EPJ Web Conf.
Volume 253, 2021ANIMMA 2021 – Advancements in Nuclear Instrumentation Measurement Methods and their Applications
|Number of page(s)||4|
|Section||Research Reactors and Particle Accelerators|
|Published online||19 November 2021|
Online optical refractive index measurement in research reactor core
CEA, DES/ISAS/DPC/SEARS/LISL, Saclay, France
2 Université Jean Monnet, CNRS, Graduate School Optics Institute, Laboratoire Hubert Curien UMR 5516, Saint-Etienne, France
3 CEA, DES/IRESNE/DER/SPESI, Cadarache, France
Published online: 19 November 2021
There is a growing interest in fiber optic measurements for applications in radiation environments. Optical fiber sensors and diagnostics can monitor many parameters of interest inside a research reactor core. For some applications, fiber optics are combined with an optical system that collects or focuses the light beam. The Radiation-Induced-Refractive-Index-Change (RIRIC) of the used glasses appears then as major phenomenon as it is a determining value for the sensor optical function. In the framework of the development of a radiation hardened confocal chromatic sensor, we implemented an on-line refractive index measuring device in order to test in a reactor core various glasses, candidates to be implemented into the sensor. The measurement relies on interferometry, which is a challenge because of the small volume available, the impossibility to make optical adjustments once installed, and the high temperature of operation. Precisely, the quantity retrieved is the optical path (product of the length L by the optical refractive index n), when L is well known, we can deduce n. But under high neutron fluence, some variation in density can be observed. The targeted online measurement of the refractive index therefore becomes an optical path measurement. We will present the device, the principle of measurement, and the first results of some index change measurement, produced by a temperature ramp from 20 °C and 350 °C. We have obtained original data for most of the candidate glasses used to design the optical system.
Key words: Optical fiber sensor / Radiation-InducedAttenuation / Interferometry / Radiation-Induced-RefractiveIndex-Change / Interferometric measurement / Rad-hard Glasses / High neutron fluence
© The Authors, published by EDP Sciences, 2021
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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