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All sources NASA NTRS DOE OSTI

DOE OSTI2021

Greater committed warming after accounting for the pattern effect

Our planet’s energy balance is sensitive to spatial inhomogeneities in sea surface temperature and sea ice changes, but this is typically ignored in climate projections. Here, we show the energy budget during recent decades can be closed by combining changes in effective radiative forcing, linear radiative damping and this pattern effect. The pattern effect is of comparable magnitude but opposite sign to Earth’s net energy imbalance in the 2000s, indicating its importance when predicting the future climate on the basis of observations. Additionally, after the pattern effect is accounted for, the best-estimate value of committed global warming at present-day forcing rises from 1.31 K (0.99–2.33 K, 5th–95th percentile) to over 2 K, and committed warming in 2100 with constant long-lived forcing increases from 1.32 K (0.94–2.03 K) to over 1.5 K, although the magnitude is sensitive to sea surface temperature dataset. Further constraints on the pattern effect are needed to reduce climate projection uncertainty.

58 GEOSCIENCES↗

DOE OSTI2022

Methanol Decomposition on Copper Surfaces under Ambient Conditions: Mechanism, Surface Kinetics, and Structure Sensitivity

Here, we study the adsorption of methanol vapor under ambient pressure and temperature conditions on low-index Cu surfaces using surface-sensitive infrared (IR) and X-ray spectroscopy techniques. The first step of methanol decomposition, i.e. , breaking of the O—H bond to form surface-bound methoxy, readily occurs under ambient conditions. Time-lapse IR spectra clearly indicate a gradually decreasing methoxy coverage, which does not obey well established kinetic models. We rationalize the initial temperature-independent, high, nonequilibrium coverage of methoxy by a H-bonded methanol assembly in the precursor state. A temperature-dependent equilibrium coverage is achieved as the excess methoxy is eliminated gradually via further dehydrogenation to CO that desorbs to the gas phase. The kinetics of this process displays a significant structure sensitivity with considerably faster kinetics on the Cu(110) surface compared to Cu(111) and Cu(100) surfaces.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2025

Temperature-dependent characterization of large-area superconducting microwire array with single-photon sensitivity in the near-infrared

Superconducting nanowire single photon detectors (SNSPDs) are a leading detector technology for time-resolved single-photon counting from the ultraviolet to the near-infrared regime. The recent advancement in single-photon sensitivity in micrometer-scale superconducting wires opens up promising opportunities to develop large area SNSPDs with applications in low background dark matter detection experiments. Here, we present the first detailed temperature-dependent study of a 4-channel 1×1 mm 2 WSi superconducting microwire single photon detector (SMSPD) array, including the internal detection efficiency, dark count rate, and importantly the coincident dark counts across pixels. The detector shows saturated internal detection efficiency for photon wavelengths ranging from 635 nm to 1650 nm, time jitter of about 160 ps for 1060 nm photons, and a low dark count rate of about 10 -2 Hz. Additionally, the coincidences of dark count rate across pixels are studied for the first time in detail, where we observed an excess of correlated dark counts, which has important implications for low background dark matter experiments. The results presented is the first step towards characterizing and developing SMSPD array systems and associated background for low background dark matter detection experiments.

