Fiber optics is now widely used for data communication, sensing and vision applications. In the nuclear industry, however, its use is still quite limited. This paper reviews two particular areas where the optical fibers could bring substantial advantages: the decommissioning of shut- down nuclear installations, and the long term storage of nuclear waste. It summarizes some expected potential benefits, but points out also the challenges to be met for wider applications of fiber optics in a nuclear environment.

A new kind of instrumentation based on Optical Fiber Bragg grating sensors is proposed for the main relevant monitoring needs in the electric power industry. The challenging metrological properties of these components are presented and their good resistance to (gamma) -ray irradiations experimentally proved.

Optical fibers find rapidly growing use also in the nuclear industry. The dependence of their radiation-induced loss on fiber type, wavelength, temperature, light power, dose rate, and radiation type (gamma rays, neutrons) is pointed out and test results of modern (1989 - 1993) single mode (SM), graded index (GI), multimode stepindex (MM SI), and polymer optical fibers (POF) are presented. Continuous ⁶⁰Co gamma irradiation of the SM fibers with a dose rate of about 1.5 Gy/s up to a final dose of 10⁶ Gy led to radiation-induced losses of only 0.85 to 1.3 dB/10 m at 1300 nm wavelength and temperatures around 30 degree(s)C, whereas the GI fibers had losses of 1.3 to 2 dB/10 m under the same conditions. The lowest radiation-induced loss show MM SI fibers with pure SiO₂ core of high OH-content: about 0.15 dB/10 m around 850 nm and about 0.1 dB/10 m around 1060 nm (10⁶ Gy, equals 30 degree(s)C). POF with a core made of polymethyl methacrylate also have loss increases of <EQ 0.1 dB/10 m (670 nm, room temperature), but only up to gamma dose values <EQ 800 Gy. The breaking stress of allglass fibers after 10⁶ Gy increased by about 2% (MM SI) up to about 10% (SM). 14 MeV neutron irradiations seem to cause higher losses and reduced breaking stress, compared with ⁶⁰ Co gamma irradiations up to the same total dose.

The suitability of different optical fiber types for use in the nuclear power industry is considered and recommendations made on methods for predicting their behavior in associated radiation fields.

Active optoelectronic devices such as light emitting diodes (LEDs), laser diodes (LDs), photodiodes (PDs), and optocouplers (OCs) were evaluated for degradation under gamma, 14 MeV neutron, and flash X-ray irradiation. Dose rates, total dose values, and neutron fluences were chosen such that we get estimates of the behavior especially in space environments and nuclear engineering. The devices are designed for wavelengths from 660 to 1550 nm. LEDs showed a decrease of output power between 0.1 and 28 dB after a total gamma does of 10⁶ Gy or neutron fluences of 4 X 10¹⁴ cm^-2 (1 MeV), respectively. The threshold current of LDs shifted to higher values with increasing dose (⁶⁰Co) and neutron fluence. Irradiations of PDs with ⁶⁰Co gammas up to a total dose of 10⁶ Gy as well as irradiations with neutrons up to fluences of 4 X 10¹⁴ cm^-2 (1 MeV) lead to a strong increase of dark current. OCs show a significant reduction of the current transfer ratio at dose values between 10³ and 10⁴ Gy. Except two types, the optocouplers did not survive neutron fluences >= 8 X 10¹¹ cm^-2 (1 MeV).

Fluorine-doped silica active and passive optical fibers for different purposes have been fabricated by two novel modifications of the plasmachemical technology. These versions of the technology are shown to be convenient in laboratory conditions and very promising in developing various types of special fibers with non-standard parameters based on pure and fluorine-doped silica.

Spectra and kinetics of decay of (gamma) -irradiation induced loss in optical fibers with pure silica and Ge- and/or F-doped silica core and F-doped cladding made by MCVD and SPCVD methods were measured at room temperature. Induced loss in short-wavelength range is shown to decrease at Ge-content decrease and at F addition to the core glass. Minimum of induced loss is located in long-wavelength range, the best result (about 2 dB/km after the dose 10 kGy) being achieved on pure silica core MCVD fiber. Induced absorption band at 630 nm is observed in pure silica core fibers and it is suppressed by F-doping of the core glass.

