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为了验证使用LIBS进行铅铋合金中杂质定量测量的可行性,文中对七种不同Ni含量的样品进行了测试,为了降低激光能量不稳定等因素的影响,每次实验测试取样品表面30个数据的平均值作为光谱数据。因为内标法可以降低测量条件的变化对测量结果的影响,为了提高结果的准确度,文中使用内标法拟合定量分析标准曲线。内标法内标元素一般选取条件为:元素含量相对稳定,与分析元素有相近的波长,并且无自吸收和背景较弱等。由于铅铋合金中铅和铋元素的含量相对稳定,因此铅和铋元素是比较合适的内标元素。最终文中选择NiⅠ:352.454 nm为分析谱线,PbⅠ:367.1491 nm为内标谱线,得到的定标曲线见图8,其中横坐标是Ni的质量含量百分比,纵坐标是Ni和Pb元素谱线强度的比值,可以看到,采用内标法测得的定标曲线的相关指数R2达到0.967,有比较好的相关性,定标曲线的关系式为INi/IPb=0.00549+1.83713[Ni]%。
定标曲线中元素的检测限求解公式为:
$$ \mathrm{L}\mathrm{O}\mathrm{D}=3\frac{{{S}}_{\mathrm{b}}}{{S}} $$ 式中:LOD表示元素的检测限;Sb为拟合曲线标准偏差;S为标准曲线的斜率。经过计算可以得到使用LIBS拟合的铅铋合金中Ni元素的检测限为:0.028 7%。在铅铋快堆的运行环境下,Ni元素在铅铋冷却剂中的质量含量溶解度在0.16%~3.3%左右,使用LIBS技术定量分析的检测限远低于该范围,因此使用LIBS进行定量分析的检测限可以满足铅堆内Ni元素杂质的测量要求。
为了研究定量分析的准确度,表1列出了五种LIBS检测限以上含量的样品使用内标法进行定量分析的结果和使用ICP-MS测出的结果以及对应的相对误差值。
表 1 使用ICP-MS和LIBS测试得到的结果比较
Table 1. Comparison of results obtained using ICP-MS and LIBS
No. Ni content measured by ICP-MS (Mass fraction) Analysis result of LIBS (Mass fraction) Relative error 1 0.0635% 0.0723% 13.9% 2 0.0945% 0.09389% 0.6% 3 0.0574% 0.06626% 15.5% 4 0.14% 0.1357% 3.1% 5 0.0283% 0.02461% 13.1% 可以看出,使用LIBS进行定量分析的最大相对误差为15.5%,最小相对误差为0.6%,基本与行业内定量测量的准确度接近。与传统测量方法相比,LIBS技术的准确度虽然不是特别高(这也是目前LIBS技术最大的缺点之一),但是在铅铋快堆正常运行中,对杂质含量的测量主要是为杂质的清除做预警,该准确度结合LIBS技术能快速在现场测量的特点足够为铅铋冷却剂的安全状态提供指导。通过本次定量测量研究,论证了LIBS在铅铋快堆中用于杂质测量的可行性,定量分析的检测限可以满足铅铋快堆Ni元素杂质测量的要求而且分析结果的准确度相对较高。
目前铅铋快堆中的杂质测量提出了几种测量方法,使用传统方式测量的主要缺点是:需要有专门的热室进行测量,反射性物质运输困难且成本高,会对设备造成放射性污染,测量时间比较长,无法实时得到含量信息,而LIBS设备则可以克服以上缺点,可以实现实时测量、降低测量难度和成本、减少放射性污染等。根据文中的结果,在实际工程中的初步应用方案为:将激光器放在离样品比较远的位置,通过光学系统将激光聚焦在取出的样品上,将收光器和光谱仪之间使用延长的光纤连接,控制电脑则放在取样室外面,通过电脑控制测量的进行,同时将激光器和光谱仪放在一个屏蔽箱内,屏蔽箱开玻璃窗口可以透过激光。这样就可以实现铅铋合金中杂质的远程测量,而且能避免设备受到放射性污染。这是一种近乎实时在线的测量方式,而且实现难度不高,可以预见LIBS技术将来在铅铋快堆中乃至核能领域内有较好的应用前景。
Study on application of laser-induced breakdown spectroscopy in impurity measurement of lead-based reactor
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摘要: 铅基堆被第四代核能系统国际论坛组织评定为有望首个实现商业应用的第四代堆,铅基堆冷却剂中杂质的存在会严重影响铅反应堆的安全运行。基于此,文中开展了脉冲激光诱导击穿光谱(LIBS)在铅铋合金中杂质测量中的应用研究。研究了激光聚焦位置、激光能量和延迟时间对Ni元素光谱信号的影响,获取了LIBS测量铅铋合金中杂质的最佳实验参数。同时使用不同Ni含量的实验样品完成了LIBS对铅铋合金中Ni元素的定量研究,获得了定量标准曲线,相关指数R2达到0.967,质量含量的探测限为0.0287%。结果表明:使用激光诱导击穿光谱技术进行铅铋合金中的杂质测量是可行的。可以推测,LIBS技术在先进核能领域有比较高的应用研究价值。
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关键词:
- 铅基堆 /
- 杂质测量 /
- 激光诱导击穿光谱(LIBS) /
- 内标法
Abstract: Lead-based reactor is rated as the first fourth-generation reactor expected to achieve commercial application by Generation IV International Forum (GIF). The coolant of lead-based fast reactor can corrode metals. The existence of impurities in coolant will affect the safe operation of the lead-based reactor. Under this background, the application of impurity measurement in lead-bismuth alloy with laser-induced breakdown spectroscopy (LIBS) technique was studied. The effects of laser focusing position, laser energy and delay time on Ni elements spectral signal were studied. The optimal experimental parameters for measuring impurities in lead-bismuth alloy with LIBS device were obtained. At the same time, quantitative analysis of Ni element in lead-bismuth alloy was performed by employing LIBS technique in the present paper. The coefficients of determination gained by internal standard method is 0.967. The detection limit of mass content is 0.0287%. The results show that it is feasible to use the laser-induced breakdown spectroscopy technique to measure impurities in lead-bismuth alloy. LIBS technique has high application research value in the field of advanced nuclear energy. -
表 1 使用ICP-MS和LIBS测试得到的结果比较
Table 1. Comparison of results obtained using ICP-MS and LIBS
No. Ni content measured by ICP-MS (Mass fraction) Analysis result of LIBS (Mass fraction) Relative error 1 0.0635% 0.0723% 13.9% 2 0.0945% 0.09389% 0.6% 3 0.0574% 0.06626% 15.5% 4 0.14% 0.1357% 3.1% 5 0.0283% 0.02461% 13.1% -
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