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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Electron Temperature Fluctuation Measurements and Transport Model Validation at Alcator C-Mod

The tokamak is a type of toroidal device used to confine a fusion plasma using large magnetic fields. Tokamaks and stellarators the leading devices for confining plasmas for fusion, and the capability to predict performance in these magnetically confined plasmas is essential for developing a sustainable fusion energy source. The magnetic configuration of tokamaks and stellarators does not exist in Nature, yet, the fundamental processes governing transport in fusion plasmas are universal – turbulence and instabilities, driven by inhomogeneity and asymmetry in the plasma, conspire to transport heat and particles across magnetic field lines and can play critical roles in impurity confinement and generation of intrinsic rotation. Turbulence exists in all plasmas, and in neutral fluids as well. The study of turbulence is essential to developing a fundamental understanding of the nature of the fourth state of matter, plasmas. Experimental studies of turbulence in tokamaks date back to early scattering observations from the late 1970s. Since that time, great advances in turbulence diagnostics have been made, all of which have significantly enhanced our knowledge and understanding of turbulence in tokamaks. Through comparisons with advanced gyrokinetic theory and turbulent-transport models a great deal of evidence exists to implicate turbulent-driven transport as an important mechanism determining transport in all channels: heat, particle and momentum However, prediction and control of turbulent-driven transport remains elusive. Key to development of predictive transport models for magnetically confined fusion plasmas is validation of the nonlinear gyrokinetic transport model, which describes transport due to turbulence. Validation of gyrokinetic codes must include detailed and quantitative comparisons with measured turbulence characteristics, in addition to comparisons with inferred transport levels and equilibrium profiles. For this reason, advanced plasma diagnostics for studying core turbulence are needed in order to assess the accuracy of gyrokinetic models for turbulent-driven particle, heat and momentum transport. New core turbulence diagnostics at the world-class tokamaks Alcator C-Mod at MIT and ASDEX Upgrade at the Max Planck Institute for Plasma Physics have been designed, developed, and operated over the course of this project. These new instruments are capable of measuring electron temperature fluctuations and the phase angle between density and temperature fluctuations locally and quantitatively. These new data sets from Alcator C-Mod and ASDEX Upgrade are being used to fill key gaps in our understanding of turbulent transport in tokamaks. In particular, this project has results in new results on the topics of the Transport Shortfall, the role of ETG turbulence in tokamak plasmas, profile stiffness, the LOC/SOC transition, and intrinsic rotation reversals. These data are used in a rigorous process of “Transport model validation”, and this group is a world-leader on using turbulence models to design new hardware and new experiments at tokamaks. A correlation electron cyclotron emission (CECE) diagnostic is an instrument used to measure micro-scale fluctuations (mm-scale, compared to the machine size of meters) of electron temperature in magnetically confined fusion plasmas, such as those in tokamaks and stellarators. These micro-scale fluctuations are associated with drift-wave type turbulence, which leads to enhanced cooling and mixing of particles in fusion plasmas and limits achieving the required temperatures and densities for self-sustained fusion reactions. A CECE system can also be coupled with a reflectometer system that measured micro-scale density fluctuations, and from these simultaneous measurements, one can extract the phase between the density (n) and temperature (T) fluctuations, creating an nT phase diagnostic. Measurements of the fluctuations and the phase angle between them are extremely useful for testing and validating predictive models for the transport of heat and particles in fusion plasmas due to turbulence. Once validated, the models are used to predict performance in ITER and other burning plasmas, such as the MIT ARC design. Most recently, data from the newly developed, so-called “CECE diagnostic” [Cima 1995, White 2008] and “nT phase angle measurements” [Haese 1999, White 2010] ]will be combined with data from density fluctuation diagnostics at ASDEX Upgrade to support a long-term program of physics research in turbulence and transport that will allow for more stringent testing and validation of gyrokinetic turbulent-transport codes. This work directly impacts the development of predictive transport models in the U.S. FES program, such as TGLF, developed by General Atomics, which are used to predict performance in ITER and other burning plasma devices as part of advancing the development of fusion energy sciences.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Investigating resource-efficient neutron/gamma classification ML models targeting eFPGAs

There has been considerable interest and resulting progress in implementing machine learning (ML) models in hardware over the last several years from the particle and nuclear physics communities. A big driver has been the release of the Python package, hls4ml, which has enabled porting models specified and trained using Python ML libraries to register transfer level (RTL) code. So far, the primary end targets have been commercial field-programmable gate arrays (FPGAs) or synthesized custom blocks on application specific integrated circuits (ASICs). However, recent developments in open-source embedded FPGA (eFPGA) frameworks now provide an alternate, more flexible pathway for implementing ML models in hardware. These customized eFPGA fabrics can be integrated as part of an overall chip design. In general, the decision between a fully custom, eFPGA, or commercial FPGA ML implementation will depend on the details of the end-use application. In this work, we explored the parameter space for eFPGA implementations of fully-connected neural network (fcNN) and boosted decision tree (BDT) models using the task of neutron/gamma classification with a specific focus on resource efficiency. We used data collected using an AmBe sealed source incident on Stilbene, which was optically coupled to an OnSemi J-series silicon photomultiplier (SiPM) to generate training and test data for this study. We investigated relevant input features and the effects of bit-resolution and sampling rate as well as trade-offs in hyperparameters for both ML architectures while tracking total resource usage. The performance metric used to track model performance was the calculated neutron efficiency at a gamma leakage of 10 -3 . The results of the study will be used to aid the specification of an eFPGA fabric, which will be integrated as part of a test chip.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

