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Advanced Modeling and Simulation Methods for Evaluation of Thermal Neutron Scattering Materials

Conference ·
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  1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
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With the rise of interest in thermal neutron scattering data for advanced reactor, criticality safety, and shielding applications, new experimental data are required for evaluation of new materials or for re-evaluation (or validations) of previously evaluated materials. New experimental data are evaluated in a three-step process: (1) computing the phonon characteristics, (2) computing the dynamic structure factor (DSF) from the data, and (3) using the experimental setup to simulate the experimental data. All three steps have challenges, ranging from the need for a sufficiently general material simulation code—a processing code that can compute the corresponding DSF—to having a detailed layout of the instrument/beamline/facility where the data were measured. Whereas phonon characteristics of materials can be computed using various methods (molecular dynamics, density functional theory, etc.), a high-fidelity computation of the DSF and the simulation of the experiment based on the DSF is vital to the accuracy of the evaluation. The latter two steps can be achieved by using the two corresponding code systems developed by instrument scientists at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory: (1) OCLIMAX, a program that calculates the dynamic structure factor from DFT and MD simulation results, and (2) MCViNE, a Monte Carlo neutron ray-tracing program designed to simulate neutron scattering experiments. Recently, polyethylene and yttrium hydride were measured at the Wide Angular-Range Chopper (ARCS) and SEQUOIA instrument stations of the SNS. These experiments are simulated using the density functional theory code, the Cambridge Serial Total Energy Package (CASTEP), to compute its phonon characteristics (eigenvalues/vectors and PDOS), which is then processed using OCLIMAX to yield the DSF, and finally the data at each instrument station are simulated by the MCViNE for comparison to the measured data for evaluation. For comparison to conventional evaluation methods, the scattering data processed from OCLIMAX are compared against those processed from the LEAPR module of NJOY, and the results from MCViNE simulations are compared against previously used simplified beamline models implemented in the Monte Carlo N-Particle (MCNP) code.

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
DOE Contract Number:
AC05-00OR22725
OSTI ID:
1994788
Report Number(s):
185621
Resource Relation:
Conference: 15. International Conference on Nuclear Data for Science and Technology (ND2022), Held Virtually, 21-29 Jul 2023; Related Information: https://indico.frib.msu.edu/event/52/overview
Country of Publication:
United States
Language:
English

References (8)

Validation of Thermal Scattering laws for Light Water at Elevated Temperatures with Diffusion Experiments journal January 2021
Methodology for Generating Covariance Data of Thermal Neutron Scattering Cross Sections journal September 2020
Methods for Processing ENDF/B-VII with NJOY journal December 2010
Simulation of Inelastic Neutron Scattering Spectra Using OCLIMAX journal January 2019
MCViNE – An object oriented Monte Carlo neutron ray tracing simulation package
  • Lin, Jiao Y. Y.; Smith, Hillary L.; Granroth, Garrett E.
  • Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 810 https://doi.org/10.1016/j.nima.2015.11.118
journal February 2016
FLASSH 1.0: Thermal Scattering Law Evaluation and Cross-Section Generation for Reactor Physics Applications journal April 2023
McStas, a general software package for neutron ray-tracing simulations journal January 1999
First principles methods using CASTEP journal January 2005

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Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
97 MATHEMATICS AND COMPUTING
Nuclear Criticality Safety Program (NCSP)
Thermal Neutron Scattering Data for Advanced Reactor
Criticality Safety
Shielding Applications
New Experimental Data
Evaluation of New Materials
Re-Evaluation
Dynamic Structure Factor (DSF)
Spallation Neutron Source (SNS)
OCLIMAX
Wide Angular-Range Chopper (ARCS)
SEQUOIA
Cambridge Serial Total Energy Package (CASTEP)
MCViNE
LEAPR Module of NJOY
Monte Carlo N-Particle (MCNP) Code