Fibrous filter pressure drop and aerosol collection efficiency were measured at low air pressures (0.2-0.8 atm) and high face velocities (5-19 m/s) to give fiber Reynolds numbers lying in the viscous-inertial transition flow regime (1-15). In this regime, contemporary filtration theory based on Kuwabara's viscous flow through an ensemble of fibers underpredicts single fiber impaction by several orders of magnitude. Streamline curvature increases substantially as air stream inertial forces become significant. Dimensionless pressure drop measurements followed the viscous-inertial theory of Robinson and Franklin (1972) rather than Darcy's linear pressure-velocity relationship. Sodium chloride and iron nano-agglomerate aerosols were tested to provide a comparison between particles of dissimilar densities and shape factors. Total filter efficiency collapsed when plotted against the particle Stokes number and fiber Reynolds number. Efficiencies were then modeled with an impactor type equation where the cutpoint Stokes number and a steepness parameter described data well in the sharply increasing portion of the curve (20%-80% efficiency). A minimum in collection efficiency was observed at small Stokes numbers and attributed to interception and diffusive effects. The cutpoint Stokes number was a linearly decreasing function of fiber Reynolds number. Single fiber efficiencies were calculated from total filter efficiencies and compared to contemporary viscous flow impaction theory (Stechkina et al. 1969), and numerical simulations of single fiber efficiencies from the literature. Existing theories underpredicted measured single fiber efficiencies, although comparison is problematic. The assumption of uniform flow conditions for each successive layer of fibers is questionable; thus, the common exponential relationship between single fiber efficiency and total filter efficiency may not be appropriate in this regime.

Particle resuspension due to mechanical impulse was studied for spherical polymethylmethacrylate (pmma) particles ranging from 1.7 to 14.4 mu m in diameter on titanium dioxide (TiO2) and silicon dioxide (SiO2) wafers. Dry powders were dispersed, electrostatically neutralized, and allowed to deposit under the influence of gravity. Contaminated surfaces were then mechanically excited with a 5 MHz piezoelectric transducer where surface accelerations (similar to 10(6) m/s(2)) and resuspension ratios were quantified with laser Doppler vibrometry (LDV) and digital microscopy, respectively. For TiO2, experiments were performed over a broad range of relative humidity (25 to 95%) to assess the effects of capillary condensation. Resuspension was a monotonically decreasing function of relative humidity. Existing theories were used to separate data into two adhesion regimes based on capillary bridge formation: van der Waals (vdW) and capillary dominated adhesion. For relative humidity above 60%, resuspension forces were nondimensionalized by the theoretical capillary force. Resuspension data for all particle sizes and relative humidity were described by a single sigmoid function dependent on the dimensionless resuspension force. Below 60% relative humidity, resuspension forces were nondimensionalized by the vdW force calculated with Johnson-Kendall-Roberts adhesion theory. The experimental work of adhesion (pmma-TiO2) was optimized such that the dimensionless resuspension curves, for capillary and vdW forces, had equivalent dimensionless resuspension forces at 50% resuspension. The calculated value, 0.047 J/m(2), was within the range of values expected from other published works. Resuspension was not observed for particles on SiO2 substrates. This result was attributed to electrostatic surface charge patches where particle charge and surface resistivities were measured to analyze the relative influence of electrostatic adhesion forces.

Direct fabrication of metal near-net shapes from a computer model typically involves melting and solidification, which can cause high residual stresses, undesirable phases, poor microstructures, rough surface finishes, warpage, and other problems. This paper describes a new technology, still under development, that might be used to directly fabricate solid, near-fulldensity, free-form shapes of many metals, and even some composite materials, at or near room temperature without melting and solidification. In this process, tentatively called Cold Spray Direct Fabrication (CSDF), powder particles in a supersonic jet of compressed gas impact a solid surface with sufficient energy to cause plastic deformation and consolidation with the underlying material by a process thought to be analogous to explosive welding. Material deposition by cold spray methods has already been successfully demonstrated by several investigators. This paper presents results of an experimental study to investigate the effects of selected process variables on cold spray particle velocities. In addition, a key technical barrier to the CSDF concept is focusing the spray stream down to dimensions that would permit a useful level of part detail, while still providing practical build rates. This paper presents results of initial research to develop an aerodynamic lens that may provide the required particle stream focusing.