The radiation-induced light absorption in bulk quartz, Polymer Clad Silica (PCS) and Gradient-Index (GI) fibers is studied. The radiation-induced absorption spectra of four kinds of bulk quartz samples in UV wavelength region are measured. The new absorption band around 215 nm is found, the increase of the sample absorption is attributed to the impurity content. Radiation-induced attenuation spectra of PCS fibers drawn from the bulk quartz materials are shown. The dependence the radiation-induced attenuation on the fiber diameter in the PCS fibers is related to the changes in the silicone optical cladding. The radiation- induced light attenuation in GI fibers is studied in the wavelength range of 450 to 1000 nm. The radiation-induced absorption band centered around 560 nm and the shift of the UV absorption edge towards the longer wavelengths are found. Simple experimental schemes are proposed on the base of these results and tested for radiation dosimetry purposes including the measurements in the nuclear power plant Dukovany.

This paper provides a summary of several needs for improved measurements in the nuclear industry and identification of where better instrumentation might benefit this industry. Several advanced prototype fiber optic sensors are described which are suited for future applications in nuclear reactor containment and nuclear waste management. The performance characteristics of the prototypes in non-nuclear applications are summarized.

Time-Resolved Laser-Induced Fluorescence has been used for uranium and nitrate remote sensing in the nuclear fuel cycle. Advantages of this technique are aside sensitivity and selectivity, its ability to perform remote measurements via fiber optics and optode. Uranium is usually determined by the standard addition method but by applying a fluorescence model taking into account complexation and absorption phenomena, it is possible to directly determine uranium concentration. Nitrate concentration is determined after spectral deconvolution of the uranium fluorescence spectrum.

The American Society for Testing and Materials (ASTM) has established a radiation standard working group under the auspices of the E13.09 subcommittee on fiber optics, which reports to the E13 committee on molecular spectroscopy. The goal of this working group is to develop and publish standards to qualify fiber optic spectroscopic systems for use in adverse nuclear environments. These goals are in line with the charter of the ASTM organization that is `the development of standards on characteristics and performance of materials, products, systems and services; and the promotion of related knowledge.' Under preliminary efforts to promote the use of fiber optic spectroscopic systems in adverse nuclear environments with an emphasis on nuclear waste storage facilities and nuclear generating stations, two draft standard guides have been prepared to measure ionizing radiation induced spectral changes in optical fibers and cables for use in Broadband systems and remote Raman fiber optic spectroscopic systems.

An optical fiber sensing system is assessed for radiation performance. The optical fibers are irradiated with gamma radiation from a cobalt 60 source. The sensing system consists of a white light source, silicon detectors and multimode optical fibers. The optical system measures the chromaticity of the light in dominant wavelength derived from either a distimulus or tristimulus measurement. Both measurement systems are generic and can operate with up to eight modulating sensors simultaneously and are designed to form part of existing monitoring or control system. All components are commercially available and the optical fiber system is undergoing trails in the nuclear, chemical and electrical power distribution industries.

A survey of fiber-optic sensors for the measurement of ionizing radiation is given. The interactions between ionizing radiation and fiber material, which are of significance for the fiber-optic detection of ionizing radiation, as well as the changes in the properties of the optical fibers induced by such interactions are discussed. Measurement and evaluation techniques for reading out the optical properties induced by ionizing radiation are described. A survey of possible applications for fiber-optic radiation sensors is given. The properties and application possibilities of fiber-optic dosimeters based on radiation-induced losses are specified. In particular, the requirements to be met by fiber-optic dosimeters for applications in radiation therapy are discussed. A fiber-optic dosimeter measuring system for radiation therapy based on radiation-induced losses is presented.

Optical components including imagefiber, periscope, glass, reflecting mirror and adhesive for lens are essential elements of in-vessel viewing system use for fusion experimental reactor and extensive of gamma irradiation tests have been conducted. These components were irradiated in the range of 1 MGy - 100 MGy under the average exposure dose rate of 1 X 10⁶ R/h. As a result, the observation limit of the imagefiber specially fabricated for radiation hard is obtained to be 12 MGy at a illuminance of 8500 lx. Deterioration of transmissivity of three kinds of glass (alkaline barium glass, lead glass and synthetic quartz glass) is small compared with standard glass for commercial periscope. A periscope which was made of these glasses is visible even after 20 MGy at 8500 lx and in case of the standard periscope, the observation limit is 1 kGy at 8500 lx. Decrease in the reflectance on chromium nitride coated reflecting mirror is extremely small than aluminum coated and platinum coated mirrors at accumulated dose of 100 MGy. Two types of adhesive made of polyester resin and epoxy resin became discolored and exfoliated after 50 MGy.

