Abstract
Fabry-Perot (FP) sensors like other Fiber Optic (FO) sensors may be of particular interest for in pile experiments in MTR with little room available thanks to their compact size. Light weight also reduces gamma heating hence limiting the thermal effect. Different physical parameters such as temperature, strain, displacement, vibration, pressure, or refractive index may be sensed through the measurement of the optical path length difference in the cavity. We have developed a Fabry-Perot extensometer able to operate at high temperature (up to 400°C), under a high level of radiation (neutron and gamma flux). The measurement based on interferometry is largely insensitive to radiation induced attenuation (RIA) thanks to the wavelength encoding of the useful signal, but for such high fluence as encountered in a reactor core, a special rad-hard fiber is needed. Operating in the wavelength domain around 1ím remains preferable to minimize the impact of irradiation. Moreover, fast neutron radiation is expected to change the structure of the fiber and possibly others materials in the transducer. Then, we revised the basic scheme of Extrinsic Fabry-Perot Interferometer (EFPI) so that the effects of compaction remain limited. Tests under mixed neutron and gamma irradiation permitted to verify the general behavior and particularly the low drift with radiation induced compaction (RIC). Also, two types of tests have been conducted to verify the accuracy at high temperature. The first ones are “measurements” of thermal dilatation of materials: the sensor is fixed on a sample and knowing its thermal expansion, it is possible to predict the measurement expected from the optical sensor when the temperature is increased from low to high temperature. The comparison between the predicted and experimental outputs informs on how the sensor is accurate. The second types are tests on a tensile test bench operating at high temperature. The Fabry-Perot measurements are compared, in the elastic domain, with the expected strain given by the Young modulus of the material, and also on a larger strain domain, with the measurements of a high temperature axial extensometer. Both types of tests are presented and commented.
Highlights
V ARIOUS R&D programs are implemented in order to improve the performance and the safety of existing and future plants as well as to assess and develop new reactor concepts
In order to make measurement of elongation, we have developed a FabryPerot Sensor (FPS) able to work under high temperature and large neutron fluence [2,3]
We will first present the principle of the sensor; we will focus on two sets of different experiments conducted to evaluate the accuracy of the FPS when operating at high temperatures
Summary
V ARIOUS R&D programs are implemented in order to improve the performance and the safety of existing and future plants as well as to assess and develop new reactor concepts. In order to make measurement of elongation, we have developed a FabryPerot Sensor (FPS) able to work under high temperature and large neutron fluence [2,3]. This development has first been carried out jointly with SCK CEN in the framework of the Joint Instrumentation Laboratory (JIL), CEA has continued the development to improve the operation at high temperature. We will first present the principle of the sensor; we will focus on two sets of different experiments conducted to evaluate the accuracy of the FPS when operating at high temperatures They are based on the study of the thermal dilatation of the support and on the tests on a tensile testing machine
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