Dual Mode Sensing for Continuous Crack Monitoring on Grout Nuclear In-Situ Decommissioning Structures

摘要

For the in-situ decommissioning (ISD) of nuclear facilities, one strategy being investigated is to fill certain portions of the facility housing hazardous and radioactive materials with grout. A critical need exists for a sensor network to assess the durability of the grout and the surrounding concrete structure. Due to the variety of deterioration sources and locations of defects, there is currently no single method that can detect and address the potential damages globally. In this paper, we present a dual mode sensing strategy to perform continuous crack detection and monitoring in grout ISD structures. The dual mode sensing strategically combines the strengths of two structural health monitoring (SHM) approaches, the passive acoustic emission (AE) and active guided ultrasonic wave (GUW) interrogation methods, based on the use of permanently installed piezoelectric sensors (PES). Active or growing cracks emit AE waves that arise from the rapid release of strain energy. Analysis of these recorded signals provides early stage information about the cracking source with very high sensitivity. The "active" SHM approaches, on the other hand, use one sensor in the array to generate interrogation waves and the others as the wave receivers. By that means, quantitative information regarding the structural state of health and integrity can be extracted. Proof-of-concept tests are performed on a small grout specimen with two types of PES transducers. Array imaging algorithms are developed for AE source localization and active damage detection, respectively. The methods demonstrated in this investigation provide promising means for imaging of cracking events both passively and actively.