基于XRD内标法测定LiF-BeF_2熔盐体系中UF_3含量

Quantitative determination of UF3 in LiF-BeF2 molten salt system based on XRD internal standard method

在氟化物熔盐相直接将UF6中转化为UF_4是熔盐堆燃料盐的合成及重构的候选工艺之一。其中,UF_(3)是该工艺过程的重要中间产物,其含量是开展工艺研究的关键参数之一。本文采用X射线衍射(X-ray Diffraction,XRD)内标法测量氟化物体系中的UF_(3)含量,分析了不同组分的固态熔盐样品,建立了UF_(3)含量的测量分析方法。首先以刚玉(α-Al_(2)O_(3))为内标,获得了UF_(3)在1.00~10.00 wt%含量范围时,LiF-BeF_(2)-UF_(3)熔盐的XRD峰高度内标曲线(R=0.986)和峰面积内标曲线(R=0.995)。然后应用这两条内标曲线测量已知含量的LiUF_(5)和UF_(3)固体混合样品,结果表明峰面积内标曲线具有更好的准确度,测量相对误差不大于8.7%。最后分别对快速冷却的LiF-BeF_(2)-UF_(3)固态熔盐样品和自然冷却的LiF-BeF_(2)-UF_(3)-LiUF_(5)固态熔盐样品进行测量,测量结果的相对误差不大于5.4%。以上结果表明:本文建立的XRD内标法可以用于混合氟盐样品的UF_(3)分析,并具有较好的测量精度和重复性。

[Background]The conversion of UF6,which is a primary nuclear product,to UF4 in fluoride molten salt phase is expected to be used in the preparation or reconstitution of nuclear fuel salt for molten salt reactors,thus simplifying the process of molten salt reactor fuel production.Determination of the concentration of the key intermediate UF_(3) plays an important role in obtaining the reaction parameters.[Purpose]This study aims to establish a method for measuring UF_(3)concentration in solid fluoride molten salts.[Methods]The X-ray diffraction(XRD)was employed to test the homemade standards and obtain the internal standard curve of UF_(3).Firstly,theα-Al2O3 was taken as the internal standard to obtain the XRD peak height internal standard curve(R=0.986)and peak area internal standard curve of LiF-BeF_(2)-UF_(3) molten salt.Then,these two internal standard curves were applied to measuring the known content of LiUF_(5) and UF_(3) solid mixed samples to compare their accuracies.Finally,measurements were conducted on rapidly cooled LiF-BeF_(2)-UF_(3) solid molten salt samples and naturally cooled LiF-BeF_(2)-UF_(3)-LiUF_(5) solid molten salt samples to evaluate the stability and accuracy of the curve,and the relative error was obtained.[Results]In the UF_(3) concentration range of 1.00~10.00 wt%,the correlation coefficient of the internal standard curve based on the peak area determined for of LiF-BeF_(2)-UF_(3) molten salt is 0.995.Measuring results of solid mixed samples of LiUF_(5) and UF_(3) with known concentrations indicate that the peak area internal standard curve achieves better accuracy with a relative measurement error of no more than 8.7%.In addition,the results of the same content samples with different cooling methods confirm the good stability and accuracy of the proposed method with less than 5.4%relative standard deviation.[Conclusions]The established method can be used for the quantitative analysis of solid LiF-BeF_(2)-UF_(3) and LiF-BeF_(2)-UF_(3)-LiUF_(5) molten salts with good measurement accuracy and repeatability.