On-line monitoring of sealing glass in electrical penetration assembly based on femto-laser inscribed fiber Bragg grating sensors

A novel method was proposed to monitor the working state (temperature and stress) of sealing glass in electrical penetration assemblies, which was used for electrical connection in containment structures or pressure vessels of nuclear power plants, based on femto-laser inscribed fiber Bragg grating (FBG) sensors. Aging tests under thermal (~200°C) and radiation (~3.5MGy) conditions were carried out to demonstrate the feasibility of FBG in harsh environment. On-line state monitoring experiments were performed under high temperature 100~400°C and high pressure 7 MPa, referring to real conditions in the nuclear reactor. During monitoring, one FBG was embedded in sealing glass and the other was set outside the glass. Experimental and numerical results showed that the femto-laser inscribed FBG sensors could achieve simultaneous temperature and stress monitoring with good accuracy (monitoring deviation less than 10%) and transient response under harsh environment. This work set a base for the long-term real-time diagnosis of electrical penetration assembly in nuclear power plant.