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DOE OSTI2020

Radiological Monitoring Plan for the Oak Ridge Y-12 National Security Complex: Surface Water

DOE Order 458.1 requires that dose estimates consider contributions from all facilities. In the Y-12 Radiological Monitoring Plan (RMP), surface water is monitored at points that reflect individual facilities, as well as at points that reflect the combined contributions of all facilities. This monitoring plan does not consider other potential routes (i.e., airborne releases and food chains). Thus, a complete determination of total effective dose (TED) cannot be made based on this plan alone. The other routes from Y-12, and all routes from other DOE facilities on the Oak Ridge Reservation (e.g., Oak Ridge National Laboratory (ORNL) and The Heritage Center), must be considered in order to satisfy DOE Order 458.1 requirements. Determination of TED from all sites and pathways is done through the use of dose-assessment models and is documented in the Annual Site Environmental Report. This monitoring plan provides adequate monitoring goals for Y-12 surface water releases to provide input of sufficient sensitivity and accuracy to reliably determine the Y-12 surface water component of the TED. The routine radiological monitoring program is designed to monitor effluents at four types of locations: (1) treatment facilities, (2) other point and area source discharges, (3) instream locations, and (4) production building roof run-off. With this sampling and analysis program, data will be obtained on primary point sources as well as on locations that represent the composite of other potential sources. This plan will be reviewed periodically to determine necessary modifications to the sampling frequencies, parameters, and locations. Modifications, if any, will be based on the analysis of the previous data and its effectiveness in satisfying the objectives of this plan. Appendix A contains graphs of the sum of the DCS fractions for locations and frequencies contained in a previous version of this plan. The data was collected from January 2009 through December 2019. Each sample was analyzed, and each result was divided by the appropriate DCS to compute a DCS fraction. These fractions were summed for all isotopes. According to DOE –STD-1196-2011, the annual average of these sums should be below 1.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2023

Resolved Resonance Region Analysis of 206 Pb, 207 Pb, and 208 Pb for Next Generation Lead-Cooled Fast Systems

Recently, great interest has been generated in using lead as a coolant for fast neutron systems and as a result it is important to investigate the ENDF/B-VIII.0 isotopic evaluations that comprise stable le ad. To this end, resonance parameters for 206 Pb, 207 Pb, and 208 Pb were re-evaluated because their resolved resonance regions extend beyond 0.5 MeV meaning resonance parameters used in reconstructing cross sections and elastic scattering angular distributions impact fast systems. The impact of resonance parameters is demonstrated by the differences between the evaluations in predicting experimental results from the fully modeled RPI Quasi-Differential Scattering Experiment via MCNPv6.2. In addition, MCNP KCODE calculations of lead-sensitive fast spectra critical benchmarks showed variations of keff on average of 400 pcm, caused solely from differences in elastic scattering angular distributions in 208 Pb. Re-evaluation entailed fitting data with the program SAMMY.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

NASA NTRS1994

Voyager measurements of the isotopic composition of cosmic-ray aluminum and implications for the propagation of cosmic rays

We report a new measurement of the cosmic-ray isotopic composition of aluminum in the low-energy range form 75 to 206 MeV per nucleon.This measurement was made using the high-energy telescope of the CRS experiment on the Voyager 1 and 2 spacecraft during the time period from 1977 to 1993 with an average solar modulation level about 497 MV, roughly the same as at Earth near sunspot minimum. We obtain approximately 430 Al events of which approximately 35 are Al-26 and 395 are Al-27. The Al isotopes were separated with an average mass resolution sigma of 0.35 amu. Our interpretation of the isotopic composition of cosmic-ray aluminum is based on a standard Leaky-Box model for the interstellar propagation of cosmic-ray nuclei using the latest cross sections of the New Mexico-Saclay collaboration as well as a disk-halo diffusion model. From our observed ratio Al-26/Al-27 of 8.3 +/- 2.4 % we deduce an average interstellar density of about 0.52 (+0.26, -0.2) atoms per cu cm. This density is larger than the value of 0.28 (+0.14, -0.11) atoms per cu cm we found from an analysis of the observed abundance of the longer lived Be-10 made using data from the Voyager detectors over almost the same time interval and using essentially the same propagation program.

