Benchmark Analysis of Experiments in Fast Critical Assemblies Using a Continuous-Energy Monte Carlo Code MVP

Abstract

Critical experiments in the FCA and ZPPR-9 assemblies were re-analyzed systematically by using a continuous-energy Monte Carlo code MVP with the JENDL-3.2 library. The experimental geometries were simulated almost as built and the neutronic parameters were calculated with the physics model where all neutron reactions given in the evaluated nuclear data library were treated explicitly. As a result, the calculated lated k _eff, values underestimated the experimental ones by 0.5–0.8Δk/k except for FCA X-2. The calculated results for most reaction rate distributions and central reaction rate ratios agree well with the measured ones within the uncertainties.

Furthermore, in order to investigate the cause of the underestimation of the k _eff, values, re-calculations were performed using the modified JENDL-3.2 library where the inelastic scattering cross sections and the energy-angular distributions for ²³⁸U were replaced by those of the ENDF/B-VI library. The k _eff values increased by 0.4–0.5Δk/k for the FCA assemblies, by −0.8Δk/k for ZPPR-9, and the C/E values were improved. It is found that the cause of the increase in the k _eff values is attributed to the energy distribution for secondary neutrons scattered inelastically by ²³⁸U.

KEYWORDS:

• ZPPR reactor
• FCA reactor
• Monte Carlo method
• MVP
• JENDL-S.2
• benchmark analysis
• effective multiplication factor
• reaction rate
• reaction rate ratio
• uranium-238 inelastic scattering cross sections
• secondary-neutron energy distribution