Nicholas A. Klymyshyn

Tip-Enhanced Near-Field Raman Spectroscopy Probing Single Dye-Sensitized TiO2 Nanoparticles

The correlated metallic tip-enhanced Raman spectroscopy and atomic force microscopy (AFM) technique was used to characterize dye-sensitized titanium oxide (TiO2) nanoparticles. We have obtained the near-field Raman spectra that are associated with the photo-induced charge transfer reaction in Ru(4,4’-dicarboxy-2,2’-bipyridine)2(NCS)2-sensitized TiO2 single nanoparticles. This method demonstrates that tip-enhanced near-field Raman spectroscopy is an effective approach for understanding inhomogeneous interfacial electron transfers with nanoscale spatial resolution.

Correlated topographic and spectroscopic imaging beyond diffraction limit by atomic force microscopy metallic tip-enhanced near-field fluorescence lifetime microscopy

A near-field optical imaging approach is demonstrated for simultaneous topographic and spectroscopic imaging with spatial resolution beyond the optical diffraction limit. The method combines metallic-tip-based tapping-mode atomic force microscopy (AFM) with fluorescence lifetime imaging microscopy (FLIM). The AFM metallic tip was formed by sputter coating a Si tapping mode tip with Au, in a way that forms a globular tip apex. Such tip apex generates high local electric field enhancement under laser illumination, which provides a strong electric-field interaction between the AFM tip and the fluorescent molecules under the tip. The tip perturbation of fluorescence gives the fluorescence lifetime changes that provide the AFM–FLIM imaging contrast. A finite element method simulation was used to further evaluate the electric near-field enhancement and electric field distribution originating from the metallic Au-coated AFM tapping-mode tip. We have demonstrated that spatially mapping the change in fluorescence ...

Multiscale analysis of stamp forming of a woven composite

The stamp forming of a woven composite with thermoplastic matrix was investigated in this study. A mesoscale finite element model of a unit cell of a 2 × 2 twill weave of pre-impregnated tows was used to estimate the effective in-plane shear properties for modeling forming processes and predicting formability. In-plane shear stiffness was shown to be a controlling factor in the formability of unconsolidated textile sheets. The stamp forming of a cone-shaped part was modeled for comparison with the experiments. Results show that the simplified process modeling scheme has the potential to predict issues with wrinkling during die closure. Furthermore, the present work suggests that complex representations of the relatively small fiber direction strains may be unwarranted for this type of process modeling.

Nanosurface enhanced Raman scattering fluctuation dynamics

Here, we report our results on excitation intensity and nanoscale Ag cluster dependent spectral fluctuation dynamics of surface enhanced Raman scattering. We have studied single-Ag-cluster surface enhanced Raman scattering (SERS) intensity fluctuations under low molecule surface coverage of rhodamine 6G (R6G) and cytochrome c. By applying both experimental and theoretical approaches, we observed that spectral fluctuation phenomena are associated with SERS not only from single-molecule loaded nanoclusters but also from submonolayer molecule loaded nanoclusters. The nanoscale confinement of the local electric field enhancement under the laser excitation defines the SERS fluctuation. A new AFM-coupled two-channel photon time-stamping system, enabling in situ correlation of the topographic and spectroscopic information for single nanoparticle clusters, was used to record Raman intensity fluctuation trajectories at sub-μs resolution. Experimentally, we found that SERS fluctuation dynamics are highly inhomogeneous amongst nanocluster interstitial sites. Although the fluctuation above ~50 W/cm2 excitation is dominated by photoinduced processes, spontaneous fluctuation can be observed at lower excitation intensity. Although a single Raman-active molecule confined within the volume of an electric field excitation gives a significant Raman spectral fluctuation, observation of the fluctuation alone may not be sufficient in identifying a single-molecule origin of a Raman spectrum. The Raman signal comes predominately from the localized electric field enhancement at interstitial sites, occuring in a very small volume at nanoscale (capable of holding only one or a few molecules), as estimated from finite-element methods simulations of an electric field enhancement using a classical electrodynamics approach. Such a small number of molecules, which are presumably under discrete diffusion and exposed to interactions with a locally strong electric field, results in the observed Raman fluctuation. The fluctuation autocorrelation amplitude is proportional to the reverse number of molecules confined at the volume of the electric field enhancement.

