Strain and Vibration Monitoring of Nuclear Components Using Fibre Optic Sensors

Abstract

Fibre optic sensors have inherent advantages over traditional types of instruments. A single fibre can include multiple sensors or even distributed sensing capability, have minimal cross-section, be virtually mass-less and not be affected by electro-magnetic fields. Due to low transmission losses within the fibre, the signal can be carried considerable distances, in some cases up to many kilometers. Applications range from temperature measurements within generator windings, strain measurement within composite structural aircraft members, health monitoring of structures such as buildings and bridges, to down-hole sensors for the oil and gas exploration industry. Recent developments include high temperature fibre Bragg gratings and all-grating fibres.

Fibre optic sensors can be placed in locations previously considered impossible or extremely difficult using conventional sensors. One example is the U-bend region of an on-power steam generator. In a program at Canadian Nuclear Laboratories’ (CNL) Chalk River labs, a fibre optic-based strain sensor is being developed, with the goal of eventually being deployed both as a research tool as well as a monitoring tool for components within the nuclear industry. To this end, a prototype tool has been tested, demonstrating that this technique can measure strain (ε) values as low as 2×10^-6 m/m and vibration frequencies up to 1000 Hz. Up to 30 sensors can be engraved within a single fibre optic strand and interrogated simultaneously, with sensor spacing that can be customized.

Measurements were carried out with multiple sensing points within a single fibre optic strand, permitting strain values under a variety of conditions to be captured within the length of a vibrating cantilever test bar system. This paper will present the operating principle of the instrument, as well as the test results.