A Roadmap for a Lightning Modeling Grand Challenge

This document is a roadmap for building an interconnected model of the physical processes that produce a lightning discharge, and its observable optical and radio signals. We call this a Lightning Modeling Grand Challenge, recognizing that significant effort and coordination of human and financial resources is required to realize the capability. The roadmap serves to outline the coordination of resources necessary to enable stitching together existing knowledge and model components to make a lightning prediction, and to test these predictions with observations. Such a capability does not currently exist. The roadmap is motivated not only by a spirit of scientific inquiry, but by practical challenges faced by US Federal and societal stakeholders. Advancements in lightning observations have outpaced our tests of integrated understanding, leaving many stakeholders unsure how to design their missions to properly detect and discriminate lightning, and unsure how to apply the sometimes-disagreeing lightning signals from diverse instruments. The time is right to connect existing theories and models to support stakeholders in understanding the signals they observe, for needs as diverse as climate monitoring, national security, weather forecasting, public safety, and protection of natural and built environments. The roadmap’s two main technical sections describe the components of a linked physical model, followed by a description of models of lightning signals and sensors that are driven by outputs from the physical model. The goal is to predict the time-varying physical properties of lightning that are self-consistent with the thunderstorm’s structure and dynamics. These lightning signals then propagate through the storm, with realistic dispersion and attenuation, to receivers on the ground or in space. At a high level, the model begins with weather (cloud) model output, including explicit prediction of the electrification of cloud particles. The cloud’s electrical structure drives a model of lightning physics, from initiation, through channel development, and discharges along those channels. Key lightning parameters, such as the temperature and currents in the channel, and their space and time distribution, are then used to produce optical and electromagnetic signal sources that propagate to modeled receivers. This architecture therefore generates a dataset suitable for comparison to existing and envisioned observing systems. The need for additional measurements and field campaigns to support model development is described. In each model sub-component, inputs, outputs, uncertainties, evaluation methods, and next steps are summarized, interleaved with references to the scientific literature. Identifying boundaries between the model sub-components aids in segmenting an integrated, complex model into practical work packages and system sub-components, allowing a diverse team to contribute and maintain the system. We estimate that at least five years of effort and a $\$$10M initial investment is necessary to make a significant step forward. Mechanisms to facilitate community coordination, including annual workshops and open-source code repositories, are described.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

SU-E-T-150: Brachytherapy QA Employing a High Resolution Liquid Filled Ionisation Chamber Array: Initial Experience and Limitations

Purpose: Verifying a complex 3D brachytherapy dose distribution by measurement is non-trivial. Ideally a photon detector array should be independent of energy and angle, have high spatial resolution and be robust for routine clinical use. Methods: An iridium-192 source was used. A PMMA jig was constructed comprising an outer slab and a central insert with eight milled channels for 1.33mm (outer diameter) steel needles, see figure. All calculations were performed using an empty CT study reconstructing eight virtual needles (QA-CT), using the v2 source model (Elekta AG, Sweden). A high resolution liquid filled ionisation chamber array SRS1000, together with Verisoft software v6.0 (PTW Freiburg, Germany), was used to perform measurements of plans of increasing complexity to evaluate its suitability for device- and patient-specific QA. The dimension of backscatter material was investigated. The patient plan dwell time distribution was entered manually into the QA-CT and the dose distribution was calculated. Results: Our measurements indicate that the array is independent of energy and angle. The resulting measured dose values are linearly interpolated to 2025 values. Shifts of 1mm of the entire needle are readily detectable. Individual dwell position shifts (2.5mm) are also readily measurable. Moreover a dwell time increase of 1 second both in the edge and central region are detectable. Conclusion: The high resolution SRS1000 array is a powerful instrument for brachytherapy QA enabling 977 simultaneous measurements to be performed. Our measurements suggest 60mm of RW3 backscatter material upstream and downstream are sufficient. Local percentage difference analysis is useful for device based QA, normalized relative percentage difference is arguably better for patient specific QA. Automated transfer of patient plan dwell time distribution to the QA plan is required to enable a comprehensive patient QA study to be performed. Moreover the described measurement technique can be used for commissioning new brachytherapy applicators.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-G-IeP4-06: Feasibility of External Beam Treatment Field Verification Using Cherenkov Imaging