FUEL ASSEMBLY SHAKER TEST SIMULATION

This report describes the modeling of a PWR fuel assembly under dynamic shock loading in support of the Sandia National Laboratories (SNL) shaker test campaign. The focus of the test campaign is on evaluating the response of used fuel to shock and vibration loads that a can occur during highway transport. Modeling began in 2012 using an LS-DYNA fuel assembly model that was first created for modeling impact scenarios. SNL’s proposed test scenario was simulated through analysis and the calculated results helped guide the instrumentation and other aspects of the testing. During FY 2013, the fuel assembly model was refined to better represent the test surrogate. Analysis of the proposed loads suggested the frequency band needed to be lowered to attempt to excite the lower natural frequencies of the fuel assembly. Despite SNL’s expansion of lower frequency components in their five shock realizations, pretest predictions suggested a very mild dynamic response to the test loading. After testing was completed, one specific shock case was modeled, using recorded accelerometer data to excite the model. Direct comparison of predicted strain in the cladding was made to the recorded strain gauge data. The magnitude of both sets of strain (calculated and recorded) are very low, compared to the expected yield strength of the Zircaloy-4 material. The model was accurate enough to predict that no yielding of the cladding was expected, but its precision at predicting micro strains is questionable. The SNL test data offers some opportunity for validation of the finite element model, but the specific loading conditions of the testing only excite the fuel assembly to respond in a limited manner. For example, the test accelerations were not strong enough to substantially drive the fuel assembly out of contact with the basket. Under this test scenario, the fuel assembly model does a reasonable job of approximating actual fuel assembly response, a claim that can be verified through direct comparison of model results to recorded test results. This does not offer validation for the fuel assembly model in all conceivable cases, such as high kinetic energy shock cases where the fuel assembly might lift off the basket floor to strike to basket ceiling. This type of nonlinear behavior was not witnessed in testing, so the model does not have test data to be validated against.a basis for validation in cases that substantially alter the fuel assembly response range. This leads to a gap in knowledge that is identified through this modeling study. The SNL shaker testing loaded a surrogate fuel assembly with a certain set of artificially-generated time histories. One thing all the shock cases had in common was an elimination of low frequency components, which reduces the rigid body dynamic response of the system. It is not known if the SNL test cases effectively bound all highway transportation scenarios, or if significantly greater rigid body motion than was tested is credible. This knowledge gap could be filled through modeling the vehicle dynamics of a used fuel conveyance, or by collecting acceleration time history data from an actual conveyance under highway conditions.

TN-68 Spent Fuel Transport Cask Analytical Evaluation for Drop Events

Abstract The US Nuclear Regulatory Commission (NRC) is responsible for licensing commercial spent nuclear fuel transported in casks certified by NRC under the Code of Federal Regulations (10 CFR), Title 10, Part 71. Both the International Atomic Energy Agency regulations for transporting radioactive materials, and 10 CFR 71·73 require casks to be evaluated for hypothetical accident conditions, which includes a 9 m (30 ft) drop impact event onto a flat, essentially unyielding, horizontal surface, in the most damaging orientation. This paper examines the behaviour of one of the NRC certified transportation casks, the TN-68, for drop impact events. The specific area examined is the behaviour of the bolted connections in the cask body and the closure lid, which are significantly loaded during the hypothetical drop impact event. Analytical work to evaluate the NRC certified TN-68 spent fuel transport cask for a 9 m (30 ft) drop impact event on a flat, unyielding, horizontal surface, was performed using the ANSYS and LS-DYNA finite element analysis codes. The models were sufficiently detailed, in the areas of bolt closure interfaces and containment boundaries, to evaluate the structural integrity of the bolted connections under 9 m (30 ft) free drop hypothetical accident conditions, as specified in 10 CFR 71·73. Evaluation of the cask for puncture, caused by a free drop through a distance of 1 m (40 in) onto a mild steel bar mounted on a flat, essentially unyielding, horizontal surface, required by 10 CFR 71·73, was not included in the current work. Based on the analyses performed to date, it is concluded that, even though brief separation of the flange and the lid surfaces may occur under some conditions, the seals would close at the end of the drop events, because the materials remain elastic during the duration of the event.