47 OTHER INSTRUMENTATION↗

DOE OSTI2026

Real-Time GPU-Accelerated OFDR With an Integrated Auxiliary Interferometer

A GPU-accelerated optical frequency domain reflectometry (OFDR) system with an improved integrated auxiliary interferometer is proposed. Unlike conventional approaches that require separate auxiliary interferometers and multiple detection channels, the proposed OFDR system embeds this functionality directly into the signal via an intentional beat component. This enables self-calibration of laser nonlinearity while maintaining a cost-effective hardware configuration. Building on this simplified configuration, the system leverages GPU acceleration with an NVIDIA RTX 4070 Ti to achieve real-time performance, delivering high-throughput signal processing for continuous OFDR interrogation. The signal processing pipeline comprises signal capture, resampling for nonlinearity compensation, and frequency shift computation, all optimized for parallel execution. Hardware benchmarking demonstrates substantial acceleration over CPU implementations, achieving up to a 45× speedup for resampling and frequency shift computations and enabling processing latencies below 30 ms. Thermal response validation is conducted under two complementary scenarios: localized heating using a water bath and cryogenic-temperature conditions using liquid nitrogen. Under localized heating, the system achieves an accuracy of 0.249 °C with a thermal sensitivity of 5.971 GHz/°C, while cryogenic-temperature validation demonstrates a frequency shift response with a sensitivity of 2.383 GHz/°C and an accuracy of 2.04 °C. The high acceleration of the proposed GPU-accelerated OFDR system and its accuracy are achieved by exploiting CUDA-based stride indexing, enabling efficient parallel segmentation and processing of large datasets without additional memory copies. The benchmarking results confirm the robustness, accuracy, and deployability of the proposed OFDR system across a wide temperature range, establishing it as a practical platform for real-time distributed fiber sensing in structurally dynamic environments.

Harb, Salah [Lawrence Berkeley National Laboratory↗

DOE OSTI2023

Thermo-acoustoelastic effect of Rayleigh wave: Theory and experimental verification

Previous studies showed that the thermally-induced ultrasonic bulk wave velocity change could be used to measure acoustoelastic coefficients and third-order elastic constants of elastic materials. This method is naturally immune from the ambient temperature effect and has improved sensitivity and a simpler test setup than the conventional acoustoelastic test. However, Rayleigh wave is preferred for thick components or structures with only one accessible surface. In this work, the thermo-hyperelastic constitutive equation, along with acoustoelastic theory, is used to derive the expression of the thermo-acoustoelastic coefficient (TAEC) of Rayleigh wave. The numerical relationship between the TAEC of Rayleigh wave and Murnaghan constants ( l, m and n ) are given for common metals. Further, the TAEC expressions for Rayleigh wave and shear wave are similar, and both are dominated by the constant m . The TAEC of Rayleigh wave was measured on an aluminum 6061 specimen using the thermal modulation experiment in a temperature range of 22 ~ 35°C. The measured TAEC shows good agreement with the theoretical calculation. Then the third-order elastic constants were calculated based on TAECs of bulk waves and Rayleigh wave.

42 ENGINEERING↗

DOE OSTI2020

Planck 2018 results

We analyse the Planck full-mission cosmic microwave background (CMB) temperature and E -mode polarization maps to obtain constraints on primordial non-Gaussianity (NG). We compare estimates obtained from separable template-fitting, binned, and optimal modal bispectrum estimators, finding consistent values for the local, equilateral, and orthogonal bispectrum amplitudes. Our combined temperature and polarization analysis produces the following final results: f NL local = -0.9 ± 5.1; f NL equil = -26 ± 47; and f NL ortho = -38 ± 24 (68% CL, statistical). These results include low-multipole (4 ≤ ℓ < 40) polarization data that are not included in our previous analysis. The results also pass an extensive battery of tests (with additional tests regarding foreground residuals compared to 2015), and they are stable with respect to our 2015 measurements (with small fluctuations, at the level of a fraction of a standard deviation, which is consistent with changes in data processing). Polarization-only bispectra display a significant improvement in robustness; they can now be used independently to set primordial NG constraints with a sensitivity comparable to WMAP temperature-based results and they give excellent agreement. In addition to the analysis of the standard local, equilateral, and orthogonal bispectrum shapes, we consider a large number of additional cases, such as scale-dependent feature and resonance bispectra, isocurvature primordial NG, and parity-breaking models, where we also place tight constraints but do not detect any signal. The non-primordial lensing bispectrum is, however, detected with an improved significance compared to 2015, excluding the null hypothesis at 3.5 σ . Beyond estimates of individual shape amplitudes, we also present model-independent reconstructions and analyses of the Planck CMB bispectrum. Our final constraint on the local primordial trispectrum shape is g NL local = (-5.8 ± 6.5) × 10 4 (68% CL, statistical), while constraints for other trispectrum shapes are also determined. Exploiting the tight limits on various bispectrum and trispectrum shapes, we constrain the parameter space of different early-Universe scenarios that generate primordial NG, including general single-field models of inflation, multi-field models (e.g. curvaton models), models of inflation with axion fields producing parity-violation bispectra in the tensor sector, and inflationary models involving vector-like fields with directionally-dependent bispectra. Our results provide a high-precision test for structure-formation scenarios, showing complete agreement with the basic picture of the ΛCDM cosmology regarding the statistics of the initial conditions, with cosmic structures arising from adiabatic, passive, Gaussian, and primordial seed perturbations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2026

