Fundamental research to understand changes in piezoelectric properties under irradiation are required if ultrasonic sensors are to be designed and deployed for nuclear reactor in-core measurements. Previous research has examined the survivability of bismuth titanate (BiT)-based ultrasonic sensors to a total dose of up to ~1021 neutrons/cm2. This paper describes efforts to quantify the changes in piezoelectric properties in these materials using piezoresponse force microscopy (PFM). PFM measurements from non-irradiated and irradiated specimens indicated a decrease in d33 from irradiation, consistent with the observed decrease in the response of a BiT transducer over the course of the irradiation test.
Ultrasonic sensors have been proposed for monitoring nuclear fuel performance during transient irradiation tests. A specific need is to monitor strain or deformation of the fuel rods during irradiation. However, challenges associated with designing sensors that can operate under typical in-core conditions while providing the necessary sensitivity have limited their application. This paper describes ultrasonic sensor concepts for measurements during transient irradiation tests and results of laboratory tests to quantify their performance. Challenges associated with designing sensors for in-core deployment and potential solutions are also discussed.
This paper reports testing results of radiation resilient fiber Bragg grating (FBG) in radiation resistant fibers in the nuclear reactor core at MIT Research Reactor Lab. FBGs were fabricated by 140-fs ultrafast laser pulse using a phase mask approach. In-core test of fiber Bragg gratings was carried out in the core region of a 6-MW research reactor at temperature > 600°C and an average fast neutron (>1 MeV) flux >1×1014 n/s/cm2. First 100-day tests of FBG sensors shows less than 5 dB reduction in FBG peak strength after over 1×1020 n/cm2 of accumulated fast neutron dosage. To test temporal responses of FBG sensors, a number of reactor anomaly events were artificially created to abruptly change reactor power, temperature, and neutron flux over short periods of time. The thermal optical coefficients and temporal responses of FBG sensors are determined at different accumulated dosages of neutron flux. Results presented in this paper reveals that temperature-stable Type-II FBGs fabricated in radiation-hardened fibers could be used as sensors to perform in-pile measurements to improve safety and efficiency of existing and next generation nuclear reactors.
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