Spatially-variant isotope production burnup modeling in a CANDU-6 reactor for nuclear treaty monitoring

•Burnup results produced complex actinide spatial distributions.•New methodology can be used for nuclear treaty monitoring.•Abundance of 237 isotopes in spent fuel are reported for a CANDU-6 burnup model. A CANDU-6 nuclear reactor is modeled as a 3D quarter-core model using Monte-Carlo and burnup techniques to quantify the spatially-variant isotope production for Nuclear Treaty Monitoring applications. Fuel shuffling and refueling techniques were applied in conjunction with the Monte-Carlo and burnup techniques to simulate the realistic operations of a CANDU-6 reactor. The methods developed serve as a prototype for spatially-variant spent fuel analysis for reactors of interest for non-proliferation. A comprehensive, spatially-dependent database of isotopic concentration distributions in spent fuel from a CANDU-6 reactor was developed for the top 237 isotopes expected from CANDU-6 spent fuel. Isotopic ratios of actinides, a common technique used to assess material origin, were determined to have complex distributions dependent on their position within the reactor. Confidence intervals of 67%, 95%, and 99% for common isotopic ratios are presented. For example, the 3-σ confidence interval for 239Pu/240Pu is 1.049-2.599, a significant variance. The database and the methods developed in this work set the framework for future reactor modeling for nuclear treaty monitoring.