Abstract
AbstractThe design of a novel MEMS (Micro-Electro-Mechanical System) sensor-based monitoring system is presented in this article for the in situ monitoring of the conditions (temperature, relative humidity) of an engineered bentonite barrier for the underground disposal of radioactive waste in a geological disposal facility (GDF). A first prototype of the monitoring system incorporating multiple state-of-the-art MEMS sensors has been developed on a PCB-based (Printed Circuit Board) structure, in order to measure the variation of temperature and relative humidity inside a cylindrical bentonite block during the hydration process. The monitoring system comprises separate sensor boards, the microcontroller-equipped interface board and the software user interface in the Labview environment. One of the main design priorities is to reduce the size of the embedded sensors in order to minimize their influence on the hydro-mechanical response of the bentonite block. The sensor boards are encapsulated in different manners to protect them from moisture, chemical corrosion and mechanical shocks. The sensor system has been tested and calibrated in the temperature range between –20°C and 120°C, and at different relative humidity levels implemented by saturated salt solutions in enclosed containers. Test results demonstrate that the sensors have shown good functionality and robustness in harsh test environments such as high temperature and high humidity. Both temperature and relative humidity sensors have shown satisfactory precision level and temporal stability, which are in good accordance with the design specification of these devices.
Highlights
THE real-time monitoring of deep geological disposal facilities (GDFs) for radioactive waste disposal has attracted increasing research interest in recent years
The objectives of this research are to identify suitable commercial MEMS sensors for simultaneous monitoring of temperature and humidity, to develop a MEMS-based monitoring device for use in subsurface environments, and to evaluate sensor reliability and accuracy over the range of values likely to be encountered within the bentonite barrier
While the measurement principle of the sensors varies, one common restraint of these traditional sensors lies in the unit size of the sensor, which limits the spatial resolution of the sensing device
Summary
THE real-time monitoring of deep geological disposal facilities (GDFs) for radioactive waste disposal has attracted increasing research interest in recent years. The compacted bentonite buffer relies on multiple THMC properties to ensure longterm safety of the system. It must generate a swelling pressure of between 2 and 10 MPa for hydraulic sealing and to minimize microbial. This research, conducted under the framework of the multi-partner SAFE Barriers Project, focuses on the design of a MEMS-based (Micro-ElectroMechanical System) sensor for the simultaneous monitoring of temperature and humidity within, or adjacent to, the compacted bentonite buffer in the EBS. Improved monitoring of bentonite will fulfil research and development needs, but will be a requirement of the regulators during GDF operation. The GDF implementer will need to demonstrate that model calculations used to predict future behaviour in the operational safety case are reliable
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