A Brief Sensitivity Analysis for the GIRM and Other Related Technique using a One-Group Cross Section Library for Graphite- Moderated Reactors

Several methods have been developed previously for estimating cumulative energy production and plutonium production from graphite-moderated reactors. These methods generally fall into the category of nuclear archaeology. The Graphite Isotope Ratio Method (GIRM) is one well-known technique of this type. This method is based on the measurement of trace isotopes in the reactor’s graphite matrix to determine the change in their isotopic ratios due to burnup. These measurements are then coupled with reactor calculations to determine the total plutonium and energy production of the reactor. To facilitate sensitivity analysis of these methods, a one-group cross section and fission product yield library for the fuel and graphite activation products has been developed for MAGNOX-style reactors. This library is intended for use in the ORIGEN computer code which calculates the buildup, decay, and processing of radioactive materials. The library was developed using a fuel cell model in Monteburns. This model consisted of a single fuel rod including natural uranium metal fuel, magnesium oxide (magnox) cladding, carbon dioxide coolant, and Grade A United Kingdom (UK) graphite. Using this library a complete sensitivity analysis can be performed for GIRM and other techniques. The brief sensitivity analysis conducted in this study assessed various input parameters including U and U cross section values, aluminum alloy concentration in the fuel, and initial concentrations of trace elements in the graphite moderator. The results of the analysis yield insight into the GIRM method and the isotopic ratios the method uses as well as the level of uncertainty that may be found in the system results.