As modern computing power grows, whole-core transport calculations become more viable. However, the computing time and memory requirement remain major burdens. As a candidate for whole-core transport calculation methods, nonoverlapping local/global (NLG) iteration has recently been developed.
In this study, the NLG iteration method is extended to make it capable of transient calculations of 3-D heterogeneous problems. It is then implemented in an in-house code, CRX-2K. Transient NLG iteration uses the 2-D/1-D fusion method as a local transport kernel, with the transient p-CMFD equation adopted as a global wrapper. In addition, a neighboring spectral index (NSI) weighting method is suggested as a tool for correcting the rod cusping phenomenon for rod ejection problems.
Four problems, including a 3-D heterogeneous problem, are computed. Numerical results show that the NLG iteration converges to the reference solution obtained by means of the whole-core p-CMFD acceleration, and the NSI weighting method is accurate to correct the rod cusping phenomenon. The NLG iteration in present implementation takes more computing times (still less than 2 times) than the whole-core p-CMFD acceleration, but has great potential in parallelization.