Lukasiak, A.↗

DOE OSTI2024

Multiscale, mechanistic modeling of irradiation-enhanced silver diffusion in TRISO particles

Tristructural isotropic (TRISO) particles are under consideration for use in several proposed advanced nuclear reactor concepts. The silicon carbide (SiC) layer in TRISO acts as a barrier to prevent the release of the fission products. However, despite remarkable retention, silver (Ag) release has been observed from intact particles, which requires investigation since the Ag isotope ( 110m Ag) has a long half-life. Previous work focused on developing a multiscale, mechanistic model for Ag diffusion accounting for temperature and microstructure effect and has been successfully validated. In this work, we expand the previous model to account for irradiation-enhanced Ag diffusivity in SiC and improve its accuracy over a wider grain size and temperature ranges relevant for advanced reactor conditions. A temperature, grain size, and flux dependent diffusivity is therefore derived using the mesoscale code MARMOT and implemented in the fuel performance code BISON. The irradiation-enhanced Ag diffusivity in SiC is compared against experimental data and validated using BISON against Ag release measurements from the Advanced Gas Reactor Fuel Development and Qualification Program (AGR-1 and AGR-2). Herein, we quantify the impact of SiC grain size, irradiation, and temperature on Ag release. In agreement with previous studies, we find accounting for SiC grain size improves agreement between BISON predictions and experimental observations for most cases. In conclusion, we also find that accounting for irradiation improves agreement for cases where Ag release was underestimated, but the impact was less significant than accounting for microstructure.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2019

Geochemical characterization of floodplain sediments from Meander C and O in the East River Watershed, CO, USA

This data package is part of the Watershed Function SFA data collection and contains geochemical characterization of sediments as a function of depth in the pumphouse vicinity, including Meander C and Meander O (oxbow). This data was used in the manuscript "Fox, P.M., Bill, M., Heckman, K., Conrad, M., Anderson, C., Keiluweit, M., and Nico, P.S.Shale as a Source of Organic Carbon in Floodplain Sediments of a Mountainous Watershed" published in Journal of Geophysical Research: Biogeosciences. Data includes sieving, total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), carbon isotopes (14C and 13C) of whole sediment. Sediment density fractionation data is also included, with measurements of TOC, TN, 14C and 13C on density fractions. Metal and carbon concentrations from various sediment extractions (HCl, dithionite, oxalate, water, and pyrophosphate) are included. Characterization of extracted carbon by fourier transform infrared spectroscopy (FTIR) and UV-Visible light spectroscopy. Characterization of density fractionated (light fractions) organic carbon by FTIR. Carbon X-ray spectroscopy (C near edge X-ray absorption fine structure spectroscopy [NEXAFS] and scanning transmission X-ray microscopy [STXM]) is also included for shale samples and sediment samples.Additional acknowledgements:1. M.K. and C.A. were supported by the Department of Energy, Office of Biological and Environmental Research, Subsurface Biosphere Research program (award no. DE-SC0016544).2. STXM and NEXAFS data was collected at the Canadian Light Source, which is supported by the Canada Foundation for Innovation, Natural Sciences and Engineering Research Council of Canada, the University of Saskatchewan, the Government of Saskatchewan, Western Economic Diversification Canada, the National Research Council Canada, and the Canadian Institutes of Health Research.3. Radiocarbon analysis was supported in part by the Radiocarbon Collaborative, which is jointly sponsored by the USDA Forest Service Northern Research Station, the KCCAMS Facility at UC Irvine, and Michigan Technological University.Update 11/06/2019: An .kml file was added with the GPS locations for all the sampling sites.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2018

The Neutron Macromolecular Crystallography Instruments at Oak Ridge National Laboratory: Advances, Challenges, and Opportunities

