Cementation of Radioactive Lime Waste from Ammonium Uranyl Carbonate Wet Process

一群研究人员最近在《杂志》上发表了一篇论文欧洲杯足球竞彩that determined the optimum operating conditions in a cement solidification method, to effectively solidify the radioactive lime waste produced by the neutralization of liquid wastes obtained from the ammonium uranyl carbonate (AUC) ((NH₄)₄UO₂(CO₃)₃) wet process.

Study:Evaluation of Disposal Stability for Cement Solidification of Lime Waste.Image Credit: Kunertus/Shutterstock.com

Background

Radioactive waste produced during the decommissioning and operation of nuclear power plants is usually processed by the AUC wet process. This process is primarily a uranium reconversion process involving substantial amounts of nitric acid (HNO₃) and AUC. Liquid wastes generated from the AUC wet process are neutralized using the hydrated lime (Ca(OH)₂), and the byproduct obtained after neutralization is referred to as radioactive lime waste.

Appropriate procedures should be followed to ensure stable disposal of the lime waste, and the lime waste must undergo cementation to fulfill waste acceptance criteria (WAC). Additionally, the chemical and physical characteristics of the cement waste form produced after the cementation of the lime waste should satisfy the WAC. The cementation of lime waste must be an affordable and simple process. Various cementation processes with multiple solidifying mediums were developed for glass, asphalt, cement, and polymer.

Among these processes, the cement solidification technique is the most efficient process owing to the use of well-known technology and materials, reasonable cost, and extensive applications. In this study, researchers determined the optimum operating conditions for the cementation of the lime waste produced from the AUC wet process and evaluated the leaching stability and structural stability of the cement waste form samples.

示意图的示意图和浪费。图片来源：Shon，J.S等人，材料欧洲杯足球竞彩

The Study

Low-level radioactive lime waste used in the experiment was dried at 105^oC for 24 h. A mortar was used to pulverize the dried lime waste to prepare uniform samples of cement waste form. Portland cement (type I) was utilized for the cementation of lime waste. The shape stability of the cement compound and the lime waste was evaluated with different lime waste contents of 80, 75, and 71 wt.% in cement waste form samples.

石灰废物的重量比保持在75 wt。％，不同的水泥（w/c）比为2.40、2.20、2.00、1.95、1.85、1.85、1.75、1.65和1.55，以计算最佳混合比。使用机械搅拌机混合石灰废物和水泥废物形式，然后将混合物倒入相对湿度30-60％和18-25的聚乙烯霉菌中^oC temperature.

The molds were cured for 28 days, and lids were used to cover the molds during that duration in order to prevent the evaporation of moisture. The workability test was performed to determine the range of w/c ratios that allows cement mixtures to possess the flowability required for cementation. WAC was employed as the evaluation criteria and method for testing the leaching stability and the structural stability of the cement waste form samples.

通过浸入水，辐照和热回收测试评估水泥废物形式样品的可处置性。浸出测试是作为无活动测试进行的，使用浸润性指数（LX）来评估水泥废物形式样品的渗漏性。

Observations

At a lime waste content of 80 wt.%, the cement mixture samples collapsed upon the removal of polyethylene molds after curing, indicating the need for a lower value of the maximum lime waste content. Thus, the weight ratio of lime waste was fixed at 75 wt.% after considering the shape stability and economic feasibility of cement waste form samples.

Curing of specimen that blocked movement of moisture with lid closed. Image Credit: Shon, J.-S et al., Materials

Observations from the workability of cement-lime mixtures indicated that the mixtures possess good flowability at a w/c of 1.95 or higher and no flowability at a w/c of 1.75, 1.65, and 1.55. The range of w/c ratios with acceptable flowability and mixability for the preparation of cement waste form samples was 1.90-2.30 when the lime waste content was 75 wt.%.

The weight of the cement waste form samples decreased by 7.33%, 15.00%, and 16.25% after the water immersion test, irradiation test, and thermal recycling test, respectively, while the volume changed by 0.3% after every test. Initially, the compressive strength of cement waste form samples after curing was 55.0 kgf/cm²，增加到61.0、76.3和61.4 kgf/cm²after the irradiation test, water immersion test, and thermal recycling test, respectively; this is higher than the acceptance criterion of 35.2 kgf/cm².

水泥废物样品的浸出测试的观察结果表明，钴（CO），锶（SR）和剖宫产（CS）核素的LX分别为10.89、8.02和7.63，这比接受标准高于接受标准6。

To summarize, the proposed cement solidification method for disposing of radioactive lime waste can be an effective approach to the cementation of lime waste powder produced during the neutralization of liquid wastes in the AUC wet process.

来源

Shon, J.-S., Lee, H.-K., Kim, G.-Y.et al. Evaluation of Disposal Stability for Cement Solidification of Lime Waste.欧洲杯足球竞彩2022, 15, 872.https://www.mdpi.com/1996-1944/15/3/872

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