Decontamination of graphite structural elements and recovery of uranium is crucial for waste minimization and recycle of nuclear fuel elements. Feasibility of intensified dissolution of uranium-impregnated graphite substrate using ultrasound has been studied with objective of establishing the effect of operating parameters and the kinetics of sonocatalytic dissolution of uranium in nitric acid. The effect of operating frequency and acoustic intensity as well as the acid concentration and temperature on the dissolution of metal has been elucidated. It was observed that at lower acid concentrations (6 M-8 M), the dissolution ratio increases by 15% on increasing the bath temperature from 45 to 70 °C. At higher acid concentration (>10 M), the increase was only around 5-7% for a similar change in temperature. With 12 M HNO3, pitting was also observed on the graphite surface along with erosion due to high local reaction rates in the presence of ultrasound. For higher frequency of applied ultrasound, lower dissolution rate of uranium was observed though it also leads to high rates of erosion of the substrate. It was thus established that suitable optimization of frequency is required based on the nature of the substrate and the choice of recycling it. The dissolution rate was also demonstrated to increase with acoustic intensity till it reaches to the maximum at the observed optimum (1.2 W/cm2 at 33 kHz). Comparison with silent conditions revealed that enhanced rate was obtained due to the use of ultrasound under optimum conditions. The work has demonstrated the effective application of ultrasound for intensifying the extent of dissolution of metal.

中文翻译：

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使用超声波增强铀从石墨基质中的溶解。

石墨结构元素的去污染和铀的回收对于减少废物和核燃料元素的回收至关重要。为了确定铀的操作参数和超声催化溶解铀在硝酸中的动力学，已经研究了利用超声强化铀浸渍的石墨基体溶解的可行性。阐明了工作频率和声强以及酸浓度和温度对金属溶解的影响。观察到，在较低的酸浓度（6 M-8 M）下，随着浴温从45°C升高到70°C，溶出度增加了15％。在较高的酸浓度（> 10 M）下，对于类似的温度变化，其增加仅约5-7％。使用12 M HNO3，在超声波的存在下，由于高的局部反应速率，在石墨表面还观察到了点蚀以及腐蚀。对于更高频率的超声应用，虽然铀的溶解速率较低，但也会导致基材的腐蚀速率较高，因此观察到较低的溶解速率。因此，已经确定，需要根据基板的性质和对其进行回收的选择来适当地优化频率。溶出速率也随着声强度的增加而增加，直到达到观察到的最佳值（在33 kHz时为1.2 W / cm2）达到最大值。与无声条件的比较表明，由于在最佳条件下使用了超声，因此获得了更高的速率。这项工作已经证明了超声波在增强金属溶解程度方面的有效应用。