Neutronic Analysis of the PSBR Using a Burnup-Coupled MCNP Simulation with MURE

The main goal of this study is to verify the accuracy of burnup-coupled neutronic calculations when employing the Monte Carlo Utility for Reactor Evolutions (MURE) and MCNP5 codes for modeling TRIGA-type reactors, in this case the Penn State Breazeale Reactor (PSBR) core. Research and educational requirements mainly direct the PSBR operating schedule. With such operating schedules, one particular area of concern, specifically relating to nuclear analytical applications, is time-dependent changes in the neutronic characteristics of the reactor, specifically within the irradiation positions. Particular concern exists among scientists performing neutron activation analysis measurements as to whether continuous variations in reactor operations would cause significant fluctuations in the neutronic characterization parameters of the irradiation positions. A secondary objective of this study is to analyze fluctuations in the neutronic characterization parameters and their dependence on various core conditions as examined by detailed burnup-coupled neutronic simulations. In this study, a burnup-coupled neutronic simulation model of the PSBR is developed using the MURE and MCNP5 codes. The simulation results are verified by a series of experiments including measurements of the core excess reactivity starting from the first core loading in 1965 to 2012, control rod worth, fission product buildup, temperature-dependent reactivity loss, integral control rod worth curves, individual fuel element worth, and neutron flux. Local neutronic calculations of the simulation are confirmed by measuring neutronic characterization parameters for one of the irradiation positions within the PSBR core, namely, dry irradiation tube 1. Analyzing time-dependent data predicted by the simulation, the neutron temperature and the measure of the nonideal epithermal neutron flux distribution are found to be reasonably static. Conversely, the thermal-to-epithermal neutron flux ratio and spectral index are found to be relatively responsive to alterations in the core.