| A performance evaluation of fiber optics under radiation conditions similar to those encountered in nuclear power plants is reported. The evaluation was accomplished by the creation of an analytical model for atomic scale radiation damage in silica glass and by the execution of an extensive fiber performance measurement program.; The analytic model calculates displacement and electronic damage rates for silica glass subjected to a specified nuclear reactor radiation environment. It accomplishes this by first generating the primary charged particle spectrum produced in silica irradiated in a nuclear reactor. The resultant spectra are then applied to the integral equations describing radiation damage in polyatomic solids.; The experimental measurements were selected to span the range of fiber types, radiation environments, temperatures, and light powers expected to be used in nuclear power plants. The basic experimental protocol was to expose the optical fibers to either a nuclear reactor or a {dollar}sp{lcub}60{rcub}{dollar}Co radiation environment while simultaneously monitoring fiber light transmission. Experimental temperatures were either {dollar}sim{dollar}23{dollar}spcirc{dollar}C or {dollar}sim{dollar}100{dollar}spcirc{dollar}C and light powers were either {dollar}-{dollar}30 dBm or {dollar}-{dollar}60 dBm. Measurements were made at each of the three standard communications wavelengths (850 nm, 1300 nm, and 1550 nm).; Several conclusions are made based on these performance measurements. First, even near the core of a nuclear reactor the vast majority of the dose to silica glass is due to gamma rays. Even with the much lower doses (factor of roughly 40) neutrons cause much more displacement damage than gamma rays (35 times the oxygen displacement rate and 500 times the silicon displacement rate). Even with neutrons having many times the displacement rate as compared with gamma rays, little if any difference is observed in the transmission losses for gamma only as compared to mixed neutron/gamma transmission losses. Therefore, atomic displacement is not a significant damage mechanism for creating transmission losses in pure silica core fibers.; The experimental measurements have also demonstrated that optical fibers are currently available which will perform in nuclear reactor containment environments. In particular, pure silica core fibers show the least radiation induced damage. |
