Polaris Depletion Calculations: Selected Best Practices [Slides]
Abstract not provided.
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Results for “Criticality Safety”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Calculation of Spent Fuel Pool Time-to-Boil using Polaris/ORIGAMI [Slides]
The goal of this experiment was to calculate time-to-boil (TTB) for a Spent Fuel Pool (SFP). TTB is important for SFP management that represents the amount of time available to address loss of forced cooling. Researchers calculated and compared TTB for two cases using SCALE: SFP containing representative LEU fuel (≤ 5 wt %) and SFP containing representative LEU+ fuel (5 – 8 wt %). There were approximately 2300 fuel assemblies in the SFP for each case. Researchers concluded that the impact of LEU+ core on time-to-boil is very small. At such low cooling times, the impact of increased decay heat is not significant. Decay heat of SFP assemblies is small compared to discharge core decay heat.
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Illustration of Neutronic Decoupling in Fresh Fuel Storage Environments [Slides]
Operations beyond static storage of fuel assemblies occur in SFPs (moving around the pool, inspection, etc.). These assemblies are assumed suitably distanced at 30 cm. When assemblies are separated by enough water, the neutrons from one cannot cause fission in another, which results in neutronic decoupling. This assumption was investigated for PWR and BWR assemblies as part of ORNL-TM/2021/2330.
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Criticality and Radiation Shielding Impacts of ENDF/B-VIII.0 [Slides]
Several impacts of ENDF/B-VIII.0 on Radiation Shielding Applications were observed by researchers. Most reaction rates, attenuation ratios, and dose rates are similar for ENDF/B-VII.1 and ENDF/B-VIII.0. A significant reduction in reactor dosimetry results was noted. Investigation continues to reveal underlying data for discrepancies.
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SCALE Sensitivity Tutorial [Slides]
In sensitivity analysis, we seek to quantify the degree to which fundamental data (i.e., nuclear data) influence a system’s response. In uncertainty analysis, we seek to quantify the degree to which uncertainty in fundamental data contributes to uncertainty in a system’s response. In SCALE, the TSUNAMI suite provides tools for sensitivity and uncertainty analysis, similarity analysis, and nuclear data and covariance adjustment.
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ORNL Neutron Cross Section Measurements of 90 Zr [Slides]
Abstract not provided.
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Isotope Effects in Thermal Neutron Scattering [Slides]
AMPX links Thermal Scattering Law (TSL) libraries to isotopes in the resolved resonance region. No guidance is given in the TSL files or the ENDF format if this is acceptable or advised, which can lead to issues for researchers.
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Cumulative χ 2 Metric for VALID for ENDF/B-VII.1 and ENDF/B-VIII.0 in SCALE 6.3b9 [Slides]
Quantifying the performance of a new evaluation is difficult and doing so for a new library is significantly more challenging. Cumulative χ 2 metric is an established approach to comparing distributions. In this case, C/E results from different libraries. Andrei Trkov and Roberto Capote have published cumulative χ 2 results for ENDF/B-VIII.0. Cumulative χ 2 metric was recently calculated for VALID library maintained at ORNL.
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American Nuclear Society Standards Committee Subcommittee 8 Meeting [Slides]
The agenda for this meeting includes an agenda discussion, ballot report/standard status report, subcommittee projects, and new business.
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American Nuclear Society ANS-8 Standards Forum [Slides]
The agenda for this forum includes an agenda discussion, membership discussion, a review of recent SC-8 & NCSCC ballots, ISO TC85/SC5/WG8 standards activity report (D. Bowen), NCSCC activity report (L. Wetzel), reports from working group chairs, and old/new business.
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Bayesian Monte-Carlo Evaluation Framework for Imperfect Nuclear Data [Slides]
BMC evaluation is a tool used to address imperfect data and models, non-linear models, and non-normal PDFs. ENDF-6 format does not allow non-normal parameter PDFs. Storing posterior sets allows for variance, covariance, skewness, etc. To better predict criticality, we should document non-normal parameter PDFs (i.e. asymmetric uncertainty) and consider non-linear sensitivity of $k_{\text{eff}}$ to resonance parameters.
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Temperature Dependent Experiments using SPRF/CX [Slides]
A range of fuel arrays has been examined for both fuel types and representative arrays were selected. Temperature dependent calculations were performed to show the performance of the arrays. Modification to the SPRF/CX facility has been proposed to aid SNL staff in the execution of temperature dependent experiments.
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Bayesian Monte-Carlo Framework: New Methods for Resonance Parameter Evaluation [Slides]
BMC evaluation is a tool to address imperfect data & models, non-linear models, and non-normal PDFs. ENDF-6 format does not allow non-normal parameter PDFs. Storing posterior sets allow for variance, covariance, skewness, etc. To better predict criticality, we could document non-normal parameter PDFs (i.e. asymmetric uncertainty), consider non-linear sensitivity of $\kappa$ eff to resonance parameters, and reduce uncertainty in key resonance parameters.
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Updates to the n+ 63,65 Cu Angular Distributions for Critical Experiments [Slides]
This work updates the evaluation of n+ 63,65 Cu for neutron energies in the resolved resonance region (RRR) and slightly higher energies. The updates strive to improve the statistical properties of the resonance parameters and the continuity of the evaluation between the RRR and the high-energy region while preserving or improving critical assembly benchmark performance. We will review our work on the resonance parameters and present the current status of our angular distribution analysis.
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ORNL Neutron Cross Section Measurements of 90 Zr NCSP ND-1 Task [Slides]
Luiz Leal's idea to integrate the experimental uncertainties, covariances, and sensitivities in this workflow and centralize the process at one location led to the creation of a cohesive tool for data testing. It has been practiced for more than two decades by the NCS and ND groups at ORNL. The development and use of the ORNL codes TSUNAMI and TSURFER within SCALE made it possible. Today, it has been extended to SAMINT which enables the coupling of differential and integral data evaluation in a continuous-energy framework.
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Advances in Nuclear Data Evaluation Theory for NCSP [Slides]
The generalized form of the Bayes’ Theorem improves UQ for NCSP of differential and/or integral data evaluations and of applications. It is being implemented in an API for use by SCALE, SAMMY, etc. Extended R-matrix formalism improves evaluations of RRR including direct reactions, direct capture, and the Reich-Moore approx., doorway state reactions with applications to RPI data on lead isotopes. Extended R-Matrix formalism will be implemented into SAMMY post modernization.
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FY 21 ORNL Integral Experiment Work [Slides]
Abstract not provided.
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Resolved Resonance Region Evaluation of n+ 140,142 Ce [Slides]
ORNL has completed new resolved resonance region (RRR) evaluations for 140,142 Ce, which were carried out using Reich-Moore formalism instead of MLBW. Lack of integral measurements makes validation difficult, but difference from Kadonis values suggest more investigation of capture cross section are warranted. The complete file (with updated File2 & File32) was submitted to NNDC repository for inclusion in next release of ENDF. Sponsor report and journal publication are in progress.
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