Characterization of radiation hardened fibers in a research grade nuclear reactor

In order to test and compare the suitability of various radiation hardened optical fibers, we have established a test site in the 5MW research grade open pool reactor located at Soreq Nuclear Research Center, Israel. Several commercial fiber samples were coiled inside a specially designed apparatus which was lowered into the reactor core. The input and output legs of each fiber coil were prepared sufficiently long to extend outside the reactor pool, and were attached to a source (input) and detector (output). The transmission/attenuation could then be measured during, and in between, operations of the reactor. Since the reactor does not operate continuously, we were able to monitor in real time both transmission changes under very high radiation rates (approx. 0.5 MGy/hr) and doses (about 20 MGy) of gamma rays and neutrons, as well as recovery processes after each reactor shut down. Results are presented comparing the RIA and recovery kinetics of different commercial radiation hardened fibers under identical exposure/relaxation cycles. This study also examined effects on fibers with different coating materials and a fiber with inscribed Bragg gratings.