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All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Configurational entropy of hydrogen-disordered ice polymorphs

The configurational entropy of several H-disordered ice polymorphs is calculated by means of a thermodynamic integration along a path between a totally H-disordered state and one fulfilling the Bernal-Fowler ice rules. A Monte Carlo procedure based on a simple energy model is used, so that the employed thermodynamic path drives the system from high temperatures to the low-temperature limit. This method turns out to be precise enough to give reliable values for the configurational entropy s{sub th} of different ice phases in the thermodynamic limit (number of molecules N → ∞). The precision of the method is checked for the ice model on a two-dimensional square lattice. Results for the configurational entropy are given for H-disordered arrangements on several polymorphs, including ices Ih, Ic, II, III, IV, V, VI, and XII. The highest and lowest entropy values correspond to ices VI and XII, respectively, with a difference of 3.3% between them. The dependence of the entropy on the ice structures has been rationalized by comparing it with structural parameters of the various polymorphs, such as the mean ring size. A particularly good correlation has been found between the configurational entropy and the connective constant derived from self-avoiding walks on the ice networks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Quantitative Imaging with a Mobile Phone Microscope

Use of optical imaging for medical and scientific applications requires accurate quantification of features such as object size, color, and brightness. High pixel density cameras available on modern mobile phones have made photography simple and convenient for consumer applications; however, the camera hardware and software that enables this simplicity can present a barrier to accurate quantification of image data. This issue is exacerbated by automated settings, proprietary image processing algorithms, rapid phone evolution, and the diversity of manufacturers. If mobile phone cameras are to live up to their potential to increase access to healthcare in low-resource settings, limitations of mobile phone–based imaging must be fully understood and addressed with procedures that minimize their effects on image quantification. Here we focus on microscopic optical imaging using a custom mobile phone microscope that is compatible with phones from multiple manufacturers. We demonstrate that quantitative microscopy with micron-scale spatial resolution can be carried out with multiple phones and that image linearity, distortion, and color can be corrected as needed. Using all versions of the iPhone and a selection of Android phones released between 2007 and 2012, we show that phones with greater than 5 MP are capable of nearly diffraction-limited resolution over a broad range of magnifications, including those relevant for single cell imaging. We find that automatic focus, exposure, and color gain standard on mobile phones can degrade image resolution and reduce accuracy of color capture if uncorrected, and we devise procedures to avoid these barriers to quantitative imaging. By accommodating the differences between mobile phone cameras and the scientific cameras, mobile phone microscopes can be reliably used to increase access to quantitative imaging for a variety of medical and scientific applications.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

The CanBikeCO Mini Pilot: Procedure and Preliminary Results

In fall 2020, the Colorado Energy Office, as part of the State of Colorado's "Can Do Colorado" initiative, initiated a project aimed at encouraging energy-efficient transportation during the COVID-19 pandemic. The initial mini-pilot provided e-bikes to 13 low-income households under an individual ownership model. This report assesses the impact of providing this additional mobility option on the travel behavior of participants. It also outlines the lessons learned from deploying a continuous monitoring platform to track the travel behavior. These lessons will influence the evaluation component for the full pilot, which will cover multiple geographic regions, start in summer 2021, and run for 2 years. The continuous data collection was enabled by a customized version of the open-source e-mission platform, called CanBikeCO, configured with a behavioral gamification feature. The Colorado Energy Office used this system to collect a unique data set consisting of 3 months of partially automated travel diaries, combining sensed and surveyed data and linked with demographic information, from 12 participants. The data collection process worked well overall: users generally liked the app, appreciated the game, and did not complain about battery life. The long tracking period introduced behavioral challenges in user engagement, which we plan to address using repeated patterns and automated status checks for the full pilot. The analysis results, based on the subset of trips with user-reported labels (68%), indicate that the e-bike was the dominant commute mode share (31%), in sharp contrast to the census bicycle commute mode share (<1%). E-bike trips primarily replaced single-occupancy vehicle (SOV) trips (28%), followed closely by walking (24%) and regular bike (20%). The non-motorized mode replacement corresponds to lower travel time and increased productivity enabled by the program. The emissions impact analysis of the program, computed using trip-level energy intensity factors, indicates savings of 1,367 lbs. of CO2. Although the results are strongly positive, the narrow demographic profile of study participants, their limited mobility alternatives, and nonuniform labeling indicate caution in broader interpretation. These preliminary results do suggest that such programs, supported by real-time education and support from program managers, can simultaneously meet equity and sustainability goals. The planned full pilot, addressing the data collection challenges and broadening the geographic scope, will provide additional insights into the generality of this approach.

ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2014

SU-E-J-123: Targeting Accuracy of Image-Guided Radiosurgery for Intracranial Lesions

Purpose: To evaluate the setup accuracies of image-guided intracranial radiosurgery across several different linear accelerator platforms. Methods: A CT scan with a slice thickness of 1.0 mm was acquired of a Rando head phantom (The Phantom Laboratory) in a U-frame mask (BrainLAB AG). The phantom had three embedded BBs, simulating a central, left, and anterior lesion. The phantom was setup with each BB placed at the radiation isocenter under image guidance. Four different setup procedures were investigated: (1) NTX-ExacTrac: 6 degree-of-freedom (6D) correction on a Novalis Tx (BrainLAB AG) with ExacTrac localization (BrainLAB AG); (2) NTX-CBCT: 4D correction on the Novalis Tx with cone-beam computed tomography (CBCT); (3) TrueBeam-CBCT: 4D correction on a TrueBeam (Varian) with CBCT; (4) Edge-CBCT: 6D correction on an Edge (Varian) with CBCT. The experiment was repeated 5 times with different initial setup error at each BB location on each platform, and the mean (μ) and one standard deviation (σ) of the residual error was compared.The congruence between radiation and imaging isocenters on each platform was evaluated by acquiring Winston Lutz (WL) images of a WL jig followed by imaging using ExacTrac or CBCT. The difference in coordinates of the jig relative to radiation and imaging isocenters was then recorded. Results: Averaged over all three BB locations, the residual vector setup errors (μ±σ) of the phantom in mm were 0.6±0.2, 1.0±0.5, 0.2±0.1, and 0.3±0.1 on NTX-ExacTrac, NTX-CBCT, TrueBeam-CBCT, and Edge-CBCT, with their ranges in mm being 0.4∼1.1, 0.4∼1.9, 0.1∼0.5, and 0.2∼0.6, respectively. And imaging isocenter was found stable relative to radiation isocenter, with the congruence to radiation isocenter in mm being 0.6±0.1, 0.7±0.1, 0.3±0.1, 0.2±0.1, respectively, on the four systems in the same order. Conclusion: Millimeter accuracy can be achieved with image-guided radiosurgery for intracranial lesions based on this set of experiments.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

SU-E-J-16: Automatic Image Contrast Enhancement Based On Automatic Parameter Optimization for Radiation Therapy Setup Verification

Purpose: In RT patient setup 2D images, tissues often cannot be seen well due to the lack of image contrast. Contrast enhancement features provided by image reviewing software, e.g. Mosaiq and ARIA, require manual selection of the image processing filters and parameters thus inefficient and cannot be automated. In this work, we developed a novel method to automatically enhance the 2D RT image contrast to allow automatic verification of patient daily setups as a prerequisite step of automatic patient safety assurance. Methods: The new method is based on contrast limited adaptive histogram equalization (CLAHE) and high-pass filtering algorithms. The most important innovation is to automatically select the optimal parameters by optimizing the image contrast. The image processing procedure includes the following steps: 1) background and noise removal, 2) hi-pass filtering by subtracting the Gaussian smoothed Result, and 3) histogram equalization using CLAHE algorithm. Three parameters were determined through an iterative optimization which was based on the interior-point constrained optimization algorithm: the Gaussian smoothing weighting factor, the CLAHE algorithm block size and clip limiting parameters. The goal of the optimization is to maximize the entropy of the processed Result. Results: A total 42 RT images were processed. The results were visually evaluated by RT physicians and physicists. About 48% of the images processed by the new method were ranked as excellent. In comparison, only 29% and 18% of the images processed by the basic CLAHE algorithm and by the basic window level adjustment process, were ranked as excellent. Conclusion: This new image contrast enhancement method is robust and automatic, and is able to significantly outperform the basic CLAHE algorithm and the manual window-level adjustment process that are currently used in clinical 2D image review software tools.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-100: Designing a QA Tool for Enhance Dynamic Wedges Based On Dynalog Files

