Estimation of uncertainty in transmutation rates of LLFPs in a fast reactor transmutation system via an estimation of the cross-section covariances

A new concept of transmutation system for six long-lived fission products (LLFPs: ⁷⁹Se, ⁹³Zr, ⁹⁹Tc, ¹⁰⁷Pd, ¹²⁹I, and ¹³⁵Cs) consisting of three small-size fast reactor cores was proposed. In order to establish a method to estimate the effects of cross-section uncertainties on the transmutation rates of the LLFPs, cross section covariances for the six LLFPs were estimated using a T6 system which includes resonance and statistical models via propagation of model uncertainties, and the uncertainties of transmutation rates and support factors of the six LLFPs in the three fast reactors were estimated based on a Total Monte Carlo (TMC) method. It was made clear that some of the transmutation rates of these LLFPs have large uncertainties indicating that the accuracy of cross sections for them is not enough, and hence the strategy for efficient transmutation may have to be reconstructed. It is concluded that the T6 system and the TMC method used in this study are quite effective not only to estimate the uncertainties of cross sections but also to assess the effect of error propagation throughout the series of calculations conducting in this study. (author)