DRYING OF MOCK SPENT NUCLEAR FUEL ELEMENTS

Abstract

Spent nuclear fuel elements are stored in underwater cooling pools until the elements can be safely handled and prepared for interim dry storage. The fuel was intended for short-term storage in water before it was to be reprocessed. However, the fuel will no longer be reprocessed, and extended storage in water has caused many of the aluminum-clad elements to degrade, exposing the uranium fuel. In addition, sludge, comprised of corroded aluminum and sediment, has accumulated in and around the fuel plates. The water in the sludge must be removed before the spent fuel elements can be placed in dry storage. Experiments have been performed on mock spent fuel elements with simulated corrosion product applied between the plates. A series of vacuum and heating cycles were used to dry the elements, and a mixture of clay and aluminum oxide was used to simulate corrosion products on the elements.

The procedures used in the experiments were determined to be adequate to dry the mock spent fuel elements, and the temperature behavior of the simulated corrosion product within the fuel elements could be used to determine when the element was dry. On plates where areas of wet simulant were found, a sharp drying front was observed that separated the wet and dry parts of the simulated corrosion product. The drying front propagated inward towards the center of the mock fuel elements over time.     

Observing the observer: non-intrusive verbalisations using the Concurrent Observer Narrative Technique

This paper presents the application of, and a discussion about, a new method of information acquisition, the Concurrent Observer Narrative Technique (CONT), that requires an expert to narrate the work of experienced colleagues. The method is explored through a case study of instructors in a training simulation environment. The method involves multiple expert users of the system equally matched in experience; one or more of which perform the task at hand, namely running the training session, whilst another, not engaged in the training activity, provides verbal reports whilst observing task progression. All are situated in the work environment concurrently. The method is discussed in terms of the richness and detail of the data obtained from the reports and in terms of some advantages and disadvantages over other verbal reporting methods, specifically collegial verbalisation (Jansson et al. in Cogn Tech Work 8:41–49, 2006) and Elicitation By Critiquing (Miller et al. in Cogn Tech Work 8: 90–102, 2006). It is argued that the CONT provides a relatively easy, inexpensive, and non-intrusive method that can supply a wealth of information that does not require further interpretation and that the method is of particular applicability in domains where the subject matter expert is unable to provide concurrent verbalisations themselves and where the subject matter is too complex to be understood by a lay person.     

Mechanical elasticity of vapour-liquid-solid grown GaN nanowires

Mechanical elasticity of hexagonal wurtzite GaN nanowires with hexagonal cross sections grown through a vapour-liquid-solid (VLS) method was investigated using a three-point bending method with a digital-pulsed force mode (DPFM) atomic force microscope (AFM). In a diameter range of 57-135?nm, bending deflection and effective stiffness, or spring constant, profiles were recorded over the entire length of end-supported GaN nanowires and compared to the classic elastic beam models. Profiles reveal that the bending behaviour of the smallest nanowire (57.0?nm in diameter) is as a fixed beam, while larger nanowires (89.3-135.0?nm in diameter) all show simple-beam boundary conditions. Diameter dependence on the stiffness and elastic modulus are observed for these GaN nanowires. The GaN nanowire of 57.0?nm diameter displays the lowest stiffness (0.98?N?m(-1)) and the highest elastic modulus (400 ± 15?GPa). But with increasing diameter, elastic modulus decreases, while stiffness increases. Elastic moduli for most tested nanowires range from 218 to 317?GPa, which approaches or meets the literature values for bulk single crystal and GaN nanowires with triangular cross sections from other investigators. The present results together with further tests on plastic and fracture processes will provide fundamental information for the development of GaN nanowire devices.     

Measurement of turbulent flow phenomena for the lower plenum of a prismatic gas-cooled reactor

Mean velocity field and turbulence data are presented that measure turbulent flow phenomena in an approximately 1:7 scale model of a region of the lower plenum of a typical prismatic gas-cooled reactor (GCR) similar to a General Atomics design (Gas-Turbine-Modular Helium Reactor). The data were obtained in the Matched-Index-of-Refraction (MIR) facility at Idaho National Laboratory (INL) and are offered as a benchmark for assessing computational fluid dynamics (CFD) software. This experiment has been selected as the first Standard Problem endorsed by the Generation IV International Forum. The primary objective of this paper is to document the experiment and present a sample of the data set that has been established for this standard problem.Present results concentrate on the region of the lower plenum near its far reflector wall (away from the outlet duct). The flow in the lower plenum consists of multiple jets injected into a confined crossflow—with obstructions. The model consists of a row of full circular posts along its centerline with half-posts on the two parallel walls to approximate flow scaled to that expected from the staggered parallel rows of posts in the reactor design. Posts, side walls and end walls are fabricated from clear, fused quartz to match the refractive index of the mineral oil working fluid so that optical techniques may be employed for the measurements. The benefit of the MIR technique is that it permits optical measurements to determine flow characteristics in complex passages and around objects to be obtained without locating intrusive transducers that will disturb the flow field and without distortion of the optical paths. An advantage of the INL system is its large size, leading to improved spatial and temporal resolution compared to similar facilities at smaller scales. A three-dimensional (3D) particle image velocimetry (PIV) system was used to collect the data. Inlet-jet Reynolds numbers (based on the hydraulic diameter of the jet and the time-mean average flow rate) are approximately 4300 and 12,400. Uncertainty analysis and a discussion of the standard problem are included.The measurements reveal complicated flow patterns that include several large recirculation zones, reverse flow near the simulated reflector wall, recirculation zones in the upper portion of the plenum and complex flow patterns around the support posts. Data include three-dimensional PIV images of flow planes, data displays along the coordinate planes (slices) and presentations that describe the component flows at specific regions in the model.     

