Validation of Thermal Neutron Scattering Cross Sections for Heavy Water based on Molecular Dynamics Simulation

Haelee Hyun,Young-Ouk Lee,Do Heon Kim,O Serot,A Chebboubi

doi:10.1051/epjconf/201921106001

Abstract

Recently, the thermal scattering libraries of ENDF/B-VIII.0 and JEFF-3.3 for light and heavy water were released with a new water model (CAB model) proposed by Damian. For the CAB model, the molecular dynamics code GROMACS was used to more accurately describe the realistic motions of water molecules. In this paper, to consider the coherent component we also generated the thermal scattering cross section of the deuterium and oxygen bound in the heavy water molecules using the GROMACS code and EPSR code. In addition, the frequency spectrum was also calculated using the GROMACS code. Thermal scattering cross sections based on the newly calculated Sköld correction factor and the frequency spectrum were generated by NJOY2016 code. Finally, the performance of the generated thermal scattering cross sections were validated by performing an ICSBEP benchmark simulation using MCNPX code.

Highlights

Light and heavy water are two of the most important materials used as a moderator in thermal-neutron reactors
The solid line represents the continuous spectrum used in the thermal scattering cross section in ENDF/B-VIII.0, and the dotted line is the spectrum calculated by GROMACS in this paper
To take into account the coherent scattering cross section which is included in the scattering cross section of heavy water, we calculated the Skö ld correction factors of the deuterium and oxygen bound in heavy water molecules, using the molecular dynamics (MD) simulation with the GROMACS and EPSR code

Summary

Introduction

Light and heavy water are two of the most important materials used as a moderator in thermal-neutron reactors. The newly evaluated nuclear data files ENDF/B-VIII.0 and JEFF-3.3 have been released, which includes measurable improvements with respect to the thermal scattering libraries of light and heavy water. A new water model of the CAB model, which was developed at the Neutron Physics Department at Centro Ató mico Bariloche (CAB model) [1] has been applied in the thermal scattering libraries of ENDF/BVIII.0 and JEFF-3.3. The significant difference between the CAB model and existing models is that the CAB model was produced using a molecular dynamics (MD) simulation with GROMACS code [2] and NJOY code [3] which are comprehensive computer code packages for producing nuclear cross sections in the ENDF format. We generated the Skö ld correction factors and frequency spectra of deuterium and oxygen to generate a thermal scattering library for heavy water using GROMACS v.5.1.4. We generated the Skö ld correction factors and frequency spectra of deuterium and oxygen to generate a thermal scattering library for heavy water using GROMACS v.5.1.4. and EPSR (Empirical Potential Structure Refinement) code [5] and compared the results against an ICSBEP [6] benchmark simulation using the MCNPX 2.7.0 code [7]

Thermal scattering law for heavy water

GROMACS and EPSP code simulations

Frequency spectrum

Comparison of thermal scattering cross sections

Criticality benchmark problems

Conclusions