###### Abstract  
As the last barrier of nuclear reactor, prestressed concrete containment vessels (PCCVs) play an important role in nuclear power plants (NPPs). To test the mechanical property of PCCV during the integrated leakage rate testing (ILRT), a fiber Bragg grating (FBG) sensor was used to monitor concrete strain. In addition, a finite element method (FEM) model was built to simulate the progress of the ILRT. The results showed that the strain monitored by FBG had the same trend compared to the inner pressure variation. The calculation results showed a similar trend compared with the monitoring results and provided much information about the locations in which the strain sensors should be installed. Therefore, it is confirmed that FBG sensors and FEM simulation are very useful in PCCV structure monitoring. p 200  
temperature change for temperature compensation. However, once the embedded strain sensors are damaged, there should be a method to compensate. Nowadays, fiber optic sensors are widely used in the civil engineering structure health monitoring (SHM). [PERSON] and [PERSON] [1] used the stiff Surveillance d'Ouvrage par Fibers Optics (SOFO) sensor to monitor the concrete deformation at a very early concrete age. The results showed that the SOFO sensor can monitor concrete deformation. SOFO was also used for concrete strain measurement system in monitoring the 1:4 scale model of the PCCV built by Sandia National Laboratories [2]. [PERSON] et al. [3] used white light interferometer (WLI) method to monitor the rebar expansion by coiling the fiber optic on the rebar's surface. Apart from these, Brillouin optical time domain analysis (BOTDA) was widely used in the tunnel, bridge, pipelines and so on. [PERSON] and [PERSON] [4] used Brillouin and Raman scattering to detect leakage in the brine and gas pipelines. They identified the leakage position successfully. In order to verify whether fiber Bragg grating (FBG) could be used in the NPP structure, [PERSON] et al. [5] did a series of experiments. Fortunately, FBG showed good resistance to \(\gamma\)-ray irradiations. This meant FBG could be used in the PCCV structure even in conditions where FBG received nuclear radiation. In order to monitor the prestress force of prestress tendon, [PERSON] et al. [6] installed FBG on the PCCV cylindrical wall during the ILRT. The results showed that the vertical strain was 17-25 \(\mu\varepsilon\) and the hoop strain was about 54-90 \(\mu\varepsilon\). Besides, the impact signal analysis technique was used in evaluating the prestress force of bonded tendons and showed good potential. Moreover, FBG was widely used in other fields. [PERSON] and [PERSON] [7] used FBG to monitor the cure progress of carbon fiber reinforced plastic (CFRP) composite materials and detected the occurred damage successfully. [PERSON] et al. [8] adopted long-gauge FBG sensors to monitor the strain and deflection of a prestressed box bridge. The FBG monitoring data was used to detect damage of the bridge. [PERSON] et al. [9] welded FBG on the strand to measure the prestress force. This weld fabrication allowed the instrumented strand to measure the stress up to 1300 MPa. [PERSON] et al. [10] used an active thermal probe to detect steel reinforcement corrosion. Due to the poor thermal conductivity of corrosion products, they used carbon fiber strands to generate heat and FBG temperature sensors to monitor the temperature change. The results suggested that there was a correlation between corrosion severity and temperature response. Since fiber optic sensors exhibit numerous advantages such as superior durability, high sensitivity, electromagnetic interference immunity and \(\gamma\)-ray irradiation immunity, using them in PCCV monitoring is a good choice. When the embedded vibrating wire strain gauges are damaged, the fiber optic sensors can compensate. In this paper, FBG was proven to be able to monitor the strain development of PCCV cylindrical wall.