Purpose: A robust quality assurance (QA) program for computer controlled enhanced dynamic wedge (EDW) has been designed and tested. Calculations to perform such QA test is based upon the EDW dynamic log files generated during dose delivery. Methods: Varian record and verify system generates dynamic log (dynalog) files during dynamic dose delivery. The system generated dynalog files contain information such as date and time of treatment, energy, monitor units, wedge orientation, and type of treatment. It also contains the expected calculated segmented treatment tables (STT) and the actual delivered STT for the treatment delivery as a verification record. These files can be used to assess the integrity and precision of the treatment plan delivery. The plans were delivered with a 6 MV beam from a Varian linear accelerator. For available EDW angles (10°, 15°, 20°, 25°, 30°, 45°, and 60°) Varian STT values were used to manually calculate monitor units for each segment. It can also be used to calculate the EDW factors. Independent verification of fractional MUs per segment was performed against those generated from dynalog files. The EDW factors used to calculate MUs in TPS were dosimetrically verified in solid water phantom with semiflex chamber on central axis. Results: EDW factors were generated from the STT provided by Varian and verified against practical measurements. The measurements were in agreement of the order of 1 % to the calculated EDW data. Variation between the MUs per segment obtained from dynalog files and those manually calculated was found to be less than 2%. Conclusion: An efficient and easy tool to perform routine QA procedure of EDW is suggested. The method can be easily implemented in any institution without a need for expensive QA equipment. An error of the order of ≥2% can be easily detected.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

File-Based One-Way BISON Coupling Through VERA: User's Manual

Activities to incorporate fuel performance capabilities into the Virtual Environment for Reactor Applications (VERA) are receiving increasing attention [1–6]. The multiphysics emphasis is expanding as the neutronics (MPACT) and thermal-hydraulics (CTF) packages are becoming more mature. Capturing the finer details of fuel phenomena (swelling, densification, relocation, gap closure, etc.) is the natural next step in the VERA development process since these phenomena are currently not directly taken into account. While several codes could be used to accomplish this, the BISON fuel performance code [8,9] being developed by the Idaho National Laboratory (INL) is the focus of ongoing work in the Consortium for Advanced Simulation of Light Water Reactors (CASL). Built on INL’s MOOSE framework [10], BISON uses the finite element method for geometric representation and a Jacobian-free Newton-Krylov (JFNK) scheme to solve systems of partial differential equations for various fuel characteristic relationships. There are several modes of operation in BISON, but, this work uses a 2D azimuthally symmetric (R-Z) smeared-pellet model. This manual is intended to cover (1) the procedure pertaining to the standalone BISON one-way coupling from VERA and (2) the procedure to generate BISON fuel temperature tables that VERA can use.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2012

Final Technical Report "Multiscale Simulation Algorithms for Biochemical Systems"