Computationally inexpensive part-scale thermal history of additive friction-stir deposition

This study presents an analytical model for steady-state power generation and tool heat loss in additive friction-stir deposition (AFSD), developed to enable part-scale thermal simulation while remaining computationally inexpensive. The model predicts total generated power, yielding 3.7–4.7 kW across deposition temperature setpoints of 400–460 °C for the deposition of AA6061 with a Be-Cu tool. This corresponds to 90–95% of the reported spindle power. Tool heat loss is experimentally determined by calibrating a steady-state energy balance between the generated power, the substrate-deposition thermal gradient, and a temperature dependent tool heat loss term: q tool (T) = a + b (T - 400°C) with a = 2.7 x 10 6 Wm -2 and b = 9.5 x 10 3 Wm -2 K -1 . The calibration indicates that about 69% of the generated heat is conducted into the tool for this configuration, which is much higher than previously reported. The calibrated heat-source is implemented in finite element software (Adamantine) to simulate the transient thermal history of a 100 cm 3 representative build in 8 min on a standard desktop (at 0.635 mm build-height resolution). For the first three layers, the substrate temperatures between simulation and experiment are within 10% mean absolute percentage error. Sensitivity analysis indicates that uncertainties in average deposition temperature and deformation localization (stir-zone geometry, depth, and spatial dependance of strain-rate and flow stress) dominate model variance, motivating additional experimental verification.

Additive Friction-Stir Deposition↗

DOE OSTI2020

Pumped Thermal Electricity Storage with Supercritical CO2 Cycles and Solar Heat Input

Pumped Thermal Electricity Storage (PTES) is an energy storage device that uses grid electricity to drive a heat pump that generates hot and cold storage reservoirs. This thermal potential is later used to power a heat engine and return electricity to the grid. In this article, a PTES variant that uses supercritical carbon dioxide (sCO2) as the working fluid is introduced. sCO2-PTES cycles have higher work ratios and power densities than the systems based on ideal gases that have been investigated to date. Furthermore, sCO2- PTES cycles may achieve higher round-trip efficiencies for a given hot storage temperature (up to 78% at 560°C). The sensitivity of PTES cycles to loss factors such as isentropic efficiencies and temperature differences between the power cycle and storage fluid is investigated. A second concept whereby an sCO2- PTES cycle is integrated with concentrating solar power (CSP) is introduced. This concept ‘time-shifts’ the recompression of an sCO2 recompression cycle to a period of lower electricity prices and stores the heat. When solar heat is dispatched, the recompressor may be avoided as the required heat is obtained from storage, thereby leading to increased heat engine efficiencies. The net work output of this integrated system is 10-18% greater than the conventional recompression cycle. Combining PTES with a CSP power cycle is therefore shown to improve the dispatch of solar heat as well as providing electricity storage services.

41 EE - Solar Energy Technologies Office (EE-4S)↗

DOE OSTI2023

Effect of Temperature on Thrombogenicity Testing of Biomaterials in an In Vitro Dynamic Flow Loop System

