Uncertainty quantification of the early Deterministic Truncation of <onte Carlo (DTMC) solutions

Abstract

In this study, a new approach to evaluate uncertainties of the multiplication factor and the pin-power distribution from the CMFD parameters is suggested for the DTMC method. The CMFD parameters from sufficiently converged inactive cycles are used to predict uncertainties of the very first active cycle, as the ultimate purpose of the DTMC method is to determine the solution only with a few, or even a single active cycle. Normal distributions of the CMFD parameters are estimated based on the uncertainties of the CMFD parameters that are calculated from the inactive cycles. Then, the parameters are resampled multiple times to calculate the uncertainty of the solution. As a preliminary study, the standard deviation predicted from the method is compared with the real standard deviation obtained from multiple independent batch calculations. Instead of solving explicit power iterations repeatedly, the first-order perturbation formula is used to calculate the uncertainty of the multiplication factor. Here, equivalence of the one-group forward flux and the one-group adjoint flux is used for the perturbation formula. By using several tens of cycles, the proposed method is able to predict the real standard deviation with a few pcm margins. The amount of contribution to the uncertainty by the CMFD parameters are calculated with the aforementioned algorithm.