Hydrogen and deuterium distributed sensing using Chirped-Pulse φOTDR

The detection and quantification of the presence of certain chemical species is of central importance regarding permanent structural health monitoring of key industrial fields and civil infrastructures such as oil extraction boreholes or radioactive waste repositories, where H-2 is released. With this work we propose and test a competitive technique able to measure the concentration of hydrogen and deuterium thanks to their diffusion into the silica glass of a standard optical fiber, already employed for the distributed monitoring of large infrastructures. The proposed technique, based on Chirped-Pulse Phase-sensitive Reflectometry (CP-phi OTDR), could represent a novel solution for this problem, thanks to its ability to provide dynamical measurements of refractive index change, with great linearity and sensitivities of 10(-8) refractive index units, featuring spatial resolutions of a few meters and kilometric sensing ranges.