International audienceRaman Distributed Temperature Sensors (RDTSs) offer exceptional advantages to monitor the envisioned French deep geological repository for nuclear wastes, called Cigéo. Both γ-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 γ-rays or combined radiations and H2 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, (αAS - αS) causes a temperature errors, up to 30° C 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 γ-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 ~ 2° C for 10 MGy irradiated samples

Raman-based Distributed Temperature Sensors (RDTS) allow performing spatially resolved (1 m) reliable temperature measurements over several km long Optical Fibers (OFs). These systems are based on the temperature dependence of the intensities of both the Stokes and anti-Stokes components of the Raman back-scattered signal. One of the specific issues associated with RDTS technology in radiation environments is the differential Radiation Induced Attenuation (RIA) between the two components that induces huge errors in the temperature evaluation. Such problem is particularly evident for commercially available single-ended DTS using one laser source. Doubleended configuration could be used to correct for the differential attenuation but are limited by RIA in terms of sensing range. In the present work, we show how a Radiation-Hardened-by-Design DTS (RHD-DTS) overcomes the observed radiation issues keeping the single-ended interrogation scheme. In the tested RHD-DTS two infrared excitation laser sources (∼1550 nm and ∼1650 nm) are employed: the wavelength of the Stokes component due to the first excitation source coincides with the wavelength of the second excitation; vice versa, the wavelength of the anti-Stokes component due to the second excitation source coincides with the wavelength of the first excitation. The overall result is that the two signal intensities are automatically corrected for the differential RIA all along the OF sensor length and the temperature measurements becomes robust against radiation effects. This study demonstrates the potential of such a sensor by reporting preliminary experimental results obtained with a prototype developed by Viavi Solutions exploiting radiationsensitive or radiation-hardened optical fibers.

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International audienceThe 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 H2 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

Raman Distributed Temperature Sensors (RDTS) offer exceptional advantages for the monitoring of the envisioned French\ud 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 H2 or g-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\ud integration of RDTS in Cigéo

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A new shape memory alloy (SMA)-based coupling system for ultra-high vacuum (UHV) applications in particle in accelerators is currently under investigation at the European organization for nuclear research (CERN). The use of such technology in some restricted-access radioactive areas within CERN accelerators could result in noticeable advantages, especially during maintenance operations. Bolt-free SMA couplers, can be activated remotely by temperature changes, resulting in significant reduction of the radiation doses collected by the technical personnel. The functional performance of SMA-based prototype systems, in terms of leak tightness, thermal mounting/dismounting and thermal outgassing properties, has been already verified. Radiation-induced microstructural damages usually cause losses in the mechanical properties, such as embrittlement in conventional engineering metals. The particle radiation effects on the functional characteristics of SMAs, in terms of microstructural transition mechanisms, represent a key issue for their application in critical accelerators areas. To this aim, specific research activities are being carried out at CERN for capturing the evolution of SMA mechanical and functional properties during and/or after particle irradiation. In this preliminary study, a few selected SMA-based prototype UHV chambers, have been exposed to a high-energy mixed particle field (up to ∼140 kGy of absorbed dose) at the CERN high-energy accelerator mixed-field (CHARM) facility. The results, in terms of post-irradiation measurements, have revealed that leak tightness and thermal dismounting are unaffected by irradiation.