Biochemical systems are inherently multiscale and stochastic. In microscopic systems formed by living cells, the small numbers of reactant molecules can result in dynamical behavior that is discrete and stochastic rather than continuous and deterministic. An analysis tool that respects these dynamical characteristics is the stochastic simulation algorithm (SSA, Gillespie, 1976), a numerical simulation procedure that is essentially exact for chemical systems that are spatially homogeneous or well stirred. Despite recent improvements, as a procedure that simulates every reaction event, the SSA is necessarily inefficient for most realistic problems. There are two main reasons for this, both arising from the multiscale nature of the underlying problem: (1) stiffness, i.e. the presence of multiple timescales, the fastest of which are stable; and (2) the need to include in the simulation both species that are present in relatively small quantities and should be modeled by a discrete stochastic process, and species that are present in larger quantities and are more efficiently modeled by a deterministic differential equation (or at some scale in between). This project has focused on the development of fast and adaptive algorithms, and the fun- damental theory upon which they must be based, for the multiscale simulation of biochemical systems. Areas addressed by this project include: (1) Theoretical and practical foundations for ac- celerated discrete stochastic simulation (tau-leaping); (2) Dealing with stiffness (fast reactions) in an efficient and well-justified manner in discrete stochastic simulation; (3) Development of adaptive multiscale algorithms for spatially homogeneous discrete stochastic simulation; (4) Development of high-performance SSA algorithms.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Computerized procedure systems: procedure edition and maintenance challenges - 232

Very few nuclear power plants are using computerized procedures to guide the control room operation. A CPS implementation consists of two processes: digitalization and computerization. The former deals with the transformation of paper-based procedure into a digital data; the latter is referred to as the addition to that data of extra information that is meaningful for decision-making. This information may include real-time data (plant parameter values and binary process values to indicate equipment states), provide access to trends and historical data, etc. In order to be efficient and to optimize the digitalization and computerization processes, these set of aids should be implemented at the same time as operating procedures are digitalized There are references of plants having successfully implemented Computerized Procedures Systems (CPS) for emergency procedures, but when questioned about normal or abnormal operating procedures, operators and plant management seem reluctant to take that step. Given that a CPS is meant, by design concept, to increase operation crew efficiency by facilitating the procedures execution and reducing human error, why are we reluctant to enjoy CPS benefits in the most common plant status (i.e. normal operation)? Although there are many answers to this question, one is shared by most of the users: CPSs are not designed for editing and maintaining procedures easily and reliably. Normal operating procedures, in opposition to the emergency procedures, are often reviewed. Nowadays, these edition activities are performed easily with a word processor software and using paper, but what is required when dealing with a CPS? (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2019

A Hermitian symmetric space Fokas–Lenells equation: Solitons, breathers, rogue waves

Highlights: • We study a Hermitian symmetric space Fokas–Lenells equation. • We obtain multi-soliton, kink–breather and rogue wave solutions for this equation. • We analyse the dynamical behaviour of these exact solutions. - Abstract: Based on the zero-curvature representation, we propose a Hermitian symmetric space Fokas–Lenells equation associated with a 4 × 4 matrix spectral problem. Resorting to the gauge transformation between spectral problems, we find a restrictive condition of the spectral functions that can ensure the symmetry of the new potential matrix, from which n-fold classical Darboux transformations and N-fold generalized Darboux transformations of this equation are constructed with the help of the limit technique and an iterative procedure. Utilizing the Darboux transformations and Mathematica software, we obtain various solutions for the Hermitian symmetric space Fokas–Lenells equation, including the multi-soliton solution, kink–breather solution, eye-shaped rogue wave solution, one-peaky shaped rogue wave solution, and dark two-peaky shaped rogue wave solution. By varying the values of the free parameters, we obtain different types of spatial–temporal distribution structures for the solutions, including the fundamental, line and triangular patterns. Furthermore, the dynamical behaviour of these solutions, including the fusion and fission processes of rogue waves, is analysed in detail.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Minimising the error in eigenvalue calculations involving the Boltzmann transport equation using goal-based adaptivity on unstructured meshes

