Development Of Temperature Monitoring System For The Near Field Of Nuclear Waste Repository Based On ROTDR

The development of nuclear energy and nuclear technology has produced more and more highly radioactive nuclear waste, and the lasting safety of large quantities of nuclear waste is a major issue for nuclear science, geology, environmental science and other related areas at present. Deep geological disposal is internationally recognized as the most effective and feasible way for nuclear waste disposal, but it also exist the risk of radioactive leaks. To reduce this risk and ensure the long-term stability of the disposal site, it is necessary to monitor related parameters of the near field, especially temperature monitoring. Temperature monitoring for the near field is of important significance to evaluate safety of the disposal repository, and it can also judge nuclear waste leak using local temperature anomalies.As for monitoring technologies, the traditional way for temperature field monitoring has many flaws such as heavy workload, high rate of missed detection, easy to be jammed by radiation, poor durability. And temperature field monitoring is in urgent need of the new technologies at present. According to the characteristics of the temperature of nuclear waste repository, this topic presents a new method to monitor temperature of the near field using distributed optical fiber sensors based on Raman Optical Time-Domain Reflect(ROTDR), and a temperature monitoring system using optical fiber sensing technology for the near field of nuclear waste repository was developed. It completely overcome the flaws which hardly monitor all in a continuous way, and has many advantages such as high radiation tolerance, long durability, easy construction.Following works have been done in this topic:(1) The basic principle and key technology of ROTDR were introduced, including Raman scattering heat effect, OTDR technology and the demodulation method of temperature. Comparing with traditional temperature monitoring method, the monitoring model of optical fiber sensing for the near field was designed. Several key indicators and their influencing factors in the system were analyzed in detail.(2) The hardware design of optical fiber temperature sensor based on ROTDR was completed, including pulse source, WDM, APD and AMP, and dual-channel high-speed data acquisition and accumulation system. And relevant temperature demodulation algorithm is completed too, including signal denoising, attenuation compensation, and temperature calibration.(3) A complete system was set up, and the test of signal denoising, attenuation compensation and temperature calibration were completed at the same time. Technical characteristics of the system have been tested through a simulation experiment. The results show that spatial resolution is up to 2 m, measurement accuracy to ±1?, measuring distance to 2km. System can carry out accurate position of anomalous points of temperature.The innovation and the value of this topic as follow:(1) In view of the temperature monitoring problem in nuclear waste repository, temperature monitoring system based on Raman Optical Time-Domain Reflect have been developed using professional technology. The system can be used to monitor decay heat of the whole disposal site and nuclear waste leak in real time. Monitoring data will help to evaluate safety state and scientific research of nuclear waste repository. It has strong feasibility and practicability.(2) Comparing with traditional temperature monitoring method, optical fiber temperature sensor based on ROTDR has great superiority for the temperature monitoring in nuclear waste repository. The system also can be applied to other disasters monitoring fields. To some extent, the problem of cross subject can be solved. The present work has a certain practical value and theoretical significance.