Radiation-Hard and Intelligent Optical Fiber Sensors for Nuclear Power Plants

Abstract

Optical fiber sensors (OFS) have a number of intrinsic advantages that make them attractive for nuclear power plant (NPP) applications, including absolute explosion safety, extremely low mass, small size, immunity to electromagnetic interference, high-accuracy, selfcalibration, and operation in extremely harsh environments, and it is a well-known fact. Civil nuclear industry essentially encompasses the complete nuclear fuel cycle and therefore the range of possible fiber applications both for communications and sensing is very broad (Berghmans & Decreton, 1994), (Korsah et al., 2006). In order to expand OFS applications in nuclear engineering it was necessary to overcome a bias that some scientists and engineers used to have at the initial stage of using an optical fiber for communication, about "darkening" of a fiber and sharp growth of optical attenuation under the conditions of ionizing radiation, i.e. availability of convincing proofs of radiation hardness of optical fibers and OFS. Safety and long-term metrological stability of OFS for NPP assumes: Radiation hardness of fiber optic sensors and cables; Absence of mechanical resonances of the gauge at frequencies up to 200 Hz; Immunity to electromagnetic effects in the range of frequencies 200 kHz and 18 – 20 MHz, High reliability of a sensitive element of the OFS ; Temperature-insensitive measurements of pressure in the working range of temperatures; Self-calibration of the gauge without stopping the process of measurement. These requirements are satisfied by modern OFS, especially intellectual optical fiber sensors which can self-calibrate, i.e. control themselves at the level of changing their internal (own) parameters depending on the calibrated value (Buymistriuc & Rogov, 2009). No optical measurement electronics will survive in, or near, an operating nuclear reactor core. Therefore, OFS light emission must be guided to the measurement electronics located in a well-controlled, benign environment. Several different implementations can be employed to accomplish this, each with their own advantages and weaknesses. Recently single material hollow-core optical fibers (referred to as photonic crystal fibers) have become