Adsorption of Iodine and Water on Silver-Exchanged Mordenite

The reprocessing of used nuclear fuel to recover the fissile materials generates off gases including radioactive nuclides namely 3H (tritiated water, H3HO), 129I, 85Kr, 135Xe, and 14C. Due to its high quantity in off-gas streams and long half-life (1.59 million years), 129I removal from the off-gas streams is a significant objective of off-gas treatment. 129I retention by solid adsorbents was recognized a better strategy in comparison to liquid scrubbers due to the simplicity of system design and low cost. Among the studied adsorbents, reduced silver-exchanged mordenite (Ag0Z) was widely recognized as the state-of-art adsorbent for iodine removal. It has been selected to be used in the Hanford Treatment and Immobilization Plant in Washington State, US, to control releases of the radioactive iodine in off-gases of spent nuclear fuel reprocessing facilities. Previous studies have shown the outstanding performance of Ag0Z for adsorption of both molecular iodine and organic iodide. However, the detailed adsorption kinetics of I2 on Ag0Z was never reported. Therefore, this study included determining the adsorption dynamics of I2 adsorption on Ag0Z through continuous -flow experiments and data analyses by kinetic models. Mass transfer, diffusion and reaction processes involved in the adsorption process were evaluated. In addition, one issue that has to be addressed when using Ag0Z for iodine removal is the potential co-adsorption of other gas species, among which is H2O vapor. Mordenites have been shown to have a considerable adsorption capacity for H2O vapor, which is also a major component in the off-gases of spent nuclear fuel reprocessing facilities. Therefore, understanding the kinetics of H2O vapor adsorption on Ag0Z is necessary for a better design of off-gas treatment systems. The kinetics and equilibrium of H2O adsorption on Ag0Z were studied. Uptake curves and isotherms were obtained at temperatures from 25 to 200 oC. Data were analyzed by kinetic and isotherm models, and parameters related to the adsorption kinetics and thermodynamics were determined. Moreover, the co-adsorption on I2 and H2O on Ag0Z were studied. Co-adsorption uptake curves were obtained to determine the performance of Ag0Z in humid gas streams and effect of H2O concentration on the capacity of Ag0Z for I2 adsorption. It was found that H2O vapor in the gas stream deactivated the iodine adsorption sites (Ag particles) in Ag0Z. The deactivation mechanism was determined by chemical analyses with XRD and SEM-EDX

Stochastic analysis of guided wave structural health monitoring for aeronautical composites

This thesis presents new methods developed for improvement of the reliability of Guided Wave Structural Health Monitoring (GWSHM) systems for aeronautical composite. Particular attention is devoted to the detection and localisation of barely visible impact damage (BVID) in Carbon-Fibre Reinforced Polymer (CFRP) structures. A novel sensor installation method is developed that offers ease of application and replacement as well as excellent durability. Electromechanical Impedance (EMI) is used to assess the durability of the sensor installation methods in simulated aircraft operational conditions, including thermal cycles, fatigue loading and hot-wet conditions. The superiority of the developed method over existing installation methods is demonstrated through extensive tests. Damage characterisation using GWSHM is investigated in different CFRP structures. Key issues in guided wave based damage identification are addressed, including wave mode /frequency selection, the influence of dynamic load, the validity of simulated damage, sensitivity of guided wave to impact damage in different CFRP materials. Identification of barely visible impact damage (BVID) are investigated on three simple CFRP panels and two stiffened CFRP panels. BVID is detected using three different damage index and located using RAPID, Delay-and-sum, Rayleigh maximum likelihood estimation (RMLE) and Bayesian inference (BI). The influence of temperature on guided wave propagation in anisotropic CFRP structures is addressed and a novel baseline reconstruction approach for temperature compensation is proposed. The proposed temperature compensation method accommodates various sensor placement and can be established using coupon level structures for the application in larger scale structures. Finally, a multi-level hierarchical approach is proposed for the quantification of ultrasonic guided wave based structural health monitoring (GWSHM) system. The hierarchical approach provides a systemic and practical way of establishing GWSHM systems for different structures under uncertainties and assessing system performance. The proposed approach is demonstrated in aircraft CFRP structures from coupon level to sub-component level.Open Acces

Dark Energy and Normalization of the Cosmological Wave Function

Dark energy is investigated from the perspective of quantum cosmology. It is found that, together with an appropriate normal ordering factor $q$, only when there is dark energy then can the cosmological wave function be normalized. This interesting observation may require further attention.Comment: Title changed, match the published versio