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  1. The National Criticality Experiments Research Center and its role in support of advanced reactor design

    Thompson, Nicholas W. ; Maldonado, Alexis ; Cutler, Theresa E. ; ... - Frontiers in Energy Research
    The National Criticality Experiments Research Center (NCERC) located at the Nevada National Security Site (NNSS) in the Device Assembly Facility (DAF) and operated by Los Alamos National Laboratory (LANL) is the only general purpose critical experiments facility in the United States. Experiments from subcritical to critical and above prompt critical are carried out at NCERC on a regular basis. In recent years, NCERC has become more involved in experiments related to nuclear energy, including the Kilopower/KRUSTY demonstration and the recent Hypatia experiment. Multiple nuclear energy related projects are currently ongoing at NCERC. This paper discusses NCERC’s role in advanced reactormore » design and how that role may change in the future.« less

  2. Modeling of the Molten Salt Reactor Experiment with SCALE

    Bostelmann, Rike ; Skutnik, Steve ; Walker, Erik ; ... - Nuclear Technology
    A SCALE model was developed for the Molten Salt Reactor Experiment (MSRE) benchmark that was recently added to the International Handbook of Evaluated Reactor Physics Benchmark Experiments. This SCALE model served as a basis for criticality calculations and nuclear data sensitivity and uncertainty analyses with the Monte Carlo code Shift and the TSUNAMI computational capabilities in the SCALE code system. The focus of this work is the assessment of the impact of nuclear data on the calculated eigenvalue results in support of the discussion of differences between the calculated and the experimental eigenvalue result. The differences in the eigenvalues obtainedmore » using the ENDF/B-VII.0, ENDF/B-VII.1, and ENDF/B-VIII.0 nuclear data libraries cover a relatively small range of ~230 pcm. Since eigenvalue sensitivity of the MSRE is dominated by the neutron multiplicity and neutron capture of 235U and elastic scattering in graphite, relevant changes in the ENDF/B libraries for nuclear reactions (such as carbon capture) that caused large differences in other graphite-moderated systems did not have a significant impact. Propagation of nuclear data uncertainty results in an eigenvalue uncertainty of ~700 pcm with the major contributors being 235U neutron multiplicity, graphite elastic scattering, and 7Li neutron capture. All calculations resulted in large differences of ~2000 pcm in eigenvalue compared to the benchmark experimental value. Several potential contributors to this difference—including uncertainties and gaps in the knowledge of the material, geometry, and nuclear data—were identified. Simplified models of the full MSRE core were developed, and similarity assessments were conduced with the full MSRE core model. It was found that simplified models can serve as adequate surrogates of the full-core model such that they can be used for performing selected nuclear data performance assessments with a lower computational burden.« less

  3. Nuclear Data Sensitivity Study for the EBR-II Fast Reactor Benchmark Using SCALE with ENDF/B-VII.1 and ENDF/B-VIII.0

    Bostelmann, Friederike ; Ilas, Germina ; Wieselquist, William - Journal of Nuclear Engineering
    The EBR-II benchmark, which was recently included in the International Handbook of Evaluated Reactor Physics Benchmark Experiments, served as a basis for assessing the performance of the SCALE code system for fast reactor analyses. A reference SCALE model was developed based on the benchmark specifications. Great agreement was observed between the eigenvalue calculated with this SCALE model and the benchmark eigenvalue. To identify potential gaps and uncertainties of nuclear data for the simulation of various quantities of interest in fast spectrum systems, sensitivity and uncertainty analyses were performed for the eigenvalue, reactivity effects, and the radial power profile of EBR-IImore » using the two most recent ENDF/B nuclear data library releases. While the nominal results are consistent between the calculations with the different libraries, the uncertainties due to nuclear data vary significantly. The major driver of observed uncertainties is the uncertainty of the 235 U (n,γ) reaction. Since the uncertainty of this reaction is significantly reduced in the ENDF/B-VIII.0 library compared to ENDF/B-VII.1, the obtained output uncertainties tend to be smaller in ENDF/B-VIII.0 calculations, although the decrease is partially compensated by increased uncertainties in 235 U fission and ν ¯ .« less

  4. Reactor Physics Benchmark of the First Criticality in the Molten Salt Reactor Experiment

    Shen, Dan ; Ilas, Germina ; Powers, Jeffrey J. ; ... - Nuclear Science and Engineering

