Evaluation of fiber optics for in-line photometry in hostile environments

Commercial fiber optic cables, both bundled and single-fiber, were evaluated for application in an in-line photometer being developed for monitoring uranium and plutonium concentrations in high radiation environments in nuclear fuel reprocessing plants. The attenuation of the optical signals due to both the radiation damage and to the couplings between lengths of optical cable was determined for specimen cables. An ultraviolet-enhanced fiber bundle demonstrated good radiation resistance to a total dose of 108 rad, which is the dose extimated to be received during a 1-y lifetime of the in-cell portion of the photometer. The loss in signal transmission at cable junctions was greater in the fiber-bundle cable than in a 1-mm-diam, silica, single-fiber cable: a loss of 6 dB across each junction in the fiber-bundle cable vs 3 dB in the single-fiber cable. Attenuation in the single-fiber cable after a dose of 106 rad was 2.5 times greater at 500 nm than that of a fiber bundle of similar length. However, the single-fiber cable was still usable at a dose greater than 107 rad. The photometer was designed to use a single-fiber optical cable with adequate radiation shielding. 5 figures