Michael Evan Rising

Evaluation and Uncertainty Quantification of Prompt Fission Neutron Spectra of Uranium and Plutonium Isotopes

Abstract The prompt fission neutron spectra (PFNS) of the low-incident-energy neutron-induced fission reactions n + 229-238U and n + 235-242Pu have been systematically evaluated using differential experimental data and the Los Alamos model (LA model). Using the first-order, linear Kalman filter, the LA model parameters are constrained using the experimental data and an evaluation of the PFNS and its uncertainties across a suite of isotopes’ results. Correlations between isotopes of each actinide are presented through the model parameter correlations, and the resulting evaluations can be used to fill in inconsistencies within the ENDF/B-VII.1 library where PFNS data are scarce or in need of an update.

Prompt Fission Neutron Spectrum Uncertainty Propagation Using Polynomial Chaos Expansion

Abstract The polynomial chaos expansion-stochastic collocation method (PCE-SCM) is demonstrated to be a computationally efficient approach for propagating nuclear data uncertainties evaluated for the prompt fission neutron spectra (PFNS) of n + 235U and n + 239Pu fission reactions through two fast neutron critical benchmark experiments. A principal component decomposition of the PFNS covariance matrices yields an efficient representation of the uncertainty in terms of two to four random variables. Both normal and uniform distributions are considered for these random variables, and the random output variables (angular flux and k-eigenvalue) are expressed in terms of Hermite and Legendre chaos expansions, respectively. Tensor product Hermite and Legendre Gauss quadrature sets, respectively, are used to relate the deterministic chaos expansion coefficients to solutions of independent transport k-eigenvalue problems, and the resulting polynomial chaos expansion provides a complete statistical characterization of the uncertainty in the output variables. Direct random sampling of the PFNS followed by repeated solution of the transport problem to create an ensemble of solutions is used to benchmark results obtained from the PCE-SCM implementation. Both direct random sampling and the PCE-SCM implementation yield comparable results where, for the Jezebel and Lady Godiva critical assemblies, the calculated uncertainties in keff resulting from the PFNS propagated uncertainties are found to be of the same order or larger than reported experimental measurement uncertainties, respectively. The PCE-SCM implementation results obtained require orders of magnitude less computational resources compared with the direct random sampling approach.

Lecture Notes on Criticality Safety Validation Using MCNP & Whisper

Training classes for nuclear criticality safety, MCNP documentation. The need for, and problems surrounding, validation of computer codes and data area considered first. Then some background for MCNP & Whisper is given--best practices for Monte Carlo criticality calculations, neutron spectra, S(α,β) thermal neutron scattering data, nuclear data sensitivities, covariance data, and correlation coefficients. Whisper is computational software designed to assist the nuclear criticality safety analyst with validation studies with the Monte Carlo radiation transport package MCNP. Whispers methodology (benchmark selection – Cks, weights; extreme value theory – bias, bias uncertainty; MOS for nuclear data uncertainty – GLLS) and usage are discussed.

Milestone 5431: Chi-Nu Measurements of Prompt Fission Neutron Spectra (PFNS)

This presentation offers an overview of the Chi-Nu project, its results, evaluation, and plans for FY17.

Lecture Notes on Sensitivity-Uncertainty Based Nuclear Criticality Safety Validation

This document is a collection of lecture notes for sensitivity-uncertainty analysis of nuclear criticality safety validation. The use of and results from MCNP and Whisper are included.

Criticality Calculations with MCNP6 - Practical Lectures

These slides are used to teach MCNP (Monte Carlo N-Particle) usage to nuclear criticality safety analysts. The following are the lecture topics: course information, introduction, MCNP basics, criticality calculations, advanced geometry, tallies, adjoint-weighted tallies and sensitivities, physics and nuclear data, parameter studies, NCS validation I, NCS validation II, NCS validation III, case study 1 - solution tanks, case study 2 - fuel vault, case study 3 - BW Describe how cross section data impact Monte Carlo and deterministic codes; Describe the importance of validation of computer codes and how it is accomplished; Describe the methodology supporting Monte Carlo codes and deterministic codes; Describe pitfalls of Monte Carlo calculations; Discuss the strengths and weaknesses of Monte Carlo and Discrete Ordinants codes; The diffusion theory model is not strictly valid for treating fissile systems in which neutron absorption, voids, and/or material boundaries are present. In the context of these limitations, identify a fissile system for which a diffusion theory solution would be adequate.

Preliminary Evaluation and Uncertainty Quantification of the Prompt Fission Neutron Spectrum of {sup 239}Pu

Abstract Low evaluated uncertainties were obtained in a previous evaluation of the 239 Pu prompt fission neutron spectrum and associated covariances for incident neutrons of 0.5 MeV, which were enlarged a-posteriori before being incorporated into ENDF/B-VII.1. These low evaluated uncertainties triggered an in-depth study and improved estimate of experimental as well as model uncertainties. Here, we will summarize these efforts and show that the improved estimate of experimental and model uncertainties leads to corresponding evaluated uncertainties in good agreement with uncertainties obtained in a statistical analysis based primarily on experimental information.

MCNP6. Simulating Correlated Data in Fission Events

This report is a series of slides discussing the MCNP6 code and its status in simulating fission. Applications of interest include global security and nuclear nonproliferation, detection of special nuclear material (SNM), passive and active interrogation techniques, and coincident neutron and photon leakage.