To develop and standardize a reliable in vitro dynamic thrombogenicity test protocol, the key test parameters that could impact thrombus formation need to be investigated and understood. In this study, we evaluated the effect of temperature on the thrombogenic responses (thrombus surface coverage, thrombus weight, and platelet count reduction) of various materials using an in vitro blood flow loop test system. Whole blood from live sheep and cow donors was used to assess four materials with varying thrombogenic potentials: negative-control polytetrafluoroethylene (PTFE), positive-control latex, silicone, and high-density polyethylene (HDPE). Blood, heparinized to a donor-specific concentration, was recirculated through a polyvinyl chloride tubing loop containing the test material at room temperature (22–24°C) for 1 hour, or at 37°C for 1 or 2 hours. The flow loop system could effectively differentiate a thrombogenic material (latex) from the other materials for both test temperatures and blood species ( p < 0.05). However, compared with 37°C, testing at room temperature appeared to have slightly better sensitivity in differentiating silicone (intermediate thrombogenic potential) from the relatively thromboresistant materials (PTFE and HDPE, p < 0.05). These data suggest that testing at room temperature may be a viable option for dynamic thrombogenicity assessment of biomaterials and medical devices.

Engineering↗

DOE OSTI2025

Multidimensional Nova Simulations with an Extended Buffer and Lower Initial Mixing Temperatures

A classical nova is a thermonuclear runaway initiated on a white dwarf accreting solar-like material from its stellar companion. Once the white dwarf accretes enough mass, the pressure at the base of the accreted layer reaches a critical point, leading to the ignition of the hydrogen fuel at their interface. This paper presents a set of two-dimensional CO classical nova simulations with an extended buffer zone of a fixed low density and temperature between the top of the accreted layer and the upper boundary, allowing us to capture the thermonuclear outburst in the domain. Our domain reduces the role of the upper-outflow boundary condition that has affected previous simulations and allows us to explore the nucleosynthesis evolution in detail. We also study the effects of the initial temperature perturbation and buffer size to explore their sensitivity in our simulations. Finally, we start our simulations with a lower temperature at the base of the accreted layer ( 7 × 10 7 K ) than previous work, allowing us to capture mixing earlier in the evolution, reducing the effects of the mixing-length-theory assumptions. This allows for a more realistic description of convective transport in our models.

Smith Clark, Alexander (ORCID:0000000159611680)↗

DOE OSTI2021

Effect of heat treatments on superconducting properties and connectivity in K-doped BaFe2As2

Abstract Fe-based superconductors and in particular K-doped BaFe 2 As 2 (K-Ba122) are materials of interest for possible future high-field applications. However the critical current density ( J c ) in polycrystalline Ba122 is still quite low and connectivity issues are suspected to be responsible. In this work we investigated the properties of high-purity, carefully processed, K-Ba122 samples synthesized with two separate heat treatments at various temperatures between 600 and 825 °C. We performed specific heat characterization and T c -distribution analysis up to 16 T and we compared them with magnetic T c and J c characterizations, and transmission-electron-microscopy (TEM) microstructures. We found no direct correlation between the magnetic T c and J c , whereas the specific heat T c -distributions did provide valuable insights. In fact the best J c -performing sample, heat treated first at 750 °C and then at 600 °C, has the peak of the T c -distributions at the highest temperatures and the least field sensitivity, thus maximizing H c2 . We also observed that the magnetic T c onset was always significantly lower than the specific heat T c : although we partially ascribe the lower magnetization T c to the small grain size (< λ , the penetration depth) of the K-Ba122 phase, this behaviour also implies the presence of some grain-boundary barriers to current flow. Comparing the T c -distribution with J c , our systematic synthesis study reveals that increasing the first heat treatment above 750 °C or the second one above 600 °C significantly compromises the connectivity and suppresses the vortex pinning properties. We conclude that high-purity precursors and clean processing are not yet enough to overcome all J c limitations. However, our study suggests that a higher temperature T c -distribution, a larger H c2 and a better connectivity could be achieved by lowering the second heat treatment temperature below 600 °C thus enhancing, as a consequence, J c .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Techno-Economic Analysis of a Nuclear Reactor System coupled with a Liquid Metal Battery

There is a need for nuclear reactor systems to become more dynamic as defossilization and renewable energy sources continue to reshape the energy grid. One option to meet these changing demands is to pair the reactor with an energy storage system. This work details a technoeconomic analysis and sensitivity analysis of a high temperature gas cooled microreactor, supercritical carbon dioxide power cycle, and liquid metal battery. Dynamic modeling has shown that these three systems compliment each other to provide load following and black-start capabilities to the grid. Current cost estimates for installing the systems yield a competitive levelized cost of electricity and levelized cost of storage, indicating that such a combined system may be economically viable as technological advances lead to them being technically feasible.

