干馏法从铀的裂变产物中分离131I

¹³¹I是一种重要的医用放射性同位素，但因湿法分离技术上的缺陷，使得从铀裂变产物中获取¹³¹I的工艺具有环境污染严重、提取效率低的缺点。因铀裂变产物中¹³¹I的产额较高，为拓展¹³¹I的获取途径，提高铀裂变产物的利用效率，开展铀裂变产物中¹³¹I分离的新工艺研究十分必要。与传统湿法分离工艺不同，本工作采用了干馏法进行铀裂变产物中¹³¹I的分离。为了得到高的¹³¹I分离效率，将分离过程分为低温粉化、高温干馏和中低温保温三个阶段，并研究高温干馏阶段温度对131I分离效率的影响。实验发现：当干馏温度高于950 ℃时，¹³¹I的分离效率≥98%。此外，研究结果还表明，在该干馏温度下，碘和¹⁰³Ru 均可挥发出铀靶片，但产物收集液中却仅含有碘。为了解释这一现象，对碘的分离过程进行分析，结合实验结果和理论计算，推测挥发物中碘和¹⁰³Ru分离的原因为：¹⁰³Ru与氧反应生成挥发性RuO₄，从铀的裂变产物挥发出；因加热管内温度较高，RuO₄在迁移过程中发生了分解，生成RuO₂沉积在加热管内部。因此，利用干馏法从铀的裂变产物中分离¹³¹I时，为了得到放化纯度高的碘产品，不仅要合理规划分离过程，还需科学设计加热管的长度。

Separation of 131I from Uranium Fission Products by Dry Distillation

¹³¹I is an important radioisotope in nuclear medicine, but due to the inherent defects of wet separation technology，the separation of 131I from uranium fission products (UFPs) has serious environmental pollution and low extraction efficiency. Considering the high yield of ¹³¹I in UFPs, it is necessary to develop a new method for separating ¹³¹I from UFPs, because it can not only expand the ways to obtain ¹³¹I, but also improve the utilization efficiency of UFPs. Unlike the traditional wet chemical separation technique, ¹³¹I was separated from UFPs by dry distillation in present work. Three stages worked under different temperatures, such as powdered the target, dry distillation and heat preservation, were involved in the separation process, so as to acquire as much as ¹³¹I from the target. The effect of dry distillation temperature on ¹³¹I separation efficiency was systematically investigated, it was found that the separation efficiency of ¹³¹I was higher than 98% when the distillation temperature was over 950 ℃. Moreover, it was also observed that both radioiodine and ¹⁰³Ru were sublimated from the UFPs at the optimum distillation condition, but only radioiodine existed in the product. In order to explain this phenomenon, a detailed analysis of the iodine separation process was carried out. By combining the experimental results with the theoretical calculations, the separation mechanism of radioiodine from ¹⁰³Ru was estimated as: ¹⁰³Ru volatilized from the UFPs through the formation of RuO₄, the volatile compound of ¹⁰³Ru may be decomposed into RuO₂ during the migration because of the high temperature in the heating tube, and then settled down. Therefore, to separate ¹³¹I from UFPs by dry distillation and obtain ¹³¹I product with high radiochemical purity, it is necessary to rationally plan the separation process, at the same time, the scientifically design of the heating tube length is also meaningful.