Abstract
Geological disposal facilities for radioactive waste pose significant challenges for robust monitoring of environmental conditions within the engineered barriers that surround the waste canister. Temperatures are elevated, due to the presence of heat generating waste, relative humidity varies from 20% to 100%, and swelling pressures within the bentonite barrier can typically be 2–10 MPa. Here, we test the robustness of a bespoke design MEMS sensor-based monitoring system, which we encapsulate in polyurethane resin. We place the sensor within an oedometer cell and show that despite a rise in swelling pressure to 2 MPa, our relative humidity (RH) measurements are unaffected. We then test the sensing system against a traditional RH sensor, using saturated bentonite with a range of RH values between 50% and 100%. Measurements differ, on average, by 2.87% RH, and are particularly far apart for values of RH greater than 98%. However, bespoke calibration of the MEMS sensing system using saturated solutions of known RH, reduces the measurement difference to an average of 1.97% RH, greatly increasing the accuracy for RH values close to 100%.
Highlights
Real-time monitoring of deep geological disposal facilities (GDFs) for radioactive waste disposal is a significant challenge
Monitoring creates significant challenges: temperatures can be highly elevated due to the presence of heat generating waste, relative humidity (RH) varies from 20% to 100%, and swelling pressures within the bentonite barrier are typically in excess of 2 MPa
For example the Swedish KBS-3V concept, are based on an engineered barrier system (EBS) composed of a compacted bentonite buffer, which surrounds the waste canister (e.g., Figure 1)
Summary
Real-time monitoring of deep geological disposal facilities (GDFs) for radioactive waste disposal is a significant challenge. Monitoring creates significant challenges: temperatures can be highly elevated due to the presence of heat generating waste, relative humidity (RH) varies from 20% to 100%, and swelling pressures within the bentonite barrier are typically in excess of 2 MPa. Most geological disposal concepts, for example the Swedish KBS-3V concept, are based on an EBS composed of a compacted bentonite buffer, which surrounds the waste canister (e.g., Figure 1). While the system, developed in [5] for monitoring relative humidity within, or adjacent to, the compacted measurement principle of the sensors varies, one common restraint of these traditional sensors lies bentonite buffer in the EBS. Application of MEMS sensors in GDFs and other civil engineering calibration, accurate measurements of compacted bentonite relative humidity can be achieved even projects faces up to RH still values of several. ® 31725 temperature sensor (Maxim Integrated, San Jose, CA, USA) [8] and the Sensirion®
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