25 ENERGY STORAGE↗

DOE OSTI2021

Online Monitoring System for Concrete Structures Affected by Alkali-Silica Reaction

This report presents a comprehensive study of developing ultrasonic wave and acoustic emission (AE) techniques for long-term monitoring of alkali-silica reaction (ASR) development in concrete. Small, medium, and full-scale concrete specimens were cast, conditioned, and monitored for various periods, from at least one year to 2.4 years. The reactive concrete specimens contain coarse or fine reactive aggregates to study the effects of different types of reactive aggregates. Confinements were also designed to simulate the 2-dimensional confinement effects of reinforcement in the shield building of nuclear power plants. The concrete specimens were stored in a environmental chamber with high humidity and high temperature to accelerate the ASR development. The ultrasonic monitoring data shows high sensitivity to ASR development and could detect cracking initiation well before visible surface cracks occurred. However, the linear ultrasonic analysis based on wave velocity is strongly affected by temperature variation. Therefore, a nonlinear ultrasonic method was proposed to measure thermally induced nonlinear acoustic responses of concrete (thermal modulation of ultrasonic wave). The measured nonlinear acoustic parameter shows a high correlation with ASR expansion across specimens with different reactive aggregates and confinement conditions. The same conclusion was obtained from nonlinear resonance tests on small concrete prisms. Compared to the linear acoustic methods, the nonlinear tests show high sensitivities to ASR damage from internal microcracking initiation at the early stage to visible cracks at the late stage of ASR. The attributes of the thermal modulation of nonlinear ultrasonic method include high sensitivity, immunity to temperature effects, and strong correlation with ASR expansion, which demonstrate great potentials of the nonlinear ultrasonic method for diagnosis of ASR damage and prediction of concrete deterioration process. Acoustic emission is a passive sensing technique for damage assessment, and access to only one surface is needed even for thick and heavily reinforced elements such as the walls utilized for nuclear shield building. Additionally, relatively few sensors are required to monitor the progression of the damage process. Results indicate that the AE data can be related to the damage rating index, which is a petrography-based means of assessing damage due to ASR in reinforced concrete. Furthermore, AE is capable of detecting ASR damage long before surface cracking is visually noticeable. Boundary conditions play in important role in the progression of ASR damage and differences in boundary conditions are reflected in the AE data. Entropy based data assessment methods provide a means to assess the damage state, and convolutional neural network based data assessment provided a means to assess the damage state in real-time. Results indicate that artificial neural network models may be used as a means to predict volumetric expansion based on AE data.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2022

Numerical study of pure rotational fs/ps CARS coherence beating at high pressure and for multi-species rotation-vibration non-equilibrium thermometry

Coherent anti-Stokes Raman scattering (CARS) has long been the gold standard for non-intrusively measuring gas temperature in reacting flows such as flames and plasmas. Recently, the development of ultrafast hybrid fs/ps CARS has enabled the exploitation of coherence beating between neighboring spectral lines to simultaneously measure rotational and vibrational temperatures from a single pure rotational spectrum. However, the influence of non-Boltzmann vibrational state distributions and limitations due to collisional dephasing at pressures greater than 1 atm remains unclear. In this work, we use spectral simulations to investigate the effects of non-Boltzmann vibrational state distributions and the applicability of coherence beating at pressures up to 10 atm. We show that short probe pulses can be leveraged to quantify non-Boltzmann vibrational state distributions of N2. Furthermore, we demonstrate that fs/ps CARS coherence beating can simultaneously provide sensitive measurements of rotational and vibrational temperatures of both O2 and N2 in air. A sensitivity analysis was conducted to qualitatively explain the accuracy and precision comparisons between probe delays.