This article presents a method for goal-based anisotropic adaptive methods for the finite element method applied to the Boltzmann transport equation. The neutron multiplication factor, k{sub eff}, is used as the goal of the adaptive procedure. The anisotropic adaptive algorithm requires error measures for k{sub eff} with directional dependence. General error estimators are derived for any given functional of the flux and applied to k{sub eff} to acquire the driving force for the adaptive procedure. The error estimators require the solution of an appropriately formed dual equation. Forward and dual error indicators are calculated by weighting the Hessian of each solution with the dual and forward residual respectively. The Hessian is used as an approximation of the interpolation error in the solution which gives rise to the directional dependence. The two indicators are combined to form a single error metric that is used to adapt the finite element mesh. The residual is approximated using a novel technique arising from the sub-grid scale finite element discretisation. Two adaptive routes are demonstrated: (i) a single mesh is used to solve all energy groups, and (ii) a different mesh is used to solve each energy group. The second method aims to capture the benefit from representing the flux from each energy group on a specifically optimised mesh. The k{sub eff} goal-based adaptive method was applied to three examples which illustrate the superior accuracy in criticality problems that can be obtained.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Debunking common myths in coastal circulation modeling

Despite tremendous progress in algorithm development, computational efficiency and transition into operations over the past two decades, coastal modeling still lacks scientific rigor due to proliferation of many ‘gray’ areas related to various modeling choices made by modelers. Here, in this paper, we propose some guiding principles for the modeling community to improve performance, and we also debunk commonly held myths that make the coastal modeling lack rigor. Using our own experience in developing seamless cross-scale unstructured-grid based models for the past two decades, we describe in unprecedented detail the end-to-end modeling process (i.e., from digital elevation models (DEMs) to mesh generation to post analysis), and demonstrate that defensible modeling is within reach for any end user by following three guiding principles: (1) Bathymetry is a first order forcing in coastal domains and thus should be respected in all aspects of modeling; (2) Oceanographic processes are driven across multiple spatial scales and so models should enable appropriate resolution as needed; and (3) Model assessment should focus on physical processes. Through qualitative and quantitative model assessments, we demonstrate the fundamental role played by bathymetry/topography as embedded in DEMs in making the results defensible, which is unfortunately glossed over in many modeling studies. Focusing on process-based assessment simplifies the calibration process. A major conclusion of this work is that model developers and operators should maximize the scientific rigor for in silico oceanography by avoiding some common pitfalls that rely on error compensation at the expense of representation of physical system processes. We present some best practice procedures for defensive and trustworthy numerical modeling.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Planck 2013 results. V. LFI calibration

We discuss the methods employed to photometrically calibrate the data acquired by the Low Frequency Instrument on Planck. Our calibration is based on a combination of the orbital dipole plus the solar dipole, caused respectively by the motion of the Planck spacecraft with respect to the Sun and by motion of the solar system with respect to the cosmic microwave background (CMB) rest frame. The latter provides a signal of a few mK with the same spectrum as the CMB anisotropies and is visible throughout the mission. In this data releasewe rely on the characterization of the solar dipole as measured by WMAP. We also present preliminary results (at 44 GHz only) on the study of the Orbital Dipole, which agree with the WMAP value of the solar system speed within our uncertainties. We compute the calibration constant for each radiometer roughly once per hour, in order to keep track of changes in the detectors’ gain. Since non-idealities in the optical response of the beams proved to be important, we implemented a fast convolution algorithm which considers the full beam response in estimating the signal generated by the dipole. Moreover, in order to further reduce the impact of residual systematics due to sidelobes, we estimated time variations in the calibration constant of the 30 GHz radiometers (the ones with the largest sidelobes) using the signal of an internal reference load at 4 K instead of the CMB dipole. We have estimated the accuracy of the LFI calibration following two strategies: (1) we have run a set of simulations to assess the impact of statistical errors and systematic effects in the instrument and in the calibration procedure; and (2) we have performed a number of internal consistency checks on the data and on the brightness temperature of Jupiter. Errors in the calibration of this Planck/LFI data release are expected to be about 0.6% at 44 and 70 GHz, and 0.8% at 30 GHz. Both these preliminary results at low and high ℓ are consistent with WMAP results within uncertainties and comparison of power spectra indicates good consistency in the absolute calibration with HFI (0.3%) and a 1.4σ discrepancy with WMAP (0.9%).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Predicting large-scale pool fire dynamics using an unsteady flamelet- and large-eddy simulation-based model suite