A 12-month prospective clinical trial of comfilcon A silicone-hydrogel contact lenses worn on a 30-day continuous wear basis.

PURPOSE: To evaluate the clinical performance of comfilcon A (Biofinity) during 12 months of continuous wear compared to other silicone-hydrogel lenses. METHOD: Forty-five subjects were fitted in one eye with the comfilcon A (test) lens. For 22 subjects, the other eye was fitted with lotrafilcon A (group A) and for the remaining 23 subjects the other eye was fitted with balafilcon A (group B). Twelve-month data are presented on 48 measured variables. RESULTS: There were no serious adverse events during the course of the study. A total of 33 subjects completed the study, with only 4 discontinuations for lens-related reasons, spread proportionately between the lenses. On preference scales, the test lens was superior to both control lenses for comfort (p<0.05) and overall preference (p<0.05) and in group A for vision (p<0.05). On grading scales, the test lens scored better than both control lenses for overall comfort (p<0.1 for group A, p<0.05 for group B), comfort during the day (p<0.05), end-of-day comfort (p<0.05) and overall preference (p<0.05), and better in group A for general vision quality (p<0.01), night vision quality (p<0.01) and handling (p<0.05). All lenses performed to a comparable degree on the basis of microcysts and corneal staining. There were significant differences between lenses in producing limbal redness (p<0.05), bulbar conjunctival hyperemia (p<0.1) and conjunctival NaFl staining (p<0.01) with the control lens in group A showing the greatest effect and the control lens in group B the least. CONCLUSION: Comfilcon A offers performance advantages over first generation silicone-hydrogel materials for continuous wear.     

Fast and accurate method for calculation of polarised modes in semiconductor rib waveguides

A new semivectorial 'spectral index' (SI) method for finding the guided modes of semiconductor rib waveguides is described. The results are shown by comparison to be of the same accuracy as well established finite difference calculations. A useful by-product is a contour map of the principal field component. The propagation constants are found using novel transcendental equations which are easy to set up and are given here explicitly. These discriminate clearly between the TE and TM modes and are variational in nature.<>     

The control of foot placement during compensatory stepping reactions: does speed of response take precedence over stability?

Rapid, reflex-like stepping movements are a prevalent and functional compensatory reaction to destabilization, however, little is known about the underlying control. In this paper, a model is developed to examine how speed and stability demands affect control of foot placement during forward and backward compensatory stepping reactions. The concept of the velocity stability margin (VSM) is introduced to characterize the degree to which the horizontal velocity of the falling body approaches biomechanical limits on the capacity to decelerate the center of mass; analogous limits on center-of-mass displacement are quantified in terms of the displacement stability margin (DSM). The model is used to predict, for any initial step characteristics, the variation in DSM and VSM that would occur as a function of changes in timing of foot placement. The VSM was found to prevail over the DSM in establishing limits of stability. Model simulations demonstrated that there typically exists a minimum swing duration that maximizes speed of response while meeting minimum requirements for stability (VSM > or = 0), as well as a slower speed of response (longer swing duration) at which stability (VSM) is maximized. Experimental data from platform-perturbation tests in 20 healthy young (22-28) and older (65-81) adults were used, in conjunction with the model, to investigate whether speed or stability takes precedence during natural behavior. Control of single-step reactions appeared to favor stability; although the model predicted that a minimally stable step (VSM = 0) could be attained by swing durations as short as 30 ms, the observed swing durations were, on average, 135 ms longer than this, and the average VSM was nearly as large (80%) as the optimally stable value predicted by the model. Control of the initial step of multiple-step reactions was distinctly different. The average swing duration was only 55 ms greater than the minimally stable value and the average VSM was 81% smaller than in the single-step reactions. This reduction in VSM is consistent with a need to execute additional steps and appears to support the validity of the model. This model may help to provide insight into the biomechanical factors that govern the neural control of compensatory stepping reactions.     

Nanowire-based delivery of Escherichia coli O157 shiga toxin 1 A subunit into human and bovine cells

Silica nanowires (NWs) were used to introduce the Shiga toxin type 1 A subunit (StxA1) into cultured bovine and human epithelial cells. We extended technology developed in our laboratories that employs fibronectin (Fn) to induce integrin-mediated uptake of NWs by coating NWs with StxA1 and Fn. The bonding strengths of Fn and StxA1 to the surface of NWs were measured by X-ray photoelectron spectroscopy. This technique demonstrated complex interactions between Fn, StxA1, and the NWs. Neutral red cytotoxicity assays and field emission scanning electron microscopy confirmed that the NW-StxA1-Fn complexes were effectively internalized and caused cell death. This indicates that NWs can carry StxA1 and potentially other toxic or therapeutic agents into eukaryotic cells. Ongoing studies include improved functionalizing of NWs aimed at increasing internalization efficiency and substituting ligands for specific cell targeting.