Chen, Timothy Y. (ORCID:0000000330269767)↗

DOE OSTI2022

Non-invasive, in situ diagnosis and monitoring of corrosion in high temperature systems

Techniques for non-invasive diagnosis and/or monitoring of corrosion in high temperature systems using specialized sensors that produce multi-mode acoustic signals in situ for accurate determination of wall loss and/or physical property changes for a vessel in contact with a high temperature, highly corrosive substance are disclosed. Sensitivity of a few microns (or about 0.1%) of wall loss, detection of changes in physical properties of vessel contents (e.g., approximately 1%), or both, at temperatures of 500° C., 600° C., or higher may be realized. Corrosion may be identified and/or monitored using time domain, frequency domain, or mixed time domain and frequency domain analysis of signal characteristics, signal delay, or both, for relatively short circumferential acoustic wave propagation (e.g., a few inches), as well as relatively long axial acoustic wave propagation (e.g., tens of feet).

Findikoglu, Alp Tugrul↗

DOE OSTI2022

Command of active and responsive elastomers by topological defects and patterns

The project resulted in the development of stimuli-responsive elastomer coatings formed by photopolymerized liquid crystal molecules. The molecular orientation of the liquid crystal elastomers is coupled to rubber-like elasticity. The project developed an approach to produce complex patterns of molecular orientation in elastomers by employing photopatterning technique based on plasmonic metamasks that convert unpolarized incoming light into a transmitted light beam with spatially-varying linear polarization. The polarization-modulated light beam aligns the film of azodye molecules, which serves as the substrate for liquid crystal elastomer coating. The alignment of the azodye molecules follows the polarization pattern with a phase shift of the alignment direction by 90 degrees. The azodye substrate imposes orientation of molecules in the adjacent liquid crystal layer which is preserved after the monomers are polymerized into a liquid crystal elastomer. By using differently aligned substrates one could produce various patterns of molecular orientation in the elastomer, which dictate the mechanical properties of the elastomers and their response to external stimuli such as temperature, humidity, and ultraviolet irradiation. In particular, the predesigned molecular orientation produces deterministically defined topography response of the liquid crystal coatings, in which their free surface changes from flat to either locally elevated or locally compressed, depending on whether the pre-inscribed molecular orientation is predesigned with a splay or bend deformation. The research established that the mechanism of this deterministic relation between the dynamic topography and pre-inscribed molecular orientation is rooted in the change of the tensorial order parameter that characterizes the degree of orientational order, and in the contraction/expansion of polymer molecules in response to the order parameter changes. In particular, lowering the order causes contraction of polymer globules. The work demonstrated that the dynamic topography of elastomer coatings with three-dimensional pattern of orientational order includes up and down motion of the material (along the normal to the coating) and also shifts in lateral directions. We demonstrate that the deterministic relationship between the orientational patterns and variations of coatings’ profile is caused by forces that are mathematically equivalent to active forces in the system of “pullers” or “pushers” in active matter, demonstrating universality of the out-of-equilibrium behavior. The project resulted in theoretical models that predictively describe the dynamic response of coatings. The topography of liquid crystal elastomers is sensitive to stimuli such as temperature, ultraviolet irradiation, and humidity. The applicability of the patterned approach to produce dynamic coatings was expanded from nematic elastomers to their smectic counterparts. The project combined a battery of imaging techniques to unveil the dynamic properties of the coatings, ranging from the state-of-the-art dynamic holographic microscopy to fluorescent confocal polarizing microscopy and polscope microscopy. The research uncovered potential applications of dynamic elastomer coatings, such as control placement of colloidal particles, engineering of living tissues with alignment patterns of cells that follow the orientational order of elastomer coatings. The approach developed in the project can be used to design programmable dynamic coatings with functionalities that mimic biological tissues such as skin.