The IMAGINE and MaNDi instruments, located at Oak Ridge National Laboratory High Flux Isotope Reactor and Spallation Neutron Source, respectively, are powerful tools for determining the positions of hydrogen atoms in biological macromolecules and their ligands, orienting water molecules, and for differentiating chemical states in macromolecular structures. The possibility to model hydrogen and deuterium atoms in neutron structures arises from the strong interaction of neutrons with the nuclei of these isotopes. Positions can be unambiguously assigned from diffraction studies at the 1.5–2.5 Å resolutions, which are typical for protein crystals. Neutrons have the additional benefit for structural biology of not inducing radiation damage to protein crystals, which can be critical in the study of metalloproteins. Here we review the specifications of the IMAGINE and MaNDi beamlines and illustrate their complementarity. IMAGINE is suitable for crystals with unit cell edges up to 150 Å using a quasi-Laue technique, whereas MaNDi provides neutron crystallography resources for large unit cell samples with unit cell edges up to 300 Å using the time of flight (TOF) Laue technique. The microbial culture and crystal growth facilities which support the IMAGINE and MaNDi user programs are also described.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Chemical Compositions of Red Giant Stars from Habitable Zone Planet Finder Spectroscopy

We have used the Habitable Zone Planet Finder (HPF) to gather high-resolution, high signal-to-noise near-infrared spectra of 13 field red horizontal branch (RHB) stars, one open cluster giant, and one very metal-poor halo red giant. The HPF spectra cover the 0.81–1.28 μm wavelength range of the zyJ bands, partially filling the gap between the optical (0.4–1.0 μm) and infrared (1.5–2.4 μm) spectra already available for the program stars. We derive abundances of 17 species from LTE-based computations involving equivalent widths and spectrum syntheses, and estimate abundance corrections for the species that are most affected by departures from LTE in RHB stars. Generally good agreement is found between HPF-based metallicities and abundance ratios and those from the optical and infrared spectral regions. Light element transitions dominate the HPF spectra of these red giants, and HPF data can be used to derive abundances from species with poor or no representation in optical spectra (e.g., C i, P i, S i, K i). Attention is drawn to the HPF abundances in two field solar-metallicity RHB stars of special interest: one with an extreme carbon isotope ratio, and one with a rare, very large lithium content. The latter star is unique in our sample in exhibiting very strong He i 10830 Å absorption. The abundances of the open cluster giant concur with those derived from other wavelength regions. Detections of C i and S i in HD 122563 are reported, yielding the lowest metallicity determination of [S/Fe] from more than one multiplet.

47 OTHER INSTRUMENTATION↗

DOE OSTI2019

Elucidation of the Reaction Mechanism for High-Temperature Water Gas Shift over an Industrial-Type Copper–Chromium–Iron Oxide Catalyst

The water gas shift (WGS) reaction is of critical importance for the chemical industry, as it constitutes, coupled with methane reforming, the main industrial route to produce hydrogen. Copper–chromium–iron oxide-based catalysts have been widely used for the high-temperature WGS reaction industrially. The WGS reaction mechanism by the CuCrFeO x catalyst has been debated for years, mainly between a “redox” mechanism involving the participation of atomic oxygen from the catalyst and an “associative” mechanism proceeding via a surface formate-like intermediate. Here, advanced in situ characterization techniques (infrared spectroscopy, temperature-programmed surface reaction (TPSR), near-ambient pressure XPS (NAP-XPS), and inelastic neutron scattering (INS)) were applied to determine the nature of the catalyst surface and identify surface intermediate species under WGS reaction conditions. The surface of the CuCrFeO x catalyst is found to be dynamic and becomes partially reduced under WGS reaction conditions, forming metallic Cu nanoparticles on Fe 3 O 4 . Neither in situ IR not INS spectroscopy detect the presence of surface formate species during WGS. TPSR experiments demonstrate that the evolution of CO 2 and H 2 from the CO/H 2 O reactants follows different kinetics than the evolution of CO 2 and H 2 from HCOOH decomposition (molecule mimicking the associative mechanism). Steady-state isotopic transient kinetic analysis (SSITKA) (CO + H 2 16 O → CO + H 2 18 O) exhibited significant 16 O/ 18 O scrambling, characteristic of a redox mechanism. Computed activation energies for elementary steps for the redox and associative mechanism by density functional theory (DFT) simulations indicate that the redox mechanism is favored over the associative mechanism. The combined spectroscopic, computational, and kinetic evidence in the present study finally resolves the WGS reaction mechanism on the industrial-type high-temperature CuCrFeO x catalyst that is shown to proceed via the redox mechanism.

