High-resolution neutron time-of-flight measurements for light water at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory

Luiz Leal,Alexander I Kolesnikov,Vaibhav Jaiswal

doi:10.1051/epjconf/202023914005

Luiz Leal, Alexander I Kolesnikov + Show 1 more

Open Access

https://doi.org/10.1051/epjconf/202023914005

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Abstract

Series of light water inelastic neutron scattering experiments have been made at the Oak Ridge National Laboratory (ORNL), Spallation Neutron Source (SNS) covering temperatures ranging from 295 K to 600 K and pressures of 1 bar and 150 bar. The temperatures and pressures ranges correspond to that of pressurized light water reactors. The inelastic scattering measurements will help the development of light water thermal scattering kernels, also known asS(α,β) thermal scattering law (TSL), in a consistent fashion given the amount and the quality of the measured data. Light water thermal scattering evaluations available in existing nuclear data libraries have certain limitations and pitfalls. This paper introduces the state of the art of the light water thermal scattering cross-section data not only for room temperature but as well as for reactor operating temperatures, i.e. 550 - 600 K. During the past few years there has been a renewed interest in re-investigating the existing TSL models and utilize the recent experimental data or perform molecular dynamics simulations. It should be pointed out that no single TSL evaluation is based entirely on experimental data and one has to rely on TSL models or a combination of both. New TOF measurement of light water at the SNS, with a detailed description of the experimental setup, measurement conditions, and the associated foreseen results is presented in this paper. The analysis of the experimental data would help in validating the existing approach based on old experimental data or based on molecular dynamic simulations using classical water models, knowledge of which is very important to generate TSL libraries at reactor operating conditions.

Highlights

Light water is the most widely used moderator in thermal nuclear reactors, such as pressurized water reactors (PWRs)
In the standard thermal scattering libraries, these effects are described by a S (α, β) function, which is often termed as thermal scattering law (TSL) [2]
TSL evaluations for light water have evolved in years, and the most recent ones differ based on the different methodologies adopted for their generation

Summary

Introduction

Light water is the most widely used moderator in thermal nuclear reactors, such as pressurized water reactors (PWRs). A promising technique which provides reliable TSL involves Molecular Dynamic (MD) simulations of light water. This method allows the computation of TSL using MD trajectories but is not completely model-free, due to the intrinsic limitation of the classical MD simulations. The accuracy of these simulations depends on the water potentials used at high temperature and pressure (reactor normal operating conditions) [9]. New experimental TSL data would facilitate the validation of MD simulations results and the applicability of water potentials at high temperature and pressure. Quantification of experimental uncertainties, both the systematic and statistical will play a very important role in generating the data covariance and will help in cross-section validation

Need for new measurements

SEQUOIA TOF Spectrometer

Experimental conditions of the measurements

Conclusions