36 MATERIALS SCIENCE↗

DOE OSTI2020

NMDQi Thermal-hydraulic Optimization, Analysis, and Scoping Tool (TOAST)

The Thermal-hydraulic Optimization, Analysis, and Scoping Tool (TOAST) is developed to support the thermal-hydraulic aspects for the design of optimal irradiation vehicles for the Nuclear Materials Discovery and Qualification initiative (NMDQi). TOAST is currently a MATLAB-based tool that utilizes a simplified steady-state analytical model where a radial thermal resistance circuit is utilized to account for conduction through up to 2 capsules, a gas gap, a thermal bond, a sample cladding, and a sample, as well as the convection from a water coolant outside the capsules. The geometry is discretized axially along the user-defined height of a basket with a user-defined number of points/nodes, essentially turning TOAST into a semi-2D heat transfer analysis utility for cylindrical irradiation vehicles with practically any configuration, solving for temperatures radially at multiple axial locations. TOAST utilizes a Graphical User Interface (GUI) in-which a user can define the geometrical layout, the materials utilized for each component, the coolant characteristics, and the required solution. The user can define the geometry by inputting the diameters, thicknesses, and heights for each component, whereas the materials are defined via the user-provided constant or variable thermal conductivities. The user can select the coolant's inlet temperature, pressure, and the pressure drop across the height of the problem (which is used to calculate the velocity of the flow). Finally, the user can choose to solve for a sample heat generation rate limit by inputting temperature limits for the sample and capsules or can choose to purely solve for the axial temperature distributions of each component by inputting a pre-selected heat generation rate. Either way, TOAST provides the user with axial temperature distributions of all the components including the coolant, and the heat generation rate limit as well as the maximum outlet coolant temperature. The user can also choose to do one of 6 sensitivity analyses in TOAST. The sensitivity analyses yield plots of the sensitivity of the heat generation rate limit, the maximum coolant temperature, and the pressure limit for the annular components due to perturbations in 1-2 unknown variables based on the selected sensitivity analysis. Benchmarks between computations in TOAST and equivalent 2D axis symmetric ABAQUS models are presented, showing that TOAST results are within less than 3% of ABAQUS results in most cases, and a maximum of 8% difference in some cases. The benchmarks also revealed that this uncertainty is tied to the selection of an appropriate Nusselt number correlation and appropriate thermal conductivities, which the user can do from the GUI. Regardless, TOAST is demonstrated as a computationally efficient, highly accessible, and accurate utility for optimization and scoping s of studies different irradiation vehicles.

42 ENGINEERING↗

DOE OSTI2022

Initial study on cross-section generation requirements for a PBR equilibrium core

A Serpent model of the equilibrium core HTR-PM small modular nuclear reactor in China, was developed for use in cross-section preparation studies in order to guide methods development for the Griffin reactor multiphysics application. The model includes detailed isotopics for 10 distinct pebble burnup groups in 126 core zones with unique fuel and moderator temperatures obtained from a coupled neutronics-thermal-fluids equilibrium core calculation using Griffin-Pronghorn. A sensitivity study of the fuel and moderator temperatures for various core regions was performed with the MOOSE stochastic tools. The results show that the uncertainties are, not unexpectedly, dominated by the value of the fluid temperature and that the power level, heat transfer coefficient and effective conduction to neighboring pebbles and fluid constitute, at best, second order effects. The temperature uncertainty range varies from 28 K to 57 K between the core entry and exit planes, respectively, but these values are probably higher. We still have to quantify the significance of these uncertainties in the preparation of cross-sections in future work. In addition, we verified that the effective pebble approximation used in the PEBBED and V.S.O.P. computer codes works well for the preparation of region averaged cross-sections. Nevertheless, there are some discrepancies in the cross-sections when compared to the multi-pebble model, which could affect the prediction of peak values and the depletion calculation. We conclude that is highly desirable for future studies with Griffin to be able to handle both the 'effective' pebble approximation and the multi-pebble approach for various pebble burnup groups. This enables Griffin users with the flexibility to perform higher-fidelity studies. Finally, we initiated the preparation of cross-sections for various core regions from the full core Serpent reference model. We quantified the differences in 26 group cross-sections from infinite domain models versus the full core approach. These reference cross-sections will serve to verify the double heterogeneity, self-shielding, and spectrum-correction methods in Griffin. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