Neutronic analysis of the Geological Survey TRIGA Reactor

•We develop a detailed MCNP model of the Geological Survey TRIGA Reactor.•We present a simplified approach to considering burnup.•The model is validated against available reactor data.•We present evidence of inaccuracies in the ENDF B/VII zirconium libraries.

The United States Geological Survey TRIGA Reactor (GSTR) is a 1 MW reactor located in Lakewood, Colorado. In support of the GSTR’s relicensing efforts, this project developed and validated a Monte Carlo N-Particle Version 5 (MCNP5) model of the GSTR reactor. The model provided estimates of the excess reactivity, power distribution and the fuel temperature, water temperature, void, and power reactivity coefficients for the current and limiting core. The MCNP5 model predicts a limiting core excess reactivity of $6.48 with a peak rod power of 22.2 kW. The fuel and void reactivity coefficients for the limiting core are strongly negative, and the core water reactivity coefficient is slightly positive, consistent with other TRIGA analyses. The average fuel temperature reactivity coefficient of the full power limiting core is −0.0135 $/K while the average core void coefficient is −0.069 $/K from 0% to 20% void. The core water temperature reactivity coefficient is +0.012 $/K.