Purpose: Cherenkov light emission has been shown to correlate with ionizing radiation (IR) dose delivery in solid tissue. In order to properly correlate Cherenkov light images with real time dose delivery in a patient, we must account for geometric and intensity distortions arising from observation angle, as well as the effect of monitor units (MU) and field size on Cherenkov light emission. To test the feasibility of treatment field verification, we first focused on Cherenkov light emission efficiency based on MU and known field size (FS). Methods: Cherenkov light emission was captured using a PI-MAX4 intensified charge coupled device(ICCD) system (Princeton Instruments), positioned at a fixed angle of 40° relative to the beam central axis. A Varian TrueBeam linear accelerator (linac) was operated at 6MV and 600MU/min to deliver an Anterior-Posterior beam to a 5cm thick block phantom positioned at 100cm Source-to-Surface-Distance(SSD). FS of 10×10, 5×5, and 2×2cm{sup 2} were used. Before beam delivery projected light field images were acquired, ensuring that geometric distortions were consistent when measuring Cherenkov field discrepancies. Cherenkov image acquisition was triggered by linac target current. 500 frames were acquired for each FS. Composite images were created through summation of frames and background subtraction. MU per image was calculated based on linac pulse delay of 2.8ms. Cherenkov and projected light FS were evaluated using ImageJ software. Results: Mean Cherenkov FS discrepancies compared to light field were <0.5cm for 5.6, 2.8, and 8.6 MU for 10×10, 5×5, and 2×2cm{sup 2} FS, respectably. Discrepancies were reduced with increasing field size and MU. We predict a minimum of 100 frames is needed for reliable confirmation of delivered FS. Conclusion: Current discrepancies in Cherenkov field sizes are within a usable range to confirm treatment delivery in standard and respiratory gated clinical scenarios at MU levels appropriate to standard MLC position segments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Photon detector response function methodology using MCNP and shift hybrid radiation transport code for wide-area contamination assay applications

Here, radiation transport modeling using the Monte Carlo N-Particle (MCNP) radiation transport code and Monte Carlo code, Shift, were employed to model detector responses for a variety of wide-area photon contamination scenarios. In this study, 2" × 2" and 3" × 3" cylindrical NaI(Tl) scintillation detector configurations at source detector-distances of 0.5 cm, 1 cm, 2.54 cm, 10 cm, and 30 cm were modeled. Media of soil, concrete, and steel were evaluated for contamination depths ranging from surface to a depth of an infinite thickness in each medium for photon energies ranging from 20 keV to 3 MeV, which correspond to the energies that current detectors can discern. Monoenergetic photon surface contamination detector responses for each of the media, source–detector distances, and detectors were estimated using MCNP v6.2. Shift was harnessed for improved variance reduction of particle transport in highly attenuating media to obtain average cell fluxes in the two MCNP NaI(Tl) scintillation detector configurations. Average cell flux values in Shift were coupled with detector responses from MCNP to convert average cell flux in a void to energy distribution of pulses in the NaI(Tl) scintillation detector crystal of interest. An optimized detector response function methodology was developed by coupling the MCNP radiation transport method with the Consistent Adjoint Driven Importance Sampling (CADIS) hybrid radiation transport method built into Shift to significantly decrease the runtime of thousands of MCNP pulse height simulations. The methodology may be utilized to quickly and accurately facilitate the assessment of a broad range of wide-area environmental contamination assay and decommissioning cleanup applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

SU-E-T-47: A Monte Carlo Model of a Spot Scanning Proton Beam Based On a Synchrotron Proton Therapy Accelerator

Purpose: To build the model of a spot scanning proton beam for the dose calculation of a synchrotron proton therapy accelerator, which is capable of accelerating protons from 50 up to 221 MeV. Methods: The spot scanning beam nozzle is modeled using TOPAS code, a simulation tool based on Geant4.9.6. The model contained a beam pipe vacuum window, a beam profile monitor, a drift chamber, two plane-parallel ionization chambers, and a spot-position monitor consisted of a multiwire ionization chamber. A water phantom is located with its upstream surface at the isocenter plane. The initial proton beam energy and anglar deflection are modeled using a Gaussian distribution with FWHM (Full Widths at Half Maximum) deponding on its beam energy. The phase space file (PSF) on a virtual surface located at the center between the two magnets is recorded. PSF is used to analyze the pencil beam features and offset the pencil beam position. The source model parameters are verificated by fitting the simulated Result to the measurement. Results: The simulated percentage depth dose (PDD) and lateral profiles of scanning pencil beams of various incident proton energies are verificated to the measurement. Generally the distance to agreement (DTA) of Bragg peaks is less than 0.2cm. The FWHM of Gaussian anglar distribution was adjusted to fit the lateral profile difference between the simulation and the measurement to less than 2∼3cm. Conclusion: A Monte Carlo model of a spot scanning proton beam was bullt based on a synchrotron proton therapy accelerator. This scanning pencil beam model will be as a block to build the broad proton beam as a proton TPS dose verification tool.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Development of a true single line of sight 3D hot-spot imaging for the National Ignition Facility