This paper summarises a multinational, four phase, spent fuel sabotage test programme that quantifies aerosol particles produced when the products of a high energy density device (HEDD) interact with and explosively particulate test rodlets (∼20 cm long rods) that contain pellets of either surrogate materials or actual spent fuel. This programme provides source term data that are relevant to plausible sabotage attack scenarios in relation to spent fuel transport and storage casks, and associated risk assessments. Details and significant results are presented from three phase 3 tests performed using depleted UO2 (DUO2) pellets plus non-radioactive fission product dopants in surrogate spent fuel test rodlets. Measured aerosol results include: respirable fractions produced; particle size distributions; measurements of volatile fission product species enhanced sorption: enrichment factors onto respirable particles; and status on determination of the spent fuel ratio (SFR), needed for scaling studies. The DUO2 aerosol particle results are compared directly with similar phase 2 results from cerium oxide ceramic pellet and fission product dopant surrogate test rodlets. A status update is provided on preparations for the final phase 4 tests using rodlets containing actual PWR spent fuel. The source term data and programme design have been tailored to support and guide follow-on computer modelling of aerosol dispersal hazards and radiological consequence assessments. This spent fuel sabotage test programme was performed primarily at Sandia National Laboratories, with support provided by both the US Department of Energy and the Nuclear Regulatory Commission. This programme is strongly supported and coordinated by US and international programme participants in Germany and France, as part of the International Working Group for Sabotage Concerns of Transport and Storage Casks (WGSTSC).

Vacuum filter socks were evaluated for recovery efficiency of powdered Bacillus atrophaeus spores from two non-porous surfaces, stainless steel and painted wallboard and two porous surfaces, carpet and bare concrete. Two surface coupons were positioned side-by-side and seeded with aerosolized Bacillus atrophaeus spores. One of the surfaces, a stainless steel reference coupon, was sized to fit into a sample vial for direct spore removal, while the other surface, a sample surface coupon, was sized for a vacuum collection application. Deposited spore material was directly removed from the reference coupon surface and cultured for enumeration of colony forming units (CFU), while deposited spore material was collected from the sample coupon using the vacuum filter sock method, extracted by sonication and cultured for enumeration. Recovery efficiency, which is a measure of overall transfer effectiveness from the surface to culture, was calculated as the number of CFU enumerated from the filter sock sample per unit area relative to the number of CFU enumerated from the co-located reference coupon per unit area. The observed mean filter sock recovery efficiency from stainless steel was 0.29 (SD = 0.14, n = 36), from painted wallboard was 0.25 (SD = 0.15, n = 36), from carpet was 0.28 (SD = 0.13, n = 40) and from bare concrete was 0.19 (SD = 0.14, n = 44). Vacuum filter sock recovery quantitative limits of detection were estimated at 105 CFU m(-2) from stainless steel and carpet, 120 CFU m(-2) from painted wallboard and 160 CFU m(-2) from bare concrete. The method recovery efficiency and limits of detection established in this work provide useful guidance for the planning of incident response environmental sampling for biological agents such as Bacillus anthracis.

Polyester-rayon blend wipes were evaluated for efficiency of extraction and recovery of powdered Bacillus atrophaeus spores from stainless steel and painted wallboard surfaces. Method limits of detection were also estimated for both surfaces. The observed mean efficiency of polyester-rayon blend wipe recovery from stainless steel was 0.35 with a standard deviation of +/-0.12, and for painted wallboard it was 0.29 with a standard deviation of +/-0.15. Evaluation of a sonication extraction method for the polyester-rayon blend wipes produced a mean extraction efficiency of 0.93 with a standard deviation of +/-0.09. Wipe recovery quantitative limits of detection were estimated at 90 CFU per unit of stainless steel sample area and 105 CFU per unit of painted wallboard sample area. The method recovery efficiency and limits of detection established in this work provide useful guidance for the planning of incident response environmental sampling following the release of a biological agent such as Bacillus anthracis.