SSITKA↗

DOE OSTI2021

The U.S. Accident Tolerant Fuels Program — Update on a National Initiative

In 2012 the U.S. Congress directed the Department of Energy’s (DOE) Office of Nuclear Energy to give priority to developing enhanced fuels and cladding for light water reactors to improve safety in the event of accidents in the reactor or spent fuel pools. DOE developed a plan with a goal to insert a Lead Test Assembly (LTA) into a commercial light water reactor by the end of FY 2022. Three of the leading commercial nuclear fuel vendors, in concert with several participating commercial nuclear utilities, are now seriously engaged in this initiative and have exceeded initial expectations by having met DOE’s goal this year, three years ahead of schedule. The early successes of the ATF program are due in part to a strong collaboration by the DOE national laboratories with both commercial nuclear fuel vendors and the U.S. Nuclear Regulatory Commission. This undertaking has recently been expanded to incorporate an effort to extend burnup from the current U.S. regulatory limit of 62 GWD/MTU and increase enrichment as necessary to support routine utilization of fuel at >75 GWD/MTU. This effort provides a critical economic incentive to accelerate the deployment of ATF technologies. This paper reviews the DOE-sponsored, industry-led ATF concepts currently under development and highlights the contributions made by the DOE laboratories in support of these ATF concepts, including: 1) steady-state irradiation testing in the Advanced Test Reactor (ATR) and High Flux Isotope Reactor (HFIR); 2) transient irradiation testing in the Transient Reactor Test Facility (TREAT); 3) fabrication process development and characterization of high density fuels, Cr-coated Zry cladding, FeCrAl cladding, and SiC cladding; and 4) post-irradiation examination of lead test rods irradiated in commercial reactors.

Goldner, Frank J.↗

DOE OSTI2015

Acquired experience resulting from transforming a chemical installation into a nuclear one

ICIT-Valcea has developed an experimental pilot-scale installation for tritium and deuterium separation. The main objective of this pilot was to demonstrate the water detritiation technology and to transfer this technology to the CANDU reactors of the Cernavoda nuclear power plant. The pilot-scale installation was initiated in 1992. The initial design and construction were performed similarly to chemical plants as the separation of isotopes was focused on only hydrogen and deuterium to assess feasibility. In a second phase we have begun to transform it into a nuclear facility with the aim of separating tritium. Moving to tritium separation has imposed a lot of changes. Changes consisted mainly of: -) re-design of the technological systems for nuclear material processing, applying specific codes and standards (ASME, Romanian nuclear specific pressure boundary prescriptions for code classification); -) design and implementation of new systems, classified as safety systems; -) re-design and implementation of command and control systems, complying with the requirements of reliability and maintenance required for the project promoted; -) revaluation of auxiliary systems (utilities, power supply); -) implementing radiation protection systems, including secondary barriers; -) implementing and maintaining environment operational program specific to the new nuclear plant; -) developing and conducting safety analyzes; and -) the production of specific documentation to obtain the necessary permits for construction, commissioning and operation of the plant.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