  5. Adaptive Reweighted Variance Estimation for Monte Carlo Eigenvalue Simulations

    Jin, Lei ; Banerjee, Kaushik - Nuclear Science and Engineering
    Monte Carlo (MC) simulation is used to solve the eigenvalue form of the Boltzmann transport equation to estimate various parameters such as fuel pin flux distributions that are crucial for the safe and efficient operation of nuclear systems (e.g., a nuclear reactor). Monte Carlo eigenvalue simulation uses a sample mean over many stationary cycles (iterations) to estimate various parameters important to nuclear systems. A variance estimate of the sample mean is often used for calculating the confidence intervals. However, MC eigenvalue simulation variance estimators that ignore the intercycle correlation underestimate the true variance of the estimated quantity. This paper presentsmore » novel data-adaptive approaches based on a simple autoregressive (AR) model and sigmoid functions to improve MC variance estimation. The standard MC sample-based variance estimator (or naïve estimator) and the spectral density–based MC variance estimator are enhanced by adding data-adaptive components that reduce their bias and improve performance. By investigating the frequency pattern of the AR(1) (order 1) model, two adaptive spectral estimators and one adaptive naïve estimator are proposed. The proposed estimators manifest superior performance when applied to three test problems compared to the standard spectral density–based estimator previously introduced by the authors. In conclusion, these new estimators are straightforward, as they use online algorithms and do not require storage of tallies from all active cycles.« less

  6. Using Machine Learning Methods to Predict Bias in Nuclear Criticality Safety

    Grechanuk, Pavel Aleksandrovi ; Rising, Michael Evan ; Palmer, Todd - Journal of Computational and Theoretical Transport
    The manuscript provides a description of the application of machine-learning (ML) tools to the prediction of bias in criticality safety analysis. In particular, a set of over 1000 experiments included in the Whisper package were fed into a variety of ML algorithms (notably Random Forest and AdaBoost) implemented in SciKit-Learn using k-eigenvalue sensitivities (with and without energy dependence) for individual nuclides, and optionally, the simulated keff as the training features. Ultimately, the ML model was used to predict the bias (ksim - kexp). The results indicate that use of energy-integrated sensitivity profiles with ksim as training features led to themore » best predictions as quantified by root-mean square and mean absolute errors. In particular, the best-case estimates came from AdaBoost, with a mean absolute error of 0.00174, which is less than the mean experimental uncertainty of 0.00328 for the experiments included.« less

  7. Improved search for heavy neutrinos in the decay π → e ν

    Aguilar-Arevalo, A. ; Aoki, M. ; Blecher, M. ; ... - Physical Review D
    In this study, a search for massive neutrinos has been made in the decay π+ → e+ν. No evidence was found for extra peaks in the positron energy spectrum indicative of pion decays involving massive neutrinos (π → e+νh). Upper limits (90 % C.L.) on the neutrino mixing matrix element |Uei|2 in the neutrino mass region 60–135 MeV/c2 were set, which are an order of magnitude improvement over previous results.

  8. A primer on criticality safety

    Costa, David A. ; Cournoyer, Michael E. ; Merhege, James F. ; ... - Journal of Chemical Health and Safety
    Criticality is the state of a nuclear chain reacting medium when the chain reaction is just self-sustaining (or critical). Criticality is dependent on nine interrelated parameters. Moreover, we design criticality safety controls in order to constrain these parameters to minimize fissions and maximize neutron leakage and absorption in other materials, which makes criticality more difficult or impossible to achieve. We present the consequences of criticality accidents are discussed, the nine interrelated parameters that combine to affect criticality are described, and criticality safety controls used to minimize the likelihood of a criticality accident are presented.

  9. Search for flavor-changing nonstandard neutrino interactions using $$\nu_{e}$$ appearance in MINOS

    Adamson, P. ; Anghel, I. ; Aurisano, A. ; ... - Phys.Rev.D
    We report new constraints on flavor-changing nonstandard neutrino interactions from the MINOS long-baseline experiment using νe and ν¯e appearance candidate events from predominantly νμ and ν¯μ beams. We used a statistical selection algorithm to separate νe candidates from background events, enabling an analysis of the combined MINOS neutrino and antineutrino data. We observe no deviations from standard neutrino mixing, and thus place constraints on the nonstandard interaction matter effect, |ϵeτ|, and phase, (δCP+δeτ), using a 30-bin likelihood fit.

  10. Search for Sterile Neutrinos Mixing with Muon Neutrinos in MINOS

    Adamson, P. ; Anghel, I. ; Aurisano, A. ; ... - Phys.Rev.Lett.
    We report results of a search for oscillations involving a light sterile neutrino over distances of 1.04 and 735 km in a νμ-dominated beam with a peak energy of 3 GeV. The data, from an exposure of 10.56×1020 protons on target, are analyzed using a phenomenological model with one sterile neutrino. We constrain the mixing parameters θ24 and Δm412 and set limits on parameters of the four-dimensional Pontecorvo-Maki-Nakagawa-Sakata matrix, |Uμ4|2 and |Uτ4|2, under the assumption that mixing between νe and νs is negligible (|Ue4|2=0). No evidence for νμ→νs transitions is found and we set a world-leading limit on θ24 for values ofmore » Δm412≲1  eV2.« less
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