Closure Bolt Modeling for Seal Evaluation Under Extreme Thermal Loads

The US Nuclear Regulatory Commission (NRC) recently completed an evaluation of a used nuclear fuel transportation package subjected to loads associated with the MacArthur Maze fire and overpass collapse of 2007. This historical event is used as the basis of an extreme accident scenario to investigate the performance of the package system under loads that are beyond regulatory limits and to assess the potential risk to the public. The accident scenario was modeled in a number of physics regimes, including fire dynamics models, thermal models, structural impact models, and structural thermal expansion models. In this case the thermal expansion behavior of the bolted closure was a key component of the leak rate calculations and offered a tough analytical challenge, which was ultimately resolved using a detailed nonlinear finite element model of the bolt threads with thread inserts discretely modeled. This paper describes the analytical steps that were taken, starting with classic bolt stress calculations and ending with sophisticated finite element analysis, while also putting the analysis into context of the larger analytical effort and the assessment of used nuclear fuel transportation package safety that is critical to the mission of the US NRC.Copyright

SNF Transportation Package Response to MacArthur Maze Fire Scenario: Leak Rate Determination After Seal Failure

Extensive and detailed modeling of the possible effect of the MacArthur Maze fire scenario on an over-the-road spent nuclear fuel transportation package has shown that the potential consequences could include release of radioactive material due to failure of the package seals. Structural and thermal modeling of the performance of the lid closure and closure bolts show that the lid closure bolts would maintain positive clamping force throughout the fire transient scenario, such that the total release possible, even with conservative and bounding modeling assumptions, is two to three orders of magnitude below the regulatory limit for accident conditions. Typical leak rate models, such as the ANSI standard ANSI N14.5, are based on the expectation of intact seals for the package. Very little analytical work has been done to investigate leak rates from failed seals, since seal failure is, by definition, unacceptable performance in real-world applications. In order to evaluate the potential release from the SNF package subjected to the conditions of this fire scenario, an analytical modeling approach was developed to determine bounding leak rate estimates through the interface of the package closure lid and body flange. This modeling approach postulates complete loss of the O-ring seal material, and assumes only metal-to-metal contact, maintained by the clamping force of the closure bolts, as it varies due to differential thermal expansion and changing internal package pressure during the transient. This paper describes the analytical approach used to perform the leak rate modeling for the SNF package, and presents results for the limiting design basis loading of the package.Copyright

Package Impact Models as a Precursor to Cladding Analysis

The evaluation of spent nuclear fuel storage casks and transportation packages under impact loading is an important safety topic that is reviewed as part of cask and package certification by the United States Nuclear Regulatory Commission. Explicit dynamic finite element models of full systems are increasingly common in industry for determining structural integrity during hypothetical drop accidents. Full cask and package model results are also used as the loading basis for single fuel pin impact models, which evaluate the response of fuel cladding under drop conditions. In this paper, a simplified package system is evaluated to illustrate several important structural dynamic phenomena, including the effect of gaps between components, the difference in local response at various points on a package during impact, and the effect of modeling various simplified representations of the basket and fuel assemblies. This paper focuses on the package impact analysis, and how loading conditions for a subsequent fuel assembly or fuel cladding analysis can be extracted.

Desensitization of Camera-Aided Manipulation to Target Specification Errors

Applications of vision-based remotely operated robotic systems range from planetary exploration to hazardous waste remediation. For space applications, where communication time lags are large, the target selection and robot positioning tasks may be performed sequentially, differing from conventional telerobotic maneuvers. For these point-and-move systems, the desired target must be defined in the image plane of the cameras either by an operator or through image processing software. Ambiguity of the target specification will naturally lead to end-effector positioning errors. In this paper, the target specification error covariance is shown to transform linearly to the end-effector positioning error. In addition, a methodology for optimal estimation of camera-view parameters of a vision-based robotic system based on target specification errors is presented. The proposed strategy is based on minimizing the end-effector error covariance matrix. Experimental results are presented demonstrating an increase in end-effector positioning, compared to traditional view parameter estimation by up to 32.