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All sources NASA NTRS DOE OSTI

DOE OSTI2022

Coupling coarse-mesh CFD with fine-mesh CFD for modeling molten-salt reactors in the Virtual Test Bed (VTB)

The Nuclear Energy Advanced Modeling and Simulation (NEAMS) program aims at developing a simulation tool kit to accelerate the development and deployment of nuclear power technologies. NEAMS multiphysics tools have been designed to provide numerical simulation support for the design and licensing of GEN IV reactors. Pronghorn is NEAMS's coarse-mesh computational fluid dynamics (CFD) tool, which is designed to run 3D core transients in GEN IV reactors at a reduced computational cost. To increase their accuracy, coarse-mesh CFD simulations require calibrated closure coefficients. One way of computing these coefficients is via the Nek5000, NEAMS's high-fidelity CFD tool. This article discusses our current research lines in informing Pronghorn closure coefficients via Nek5000 to enable multiphysics simulations of the core cavity of the molten-salt fast reactor. We present an application in which Pronghorn mixing length turbulent viscosity has been calibrated from Nek5000 simulations. The resulting Pronghorn thermal-hydraulics model is then coupled to Griffin, the NEAMS neutron transport solver, to solve for the steady-state configuration of the molten-salt fast reactor. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

DOE OSTI2020

As-Run Thermal Analysis for the CSM-10584 Experiment

The purpose of this document is to present the as-run specimen temperatures for the CSM-10584 experiment irradiated in position B-5 of the Advanced Test Reactor (ATR) for Cycles 164A and 164B.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

NASA NTRS1972

Measured drift of irradiated and unirradiated W3%Re/W25%Re thermocouples at a nominal 2000 K.

Seven tantalum sheathed, BeO insulated, 0.157-cm-diam, grounded-junction W-3%Re/W-25%Re thermocouples were irradiated in a helium-argon environment at a temperature of 1900 to 2100 K. Six other thermocouples from the same lot were operated out-of-pile with the same temperature history as the in-pile thermocouples. Drift-in-pile was determined by periodically replacing a 'reference' thermocouple in the irradiation capsule. Drift out-of-pile was determined with an optical pyrometer. After 8000 hours irradiation, the estimated neutron fluence was 4 x 10 to the 21st power thermal neutrons/sq cm and 0.9 x 10 to the 21st power fast neutrons/sq cm (E greater than 0.18 MeV). At this time the in-pile group had decreased in output the equivalent of 340 K at 2073 K, while the out-of-pile group had decreased in output the equivalent of 54 K at 2073 K. The maximum deviation in drift between thermocouples of the in-pile group and between thermocouples of the out-of-pile group was less than plus or minus 15 K and less than plus or minus 10 K, respectively.

Heckelman, J. D.↗

NASA NTRS1981

Spectroscopy from 2 to 200 keV

The astrophysical processes responsible for line and continuum emission in the spectra range 2 keV to 200 keV are examined from the viewpoint of designing a spectrometer which would operate in this regime. Phenomena considered include fluorescent line radiation in X-ray binaries, magnetically shifted iron lines and cyclotron emission from neutron star surfaces, line emission from cosmically abundant elements in thermal plasmas, and nuclear deexcitation lines in fresh nucleosynthetically produced matter. An instrument consisting of a approximately 10 sq cm array of planar germanium detectors surrounded by a large sodium-iodide anticoincidence shield is described and projected background rates and sensitivities are considered. A sample observing program for a two-day shuttle-based mission is included as an example of the wide range of scientific questions which could be addressed by such an instrument.

Helfand, D. J.↗

NASA NTRS1996

Infrared bolometers with silicon nitride micromesh absorbers

Sensitive far infrared and millimeter wave bolometers fabricated from a freestanding membrane of low stress silicon nitride are reported. The absorber, consisting of a metallized silicon nitride micromesh thermally isolated by radial legs of silicon nitride, is placed in an integrating cavity to efficiently couple to single mode or multiple mode infrared radiation. This structure provides low heat capacity, low thermal conduction and minimal cross section to energetic particles. A neutron transmutation doped Ge thermister is bump bonded to the center of the device and read out with evaporated Cr-Au leads. The limiting performance of the micromesh absorber is discussed and the recent results obtained from a 300 mK cold stage are summarized.

