Radiolytically-induced novel materials and their application to waste processing

In the present NEER project we investigated two different types of gel materials with respect to potential applications in environmental remediation, including mixed waste generated from the nuclear fuel cycles. The materials under study were: (1) silica-polymer based aerogel composites into which specific metallic cations diffuse into and remain, and (2) polymer gels made of thermo-sensitive polymer networks, whose functional groups can be ''tailored'' to have a preferred affinity for specific cations, again diffusing into and remaining in the network under a volumetrically, contractive phase-transition. The molecular, diffusion of specific cations, including those of concern in low-level waste streams, into the gel materials studied here indicates that a scaled, engineered system can be designed so that it is passive; that is, minimal (human) intervention and risk would be involved in encapsulating LLW species. In addition, the gel materials hold potential significance in environmental remediation of and recovery of metallic cations identified in respective domains and physico-chemical processes. In brief, silica gels start as aqueous/liquid solutions of base catalyzed silica hydrogels and metal ions (targeted species), such as silver. The metal ions are reduced radiolytically and migrate through the solution to form clusters. Upon post-irradiation processing, aerogel monoliths, extremely lightweight but mechanically strong, that encapsulate the metals are produced. Interestingly the radiolytic or photonic source can be gamma-rays and/or other rays from ''artificial sources'', such as reactors, or ''inherent sources'' like those characterizing mixed waste. Polymer gels, in contrast exhibit thermally-induced volumetric contraction at 20-50 C by expelling water from the gels physical state. Further, some functional groups that capture di- or tri-valent cations from aqueous solutions can be incorporated into the polymer networks on synthesis, including by radiolytic means. These polymer gels retain cations after volumetric contraction and have the ability to trap solid particulates in liquid waste streams. With both silica and polymer gels, functional design of a prototypic ''recovery'' systems, such as by natural convection in a rectangular cell, appears possible. Additional and specific details are provided in the rest of this Final Report

Experimental Development and Demonstration of Ultrasonic Measurement Diagnostics for Sodium Fast Reactor Thermal-hydraulics

This research project will address some of the principal technology issues related to sodium-cooled fast reactors (SFR), primarily the development and demonstration of ultrasonic measurement diagnostics linked to effective thermal convective sensing under normatl and off-normal conditions. Sodium is well-suited as a heat transfer medium for the SFR. However, because it is chemically reactive and optically opaque, it presents engineering accessibility constraints relative to operations and maintenance (O&M) and in-service inspection (ISI) technologies that are currently used for light water reactors. Thus, there are limited sensing options for conducting thermohydraulic measurements under normal conditions and off-normal events (maintenance, unanticipated events). Acoustic methods, primarily ultrasonics, are a key measurement technology with applications in non-destructive testing, component imaging, thermometry, and velocimetry. THis project would have yielded a better quantitative and qualitative understanding of the thermohydraulic condition of solium under varied flow conditions. THe scope of work will evaluate and demonstrate ultrasonic technologies and define instrumentation options for the SFR

Bimetallic Pt-Ag and Pd-Ag Nanoparticles

We report studies of bimetallic nanoparticles with 15%-16% atomic crystal parameters size mismatch. The degree of alloying was probed in a 2-nm Pt core (smallest attainable core size) of Pt-Ag nanoparticles (completely immiscible in bulk) and 20-nm-diameter Pd-Ag nanowires (completely miscible in bulk). Particles were synthesized radiolytically, and depending on the initial parameters, they assume spherical or cylindrical (nanowire) morphologies. In all cases, the metals are seen to follow their bulk alloying characteristics. Pt and Ag segregate in both spherical and wire forms, which indicates that strain due to crystallographic mismatch overcomes the excess surface free energy in the small particles. The Pd-Ag nanowires alloy similar to previously reported spherical Pd-Ag particles of similar diameter and composition

Nanometal Containing Nanocomposites and Photolithographic Polyaniline Nanofibers

A report on recent progress from our laboratories on the nanostructures produced from novel synthesis techniques will be discussed. Using high-energy radiation (γ-rays) we have been able to produce conducting polymer nanofibers and nanorods of polyaniline and polypyrrole without the use of a separate template or capping agent. This technique has been extended, with the addition of metal ions, to a one pot synthesis, producing conducting nanocomposites. These nanocomposites contain metal nanoparticles which decorate the conducting nanofibers. We have also recently shown that these systems can be photopatterned to produce novel structures. We believe that these systems will be useful in novel or significantly improved electronic devices

Specialized CNT-based Sensor Framework for Advanced Motion Tracking

In this work, we discuss the design and development of an advanced framework for high-fidelity finger motion tracking based on Specialized Carbon Nanotube (CNT) stretchable sensors developed at our research facilities. Earlier versions of the CNT sensors have been employed in the high-fidelity finger motion tracking Data Glove commercialized by Yamaha, Japan. The framework presented in this paper encompasses our continuing research and development of more advanced CNT-based sensors and the implementation of novel high-fidelity motion tracking products based on them. The CNT sensor production and communication framework components are considered in detail and wireless motion tracking experiments with the developed hardware and software components integrated with the Yamaha Data Glove are reported

