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Tag: Nuclear Physics & Engineering

  • Four-parameter model improves LBE heat-transfer prediction

    What the study found

    The study presents a four-parameter turbulence heat transfer model for liquid lead-bismuth eutectic (LBE) systems and a solver called LBEHMTFoam. The authors report that the model was validated against direct numerical simulation (DNS) data for planar flow heat transfer and then applied to LBE fuel assembly simulations.

    Why the authors say this matters

    The authors state that LBE is a coolant for fast reactors and that its low Prandtl number means a constant turbulent Prandtl number is difficult to use in complex turbulent heat transfer calculations. The study suggests that a more accurate model could be useful for predicting thermo-hydraulic coupled corrosion behavior in LBE systems.

    What the researchers tested

    The researchers systematically derived a four-parameter turbulence heat transfer model and its boundary conditions for a constant heat flux boundary. They implemented the model in the open-source CFD (computational fluid dynamics) software OpenFOAM and built the LBEHMTFoam solver. They then compared planar flow heat transfer simulations with DNS data and performed heat and mass transfer simulations for LBE fuel assemblies, comparing those results with empirical correlations.

    What worked and what didn't

    The abstract says the model was validated by agreement checks against DNS data, but it does not provide detailed numerical results in the summary. It also states that the model was used for LBE fuel assembly simulations, though specific improvements or failures are not described here.

    What to keep in mind

    The available summary does not give detailed performance metrics, error values, or a full accounting of limitations. It also does not specify how broadly the results apply beyond the planar flow validation and the LBE fuel assembly cases mentioned.

    • A four-parameter heat transfer turbulence model was derived for liquid lead-bismuth eutectic systems.
    • The model was implemented in OpenFOAM as a solver named LBEHMTFoam.
    • Planar flow heat transfer simulations were validated against direct numerical simulation data.
    • Heat and mass transfer simulations were also run for LBE fuel assemblies and compared with empirical correlations.
    • The authors say the approach is relevant for predicting thermo-hydraulic coupled corrosion behavior in LBE systems.

  • Uncertain neutron-capture data affect r-process abundance estimates

    What the study found

    The study found that uncertainties in s-process isotopic abundances can make some r-process residuals significantly uncertain. It also identified a short list of isotopes that are good candidates for improved neutron-capture measurements.

    Why the authors say this matters

    The authors conclude that refining key neutron-capture cross sections could improve the r-process isotopic abundance pattern used as a benchmark in stellar models of explosive nucleosynthesis. They also say the work provides a practical way to prioritize future experiments at CERN n_TOF, a neutron time-of-flight facility used for measuring neutron-capture reactions.

    What the researchers tested

    The researchers revisited how r-process residuals are derived by using updated solar abundances, s-process contributions, and a simplified approach to estimate uncertainty. They assumed that relative uncertainty in s-process isotopic abundances scales linearly with Maxwellian Averaged Cross Section (MACS) uncertainties from the KADoNiS data library.

    What worked and what didn't

    Using this approach, they identified a subset of isotopes for which the r-process residuals remain significantly uncertain. They also produced a short list of isotopes that they say are prime candidates for future (n,γ) measurements, where (n,γ) means neutron-capture reactions that emit gamma rays.

    What to keep in mind

    The abstract describes a simplified uncertainty treatment, so the results are framed as a practical prioritization rather than a full reanalysis. The available summary does not give the specific isotope list or detail any experimental outcomes.

    • Uncertainties in s-process abundance estimates propagate into r-process residuals.
    • The authors used updated solar abundances and published s-process contributions.
    • They linked abundance uncertainty to MACS uncertainties from KADoNiS.
    • A subset of isotopes was identified as having significantly uncertain r-process residuals.
    • The study proposes targets for future neutron-capture measurements at CERN n_TOF.