Bock, J. J.↗

NASA NTRS1998

Investigation and Feasibility Assessment of TOPAZ-2 Derivations for Space Power Applications

The ability to provide continuous power at significant levels is of utmost importance for many space missions, from simple satellite operations to manned Mars missions. One of the main problems faced in delivering solar or chemical space power in the tens of kW range, is the increasingly massive nature of the power source and the costs associated with its launch, operation and maintenance. A national program had been initiated to study the feasibility of using certain advanced technologies in developing an efficient lightweight space power source. The starting point for these studies has been the Russian TOPAZ-2 space reactor system, with the ultimate goal to aid in the development of a TOPAZ-2 derivative which will be ready for flight by the year 2000. The main objective of this project has been to perform feasibility assessment and trade studies which would allow the development of an advanced space nuclear power system based on the in-core thermionic fuel element technology currently used in the Russian TOPAZ-2 reactor. Two of the important considerations in developing the concept are: (1) compliance of the current TOPAZ-2 and of any advanced designs with U.S. nuclear safety expectations, and (2) compliance of the design with the seven years lifetime requirement. The project was composed of two major phases. The initial phase of the project has concentrated on understanding the TOPAZ-2 thermionic reactor in sufficient detail to allow several follow-on tasks. The primary interest during this first phase has been given on identifying the potential of the TOPAZ-2 design for further improvements. The second phase of the project has focused on the feasibility of a TOPAZ-2 system capable of delivering 30-50 kWe. Towards the elimination of single-point failures in the load voltage regulation system an active voltage regulator has been designed to be used in conjunction with the available shunt load voltage regulator. The possible use of a dual-loop, model-based adaptive control system for load-following in the TOPAZ-2 has also been investigated. The objective of this fault-tolerant, autonomous control system is to deliver the demanded electric power at the desired voltage level, by appropriately manipulating the neutron power through the control drums. As a result, sufficient thermal power is produced to meet the required demand in the presence of dynamically changing system operating conditions and potential sensor failures. The designed controller is proposed for use in combination with the currently available shunt regulators, or as a back-up controller when other means of power system control, including some of the sensors, fail.

Parlos, Alexander G.↗

DOE OSTI2020

BISON Capability, Validation and Demonstration for Reactivity-Initiated Accidents

Reactivity Initiated Accidents (RIA) are design basis accidents that could have adverse impacts on the core coolability. In the unlikely event that sufficient reactivity is inserted into the reactor core by the ejected/dropped control rod, prompt energy deposition into the fuel can occur, which when sufficiently high can lead to fuel rod failure or, at large energy deposition levels, expulsion of UO2 fragments or molten UO2 material from the fuel rod. This results in a release of fission product and fuel into the coolant and has the potential to compromise core coolability and threatening the pressure boundary of the primary coolant system. The design basis RIA is one of the industry challenging problems that the CASL aimed to address; the CASL RIA Challenge Problem Charter [1] states, ?The Pressurized Water Reactor (PWR) Rod Ejection Accident (REA) and Boiling Water Reactor (BWR) Control Rod Drop Accident (CRDA) are postulated accidents with consequences that are important to nuclear safety (fuel rod integrity and core coolability). Currently each reload core design must be analyzed to meet regulatory acceptance criteria. The goal of CASLs ModSim capability for RIA is to model the event at a higher fidelity, with validation to existing tests, to better model the transient neutronics and the progression of the fuel and cladding thermal-mechanical behavior. These improved analytical capabilities can be used to better inform reload core design, limits on fuel assembly discharge burnup, restrictions on placement of fuel in the reactor, control rod insertion limits, operating margin, and performance sensitivities.? In support of that charter, BISON, the fuel performance code has been used to demonstrate the simulation of thermal-mechanical behavior of LWR fuels during a reactivity-initiated accident. The combination of mechanical, thermal, and thermal-hydraulic phenomena all present during an RIA makes a multi-physics code such as BISON a valuable tool for modeling these scenarios. This paper will highlight many of the activities associated with BISON relevant to reactivity-initiated accident capability development and validation efforts. These efforts have been performed under both CASL and the Nuclear Energy Advanced Modeling and Simulation (NEAMS) programs.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2023

Validation of Pronghorn’s Subchannel code using the EBR-II shutdown heat removal tests

A Subchannel application (Pronghorn-SC) is developed in MOOSE, which affords the required flow field resolution, while still preserving an engineering-scale approach. This new solver can be natively coupled to Pronghorn and other MOOSE objects to enable full-core, multi-physics, multi-scale engineering studies. This work utilizes the EBR-II SHRT tests to validate the subchannel capabilities. Multi-scale and multi-physics coupling is used to improve the fidelity of the subchannel code calculations.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2022

Coupling coarse mesh CFD with fine mesh CFD for modeling for Molten Salt Reactors in the Virtual Test Bed VTB