A low-Mach, unstructured, large-eddy-simulation-based, unsteady flamelet approach with a generalized heat loss combustion methodology (including soot generation and consumption mechanisms) is deployed to support a large-scale, quiescent, 5-m JP-8 pool fire validation study. The quiescent pool fire validation study deploys solution sensitivity procedures, i.e., the effect of mesh and time step refinement on capturing key fire dynamics such as fingering and puffing, as mesh resolutions approach O(1) cm. A novel design-order, discrete-ordinate-method discretization methodology is established by use of an analytical thermal/participating media radiation solution on both low-order hexahedral and tetrahedral mesh topologies in addition to quadratic hexahedral elements. Here, the coupling between heat losses and the flamelet thermochemical state is achieved by augmenting the unsteady flamelet equation set with a heat loss source term. Soot and radiation source terms are determined using flamelet approaches for the full range of heat losses experienced in fire applications including radiative extinction. The proposed modeling and simulation paradigm are validated using pool surface radiative heat flux, maximum centerline temperature location, and puffing frequency data, all of which are predicted within 10% accuracy. Simulations demonstrate that under-resolved meshes predict an overly conservative radiative heat flux magnitude with improved comparisons as compared to a previously deployed hybrid Reynolds-averaged Navier–Stokes/eddy dissipation concept-based methodology.

42 ENGINEERING↗
DOE OSTI2014

Poster — Thur Eve — 06: Dose assessment of cone beam CT imaging protocols as part of SPECT/CT examinations

Purpose: To assess radiation dose from the cone beam CT (CBCT) component of SPECT/CT studies and to compare with other CT examinations performed in our institution. Methods: We used an anthropomorphic chest phantom and the 6 cc ion chamber to measure entrance breast dose for several CBCT and diagnostic CT acquisition protocols. The CBCT effective dose was calculated with ImPACT software; the CT effective dose was evaluated from the DLP value and conversion factor, dependent on the anatomic region. The RADAR medical procedure radiation dose calculator was used to assess the nuclear medicine component of exam dose. Results: The entrance dose to the breast measured with the anthropomorphic phantom was 0.48 mGy and 9.41 mGy for cardiac and chest CBCT scans; and 4.59 mGy for diagnostic thoracic CT. The effective doses were 0.2 mSv, 3.2 mSv and 2.8 mSv respectively. For a small patient represented by the anthropomorphic phantom, the dose from the diagnostic CT was lower than from the CBCT scan, as a result of the exposure reduction options available on modern CT scanners. The CBCT protocols used the same fixed scanning techniques. The diagnostic CT dose based on the patient data was 35% higher than the phantom dose. For most SPECT/CT studies the dose from the CBCT component was comparable with the dose from the radiopharmaceutical. Conclusions: The patient radiation dose from the cone beam CT scan can be higher than that from a diagnostic CT and should be taken into consideration in evaluating total SPECT/CT patient dose.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Multiscale Simulation Framework for Coupled Fluid Flow and Mechanical Deformation