Laser Writing of Semiconductor Nanoparticles and Quantum Dots

Silica aerogels were patterned with CdS using a photolithographic technique based on local heating with infrared (IR) light. The solvent of silica hydrogels was exchanged with an aqueous solution of the precursors CdNO3 and NH4 OH, all precooled to a temperature of 5°C. Half of the bathing solution was then replaced by a thiourea solution. After thiourea diffused into the hydrogels, the samples were exposed to a focused IR beam from a continuous wave, Nd-YAG laser. The precursors reacted in the spots heated by the IR beam to form CdS nanoparticles. We lithographed features with a diameter of about 40 µm, which extended inside the monoliths for up to 4 mm. Samples were characterized with transmission electron microscopy and optical absorption, photoluminescence, and Raman spectroscopies. Spots illuminated by the IR beam were made up by CdS nanoparticles dispersed in a silica matrix. The CdS nanoparticles had a diameter in the 4-6 nm range in samples exposed for 4 min to the IR beam, and of up to 100 nm in samples exposed for 10 min

Temperature Dependence of Density of Polymer Gels: Effects of Ionizable Groups in Copoly(N-isopropylacrylamide/acrylic Acid Or Sodium Acrylate)-water Systems

Effects of ionizable groups in hydrogels of copolymer networks on the volumetric contraction-expansion process were investigated. Polymer networks used were: copoly[N-isopropylacrylamide (NIPA)(1 − x)/acrylic acid (HAc) or sodium acrylate (NaAc)(x)] with mole fraction of minor component (x) assuming 0.0114 and 0.0457. From the temperature (T) dependence of total volume of gels, densities of the polymer and solvent (water) components, and stoichiometry, we evaluated (1) the volume of gels occupied by a single mean polymeric residue and associated water molecules (expressed in units of nm3), mean vsp(gel), and (2) number of water molecules per single mean polymeric residue, mean Ns(gel), from near 273 K to 323 K. These quantities (1) and (2) listed above showed how acid and salt forms affect differently on volumetric changes of gels over 50 K. We developed an approach to evaluate volumetric changes of gels solely caused by a single polymeric residue of a minor component (x \u3c 0.05) plus associated water by applying thermodynamic first-order perturbation theory. They are specific vsp(gel)(T) for a single HAc or NaAc polymeric residue plus associated water and the corresponding specific Ns(gel)(T). Specific vsp(gel)(HAc or NaAc)(T) and the corresponding specific Ns(gel(T)) revealed specific characteristics in thermal behavior near their respective transition temperatures from the swollen to shrunken states. We found these thermal changes shown at the nano-scale match very well with specific changes in the molality(T) of both ionizable groups. In fact, these are directly triggered by varying contents of water in gels. Based on the understanding of dissociative equilibrium attained by ionizable groups, we successfully replaced Na+ in hydrogels of copoly[NIPA(1 − x)/NaAc(x)] (x = 0.0457) by hydrogen ions. Absence of Na+ in treated hydrogels was experimentally verified by 23Na NMR and Na atomic absorption flame photometry. Discontinuity in the volumetric contraction-expansion process from the swollen to shrunken states and vice versa was not observed in contradiction to the previous reports [Hirotsu S, Hirokawa Y, Tanaka T. J Chem Phys 1987;87:1392-5. Matsuo SE, Tanaka T. J Chem Phys 1988;89:1695-703.] obtained by the conventional swelling experiments

Natural convection heat transfer enhancement in mercury with gas injection and in the presence of a transverse magnetic field

A natural convection heat transfer experiment using a vertical plate held at constant heat flux in mercury with gas injection and a transverse magnetic field was performed. The experiment was conducted with heat fluxes up to 16 kW/m\sp2 (10\sp5 $\u3c$ Bo\sb{\rm x}\sp{\*} $\u3c$ 10\sp9), gas injection rates up to 9 cm\sp3/sec and magnetic field intensities up to 0.5 Tesla. Local heat transfer and bubble measurements were made using thermo-couple and double conductivity probes. Measurements at low heat flux, where the flow was mostly laminar, indicated that gas injection enhanced the heat transfer coefficient two to three times. At high heat flux, where the flow was mostly turbulent and strong stratification was present, the observed enhancement was less pronounced. The enhancement mechanism at low heat flux was attributed to the bubbles which populate and induce turbulence inside a thick laminar thermal boundary layer. At high heat flux, however, the bubbles reside mostly outside a thin turbulent thermal boundary layer and act to suppress the stratification. In the presence of a transverse magnetic field, the single-phase data at low heat flux agreed with the theoretical results of past investigations, while, at high heat flux, the heat transfer coefficient did not decrease as much in contrast with the same theory. This was attributed to the increasing influence of three-dimensional effects in turbulent magneto-fluid-mechanic natural convection. With the addition of gas injection at low heat flux, a magnetic field intensity of 0.07 Tesla decreased the heat transfer coefficient six-fold in contrast to the enhanced value observed with injection. At a field intensity of 0.35 Tesla, the reduction was fifteen-fold. At high heat flux, equivalent field intensities reduced the heat transfer coefficient slightly at 0.07 Tesla and two-fold at 0.35 Tesla. These results were attributed to the suppression of both thermally and bubble-induced fluid motions at low heat flux while mainly the thermally-induced turbulence was suppressed at high heat flux. These trends were further explained in terms of the changes in the bubble size and rise velocity with magnetic field intensity. The influence of thermal stratification in natural convection was additionally investigated. A new stratified Nusselt number, sNu, incorporating the stratification parameter, S, was introduced through theoretical arguments and shown to successfully correlate both present and past stratified natural convection data. Some theoretical considerations have also been forwarded to analyze our and other available data of the effect of the aspect ratio in natural convection in an enclosure