Contribution of Energetically Reactive Surface Features to the Dissolution of CeO2 and ThO2 Analogues for Spent Nuclear Fuel Microstructures

In the safety case for the geological disposal of nuclear waste, the release of radioactivity from the repository is controlled by the dissolution of the spent fuel in groundwater. There remain several uncertainties associated with understanding spent fuel dissolution, including the contribution of energetically reactive surface sites to the dissolution rate. In this study, we investigate how surface features influence the dissolution rate of synthetic CeO2 and ThO2, spent nuclear fuel analogues that approximate as closely as possible the microstructure characteristics of fuel-grade UO2 but are not sensitive to changes in oxidation state of the cation. The morphology of grain boundaries (natural features) and surface facets (specimen preparation-induced features) was investigated during dissolution. The effects of surface polishing on dissolution rate were also investigated. We show that preferential dissolution occurs at grain boundaries, resulting in grain boundary decohesion and enhanced dissolution rates. A strong crystallographic control was exerted, with high misorientation angle grain boundaries retreating more rapidly than those with low misorientation angles, which may be due to the accommodation of defects in the grain boundary structure. The data from these simplified analogue systems support the hypothesis that grain boundaries play a role in the so-called “instant release fraction” of spent fuel, and should be carefully considered, in conjunction with other chemical effects, in safety performance assessements for the geological disposal of spent fuel. Surface facets formed during the sample annealing process also exhibited a strong crystallographic control and were found to dissolve rapidly on initial contact with dissolution medium. Defects and strain induced during sample polishing caused an overestimation of the dissolution rate, by up to 3 orders of magnitude

Mineralization of greywater organics by the ozone-UV advanced oxidation process: kinetic modeling and efficiency

Ozone-UV advanced oxidation treatment can mineralize total organic carbon (TOC) in water without the addition of chemicals, representing an alternative to phase-transfer processes such as reverse osmosis for water reuse. However, efficiency is governed by competing principal reaction pathways, and limited information has been available for optimizing treatments in such applications. In this study, a 1.2 m3 per day (320 GPD) pilot ozone-UV greywater reuse system was tested using simulated and real shower water, and the resulting kinetic data were used to develop a kinetic model of TOC mineralization. H2O2 is produced by photolysis with ozone, and subsequent reactions produce hydroxyl radicals, which mineralize TOC. TOC mineralization efficiency is governed by TOC concentration (controlling transmissivity), pH throughout the treatment, ozone-UV dose ratio, and the evolution of pH due to CO2 production from TOC, which impacts oxidative efficiency dynamically. Modeled hydroxyl radical concentrations were ∼10−10 M, as expected during water treatment and reuse, and the second order rate constant for the reaction of hydroxyl radicals with TOC was [1.7–7.6] × 107 M−1 s−1, similar to others reported for the mineralization of wastewater organics. The minimum electrical energy for commercial UV and ozone equipment was assessed at 3.73 kW h per order per m3 of TOC mineralization, and modeling indicated a wide range of optimal dosing ratios. Treatment efficiency was found to depend strongly on a reactor design that ensures an influent TOC concentration low enough to allow the effective transmission of UV radiation. Further development of the kinetic model to account dynamically for pH evolution as a function of TOC mineralization, reactor hydraulics, and mixing is recommended

Correction: Ozone–UV net-zero water wash station for remote emergency response healthcare units: design, operation, and results

Correction for ‘Ozone–UV net-zero water wash station for remote emergency response healthcare units: design, operation, and results’ by Lucien W. Gassie et al., Environ. Sci.: Water Res. Technol., 2019, 5, 1971–1984, DOI: 10.1039/C9EW00126C

Ozone–UV net-zero water wash station for remote emergency response healthcare units: design, operation, and results