Our work in this project is aimed at making fundamental advances in multiscale methods for flow and transport in highly heterogeneous porous media. The main thrust of this research is to develop a systematic multiscale analysis and efficient coarse-scale models that can capture global effects and extend existing multiscale approaches to problems with additional physics and uncertainties. A key emphasis is on problems without an apparent scale separation. Multiscale solution methods are currently under active investigation for the simulation of subsurface flow in heterogeneous formations. These procedures capture the effects of fine-scale permeability variations through the calculation of specialized coarse-scale basis functions. Most of the multiscale techniques presented to date employ localization approximations in the calculation of these basis functions. For some highly correlated (e.g., channelized) formations, however, global effects are important and these may need to be incorporated into the multiscale basis functions. Other challenging issues facing multiscale simulations are the extension of existing multiscale techniques to problems with additional physics, such as compressibility, capillary effects, etc. In our project, we explore the improvement of multiscale methods through the incorporation of additional (single-phase flow) information and the development of a general multiscale framework for flows in the presence of uncertainties, compressible flow and heterogeneous transport, and geomechanics. We have considered (1) adaptive local-global multiscale methods, (2) multiscale methods for the transport equation, (3) operator-based multiscale methods and solvers, (4) multiscale methods in the presence of uncertainties and applications, (5) multiscale finite element methods for high contrast porous media and their generalizations, and (6) multiscale methods for geomechanics.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Improved Modelling for the Assembly Discontinuity Factors in the APEC Method

Modern reactor analysis of light water reactor depends largely on a two-step procedure based on the simplified equivalence theory (SET). Consequently, the resulting homogenized two-group cross-section (XS) and associated discontinuity factor (DF) are subject to noticeable, intrinsic uncertainties. In our previous study, we introduced the albedo-corrected parameterized equivalence constants (APEC) method, which is a new leakage correction method applicable to the fuel assembly homogenized two-group XS of the standard two-step procedure. In the APEC method, fuel assembly two-group XS is expressed as a simple polynomial function of assembly-wise current-to-flux ratio (CFR), and it was demonstrated that two-group XSs can be well corrected during a nodal calculation and the nodal accuracy is improved a lot. However, since the conventional assembly discontinuity factor (ADF) is still used in the current APEC method, a small but non-negligible error is unavoidable. Therefore, it is necessary to include improved DF model in the APEC method for a higher accuracy. The functionalized discontinuity factor (FDF) using the definition of CFR was investigated by authors before the development of the APEC method, where it was motivated by the boundary perturbation theory by F. Rahnema. However, in our previous study on FDF, lattice calculations were performed only with one-dimensional two-group diffusion equation and could not be applied to actual core analysis. In this paper, feasibility study of DF functionalization is performed based on a 2-D method of characteristics (MOC) lattice code, DeCART2D.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2012

The Role of Computed Tomography in the Management of the Neck After Chemoradiotherapy in Patients With Head-and-Neck Cancer

Purpose: The aim of this study was to describe the outcome in patients with head-and neck-squamous cell carcinoma (HNSCC) followed up without neck dissection (ND) after concomitant chemoradiotherapy (CRT) based on computed tomography (CT) response. The second objective was to establish CT characteristics that can predict which patients can safely avoid ND. Methods and Materials: Between 1998 and 2007, 369 patients with node-positive HNSCC were treated with primary CRT at our institution. After a clinical and a radiologic evaluation based on CT done 6 to 8 weeks after CRT, patients were labeled with a complete neck response (CR) or with a partial neck response (PR). Results: The median follow-up was 44 months. The number of patients presenting with N3, N2, or N1 disease were 54 (15%), 268 (72%), and 47 (13%), respectively. After CRT, 263 (71%) patients reached a CR, and 253 of them did not undergo ND. Ninety-six patients reached a PR and underwent ND. Of those, 34 (35%) had residual disease on pathologic evaluation. A regression of the diameter of {>=}80% and a residual largest diameter of 15 mm of nodes had negative pathologic predictive values of 100% and 86%, respectively. The 3-year regional control and survival rates were not different between patients with CR who had no ND and patients with PR followed by ND. Conclusion: Node-positive patients presenting a CR as determined by CT evaluation 6 to 8 weeks after CRT had a low rate of regional recurrence without ND. This study also suggests that lymph node residual size and percentage of regression on CT after CRT may be useful criteria to guide clinical decisions regarding neck surgery. Those results can help diminish the number of ND procedures with negative results and their associated surgical complications.

62 RADIOLOGY AND NUCLEAR MEDICINE↗