High resolution 3D self-emission x-ray imaging during inertial confinement fusion capsule implosion enables the measurement of the shape of the hotspot. While current 3D imaging capabilities use multiple lines of sight to perform image reconstruction, it would be highly desirable to use only one line of sight, as this would significantly reduce the number of windows in the target hohlraum and decrease their impacts on implosion symmetry. Such a goal is achievable using the zone plate coded imaging technique developed by N. M. Ceglio [Proc. SPIE 0106, 55-62 (1977)]. It consists of fielding a visible light Fresnel zone plate on shot to record a shadowgraph. Here, the image can then be reconstructed either by printing the shadowgraph on a transparent film and shining a suitable wavelength light through it or by numerical reconstruction. A new approach using numerical reconstruction is presented, and it relaxes the constraint by an order of magnitude on the optic design, thus enabling an easier fabrication process, as it allows a scaling-up of the optic dimensions. The design, fabrication process, and testing with an x-ray source of a prototype is presented. The reconstruction of an ~14.5 × 17 μm 2 broadband x-ray source was successful and shows that the performances are in line with expectation with an at least 5 mm axial resolution.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

A new set-up for in-situ probing of radiation effects in materials and electronic devices

The micro-probe facility installed at the Van de Graff accelerator at CTN/IST permits simultaneous measurements of Rutherford Backscattering Spectrometry (RBS), Particle Induced X-ray Emission (PIXE) and Iono-Luminescence (IL). Here we present a recent up-grade of the measurement chamber allowing improved optical sensitivity in IL measurements and opening the possibility to perform simultaneously electrical measurements. Combinations of all these characterization techniques make this setup a powerful tool to characterize and modify different materials with spatial resolution. In particular, it can be used to study radiation effects in different materials and electronic devices in-situ. IL is a luminescence technique that uses the ion beam as the excitation source. Compared with other luminescence techniques with spatial resolution like Cathodoluminescence, this technique has the advantage to probe deeper regions of the sample, several microns below the surface. The same ion beam used to produce luminescence, can create a high density of defects, in a controllable way and the new set-up allows monitoring optical and electrical properties in realtime. In this work we combine IL with I-V curve measurements to assess the response of Ga{sub 2}O{sub 3} and GaN to proton irradiation. Ga{sub 2}O{sub 3} and GaN are emerging materials for applications in high power electronics and are considered for radiation resistant electronics. We will present a systematic study of the changes in IL and conductivity in Ga{sub 2}O{sub 3} and GaN samples with the energy of the ion beam and with the time of exposure. In particular, it was observed that during the irradiation some luminescence bands related with intrinsic point defects decrease while other new bands appear. Simulations using the SRIM code were used to determine the depth profiles of ionization and displacement events, helping to correlate the optical and electrical response of the materials with certain radiation effects. These studies show the potentialities of measuring simultaneously IL and electrical conductivity and how these two characterization techniques can work as a sensitive tool to detect and quantify radiation effects. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Gamma Spectrometry Code Rodeo for Uranium Enrichment—FY 2021 Report

In FY22, the participating Department of Energy (DOE) laboratories continued the work on the project “Gamma Spectrometry Code Rodeo for Uranium Enrichment”. Oak Ridge National Laboratory (ORNL) and Lawrence Livermore National Laboratory (LLNL) continued their efforts to acquire spectra using uranium sources. A collimator (with side and back shields) was custom designed and constructed at ORNL. Spectra were acquired at ORNL using the uranium enrichment standards supplied by New Brunswick Laboratory (NBL) and the collimated M400 detector. Spectra were also acquired using steel absorbers of different thickness placed between the source and the collimated M400 detector. The plan was to ship the collimator to LLNL so that spectra could be acquired using the LLNL detector in collimated geometries. This activity was suspended since problems were noticed with the performance of the LLNL M400 detector. Also, it was brought to light to the project team that some of the aspects of the M400 detector had been updated by the vendor H3D in response to requests by the IAEA. In February 2021, the ORNL and LLNL M400 detectors were returned to the H3D factory in order to resolve the problems with the LLNL detector and to update ORNL and LLNL detectors to the same configuration as the M400 supplied to the IAEA. H3D repaired the LLNL M400 and performed the IAEA updates on both the ORNL and LLNL detectors. ORNL and LLNL received the detectors in April 2021. Data acquisition was continued using the upgraded detectors. ORNL re-collected the spectra using point sources and the NBL standards in uncollimated and collimated geometries. The collimator was shipped from ORNL to LLNL. Spectra were acquired at LLNL through Q4 of FY22. When the ORNL spectra were examined closely, it became apparent that there were spurious artifacts present in some of the spectra. This rendered suspect the ORNL spectra collected in June/July 2021 time frame. ORNL contacted H3D and per H3D’s advice, the M400 detector was returned to H3D for repairs in mid-August 2021. H3D diagnosed the problem and established that the root cause was the extra tight packaging that created a strain on the CZT crystals, causing one of them to break down. The repaired M400 was returned to ORNL in early September 2021. ORNL re-started data acquisition for the third time. Data was continued to be acquired at ORNL and LLNL through September 2021. The ORNL and LLNL data will be shared with the principal investigators from the analyzing laboratories. The GADRAS code and FRAM have been developed to have the capability to analyze the M400 spectra. Good quality spectra from FY21 have been analyzed using modified versions of GADRAS and FRAM. The spectra have also been analyzed using the GEM code. The analysis results from GADRAS, FRAM and GEM codes are presented and discussed in this report. Some preliminary results from FRAM and GEM analysis were presented in February 2021 at the U-Pu Isotopics Workshop sponsored by the IAEA. CZTU code is being modified to analyze M400 spectra. Data collection, code development and analysis will be continued in FY22 as per the FY22 Project Work Plan (PWP).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2012

