Development of a hollow core fibre phosphor thermometer prototype for nuclear decommissioning

Abstract

Phosphor based thermometry is a well-known technique for surface temperature measurement. When combined with fibre-optic cables, a reliable tool for remote measurement can be obtained. For application in nuclear decommissioning sites standard glass-based fibres experience signals degradation because of photodarkening phenomena. In this thesis we study the potential use of hollow core fibres as key component for radiation immune fibre phosphor-tipped thermometers. We report the design and implementation of an experimental setup to measure radiation-induced losses in the transmission rates of hollow core fibres fabricated in-house at the excitation and emission wavelengths of the manganese-doped magnesium fluoro-germanate phosphor. Such experiments are carried out simultaneously in standard single-mode fibres and commercially available radiation hard fibres. We find that for a gamma ray dose of 5.4 kGy (equivalent to 100 years in a nuclear waste storage environment), the hollow-core fibre is virtually unaffected by gamma rays at both wavelengths. A functioning prototype based on phosphor intensity ratio method incorporating this hollow fibre and a solid core fibre, which unexpectedly proved to be highly resistant to gamma rays, is demonstrated. We also use a finite element mode solver to optimize the design of hollow core antiresonant fibres for visible light transmission and investigate their capacity to recapture the light re-emitted by the phosphor upon excitation. The data obtained paves the way for the implementation of a fully-fledged gamma radiation immune temperature sensor.

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Identifiers

ORCID for Francesco Poletti: orcid.org/0000-0002-1000-3083

ORCID for Eric Numkam Fokoua: orcid.org/0000-0003-0873-911X

ORCID for Radan Slavik: orcid.org/0000-0002-9336-4262

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