  • Snippet-based covariance estimation improves Feynman-α analysis

    What the study found

    The study found that a snippet-based algorithm can estimate the covariance information needed for Feynman-α analysis within practical limits of measurement time and computational resources. It also found that ignoring correlations between data points leads to unreliable uncertainty estimates for the alpha parameter.

    Why the authors say this matters

    The authors say this matters because Feynman-α analysis depends on fitting correlated data correctly, and the study suggests that a practical covariance estimate can make those fits reliable. They conclude that the method supports a more robust framework for analyzing data produced by the bunching technique.

    What the researchers tested

    The researchers examined Feynman-α analysis, where the variance-to-mean ratio Y(T) is computed for different bin sizes T from bunched neutron count data. They tested fitting approaches with and without the covariance matrix, and they proposed a new snippet-based algorithm using thinning and batching to estimate covariance from limited data.

    What worked and what didn't

    Uncorrelated fits that ignored the covariance matrix did not provide reliable estimates of alpha or its uncertainties, because the Y(T) points were significantly correlated. Fits that included an accurately estimated covariance matrix gave correct results for alpha and its uncertainties. The abstract also says synthetic data validated the method and that about 200 snippets yielded stable covariance estimates for reactor noise.

    What to keep in mind

    The abstract says that estimating the full covariance matrix directly from measurements requires extensive data and can take significant measurement time and computational effort. It also notes that theoretical estimation of the covariance matrix remains an open problem. No other limitations are described in the available summary.

    • The study says correlations in Feynman-α Y(T) data make uncorrelated fitting unreliable for alpha uncertainties.
    • Including an accurately estimated covariance matrix produced correct alpha and uncertainty estimates.
    • A new snippet-based algorithm was proposed to estimate covariance with practical time and computing demands.
    • Thinning and batching are reported to drastically reduce the amount of data needed for covariance estimation.
    • Synthetic data validated the approach, and about 200 snippets were reported as feasible for stable reactor-noise covariance estimates.

  • Full-resolution MSRE model matches benchmark and experimental trends

    What the study found

    The study found that a full-resolution multiphysics model of the Molten Salt Reactor Experiment can agree well with benchmark data and reproduce major experimental flow trends. The authors also report that it can capture three-dimensional flow structures that axisymmetric models do not represent.

    Why the authors say this matters

    The authors conclude that high-fidelity simulation techniques may help support reactor start-up procedures and digital-twin applications. They also suggest the model can be used to infer missing design data from experimental observations when some design parameters are uncertain.

    What the researchers tested

    The researchers built a full-resolution model of the Molten Salt Reactor Experiment, resolving the entire reactor vessel and internal structures without porous-media or axisymmetric approximations. They coupled Monte Carlo neutron-photon transport, a method for simulating particle behavior, with conjugate heat transfer and turbulent flow simulation on unstructured meshes, and iterated the model to convergence with temperature and density feedback.

    What worked and what didn't

    The predicted effective multiplication factor and power fractions showed good agreement with benchmark data. Velocity profiles in the volute, annulus, and core passages were compatible with experimental measurements and previous simulations within known uncertainties, and the model reproduced major experimental flow trends in the lower plenum. Some discrepancies remained, mainly due to input uncertainties and limitations of Reynolds-averaged Navier-Stokes (RANS) turbulence models under strong adverse pressure gradients.

    What to keep in mind

    The abstract notes that some inputs and operating conditions were uncertain, which affects interpretation of the comparisons. It also says the current discrepancies point to possible future extensions to large-eddy simulation (LES) turbulence modeling, but no further limitations are described in the available summary.

