Development of Under Sodium Inspection Techniques for FBR

摘要

The reactor vessel of a fast breeder reactor (FBR) is filled with opaque liquid sodium and ultrasonic inspection techniques are effective and useful for observing the in-vessel structures under sodium. The under sodium visual inspection technique and the under sodium volumetric inspection technique are developed in order to apply in-sodium inspection to a demonstration fast breeder reactor (DFBR). Firstly, in the development of the under sodium visual inspection technique, the synthetic aperture focusing technique (SAFT) and cross-correlation processing have been applied to realize ultrasonic 3-dimensional cross-correlation image processing with high resolution. Cross-correlation processing improves the S/N ratio of the ultrasonic echoes which are deteriorated, by sodium wetting, and realizes high-density integration of the matrix arrayed transducer. Matrix arrayed transducer, in which 100 piezoelectric elements are arranged as a 10×10 matrix array, has been manufactured for the in-water visualizing test. High-speed data processing and temperature-compensation processing have been realized to reduce the influence of the change of water temperature. It has been confirmed that clear and high-resolution 3-dimensional ultrasonic images are acquired at 0.8 m distance in the in-water visualizing test Secondly, in the development of the under sodium volumetric inspection technique, a prototype electric scanning UT sensor has been developed for the volumetric test of the core support structures in the reactor vessel. The UT sensor consists of 60 arrayed piezoelectric elements, non-organic materials such as ceramic backing. Ultrasonic echoes transmitted from the elements is scanned electronically and real-time B-scope images of the structures can be realized. A prototype UT sensor has been tested to evaluate the acoustic characteristics in water and confirm the heat-proof performance under high temperature silicone oil. The performance of the UT sensor satisfied the requirements. The above-mentioned investigations have confirmed the development of advanced image processing for under sodium visual inspection and the in-sodium UT sensor for under sodium volumetric inspection. In-sodium tests of this image, processing and UT sensor are to be carried out in the next phase of this work.