熔盐中微量金属元素的激光诱导击穿光谱在线定量

Online quantification of trace element is of huge difficulty and challenge in the area of elementary analysis. Laser-induced breakdown spectroscopy (LIBS) is a type of atomic emission spectroscopy that utilizes a high power pulsed laser to create localized plasma on a sample. The resulting ionic and atomic line emission is characteristic of the composition of the sample. As a very promising technique, LIBS possesses unique character required for in situ chemical sensing in extreme environments, such as high temperature, corrosive and radioactive fields. The key problem faced by LIBS in industrial application by now is quantification. This project is to figure out how to online determine trace metal elements (Cr, K, Eu) quantitatively with LIBS in molten LiF-BeF2 salt. The relationship between LIBS spectrum and different experimental parameters including excitation parameters, measurement parameters and temperature of molten salt is studied by measuring the electron density and temperature of laser induced plasma. A protocol to pre-sentence the effectiveness of spectrum for quantitative analysis will be established. The detection limit of each element with LIBS is determined with calibration curves by measuring spectra of metallic elements at different concentrations. The quantification based on calibration free method will be developed and the feasibility of applying partial least square method to quantification will be assessed. This work is important for a better understanding of the mechanism of laser sputtering plasma in different environment. The results will provide reference for field applications such as control analysis of spent fuel reprocessing and online monitoring fuel quality in molten salt reactor.

微量元素的原位在线定量是目前元素分析技术研究的难点与挑战。激光诱导击穿光谱（LIBS）利用脉冲激光束使物质局部电离，产生包含分析对象的元素种类和浓度信息的特征谱线，是目前高温、强腐蚀、高放射性等恶劣条件下最具前景的在线分析技术之一，但定量化是该技术工业应用面临的关键问题。本项目围绕LiF-BeF2熔盐中微量金属元素（Cr、K、Eu）的LIBS在线定量开展研究，通过测量等离子体的电子密度和温度，系统评估激发参数、测量参数、熔盐温度变化对LIBS光谱的影响机制，建立预判光谱定量分析有效性的方法；在对熔盐中不同浓度金属元素光谱测量的基础上，考察LIBS检测灵敏度，建立基于自由定标法的微量金属元素定量分析方法，探索偏最小二乘法定量应用的可行性。本项目的开展，对深入认识在不同环境下激光溅射等离子体机理具有重要意义，可为LIBS技术在乏燃料后处理工艺控制分析，反应堆燃料质量在线监控等现场应用提供参考。

由于具有优良的传热性能、使用温度高、成本低、安全等优点，熔盐被公认为最具潜力的传热蓄热介质，在太阳能热发电、光热发电和核反应堆中具有诱人前景。然而在熔盐使用过程中的原位在线质量监测是熔盐堆临堆检测面临的难点与挑战。激光诱导击穿光谱（LIBS）利用脉冲激光束使物质局部电离，产生包含分析对象的元素种类和浓度信息的特征谱线，是目前高温、强腐蚀、高放射性等恶劣条件下最具前景的在线分析技术之一。本项目针对钍基熔盐先进核能系统在临堆分析检测的特殊需求，基于实验室商业化设备，搭建适用于高温熔盐的LIBS装置，开展了FLiBe和FLiBeU熔盐体系的LIBS研究，获取了两类熔盐体系中腐蚀产物、关键裂变产物的 LIBS光谱，并对元素的特征谱线进行指认，为后期临堆在线监测提供了关键基础数据。本项目研究表明LIBS技术有望解决高温熔盐原位监测的难题，为LIBS技术在乏燃料后处理工艺控制分析，反应堆燃料质量在线监控等现场应用提供参考。