Real time monitoring of water level and temperature in storage fuel pools through optical fibre sensors

Abstract

We present an innovative architecture of a Rayleigh-based optical fibre sensor for the monitoring of water level and temperature inside storage nuclear fuel pools. This sensor, able to withstand the harsh constraints encountered under accidental conditions such as those pointed-out during the Fukushima-Daiichi event (temperature up to 100 °C and radiation dose level up to ~20 kGy), exploits the Optical Frequency Domain Reflectometry technique to remotely monitor a radiation resistant silica-based optical fibre i.e. its sensing probe. We validate the efficiency and the robustness of water level measurements, which are extrapolated from the temperature profile along the fibre length, in a dedicated test bench allowing the simulation of the environmental operating and accidental conditions. The conceived prototype ensures an easy, practical and no invasive integration into existing nuclear facilities. The obtained results represent a significant breakthrough and comfort the ability of the developed system to overcome both operating and accidental constraints providing the distributed profiles of the water level (0–to–5 m) and temperature (20–to–100 °C) with a resolution that in accidental condition is better than 3 cm and of ~0.5 °C respectively. These new sensors will be able, as safeguards, to contribute and reinforce the safety in existing and future nuclear power plants.

Long-Reach DWDM-Passive Optical Fiber Sensor Network for Water Level Monitoring of Spent Fuel Pool in Nuclear Power Plant

“…However, after transmission of 10 km the extinction ratio (Δ𝑃) is still >5 dB, being the minimum margin required to guarantee the correct water level determination regardless of the internal and external environmental changes as previously discussed in [ 15 ]. Here, the radiation induced attenuation loss can be also included in the required minimum margin within the additional power margin of 1 dB [ 26 , 27 ].…”

Distributed and discrete hydrogen monitoring through optical fiber sensors based on optical frequency domain reflectometry

“…Moreover, OFDR sensors are sensitive to environmental changes such as temperature variation or evolving strain. Even if it is possible to design proper sensor architecture in order to eliminate the strain contribution from the spectral shift [46], temperature variation influence is more complex to control. As already suggested in [35], the use of hermeticcoated optical fibers (such as carbon coating) can be useful for the monitoring of the only temperature parameter in order to decouple the hydrogen induced changes from temperature variation.…”

A Simple All-Optical Water Level Monitoring System Based on Wavelength Division Multiplexing with an Arrayed Waveguide Grating

“…Moreover, it is not easy to operate the level meter during a loss of power accident. To overcome these limitations, there have been several approaches to apply an optical fiber sensor (OFS) to nuclear facilities, due to its advantages such as passive sensing capability, remote transmission, EMI-tolerance, radiation-resistance and redundancy [5,6,7,8]. Specifically, many studies have been done with the various types of optical sensing techniques to monitor important physical parameters under harsh environments such as neutron and gamma radiation [8,9,10,11,12].…”

“…To overcome these limitations, there have been several approaches to apply an optical fiber sensor (OFS) to nuclear facilities, due to its advantages such as passive sensing capability, remote transmission, EMI-tolerance, radiation-resistance and redundancy [5,6,7,8]. Specifically, many studies have been done with the various types of optical sensing techniques to monitor important physical parameters under harsh environments such as neutron and gamma radiation [8,9,10,11,12]. For the water level measurement, there have been reported a number of quasi-distributed optical fiber sensors based on several multiplexed sensing techniques [6,7,13,14,15,16,17,18].…”