NRX Reactor Spent Fuel Study

In safeguards and nonproliferation, the ability to estimate isotopic inventories of spent fuel is very important. However, those estimates are usually produced without reporting uncertainties which limit their usability. In this work, a method is described for generating uncertainty estimates from Monte Carlo based reactor physics codes. The NRX reactor model is used as an example. The Canadian NRX research reactor was operated for more than 50 years and produced vast amounts of plutonium in spent fuel before its shutdown in 1993. The NRX is a heavy-water moderated, lightwater cooled, and natural uranium fueled 40 MWth research reactor with an average core burnup of 1300 MWd/MTU. In recent history, a small number of countries have built test reactors similar to the NRX. In this research the amount of plutonium in spent fuel is quantified, with uncertainty estimates, in a typical refueling cycle of the NRX with an average burnup of 1300 MWd/MTU. Details of the NRX modeling and execution of simulations to calculate the isotopic inventory of spent fuel from the NRX reactor and to estimate uncertainties in those inventories due to modeling imprecision are given. The simulation was performed using the MONTEBURNS code package from Los Alamos National Laboratory.