DOE OSTI2014

A Multi-Contact, Low Capacitance HPGe Detector for High Rate Gamma Spectroscopy

The detection, identification and non-destructive assay of special nuclear materials and nuclear fission by-products are critically important activities in support of nuclear non-proliferation programs. Both national and international nuclear safeguard agencies recognize that current accounting methods for spent nuclear fuel are inadequate from a safeguards perspective. Radiation detection and analysis by gamma-ray spectroscopy is a key tool in this field, but no instrument exists that can deliver the required performance (energy resolution and detection sensitivity) in the presence of very high background count rates encountered in the nuclear safeguards arena. The work of this project addresses this critical need by developing a unique gamma-ray detector based on high purity germanium that has the previously unachievable property of operating in the 1 million counts-per-second range while achieving state-of-the-art energy resolution necessary to identify and analyze the isotopes of interest. The technical approach was to design and fabricate a germanium detector with multiple segmented electrodes coupled to multi-channel high rate spectroscopy electronics. Dividing the germanium detector’s signal electrode into smaller sections offers two advantages; firstly, the energy resolution of the detector is potentially improved, and secondly, the detector is able to operate at higher count rates. The design challenges included the following; determining the optimum electrode configuration to meet the stringent energy resolution and count rate requirements; determining the electronic noise (and therefore energy resolution) of the completed system after multiple signals are recombined; designing the germanium crystal housing and vacuum cryostat; and customizing electronics to perform the signal recombination function in real time. In this phase I work, commercial off-the-shelf electrostatic modeling software was used to develop the segmented germanium crystal geometry, which underwent several iterations before an optimal electrode configuration was found. The model was tested and validated against real-world measurements with existing germanium detectors. Extensive modeling of electronic noise was conducted using established formulae, and real-world measurements were performed on candidate front-end electronic components. This initial work proved the feasibility of the design with respect to expected high count rate and energy resolution performance. Phase I also delivered the mechanical design of the detector housing and vacuum cryostat to be built in Phase II. Finally, a Monte Carlo simulation was created to show the response of the complete design to a Cs-137 source. This development presents a significant advance for nuclear safeguards instrumentation with increased speed and accuracy of detection and identification of special nuclear materials. Other significant applications are foreseen for a gamma-ray detector that delivers high energy resolution (1keV FWHM noise) at high count rate (1 Mcps), especially in the areas of physics research and materials analysis.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

NASA NTRS1987

The delta upsilon = 1 fundamental bands of carbon monoxide in late-type stars

A program was begun to develop the fundamental vibration-rotation bands of CO near 4.7 micron, as a tool to investigate the properties of late type stellar atmospheres. The strong delta v = 1 lines are sensitive probes of the thermal structure of the outer layers, which can be strongly affected by the CO, itself: cooling in the fundamental lines can depress the surface temperature to low values that are in sharp contrast with those derived from chromospheric diagnostics like Ca II K and Mg II k. Cool atmospheric models are being constructed to reproduce observed high resolution CO spectra of several late-type stars. The sensitivity is illustrated of CO LTE spectra to variations in T sub eff, log g, (Fe/H), and isotopic abundances of C and O for a grid of such models. In parallel, the assumptions of LTE line formation are tested using newly available cross sections for translational-to-vibrational energy exchange in collisions of atomic H on CO. In addition, spectra of CO and Ca II K calculated from semi-empirical UV based hot chromospheric models are used to estimate geometrical filling factors for the CO dominated and chromospheric regions on the stellar surface, in the spirit of Ayres' thermal bifurcation scenario.

Wiedemann, G.↗

NASA NTRS2003

Formation of Primitive Bodies in the Protoplanetary Nebula

We have developed a simple model of global transport of solids in the protoplanetary nebula, including radial drift of large particles and diffusion of small ones. The model has been applied to the formation and redistribution of the Ca-A1 rich refractory mineral inclusions (CAIs) found in primitive chondrites. These objects form at much higher temperatures, and appear to be 1-3 million years older than, the dominant (chondrule) components found in the same parent bodies. A widespread concern has been the retention of CAIs for this long against gas-drag-induced radial drift into the sun. We show that outward radial diffusion in a weakly turbulent nebula can overwhelm inward drift, and prevent significant numbers of CAI-size particles from being lost into the sun for tines on the order of several Myr. An element of this model is rapid inward radial drift of boulder-sized primitive (carbon-rich) silicate material, more like Halley-dust than CI chondrites in the early days of the nebula. Thls process can enrich the abundance of silicate and carbon material in the inner nebula, and may provide possible explanations for both chemical and isotopic properties of CAIs. The predicted enhancement of CO relative to water might be of relevance to recent IR astronomical observations of CO in the inner disks of several actively accreting T Tauri stars. This process has applications to the transport and redistribution of volatiles in general. Depending on the rubble particle size distribution, rapid radial drift of boulder-sized solids can bring more material inwards across a condensation front, to evaporate, than can subsequently be removed by nebula advection or diffusion, until a strong local enhancement is produced which allows diffusive loss to balance the drifting source. Application of this process to enhancement of the abundance of water near the "ice line" will be discussed. Supported by the Origins of Solar Systems program.

