We investigated the Bragg Wavelength Shift (BWS) induced by X-rays in a large set of conventional FBGs up to 100kGy dose. Obtained results give some insights on the influence of irradiation parameters such as dose, dose rate as well as the impact of some writing process parameters such as thermal treatment or acrylate recoating on the FBG radiation tolerance.
HOBAN (Development of Hard Optical Fiber BrAgg GratiNgs Sensors) is an European H2020 project granted by Kic InnoEnergy and aiming the development of fiber-based temperature and strain monitoring systems that can withstand harsh nuclear environment (350°C temperature and MGy dose levels). The objective will be achieved by employing ‘ad hoc’ fiber Bragg grating (FBG) sensors and their associated instrumentation system which will bring to the market new tools for optimizing the running and the services in current and future nuclear power plants. We’ll present the challenges associated with this project and recent advances at the OFS conference.
Temperature response of radiation-tolerant OFDR-based sensors is here investigated, with particular attention on the impact of coating on OFS. By performing consecutive thermal treatments we developed a controlled system to evaluate the performances of our distributed temperature sensor and to estimate the radiation impact. We show an important evolution of the temperature coefficient measurements with thermal treatments for non-irradiated fiber and that the amplitude of this change decreases increasing radiation dose. As final results, we demonstrate that sensor performances are improved if we performed a pre-thermal treatment on the fiber-based system permitting to monitor temperature with an error of 0.05°C.
The difficulties encountered in the implementation of a temperature or strain sensor based on Fiber Bragg Grating in a harsh radiative environment are introduced. We present the choices made to select both a radiation-resistant fiber in terms of transmission and also the grating inscription conditions necessary to write radiation tolerant FBGs in such fibers with a femto-second laser. The response of different classes of gratings was also studied under radiation at high doses (<1MGy). The comparison between F- and Ge-doped fibers was highlighted.