High-Temperature Measurements With a Fabry–Perot Extensometer

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.

“…That is what happens with an extrinsic Fabry-Perot interferometer [5]. However, doing this way, experimental results are shifted by 150 µm to 250 µm.…”

Section: Figure 3: Example Of a Fft Applied To An Experimental Signal The Red Rectangle Corresponds To The Domain Where We Expect To Findmentioning

confidence: 84%

Online optical refractive index measurement in research reactor core

Fourneau¹,

Agoyan

Chemol³

et al. 2021

“… Electrical: heating power supply,  Instrumentation: flow meter, thermocouples, LVDT, nuclear measurements, Its advantages are numerous: Geometry: an optical fiber has a diameter of about 200microns compared to 1 mm or more for a standard thermocouple. A hardened Fabry-Pérot type fiber optic elongation sensor for MTR application has a diameter of 2 mm compared to more than 10 mm for an LVDT [3].…”

Section: The Tightness Feedthroughsmentioning

confidence: 99%

“…Hardened FOS or measurement using optical fibers for irradiation rig have already been developed (for temperature [ref 2 ter], elongation [3]) and tested under irradiation (ATR, MITR, BR2,...) up to more than 10E20 n/mc² and GGy. One studied application correspond to a sensor for measuring displacement / swelling.…”

Section: Immunity To Electromagnetic Interferencementioning

confidence: 99%

Fuel Irradiation Devices Test of Feedthroughs Equipped With Optical Fibers in support of the development of innovative instrumentation

Gaillot,

Destouches,

Cheymol

et al. 2023

Self Cite

As part of the activities for developing experimental devices for research reactors and associated test loops, some concern the development and qualification of instrumentation. The on-board instrumentation makes it possible to monitor online the evolution of physical parameters of samples and/or components subjected to different stresses (thermal, hydraulic, chemical and nuclear, etc.). In addition to the so-called “classic” instrumentation implemented in this type of equipment (pressure, temperature, flow, elongation), R&D actions are in progress in order to propose innovative instrumentation, able to improve the experimental offer and describe the physical phenomena with more accuracy. This is the case of optical measurements which present many advantages (compactness, insensitivity to EM waves, complex measurements by optical interrogation of a single fiber). In addition, actions are underway for the selection of optical fibers that can be used for applications in a nuclear reactor (in particular resistance to the irradiation). The tests presented in this paper relate to the behavior of sealed feedthroughs for optical fibers to the thermal hydraulics conditions of light water reactors. These tests are part of the safety demonstration in so-called degraded operating cases i.e. corresponding to a configuration where the optical fiber is placed directly in the process fluid (pressurized water). One note that in normal operation, the optical fiber is isolated from the process fluid by a jacket consisting of a metal capillary. After an introduction and a brief presentation of the use of optical fibers in experimental equipment, the paper describes the tightness feedthroughs used, the tests carried out, indicate the main results obtained and opens up some perspectives for future development phases.

“…HIS work is made in the framework of the instrumentation for nuclear applications (INSNU) project, aiming to develop instrumentation and sensors for experiments in the Jules Horowitz reactor (Cadarache, France). Among other technologies are developed optical sensors: fiber Bragg gratings [1], fiber-optic distributed sensors to measure temperature and strain, pyrometric measurement [2], Fabry-Perot extensometer [3] and confocal chromatic sensor: a displacement sensor which is the object of this article.…”

Section: Introductionmentioning

confidence: 99%

“…Data relative to refractive index dependence to temperature from the literature are needed and if none is available, dedicated experiments will be mandatory. -Radiation darkens the optical glasses [3] and optical fibers [5]. Moreover, large fast neutron fluence is also known to modify the glass refractive index, at least of the silica [6] [7].…”

Section: Introductionmentioning

confidence: 99%

Confocal chromatic sensor for displacement monitoring in research reactor

Agoyan

Fourneau²,

Cheymol³

et al. 2021

Confocal chromatic microscopy is an optical technique allowing measuring displacement, thickness, and roughness with a sub-micrometric precision. Its operation principle is based on a wavelength encoding of the object position. Historically, the company STIL based in the south of France has first developed this class of sensors in the 90’s. Of course, this sensor can only operate in a sufficiently transparent medium in the used spectral domain. It presents the advantage of being contactless, which is a crucial advantage for some applications such as the fuel rod displacement measurement in a nuclear research reactor core and in particular for cladding-swelling measurements. The extreme environmental conditions encountered in such experiments i.e. high temperature, high pressure, high radiations flux, strong vibrations, surrounding turbulent flow can affect the performances of this optical system. We then need to implement mitigation techniques to optimize the sensor performance in this specific environment. Another constraint concerns the small volume available in the irradiation rig next to the rod to monitor, implying the challenge to conceive a miniaturized sensor able to operate under these constraints.