Year
2015
Abstract
From nuclear materials accountability to detection of SNM, the need for better modeling of fission has grown over the past decades. Current radiation transport codes compute average quantities with great accuracy and performance, but performance and averaging comes at the price of limited interaction-by-interaction modeling. For fission applications, these codes often lack the capability of modeling interactions exactly: energy is not conserved, energies of emitted particles are uncorrelated, prompt fission neutron and gamma multiplicities are uncorrelated. Many modern applications require more exclusive quantities than averages, such as the fluctu- ations in certain observables (e.g. the neutron multiplicity) and correlations between neutrons and photons. The new computational model, FREYA (Fission Reaction Event Yield Algorithm), aims to meet this need by modeling complete fission events. Thus it automatically includes fluctuations as well as correlations resulting conservation of energy and momentum. FREYA has been integrated into the LLNL Fission Library, which is an integral part of MCNP6. By comparing Monte Carlo simulations performed with and without the new fis- sion model, we will see that the fluctuations and correlations introduced lead to significant differences that can be measured experimentally using detectors. The first part of this paper will focus on the new fission model FREYA and the LLNL Fission Library, while the second part will concentrate on results of simulations and comparisons to experimental data.