In situ radiation testing of KU and KS-4V optical fibers in a reactor environment

In situ radiation testing of pure-silica-core hardened (H2-loaded and pre-irradiated) and as-drawn (untreated) optical fibers with high-OH low-Cl KU core and low-OH low-Cl KS-4V core in neutron and gamma fluxes was carried out according to IR-8 reactor power. Both the radioluminescent and radiation-induced loss spectra were measured. Hardening technology (i.e. H2-loading and pre-irradiation) for both KU and KS-4V fibers provides high radiation resistivity and reduced luminescence level. The level of induced loss in the visible spectral region is lower than ∼2.5 dB/m up to a fast neutron fluence (En>0.1 MeV) of about 1×1016 n/cm2. KU fiber demonstrates a rather flat induced absorption spectrum, while the KS-4V fiber has a specific point in the loss spectrum in the vicinity of 460 nm: the induced loss retains level from 0.2 to 0.5 dB/m at the fast neutron fluence up to 3×1015 n/cm2. The KS-4V hardened fiber demonstrates recovering of transmission after neutron flux shutdown.