Radiation hardness of fiber optic sensors for monitoring and remote handling applications in nuclear environments

TLDR

The study irradiated various commercial fiber‑optic sensors—temperature sensors, a multimode extrinsic Fabry‑Perot strain sensor, and fiber Bragg gratings—to assess their radiation response. Gamma irradiation does not alter the basic sensing mechanism of fiber‑optic temperature sensors, but the optical fiber itself limits radiation hardness; semiconductor absorption sensors tolerate up to 250 kGy, whereas Fabry‑Perot and fluorescence sensors degrade below the kGy level, though using radiation‑resistant fibers extends their tolerance by orders of magnitude; neutron exposure still compromises performance, and Bragg‑grating wavelength shifts occur while temperature sensitivity remains intact.

Abstract

We report on our irradiation experiments on different types of fiber-optic sensors, including three types of commercially available temperature sensors, a multimode extrinsic Fabry-Perot cavity strain sensor and fiber Bragg- gratings. For the temperature sensors, results show that gamma radiation does not interfere with the basic sensing mechanism and that the most critical component turns out to be the optical fiber itself. Semiconductor absorption temperature sensor showed no degradation up to total doses of 250 kGy, whereas the specifications of Fabry-Perot type sensor and fluorescence temperature sensors were already dramatically influenced below the kGy-level. Replacing the optical fiber by a more radiation resistant version allowed to increase the radiation hardness of the fluorescence sensors system by orders of magnitude. The use of fiber- optic sensors in the presence of neutron radiation remains compromised. Similar conclusions are valid for the Fabry- Perot type fiber-optic strain sensors. We finally show that the Bragg-grating resonance wavelength can shift with radiation dose, but that the temperature sensitivity remains unaltered.