Fiber-optical and television endoscopes have been developed for visual inspection of nuclear power plants equipment. Construction peculiarities, radiational properties are described as well as fields and examples of application. Suggestions on further development of endoscopes- based devices are declared.

The 10th International Conference on Optical Fibre Sensors took place in Glasgow from 1 1 - 13 October 1994. The OFS series began in London in April 1983 and has established itself as the only globally peripatetic conference in optical fibre sensor technology. Traditionally the emphasis in these meetings has been on emerging science applied to fibre optic sensors and the relevance ofthis science in the context ofpotential and real applications.

In this paper we discuss two particular topologies of fiber-optic sensors developed recently at the Laboratory of Optoelectronics at UQAH, based on pressure induced birefringence effects occurring in HB fibers, and both in temperature-compensating configurations. We present a thorough analysis of the performance of our first industrial prototype of fiber-optic stress cell developed around the concept of polarimetric pressure sensor. This prototype is based on all- fiber configuration and uses a Corning highly birefringent fiber for sensing, for temperature compensation and for transmission of light signal; a 3M polarizing fiber is also employed as a distributed polarizer. The leading input and output HB fibers are connectorized to the semiconductor laser diode and to the portable electronic detection unit. Metrological data presented in this paper show an overall accuracy of the system better than 1% of full scale in the pressure range up to 21 MPa, including stability, repeatability and temperature drift in the range of about 35 degree(s)C. Both pressure hysteresis effects and sensitivity of the leading fibers to external perturbations are negligible, and the excellent power budget of the sensor allows for remote operation up to several kilometers. The paper presents also a novel configuration of the white-light interferometric pressure sensor based entirely on HB fibers and employing electronic scanning to improve mechanical stability of the receiving interferometer, where the white-light interference pattern registered by the CCD detector is transversally shifted with pressure. We present metrological evaluation of the laboratory prototype of this sensor for the pressures up to 40 MPa for the temperatures from 10 to 35 deg. C. We also evaluate the application of coherence multiplexing for networking this type of sensors.

This paper presents comparative analysis of electronics and different types of optical links for transmissions of results of measurements from a `hot' zone. This problem is important in high energy physics experiments with accelerators and in experiments with nuclear reactors. It is generally preferable to use an optical fiber link before the electronic link. We compare parameters of optical links with light emission diode and with semiconductor laser, with external and with internal modulation, for analogical and for digital signals. The specified demands are conditioned by bandwidth more than 10<sup>8</sup> Hz and distance less than 10<sup>2</sup> m. The design and results of measurements of the technical parameters of the optical links with light emission diode and with low-threshold semiconductor Ga-As microlaser are shown. The program of the radiation resistance testing of this equipment in framework of the `ENTOREL' project is also discussed.

Review results on the investigation of the nature and properties of certain radiation color centers (RCC) arising in (gamma) -irradiated pure silica core fibers was presented in our work. These RCC with the absorption bands 670,800 nm and the low-temperature IR- absorption are unstable at the room temperature and bring the large contribution in the induced absorption value of fibers at (lambda) equals 850 nm.

Test results of residual passive components of fiber optic systems (apart from optical fibers), such as connectors, couplers, wavelength division multiplexers (WDMs), and optical glues are presented. Most of the components were only irradiated at a ⁶⁰Co gamma ray source with a dose rate of about 0.2 Gy/s up to a final dose of 100 (integrated optic devices) or 10⁴ Gy (fiber optic components). Direct connectors can contribute <EQ 0.3 dB to the total loss (10⁴ Gy), compared with 0.3 to 0.6 dB for lens connectors. The measured coupler inherent losses were between about 0.01 dB (fused coupler, high OH multimode stepindex fibers, (lambda) equals 865 nm) and about 50 dB (coupler made of GRIN lenses, (lambda) equals 865 nm). Fused WDMs showed negligible loss increase at the high power outputs and an increase of output power of up to several dB at the isolating output, as well as shifts of the isolating and throughput regions between about 5 and 14 nm (10⁴ Gy). Optical glues of 20 to 40 micrometers thickness showed noticeable loss increase only for wavelengths <EQ 500 nm (10⁴ and 10⁵ Gy).