Upgrade and Simulation of the Subcritical Assembly at Missouri University of Science and Technology

The Missouri University of Science and Technology Subcritical Assembly has been brought back into service and upgraded with a new neutron detection system and Internet accessibility. Before the upgrade, neutron counting was possible in only one location. Using a movable detection system housed in acrylic tubes, measurements can now be taken in any empty fuel location and at any height within the tube, making three-dimensional flux mapping possible. By connecting the new detection system to a Canberra Lynx Digital Signal Analyzer, remote users can have limited data-collecting capabilities. To further enhance the potential of the facility, a Monte Carlo N-Particle transport code (MCNP) model of the subcritical assembly was created and validated by comparing its simulated predictions to experiments conducted at the facility. An approach to the criticality experiment using the 1/M approximation showed that the MCNP model accurately predicts k_eff if the detectors are placed between 27 and 36 cm from the neutron source. The results of an axial flux measurement experiment taken 20.3 cm from the neutron source differed from the MCNP-simulated results by an average of 12%. Finally, the validated MCNP model was used to show the effect of removing the facility’s fixed detector tube and redistributing its fuel. MCNP simulation predicts that the new configuration would increase the multiplication factor from 0.73481 ± 0.00008 to 0.76844 ± 0.00004.