Cuzzi, Jeffrey N.↗

NASA NTRS2003

Magnetized Target Fusion in Advanced Propulsion Research

The Magnetized Target Fusion (MTF) Propulsion lab at NASA Marshall Space Flight Center in Huntsville, Alabama has a program in place that has adopted to attempt to create a faster, lower cost and more reliable deep space transportation system. In this deep space travel the physics and development of high velocity plasma jets must be understood. The MTF Propulsion lab is also in attempt to open up the solar system for human exploration and commercial use. Fusion, as compared to fission, is just the opposite. Fusion involves the light atomic nuclei combination to produce denser nuclei. In the process, the energy is created by destroying the mass according to the distinguished equation: E = mc2 . Fusion energy development is being pursued worldwide as a very sustainable form of energy that is environmentally friendly. For the purposes of space exploration fusion reactions considered include the isotopes of hydrogen-deuterium (D2) and tritium (T3). Nuclei have an electrostatic repulsion between them and in order for the nuclei to fuse this repulsion must be overcome. One technique to bypass repulsion is to heat the nuclei to very high temperatures. The temperatures vary according to the type of reactions. For D-D reactions, one billion degrees Celsius is required, and for D-T reactions, one hundred million degrees is sufficient. There has to be energy input for useful output to be obtained form the fusion To make fusion propulsion practical, the mass, the volume, and the cost of the equipment to produce the reactions (generally called the reactor) need to be reduced by an order of magnitude or two from the state-of-the-art fusion machines. Innovations in fusion schemes are therefore required, especially for obtaining thrust for propulsive applications. Magnetized target fusion (MTF) is one of the innovative fusion concepts that have emerged over the last several years. MSFC is working with Los Alamos National Laboratory and other research groups in studying the underlying principles involved in MTF. Magnetized Target Fusion is an attempt to combine MCF (magnetic confinement fusion) for energy confinement and ICF (inertial confinement fusion) for efficient compression heating and wall free containment of the fusing plasma. It also seeks to combine the best features to these two main commonplace approaches to fusion.

Cylar, Rashad↗

DOE OSTI2019

Overview of the Recent BWR Burnup Credit Project at Oak Ridge National Laboratory

Oak Ridge National Laboratory (ORNL) and the US Nuclear Regulatory Commission (NRC) have completed a five-year program to investigate burnup credit (BUC) for boiling-water reactor (BWR) spent nuclear fuel (SNF) stored in storage and transportation systems. The project examined both peak reactivity BUC, also sometimes called gadolinium credit, and extended BWR BUC. Here extended refers to credit for burnups beyond that associated with peak reactivity. The findings related to peak reactivity BUC are summarized in NUREG/CR-7194, and four additional NUREG/CR documents present the results of the studies of extended BWR BUC. The first of these documents, NUREG/CR-7224, presents results of investigations to determine the effects of axial moderator density profiles, control blade use, and axial burnup profiles. Studies on the impact of core operating conditions and assembly-specific depletion conditions are addressed in NUREG/CR-7240, validation of depleted SNF isotopic predictions is addressed in NUREG/CR-7251, and validation of keff calculations for extended BWR BUC are discussed in NUREG/CR-7252. A summary of the entire project, including major conclusions regarding each of the studies, is included in this paper.

Marshall, William (B.J.)↗

DOE OSTI2020

Technical Interface Coordination with SHINE (FY2020 Summary)

In FY20, Los Alamos National Laboratory (LANL) performed technical interface coordination with SHINE including coordination of SHINE CFD and thermal hydraulics conference calls, national laboratory conference calls, and program management activities such as reporting and tracking requirements for current FY20 activities. SHINE did not request any general technology consultation support for emergent issues. LANL has participated in the bi-weekly conference calls with SHINE and other national laboratories regarding LANL’s current activities. Activities discussed include the Supo 3-D CFD model geometry validation, releasing the CFD-MCNP coupled codes for the generic solution vessel simulations, and the ANL bubble experiment #2 design, preparation, and collaboration.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2015