The Nuclear Energy Advanced Modeling and Simulation (NEAMS) program aims at developing a simulation tool kit to accelerate the development and deployment of nuclear power technologies. NEAMS multiphysics tools have been designed to provide numerical simulation support for the design and licensing of GEN IV reactors. Pronghorn is NEAMS’s coarse-mesh computational fluid dynamics (CFD) tool, which is designed to run 3D core transients in GEN IV reactors at a reduced computational cost. To increase their accuracy, coarse-mesh CFD simulations require calibrated closure coefficients. One way of computing these coefficients is via the Nek5000, NEAMS’s high-fidelity CFD tool. This article discusses our current research lines in informing Pronghorn closure coefficients via Nek5000 to enable multiphysics simulations of the core cavity of the molten-salt fast reactor. We present an application in which Pronghorn mixing length turbulent viscosity has been calibrated from Nek5000 simulations. The resulting Pronghorn thermal-hydraulics model is then coupled to Griffin, the NEAMS neutron transport solver, to solve for the steady-state configuration of the molten-salt fast reactor.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2021

Astromers in the Radioactive Decay of r-process Nuclei

Certain nuclear isomers are well known to affect nucleosynthesis with important observable consequences (e.g., 26 Al and 180 Ta). We study the impact of nuclear isomers in the context of rapid neutron capture process (r-process) nucleosynthesis. Here we demonstrate that nuclear isomers are dynamically populated in the r process and that some are populated far from thermal equilibrium; this makes them astrophysical isomers, or "astromers." We compute thermally mediated transition rates between long-lived isomers and the corresponding ground states in neutron-rich nuclei. We calculate the temperature-dependent β-decay feeding factors, which represent the fraction of material going to each of the isomer and ground state daughter species from the β-decay parent species. We simulate nucleosynthesis following the decay of a solar-like r-process composition and include as separate species nuclear excited states with measured terrestrial half-lives greater than 100 μs. We introduce a new metric to identify those astromers most likely to be influential and summarize them in a table. Notable entries include many second peak nuclei (e.g., the Te isotopic chain) and previously overlooked isomers in stable nuclei (e.g., 119 Sn, 131 Xe, and 195 Pt). Finally, we comment on the capacity of isomer production to alter radioactive heating in an r-process environment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

NASA NTRSDate not supplied

Nuclear Thermal Propulsion Material Trade for Additively Manufactured Regenerative Chambers

Nuclear thermal propulsion (NTP) is a game changing technology with advantages over chemical propulsion systems for deep space missions but comes with many engineering challenges. This paper focuses on the challenge of material selection for a regeneratively-cooled chamber for use in a nuclear environment with minimal design margins. Chemical compatibility with reactants and products following energy extraction (be it through combustion or neutron bombardment) must be considered. Similarly, mechanical and thermophysical properties (e.g., density, thermal conductivity, yield strength, etc.) as functions of temperature are critical. While hydrogen embrittlement environment (HEE) is a risk and consideration for traditional chemical combustion chambers, application in a nuclear thermal engine adds additional material compatibility and resilience requirements to long-term nuclear radiation exposure. Chamber materials in this trade included, but were not limited to, A-286, Haynes 230, Haynes 282, CRES 347, GRCop-42, GRCop-84, Inconel 625, JBK-75, and NASA HR-1. The material trade focuses on modern additive manufacturing techniques and hypothetical geometric constraints.

Nuclear Thermal Propulsion↗

NASA NTRSDate not supplied

Nuclear Thermal Propulsion Material Trade for Additively Manufactured Regenerative Chambers

Nuclear Thermal Propulsion↗

NASA NTRS1976

The electron Boltzmann equation in a plasma generated by fission fragments

A Boltzmann equation formulation is presented for the determination of the electron distribution function in a plasma generated by fission fragments. The formulation takes into consideration ambipolar diffusion, elastic and inelastic collisions, recombination and ionization, and allows for the fact that the primary electrons are not monoenergetic. Calculations for He in a tube coated with fissionable material show that, over a wide pressure and neutron flux range, the distribution function is non-Maxwellian, but the electrons are essentially thermal. Moreover, about a third of the energy of the primary electrons is transferred into the inelastic levels of He. This fraction of energy transfer is almost independent of pressure and neutron flux but increases sharply in the presence of a sustainer electric field.

Hassan, H. A.↗

NASA NTRS1976

Electron distribution function in a plasma generated by fission fragments

A Boltzmann equation formulation is presented for the determination of the electron distribution function in a plasma generated by fission fragments. The formulation takes into consideration ambipolar diffusion, elastic and inelastic collisions, recombination and ionization, and allows for the fact that the primary electrons are not monoenergetic. Calculations for He in a tube coated with fissionable material shows that, over a wide pressure and neutron flux range, the distribution function is non-Maxwellian, but the electrons are essentially thermal. Moreover, about a third of the energy of the primary electrons is transferred into the inelastic levels of He. This fraction of energy transfer is almost independent of pressure and neutron flux.

