the standard: the compressive strength of 28d is over 7 MPa); when the leaching solution is deionized waterThe 42d leaching rate of the solidified body to the nuclide Cs is 6.4 × 10^-5The cumulative leaching rate of cm/d and 42d is about 0.01cm, and the leaching rate of 42d of the nuclide Sr is 4.6 × 10^-4The accumulated leaching fractions of cm/d and 42d are about 0.07cm and are far lower than the standard limit value required by the specification; meanwhile, the solidified body also has good impact resistance, soaking resistance and freeze-thaw resistance, meets the national standard requirements which the cement solidified body should meet, and has wide application prospect in the treatment of nuclear waste.

Detailed Description

The present invention will be described in further detail with reference to examples.