THE CALCULATION OF BURNABLE POISON CORRECTION FACTORS FOR PWR FRESH FUEL ACTIVE COLLAR MEASUREMENTS

Verification of commercial low enriched uranium light water reactor fuel takes place at the fuel fabrication facility as part of the overall international nuclear safeguards solution to the civilian use of nuclear technology. The fissile mass per unit length is determined nondestructively by active neutron coincidence counting using a neutron collar. A collar comprises four slabs of high density polyethylene that surround the assembly. Three of the slabs contain {sup 3}He filled proportional counters to detect time correlated fission neutrons induced by an AmLi source placed in the fourth slab. Historically, the response of a particular collar design to a particular fuel assembly type has been established by careful cross-calibration to experimental absolute calibrations. Traceability exists to sources and materials held at Los Alamos National Laboratory for over 35 years. This simple yet powerful approach has ensured consistency of application. Since the 1980's there has been a steady improvement in fuel performance. The trend has been to higher burn up. This requires the use of both higher initial enrichment and greater concentrations of burnable poisons. The original analytical relationships to correct for varying fuel composition are consequently being challenged because the experimental basis for them made use of fuels of lower enrichment and lower poison content than is in use today and is envisioned for use in the near term. Thus a reassessment of the correction factors is needed. Experimental reassessment is expensive and time consuming given the great variation between fuel assemblies in circulation. Fortunately current modeling methods enable relative response functions to be calculated with high accuracy. Hence modeling provides a more convenient and cost effective means to derive correction factors which are fit for purpose with confidence. In this work we use the Monte Carlo code MCNPX with neutron coincidence tallies to calculate the influence of Gd{sub 2}O{sub 3} burnable poison on the measurement of fresh pressurized water reactor fuel. To empirically determine the response function over the range of historical and future use we have considered enrichments up to 5 wt% {sup 235}U/{sup tot}U and Gd weight fractions of up to 10 % Gd/UO{sub 2}. Parameterized correction factors are presented.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Study of influence of plastic scintillators thicknesses to detect Beta particles and Gamma radiation by means of spectral analysis of {sup 90}Sr, {sup 90}Y and {sup 137}Cs sources

The Nuclear and Energy Research Institute - IPEN, offers post-graduate programs, namely: Nuclear Technology - Applications (TNA), Nuclear Technology - Materials (TNM), Nuclear Technology - Reactors (TNR). The Institute programs mission is to form expert technicians, physicists and engineers with a strong knowledge in their discipline to work in the nuclear area. The course: 'Theoretical Fundamentals and Practices of the Instrumentation used in Nuclear Data Acquisition' covers the use of laboratory nuclear instrumentation and the accomplishment of experiments to obtain nuclear parameters. One of these experimental exercises is object of this work: 'Study of influence of plastic scintillators to detect Beta particles and Gamma radiation by means of spectral analysis of {sup 90}Sr, {sup 90}Y and {sup 137}Cs sources'. The use of scintillators plastic for the detection has the advantage of low cost, high mechanical strength, is not hygroscopic and can be manufactured in large volumes. This work aims to present the analysis of relative efficiency of detection of plastic scintillators of various thicknesses for beta particles and gamma radiation by the spectrum of {sup 137}Cs and {sup 90}Sr. Due to lack of resolution of the detectors plastic scintillators we worked with relative efficiency. The evaluation was done by reading deposited energy, using the software MAESTRO, for each detector thickness. For beta particles was observed an ideal thickness around 3 mm and the better photon efficiency was observed with increasing the thickness of the detector. The present experiment does not intend to establish a new technique for this subject: it solely aims student's practical exercises in nuclear properties of elements and detectors being part of the nuclear experimental course. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Two Photon Absorption Laser Induced Fluorescence for Neutral Hydrogen Profile Measurements

