KENO-NR: A Monte Carlo Code for Simulating ²⁵²Cf-Source-Driven Noise Measurements to Determine Subcriticality

The KENO-NR Monte Carlo code was developed to simulate the measurement of R(ω) = G*₁₂(ω)G₁₃(ω)/G₁₁(ω)G₂₃(ω), a ratio of spectral densities measured by the ²⁵²Cf source-driven noise analysis (CSDNA) method for determining subcriticality. From a direct comparison of simulated and measured R(ω), cross sections and the physical system model can be benchmarked and then used in standard criticality codes for determining k_eff for a multiplying system. This procedure eliminates the dependence of the CSDNA method on the point-kinetics model and allows cross-section and geometry models to be validated for noncritical configurations. For a set of uranium cylinders (93.2 wt% ²³⁵sU and 17.7-cm outer diameter) of varying height, the simulated and the measured R(ω) values in the low-frequency limit and the prompt neutron decay constant a agreed to within 10%. These results indicate that the approach of validating a simulation of the direct experimental data should lead to improved neutronic parameters for fissile systems.