Analysis on the 237Np sphere surrounded by 235U shells experiment

The Neptunium sphere reflected by highly enriched uranium hemi-shells experiment was performed using the Planet universal critical assembly at the Los Alamos Critical Experiment Facility (LACEF) at Los Alamos National Laboratory. The experiment consisted of surrounding a Np sphere by matching pairs of highly enriched uranium hemisphere shells. This experiment was performed in an effort to decrease the uncertainty in the critical mass of 237Np for criticality safety and nonproliferation issues. The initial configuration went critical on September of 2002. The final experimental configuration consisted of a 6.07 kg Np sphere and 62.555 kg of HEU separated by a 0.3175-cm aluminum spacer. The critical configuration had an experimental keff of 1.003. The uncertainties affecting the experiment were divided into three categories: mass measurements, geometry and material composition. The sensitivity analysis on this experiment yielded an uncertainty in the measured keff of ±0.0044. (author)