Evaluation of nuclear cross-section uncertainty effects on the graphite isotope ratio method (GIRM)
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This study investigates uncertainties in the Graphite Isotope Ratio Method (GIRM) due to nuclear cross-section uncertainties, using the McCARD Monte Carlo (MC) code and a HANARO reactor model. The irradiation of UO2 fuel and graphite specimens was simulated, and uncertainties were quantified through a stochastic approach. Depletion calculations were conducted with 100 sampled cross-section sets based on covariance data from the evaluated nuclear data libraries. Indicator nuclides in GIRM and those related to plutonium production were included in the analysis. Based on these calculations, uncertainties in plutonium quantities derived from GIRM were evaluated and the contribution of each parameter was analyzed. Stochastic impacts, inherent to MC codes, were consistent across indicator nuclides and were considered in analyzing other parameters. Results indicate that uncertainties in GIRM vary depending on the indicator nuclide. Iron exhibits the highest uncertainties due to large standard deviations in its key cross-sections, while boron and uranium have the smallest uncertainties, largely due to the consistent influence of 238U cross-section uncertainties in UO2 fuel. This study confirms that cross-section uncertainties significantly affect GIRM, with 238U playing a dominant role in uncertainty levels.
Abstract
This study investigates uncertainties in the Graphite Isotope Ratio Method (GIRM) due to nuclear cross-section uncertainties, using the McCARD Monte Carlo (MC) code and a HANARO reactor model. The irradiation of UO2 fuel and graphite specimens was simulated, and uncertainties were quantified through a stochastic approach. Depletion calculations were conducted with 100 sampled cross-section sets based on covariance data from the evaluated nuclear data libraries. Indicator nuclides in GIRM and those related to plutonium production were included in the analysis. Based on these calculations, uncertainties in plutonium quantities derived from GIRM were evaluated and the contribution of each parameter was analyzed. Stochastic impacts, inherent to MC codes, were consistent across indicator nuclides and were considered in analyzing other parameters. Results indicate that uncertainties in GIRM vary depending on the indicator nuclide. Iron exhibits the highest uncertainties due to large standard deviations in its key cross-sections, while boron and uranium have the smallest uncertainties, largely due to the consistent influence of 238U cross-section uncertainties in UO2 fuel. This study confirms that cross-section uncertainties significantly affect GIRM, with 238U playing a dominant role in uncertainty levels.