氢同位素形态对电离室氚测量的影响

Effect of Hydrogen Isotope Morphology in Ionization Chamber on Tritium Measurement

电离室是在线含氚气体测量的重要手段,其测量响应快但却受到多种因素影响。在聚变堆包层氚载带提取的氦气中存在不同形态的氢同位素气体(如H_(2)O、HTO与HT),为了研究其对电离室氚测量的影响,本文结合电离室、色谱、露点仪等测量设备建立了一套循环实验系统。在该系统中,分别配制了湿润的高纯氦气、湿润的含氚氦气、干燥的含氚氦气,将其缓慢充入循环系统,以此实验方式研究了水汽对电离室和色谱测量的影响,分析了高浓度氚环境下电离室测量时的离子复合效应。再通过不同氢浓度的氦载气中氚活度浓度测量实验验证了在He-H_(2)体系下氢气对电离室氚测量电离增强效应的影响。结果表明,当系统中H_(2)O、HTO与HT的浓度增加将导致电离离子的复合效应增强,电离室氚活度浓度测量结果降低,色谱测量得到的结果在水汽影响情况下比实际值低。在He-H_(2)环境中,氚活度浓度测量值受到氢气含量电离增强效应的影响。

Ionization chamber is an important means for on-line measurement of tritium containing gas.Its response is fast but it is affected by many factors.With the development of fusion reactor and other tritium-related systems,on-line tritium activity concentration measurement is more accurate.There are gases with different hydrogen isotope forms(such as H_(2)O,HTO and HT)in the helium extracted from the tritium carrier band of the envelope of fusion reactor.In order to study their influence on the tritium measurement in the ionization chamber,a tritium measurement experiment system was established in this study,which mainly included gas allocation unit,gas path circulation unit,ionization chamber unit,chromatographic analysis unit and water vapor drying unit.The system can accurately simulate the cycle state of tritium extraction in the cladding of fusion reactor,and can realize the functions of gas preparation,gas concentration measurement and tritium activity measurement.In this paper,the compound effect theory and He+H_(2)system theory in ionization chamber tritium measurement,combined with ionization chamber,chromatography,dew point meter and other measuring means,were used to analyze the influence of different hydrogen isotope gas forms containing H_(2)O,HTO,H_(2)in He on tritium measurement.In the experiment,wet high-purity helium,wet tritium-containing helium and dry tritium-containing helium were prepared respectively and slowly filled into the circulation system.In this way,the influence of water vapor on the measurement of ionization chamber and chromatography was studied,and the ion recombination effect during the measurement of ionization chamber under high concentration of tritium was analyzed.The influence of hydrogen on the enhancement effect of tritium measurement in the ionization chamber was verified by measuring the tritium activity concentration in helium carrier gas with different hydrogen concentration.The results show that the detection efficiency of hydrogen isotope gas by ionization chamber and chromatography is lower in water vapor environment than in dry gas environment.In order to ensure the accuracy of measurement,water vapor should be separated or removed during measurement.When the concentration of H_(2)O,HTO and HT in the carrier gas increases,the recombination effect in the measurement of the ionization chamber is enhanced,resulting in the measurement results of the ionization chamber being lower than the actual value.The problem can be solved by increasing the working voltage of the ionization chamber or modifying the calibration recombination coefficient.When hydrogen exists in the environment of helium carrier gas,the tritium activity concentration measurement result will increase due to the influence of ionization enhancement effect,but when the hydrogen content exceeds 2000 ppm,the ionization enhancement effect will approach the saturation state.