Novel MEMS Capacitive Sensor Excited at Electrical Resonance for Detecting Helium Based on Changes in Air Electrical Properties

Abstract

Dry cask storage (DCS) is increasingly used for extended long-term storage of spent nuclear fuel. The canister is vacuum dried and then pressurized with helium to ensure an inert atmosphere and efficient heat transfer. Thus, helium leakage detection plays an important part in ensuring the safety of nuclear waste storage facilities. However, as it is a noble light gas with no order or color, using conventional gas sensing techniques for detecting Helium is a challenge. To overcome this challenge, in this paper we present the working principle of a simple electrostatic MEMS structure to detect Helium in ambient air. The working principle of this novel sensor is based on the decrease in the air die-electric constant due to the presence of Helium. While this change is small, we show that activating the MEMS RLC circuit can significantly amplify the sensor response and hence increase its sensitivity. The sensor response is simulated at different Helium concentration levels using a finite element model. The simulations showed that an electrostatic MEMS sensor operating close to the electrical resonance frequency of an RLC circuit showed different deflection and as such a different capacitance at different levels of helium. A decrease up to 20% of the MEMS deflection was observed at 20% Helium concentration compared to near 0% concentration.