There is a large amount of tritium in tail gas emitting from the molten salt reactor. The content of tritium content in tail gas must be measured and controlled according to the national standard. Nowadays, the ionization chamber and the liquid scintillation counter are mainly used for tritium monitoring. The proportional counter required pure sampling gas, and the liquid scintillation cannot measure the radioactivity online. Only the ionization chamber could measure the activities of off-gas from molten salt reactor. In order to reduce tritium contamination in the ionization chamber, a wire type high pressure ionization chamber was used in measuring tail gas from molten salt reactor. In order to improve the ion collection efficiency of the wire type electrode ionization chamber, it is necessary to optimize the number of the electrodes. In this study, the electric field of ionization chamber with different numbers of electrodes, such as 3, 6, 12, 18, 24, 30, 36, 42, 48, were simulated by COMSOL software. The equipotential line of electric field near the collector is round. The equipotential line of electric field near the high voltage wires present as undulate. From the results, the optimum number of wires was 36. The difference of electric field between two types chambers were less than 5%. After that, collection efficiency was simulated as well. Increasing the number of the high voltage electrode at top and bottom of effective area could not improve the electron collection efficiency. Making the ionization chamber shell as an insulator can effectively improve the electrons collection efficiency.

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