Th and U fuel photofission study by NTD for AD-MSR subcritical assembly

During the last decade a considerable effort has been devoted for developing energy generating systems based on advanced nuclear technology within the design concepts of GEN-IV. Thorium base fuel systems such as accelerator driven nuclear reactors are one of the often mentioned attractive and affordable options. Several radiotherapy linear accelerators are on the market and due to their reliability, they could be employed as drivers for subcritical liquid fuel assemblies. Bremsstrahlung photons with energies above 5.5MeV, induce (γ,n) and (e,e’n) reactions in the W-target. Resulting gamma radiation and photo or fission neutrons may be absorbed in target materials such as thorium and uranium isotopes to induce sustained fission or nuclear transmutation in waste radioactive materials. Relevant photo driven and photo-fission reaction cross sections are important for actinides {sup 232}Th, {sup 238}U and {sup 237}Np in the radiotherapy machines energy range of 10-20 MV. In this study we employ passive nuclear track detectors (NTD) to determine fission rates and neutron production rates with the aim to establish the feasibility for gamma and photo-neutron driven subcritical assemblies. To cope with these objectives a 20 MV radiotherapy machine has been employed with a mixed fuel target. Results will support further development for a subcritical assembly employing a thorium containing liquid fuel. It is expected that acquired technological knowledge will contribute to the Venezuelan nuclear energy program.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2026

Integration of Online Cross-Section Generation Capability with Depletion and Transient Solvers in Griffin

Griffin is a Multiphysics Object-Oriented Simulation Environment (MOOSE)-based reactor multiphysics analysis application jointly developed by Argonne and Idaho National Laboratories under the DOENE Nuclear Energy Advanced Modeling and Simulation (NEAMS) program. In FY25, an online crosssection generation capability based on the Self-Shielding Application Programming Interface (SSAPI) was demonstrated for TRISO-fueled reactor problems under steady-state conditions. This fiscal year, that capability was extended to support depletion and transient multiphysics calculations, enabling high-fidelity analyses that generate self-shielded cross sections on the fly from the actual evolving composition and temperature states rather than from pre-tabulated libraries. For depletion, a two-way coupling was established in which SSAPI computes compact-averaged self-shielded cross sections that the depletion solver then uses to advance the Bateman equations, with the updated compositions returned to SSAPI at each step; the depletion module was refactored to support both library-based and SSAPI-based cross sections, and additional logic was added to track daughter isotopes and to exclude minor isotopes for efficiency. For transient analysis, the SSAPI multigroup library was extended with the kinetics data required for time-dependent calculations, the Improved Quasi-Static (IQS) scheme was coupled with SSAPI, and several supporting capabilities were implemented, including a self-shielding treatment that lets control rods and drums move within a self-shielded model, which had previously been impossible and had ruled out rod- and drum-movement transients with on-the-fly cross sections altogether, a new mixing scheme for delayed-neutron precursor decay constants, a checkpoint-based restart workflow, and performance improvements such as pointwise cross-section interpolation and the bypassing of unnecessary Dancoff factor calculations. The implemented capabilities were verified against Serpent Monte Carlo solutions. For depletion, a prismatic pin-cell problem based on a Next Generation Nuclear Plant (NGNP) Very High Temperature Reactor benchmark showed excellent agreement, with eigenvalue differences within 200 pcm over the entire burnup range (up to 140 MWD/kgU) and fission-product and actinide inventories agreeing to within 0.8% and 2.5%, respectively; a heat-pipe microreactor assembly problem with a much higher fuel loading confirmed the same behavior and quantified the bias introduced when the multigroup equivalence effect is neglected. For transient analysis, a pin-cell problem with a step reactivity insertion and temperature feedback reproduced the analytically expected asymptotic power and showed close agreement between the direct and IQS solutions, and a two-dimensional microreactor core problem with control-drum rotation exercised the new moving-drum self-shielding treatment and demonstrated successful coupling of the online crosssection generation with both the direct and IQS transient methods. The capability was further exercised on a full-core pebble-bed problem, in which Griffin was coupled with the System Analysis Module (SAM) to simulate load-following operation of the gPBR with the Doppler feedback resolved at the TRISO fuel kernel temperature. These developments in Griffin provide a convenient, high-fidelity approach to cross-section generation for advanced thermal reactors with geometrically complex and highly heterogeneous configurations, including TRISO-fueled prismatic and pebble-bed systems, and support steady-state, depletion, and transient multiphysics calculations. They also enable self-shielded cross sections to be evaluated directly at the actual coupled state of the system, thereby establishing a foundation for high-fidelity, fully coupled multiphysics analysis of advanced reactors

Park, H.↗