En-Sti

—The integration of Raman-distributed temperature fiber-based sensors (RDTS) into the envisioned French deep geological repository for nuclear wastes, called Cigéo requires evaluating how the performances of RDTS evolve in harsh environments, more precisely in presence of H2 or γ-rays. Both H 2 and radiations are shown to affect the temperature measurements made with the single-ended RDTS technology. The amplitudes of the observed effects depend on the different classes of multimode fibers varying in terms of composition and coatings. By selecting the most tolerant fiber structure for the sensing, we could maintain the RDTS performances for such application. A hardening by system studies will be mandatory before integration of single-ended RDTS in Cigéo.

Brillouin optical time-domain analysis (BOTDA) sensors offer remarkable advantages for the surveillance of the planned French deep geological radioactive wastes repository, called Cigéo 1,2. In this work we study the performances of Brillouin distributed sensors in harsh environment. We evaluate the radiation tolerance of different sensor classes and their responses evolution during -ray exposition with 1kGy/h dose rate (to reach ~0.2MGy) and after 1, 3, 6 and 10 MGy accumulated doses. Measurements on strained Ge-doped SMF are reported to highlight the variation on Brillouin scattering proprieties, both intrinsic frequency position of Brillouin shift and its dependence on temperature and strain.

Raman Distributed Temperature Sensors (RDTS) offer exceptional advantages for the monitoring of the envisioned French deep geological repository for nuclear wastes, called Cigéo. Here, we present experimental studies on how the performances of RDTS evolve in harsh environments like those associated with H 2 or γ-rays. Both of them are shown to strongly affect the temperature measurements made with RDTS. We showed that by adapting the characteristics of the used fiber for the sensing, we could limit its degradation but that additional hardening by system studies will have to be developed before integration of RDTS in Cigéo.

(35 words) The radiation tolerance of different distributed Raman based sensor classes and/or their responses evolution during gamma-ray exposure at 1 kGy/h dose rate (to reach ~0.1 MGy) was investigated to monitor radioactive waste deep geological repository. Abstract—We report distributed fiber optic temperature measurements based on Raman scattering performed during -radiation with a dose rate of 1 kGy/h to reach accumulated dose up to ~ 0.1 MGy. We assess the performances evolution of Raman distributed temperature sensor (RDTS) comparing different classes of standard multimode fibers (MMFs) irradiated in view of their integration into the French deep geological repository for radioactive waste, called Cigeo (in project). Under -rays the sensor response is affected by the radiation induced attenuation phenomena leading to errors in the RDTS temperature measurements. The amplitude of this error strongly depends on the fiber type and the irradiation conditions. For the single-ended RDTS operation in the Cigeo application, a selection of the most online-radiation tolerant sensing fiber will be mandatory.

Abstract—We report distributed temperature measurements based on Raman scattering performed during steady state gamma-ray irradiation at a dose rate of 1 kGy(SiO 2)/h and up to a total ionizing dose (TID) of ~ 0.1 MGy. We characterize on-line the evolution of the performances of a single-ended Raman distributed temperature sensor (RDTS) during the -ray exposure of different classes of commercial multimode fibers (MMFs) acting as the sensing element. RDTS is influenced by the radiation-induced attenuation (RIA) phenomena leading to both large errors in the temperature measurements and a diminution of the useful sensing length. The amplitude of the radiation-induced temperature error strongly depends on the fiber choice and on the irradiation conditions. For the single-ended RDTS operation in the targeted Cigéo application the selection of a radiation tolerant sensing fiber will be mandatory, but not sufficient, to overcome the expected severe ambient conditions around radioactive wastes. For efficient temperature sensing up to an accumulated dose of 0.1 MGy, pre-irradiation of the selected radiation resistant (RR) fibers appears also necessary to improve the sensor performances.

—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 understand 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.

In this paper, we demonstrate and highlight a proof of concept for the feasibility of an innovative technique to regenerate on-site irradiated optical fiber links in nuclear facilities. Using Hole-Assisted optical fibers (HAOF), a longitudinal gas-loading is easy to perform thanks to the fibers' dedicated holes located in the outer part of the cladding. All along the fiber length, gas (or) diffuses from the holes into the silica matrix, interacts with radiation induced point defects and passivates them, reducing the Radiation Induced Attenuation (RIA) levels. The validity of our approach is demonstrated considering the changes occurring at infrared wavelengths during the treatment of a MGy irradiated single mode Ge-doped HAOF. Within just a few hours, a reduction of about 50% is observed for the RIA at 1550 nm of the 10 MGy irradiated HAOF, acting only from one of its two ends. An additional study is done on a set of fibers with various core dopants (F, Ge, P) and without holes to give an overview of the pertinence of developing HAOF fibers with these dopants for various applications. Using HAOF and this recovery technique appears very promising for samples based on pure-silica, Ge or F-doped cores and operating in the ultraviolet-visible spectral domains such as plasma diagnostics. This approach exhibits another interesting feature which may be extension to higher dose ranges and lifetime of P-doped distributed dosimeters used in high energy physics facilities or nuclear power plants.