Irradiation Campaign in the EOLE Critical Facility of Fiber Optic Bragg Gratings Dedicated to the Online Temperature Measurement in Zero Power Research Reactors

The control of temperature during operation of zero power research reactors participates to the overall control of experimentation conditions and reveals itself of a major importance when measuring neutronic parameters such as multiplication factors. Within the framework of the refurbishment of the MASURCA facility, the development of a new temperature measurement system based on the optical fiber Bragg grating (FBG) technology is under consideration. In a first step, a series of FBGs is irradiated in the EOLE critical facility with the aim to select the most appropriate. Online temperature measurements are performed during a set of irradiations that should allow reaching a fast neutron fluence of nearly $5\cdot 10^{14}$ n.cm $^{-2}$ and a total gamma dose lower than 4 kGy. The results obtained, especially the Bragg wavelength shifts during the irradiation campaign, are discussed in this paper and compared to data from standard PT100 temperature sensors to highlight possible radiation effects on sensor performances. Work to be conducted during the second step of the project, aiming to a feasibility demonstration using a MASURCA assembly, is also presented.