Relative humidity sensors are the typical and conventional water vapor detection devices employed in the nuclear industry – especially in the used fuel management sector. However, the usage of these detection devices is restricted by the operable temperature range, radiation tolerance, embrittlement and potential fiber darkening. In addition, the sensitivity of these devices is also a subject of concern. In this work, we propose plasma optical emission spectroscopy as a means of detecting and quantifying water vapor concentration in gas mixtures. An application is sought for quantifying the amount of water vapor removed in the process of used fuel drying for dry cask storage. The robust nature of this approach further permits the measurement of water (water vapor) removed throughout the drying process making this a powerful tool in the development of drying models to apply to a wide range of used fuel and cask loading conditions. A low pressure direct current driven glow discharge plasma is employed for generating the different and relevant electronically excited states to acquire the unique optical emission spectrum. The presence of trace amount of water vapor in a gas stream results in emission at 656.2 nm due to excited H atom resulting from a dissociated H2O molecule. The response of the emission intensity at 656.2 nm was found to be strongly dependent on the water concentration of the system; as such, emission at this wavelength was selected as a marker for quantifying the water concentration. A calibration setup was fabricated together with the low pressure plasma discharge cell and a calibration methodology was developed. Binary mixtures of water vapor – helium having a wide range of composition was produced by injecting water by a metered syringe pump to a heated chamber through which metered quantity of helium was flowing. The temperature of the chamber was maintained at 200?C to ensure that water condensation was not taking place through the lines. Binary gas mixtures of known composition were fed into the plasma chamber to calibrate the emission intensity (H/He) to the water concentration level. The calibration experiments were conducted over a range of pressure(s) and for different plasma discharge currents. A strong linear correlation was found between the peak ratio of H/He to flow ratio of H2O/He in each case. The calibration curves were found to have a very weak dependence on the discharge current. Each experiment was repeated multiple times to ensure repeatability and quantify the uncertainties in the measurements. This plasma device will be utilized in a full blown mock nuclear fuel assembly drying experiment to quantify the water removal by the vacuum drying process for the development of drying models for potential use by regulators, vendors, and the industry.