A technique for conducting of reactor in-situ tests of optical fibres and FBG-sensors intended for in-vessel applications in thermonuclear facilities

A method for in-situ studies of the optical fibres (OFs) and the fibre Bragg grating (FBG) sensors radiation resistance under irradiation at the IVG.1 M research reactor (Kurchatov, Kazakhstan) was developed. For this purpose, an irradiation ampoule device (AD) was developed that makes it possible to carry out joint irradiation of investigated samples with a fast neutron flux of up to 2.4 10(13) n/(cm(2)center dot s) and a dose rate of up to 1.57 kGy/s in the temperature range from 200 to 700.C and pressures of 10-80 Pa. Studies of radiation-induced attenuation (RIA) of single-mode OF in various protective coatings (copper, aluminium and polyimide at a wavelength of 1.55 mu m and in the spectral range from 1.1 to 1.7 mu m were carried out. Fast neutron fluence and absorbed dose were Phi(E > 0.1MeV)=1.72 center dot 10(17) n/cm(2) and D gamma=11.3 MGy, respectively. It has been established that the method of fibre winding in AD has a critical influence and leads to a parasitic contribution of temperature-induced stress-related losses to optical losses arising during reactor irradiation. The operability of FBG sensors up to a temperature of 500(circle)C has been demonstrated. The developed methods make it possible to conduct in-situ studies of the radiation resistance of fibre-optic components under conditions close to their applications in thermonuclear and nuclear facilities.