The magnitude and spatial dependence of neutral density in magnetic confinement fusion experiments is a key physical parameter, particularly in the plasma edge. Modeling codes require precise measurements of the neutral density to calculate charge-exchange power losses and drag forces on rotating plasmas. However, direct measurements of the neutral density are problematic. In this work, we proposed to construct a laser-based diagnostic capable of providing spatially resolved measurements of the neutral density in the edge of plasma in the DIII-D tokamak. The diagnostic concept is based on two-photon absorption laser induced fluorescence (TALIF). By injecting two beams of 205 nm light (co or counter propagating), ground state hydrogen (or deuterium or tritium) can be excited from the n = 1 level to the n = 3 level at the location where the two beams intersect. Individually, the beams experience no absorption, and therefore have no difficulty penetrating even dense plasmas. After excitation, a fraction of the hydrogen atoms decay from the n = 3 level to the n = 2 level and emit photons at 656 nm (the H α line). Calculations based on the results of previous TALIF experiments in magnetic fusion devices indicated that a laser pulse energy of approximately 3 mJ delivered in 5 ns would provide sufficient signal-to-noise for detection of the fluorescence. In collaboration with the DIII-D engineering staff and experts in plasma edge diagnostics for DIII-D from Oak Ridge National Laboratory (ORNL), WVU researchers designed a TALIF system capable of providing spatially resolved measurements of neutral deuterium densities in the DIII-D edge plasma. The laser systems were specified, purchased, and assembled at WVU. The TALIF system was tested on a low-power hydrogen discharge at WVU and the plan was to move the instrument to DIII-D for installation in collaboration with ORNL researchers. After budget cuts at DIII-D, the DIII-D facility declined to support installation on their tokamak. Instead, after a no-cost extension, the apparatus was moved to the University of Washington-Seattle and successfully tested on the HIT-SI3 spheromak experiment. As a result of this project, TALIF measurements of the absolutely calibrated neutral density hydrogen and deuterium were obtained in a helicon source and in a spheromak, designs were developed for installation of a TALIF system on a tokamak, and a new, xenon-based calibration scheme was proposed and demonstrated. The xenon-calibration scheme eliminates significant problems that were identified with the standard krypton calibration scheme.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

ADVANTG Results for a Proposed NDA System for Detecting Pin Diversion from SNF - Paper 120

This summary describes the results of applying the ADVANTG variance reduction parameter generator to accelerate continuous-energy Monte Carlo simulations of the {sup 252}Cf Interrogation with Prompt Neutron (CIPN) detection system proposed by Hu et al. for detecting the diversion of fuel elements from spent nuclear fuel (SNF) assemblies. In previous work, ADVANTG was applied to a suite of nine radiation detection, special nuclear material (SNM) movement detection, and safeguards test cases. That effort demonstrated that ADVANTG was able to provide large increases in tally figures of merit (FOMs) in nearly all of the cases without introducing bias into the Monte Carlo results. The objective of the work described here is to further evaluate ADVANTG, and also to identify gaps in capability with regard to nuclear safeguards applications, by applying the code to a challenging problem that is of a different nature from the ones previously studied. The CIPN nondestructive assay (NDA) system consists of three fission chambers embedded in a C-shaped block of polyethylene and a polyethylene-moderated {sup 252}Cf source that are placed on opposite sides of a subject SNF assembly. The idea of the detection system is to measure the difference between the background neutron count rate, due to spontaneous fission in the fuel material, and the count rate observed once the source is introduced, which is dominated by multiplication within the assembly. Based on the difference between these count rates, the fissile content of the assembly can be inferred, and this information can be used to determine if some fraction of the original fuel pins have been replaced with depleted uranium substitutes. The authors report that the system can detect the replacement of at least eight pins (3% of total mass). The ADVANTG code generates space- and energy-dependent weight-window bounds and biased source distributions based on approximate transport solutions that are efficiently generated by the Denovo 3-D discrete ordinates package. ADVANTG implements the Consistent Adjoint Driven Importance Sampling (CADIS) method for accelerating individual tallies and the Forward-Weighted CADIS (FW-CADIS) method for obtaining relatively uniform uncertainties across tallies over multiple regions and/or energy bins. The variance reduction parameters are generated in a format directly usable by standard versions of MCNP5 and MCNPX. In this work, the ADVANTG variance reduction parameter generator was applied to accelerate continuous energy MCNPX simulations of the {sup 252}Cf Interrogation with Prompt Neutron detection system for detecting the diversion of fuel elements from SNF assemblies. Variance reduction parameters generated with the existing version of ADVANTG actually slowed down tally convergence in all cases. The cause of the poor performance was found to be the lack of an induced fission source treatment in the fixed-source discrete ordinates calculations employed by ADVANTG. Because fission was treated as capture and not as a source, the importance maps generated by ADVANTG significantly underestimated the importance of thermal neutrons in and around the fuel elements. In order to obtain improved results, we developed an experimental implementation of a fission source outer iteration for the adjoint calculations. We used this prototype capability to generate new variance reduction parameters and found that the mean fission rates agreed well with those predicted by the conventional MCNPX simulations, as was expected. With these new parameters, speedup factors of 59 to 80 were obtained for the case with the background source, and factors of 17 to 24 were obtained for the cases with the interrogating source. These results demonstrate that a fission source treatment is needed to improve the effectiveness of ADVANTG in problems where the effects of induced fission are important. This includes many types of NDA problems that are relevant to safeguards applications. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Deadtime Determination of Helium Detector Using MCNP Code

