title: Steady γ-Ray Effects on the Performance of PPP-BOTDA and TW-COTDR Fiber Sensing.
abstract: We investigated the evolution of the performances of Pulse Pre Pump-Brillouin Time Domain Analysis (PPP-BOTDA) and Tunable Wavelength Coherent Optical Time Domain Reflectometry (TW-COTDR) fiber-based temperature and strain sensors when the sensing optical fiber is exposed to two γ-ray irradiation conditions: (i) at room temperature and a dose rate of 370 Gy(SiO2)/h up to a total ionizing dose (TID) of 56 kGy; (ii) at room temperature and a dose rate of 25 kGy(SiO2)/h up to a TID of 10 MGy. Two main different classes of single-mode optical fibers have been tested in situ, radiation-tolerant ones: fluorine-doped or nitrogen-doped core fibers, as well as Telecom-grade germanosilicate ones. Brillouin and Rayleigh Sensitivities of N-Doped fibers were not reported yet, and these characterizations pave the way for a novel and alternative sensing scheme. Moreover, in these harsh conditions, our results showed that the main parameter affecting the sensor sensitivity remains the Radiation Induced Attenuation (RIA) at its operation wavelength of 1550 nm. RIA limits the maximal sensing range but does not influence the measurement uncertainty. F-doped fiber is the most tolerant against RIA with induced losses below 8 dB/km after a 56 kGy accumulated dose whereas the excess losses of other fibers exceed 22 dB/km. Both Rayleigh and Brillouin signatures that are exploited by the PPP-BOTDA and the TW-COTDR remain unchanged (within our experimental uncertainties). The strain and temperature coefficients of the various fibers under test are not modified by radiations, at these dose/dose rate levels. Consequently, this enables the design of a robust strain and temperature sensing architecture for the monitoring of radioactive waste disposals.
authors.affiliation: Univ Lyon, Laboratoire Hubert Curien (LabHC), Université de Lyon, CNRS UMR 5516, F-42000 Saint-Etienne, France. isabelle.planes@univ-st-etienne.fr.|Agence Nationale Pour la gestion des Déchets Radioactifs (Andra), F-92298 Châtenay-Malabry, France. isabelle.planes@univ-st-etienne.fr.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Planes
authors.affiliation: Univ Lyon, Laboratoire Hubert Curien (LabHC), Université de Lyon, CNRS UMR 5516, F-42000 Saint-Etienne, France. sylvain.girard@univ-st-etienne.fr.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Girard
authors.affiliation: Univ Lyon, Laboratoire Hubert Curien (LabHC), Université de Lyon, CNRS UMR 5516, F-42000 Saint-Etienne, France. aziz.boukenter@univ-st-etienne.fr.
authors.forename: Aziz
authors.initials: A
authors.lastname: Boukenter
authors.affiliation: Univ Lyon, Laboratoire Hubert Curien (LabHC), Université de Lyon, CNRS UMR 5516, F-42000 Saint-Etienne, France. emmanuel.marin@univ-st-etienne.fr.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Marin
authors.affiliation: Agence Nationale Pour la gestion des Déchets Radioactifs (Andra), F-92298 Châtenay-Malabry, France. sylvie.lesoille@andra.fr.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Delepine-Lesoille
authors.affiliation: CEA DAM DIF (French Alternative Energies and Atomic Energy Commission), F-91297 Arpajon, France. claude.marcandella@cea.fr.
authors.forename: Claude
authors.initials: C
authors.lastname: Marcandella
authors.affiliation: Univ Lyon, Laboratoire Hubert Curien (LabHC), Université de Lyon, CNRS UMR 5516, F-42000 Saint-Etienne, France. ouerdane@univ-st-etienne.fr.
authors.forename: Youcef
authors.initials: Y
authors.lastname: Ouerdane
keywords: Brillouin scattering; PPP-BOTDA; Rayleigh scattering; TW-COTDR; gamma radiation; optical fiber; optical sensors