    • The model resolved the entire MSRE vessel and internal structures without porous-media or axisymmetric approximations.
    • Predicted effective multiplication factor and power fractions agreed well with benchmark data.
    • Velocity profiles in several reactor passages were compatible with experimental measurements and previous simulations within known uncertainties.
    • The model reproduced major lower-plenum flow trends and revealed three-dimensional structures missed by axisymmetric surrogates.
    • Remaining discrepancies were attributed mainly to input uncertainties and RANS-model limits under strong adverse pressure gradients.
  • Wave-like reactivity may explain Windscale criticality incident

    Wave-like reactivity may explain Windscale criticality incident

    What the study found

    The study found that a wave-like reactivity variation may have governed the Windscale Works criticality incident. The authors report that the short-duration inrush and the stable emulsion might both have influenced the criticality, with the effective multiplication factor exceeding 1 under some conditions.

    Why the authors say this matters

    The authors conclude that their findings support a hypothesis about the incident's criticality mechanism. They suggest this helps clarify a previously unclear criticality scenario by linking the event to time-varying reactivity, meaning changes in how readily a nuclear chain reaction can sustain itself.

    What the researchers tested

    The researchers performed a multiphysics analysis, combining computational fluid dynamics (CFD, computer simulations of fluid flow) with Monte Carlo neutron transport calculations. They examined the effects of a short-duration inrush and a stable emulsion, then used simplified wave-like reactivity variations in neutronic kinetics analyses.

    What worked and what didn't

    According to the abstract, the CFD results produced space- and time-dependent material distributions that were used to evaluate the effective multiplication factor. The results suggest that both the inrush and the stable emulsion might have contributed to conditions where the effective multiplication factor exceeded 1, and the simplified kinetics analyses were consistent with historical records under certain conditions.

    What to keep in mind

    The abstract describes a possible mechanism rather than a confirmed reconstruction of the incident. It also notes that the detailed criticality scenario remains unclear, and the compatibility with historical records is stated only for certain conditions.

    • The study proposes that a wave-like reactivity variation may have governed the Windscale Works criticality incident.
    • The analysis considered a short-duration inrush and a stable emulsion, which were not included in the previous study.
    • CFD results were used to create space- and time-dependent material distributions for neutron transport calculations.
    • The results suggest the effective multiplication factor may have exceeded 1 under some conditions.
    • Simplified neutronic kinetics analyses were consistent with historical records under certain conditions.

  • Four-parameter turbulence model improves lead-bismuth heat transfer prediction

    What the study found

    The study developed a four-parameter turbulence heat transfer model for liquid lead-bismuth eutectic (LBE) systems and a solver called LBEHMTFoam. The authors report that the model was validated against direct numerical simulation (DNS) data for planar flow heat transfer and then applied to LBE fuel assemblies.

    Why the authors say this matters

    The authors say LBE is a coolant with good thermo-hydraulic properties and chemical inertness for fast reactors, but its low Prandtl number and nonlinear local turbulent Prandtl number make constant-Prandtl-number approaches difficult for complex turbulent heat transfer. They conclude that more accurate prediction tools have significant engineering value and could be useful for predicting thermo-hydraulic coupled corrosion behavior in LBE systems.

    What the researchers tested

    The researchers systematically derived the four-parameter turbulence heat transfer model and its boundary conditions under a constant heat flux boundary. They implemented the model in the open-source CFD (computational fluid dynamics) software OpenFOAM as the solver LBEHMTFoam, then compared planar flow heat transfer simulations with DNS data and compared fuel-assembly heat and mass transfer simulations with empirical correlations.

    What worked and what didn't

    The abstract says the model's accuracy was validated by agreement with DNS data for planar flow heat transfer. It also says simulations for LBE fuel assemblies were compared with empirical correlations, but it does not provide specific numerical performance results in the abstract.

    What to keep in mind

    The available summary does not report detailed quantitative results, error measures, or limitations. It also does not specify how broadly the model applies beyond the tested planar flow case and the 19-pin fuel assembly context in LBE-cooled reactors.

