γ能谱法测量分析阀门中铀滞留量技术研究

Study on Holdup Measurement of Uranium in Valve byγ-ray Spectrometry

定量测量工艺设备中的滞留量是核设施核材料测量的技术难点之一,对辐射防护、核材料临界安全和核材料闭合衡算具有重要意义。在核材料工艺生产线上,阀门与管道的连接方式不利于取样,因此,非破坏性分析方法更适合用于开展阀门中滞留量的测量。本文采用无源效率刻度,针对球阀和蝶阀这两种最常见的阀门,建立了探测器全能峰绝对探测效率分析模型。运用坐标变换方法,实现了阀门分析模型的快速建立。在实验室条件下采用标准点源和铀样品进行了初步验证,铀样品中235 U含量的测量分析结果和标称值的相对偏差小于15%。坐标变换方法可快速准确地建立各种类型阀门的分析模型,为测量分析模型的建立提供了简便易行的解决方案。

During the production and operation of some bulk handling facilities,nuclear material deposits remaining after cleaning in and about process equipment,interconnecting piping,filters and adjacent work area or equipment,which is called holdup.In order to meet the requirements of nuclear material accounting management,the physical inventory of nuclear materials shall be carried out according to the specified frequency,and the amount of nuclear materials shall be the measured value.Quantitative measurement of holdup in equipment is one of the technical difficulties in nuclear material measurement for nuclear facilities.Holdup measurement is important for radiation protection,critical safety and nuclear material management.The valve is a key component to control the material transfer in the process of nuclear material production.The valve is welded to pipe,which is not conducive to sampling.In this paper,mass of uranium in the valve was measured byγ-ray spectroscopy.It is necessary to study absolute detection efficiencies of the detector for known source distribution.Firstly,the passive efficiency calibration was selected to simulate the absolute detection efficiencies.Analysis models consist of detector model and valve models,they were placed under the same observation system by the transforming coordinate method.Analysis models of detector and valves were built based on information of the detector and design drawing of the valves.Two point sources,57 Co and 137 Cs,were used to verify the model.Under the combination of different crystal radius and length parameters,the absolute detection efficiencies for full-energyγ-rays peak were simulated.The crystal parameters of the LaBr 3 detector were adjusted.The root mean square of the relative deviation between the simulation results and the experimental results was calculated.The crystal parameters with the smallest root mean square are the best parameters.The relative deviation between the experimental results and Monte Carlo simulation results for point sources is within 5%.The standard uranium sample was used to carry out experiments.The count rate of characteristicγ-ray was measured by the LaBr 3 detector.The absolute detection efficiencies were simulated by the analysis model.The holdup was calculated according to the relationship between count rate of characteristicγ-ray and the mass of uranium.The results show that the relative deviation between the measured results and the reference values of uranium mass is within 15%.The feasibility of the method for measuring the uranium holdup in the valves is preliminarily confirmed by the experiments.The transforming coordinate,a simple and easy solution,by which the analysis model can be quickly and accurately built.