Influence of Optic Cable Construction Parts on Recovery Process after Gamma Irradiation

Fibre optic cables are widely used as communication cables in Instrumentation and Control (I&C) systems. In the case of nuclear power plants (NPPs), using optic cables in mild environments outside of containment areas are very common. However, at present, there is a need for fibre optic cables to be used in containment areas, i.e., with radiation. An optical fibre consists of a highly transparent core that possesses a higher refractive index than the surrounding transparent cladding, which possesses a lower refractive index. Most optical fibres are manufactured from glass (silica with required dopants) which is created at high temperatures from the reaction between gasses. The glass used in optical fibres is sensitive; it becomes dark during exposure to radiation, which compromises the optic functions. That is why there has been a slow infiltration of optic cable in NPP containment areas. Radiation resistant optic fibres have been developed. Although these fibres are called “radiation resistant,” they go through a darkening process (absorbance increase) as well, but not as quickly. Immediately after the irradiation has stopped, a recovery process starts in the glass structure. During this period, optical losses of the glass improve, but not to the original level as before the irradiation. During the testing of optic cables for the installation in nuclear power plant containment areas, we observed an unusual recovery process. In the beginning, a healing effect was observed. However, after a few days of recovery, the healing process stopped, and the trend changed again as a worsening of the optical properties was observed. This paper describes experiments which explain the reasons for such an unexpected behaviour.

YAG : R3+ (R = Ce, Dy, Yb) nanophosphor-based luminescent fibre-optic sensors for temperature measurements in the range 20–500 °C

We report the development of a group of luminescent fibre-optic temperature sensors that use Ce3+-, Dy3+-, and Yb3+-doped yttrium aluminium garnet (YAG) nanophosphors as thermosensitive materials. The nanophosphors have been prepared in the form of powders with a crystallite size from 19 to 27 nm by a polymer ? salt method and exhibit bright luminescence at 550 (YAG : Ce3+), 400, 480 (YAG : Dy3+), and 1030 nm (YAG : Yb3+). The sensor design includes a silica capillary, partially filled with a nanophosphor, and two large-aperture multimode optical fibres located in the capillary, which deliver excitation light and receive and transmit the photoluminescence signal. The photoluminescence signal amplitude of all the sensors decreases exponentially with increasing temperature, pointing to characteristic thermal quenching of photoluminescence and adequate operation of the devices up to 500 °C. The highest temperature sensitivity among the fibre-optic sensors is offered by the YAG : Ce3+ nanophosphor-based devices.

FIBRE OPTIC BRAGG STRUCTURES WITH MONOTONIC APODISATION CHARACTERISTICS

The article discusses the principle of operation and the structure of chirped and uniform gratings. It presents the method of producing gratings with monotonic apodisation characteristics, and compares the spectral features of produced gratings with the those obtained by mathematical modelling.

Revisiting the Power Co-ordination Challenges of the Original Snowy Mountains Scheme

The Snowy Mountains Scheme (1949–1972) was an Australian hydro-electricity generation triumph. However, the power co-ordination challenges were significant before the invention of fibre optic cable, as this historic paper from June 1964 attests.