GROWTH OF OPTICAL-TRANSMISSION LOSS AT 850 NM IN SILICA CORE OPTICAL FIBERS DURING FISSION REACTOR IRRADIATION

Pure, OH-doped and F-doped silica core optical fibers were irradiated in a fission reactor at 400 +/- 10 K using an electric heater at a rea ctor power greater than 10 MW (20% of the full power). The temperature was not controlled well at the early stage of the reactor startup, wh en the temperature was about 320-340 K. The optical fibers were irradi ated with a fast neutron (E > 1 MeV) flux of 3.2 x 10(17) n/cm(2)s and a gamma dose rate of 3 x 10(3) Gy/s for 527 h, Optical transmission l oss at 850 nm was measured in situ during irradiation. A prompt increa se in optical transmission loss was observed as irradiation started, w hich was probably due to dynamic irradiation effects caused by short-l ived and transient defects and is probably recoverable when irradiatio n ceases. After the prompt increase in optical transmission loss, a so -called radiation hardening was observed in fibers containing OH. Radi ation hardening was also observed in 900 ppm OH-doped fiber at the sec ond startup. The optical transmission loss increased linearly with irr adiation dose, denoted as the accumulated loss, which we believe is du e to irradiation-induced long-lived defects. Accumulated loss dominate s radiation-induced optical transmission loss in a fission reactor irr adiation. (C) 1998 Elsevier Science B.V.