Theoretical investigation of tritium concentration quantification method for DT fuel system using β-ray induced X-rays

Abstract

Tritium measurement is one of the most important issues in DT fuel system of a fusion reactor. Beta-ray Induced X-ray Spectrometry (BIXS) method is a promising way to obtain tritium concentration in-line, especially for fuel processing system. However, till now there is no theory to establish the quantification relationship between tritium concentration and gas information including gas composition and pressure. Theoretical relationship between tritium concentration and X-ray spectrum in BIXS measurement is derived, and a quantitative method was proposed to determine tritium concentration directly by using the counts of X-ray spectrum. Non-linear Response Coefficients (NRCs) are introduced in the method to indicate the response of X-ray detector at different gas pressures for different gas compositions. Effects of both gas compositions (hydrogen/deuterium/tritium) and gas pressure (over five orders of magnitude, 1 Pa to 100 kPa) have been investigated quantitatively by Monte-Carlo simulations to determine the key parameters in the proposed method. Results show that for gas composed of hydrogen, deuterium, and tritium, NRCs are independent of gas composition within gas pressure from 1 Pa to 100 kPa. And NRCs can be obtained from the counts calculated within any energy region of X-ray spectrum detected in BIXS measurements. With the calculated NRCs, the tritium concentration can be obtained using only one reference experiment performed at any gas pressure (1 Pa to 100 kPa) for gas composed of any hydrogen isotopes. For gas composition including hydrogen, deuterium and tritium with different concentration, the error of NRCs in the proposed method is estimated to be 1.4%.