CFD calculations of response time for ionization chambers in tritium measurements

Abstract

Response time of ionization chambers for tritium measurements in dynamic mode is very important to indicate the change of tritium concentration in line. CFD software ANSYS FLUENT is firstly introduced to evaluated the response time of ionization chambers quantitatively, and effects of parameters including chamber size, gas flow velocity, size of inlet/outlet pipe, et al., have been calculated. Results show that both chamber size and shape have significant influence on response time of an ionization chamber. Chambers with small volume or larger diameter/length ratio at given volume help greatly to reduce response time. For a given chamber, increasing the size of both inlet and outlet pipe connected to the chamber is also an effective way to improve response time. Comparing with helium, air and methane as carrier gas, argon gives the fastest response time at the same condition. Besides, a decrease in tritium concentration in inlet carrier gas will take longer time to be indicated by an ionization chamber than the time for increased tritium concentration.