In detector systems, the minimum time separation between the events is called detector's deadtime. The The intrinsic properties of the detector and the pulse processing circuitry's characteristics are the sources of deadtime. Researchers have been working on improving a detector deadtime model that can implicitly characterize a detection system's behavior while reducing counting errors. There are two commonly known dead-time models: the 'Paralyzing' and the 'Non-paralyzing' models. In reality, detection systems fit neither of these idealized models perfectly, instead falling somewhere between the two models. The paralyzing model is mathematically expressed by eq. 1, where m is the measured count rate, n is the true count rate and t is dead-time. This model assumes that each event during the dead-time will reset it to a fixed duration, thus extending the deadtime. The dead-time extension depends on the count rate. According to the non-paralyzing model, deadtime is fixed after each detected event, and all events occurring during deadtime are lost. The fraction of time during which an apparatus is sensitive is 1-mt. Therefore, the fraction of the true number of events can be recorded. In this study, a Canberra {sup 3}He neutron detector (0.5NH1/1K) deadtime value was estimated using a combination of experimental subcritical assembly measurements and theoretical MCNP simulations. The deadtime of the Canberra 10 mm diameter {sup 3}He tube detector was calculated by comparing measured counts from different locations in the subcritical assembly at Missouri University of Science and Technology Reactor (MSTR) with MCNP (Monte Carlo N-Particle Code) simulations. The deadtime calculations are provided for both the paralyzing and non-paralyzing models for the Canberra 10 mm diameter {sup 3}He tube detector. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): BINARIES, PULSATIONS, AND EXPLOSIONS

We substantially update the capabilities of the open-source software instrument Modules for Experiments in Stellar Astrophysics (MESA). MESA can now simultaneously evolve an interacting pair of differentially rotating stars undergoing transfer and loss of mass and angular momentum, greatly enhancing the prior ability to model binary evolution. New MESA capabilities in fully coupled calculation of nuclear networks with hundreds of isotopes now allow MESA to accurately simulate the advanced burning stages needed to construct supernova progenitor models. Implicit hydrodynamics with shocks can now be treated with MESA, enabling modeling of the entire massive star lifecycle, from pre-main-sequence evolution to the onset of core collapse and nucleosynthesis from the resulting explosion. Coupling of the GYRE non-adiabatic pulsation instrument with MESA allows for new explorations of the instability strips for massive stars while also accelerating the astrophysical use of asteroseismology data. We improve the treatment of mass accretion, giving more accurate and robust near-surface profiles. A new MESA capability to calculate weak reaction rates “on-the-fly” from input nuclear data allows better simulation of accretion induced collapse of massive white dwarfs and the fate of some massive stars. We discuss the ongoing challenge of chemical diffusion in the strongly coupled plasma regime, and exhibit improvements in MESA that now allow for the simulation of radiative levitation of heavy elements in hot stars. We close by noting that the MESA software infrastructure provides bit-for-bit consistency for all results across all the supported platforms, a profound enabling capability for accelerating MESA's development.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Tracking Radioactive Isotopes in HVAC and Application for Hot Cell Analyses - 20155

