IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 61, NO. 6, DECEMBER 2014 3315 Development of a Temperature Distributed Monitoring System Based On Raman Scattering in Harsh Environment C. Cangialosi, Student Member, IEEE, Y. Ouerdane, S. Girard, Senior Member, IEEE, A. Boukenter, S. Delepine-Lesoille, J. Bertrand, C. Marcandella, P. Paillet, Senior Member, IEEE, and M. Cannas Abstract—Raman Distributed Temperature Sensors (RDTSs) offer exceptional advantages to monitor the envisioned French deep geological repository for nuclear wastes, called Cigéo. Both -ray and hydrogen release from nuclear wastes can strongly affect the temperature measurements made with RDTS. We present experimental studies on how the performances of RDTS evolve in harsh environments like those associated with -rays or combined radiations and release. The response of two standard and one radiation tolerant multimode fibers (MMFs) are investigated. In all fibers the differential induced attenuation between Stokes and anti-Stokes signal, causes a temperature errors, up to with standard multimode fibers (100 m) irradiated at 10 MGy dose. This degradation mechanism that is more detrimental than the radiation induced attenuation (RIA) limiting only the sensing range. The attenuation in the [800-1600 nm] spectral range at room temperature is explored for the three fibers -irradiated and/or hydrogen loaded to under- stand the origin of the differential RIA. We show that by adapting the characteristics of the used fiber for the sensing, we could limit its degradation but that additional hardening by system procedure is necessary to correct the T error in view of the integration of our RDTS technology in Cigéo. The current version of our correction technique allows today to limit the temperature error to for 10 MGy irradiated samples. Index Terms—Distributed temperature, gamma radiation, hy- drogen release, optical fiber sensing, radiation effects, Raman scat- tering. I. INTRODUCTION D ISTRIBUTED optical fiber temperature sensors based on the temperature dependence of Raman scattering in silica have been intensively investigated during the last years [1], [2]. Manuscript received July 11, 2014; revised October 07, 2014; accepted Oc- tober 31, 2014. Date of publication December 04, 2014; date of current version December 11, 2014. C. Cangialosi is with Lab. Hubert Curien, Université de Saint-Etienne, F-42000 Saint-Etienne, France, and also with Dipartimento di Fisica e Chimica, Università degli Studi di Palermo, 90100 Palermo, Italy (e-mail: chiara.cangialosi@univ-st-etienne.fr). Y. Ouerdane, S. Girard, and A. Boukenter are with Lab. Hubert Curien, Université de Saint-Etienne, F-42000 Saint-Etienne, France (e-mail: ouerdane@univ-st-etienne.fr; sylvain.girard@univ-st-etienne.fr; aziz.boukenter@univ-st-etienne.fr). S. Delepine-Lesoille and J. Bertrand are with the French National Radioactive Waste Management Agency (Andra), 92298 Chatenay-Malabry, France (e-mail: Sylvie.Lesoille@andra.fr; Johan.Bertrand@andra.fr). C. Marcandella and P. Paillet are with CEA DAM DIF, F91297 Arpajon, France (e-mail: claude.marcandella@cea.fr; philippe.paillet@cea.fr). M. Cannas is with Dipartimento di Fisica e Chimica, Università degli Studi di Palermo, 90100 Palermo, Italy (e-mail: marco.cannas@unipa.it). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TNS.2014.2368787 They are now employed in various industrial application ranges such as the fields of (i) public safety like fire detection inside buildings and tunnel or (ii) the industrial process monitoring. This technology has also recently shown considerable promise for the temperature monitoring of nuclear facility [3]–[6]. Raman Distributed Temperature Sensors (RDTS) are in- trinsic optical fiber sensors, in which the optical fiber is not only a transmission medium but also the sensing material. RDTS offer exceptional advantages over traditional electronic sensors for temperature monitoring of the envisioned French deep geological repository for long-lived high-level (LL/HL) and intermediate-level (LL/IL) nuclear wastes, called Cigéo [7]. In particular, they provide temperature changes along the fiber over distances extending up to several kilometers with one meter spatial resolution and thus overcome limitations of traditional sensors, whose information is restricted to local effects. The study of the vulnerability of RDTS technology in Cigéo radiation environment requires evaluating the influence of different constraints such as -rays and hydrogen effects on their performances. Inside the storage cell, the temperature varies between and . The gamma radiation dose rate varies between 1Gy/h and 10Gy/h depending on the considered wastes. These radiation levels lead to a significant degradation of Telecom-grade optical fibers over the facility lifetime (100 years) through the radiation induced attenuation (RIA) phenomenon. Moreover, small hydrogen releases ( mmol/hour for few IL nuclear wastes) originating from nuclear waste release and anoxic corrosion of materials are expected. These small concentrations could slowly and regularly increase when ventilation stops with cell closure. Its maximum levels could approach 100% hydrogen content in the atmosphere [8]. So, these mobile species can diffuse into the fiber and affect its transmission properties. We recently investigated the degradation mechanisms of RDTS for some types of aggressions, such as those associated with or -rays [9], [10]. We tested diverse classes of stan- dard fibers, with different dopant species, cladding and coating composition. We observed that the Raman response is strongly influenced by the dose and by the hydrogen presence into the fiber core. The RIA influences the relative intensities of Stokes and anti-Stokes components used by the RDTS system to mon- itor temperature, leading to both large errors in the temperature measurements and limiting measurable range of length. Indeed, we observed the impossibility to use P-doped fibers as RDTS 0018-9499 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.