Preliminary Study on Endoscopic Ultrasound System for In-Service Inspection of Helical Tube Once-Through Steam Generator

Abstract The Helical-tube Once-through Steam Generator (H-OTSG) is a crucial component of the gas-cooled reactor, with the helical heat exchanger tube in the H-OTSG forming an integral part of the reactor’s primary pressure boundary. The volumetric in-service inspection of this helical heat exchanger tube presents a significant challenge due to constraints of accessibility, material, and weld inspection. To address this problem, an Endoscopic Ultrasound (EUS) inspection system is proposed. The structure and working mode of the EUS inspection system are described in detail. Then, the key sensor of the inspection system, EUS transducer, is presented and highlighted. Three array EUS transducers are designed. After outlining the geometric model and inspection modality of the EUS transducers, a preliminary EUS inspection experiment is conducted to demonstrate the inspection performance of the transducers. Two types of reflectors are fabricated on an actual H-OTSG’s heat exchanger tube in the High-Temperature Reactor Pebble-bed Module (HTR-PM) according to ASME code methods to simulate the volumetric and planar defects in different positions. The experimental results show that the proposed array EUS transducers offer high detection robustness and excellent sizing ability on account of the 3-D focused acoustic beam.