This paper introduces a new stochastic method for taking the effect of thermal motion into account on the fly in a Monte Carlo neutron transport calculation. The method is based on explicit treatment of the motion of target nuclei at collision sites and, consequently, requires simply cross sections at a temperature of 0 K regardless of the number of temperatures in the problem geometry. It utilizes rejection sampling techniques to manage the fact that total cross sections become distributed quantities. The method has a novel capability of accurately modeling continuous temperature distributions.

The new stochastic method is verified using a simple test program, which compares its results to an analytical reference solution based on NJOY-broadened cross sections. Future implementation to Monte Carlo reactor physics code Serpent is also discussed shortly.