Abstract
Effective fission source acceleration method is studied in criticality safety analysis for a realistic spent fuel transport cask. Various axial burnup profiles from almost symmetry to strong asymmetry based on in-core flux measurements are proposed in the OECD/NEA Phase II-C burnup credit benchmark problem. In some cases, calculations by ordinary Monte Carlo method show very slow convergence of fission source distribution, and unacceptably large skipped cycles are needed to obtain a reliable fission source distribution for statistic criticality estimation. The matrix eigenvector calculation developed and incorporated in the ordinary Monte Carlo calculation to accelerate the slow fission source convergence is applied to the benchmark. The efficiency of acceleration by the matrix eigenvector calculation depends on the precision of fission matrix elements. In a certain stage of source iteration with acceleration repetition of fission source distribution, especially for this benchmark problem of very slow convergence, more acceleration repetitions cause anomalous results because of large statistic fluctuations of the estimation of fission matrix elements for regions with very low source levels. Here, we propose a new source acceleration method to detail with the slow convergence with less calculation time by modeling the division of fissile fuel region.
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