Development of radiation-resistant ultrasonic sensor unit

The use of ultrasonic sensors has been proposed as a method for understanding the status of decommissioning work at the Fukushima Daiichi Nuclear Power Station (FDNPS). Piezoelectric materials for ultrasonic transducers are known to have high radiation-resistance. Therefore, radiation-resistance related electronic modules such as pulsers and preamplifiers for ultrasonic sensors are also required. Since high radiation fields exist inside the PCV (Primary Containment Vessel) and RPV (Reactor Pressure Vessel), it is difficult to use electronic equipment incorporating conventional semiconductor integrated circuits. In this study, high-radiation-resistant pulser and preamplifier for ultrasonic sensors were fabricated, and their performance tests were performed in a 60Co gamma-ray irradiation facility. The electronic circuits of the pulser and the preamplifier consisted of SiC-JFETs, ceramic capacitors, and resistors to improve the radiation-resistance. The electronic characteristics of SiC-JFET were investigated. The IDS-VGS characteristics of the SiC-JFET did not change significantly up to an absorbed dose of 10 MGy (in water). The ultrasonic sensor unit for distance measurement with 1.7 MHz ultrasonic waves was normally operated at a dose rate of approximately 1.8 kGy/h (in water).