    • A four-parameter turbulence heat transfer model was developed for liquid lead-bismuth eutectic systems.
    • The model was implemented in OpenFOAM as a solver named LBEHMTFoam.
    • Planar flow heat transfer simulations were validated against direct numerical simulation data.
    • Fuel-assembly heat and mass transfer simulations were compared with empirical correlations.
    • The abstract says the tool may be useful for predicting thermo-hydraulic coupled corrosion behavior in LBE systems.

  • Odd isotope selectivity in calcium was enhanced by polarization control

    What the study found

    The study found that odd-even isotope selectivity in calcium could be controlled with linearly polarized light in a resonance ionization scheme. In this setup, calcium-40, the abundant even isotope, was suppressed while calcium-43, a rare odd isotope, was selected.

    Why the authors say this matters

    The authors conclude that this relatively simple method may have application in separating rare odd calcium isotopes. They note possible relevance for quantum information via ion trapping for calcium-43, and for cosmology and biomedicine for calcium-41.

    What the researchers tested

    The researchers investigated odd-even isotope selectivity in calcium using a laser resonance ionization transition scheme with a J=0-1-0 transition. They used linearly polarized light and changed the polarization angle with a half-waveplate to apply angular momentum selection rules.

    What worked and what didn't

    Suppression of calcium-40 and selection of calcium-43 were confirmed as the linear polarization angle changed. The abstract says that setting transition polarizations to be linearly orthogonal forbids excitation of the even isotopes while allowing excitation of the odd isotope in the electric dipole basis. Spectroscopy in the Rydberg level transition also showed selectivity, with a reported maximum separation coefficient of 9e3, depending on the hyperfine transition.

    What to keep in mind

    The reported selectivity depends on the specific hyperfine transition. The abstract does not describe experimental limits beyond this dependence, and it does not give details on broader performance outside the tested calcium isotope transitions.

    • Linearly polarized light was used to control calcium isotope selectivity in resonance ionization.
    • Calcium-40 was suppressed while calcium-43 was selected.
    • Orthogonal transition polarizations were described as forbidding even-isotope excitation in the electric dipole basis.
    • A maximum separation coefficient of 9e3 was reported, depending on the hyperfine transition.
    • The authors say the method may be useful for separating rare odd calcium isotopes.

  • Passive safety systems handled the cold-leg LBLOCA case

    What the study found

    The study found that the cold-leg LBLOCA, a large-break loss-of-coolant accident in a cold-leg pipe, could be handled by passive safety systems in the SCW-SMR reactor concept. It also found that high-pressure injection was not required, while hot-leg steam blowdown was crucial.

    Why the authors say this matters

    The authors say the work helps determine the minimum set of safety systems required for this reactor concept. They also present it as part of the comprehensive assessment of the SCW-SMR design developed in the EU ECC-SMART project.

    What the researchers tested

    The researchers used an Apros system code model of the supercritical-pressure water-cooled small modular reactor, or SCW-SMR. They analyzed the 200% guillotine break of one cold-leg pipeline inside containment and examined cooling and flooding conditions in the reactor vessel flow path.

    What worked and what didn't

    Across 27 cases, the parameter analysis showed that passive safety systems were sufficient for the cold-leg LBLOCA event. High-pressure injection was not needed, but hot-leg steam blowdown was described as crucial. The abstract also says effective in-vessel heat removal was provided even without low-pressure injection.

    What to keep in mind

    The summary describes one initiating event in one reactor concept, so the results are limited to this case. The abstract does not provide detailed numeric outcomes, and it does not describe limitations beyond the scope of the 27 analyzed cases.

    • The study examined a cold-leg LBLOCA, a large-break loss-of-coolant accident, in the SCW-SMR concept.
    • The authors report that passive safety systems could handle the event.
    • High-pressure injection was not required in the analyzed cases.
    • Hot-leg steam blowdown was described as crucial.
    • Effective in-vessel heat removal was reported even without low-pressure injection.