In recent years, the surge in the number of isotope production facilities under design has increased the need to analyze isotope migration in facility Heating, Ventilation, and Air Conditioning (HVAC) during normal operations and accident scenarios. These facilities are used to produce isotopes for medical, security, and industrial applications and as such are subject to license and regulatory requirements 10CFR20, 10CFR30, 10CFR50, and 10CFR70. GOTHIC, a general-purpose thermal-hydraulics software package, includes the ability to model isotopic tracers, radioactive decay and isotope migration as well as HEPA and charcoal filters for isotope retention. A GOTHIC model was developed by Zachry Nuclear Engineering (ZNE) to examine the effect of negative room pressure, HEPA filtration, and HVAC fluctuations on radiation areas, hot cells and gloveboxes. Radioactive tracers were used to simulate the concentration of spills within contaminated areas, track the migration of isotopes of interest, and determine the isotopic retention and buildup on facility HEPA filters. A variety of isotopes with concern to dose (e.g., Kr-85, Sr-90, I-131, etc.), including their decay and progeny, are included in the analysis. Negative pressures are maintained in the regions of interest by a representative central HVAC system equipped with a volumetric fan that exhausts to the environment after a series of isolation valves and HEPA filters. GOTHIC is an industry trusted tool for providing engineering solutions for a variety of applications, including fission product tracking, aerosol and particulate transport and ventilation assessments. The software provides an integrated analysis environment that includes a graphical user interface (GUI) for constructing analysis models, a numerical solver that includes parallel processing capabilities and a post-processor for evaluating simulation results. It solves the conservation equations for mass, momentum and energy for multicomponent, multi-phase flow in lumped parameter and multi-dimensional geometries (1, 2, or full 3D), including the effects of turbulence, diffusion and buoyancy. It has been developed and maintained under a Quality Assurance program in compliance with the requirements of 10CFR50 Appendix B and applicable portions of ASME NQA-1 since 1995. GOTHIC has been used for assessing both forced and natural convection conditions for a wide range of applications, including: - Tracking concentration of hazardous gases and chemicals for habitability and safety assessments - Determining ventilation and filtration requirements and optimizing location and arrangement of these systems - Room heat-up, including diverse and Flexible coping strategies for Extended Loss of AC Power (FLEX/ELAP) - Equipment Qualification (EQ) A distinctive feature of GOTHIC is the ability to track many different fields/substances in a simulation, including user defined tracer elements, in the liquid, vapor and droplet fields as well as surfaces and filters. This capability allows GOTHIC to model fission product transport and release or the removal of particulates or harmful toxins from exhaust gases using a spray scrubber or other types of filtration systems. GOTHIC also includes models for engineered equipment, such as fans, filters, charcoal filters, dryers/demisters, dampers, etc. The aerosols and other filtered material are removed or accumulated in these components. The range of aerosol and radiological applications that GOTHIC has been used for includes: - Source Term: Primary Coolant (Equilibrium) Activity; Non-Water Coolant Source/Leakage. - Conditions for Iodine Re-evolution: Sump/Suppression Pool Conditions and pH; - RWST Conditions and pH. - Isotope Removal Mechanisms: Containment Sprayed and Unsprayed Region Mixing; Charcoal Filter Heating due to Iodine decay. - Radionuclide Transport and Decay: Post-LOCA Release in containment; Transport between connected Compartments and vent systems; Groundwater transport of radionuclides. - Non-Newtonian Fluid modeling for sludge, waste tanks, etc. ADAMS ML071581053 (titled 'Best Practice Guidelines for the use of CFD in Nuclear Reactor Safety Applications') poses guidelines for applying single phase CFD codes in nuclear reactor safety problems and GOTHIC is listed as a 'tool for 3D flows' and 'dispersal and deposition of radionuclides.' The Nuclear Quality Assurance (NQA) pedigree of GOTHIC is an important aspect for applications in the nuclear industry. The fundamental tracer models (convective transport, molecular and turbulent diffusion, removal mechanisms, etc.) have been verified using analytical solutions and validated against applicable separate effects tests. Also, GOTHIC has been benchmarked to many integrated effects tests, including Phebus FP (Fission Product). GOTHIC gives good agreement for the buildup and decay of fission products in Phebus Test 3. The model developed by ZNE demonstrates GOTHIC's applicability and acceptability for use in analyzing the migration and retention of radioactive isotopes and their progeny in normal operation and accident scenario analyses for isotope production facilities, hot cells, and gloveboxes. The tracer activities calculated by GOTHIC can then be used in downstream radiation transport and shielding codes like RADTRAD-NAI{sup C}, MCNP{sup R}, and MicroShield{sup R} to determine on-site and of-site doses. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Improving the Field Portability of Neutron and Gamma Counting Techniques

Savannah River National Laboratory (SRNL) puts science to work by developing techniques that better meet customers needs for in-situ measurements. There is high demand for laboratory quality measurements in field situations, improving the cost and speed for first responders and environmental monitoring. This work focused on two improvements (1) reading a signal from a neutron detector using a Raspberry Pi (2) testing the Peak-to-Valley method for determining the depth of a source in soil contamination measurements. A Raspberry Pi is a cheap, compact computer. This affordable, compact computer is able to do simple tasks that a desktop computer is able to do, like spreadsheets, browse the internet, play games and even program a simple robot. Additionally, a Raspberry Pi can run off of a battery, so it could be deployed for long term measurements in adverse conditions like neutron monitors deployed in a shipping port. Using the Raspberry Pi and libraries easily accessible on the internet, a code was written in Python that allows the Pi to keep track of how many times a button is pushed. This work will be used with the future goal of creating low power-budget neutron detectors. 1) Make sure Python was correctly installed on the Raspberry Pi. 2) Write a code that will keep track of how many times a button connected to the Pi is pressed. A code was written to use the Raspberry Pi to count the number of times the button was pushed. Moving forward the Raspberry Pi will be tested with a neutron counter. Ideally, each signal from the neutron pulse will be equivalent of 'push the button' and be counted. In the characterization of a soil contamination area both the location and the depth of the source is important. Attenuation of the source by the soil can make determining its depth challenging, particularly for monoenergetic radionuclides like Cs-137. To address this issue, a method of calculating the 'peak-to-valley' ratio of the gamma count spectra is implemented to help calculate the known depth of the source. 1) Determine the 'peak-to-valley' ratio of a Cs-137 source at different depths. 2) Find an appropriate function to serve as a model for the peak-to-valley ratio as a function of depth. Several Petri dishes, filled with sand, were stacked with one containing a Cs-137 source. The individual Petri dishes allowed for the source to be placed at different depths. A bucket was placed over the sand and source, to keep the detector at a consistent height. A Petri dish containing a Eu-155 source, which acted as an internal calibration standard, was placed on top of the bucket. A NaI detector was place on top of the Eu-155 source and the assembly was surrounded by a tungsten shield. Count times were 20 minutes and the data was analyzed using PeakEasy. Data was recorded for Cs-137 at a series of depths in sand. Both exponential and logarithmic functions provided a reasonable fit to the data. The experimental data showed a decreasing 'peak-to-valley' ratio as the depth was increased. The next steps for this project involves determining the optimum fit function and combining the results from sand to different soil types to get a better representation of the soil found at SRS. Eventually, the peak-to-valley ratio will be used to estimate the depth of contamination in field measurements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