Because disease pandemics can accelerate rapidly in areas with limited clean-water access, a portable greywater reuse system may be useful to provide wash water at emergency health care units. In this study, a novel fed-batch (hybrid continuous-batch flow) net-zero water (NZW), or nearly closed-loop, reuse system comprising screening, 5 μm filter, and ozone–UV advanced oxidation was designed, constructed, and tested for performance with simulated and actual human showers. Water quality was tested for compliance with US drinking water standards, total organic carbon < 0.5 mg L−1, and pathogen inactivation including 12 log10 virus, 10 log10 protozoa, and 9 log10 bacteria as has been recommended for direct potable reuse. Energy, operation, and maintenance requirements were also evaluated, along with the system's capacity to handle shock events such as unintentional contamination with urine. Design goals were achieved without the addition of GAC point-of-use filter, except compliance with bromate and nitrate drinking water standards, which were met only for temporary use of up to three years per person. A capacity of 32 showers per day at 1920 W continuous power is projected, without generation of potentially-infectious concentrate. To avoid the further increase in system weight and energy demand needed to address urine input, future integrated urine diversion and collection, and system drain-and-fill following detection of urine in recycled water by electrical conductivity, are suggested for the field unit. Field testing is recommended. Further research should focus on potential need for bromate/nitrate mitigation, and longer-term study of microbiological inactivation

Cookies That Give You Away: The Surveillance Implications of Web Tracking

We study the ability of a passive eavesdropper to leverage "third-party" HTTP tracking cookies for mass surveillance. If two web pages embed the same tracker which tags the browser with a unique cookie, then the adversary can link visits to those pages from the same user (i.e., browser instance) even if the user's IP address varies. Further, many popular websites leak a logged-in user's identity to an eavesdropper in unencrypted traffic. To evaluate the effectiveness of our attack, we introduce a methodology that combines web measurement and network measurement. Using OpenWPM, our web privacy measurement platform, we simulate users browsing the web and find that the adversary can reconstruct 62-73% of a typical user's browsing history. We then analyze the effect of the physical location of the wiretap as well as legal restrictions such as the NSA's "one-end foreign" rule. Using measurement units in various locations - Asia, Europe, and the United States - we show that foreign users are highly vulnerable to the NSA's dragnet surveillance due to the concentration of third-party trackers in the U.S. Finally, we find that some browser-based privacy tools mitigate the attack while others are largely ineffective

Impedance measurement of absolute blood flow using an angioplasty catheter: A validation study

An angioplasty catheter was developed to allow measurement of absolute coronary blood flow during interventional procedures. This method uses electrical impedance changes induced by a 0.5 ml bolus of 5% dextrose solution and indicator-dilution principles. The indicator is injected through a port located just proximal to the dilating balloon and the resulting changes in blood impedance are measured by electrodes at the catheter tip. Excellent linear correlations were found between known flow in 2 to 4 mm to diameter plastic tubes and catheter measurements (r = 0.99) and between timed collection canine femoral artery flow and catheter measurements (r = 0.97). Final validation was performed in canine coronary arteries using electromagnetic flowmeter data as the standard (r = 0.94). Thus accurate clinical determination of absolute coronary blood flow can be accomplished using this relatively inexpensive and simple catheter technique. © 1991

Mineralizing urban net-zero water treatment: Phase II field results and design recommendations

Net-zero water (NZW) systems, or water management systems achieving high recycling rates and low residuals generation so as to avoid water import and export, can also conserve energy used to heat and convey water, while economically restoring local eco-hydrology. However, design and operating experience are extremely limited. The objective of this paper is to present the results of the second phase of operation of an advanced oxidation-based NZW pilot system designed, constructed, and operated for a period of two years, serving an occupied four-person apartment. System water was monitored, either continuously or thrice daily, for routine water quality parameters, minerals, and MicroTox® in-vitro toxicity, and intermittently for somatic and male-specific coliphage, adenovirus, Cryptosporidium, Giardia, emerging organic constituents (non-quantitative), and the Florida drinking water standards. All 115 drinking water standards with the exception of bromate were met in this phase. Neither virus nor protozoa were detected in the treated water, with the exception of measurement of adenovirus genome copies attributed to accumulation of inactive genetic material in hydraulic dead zones. Chemical oxygen demand was mineralized to 90% in treatment. Total dissolved solids were maintained at ∼500 mg/L at steady state, partially through aerated aluminum electrocoagulation. Bromate accumulation is projected to be controlled by aluminum electrocoagulation with separate disposal of backwash water. Further development of such systems and their automated/remote process control systems is recommended. [Display omitted] •An urban net-zero water system was operated for 18 months for direct potable reuse.•Organics were effectively mineralized with UV-hydrogen peroxide advanced oxidation.•Of 1006 emerging organics, 56 were detected in the influent, with 50 removed >90%.•No Cryptosporidium, Giardia, or coliphage were detected in the treated water.•Backwash water disposal, aluminum electrocoagulation suggested for bromate control