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Neutron noise in nuclear power reactors refers to the small fluctuationsaround the average neutron flux at steady state resulting from time-dependentperturbations inside the core. The neutron noise equations in the frequencydomain can be solved using Monte Carlo simulation codes, which are capable ofobtaining reference solutions involving almost no approximations, but arehindered by severe issues affecting the statistical convergence: thesimultaneous presence of positive and negative particles, which is required bythe nature of the complex noise equations, leads to catastrophically largevariance in the tallies. In this work, we consider the important case ofneutron noise problems induced by mechanical vibrations. First, we derive a newexact sampling strategy for the noise source. Then, building upon our previousfindings in other contexts, we show that weight cancellation methods can behighly beneficial in dealing with the presence of negative weights, enablingextremely large gains in the figure of merit. We successfully demonstrate ourresults on a benchmark configuration consisting of a fuel assembly with avibrating pin and we discuss possible pathways for further improvements.

Variance Reduction and Noise Source Sampling Techniques for Monte Carlo Simulations of Neutron Noise Induced by Mechanical Vibrations