Hassan, H. A.↗

DOE OSTI2025

Suppression of irradiation hardening in tungsten-coated ferritic steel for fusion reactor blanket applications

W-coated reduced activation ferritic steels have been developed for use as plasma facing components in fusion reactor blankets, offering excellent sputtering resistance and structural strength. Previous high-temperature coating methods, such as diffusion bonding and brazing, caused interfacial deterioration due to thermal stress from mismatched thermal expansion between W and reduced activation ferritic steel. To address this, underwater explosive welding was introduced as a high-velocity cold process that joins dissimilar materials while maintaining a strong, thin interface without the thermal issues associated with traditional methods. In this study, the effects of neutron irradiation on the hardness and microstructure in W-coated F82H reduced activation ferritic steel (W/F82H) joined by underwater explosive welding are investigated. Following neutron irradiation at 290 °C, irradiation hardening is suppressed in W, F82H, and their interface within the W/F82H material. Furthermore, microstructural observations indicate that the recovery of work hardening and relaxation of elastic strain introduced during coating significantly contribute to the suppression of irradiation hardening in W/F82H. In conclusion, W/F82H exhibits significantly suppressed irradiation hardening compared with those in stand-alone materials. This suppression is explained by residual stress from thermal expansion mismatch and the unique microstructure at the interface. These results provide valuable insights for the development of more durable materials in nuclear fusion applications.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Status Report on the Development of Cladding Inner-wall and Outer-wall Coatings

Advanced cladding is critical for nuclear reactors with enhanced performance in radiation tolerance, neutron transparency and reactor safety. Using advanced cladding will ensure the adequate thermal conductivity and mechanical stability of the cladding base material, corrosion resistance and high-temperature coolant compatibility of the cladding surface, and chemical stability in the cladding inner wall against fuel cladding chemical interaction (FCCI). An innovative cladding with a three-layer structure (i.e., a modified outer surface, a robust clad base material, and a modified inner wall) promises to meet all these requirements. In this status report, the initial efforts on the development of cladding inner-wall and outer-wall coatings are summarized. The activities covered in this report are (1) High-resolution TEM studies of TiN/HT-9 interface atomic structure and chemistry after ion irradiation, (2) High-resolution TEM studies of TiN/14YWT ODS interface atomic structure after thermal cycling, (3) Inner-wall TiN coating for an experimental 14YWT ODS cladding, and (4) Corrosion test of TiN coated Ziracloy-4 bar samples.

36 - MATERIALS SCIENCE↗

NASA NTRS2020

Residual Stress Measurements of Ni-base Superalloys through Neutron Diffraction

Linear friction welding (LFW) is being considered for joining single crystal to polycrystalline nickel-base alloys for advanced high temperature gas turbine disks. Unfortunately, the transient thermal cycle during the welding generates undesirable residual stresses. Additionally, upon thermal treatment to relieve these residual stresses the weld joints often crack. To understand this issue, state-of-the-art neutron diffraction was performed near weld joints to quantify the residual stresses created by varying linear friction weld conditions. The residual stresses were measured along three orthogonal axes in both the polycrystalline LSHR and single crystal SC-180 alloys. Residual stress measurements using a contour method were used to compare the calculations obtained by neutron diffraction. The results suggest high residual stresses can be successfully reduced using both pre- and post-weld processing steps. Moreover, the effect of grain size and pre-heat temperatures on the LFW process were explored.

Superalloys↗

DOE OSTI2026

Electric Field Control of Phonon Lifetimes and Thermal Conductivity in Relaxor-Based Ferroelectric

The demand for high energy efficiency drives intense interest in thermal-management technology. Phonons are a major contributor to heat transfer in solids and controlling them through external stimuli is a key challenge for thermal management due to their weak interactions with applied fields. We report significant changes in phonon transport with the application of an electric field over a broad temperature range in a relaxor-based ferroelectric using neutron-scattering and -transport measurements. Phonon lifetimes increase along the applied poling field and this results in a tripling of the thermal conductivity in that direction. We also observe a suppression of nanoscale antiferroelectric fluctuations along the poling direction and argue that this increases the phonon lifetimes. Our results highlight a promising yet underexplored route to realistic solid-state heat switching from electric-field-modified nanostructures altering the phonon lifetimes in disordered functional materials.

Phonons↗