  • Snippet-based covariance estimation improves Feynman-α uncertainty fitting

    What the study found

    The study found that accounting for correlations between binned count data is necessary for reliable Feynman-α analysis, where Feynman-α is a parameter used in reactor noise measurements. It also found that a new snippet-based algorithm can estimate the needed covariance information within practical measurement and computing limits.

    Why the authors say this matters

    The authors conclude that this approach makes it possible to fit correlated data from the bunching technique more accurately. They also state that it reinforces the theoretical basis of Feynman-α analysis and provides a robust framework for fitting such data.

    What the researchers tested

    The researchers examined Feynman-α analysis, using the bunching technique that combines smaller count bins into larger ones and produces a variance-to-mean ratio Y(T) for each bin size T. They compared uncorrelated fitting methods with fits that include a covariance matrix, and they proposed a snippet-based algorithm using thinning and batching to estimate covariance with less data. They also tested the method on synthetic data and considered feasibility for reactor noise measurements.

    What worked and what didn't

    Uncorrelated fits that ignore the covariance matrix did not give reliable uncertainty estimates because the Y(T) points were strongly correlated. Fits that included an accurately estimated covariance matrix gave correct results for alpha and its uncertainties. The new snippet-based method was reported to reduce the data needed for covariance estimation, and the abstract says about 200 snippets yield stable covariance estimates for reactor noise.

    What to keep in mind

    The abstract says that direct estimation of the full covariance matrix from real measurements requires extensive data, measurement time, and computational effort. It also notes that theoretical estimation of the covariance matrix remains an open problem. Limitations beyond these points are not described in the available summary.

    • Ignoring correlations in Y(T) led to unreliable uncertainty estimates for alpha.
    • Including an accurate covariance matrix produced correct alpha estimates and uncertainties.
    • A new snippet-based algorithm was developed to estimate covariance more practically.
    • Thinning and batching were reported to greatly reduce the data required.
    • The abstract says roughly 200 snippets were enough for stable covariance estimates in reactor noise.

  • First ab initio calculation of the fluorine-19 nuclear Schiff moment

    What the study found

    The study reports the first calculation of a nuclear Schiff moment, a measure related to violations of time-reversal and parity-inversion symmetry, for fluorine-19. It also reports that this work, combined with measurements on hafnium monofluoride cation, enabled the first experimental bound on the fluorine-19 nuclear Schiff moment.

    Why the authors say this matters

    The authors say nuclear Schiff moments are sensitive probes for physics beyond the standard model of particle physics. They conclude that this work establishes a foundation for constraining pion-nucleon-nucleon interactions using nuclear ab initio methods.

    What the researchers tested

    The researchers used a nuclear ab initio framework, specifically the no-core shell model, to study fluorine-19. They also carried out quantum-chemistry calculations to evaluate how sensitive hafnium monofluoride cation is to the fluorine-19 nuclear Schiff moment.

    What worked and what didn't

    The calculation produced the first nuclear Schiff moment result for fluorine-19 in this framework. Combined with recent high-precision measurements of the molecular electric dipole moment of hafnium monofluoride cation, it enabled the first experimental bound on the fluorine-19 nuclear Schiff moment. The abstract says the resulting bounds on the pion-nucleon-nucleon coupling constants are not yet the most stringent.

    What to keep in mind

    The abstract does not describe detailed limitations beyond noting that the pion-nucleon-nucleon coupling constant bounds are not yet the strongest. The summary available here is limited to fluorine-19 and hafnium monofluoride cation.

    • The paper reports the first nuclear Schiff moment calculation for fluorine-19.
    • The researchers used the no-core shell model, a nuclear ab initio method, for the calculation.
    • They also calculated the sensitivity of hafnium monofluoride cation to the fluorine-19 nuclear Schiff moment.
    • Combined with recent measurements, the work enabled the first experimental bound on the fluorine-19 nuclear Schiff moment.
    • The authors say the work lays a foundation for constraining pion-nucleon-nucleon interactions with nuclear ab initio methods.